WorldWideScience

Sample records for atomic clusters irradiated

  1. Characterization of atom clusters in irradiated pressure vessel steels and model alloys

    International Nuclear Information System (INIS)

    Auger, P.; Pareige, P.; Akamatsu, M.; Van Duysen, J.C.

    1993-12-01

    In order to characterize the microstructural evolution of the iron solid solution under irradiation, two pressure vessel steels irradiated in service conditions and, for comparison, low copper model alloys irradiated with neutrons and electrons have been studied. The characterization has been carried out mainly thanks to small angle neutron scattering and atom probe experiments. Both techniques lead to the conclusion that clusters develop with irradiations. In Fe-Cu model alloys, copper clusters are formed containing uncertain proportions of iron. In the low copper industrial steels, the feature is more complex. Solute atoms like Ni, Mn and Si, sometimes associated with Cu, segregate as ''clouds'' more or less condensed in the iron solid solution. These silicides, or at least Si, Ni, Mn association, may facilitate the copper segregation although the initial iron matrix contains a low copper concentration. (authors). 24 refs., 3 figs., 2 tabs

  2. Concentration dependence of solute atoms on vacancy cluster formation in neutron irradiated Ni alloy

    International Nuclear Information System (INIS)

    Sato, K.; Itoh, D.; Yoshiie, T.; Xu, Q.

    2007-01-01

    Full text of publication follows: One dimensional (1-D) motion of interstitial clusters is important for the microstructural evolution in metals. The movement of interstitial clusters was often observed in neutron irradiated metals by transmission electron microscopy (TEM). Alloying elements are expected to affect the motion of interstitial clusters. Yoshiie et al. have studied the effect of alloying elements in Ni. For example, in neutron irradiated pure Ni, well-developed dislocation networks and voids were observed at 573 K at a dose of 0.026 dpa by TEM. After the addition of 2at.%Si (-5.81% volume size factor to Ni) and Sn (74.08% volume size factor), no voids were detected by TEM observation and positron lifetime measurement. Alloying elements of Si and Sn were expected to prevent the 1-D motion of the interstitial clusters. In this study, the concentration dependence of alloying elements on the 1-D motion of the interstitial clusters was investigated by positron annihilation lifetime measurements, and the microstructural evolution was discussed. Specimens irradiated were 99.99 pure Ni (Johnson Matthey) and Ni based binary alloys, which contain Si, Cu, Ge and Sn as solute atoms. The concentration of solute atoms was 0.05at.%o, 0.3at.% and 2at.%. Neutron irradiation was performed with the Kyoto University Reactor (KUR) and Japan materials testing reactor (JMTR) at Japan Atomic Energy Agency. Neutron dose was 6x10 -5 -1x10 -2 dpa at KUR, and 8x10 -3 -0.3 dpa at JMTR. Irradiation temperature was 573 K at KUR and 563 K at JMTR. After the neutron irradiation, positron annihilation lifetime measurements were performed at room temperature. Microvoids were detected in pure Ni, Ni-0.05%Si, Ni-0.05%Sn, Ni-Cu and Ni-Ge alloys. In Ni-Si and Ni-Sn alloys, the size of microvoids decreased as the concentration of solute atoms increased. This is because the frequency of 1-D motion of the interstitial clusters depends on the alloy concentration. High concentration of alloying

  3. Concentration dependence of solute atoms on vacancy cluster formation in neutron irradiated Ni alloy

    Energy Technology Data Exchange (ETDEWEB)

    Sato, K.; Itoh, D.; Yoshiie, T.; Xu, Q. [Kyoto Univ., Research Reactor Institute, Osaka (Japan)

    2007-07-01

    Full text of publication follows: One dimensional (1-D) motion of interstitial clusters is important for the microstructural evolution in metals. The movement of interstitial clusters was often observed in neutron irradiated metals by transmission electron microscopy (TEM). Alloying elements are expected to affect the motion of interstitial clusters. Yoshiie et al. have studied the effect of alloying elements in Ni. For example, in neutron irradiated pure Ni, well-developed dislocation networks and voids were observed at 573 K at a dose of 0.026 dpa by TEM. After the addition of 2at.%Si (-5.81% volume size factor to Ni) and Sn (74.08% volume size factor), no voids were detected by TEM observation and positron lifetime measurement. Alloying elements of Si and Sn were expected to prevent the 1-D motion of the interstitial clusters. In this study, the concentration dependence of alloying elements on the 1-D motion of the interstitial clusters was investigated by positron annihilation lifetime measurements, and the microstructural evolution was discussed. Specimens irradiated were 99.99 pure Ni (Johnson Matthey) and Ni based binary alloys, which contain Si, Cu, Ge and Sn as solute atoms. The concentration of solute atoms was 0.05at.%o, 0.3at.% and 2at.%. Neutron irradiation was performed with the Kyoto University Reactor (KUR) and Japan materials testing reactor (JMTR) at Japan Atomic Energy Agency. Neutron dose was 6x10{sup -5}-1x10{sup -2} dpa at KUR, and 8x10{sup -3} -0.3 dpa at JMTR. Irradiation temperature was 573 K at KUR and 563 K at JMTR. After the neutron irradiation, positron annihilation lifetime measurements were performed at room temperature. Microvoids were detected in pure Ni, Ni-0.05%Si, Ni-0.05%Sn, Ni-Cu and Ni-Ge alloys. In Ni-Si and Ni-Sn alloys, the size of microvoids decreased as the concentration of solute atoms increased. This is because the frequency of 1-D motion of the interstitial clusters depends on the alloy concentration. High

  4. Effect of solute atom concentration on vacancy cluster formation in neutron-irradiated Ni alloys

    Science.gov (United States)

    Sato, Koichi; Itoh, Daiki; Yoshiie, Toshimasa; Xu, Qiu; Taniguchi, Akihiro; Toyama, Takeshi

    2011-10-01

    The dependence of microstructural evolution on solute atom concentration in Ni alloys was investigated by positron annihilation lifetime measurements. The positron annihilation lifetimes in pure Ni, Ni-0.05 at.%Si, Ni-0.05 at.%Sn, Ni-Cu, and Ni-Ge alloys were about 400 ps even at a low irradiation dose of 3 × 10 -4 dpa, indicating the presence of microvoids in these alloys. The size of vacancy clusters in Ni-Si and Ni-Sn alloys decreased with an increase in the solute atom concentration at irradiation doses less than 0.1 dpa; vacancy clusters started to grow at an irradiation dose of about 0.1 dpa. In Ni-2 at.%Si, irradiation-induced segregation was detected by positron annihilation coincidence Doppler broadening measurements. This segregation suppressed one-dimensional (1-D) motion of the interstitial clusters and promoted mutual annihilation of point defects. The frequency and mean free path of the 1-D motion depended on the solute atom concentration and the amount of segregation.

  5. Microstructural characterization of atom clusters in irradiated pressure vessel steels and model alloys

    International Nuclear Information System (INIS)

    Auger, P.; Pareige, P.; Akamatsu, M.; Van Duysen, J.C.

    1993-01-01

    In order to characterize the microstructural evolution of iron solid solution under irradiation, two pressure vessel steels irradiated in service conditions, and, for comparison, low copper model alloys irradiated with neutrons and electrons, have been studied through small angle neutron scattering and atom probe experiments. In Fe-Cu model alloys, copper clusters are formed containing uncertain proportions of iron. In the low copper industrial steels, the feature is more complex; solute atoms such as Ni, Mn and Si, sometimes associated with Cu, segregate as ''clouds'' more or less condensed in the iron solid solution. These silicides, or at least Si, Ni, Mn association, may facilitate the copper segregation although the initial iron matrix contains a low copper concentration. (authors). 24 refs., 3 figs., 2 tabs

  6. Microstructural characterization of atom clusters in irradiated pressure vessel steels and model alloys

    Energy Technology Data Exchange (ETDEWEB)

    Auger, P; Pareige, P [Rouen Univ., 76 - Mont-Saint-Aignan (France); Akamatsu, M; Van Duysen, J C [Electricite de France (EDF), 77 - Ecuelles (France)

    1994-12-31

    In order to characterize the microstructural evolution of iron solid solution under irradiation, two pressure vessel steels irradiated in service conditions, and, for comparison, low copper model alloys irradiated with neutrons and electrons, have been studied through small angle neutron scattering and atom probe experiments. In Fe-Cu model alloys, copper clusters are formed containing uncertain proportions of iron. In the low copper industrial steels, the feature is more complex; solute atoms such as Ni, Mn and Si, sometimes associated with Cu, segregate as ``clouds`` more or less condensed in the iron solid solution. These silicides, or at least Si, Ni, Mn association, may facilitate the copper segregation although the initial iron matrix contains a low copper concentration. (authors). 24 refs., 3 figs., 2 tabs.

  7. Electron-ion collision rates in atomic clusters irradiated by femtosecond laser pulses

    International Nuclear Information System (INIS)

    Moll, M; Hilse, P; Schlanges, M; Bornath, Th; Krainov, V P

    2010-01-01

    In atomic clusters irradiated by femtosecond laser pulses, plasmas with high density and high temperature are created. The heating is mainly caused by inverse bremsstrahlung, i.e. determined by electron-ion collisions. In the description of the scattering of electrons on noble gas ions in such plasmas, it is important to account for the inner structure of the ions and the screening by the surrounding plasma medium which can be accomplished by using suitable model potentials. In the wide parameter range met in experiments, the Born approximation is not applicable. Instead, the electron-ion collision frequency is calculated on the basis of classical momentum transport cross sections. Results are presented for xenon, krypton and argon ions in different charge states. A comparison of these results to those for the scattering on Coulomb particles with the same charge shows an enhancement of the collision frequency. The Born approximation, however, leads to an overestimation.

  8. Influence of oxygen impurity atoms on defect clusters and radiation hardening in neutron-irradiated vanadium

    International Nuclear Information System (INIS)

    Bajaj, R.; Wechsler, M.S.

    1975-01-01

    Single crystal TEM samples and polycrystalline tensile samples of vanadium containing 60-640 wt ppm oxygen were irradiated at about 100 0 C to about 1.3 x 10 19 neutrons/cm 2 (E greater than 1 MeV) and post-irradiation annealed up to 800 0 C. The defect cluster density increased and the average size decreased with increasing oxygen concentration. Higher oxygen concentrations caused the radiation hardening and radiation-anneal hardening to increase. The observations are consistent with the nucleation of defect clusters by small oxygen or oxygen-point defect complexes and the trapping of oxygen at defect clusters upon post-irradiation annealing

  9. Three-atom clusters

    International Nuclear Information System (INIS)

    Pen'kov, F.M.

    1998-01-01

    The Born-Oppenheimer approximation is used to obtain an equation for the effective interaction in three atoms bound by a single electron. For low binding energies in an 'electron + atom' pair, long-range forces arise between the atoms, leading to bound states when the size of the three-atom cluster is a few tens of angstrom. A system made of alkali-metal atoms is considered as an example

  10. Atomic cluster collisions

    Science.gov (United States)

    Korol, Andrey V.; Solov'yov, Andrey

    2013-01-01

    Atomic cluster collisions are a field of rapidly emerging research interest by both experimentalists and theorists. The international symposium on atomic cluster collisions (ISSAC) is the premier forum to present cutting-edge research in this field. It was established in 2003 and the most recent conference was held in Berlin, Germany in July of 2011. This Topical Issue presents original research results from some of the participants, who attended this conference. This issues specifically focuses on two research areas, namely Clusters and Fullerenes in External Fields and Nanoscale Insights in Radiation Biodamage.

  11. Low-energy irradiation effects of gas cluster ion beams

    International Nuclear Information System (INIS)

    Houzumi, Shingo; Takeshima, Keigo; Mochiji, Kozo; Toyoda, Noriaki; Yamada, Isao

    2007-01-01

    A cluster-ion irradiation system with cluster-size selection has been developed to study the effects of the cluster size for surface processes using cluster ions. A permanent magnet with a magnetic field of 1.2 T is installed for size separation of large cluster ions. Trace formations at HOPG surface by the irradiation with size-selected Ar-cluster ions under acceleration energy of 30 keV were investigated by a scanning tunneling microscopy. Generation behavior of the crater-like traces is strongly affected by the number of constituent atoms (cluster size) of the irradiating cluster ion. When the incident cluster ion is composed of 100-3000 atoms, crater-like traces are observed on the irradiated surfaces. In contrast, such traces are not observed at all with the irradiation of the cluster-ions composed of over 5000 atoms. Such the behavior is discussed on the basis of the kinetic energy per constituent atom of the cluster ion. To study GCIB irradiation effects against macromolecule, GCIB was irradiated on DNA molecules absorbed on graphite surface. By the GCIB irradiation, much more DNA molecules was sputtered away as compared with the monomer-ion irradiation. (author)

  12. Giant light enhancement in atomic clusters

    International Nuclear Information System (INIS)

    Gadomsky, O. N.; Gadomskaya, I. V.; Altunin, K. K.

    2009-01-01

    We show that the polarizing effect of the atoms in an atomic cluster can lead to full compensation of the radiative damping of excited atomic states, a change in the sign of the dispersion of the atomic polarizability, and giant light enhancement by the atomic cluster.

  13. Irradiation effects of Ar cluster ion beams on Si substrates

    International Nuclear Information System (INIS)

    Ishii, Masahiro; Sugahara, Gaku; Takaoka, G.H.; Yamada, Isao

    1993-01-01

    Gas-cluster ion beams can be applied to new surface modification techniques such as surface cleaning, low damage sputtering and shallow junction formation. The effects of energetic Ar cluster impacts on solid surface were studied for cluster energies of 10-30keV. Irradiation effects were studied by RBS. For Si(111) substrates, irradiated with Ar ≥500 clusters to a dose of 1x10 15 ion/cm 2 at acceleration voltage 15kV, 2x10 14 atoms/cm 2 implanted Ar atoms were detected. In this case, the energy per cluster atom was smaller than 30eV; at this energy, no significant implantation occurs in the case of monomer ions. Ar cluster implantation into Si substrates occurred due to the high energy density irradiation. (author)

  14. Determination of atomic cluster structure with cluster fusion algorithm

    DEFF Research Database (Denmark)

    Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.

    2005-01-01

    We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters.......We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters....

  15. Electronic and atomic impacts on large clusters

    International Nuclear Information System (INIS)

    Gspann, J.

    1982-01-01

    Describing first the generation and properties of molecular beams of large Van der Waals clusters such as speed distribution, cluster size distribution, and internal temperature of the clusters, the review then features the results of electronic impacts on large clusters: metastable electronic cluster excitations, ejection of positive cluster ions of less than 100 atoms from much larger parent clusters, and ionization of the large clusters. Atomic impacts at thermal energies are treated with respect to the scattering cross section of the clusters, their drag coefficient in free molecular flow, and the peculiarities of impacts on helium clusters of either isotope. (Auth.)

  16. Clustering of Helium Atoms at a ½

    NARCIS (Netherlands)

    Berg, F. v.d.; Heugten, W. v.; Caspers, L.M.; Veen, A. v.; Hosson, J.Th.M. de

    1977-01-01

    Atomistic calculations on a ½<111>{110} edge dislocation show a restricted tendency of clustering of helium atom along this dislocation. Clusters with up to 4 helium atoms have been studied. A cluster with 3 helium proved to be most stable.

  17. Atoms, molecules, clusters and synchrotron radiation

    International Nuclear Information System (INIS)

    Kui Rexi; Ju Xin

    1995-01-01

    The importance of synchrotron radiation, especially the third generation synchrotron radiation light source, in atomic, molecular and cluster physics is discussed and some views are presented on new methods which may become available for research in the above fields

  18. Defect clustering in concentrated alloys during irradiation

    International Nuclear Information System (INIS)

    Hashimoto, T.; Shigenaka, N.; Fuse, M.

    1992-01-01

    A rate theory based model is presented to investigate the kinetics of interstitial clustering processes in a face-centered cubic (fcc) binary alloy containing A- and B-atoms. Three types of interstitial dumbbells, AA-, BB- and AB-type dumbbells, are considered. Conversions between these interstitial dumbbells are explicitly introduced into the formulation, based on the consideration of dumbbell configurations and movements. A di- interstitial is assumed to be the nucleus of a dislocation loop. Reactions of point defect production by irradiation, mutual recombination of an interstitial and a vacancy, dislocation loop nucleation and their growth are included in the model. Parameter values are chosen based on the atom size of the alloy elements, and dislocation loop formation kinetics are investigated while varying alloy compositions. Two different types of kinetics are obtained in accordance with the dominant loop nucleus types. Conversions between interstitial dumbbells are important in the determination of the interstitial dumbbell concentration ratios, of the dominant nucleus types, and consequently, the loop formation kinetics. Dislocation loop concentration decreases with increasing undersized atom content, but dose rate and temperature dependence of loop concentration are insensitive to alloy compositions. (author)

  19. On clusters and clustering from atoms to fractals

    CERN Document Server

    Reynolds, PJ

    1993-01-01

    This book attempts to answer why there is so much interest in clusters. Clusters occur on all length scales, and as a result occur in a variety of fields. Clusters are interesting scientifically, but they also have important consequences technologically. The division of the book into three parts roughly separates the field into small, intermediate, and large-scale clusters. Small clusters are the regime of atomic and molecular physics and chemistry. The intermediate regime is the transitional regime, with its characteristics including the onset of bulk-like behavior, growth and aggregation, a

  20. The atomic structure of transition metal clusters

    International Nuclear Information System (INIS)

    Riley, S.J.

    1995-01-01

    Chemical reactions are used to probe the atomic (geometrical) structure of isolated clusters of transition metal atoms. The number of adsorbate molecules that saturate a cluster, and/or the binding energy of molecules to cluster surfaces, are determined as a function of cluster size. Systematics in these properties often make it possible to propose geometrical structures consistent with the experimental observations. We will describe how studies of the reactions of cobalt and nickel clusters with ammonia, water, and nitrogen provide important and otherwise unavailable structural information. Specifically, small (less than 20 atoms) clusters of cobalt and nickel atoms adopt entirely different structures, the former having packing characteristic of the bulk and the latter having pentagonal symmetry. These observations provide important input for model potentials that attempt to describe the local properties of transition metals. In particular, they point out the importance of a proper treatment of d-orbital binding in these systems, since cobalt and nickel differ so little in their d-orbital occupancy

  1. Fine interstitial clusters as recombinators in decomposing solid solutions under irradiation

    International Nuclear Information System (INIS)

    Trushin, Yu.V.

    1991-01-01

    Behaviour of interstitial clusters and their roll in processes of radiation swelling of metals are described. It is shown that occurrence of coherent advanced precipitations during decomposition of solid solutions under irradiation leads to matrix supersaturation over interstitial atoms. This enhances recombination of unlike defects due to vacancy precipitation on fine interstitial clusters. Evaluation of cluster sizes was conducted

  2. Concomitant formation of different nature clusters and hardening in reactor pressure vessel steels irradiated by heavy ions

    International Nuclear Information System (INIS)

    Fujii, K.; Fukuya, K.; Hojo, T.

    2013-01-01

    Specimens of A533B steels containing 0.04, 0.09 and 0.21 wt%Cu were irradiated at 290 °C to 3 dpa with 3 MeV Fe ions and subjected to atom probe analyses, transmission electron microscopy observations and hardness measurements. The atom probe analysis results showed that two types of solute clusters were formed: Cu-enriched clusters containing Mn, Ni and Si atoms as irradiation-enhanced solute atom clusters and Mn/Ni/Si-enriched clusters as irradiation-induced solute atom clusters. Both cluster types occurred in the highest Cu-content steel and the ratio of Mn/Ni/Si-enriched clusters to Cu-enriched clusters increased with irradiation doses. It was confirmed that the cluster formation was a key factor in the microstructure evolution until the high dose irradiation was reached even in the low Cu content steels though the dislocation loops with much lower density than that of the clusters were observed as matrix damage. The difference in the hardening efficiency due to the difference in the nature of the clusters was small. The irradiation-induced clustering of undersized Si atoms suggested that a clustering driving force other than vacancy-driven diffusion, probably an interstitial mechanism, may become important at higher dose rates

  3. Concomitant formation of different nature clusters and hardening in reactor pressure vessel steels irradiated by heavy ions

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, K., E-mail: fujiik@inss.co.jp [Institute of Nuclear Safety System, Inc., Mihama 919-1205 (Japan); Fukuya, K. [Institute of Nuclear Safety System, Inc., Mihama 919-1205 (Japan); Hojo, T. [Japan Nuclear Energy Safety Organization, Toranomon, Minato-ku, Tokyo 105-0001 (Japan)

    2013-11-15

    Specimens of A533B steels containing 0.04, 0.09 and 0.21 wt%Cu were irradiated at 290 °C to 3 dpa with 3 MeV Fe ions and subjected to atom probe analyses, transmission electron microscopy observations and hardness measurements. The atom probe analysis results showed that two types of solute clusters were formed: Cu-enriched clusters containing Mn, Ni and Si atoms as irradiation-enhanced solute atom clusters and Mn/Ni/Si-enriched clusters as irradiation-induced solute atom clusters. Both cluster types occurred in the highest Cu-content steel and the ratio of Mn/Ni/Si-enriched clusters to Cu-enriched clusters increased with irradiation doses. It was confirmed that the cluster formation was a key factor in the microstructure evolution until the high dose irradiation was reached even in the low Cu content steels though the dislocation loops with much lower density than that of the clusters were observed as matrix damage. The difference in the hardening efficiency due to the difference in the nature of the clusters was small. The irradiation-induced clustering of undersized Si atoms suggested that a clustering driving force other than vacancy-driven diffusion, probably an interstitial mechanism, may become important at higher dose rates.

  4. Metal cluster compounds - chemistry and importance; clusters containing isolated main group element atoms, large metal cluster compounds, cluster fluxionality

    International Nuclear Information System (INIS)

    Walther, B.

    1988-01-01

    This part of the review on metal cluster compounds deals with clusters containing isolated main group element atoms, with high nuclearity clusters and metal cluster fluxionality. It will be obvious that main group element atoms strongly influence the geometry, stability and reactivity of the clusters. High nuclearity clusters are of interest in there own due to the diversity of the structures adopted, but their intermediate position between molecules and the metallic state makes them a fascinating research object too. These both sites of the metal cluster chemistry as well as the frequently observed ligand and core fluxionality are related to the cluster metal and surface analogy. (author)

  5. Genetic algorithm optimization of atomic clusters

    International Nuclear Information System (INIS)

    Morris, J.R.; Deaven, D.M.; Ho, K.M.; Wang, C.Z.; Pan, B.C.; Wacker, J.G.; Turner, D.E.; Iowa State Univ., Ames, IA

    1996-01-01

    The authors have been using genetic algorithms to study the structures of atomic clusters and related problems. This is a problem where local minima are easy to locate, but barriers between the many minima are large, and the number of minima prohibit a systematic search. They use a novel mating algorithm that preserves some of the geometrical relationship between atoms, in order to ensure that the resultant structures are likely to inherit the best features of the parent clusters. Using this approach, they have been able to find lower energy structures than had been previously obtained. Most recently, they have been able to turn around the building block idea, using optimized structures from the GA to learn about systematic structural trends. They believe that an effective GA can help provide such heuristic information, and (conversely) that such information can be introduced back into the algorithm to assist in the search process

  6. Clusters of atoms and molecules theory, experiment, and clusters of atoms

    CERN Document Server

    1994-01-01

    Clusters of Atoms and Molecules is devoted to theoretical concepts and experimental techniques important in the rapidly expanding field of cluster science. Cluster properties are dicussed for clusteres composed of alkali metals, semiconductors, transition metals, carbon, oxides and halides of alkali metals, rare gases, and neutral molecules. The book is composed of several well-integrated treatments all prepared by experts. Each contribution starts out as simple as possible and ends with the latest results so that the book can serve as a text for a course, an introduction into the field, or as a reference book for the expert.

  7. Investigations of Atomic Transport Induced by Heavy Ion Irradiation

    Science.gov (United States)

    Banwell, Thomas Clyde

    The mechanisms of atomic transport induced by ion irradiation generally fall into the categories of anisotropic or isotropic processes. Typical examples of these are recoil implantation and cascade mixing, respectively. We have measured the interaction of these processes in the mixing of Ti/SiO(,2)/Si, Cr/SiO(,2)/Si and Ni/SiO(,2)/Si multi-layers irradiated with Xe at fluences of 0.01 - 10 x 10('15)cm('-2). The fluence dependence of net metal transport into the underlying layers was measured with different thicknesses of SiO(,2) and different sample temperatures during irradiation (-196 to 500C). There is a linear dependence at low fluences. At high fluences, a square-root behavior predominates. For thin SiO(,2) layers (primary recoils is quite pronounced since the gross mixing is small. A significant correlation exists between the mixing and the energy deposited through elastic collisions F(,D ). Several models are examined in an attempt to describe the transport process in Ni/SiO(,2). It is likely that injection of Ni by secondary recoil implantation is primarily responsible for getting Ni into the SiO(,2). Secondary recoil injection is thought to scale with F(,D). Trends in the mixing rates indicate that the dominant mechanism for Ti and Cr could be the same as for Ni. The processes of atomic transport and phase formation clearly fail to be separable at higher temperatures. A positive correlation with chemical reactivity emerges at higher irradiation temperatures. The temperature at which rapid mixing occurs is not much below that for spontaneous thermal reaction. Less Ni is retained in the SiO(,2) at high irradiation temperatures. Ni incorporated in the SiO(,2) by low temperature irradiation is not expelled during a consecutive high temperature irradiation. The Ni remains trapped within larger clusters during a sequential 500C irradiation. (Abstract shortened with permission of author.).

  8. Fragmentation of atomic clusters: A theoretical study

    International Nuclear Information System (INIS)

    Lopez, M.J.; Jellinek, J.

    1994-01-01

    Collisionless fragmentation of nonrotating model n-atom metal clusters (n=12, 13, and 14) is studied using isoergic molecular-dynamics simulations. Minimum-energy paths for fragmentation are mapped out as functions of the distance between the centers of mass of the fragments. These paths provide information on the fragmentation energies for the different fragmentation channels. Fragmentation patterns (distributions of the fragmentation channel probabilities) and global and channel-specific fragmentation rate constants are computed and analyzed as functions of the internal energy and of the size of the clusters. The trends derived from the dynamics are compared with those obtained using the RRK and TST statistical approaches. The dynamics of the fragmentation process is analyzed in terms of characteristic quantities such as the distance between the centers of mass of the fragments, their relative translational energy, and their interaction energy, all considered as functions of time

  9. Unraveling the atomic structure of ultrafine iron clusters

    KAUST Repository

    Wang, Hongtao; Li, Kun; Yao, Yingbang; Wang, Qingxiao; Cheng, Yingchun; Schwingenschlö gl, Udo; Zhang, Xixiang; Yang, Wei

    2012-01-01

    Unraveling the atomic structures of ultrafine iron clusters is critical to understanding their size-dependent catalytic effects and electronic properties. Here, we describe the stable close-packed structure of ultrafine Fe clusters for the first

  10. Nanophase materials assembled from atomic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, R.W.

    1989-09-01

    The preparation of atomic clusters of metals and ceramics by means of the gas-condensation method, followed by their in situ consolidation under high-vacuum conditions, has recently led to the synthesis of a new class of ultrafine-grained materials for which their physics is intimately coupled with their application. These nanophase materials, with 2 to 20 nm grain sizes, appear to have properties that are often rather different from conventional materials, and also processing characteristics that are greatly improved. The nanophase synthesis method described here should enable the design of materials heretofore unavailable, with improved or unique properties, based upon an understanding of the physics of these new materials. 23 refs., 8 figs.

  11. Nanophase materials assembled from atomic clusters

    International Nuclear Information System (INIS)

    Siegel, R.W.

    1989-09-01

    The preparation of atomic clusters of metals and ceramics by means of the gas-condensation method, followed by their in situ consolidation under high-vacuum conditions, has recently led to the synthesis of a new class of ultrafine-grained materials for which their physics is intimately coupled with their application. These nanophase materials, with 2 to 20 nm grain sizes, appear to have properties that are often rather different from conventional materials, and also processing characteristics that are greatly improved. The nanophase synthesis method described here should enable the design of materials heretofore unavailable, with improved or unique properties, based upon an understanding of the physics of these new materials. 23 refs., 8 figs

  12. Atomically precise cluster catalysis towards quantum controlled catalysts

    International Nuclear Information System (INIS)

    Watanabe, Yoshihide

    2014-01-01

    Catalysis of atomically precise clusters supported on a substrate is reviewed in relation to the type of reactions. The catalytic activity of supported clusters has generally been discussed in terms of electronic structure. Several lines of evidence have indicated that the electronic structure of clusters and the geometry of clusters on a support, including the accompanying cluster-support interaction, are strongly correlated with catalytic activity. The electronic states of small clusters would be easily affected by cluster–support interactions. Several studies have suggested that it is possible to tune the electronic structure through atomic control of the cluster size. It is promising to tune not only the number of cluster atoms, but also the hybridization between the electronic states of the adsorbed reactant molecules and clusters in order to realize a quantum-controlled catalyst. (review)

  13. Characterization of Radiation-Induced Clustering using Atom Probe Tomography in Nuclear Structural Materials

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Gyeong Geun; Lim, Sang Yeob; Chang, Kun Ok; Ha, Jin Hyung; Kwon, Jun Hyun [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    The degradations include the change in mechanical properties, which are related to the microstructure evolution caused by irradiation. The most widely used tool for the imaging irradiated microstructure is transmission electron microscopy (TEM). The composition of irradiation defects can be analyzed using X-ray spectroscopy (EDS) equipped in the TEM. However, composition characterization of the nano-sized irradiation defects in the matrix is limited due to the beam broadening of TEM and the overlapping of the probed volume during EDS analysis. Recently, Atom probe tomography (APT) has been introduced to the characterization of irradiation defects. APT provides sub-nano scale position of atoms and the chemical composition of a selected volume. SS316 irradiated with Fe ions at above 300 .deg. C caused significant clustering and segregation of Si and Ni at defect sinks. The neutron irradiated low alloy steel showed similar clustering of Ni and Si. The approach of using APT was demonstrated to be well suited for discovering the structure of irradiation defects and performing quantitative analysis in nuclear materials irradiated at high temperature.

  14. Unraveling the atomic structure of ultrafine iron clusters

    KAUST Repository

    Wang, Hongtao

    2012-12-18

    Unraveling the atomic structures of ultrafine iron clusters is critical to understanding their size-dependent catalytic effects and electronic properties. Here, we describe the stable close-packed structure of ultrafine Fe clusters for the first time, thanks to the superior properties of graphene, including the monolayer thickness, chemical inertness, mechanical strength, electrical and thermal conductivity. These clusters prefer to take regular planar shapes with morphology changes by local atomic shuffling, as suggested by the early hypothesis of solid-solid transformation. Our observations differ from observations from earlier experimental study and theoretical model, such as icosahedron, decahedron or cuboctahedron. No interaction was observed between Fe atoms or clusters and pristine graphene. However, preferential carving, as observed by other research groups, can be realized only when Fe clusters are embedded in graphene. The techniques introduced here will be of use in investigations of other clusters or even single atoms or molecules.

  15. Giant resonances in free atoms and in clusters

    International Nuclear Information System (INIS)

    Brechignac, C.; Connerade, J.P.

    1994-01-01

    A review of recent developments in the study of giant resonances in free atoms and in clusters is presented, with particular emphasis on the transition from free atoms to atoms in the condensed phase. Giant resonances in alkali and related metallic clusters due to the excitation of closed shells of delocalized electrons are also reviewed and the relation between different types of collective oscillations is discussed. (author)

  16. Study of Si wafer surfaces irradiated by gas cluster ion beams

    International Nuclear Information System (INIS)

    Isogai, H.; Toyoda, E.; Senda, T.; Izunome, K.; Kashima, K.; Toyoda, N.; Yamada, I.

    2007-01-01

    The surface structures of Si (1 0 0) wafers subjected to gas cluster ion beam (GCIB) irradiation have been analyzed by cross-sectional transmission electron microscopy (XTEM) and atomic force microscopy (AFM). GCIB irradiation is a promising technique for both precise surface etching and planarization of Si wafers. However, it is very important to understand the crystalline structure of Si wafers after GCIB irradiation. An Ar-GCIB used for the physically sputtering of Si atoms and a SF 6 -GCIB used for the chemical etching of the Si surface are also analyzed. The GCIB irradiation increases the surface roughness of the wafers, and amorphous Si layers are formed on the wafer surface. However, when the Si wafers are annealed in hydrogen at a high temperature after the GCIB irradiation, the surface roughness decreases to the same level as that before the irradiation. Moreover, the amorphous Si layers disappear completely

  17. On the electronic and geometrical structures of small atomic clusters

    International Nuclear Information System (INIS)

    Malrieu, J.P.; Maynau, D.

    1987-01-01

    This paper recalls the main challenges and difficulties of the theoretical study of small clusters of atoms. It briefly summarizes some informations concerning rare-gas clusters and clusters of normal elements such as C or Si. The main discussion is devoted to the small clusters of the simplest metal (Li), comparing the agreement and discrepancies between two crude models - the jellium model and the tight-binding one - with the most refined ab initio calculations. 28 refs

  18. Structures of 38-atom gold-platinum nanoalloy clusters

    Energy Technology Data Exchange (ETDEWEB)

    Ong, Yee Pin; Yoon, Tiem Leong [School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lim, Thong Leng [Faculty of Engineering and Technology, Multimedia University, Melaka Campus, 75450 Melaka (Malaysia)

    2015-04-24

    Bimetallic nanoclusters, such as gold-platinum nanoclusters, are nanomaterials promising wide range of applications. We perform a numerical study of 38-atom gold-platinum nanoalloy clusters, Au{sub n}Pt{sub 38−n} (0 ≤ n ≤ 38), to elucidate the geometrical structures of these clusters. The lowest-energy structures of these bimetallic nanoclusters at the semi-empirical level are obtained via a global-minimum search algorithm known as parallel tempering multi-canonical basin hopping plus genetic algorithm (PTMBHGA), in which empirical Gupta many-body potential is used to describe the inter-atomic interactions among the constituent atoms. The structures of gold-platinum nanoalloy clusters are predicted to be core-shell segregated nanoclusters. Gold atoms are observed to preferentially occupy the surface of the clusters, while platinum atoms tend to occupy the core due to the slightly smaller atomic radius of platinum as compared to gold’s. The evolution of the geometrical structure of 38-atom Au-Pt clusters displays striking similarity with that of 38-atom Au-Cu nanoalloy clusters as reported in the literature.

  19. Effects on energetic impact of atomic clusters with surfaces

    International Nuclear Information System (INIS)

    Popok, V.N.; Vuchkovich, S.; Abdela, A.; Campbell, E.E.B.

    2007-01-01

    A brief state-of-the-art review in the field of cluster ion interaction with surface is presented. Cluster beams are efficient tools for manipulating agglomerates of atoms providing control over the synthesis as well as modification of surfaces on the nm-scale. The application of cluster beams for technological purposes requires knowledge of the physics of cluster-surface impact. This has some significant differences compared to monomer ion - surface interactions. The main effects of cluster-surface collisions are discussed. Recent results obtained in experiments on silicon surface nanostructuring using keV-energy implantation of inert gas cluster ions are presented and compared with molecular dynamics simulations. (authors)

  20. Atomic cluster physics: new challenges for theory and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Greiner, Walter [Frankfurt Institute for Advanced Studies, Max-von-Laue Str. 1, Frankfurt am Main 60438 (Germany); Solov' yov, Andrey [Frankfurt Institute for Advanced Studies, Max-von-Laue Str. 1, Frankfurt am Main 60438 (Germany)

    2005-08-01

    A brief introduction to atomic cluster physics, the inter-disciplinary field, which developed fairly successfully during last years, is presented. A review of recent achievements in the detailed ab initio description of structure and properties of atomic clusters and complex molecules is given. The main trends of development in the field are discussed and some of its new focuses are outlined. Particular attention is devoted to the role of quantum and many-body phenomena in the formation of complex multi-atomic systems and the methods of theoretical investigation of their specific properties. The role of the simplified model approaches accurately developed from the fundamental physical principles is stressed. Various illustrations are made for sodium, magnesium clusters, fullerenes and clusters of noble gas atoms.

  1. Enhanced Electromagnetic and Chemical/Biological Sensing. Properties of Atomic Cluster-Derived Materials

    National Research Council Canada - National Science Library

    Schatz, George

    2003-01-01

    The Center for Atomic Clusters-derived Materials performed a broad range of research concerned with synthesizing, characterizing and utilizing atomic and molecular clusters, nanoparticles and nanomaterial...

  2. SASP - Symposium on atomic, cluster and surface physics `94

    Energy Technology Data Exchange (ETDEWEB)

    Maerk, T D; Schrittwieser, R; Smith, D

    1994-12-31

    This international symposium (Founding Chairman: W. Lindinger, Innsbruck) is one in a continuing biennial series of conferences which seeks to promote the growth of scientific knowledge and its effective exchange among scientists in the field of atomic, molecular, cluster and surface physics and related areas. The symposium deals in particular with interactions between ions, electrons, photons, atoms, molecules, and clusters and their interactions with surfaces. (author).

  3. Clustering methods for the optimization of atomic cluster structure

    Science.gov (United States)

    Bagattini, Francesco; Schoen, Fabio; Tigli, Luca

    2018-04-01

    In this paper, we propose a revised global optimization method and apply it to large scale cluster conformation problems. In the 1990s, the so-called clustering methods were considered among the most efficient general purpose global optimization techniques; however, their usage has quickly declined in recent years, mainly due to the inherent difficulties of clustering approaches in large dimensional spaces. Inspired from the machine learning literature, we redesigned clustering methods in order to deal with molecular structures in a reduced feature space. Our aim is to show that by suitably choosing a good set of geometrical features coupled with a very efficient descent method, an effective optimization tool is obtained which is capable of finding, with a very high success rate, all known putative optima for medium size clusters without any prior information, both for Lennard-Jones and Morse potentials. The main result is that, beyond being a reliable approach, the proposed method, based on the idea of starting a computationally expensive deep local search only when it seems worth doing so, is capable of saving a huge amount of searches with respect to an analogous algorithm which does not employ a clustering phase. In this paper, we are not claiming the superiority of the proposed method compared to specific, refined, state-of-the-art procedures, but rather indicating a quite straightforward way to save local searches by means of a clustering scheme working in a reduced variable space, which might prove useful when included in many modern methods.

  4. Equilibrium structure and atomic vibrations of Nin clusters

    Science.gov (United States)

    Borisova, Svetlana D.; Rusina, Galina G.

    2017-12-01

    The equilibrium bond lengths and binding energy, second differences in energy and vibrational frequencies of free clusters Nin (2 ≤ n ≤ 20) were calculated with the use of the interaction potential obtained in the tight-binding approximation (TBA). The results show that the minimum vibration frequency plays a significant role in the evaluation of the dynamic stability of the clusters. A nonmonotonic dependence of the minimum vibration frequency of clusters on their size and the extreme values for the number of atoms in a cluster n = 4, 6, 13, and 19 are demonstrated. This result agrees with the theoretical and experimental data on stable structures of small metallic clusters.

  5. Fusion and fission of atomic clusters: recent advances

    DEFF Research Database (Denmark)

    Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.

    2005-01-01

    We review recent advances made by our group in finding optimized geometries of atomic clusters as well as in description of fission of charged small metal clusters. We base our approach to these problems on analysis of multidimensional potential energy surface. For the fusion process we have...... developed an effective scheme of adding new atoms to stable cluster geometries of larger clusters in an efficient way. We apply this algorithm to finding geometries of metal and noble gas clusters. For the fission process the analysis of the potential energy landscape calculated on the ab initio level...... of theory allowed us to obtain very detailed information on energetics and pathways of the different fission channels for the Na^2+_10 clusters....

  6. High Intensity Femtosecond XUV Pulse Interactions with Atomic Clusters: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Ditmire, Todd [Univ. of Texas, Austin, TX (United States). Center for High Energy Density Science

    2016-10-12

    We propose to expand our recent studies on the interactions of intense extreme ultraviolet (XUV) femtosecond pulses with atomic and molecular clusters. The work described follows directly from work performed under BES support for the past grant period. During this period we upgraded the THOR laser at UT Austin by replacing the regenerative amplifier with optical parametric amplification (OPA) using BBO crystals. This increased the contrast of the laser, the total laser energy to ~1.2 J , and decreased the pulse width to below 30 fs. We built a new all reflective XUV harmonic beam line into expanded lab space. This enabled an increase influence by a factor of 25 and an increase in the intensity by a factor of 50. The goal of the program proposed in this renewal is to extend this class of experiments to available higher XUV intensity and a greater range of wavelengths. In particular we plan to perform experiments to confirm our hypothesis about the origin of the high charge states in these exploding clusters, an effect which we ascribe to plasma continuum lowering (ionization potential depression) in a cluster nano-­plasma. To do this we will perform experiments in which XUV pulses of carefully chosen wavelength irradiate clusters composed of only low-Z atoms and clusters with a mixture of this low-­Z atom with higher Z atoms. The latter clusters will exhibit higher electron densities and will serve to lower the ionization potential further than in the clusters composed only of low Z atoms. This should have a significant effect on the charge states produced in the exploding cluster. We will also explore the transition of explosions in these XUV irradiated clusters from hydrodynamic expansion to Coulomb explosion. The work proposed here will explore clusters of a wider range of constituents, including clusters from solids. Experiments on clusters from solids will be enabled by development we performed during the past grant period in which we constructed and

  7. Computer simulation of void formation in residual gas atom free metals by dual beam irradiation experiments

    International Nuclear Information System (INIS)

    Shimomura, Y.; Nishiguchi, R.; La Rubia, T.D. de; Guinan, M.W.

    1992-01-01

    In our recent experiments (1), we found that voids nucleate at vacancy clusters which trap gas atoms such as hydrogen and helium in ion- and neutron-irradiated copper. A molecular dynamics computer simulation, which implements an empirical embedded atom method to calculate forces that act on atoms in metals, suggests that a void nucleation occurs in pure copper at six and seven vacancy clusters. The structure of six and seven vacancy clusters in copper fluctuates between a stacking fault tetrahedron and a void. When a hydrogen is trapped at voids of six and seven vacancy, a void can keep their structure for appreciably long time; that is, the void do not relax to a stacking fault tetrahedron and grows to a large void. In order to explore the detailed atomics of void formation, it is emphasized that dual-beam irradiation experiments that utilize beams of gas atoms and self-ions should be carried out with residual gas atom free metal specimens. (author)

  8. Absorption of femtosecond laser pulses by atomic clusters

    International Nuclear Information System (INIS)

    Lin Jingquan; Zhang Jie; Li Yingjun; Chen Liming; Lu Tiezheng; Teng Hao

    2001-01-01

    Energy absorption by Xe, Ar, He atomic clusters are investigated using laser pulses with 5 mJ energy in 150 fs duration. Experimental results show that the size of cluster and laser absorption efficiency are strongly dependent on several factors, such as the working pressure of pulse valve, atomic number Z of the gas. Absorption fraction of Xe clusters is as high as 45% at a laser intensity of 1 x 10 15 W/cm 2 with 20 x 10 5 Pa gas jet backing pressure. Absorption of the atomic clusters is greatly reduced by introducing pre-pulses. Ion energy measurements confirm that the efficient energy deposition results in a plasma with very high ion temperature

  9. Deposition of size-selected atomic clusters on surfaces

    International Nuclear Information System (INIS)

    Carroll, S.J.

    1999-06-01

    This dissertation presents technical developments and experimental and computational investigations concerned with the deposition of atomic clusters onto surfaces. It consists of a collection of papers, in which the main body of results are contained, and four chapters presenting a subject review, computational and experimental techniques and a summary of the results presented in full within the papers. Technical work includes the optimization of an existing gas condensation cluster source based on evaporation, and the design, construction and optimization of a new gas condensation cluster source based on RF magnetron sputtering (detailed in Paper 1). The result of cluster deposition onto surfaces is found to depend on the cluster deposition energy; three impact energy regimes are explored in this work. (1) Low energy: n clusters create a defect in the surface, which pins the cluster in place, inhibiting cluster diffusion at room temperature (Paper V). (3) High energy: > 50 eV/atom. The clusters implant into the surface. For Ag 20 -Ag 200 clusters, the implantation depth is found to scale linearly with the impact energy and inversely with the cross-sectional area of the cluster, with an offset due to energy lost to the elastic compression of the surface (Paper VI). For smaller (Ag 3 ) clusters the orientation of the cluster with respect to the surface and the precise impact site play an important role; the impact energy has to be 'focused' in order for cluster implantation to occur (Paper VII). The application of deposited clusters for the creation of Si nanostructures by plasma etching is explored in Paper VIII. (author)

  10. Pulsar-irradiated stars in dense globular clusters

    Science.gov (United States)

    Tavani, Marco

    1992-01-01

    We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

  11. Reactivity and Catalytic Activity of Hydrogen Atom Chemisorbed Silver Clusters.

    Science.gov (United States)

    Manzoor, Dar; Pal, Sourav

    2015-06-18

    Metal clusters of silver have attracted recent interest of researchers as a result of their potential in different catalytic applications and low cost. However, due to the completely filled d orbital and very high first ionization potential of the silver atom, the silver-based catalysts interact very weakly with the reacting molecules. In the current work, density functional theory calculations were carried out to investigate the effect of hydrogen atom chemisorption on the reactivity and catalytic properties of inert silver clusters. Our results affirm that the hydrogen atom chemisorption leads to enhancement in the binding energy of the adsorbed O2 molecule on the inert silver clusters. The increase in the binding energy is also characterized by the decrease in the Ag-O and increase in the O-O bond lengths in the case of the AgnH silver clusters. Pertinent to the increase in the O-O bond length, a significant red shift in the O-O stretching frequency is also noted in the case of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbed silver clusters show low reaction barriers and high heat of formation of the final products for the environmentally important CO oxidation reaction as compared to the parent catalytically inactive clusters. The obtained results were compared with those of the corresponding gold and hydrogen atom chemisorbed gold clusters obtained at the same level of theory. It is expected the current computational study will provide key insights for future advances in the design of efficient nanosilver-based catalysts through the adsorption of a small atom or a ligand.

  12. High-order harmonic generation in clusters irradiated by an infrared laser field of moderate intensity

    International Nuclear Information System (INIS)

    Zaretsky, D F; Korneev, Ph; Becker, W

    2010-01-01

    Extending the Lewenstein model of high-order harmonic generation (HHG) in a laser-irradiated atom, a model of HHG in a cluster is formulated. The constituent atoms of the cluster are assumed to be partly ionized. An electron freed through tunnelling may recombine either with its parent ion or with another ion in the vicinity. Harmonics due to the former process are coherent within the same cluster and may be coherent between different clusters, while harmonics due to the latter process are incoherent. Depending on the density of available ions, the incoherent mechanism may dominate the total harmonic yield, and the harmonic spectrum, which extends to higher energies, has a less distinct cutoff and an enhanced low-energy part.

  13. Structural and electrical evolution of He ion irradiated hydrocarbon films observed by conductive atomic force microscopy

    International Nuclear Information System (INIS)

    Fan, Hongyu; Yang, Deming; Sun, Li; Yang, Qi; Niu, Jinhai; Bi, Zhenhua; Liu, Dongping

    2013-01-01

    Polymer-like hydrocarbon films are irradiated with 100 keV He ion at the fluences of 1.0 × 10 15 –1.0 × 10 17 ions/cm 2 or at the irradiation temperature ranging from 25 to 600 °C. Conductive atomic force microscopy (CAFM) has been used to evaluate the nanoscale electron conducting properties of these irradiated hydrocarbon films. Nanoscale and conducting defects have been formed in the hydrocarbon films irradiated at a relatively high ion fluence (1.0 × 10 17 ions/cm 2 ) or an elevated sample temperature. Analysis indicates that He ion irradiation results in the evolution of polymer-like hydrocarbon into a dense structure containing a large fraction of sp 2 carbon clusters. The sp 2 carbon clusters formed in irradiated hydrocarbon films can contribute to the formation of filament-like conducting channels with a relatively high local field-enhancing factor. Measurements indicate that the growth of nanoscale defects due to He ion irradiation can result in the surface swelling of irradiated hydrocarbon films at a relatively high ion fluences or elevated temperature

  14. Structural and electrical evolution of He ion irradiated hydrocarbon films observed by conductive atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Hongyu [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); Yang, Deming [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); School of Science, Changchun University of Science and Technology, Changchun, Jilin 130022 (China); Sun, Li [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); School of Physics, Liaoning Normal University, Dalian 116023 (China); Yang, Qi; Niu, Jinhai; Bi, Zhenhua [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); Liu, Dongping, E-mail: dongping.liu@dlnu.edu.cn [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); Fujian Key Laboratory for Plasma and Magnetic Resonance, Department of Electronic Science, Aeronautics, School of Physics and Mechanical and Electrical Engineering, Xiamen University, Xiamen, Fujian 361005 (China)

    2013-10-01

    Polymer-like hydrocarbon films are irradiated with 100 keV He ion at the fluences of 1.0 × 10{sup 15}–1.0 × 10{sup 17} ions/cm{sup 2} or at the irradiation temperature ranging from 25 to 600 °C. Conductive atomic force microscopy (CAFM) has been used to evaluate the nanoscale electron conducting properties of these irradiated hydrocarbon films. Nanoscale and conducting defects have been formed in the hydrocarbon films irradiated at a relatively high ion fluence (1.0 × 10{sup 17} ions/cm{sup 2}) or an elevated sample temperature. Analysis indicates that He ion irradiation results in the evolution of polymer-like hydrocarbon into a dense structure containing a large fraction of sp{sup 2} carbon clusters. The sp{sup 2} carbon clusters formed in irradiated hydrocarbon films can contribute to the formation of filament-like conducting channels with a relatively high local field-enhancing factor. Measurements indicate that the growth of nanoscale defects due to He ion irradiation can result in the surface swelling of irradiated hydrocarbon films at a relatively high ion fluences or elevated temperature.

  15. Classical plasma dynamics of Mie-oscillations in atomic clusters

    Science.gov (United States)

    Kull, H.-J.; El-Khawaldeh, A.

    2018-04-01

    Mie plasmons are of basic importance for the absorption of laser light by atomic clusters. In this work we first review the classical Rayleigh-theory of a dielectric sphere in an external electric field and Thomson’s plum-pudding model applied to atomic clusters. Both approaches allow for elementary discussions of Mie oscillations, however, they also indicate deficiencies in describing the damping mechanisms by electrons crossing the cluster surface. Nonlinear oscillator models have been widely studied to gain an understanding of damping and absorption by outer ionization of the cluster. In the present work, we attempt to address the issue of plasmon relaxation in atomic clusters in more detail based on classical particle simulations. In particular, we wish to study the role of thermal motion on plasmon relaxation, thereby extending nonlinear models of collective single-electron motion. Our simulations are particularly adopted to the regime of classical kinetics in weakly coupled plasmas and to cluster sizes extending the Debye-screening length. It will be illustrated how surface scattering leads to the relaxation of Mie oscillations in the presence of thermal motion and of electron spill-out at the cluster surface. This work is intended to give, from a classical perspective, further insight into recent work on plasmon relaxation in quantum plasmas [1].

  16. Generation of even harmonics in a relativistic laser plasma of atomic clusters

    International Nuclear Information System (INIS)

    Krainov, V.P.; Rastunkov, V.S.

    2004-01-01

    It is shown that the irradiation of atomic clusters by a superintense femtosecond laser pulse gives rise to various harmonics of the laser field. They arise as a result of elastic collisions of free electrons with atomic ions inside the clusters in the presence of the laser filed. The yield of even harmonics whose electromagnetic field is transverse is attributed to the relativism of the motion of electrons and the consideration of their drift velocity associated with the internal ionization of atoms and atomic ions of a cluster. These harmonics are emitted in the same direction as odd harmonics. The conductivities and electromagnetic fields of the harmonics are calculated. The generation efficiency of the harmonics slowly decreases as the harmonic number increases. The generation of even harmonics ceases when the drift velocity of electrons becomes equal to zero and only the oscillation velocity of electrons is nonzero. The results can also be applied to the irradiation of solid-state targets inside a skin layer

  17. Formation mechanism of solute clusters under neutron irradiation in ferritic model alloys and in a reactor pressure vessel steel: clusters of defects

    International Nuclear Information System (INIS)

    Meslin-Chiffon, E.

    2007-11-01

    The embrittlement of reactor pressure vessel (RPV) under irradiation is partly due to the formation of point defects (PD) and solute clusters. The aim of this work was to gain more insight into the formation mechanisms of solute clusters in low copper ([Cu] = 0.1 wt%) FeCu and FeCuMnNi model alloys, in a copper free FeMnNi model alloy and in a low copper French RPV steel (16MND5). These materials were neutron-irradiated around 300 C in a test reactor. Solute clusters were characterized by tomographic atom probe whereas PD clusters were simulated with a rate theory numerical code calibrated under cascade damage conditions using transmission electron microscopy analysis. The confrontation between experiments and simulation reveals that a heterogeneous irradiation-induced solute precipitation/segregation probably occurs on PD clusters. (author)

  18. Computer codes for simulating atomic-displacement cascades in solids subject to irradiation

    International Nuclear Information System (INIS)

    Asaoka, Takumi; Taji, Yukichi; Tsutsui, Tsuneo; Nakagawa, Masayuki; Nishida, Takahiko

    1979-03-01

    In order to study atomic displacement cascades originating from primary knock-on atoms in solids subject to incident radiation, the simulation code CASCADE/CLUSTER is adapted for use on FACOM/230-75 computer system. In addition, the code is modified so as to plot the defect patterns in crystalline solids. As other simulation code of the cascade process, MARLOWE is also available for use on the FACOM system. To deal with the thermal annealing of point defects produced in the cascade process, the code DAIQUIRI developed originally for body-centered cubic crystals is modified to be applicable also for face-centered cubic lattices. By combining CASCADE/CLUSTER and DAIQUIRI, we then prepared a computer code system CASCSRB to deal with heavy irradiation or saturation damage state of solids at normal temperature. Furthermore, a code system for the simulation of heavy irradiations CASCMARL is available, in which MARLOWE code is substituted for CASCADE in the CASCSRB system. (author)

  19. Irradiation-Induced Solute Clustering in a Low Nickel FeMnNi Ferritic Alloy

    International Nuclear Information System (INIS)

    Meslin, E.; Barbu, A.; Radiguet, B.; Pareige, P.; Toffolon, C.

    2011-01-01

    Understanding the radiation embrittlement of reactor pressure vessel (RPV) steels is required to be able to operate safely a nuclear power plant or to extend its lifetime. The mechanical properties degradation is partly due to the clustering of solute under irradiation. To gain knowledge about the clustering process, a Fe-1.1 Mn-0.7 Ni (at.%) alloy was irradiated in a test reactor at two fluxes of 0.15 and 9 *10 17 n E≥1MeV . m -2 .s -1 and at increasing doses from 0.18 to 1.3 *10 24 n E≥1MeV ) . m -2 at 300 degrees C. Atom probe tomography (APT) experiments revealed that the irradiation promotes the formation in the α iron matrix of Mn/Mn and/or Ni/Ni pair correlations at low dose and Mn-Ni enriched clusters at high dose. These clusters dissolve partially after a thermal treatment at 400 degrees C. Based on a comparison with thermodynamic calculations, we show that the solute clustering under irradiation can just result from an induced mechanism. (authors)

  20. Thermodynamics of small clusters of atoms: A molecular dynamics simulation

    DEFF Research Database (Denmark)

    Damgaard Kristensen, W.; Jensen, E. J.; Cotterill, Rodney M J

    1974-01-01

    The thermodynamic properties of clusters containing 55, 135, and 429 atoms have been calculated using the molecular dynamics method. Structural and vibrational properties of the clusters were examined at different temperatures in both the solid and the liquid phase. The nature of the melting...... transition was investigated, and a number of properties, such as melting temperature, latent heat of melting, and premelting phenomena, were found to vary with cluster size. These properties were also found to depend on the structure of the solid phase. In this phase the configuration of lowest free energy...

  1. Percolation approach for atomic and molecular cluster formation

    International Nuclear Information System (INIS)

    Knospe, O.; Seifert, G.

    1987-12-01

    We apply a percolation approach for the theoretical analysis of mass spectra of molecular microclusters obtained by adiabatic expansion technique. The evolution of the shape of the experimental size distributions as function of stagnation pressure and stagnation temperature are theoretically reproduced by varying the percolation parameter. Remaining discrepancies between theory and experiment are discussed. In addition, the even-odd alternation as well as the 'magic' shell structure within metallic, secondary ion mass spectra are investigated by introducing statistical weights for the cluster formation probabilities. Shell correction energies of atomic clusters as function of cluster-size are deduced from the experimental data. (orig.)

  2. Impact and spreading behavior of cluster atoms bombarding substrates

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Te-Hua, E-mail: fang.tehua@msa.hinet.net [Institute of Mechanical and Electromechanical Engineering, National Formosa University, Yunlin 632, Taiwan (China); Kang, Shao-Hui; Liao, Jia-Hung [Institute of Mechanical and Electromechanical Engineering, National Formosa University, Yunlin 632, Taiwan (China)

    2009-12-15

    The purpose of this study is to investigate the behavior of copper cluster atoms bombarding a substrate using molecule dynamics based on tight-binding second moment approximation (TB-SMA) potential. The simulated results show that a crater on the substrate surface was created by the impact of the clusters. The variations of kinetic energy of cluster bombardments can be divided into three stages. At the initial impact level, the kinetic energies of the clusters and the substrate were constant. Then, the system went into a sluggish stage of energy variation, in which the kinetic energy of the clusters reduced. In the final stage, the kinetic energy of the system became stable. The high slip vector region around the crater had a disorder damage zone. The symmetry-like cross-slip occurred beneath the top layer of the substrate along the <1 1 0> orientations. The spreading index, temperature, and potential functions that affect the bombardments are also discussed.

  3. Impact and spreading behavior of cluster atoms bombarding substrates

    International Nuclear Information System (INIS)

    Fang, Te-Hua; Kang, Shao-Hui; Liao, Jia-Hung

    2009-01-01

    The purpose of this study is to investigate the behavior of copper cluster atoms bombarding a substrate using molecule dynamics based on tight-binding second moment approximation (TB-SMA) potential. The simulated results show that a crater on the substrate surface was created by the impact of the clusters. The variations of kinetic energy of cluster bombardments can be divided into three stages. At the initial impact level, the kinetic energies of the clusters and the substrate were constant. Then, the system went into a sluggish stage of energy variation, in which the kinetic energy of the clusters reduced. In the final stage, the kinetic energy of the system became stable. The high slip vector region around the crater had a disorder damage zone. The symmetry-like cross-slip occurred beneath the top layer of the substrate along the orientations. The spreading index, temperature, and potential functions that affect the bombardments are also discussed.

  4. Phase behavior of the 38-atom Lennard-Jones cluster

    International Nuclear Information System (INIS)

    Sehgal, Ray M.; Maroudas, Dimitrios; Ford, David M.

    2014-01-01

    We have developed a coarse-grained description of the phase behavior of the isolated 38-atom Lennard-Jones cluster (LJ 38 ). The model captures both the solid-solid polymorphic transitions at low temperatures and the complex cluster breakup and melting transitions at higher temperatures. For this coarse model development, we employ the manifold learning technique of diffusion mapping. The outcome of the diffusion mapping analysis over a broad temperature range indicates that two order parameters are sufficient to describe the cluster's phase behavior; we have chosen two such appropriate order parameters that are metrics of condensation and overall crystallinity. In this well-justified coarse-variable space, we calculate the cluster's free energy landscape (FEL) as a function of temperature, employing Monte Carlo umbrella sampling. These FELs are used to quantify the phase behavior and onsets of phase transitions of the LJ 38 cluster

  5. The adsorption of helium atoms on small cationic gold clusters.

    Science.gov (United States)

    Goulart, Marcelo; Gatchell, Michael; Kranabetter, Lorenz; Kuhn, Martin; Martini, Paul; Gitzl, Norbert; Rainer, Manuel; Postler, Johannes; Scheier, Paul; Ellis, Andrew M

    2018-04-04

    Adducts formed between small gold cluster cations and helium atoms are reported for the first time. These binary ions, Aun+Hem, were produced by electron ionization of helium nanodroplets doped with neutral gold clusters and were detected using mass spectrometry. For a given value of n, the distribution of ions as a function of the number of added helium atoms, m, has been recorded. Peaks with anomalously high intensities, corresponding to so-called magic number ions, are identified and interpreted in terms of the geometric structures of the underlying Aun+ ions. These features can be accounted for by planar structures for Aun+ ions with n ≤ 7, with the addition of helium having no significant effect on the structures of the underlying gold cluster ions. According to ion mobility studies and some theoretical predictions, a 3-D structure is expected for Au8+. However, the findings for Au8+ in this work are more consistent with a planar structure.

  6. Photoelectron imaging, probe of the dynamics: from atoms... to clusters

    International Nuclear Information System (INIS)

    Lepine, F.

    2003-06-01

    This thesis concerns the study of the deexcitation of clusters and atoms by photoelectron imaging. The first part is dedicated to thermionic emission of a finite size system. A 3-dimensional imaging setup allows us to measure the time evolution of the kinetic energy spectrum of electrons emitted from different clusters (W n - , C n - , C 60 ). Then we have a direct access to the fundamental quantities which characterize this statistical emission: the temperature of the finite heat bath and the decay rate. The second part concerns the ionization of atomic Rydberg states placed in a static electric field. We performed the first experiment of photoionization microscopy which allows us to obtain a picture which is the macroscopic projection of the electronic wave function. Then we have access to the detail of the photoionization and particularly to the quantum properties of the electron usually confined at the atomic scale. (author)

  7. Model study in chemisorption: atomic hydrogen on beryllium clusters

    International Nuclear Information System (INIS)

    Bauschlicher, C.W. Jr.

    1976-08-01

    The interaction between atomic hydrogen and the (0001) surface of Be metal has been studied by ab initio electronic structure theory. Self-consistent-field (SCF) calculations have been performed using minimum, optimized minimum, double zeta and mixed basis sets for clusters as large as 22 Be atoms. The binding energy and equilibrium geometry (the distance to the surface) were determined for 4 sites. Both spatially restricted (the wavefunction was constrained to transform as one of the irreducible representations of the molecular point group) and unrestricted SCF calculations were performed. Using only the optimized minimum basis set, clusters containing as many as 22 beryllium atoms have been investigated. From a variety of considerations, this cluster is seen to be nearly converged within the model used, providing the most reliable results for chemisorption. The site dependence of the frequency is shown to be a geometrical effect depending on the number and angle of the bonds. The diffusion of atomic hydrogen through a perfect beryllium crystal is predicted to be energetically unfavorable. The cohesive energy, the ionization energy and the singlet-triplet separation were computed for the clusters without hydrogen. These quantities can be seen as a measure of the total amount of edge effects. The chemisorptive properties are not related to the total amount of edge effects, but rather the edge effects felt by the adsorbate bonding berylliums. This lack of correlation with the total edge effects illustrates the local nature of the bonding, further strengthening the cluster model for chemisorption. A detailed discussion of the bonding and electronic structure is included. The remaining edge effects for the Be 22 cluster are discussed

  8. Similarities and Differences Between Atomic Nuclei and Clusters: Toward a Unified Development of Cluster Science. Proceedings

    International Nuclear Information System (INIS)

    Abe, Y.; Arai, I.; Lee, S.; Yabana, K.

    1998-01-01

    These proceedings represent papers presented at the symposium on Similarities and Differences Between Atomic Nuclei and Clusters held in Tsukuba, Japan in July, 1997. A wide range of topics were covered including the quantum and thermal properties of free clusters to high energy impacts of clusters on solid surfaces. Fullerenes and carbon clusters chemistry was discussed in some detail. This symposium brought together scientists from many disciplines: nuclear and solid state physicists, chemists, and material scientists. There are 62 papers in the proceedings and 3 have been abstracted for the Energy Science and Technology database

  9. Investigations on carbon cluster formation in heavy ion irradiated polymers

    International Nuclear Information System (INIS)

    Tripathy, S.P.; Mishra, R.; Mawar, A.K.; Dwivedi, K.K.; Khathing, D.T.; Srivastava, A.; Avasthi, D.K.; Ghosh, S.; Fink, D.

    2000-01-01

    In polymers, the carbonaceous clusters are supposed to be responsible for the electrical conductivity. So, the irradiation of organic polymers namely polypropylene (8μ) and polyimide (50μ) by energetic heavy ions 28 Si and 58 Ni produce significant changes in the size of these clusters leading to the corresponding change in the band gap and other electrical properties as revealed by the UV-VIS spectroscopic examinations. (author)

  10. Spin magnetic moments from single atoms to small Cr clusters

    Energy Technology Data Exchange (ETDEWEB)

    Boeglin, C.; Decker, R.; Bulou, H.; Scheurer, F.; Chado, I. [IPCMS-GSI - UMR 7504, 67037 Strasbourg Cedex (France); Ohresser, P. [LURE, 91405 Orsay (France); Dhesi, S.S. [ESRF, BP 220, 38043 Grenoble Cedex (France); Present permanent address: Diamond Light Source, Chilton, Didcot OX11 0QX (United Kingdom); Gaudry, E. [LMCP, 4, place Jussieu, 75252 Paris (France); Lazarovits, B. [CCMS, T.U. Vienna, Gumpendorfstr. 1a, 1060 Wien (Austria)

    2005-07-01

    Morphology studies at the first stages of the growth of Cr/Au(111) are reported and compared to the magnetic properties of the nanostructures. We analyze by Scanning Tunneling Microscopy and Low Energy Electron Diffraction the Cr clusters growth between 200 K and 300 K. In the early stages of the growth the morphology of the clusters shows monoatomic high islands located at the kinks of the herringbone reconstructed Au(111) surface. By X-ray Magnetic Circular Dichroism performed on the Cr L{sub 2,3} edges it is shown that the temperature dependent morphology strongly influences the magnetic properties of the Cr clusters. We show that in the sub-monolayer regime Cr clusters are antiferromagnetic and paramagnetic when the size reaches the atomic limit. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Numerical atomic scale simulations of the microstructural evolution of ferritic alloys under irradiation

    International Nuclear Information System (INIS)

    Vincent, E.

    2006-12-01

    In this work, we have developed a model of point defect (vacancies and interstitials) diffusion whose aim is to simulate by kinetic Monte Carlo (KMC) the formation of solute rich clusters observed experimentally in irradiated FeCuNiMnSi model alloys and in pressure vessel steels. Electronic structure calculations have been used to characterize the interactions between point defects and the different solute atoms. Each of these solute atoms establishes an attractive bond with the vacancy. As for Mn, which is the element which has the weakest bond with the vacancy, it establishes more favourable bonds with interstitials. Binding energies, migration energies as well as other atomic scale properties, determined by ab initio calculations, have led to a parameter set for the KMC code. Firstly, these parameters have been optimised on thermal ageing experiments realised on the FeCu binary alloy and on complex alloys, described in the literature. The vacancy diffusion thermal annealing simulations show that when a vacancy is available, all the solutes migrate and form clusters, in agreement with the observed experimental tendencies. Secondly, to simulate the microstructural evolution under irradiation, we have introduced interstitials in the KMC code. Their presence leads to a more efficient transport of Mn. The first simulations of electron and neutron irradiations show that the model results are globally qualitatively coherent with the experimentally observed tendencies. (author)

  12. High-accuracy coupled cluster calculations of atomic properties

    Energy Technology Data Exchange (ETDEWEB)

    Borschevsky, A. [School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel and Centre for Theoretical Chemistry and Physics, The New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand); Yakobi, H.; Eliav, E.; Kaldor, U. [School of Chemistry, Tel Aviv University, 69978 Tel Aviv (Israel)

    2015-01-22

    The four-component Fock-space coupled cluster and intermediate Hamiltonian methods are implemented to evaluate atomic properties. The latter include the spectra of nobelium and lawrencium (elements 102 and 103) in the range 20000-30000 cm{sup −1}, the polarizabilities of elements 112-114 and 118, required for estimating their adsorption enthalpies on surfaces used to separate them in accelerators, and the nuclear quadrupole moments of some heavy atoms. The calculations on superheavy elements are supported by the very good agreement with experiment obtained for the lighter homologues.

  13. High-accuracy coupled cluster calculations of atomic properties

    International Nuclear Information System (INIS)

    Borschevsky, A.; Yakobi, H.; Eliav, E.; Kaldor, U.

    2015-01-01

    The four-component Fock-space coupled cluster and intermediate Hamiltonian methods are implemented to evaluate atomic properties. The latter include the spectra of nobelium and lawrencium (elements 102 and 103) in the range 20000-30000 cm −1 , the polarizabilities of elements 112-114 and 118, required for estimating their adsorption enthalpies on surfaces used to separate them in accelerators, and the nuclear quadrupole moments of some heavy atoms. The calculations on superheavy elements are supported by the very good agreement with experiment obtained for the lighter homologues

  14. Atomic structure of radiation damages in FCC-metals after neutron irradiation

    International Nuclear Information System (INIS)

    Popova, E.V.; Ivchenko, V.A.; Kozlov, A.V.

    2005-01-01

    Full text: Radiation clusters, formed at a neutron irradiation, are a product of evolution of cascade areas. The quantitative information about clusters can be used for verification of calculations of cascade damage ability, in particular, cascade efficiency. Data about concentration clusters and an average of the vacancies containing in them, allow to receive total of the vacancies reserved in them and to use them for comparison to results of calculations of cascade damage ability. A correctness of such comparison by that above, than below temperature of a neutron irradiation. The purpose of work was experimental studying radiation clusters formed in FCC-metals at a low temperature neutron irradiation methods of dilatometry, field ion (FIM) and transmission electronic microscopy (TEM). Radiation clusters were studied: in industrial austenite steel C0.05Crl6Nil5Mo2Mnl, irradiated in reactor Rw-2a at temperature 310 K up to fluence intermediate and fast neutrons (with E > 0,1 MeV) 6.7·l0 21 m -2 ; in a modelling material - Pt (cleanliness of 99.99 %) with the same - FCC-structure in an initial condition and after an irradiation in reactor RWW-2M at temperature 310 K up to fluence intermediate and fast neutrons (with E > 0.1 MeV) 3.5·10 22 m -2 . As a result of an irradiation of steel and pure Pt, in these materials by methods FIM and TEM many radiation clusters, the accelerated neutrons initiated by interaction with substance was revealed. It is established that these damage areas represent the depleted zones containing separate vacancies, and also small vacancy complexes, with the 'belt' interstitial atoms. The quantitative estimation of the sizes of such radiating defects is lead and their density in volume is experimentally established. So the neutron irradiation of steel at temperature 310 K up to fluence 6.7·10 21 m -2 causes formation radiation clusters which average diameter according to TEM makes 3 nanometers. Observable by methods FIM clusters have the

  15. Theory of small atomic-like 2D dust clusters

    International Nuclear Information System (INIS)

    Amiranashvili, Sh.G.; Gousein-zade, N.G.; Tsytovich, V.N.

    2002-01-01

    In several experiments atom-like dust clusters with parabolic confining potential were observed [1-3]. Here we present a general theory of 2D clusters confined by (1/2)m dω 0 2 r2 potential with arbitrary pair interaction potential depending on the inter-dust distance. It describes the equilibrium conditions, normal modes, their frequencies and possible instabilities of clusters with arbitrary N number of grains. The mono-layer clusters can have 2N frequencies of oscillations in the cluster plane among which 3 modes are trivial (ω = 0 and double degenerate frequency of oscillation in the potential well). The 2N - 3 non-trivial modes are considered. For example, for square dust cluster with potential V(r) the equilibrium is described by ω 0 2 = -(4/m) [V'(√(2)R) + V'(2R)], the frequency of radial oscillations is ω2 = (16R2/m) [V''(√(2)R) + 2V''(2R)], the two single modes frequencies are ω2 (32R2/m)V''(2R); ω2 = (16R2/m)V''(√(2)r) and one double degenerated mode frequency is ω2 = (1/m) [V'√(2)R) - V'(2R) + 4R2V''(√(2)R)] where ' corresponds to the differentiation of the potential V(r) with respect to √(r). The general stability criterion was found and investigated for N ≥ 4. The pair interaction potential V(r) is considered as a sum of different attraction and repulsion terms , including that which describe the non-screened collective and non collective attraction, the screened non-Coulomb interaction and the non-screened repulsion. The collective non-screened potential causes the absence of equilibria at certain dust cluster sizes. For screened Coulomb potential Vc(r) = (Z d 2 e2αscr/r)exp(-r/λscr) the clusters with the size R are considered. The pentagon cluster is found to be stable for R < 3.3λscr and the clusters with N ≥ 6 are found to be always unstable. The measurements of the frequencies of the cluster modes, the thresholds of cluster equilibria and the stability of the clusters can be used for detection of the dust

  16. Atom probe tomography of the evolution of the nanostructure of oxide dispersion strengthened steels under ion irradiation

    Science.gov (United States)

    Orlov, N. N.; Rogozhkin, S. V.; Bogachev, A. A.; Korchuganova, O. A.; Nikitin, A. A.; Zaluzhnyi, A. G.; Kozodaev, M. A.; Kulevoy, T. V.; Kuibeda, R. P.; Fedin, P. A.; Chalykh, B. B.; Lindau, R.; Hoffmann, Ya.; Möslang, A.; Vladimirov, P.

    2017-09-01

    The atom probe tomography of the nanostructure evolution in ODS1 Eurofer, ODS 13.5Cr, and ODS 13.5Cr-0.3Ti steels under heavy ion irradiation at 300 and 573 K is performed. The samples were irradiated by 5.6 MeV Fe2+ ions and 4.8 MeV Ti2+ ions to a fluence of 1015 cm-2. It is shown that the number of nanoclusters increases by a factor of 2-3 after irradiation. The chemical composition of the clusters in the steels changes after irradiation at 300 K, whereas the chemical composition of the clusters in the 13.5Cr-0.3Ti ODS steel remains the same after irradiation at 573 K.

  17. Chemically induced magnetism in atomically precise gold clusters.

    Science.gov (United States)

    Krishna, Katla Sai; Tarakeshwar, Pilarisetty; Mujica, Vladimiro; Kumar, Challa S S R

    2014-03-12

    Comparative theoretical and experimental investigations are reported into chemically induced magnetism in atomically-precise, ligand-stabilized gold clusters Au25 , Au38 and Au55 . The results indicate that [Au25 (PPh3 )10 (SC12 H25 )5 Cl2 ](2+) and Au38 (SC12 H25 )24 are diamagnetic, Au25 (SC2 H4 Ph)18 is paramagnetic, and Au55 (PPh3 )12 Cl6 , is ferromagnetic at room temperature. Understanding the magnetic properties resulting from quantum size effects in such atomically precise gold clusters could lead to new fundamental discoveries and applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Clustered field evaporation of metallic glasses in atom probe tomography

    International Nuclear Information System (INIS)

    Zemp, J.; Gerstl, S.S.A.; Löffler, J.F.; Schönfeld, B.

    2016-01-01

    Field evaporation of metallic glasses is a stochastic process combined with spatially and temporally correlated events, which are referred to as clustered evaporation (CE). This phenomenon is investigated by studying the distance between consecutive detector hits. CE is found to be a strongly localized phenomenon (up to 3 nm in range) which also depends on the type of evaporating ions. While a similar effect in crystals is attributed to the evaporation of crystalline layers, CE of metallic glasses presumably has a different – as yet unknown – physical origin. The present work provides new perspectives on quantification methods for atom probe tomography of metallic glasses. - Highlights: • Field evaporation of metallic glasses is heterogeneous on a scale of up to 3 nm. • Amount of clustered evaporation depends on ion species and temperature. • Length scales of clustered evaporation and correlative evaporation are similar.

  19. Cluster dynamics models of irradiation damage accumulation in ferritic iron. I. Trap mediated interstitial cluster diffusion

    Energy Technology Data Exchange (ETDEWEB)

    Kohnert, Aaron A.; Wirth, Brian D. [University of Tennessee, Knoxville, Tennessee 37996-2300 (United States)

    2015-04-21

    The microstructure that develops under low temperature irradiation in ferritic alloys is dominated by a high density of small (2–5 nm) defects. These defects have been widely observed to move via occasional discrete hops during in situ thin film irradiation experiments. Cluster dynamics models are used to describe the formation of these defects as an aggregation process of smaller clusters created as primary damage. Multiple assumptions regarding the mobility of these damage features are tested in the models, both with and without explicit consideration of such irradiation induced hops. Comparison with experimental data regarding the density of these defects demonstrates the importance of including such motions in a valid model. In particular, discrete hops inform the limited dependence of defect density on irradiation temperature observed in experiments, which the model was otherwise incapable of producing.

  20. Atom transfer radical polymerization of styrene under pulsed microwave irradiation

    International Nuclear Information System (INIS)

    Cheng Zhenping; Zhu Xiulin; Zhou Nianchen; Zhu Jian; Zhang Zhengbiao

    2005-01-01

    A homogeneous solution atom transfer radical polymerization (ATRP) and reverse atom transfer radical polymerization (RATRP) of styrene (St) in N,N-dimethylformamide (DMF) were successfully carried out under pulsed microwave irradiation (PMI), using 1-bromo-1-phenylethane (1-PEBr)/CuCl/N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA) as an initiating system at 85 deg. C and 2,2'-azo-bis-isobutyrontrile (AIBN)/CuCl 2 /PMDETA as an initiating system at 95 deg. C, respectively. The polymerization rates under PMI were greatly increased in comparison with those under identical conventional heating (CH)

  1. Preliminary irradiation test results from the Yankee Atomic Electric Company reactor vessel test irradiation program

    International Nuclear Information System (INIS)

    Biemiller, E.C.; Fyfitch, S.; Campbell, C.A.

    1993-01-01

    The Yankee Atomic Electric Company test irradiation program was implemented to characterize the irradiation response of representative Yankee Rowe reactor vessel beltline plate materials and to remove uncertainties in the analysis of existing irradiation data on the Yankee Rowe reactor vessel steel. Plate materials each containing 0.24 w/o copper, but different nickel contents at 0.63 w/o and 0.19 w/o, were heat treated to simulate the Yankee vessel heat treatment (austenitized at 1800 deg F) and to simulate Regulatory Guide 1.99 database materials (austenitized at 1600 deg. F). These heat treatments produced different microstructures so the effect of microstructure on irradiation damage sensitivity could be tested. Because the nickel content of the test plates varied and the copper level was constant, the effect of nickel on irradiation embrittlement was also tested. Correlation monitor material, HSST-02, was included in the program to benchmark the Ford Nuclear Reactor (U. of Michigan Test Reactor) which had never been used for this type of irradiation program. Materials taken from plate surface locations (vs. 1/4T) were included to test whether or not the improved toughness properties of the plate surface layer, resulting from the rapid quench, is maintained after irradiation. If the improved properties are maintained, pressurized thermal shock calculations could utilize this margin. Finally, for one experiment, irradiations were conducted at two irradiation temperatures (500 deg. F and 550 deg. F) to determine the effect of irradiation temperature on embrittlement. The preliminary results of the irradiation program show an increase in T 30 shift of 69 deg. F for a decrease in irradiation temperature of 50 deg. F. The results suggest that for nickel bearing steels, the superior toughness of plate surface material is maintained after irradiation and for the copper content tested, nickel had no apparent effect on irradiation response. No apparent microstructure

  2. APFIM investigation of clustering in neutron-irradiated Fe-Cu alloys and pressure vessel steels

    International Nuclear Information System (INIS)

    Auger, P.; Pareige, P.; Blavette, D.

    1996-01-01

    Pressure vessel steels used in PWRs are known to be prone to hardening and embrittlement under neutron irradiation. The changes in mechanical properties are commonly supposed to result from the formation of point defects, dislocation loops, voids and copper-rich precipitates. However, the real nature of the irradiation induced damage, in these particularly low copper steels (>0,1 wt%), has not been clearly identify yet. A new experimental work has been carried out thanks to atom probe and field ion microscopy (APFIM) facilities and, more particularly with a new generation of atom probe recently developed, namely the tomographic atom probe (TAP), in order to improve: the understanding of the complex behavior of copper precipitation which occurs when low-alloyed Fe-Cu model alloys are irradiated with neutrons; the microstructural characterization of the pressure vessel steel of the CHOOZ A reactor under various fluences (French Surveillance Programme). The investigations clearly reveal the precipitation of copper-rich clusters in irradiated Fe-Cu alloys while more complicated Si, Ni, Mn and Cu-solute 'clouds' were observed to develop in the low-copper ferritic solid solution of the pressure vessel steel. (authors)

  3. Atomic size effect on the formation of ionized cluster beam epitaxy in Lennard-Jones systems

    International Nuclear Information System (INIS)

    Hsieh Horngming; Averback, R.S.

    1991-01-01

    Ionized cluster beam deposition is studied by molecular dynamics simulations in which the atomic size of incident cluster atoms is different from the size of substrate atoms. Lennard-Jones interatomic potentials are used for the two-component system. The results provide the morphologies of the overlayers for various atomic sizes and are compared to simulation results of molecular beam epitaxy. (orig.)

  4. Plasmon excitations in doped square-lattice atomic clusters

    Science.gov (United States)

    Wang, Yaxin; Yu, Ya-Bin

    2017-12-01

    Employing the tight-binding model, we theoretically study the properties of the plasmon excitations in doped square-lattice atomic clusters. The results show that the dopant atoms would blur the absorption spectra, and give rise to extra plasmon resonant peaks as reported in the literature; however, our calculated external-field induced oscillating charge density shows that no obvious evidences indicate the so-called local mode of plasmon appearing in two-dimensional-doped atomic clusters, but the dopants may change the symmetry of the charge distribution. Furthermore, we show that the disorder of the energy level due to dopant makes the absorption spectrum has a red- or blue-shift, which depends on the position of impurities; disorder of hopping due to dopant makes a blue- or red-shift, a larger (smaller) hopping gives a blue-shift (red-shift); and a larger (smaller) host-dopant and dopant-dopant intersite coulomb repulsion induces a blue-shift (red-shift).

  5. Spectra of matrix isolated metal atoms and clusters

    International Nuclear Information System (INIS)

    Meyer, B.

    1977-01-01

    The matrix isolation spectra of all of the 40 presently known atomic metal species show strong matrix effects. The transition energies are increased, and the bands are broad and exhibit splitting of sublevels which are degenerate in the gas phase. Several models have been proposed for splitting of levels, but basic effects are not yet understood, and spectra cannot be predicted, yet it is possible to correlate gas phase and matrix in many of the systems. Selective production of diatomics and clusters via thermal and optical annealing of atomic species can be monitored by optical spectra, but yields spectroscopically complex systems which, however, especially in the case of transition metals, can be used as precursors in novel chemical reactions. A combination of absorption, emission, ir, Raman, ESR, and other methods is now quickly yielding data which will help correlate the increasing wealth of existing data. 55 references, 6 figures

  6. Study on interaction of swift cluster ion beam with matter and irradiation effect (Joint research)

    International Nuclear Information System (INIS)

    Saito, Yuichi; Shibata, Hiromi

    2010-07-01

    This review covers results of the 'Study of interaction on swift cluster ion beam with matter and irradiation effect' supported by the Interorganization Atomic Energy Research Program from 2006FY to 2008FY. It is composed of a research abstract for each sub-group with viewgraphs which were presented at the group meeting held on March 2009 or 'Meeting of High LET radiation -From fundamental study among physics, chemistry and biology to medical applications-' sponsored by Japan Society of Radiation Chemistry, cosponsored by this research group. (author)

  7. Microstructure and fracture toughness of irradiated stainless steel retrieved from the field: the potential role of radiation-induced clusters

    International Nuclear Information System (INIS)

    Chou, P.; Soneda, N.; Nishida, K.; Dohi, K.; Marquis, E.A.; Chen, Y.

    2015-01-01

    The microstructures of six material/fluence combinations of stainless steels retrieved from BWR components (top guide and control rods) have been examined by atom probe tomography; the irradiated microstructure had been already characterized by transmission electron microscopy (TEM). The fracture toughness of two material/fluence combinations had been previously measured. The aggregate results strongly suggest that radiation-induced clusters play a significant role in the degradation of fracture toughness that occurs at fluences below ∼ 13 dpa. Because TEM has not been able to consistently identify and quantify the nano-sized clusters in this fluence range, it has not highlighted the potential role of radiation-induced clusters. (authors)

  8. Irradiated foodstuff: atom, junk-food and globalization; Aliments irradies: Atome, malbouffe et mondialisation

    Energy Technology Data Exchange (ETDEWEB)

    Azam, Genevieve; Berlan, Jean-Pierre; Desbordes, Roland; Dufour, Francois; Fievet, Yann; Folliard, Thierry; Gallais, Veronique; Hauter, Wenonah; Jacquiau, Christian; Kastler, Guy; Lannoye, Paul; Le Goff, Lylian; Le Rohellec, Catherine; Louchard, Olivier; Marechal, Gilles; Nicolas, Yveline; Remesy, Christian; Trouve, Aurelie; Veillerette, Francois

    2008-07-01

    Food irradiation is officially presented as an ideal technology at the service of worldwide health safety and as an alternative to chemical processing of foodstuff. It is first of all a multi-usage technology for the preservation, disinfestation, ripening slowing down, and germination inhibition of products which serves the interests of multinational companies of the agriculture and food industry. According to the authors, it is also an instrument for the globalization of foodstuff trade encouraged by the international institutions and by some governments. The book stresses on the health, socio-economic and environmental risks of this technology: vitamins loss, carcinogenesis, mutagenesis, impact on local employment and economy, risks linked with the use of irradiation devices etc

  9. Electron paramagnetic resonance studies on silver atoms and clusters in regularly interstratified clay minerals

    International Nuclear Information System (INIS)

    Yamada, H.; Tamura, K.; Shimomura, S.; Sadlo, J.; Turek, J.; Michalik, J.

    2004-01-01

    The formation and stabilization of reduced silver species in the regularly interstratified clay minerals, trioctahedral smectite/chlorite (tri-Sm/Ch) and dioctahedral smectite/mica (di-Sm/M), have been studied by electron paramagnetic resonance (EPR) spectroscopy. Both minerals loaded with Ag + cations after degassing and dehydration were γ-irradiated at 77 K and monitored by EPR as the temperature increased. Some samples were exposed to water or methanol vapor after dehydration. In both hydrated and dehydrated samples only the doublets to Ag 0 atoms were observed with no evidence of the formation of Ag clusters. However, the EPR parameter of silver atoms in both matrices are different. In tri-Sm/Ch the narrow anisotropic EPR lines overlap with the broader isotropic lines, whereas in di-Sm/M only broad lines are recorded. The hyperfine splitting - A iso (Ag 0 ) is larger in tri-Sm/Ch than in di-Sm/M. Also the stability of Ag 0 in both clay minerals is distinctly different. Ag 0 doublet in di-Sm/M disappears completely above 230 K, Whereas in tri-Sm/Ch it is still recorded at 310 K. It is proposed, basing on the EPR results that Ag 0 atoms appear at different sites in both matrices: - in tri-Sm/Ch in the middle of smectite interlayer and in hexagonal cavities in the silicate sheets of tetrahedron layer and in di-Sm.M in hexagonal cavities only. When samples had been exposed to methanol before irradiation, the silver clusters become stabilized in the interlayer sites. In tri-Sm/M matrix the silver dimer Ag 2 + formed by gamma-irradiation at 77 K is transformed to tetrameric cluster, Ag 4 + at 150 K. In di-Sm/M the radiation-induced silver agglomeration proceeds in a similar way, but with a slower rate and Ag tetramer is formed only above 190 K. In both clay minerals, Ag 4 + clusters decay above 250 K. (author)

  10. Preliminary irradiation test results from the Yankee Atomic Electric Company reactor vessel test irradiation program

    International Nuclear Information System (INIS)

    Biemiller, E.C.; Fyfitch, Stephen; Campbell, C.A.

    1994-01-01

    The Yankee Atomic Electric Company test irradiation program was implemented to characterize the irradiation response of representative Yankee Rowe reactor vessel beltline plate materials and to remove uncertainties in the analysis of existing irradiation data on the Yankee Rowe reactor vessel steel. Plate materials each containing 0.24 w/o copper, but different nickel contents at 0.63 w/o and 0.19 w/o, were heat treated to simulate the Yankee vessel heat treatment (austenitized at 982 o C (1800 o F)) and to simulate Regulatory Guide 1.99 database materials (austenitized at 871 o C (1600 o F)). These heat treatments produced different microstructures so the effect of microstructure on irradiation damage sensitivity could be tested. Because the nickel content of the test plates varied and the copper level was constant, the effect of nickel on irradiation embrittlement was also tested. Correlation monitor material, HSST-02, was included in the program to benchmark the Ford Nuclear Reactor (University of Michigan Test Reactor) which had never been used before for this type of irradiation program. Materials taken from plate surface locations (versus 1/4 T) were included to test whether or not the improved toughness properties of the plate surface layer, resulting from the rapid quench, are maintained after irradiation. If the improved properties are maintained, pressurized thermal shock calculations could utilize this margin. Finally, for one experiment, irradiations were conducted at two irradiation temperatures (260 o C and 288 o C) to determine the effect of irradiation temperature on embrittlement. (Author)

  11. The interaction of super-intense ultra-short laser pulse and micro-clusters with large atomic clusters

    International Nuclear Information System (INIS)

    Miao Jingwei; Yang Chaowen; An Zhu; Yuan Xuedong; Sun Weiguo; Luo Xiaobing; Wang Hu; Bai Lixing; Shi Miangong; Miao Lei; Zhen Zhijian; Gu Yuqin; Liu Hongjie; Zhu Zhouseng; Sun Liwei; Liao Xuehua

    2007-01-01

    The fusion mechanism of large deuterium clusters (100-1000 Atoms/per cluster) in super-intense ultra-short laser pulse field, Coulomb explosions of micro-cluster in solids, gases and Large-size clusters have been studied using the interaction of a high-intensity femtosecond laser pulses with large deuterium clusters, collision of high-quality beam of micro-cluster from 2.5 MV van de Graaff accelerator with solids, gases and large clusters. The experimental advance of the project is reported. (authors)

  12. Modeling of 1D motion of interstitial clusters in iron under HVEM irradiation

    International Nuclear Information System (INIS)

    Satoh, Y.; Hamaoka, T.; Matsui, H.

    2007-01-01

    Full text of publication follows: We examined 1D motion of interstitial clusters in Fe under electron irradiation at room temperature using high voltage electron microscopy (HVEM). We found that some impurities have essential effects on the experimental 1D motion behavior. The characteristics of experimental 1D motion were obtained as follows: 1) 1D motion appears as discrete jumps (namely, stepwise positional changes) at irregular intervals. 2) Sometimes a set of several successive jumps occurs between certain two points (back and forth motion). 3) The frequency of 1D jumps is almost proportional to the electron beam intensity, while the distribution of 1D jump distance does not change much with the intensity. Very few 1D jumps are observed with a 200 kV TEM at room temperature. 4) The distance and the frequency of 1D jumps are greatly reduced in a specimen of low purities. Taking account for effects of impurities, we propose a mechanism of the experimental 1D jumps, as follows. Small interstitial clusters are regarded to be essentially mobile as crowdion bundles. Then interstitial clusters in a stationary state are trapped by impurity atom(s), due to elastic interactions between impurities and crowdion bundle. The electron irradiation changes the cluster into a mobile state by a detrapping: for example, the impurity atom is displaced to apart from the crowdion bundle. Then the crowdion bundle makes a free 1D migration until it is trapped by another impurity atom. Because of small activation energy for 1D migration, we cannot observe the detailed 1D random walk process, but a stepwise positional change from an impurity to another impurity. The average size of interstitial clusters observed in the present experiments was around 5 nm, corresponding to a bundle of 300 crowdions. In a rough estimate assuming that an impurity atom on any crowdion in the crowdion bundle prevent the migration of the bundle, the mean free path is about 75 nm and 7.5 nm at the impurity

  13. Microstructural characterization of irradiated PWR steels using the atom probe field-ion microscope

    International Nuclear Information System (INIS)

    Miller, M.K.; Burke, M.G.

    1987-08-01

    Atom probe field-ion microscopy has been used to characterize the microstructure of a neutron-irradiated A533B pressure vessel steel weld. The atomic spatial resolution of this technique permits a complete structural and chemical description of the ultra-fine features that control the mechanical properties to be made. A variety of fine scale features including roughly spherical copper precipitates and clusters, spherical and rod-shaped molybdenum carbide and disc-shaped molybdenum nitride precipitates were observed to be inhomogeneously distributed in the ferrite. The copper content of the ferrite was substantially reduced from the nominal level. A thin film of molybdenum carbides and nitrides was observed on grain boundaries in addition to a coarse copper-manganese precipitate. Substantial enrichment of manganese and nickel were detected at the copper-manganese precipitate-ferrite interface and this enrichment extended into the ferrite. Enrichment of nickel, manganese and phosphorus were also measured at grain boundaries

  14. Energy spectra of primary knock-on atoms under neutron irradiation

    International Nuclear Information System (INIS)

    Gilbert, M.R.; Marian, J.; Sublet, J.-Ch.

    2015-01-01

    Materials subjected to neutron irradiation will suffer from a build-up of damage caused by the displacement cascades initiated by nuclear reactions. Previously, the main “measure” of this damage accumulation has been through the displacements per atom (dpa) index, which has known limitations. This paper describes a rigorous methodology to calculate the primary atomic recoil events (often called the primary knock-on atoms or PKAs) that lead to cascade damage events as a function of energy and recoiling species. A new processing code SPECTRA-PKA combines a neutron irradiation spectrum with nuclear recoil data obtained from the latest nuclear data libraries to produce PKA spectra for any material composition. Via examples of fusion relevant materials, it is shown that these PKA spectra can be complex, involving many different recoiling species, potentially differing in both proton and neutron number from the original target nuclei, including high energy recoils of light emitted particles such as α-particles and protons. The variations in PKA spectra as a function of time, neutron field, and material are explored. The application of PKA spectra to the quantification of radiation damage is exemplified using two approaches: the binary collision approximation and stochastic cluster dynamics, and the results from these different models are discussed and compared. - Highlights: • Recoil cross-section matrices under neutron irradiation are generated. • Primary knock-on atoms (PKA) spectra are calculated for fusion relevant materials. • Variation in PKA spectra due to changes in geometry are considered. • Inventory simulations to consider time-evolution in PKA spectra. • Damage quantification using damage functions from different approximations.

  15. Change of Cr atoms distribution in Fe85Cr15 alloy caused by 250 keV He+ ion irradiation to different doses

    International Nuclear Information System (INIS)

    Dubiel, S.M.; Żukrowski, J.

    2015-01-01

    Highlights: • Effect of He-ion irradiation dose on Fe 85 Cr 15 alloy. • Irradiation-induced clustering of Cr atoms. • Irradiation-caused reorientation of the surface magnetization vector. • Irradiation-caused increase of Fe-site spin-density. - Abstract: Redistribution of Cr atoms in a Fe 85 Cr 15 alloy caused by its irradiation with 250 keV He + ions to different doses, D = 8 ⋅ 10 16 , 16 ⋅ 10 16 and 48 ⋅ 10 16 ions/cm 2 was investigated by means of conversion electrons Mössbauer spectroscopy. The redistribution was expressed in terms of the Warren–Cowley short-range order parameters α 1 , α 2 and α 12 pertaining to the first (1NN), second (2NN) and both i.e. 1NN + 2NN shells, respectively. Clear evidence was found, both for non-irradiated and irradiated samples that the actual distribution of Cr atoms is characteristic of the shell, and for a given shell it depends on the irradiation dose. In particular, α 1 is positive, hence indicates an under population of Cr atoms in 1NN with respect to the random case, α 2 is negative, giving evidence thereby that 2NN is overpopulated by Cr atoms, and α 12 is weakly positive. Under the applied irradiation the number of Cr atoms in both neighbor shells decreased signifying thereby a clustering of Cr atoms. The underlying decrease of Cr concentration within the 1NN–2NN volume around the probe Fe atoms was estimated at 1.5 at.% ranging between 2.1 for the lowest and 0.8 at.% for the highest dose

  16. Atom probe characterization of nano-scaled features in irradiated Eurofer and ODS Eurofer steel

    International Nuclear Information System (INIS)

    Rogozkin, S.; Aleev, A.; Nikitin, A.; Zaluzhnyi, A.; Vladimirov, P.; Moeslang, A.; Lindau, R.

    2009-01-01

    Outstanding performance of oxide dispersion strengthened (ODS) steels at high temperatures and up to high doses allowed to consider them as potential candidates for fusion and fission power plants. At the same time their mechanical parameters strongly correlate with number density of oxide particles and their size. It is believed that fine particles are formed at the last stage of sophisticated production procedures and play a crucial role in higher heat- and radiation resistance in comparison with conventional materials. However, due to their small size - only few nanometers, characterization of such objects requires considerable efforts. Recent study of ODS steel by tomographic atom probe, the most appropriate technique in this case, shown considerable stability of these particles under high temperatures and ion-irradiation. However, these results were obtained for 12/14% Cr with addition of 0.3% Y 2 O 3 and titanium which is inappropriate in case of ODS Eurofer 97 and possibility to substitute neutron by ion irradiation is still under consideration. In this work effect of neutron irradiation on nanostructure behaviour of ODS Eurofer are investigated. Irradiation was performed on research reactor BOR-60 in SSC RF RIAR (Dimitrovgrad, Russia) up to 30 dpa at 280 deg. C and 580 deg. C. Recent investigation of unirradiated state revealed high number density of nano-scaled features (nano-clusters) even without addition of Ti in steel. It was shown that vanadium played significant role in nucleation process and core of nano-clusters was considerably enriched with it. In irradiated samples solution of vanadium in matrix was observed while the size of particles stayed practically unchanged. Also no nitrogen was detected in these particles in comparison with unirradiated state where bond energy of N with V was considered to be high as VN 2+ ions were detected on mass-spectra. (author)

  17. Clustered DNA damage induced by proton and heavy ion irradiation

    International Nuclear Information System (INIS)

    Davidkova, M.; Pachnerova Brabcova, K; Stepan, V.; Vysin, L.; Sihver, L.; Incerti, S.

    2014-01-01

    Ionizing radiation induces in DNA strand breaks, damaged bases and modified sugars, which accumulate with increasing density of ionizations in charged particle tracks. Compared to isolated DNA damage sites, the biological toxicity of damage clusters can be for living cells more severe. We investigated the clustered DNA damage induced by protons (30 MeV) and high LET radiation (C 290 MeV/u and Fe 500 MeV/u) in pBR322 plasmid DNA. To distinguish between direct and indirect pathways of radiation damage, the plasmid was irradiated in pure water or in aqueous solution of one of the three scavengers (coumarin-3-carboxylic acid, dimethylsulfoxide, and glycylglycine). The goal of the contribution is the analysis of determined types of DNA damage in dependence on radiation quality and related contribution of direct and indirect radiation effects. The yield of double strand breaks (DSB) induced in the DNA plasmid-scavenger system by heavy ion radiation was found to decrease with increasing scavenging capacity due to reaction with hydroxyl radical, linearly with high correlation coefficients. The yield of non-DSB clusters was found to occur twice as much as the DSB. Their decrease with increasing scavenging capacity had lower linear correlation coefficients. This indicates that the yield of non-DSB clusters depends on more factors, which are likely connected to the chemical properties of individual scavengers. (authors)

  18. Effect of self-interstitial diffusion anisotropy in electron-irradiated zirconium: A cluster dynamics modeling

    International Nuclear Information System (INIS)

    Christien, F.; Barbu, A.

    2005-01-01

    A model based on the cluster dynamics approach was proposed in [A. Hardouin Duparc, C. Moingeon, N. Smetniansky-de-Grande, A. Barbu, J. Nucl. Mater. 302 (2002) 143] to describe point defect agglomeration in metals under irradiation. This model is restricted to materials where point defect diffusion is isotropic and is thus not applicable to anisotropic metals such as zirconium. Following the approach proposed by Woo [C.H. Woo, J. Nucl. Mater. 159 (1988) 237], we extended in this work the model to the case where self-interstitial atoms (SIA) diffusion is anisotropic. The model was then applied to the loop microstructure evolution of a zirconium thin foil irradiated with electrons in a high-voltage microscope. First, the inputs were validated by comparing the numerical results with Hellio et al. experimental results [C. Hellio, C.H. de Novion, L. Boulanger, J. Nucl. Mater. 159 (1988) 368]. Further calculations were made to evidence the effect of the thin foil orientation on the dislocation loop microstructure under irradiation. The result is that it is possible to reproduce for certain orientations the 'unexpected' vacancy loop growth experimentally observed in electron-irradiated zirconium [M. Griffiths, M.H. Loretto, R.E. Sallmann, J. Nucl. Mater. 115 (1983) 313; J. Nucl. Mater. 115 (1983) 323; Philos. Mag. A 49 (1984) 613]. This effect is directly linked to SIA diffusion anisotropy

  19. Time-series clustering of gene expression in irradiated and bystander fibroblasts: an application of FBPA clustering

    Directory of Open Access Journals (Sweden)

    Markatou Marianthi

    2011-01-01

    Full Text Available Abstract Background The radiation bystander effect is an important component of the overall biological response of tissues and organisms to ionizing radiation, but the signaling mechanisms between irradiated and non-irradiated bystander cells are not fully understood. In this study, we measured a time-series of gene expression after α-particle irradiation and applied the Feature Based Partitioning around medoids Algorithm (FBPA, a new clustering method suitable for sparse time series, to identify signaling modules that act in concert in the response to direct irradiation and bystander signaling. We compared our results with those of an alternate clustering method, Short Time series Expression Miner (STEM. Results While computational evaluations of both clustering results were similar, FBPA provided more biological insight. After irradiation, gene clusters were enriched for signal transduction, cell cycle/cell death and inflammation/immunity processes; but only FBPA separated clusters by function. In bystanders, gene clusters were enriched for cell communication/motility, signal transduction and inflammation processes; but biological functions did not separate as clearly with either clustering method as they did in irradiated samples. Network analysis confirmed p53 and NF-κB transcription factor-regulated gene clusters in irradiated and bystander cells and suggested novel regulators, such as KDM5B/JARID1B (lysine (K-specific demethylase 5B and HDACs (histone deacetylases, which could epigenetically coordinate gene expression after irradiation. Conclusions In this study, we have shown that a new time series clustering method, FBPA, can provide new leads to the mechanisms regulating the dynamic cellular response to radiation. The findings implicate epigenetic control of gene expression in addition to transcription factor networks.

  20. Controllable irregular melting induced by atomic segregation in bimetallic clusters with fabricating different initial configurations

    International Nuclear Information System (INIS)

    Li Guojian; Liu Tie; Wang Qiang; Lue Xiao; Wang Kai; He Jicheng

    2010-01-01

    The melting process of Co, Co-Cu and Co-Ni clusters with different initial configurations is studied in molecular dynamics by a general embedded atom method. An irregular melting, at which energy decreases as the temperature increase near the melting point, is found in the onion-like Co-Cu-Co clusters, but not in the mixed Co-Cu and onion-like Co-Ni-Co clusters. From the analysis of atomic distributions and energy variation, the results indicate the irregular melting is induced by Cu atomic segregation. Furthermore, this melting can be controlled by doping hetero atoms with different surface energies and controlling their distributions.

  1. Reactivity Control of Rhodium Cluster Ions by Alloying with Tantalum Atoms.

    Science.gov (United States)

    Mafuné, Fumitaka; Tawaraya, Yuki; Kudoh, Satoshi

    2016-02-18

    Gas phase, bielement rhodium and tantalum clusters, RhnTam(+) (n + m = 6), were prepared by the double laser ablation of Rh and Ta rods in He carrier gas. The clusters were introduced into a reaction gas cell filled with nitric oxide (NO) diluted with He and were subjected to collisions with NO and He at room temperature. The product species were observed by mass spectrometry, demonstrating that the NO molecules were sequentially adsorbed on the RhnTam(+) clusters to form RhnTam(+)NxOx (x = 1, 2, 3, ...) species. In addition, oxide clusters, RhnTam(+)O2, were also observed, suggesting that the NO molecules were dissociatively adsorbed on the cluster, the N atoms migrated on the surface to form N2, and the N2 molecules were released from RhnTam(+)N2O2. The reactivity, leading to oxide formation, was composition dependent: oxide clusters were dominantly formed for the bielement clusters containing both Rh and Ta atoms, whereas such clusters were hardly formed for the single-element Rhn(+) and Tam(+) clusters. DFT calculations indicated that the Ta atoms induce dissociation of NO on the clusters by lowering the dissociation energy, whereas the Rh atoms enable release of N2 by lowering the binding energy of the N atoms on the clusters.

  2. Radiation enhanced copper clustering processes in Fe-Cu alloys during electron and ion irradiations as measured by electrical resistivity

    International Nuclear Information System (INIS)

    Ishino, S.; Chimi, Y.; Bagiyono; Tobita, T.; Ishikawa, N.; Suzuki, M.; Iwase, A.

    2003-01-01

    To study the mechanism of radiation-enhanced clustering of copper atoms in Fe-Cu alloys, in situ electrical resistivity measurements are performed during irradiation with 100 MeV carbon ions and with 2 MeV electrons at 300 K. Two kinds of highly pure Fe-Cu alloys with Cu content of 0.02 and 0.6 wt% are used. The results are summarized as follows: - Although there is a steep initial resistivity increase below about 10 μdpa, the resistivity steadily decreases after this initial transient in Fe-0.6wt%Cu alloy, while in Fe-0.02wt%Cu alloy, the resistivity either decreases slowly or stays almost constant. The rate of change in resistivity depends on copper concentration. - The rate of change in resistivity per dpa is larger for electron irradiation than for ion irradiation. - Change in dose rate from 10 -8 to 10 -9 dpa/s slightly enhances the rate of resistivity change per dpa. The decrease in resistivity with dose is considered to be due to clustering or precipitation of copper atoms. The initial abrupt increase in resistivity is too large to be accounted for by initial introduction of point defects before copper clustering. Tentatively the phenomenon is explained as due to the formation of embryos of copper precipitates with a large strain field around them. Quantitative evaluation of the results using resistivity contribution of a unit concentration of Frenkel pairs and that of copper atoms gives an important conclusion that more than one copper atom are removed from solid solution by one Frenkel pair. The clustering efficiency is surprisingly high in the present case compared with the ordinary radiation-induced or radiation-enhanced precipitation processes

  3. A DFT study of the stability of SIAs and small SIA clusters in the vicinity of solute atoms in Fe

    Science.gov (United States)

    Becquart, C. S.; Ngayam Happy, R.; Olsson, P.; Domain, C.

    2018-03-01

    The energetics, defect volume and magnetic properties of single SIAs and small SIA clusters up to size 6 have been calculated by DFT for different configurations like the parallel 〈110〉 dumbbell, the non parallel 〈110〉 dumbbell and the C15 structure. The most stable configurations of each type have been further analyzed to determine the influence on their stability of various solute atoms (Ti, V, Cr, Mn, Co, Ni, Cu, Mo, W, Pd, Al, Si, P), relevant for steels used under irradiation. The results show that the presence of solute atoms does not change the relative stability order among SIA clusters. The small SIA clusters investigated can bind to both undersized and oversized solutes. Several descriptors have been considered to derive interesting trends from results. It appears that the local atomic volume available for the solute is the main physical quantity governing the binding energy evolution, whatever the solute type (undersized or oversized) and the cluster configuration (size and type).

  4. Platinum clusters with precise numbers of atoms for preparative-scale catalysis.

    Science.gov (United States)

    Imaoka, Takane; Akanuma, Yuki; Haruta, Naoki; Tsuchiya, Shogo; Ishihara, Kentaro; Okayasu, Takeshi; Chun, Wang-Jae; Takahashi, Masaki; Yamamoto, Kimihisa

    2017-09-25

    Subnanometer noble metal clusters have enormous potential, mainly for catalytic applications. Because a difference of only one atom may cause significant changes in their reactivity, a preparation method with atomic-level precision is essential. Although such a precision with enough scalability has been achieved by gas-phase synthesis, large-scale preparation is still at the frontier, hampering practical applications. We now show the atom-precise and fully scalable synthesis of platinum clusters on a milligram scale from tiara-like platinum complexes with various ring numbers (n = 5-13). Low-temperature calcination of the complexes on a carbon support under hydrogen stream affords monodispersed platinum clusters, whose atomicity is equivalent to that of the precursor complex. One of the clusters (Pt 10 ) exhibits high catalytic activity in the hydrogenation of styrene compared to that of the other clusters. This method opens an avenue for the application of these clusters to preparative-scale catalysis.The catalytic activity of a noble metal nanocluster is tied to its atomicity. Here, the authors report an atom-precise, fully scalable synthesis of platinum clusters from molecular ring precursors, and show that a variation of only one atom can dramatically change a cluster's reactivity.

  5. Cluster dynamics modeling of the effect of high dose irradiation and helium on the microstructure of austenitic stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    Brimbal, Daniel, E-mail: Daniel.brimbal@areva.com [AREVA NP, Tour AREVA, 1 Place Jean Millier, 92084 Paris La Défense (France); Fournier, Lionel [AREVA NP, Tour AREVA, 1 Place Jean Millier, 92084 Paris La Défense (France); Barbu, Alain [Alain Barbu Consultant, 6 Avenue Pasteur Martin Luther King, 78230 Le Pecq (France)

    2016-01-15

    A mean field cluster dynamics model has been developed in order to study the effect of high dose irradiation and helium on the microstructural evolution of metals. In this model, self-interstitial clusters, stacking-fault tetrahedra and helium-vacancy clusters are taken into account, in a configuration well adapted to austenitic stainless steels. For small helium-vacancy cluster sizes, the densities of each small cluster are calculated. However, for large sizes, only the mean number of helium atoms per cluster size is calculated. This aspect allows us to calculate the evolution of the microstructural features up to high irradiation doses in a few minutes. It is shown that the presence of stacking-fault tetrahedra notably reduces cavity sizes below 400 °C, but they have little influence on the microstructure above this temperature. The binding energies of vacancies to cavities are calculated using a new method essentially based on ab initio data. It is shown that helium has little effect on the cavity microstructure at 300 °C. However, at higher temperatures, even small helium production rates such as those typical of sodium-fast-reactors induce a notable increase in cavity density compared to an irradiation without helium. - Highlights: • Irradiation of steels with helium is studied through a new cluster dynamics model. • There is only a small effect of helium on cavity distributions in PWR conditions. • An increase in helium production causes an increase in cavity density over 500 °C. • The role of helium is to stabilize cavities via reduced emission of vacancies.

  6. Previsions of the microstructural evolution of ferritic alloys under irradiation by numerical atomic scale simulations

    International Nuclear Information System (INIS)

    Ngayam Happy, R.

    2010-01-01

    In this work, we have improved a diffusion model for point defects (vacancies and self-interstitials) by introducing hetero-interstitials. The model has been used to simulate by Kinetic Monte Carlo (KMC) the formation of solute rich clusters that are observed experimentally in irradiated ferritic model alloys of type Fe - CuMnNiSiP - C.Electronic structure calculations have been used to characterize the interactions between self-interstitials and all solute atoms, and also carbon. P interacts with vacancies and strongly with self-interstitials. Mn also interacts with self-interstitials to form mixed dumbbells. C, with occupies octahedral sites, interacts strongly with vacancies and less with self-interstitials. Binding and migration energies, as well as others atomic scale properties, obtained by ab initio calculations, have been used as parameters for the KMC code. Firstly, these parameters have been optimized over isochronal annealing experiments, in the literature, of binary alloys that have been electron-irradiated. Isochronal annealing simulations, by reproducing experimental results, have allowed us to link each mechanism to a single evolution of the resistivity during annealing. Moreover, solubility limits of all the elements have been determined by Metropolis Monte Carlo. Secondly, we have simulated the evolution at 300 C of the microstructure under irradiation of different alloys of increasing complexity: pure Fe, binary alloys, ternaries, quaternaries, and finally complex alloys which compositions are close to those of pressure vessel steels. The results show that the model globally reproduces all the experimental tendencies, what has led us to propose mechanisms to explain the behaviours observed. (author)

  7. Dechanneling measurements of defect depth profiles and effective cross-channel distribution of misaligned atoms in ion irradiated gold

    International Nuclear Information System (INIS)

    Pronko, P.P.

    1975-01-01

    Defect depth profiles for self ion and He + irradiated gold are obtained from single and multiple scatter dechanneling analysis in single crystal gold films. Quantitative defect densities are obtained through use of atomic scattering cross sections. Integral damage profiles are extracted from the dechanneling spectra and subsequently differentiated to yield the volume concentration of defects as a function of depth. Results from the self ion irradiations suggest that incident ions produce defect distributions across depths much greater than predicted by random stopping theory. This is in agreement with TEM observations of others. Comparison of the experimental profiles is made with theoretical vacancy distributions predicted by defect diffusion in a radiation environment. Similarities are observed for the low fluence irradiations suggesting that profile characteristics may be controlled by rapid migration and loss of interstitials to the film surfaces during irradiation. Information on the across-channel distribution of misaligned atoms in the damaged films is obtained with the steady increase of transverse energy model applied to the dechanneling spectra. A predominance of slight misalignment is observed with no contribution to dechanneling coming from atoms displaced significantly close to the center of the channels. This is in keeping with what is expected for crystal distortions caused by the strain fields associated with vacancy cluster defects

  8. Dechanneling measurements of defect depth profiles and effective cross-channel distribution of misaligned atoms in ion-irradiated gold

    International Nuclear Information System (INIS)

    Pronko, P.P.

    1976-01-01

    Defect depth profiles for self-ion and He + irradiated gold are obtained from single and multiple scatter dechanneling analysis in single-crystal gold films. Quantitative defect densities are obtained through use of atomic-scattering cross sections. Integral damage profiles are extracted from the dechanneling spectra and subsequently differentiated to yield the volume concentration of defects as a function of depth. Results from the self-ion irradiations suggest that incident ions produce defect distributions across depths much greater than predicted by random stopping theory. This is in agreement with TEM observations of others. Comparison of the experimental profiles is made with theoretical vacancy distributions predicted by defect diffusion in a radiation environment. Similarities are observed for the low-fluence irradiations, suggesting that profile characteristics may be controlled by rapid migration and loss of interstitials to the film surfaces during irradiation. Information on the across-channel distribution of misaligned atoms in the damaged films is obtained with the steady increase of transverse energy model. A predominance of slight misalignment is observed with no contribution to dechanneling coming from atoms displaced significantly close to the center of the channels. This is in keeping with what is expected for crystal distortions caused by the strain fields associated with vacancy cluster defects. (Auth.)

  9. Atomic characterization of Au clusters in vapor-liquid-solid grown silicon nanowires

    International Nuclear Information System (INIS)

    Chen, Wanghua; Roca i Cabarrocas, Pere; Pareige, Philippe; Castro, Celia; Xu, Tao; Grandidier, Bruno; Stiévenard, Didier

    2015-01-01

    By correlating atom probe tomography with other conventional microscope techniques (scanning electron microscope, scanning transmission electron microscope, and scanning tunneling microscopy), the distribution and composition of Au clusters in individual vapor-liquid-solid grown Si nanowires is investigated. Taking advantage of the characteristics of atom probe tomography, we have developed a sample preparation method by inclining the sample at certain angle to characterize the nanowire sidewall without using focused ion beam. With three-dimensional atomic scale reconstruction, we provide direct evidence of Au clusters tending to remain on the nanowire sidewall rather than being incorporated into the Si nanowires. Based on the composition measurement of Au clusters (28% ± 1%), we have demonstrated the supersaturation of Si atoms in Au clusters, which supports the hypothesis that Au clusters are formed simultaneously during nanowire growth rather than during the cooling process

  10. Atomic characterization of Au clusters in vapor-liquid-solid grown silicon nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wanghua; Roca i Cabarrocas, Pere [Laboratoire de Physique des Interfaces et Couches Minces (LPICM), UMR 7647, CNRS, Ecole Polytechnique, 91128 Palaiseau (France); Pareige, Philippe; Castro, Celia [Groupe de Physique des Matériaux (GPM), Université et INSA de Rouen, UMR 6634, CNRS, Av. de l' Université, BP 12, 76801 Saint Etienne du Rouvray (France); Xu, Tao; Grandidier, Bruno; Stiévenard, Didier [Institut d' Electronique et de Microélectronique et de Nanotechnologies (IEMN), UMR 8520, CNRS, Département ISEN, 41 bd Vauban, 59046 Lille Cedex (France)

    2015-09-14

    By correlating atom probe tomography with other conventional microscope techniques (scanning electron microscope, scanning transmission electron microscope, and scanning tunneling microscopy), the distribution and composition of Au clusters in individual vapor-liquid-solid grown Si nanowires is investigated. Taking advantage of the characteristics of atom probe tomography, we have developed a sample preparation method by inclining the sample at certain angle to characterize the nanowire sidewall without using focused ion beam. With three-dimensional atomic scale reconstruction, we provide direct evidence of Au clusters tending to remain on the nanowire sidewall rather than being incorporated into the Si nanowires. Based on the composition measurement of Au clusters (28% ± 1%), we have demonstrated the supersaturation of Si atoms in Au clusters, which supports the hypothesis that Au clusters are formed simultaneously during nanowire growth rather than during the cooling process.

  11. Microstructural evolution of Fe−22%Cr model alloy under thermal ageing and ion irradiation conditions studied by atom probe tomography

    Energy Technology Data Exchange (ETDEWEB)

    Korchuganova, Olesya A., E-mail: KorchuganovaOA@gmail.com [National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow (Russian Federation); State Scientific Center of the Russian Federation, Institute for Theoretical and Experimental Physics of National Research Centre “Kurchatov Institute”, 117218, Moscow (Russian Federation); Thuvander, Mattias [Chalmers University of Technology, SE-412 96, Göteborg (Sweden); Aleev, Andrey A.; Rogozhkin, Sergey V. [National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow (Russian Federation); State Scientific Center of the Russian Federation, Institute for Theoretical and Experimental Physics of National Research Centre “Kurchatov Institute”, 117218, Moscow (Russian Federation); Boll, Torben [Chalmers University of Technology, SE-412 96, Göteborg (Sweden); Kulevoy, Timur V. [State Scientific Center of the Russian Federation, Institute for Theoretical and Experimental Physics of National Research Centre “Kurchatov Institute”, 117218, Moscow (Russian Federation); National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow (Russian Federation)

    2016-08-15

    Nanostructure evolution during ion irradiation of two thermally aged binary Fee22Cr alloys has been investigated using atom probe tomography. Specimens aged at 500 °C for 50 and 200 h were irradiated by 5.6 MeV Fe ions at room temperature up to fluences of 0.3 × 10{sup 15} ions/cm{sup 2} and 1 × 10{sup 15} ions/cm{sup 2}. The effect of irradiation on the material nanostructure was examined at a depth of 1 μm from the irradiated surface. The analysis of Cr radial concentration functions reveals that dense α′-phase precipitates in the 200 h aged alloy become diffuse and thereby larger when subjected to irradiation. On the other hand, less Cr-enriched precipitates in the alloy aged for 50 h are less affected. The CreCr pair correlation function analysis shows that matrix inhomogeneity decreases under irradiation. Irradiation leads to a decrease in the number density of diffuse clusters, whereas in the case of well-developed precipitates it remains unchanged.

  12. Microstructural evolution of Fe−22%Cr model alloy under thermal ageing and ion irradiation conditions studied by atom probe tomography

    International Nuclear Information System (INIS)

    Korchuganova, Olesya A.; Thuvander, Mattias; Aleev, Andrey A.; Rogozhkin, Sergey V.; Boll, Torben; Kulevoy, Timur V.

    2016-01-01

    Nanostructure evolution during ion irradiation of two thermally aged binary Fee22Cr alloys has been investigated using atom probe tomography. Specimens aged at 500 °C for 50 and 200 h were irradiated by 5.6 MeV Fe ions at room temperature up to fluences of 0.3 × 10 15 ions/cm 2 and 1 × 10 15 ions/cm 2 . The effect of irradiation on the material nanostructure was examined at a depth of 1 μm from the irradiated surface. The analysis of Cr radial concentration functions reveals that dense α′-phase precipitates in the 200 h aged alloy become diffuse and thereby larger when subjected to irradiation. On the other hand, less Cr-enriched precipitates in the alloy aged for 50 h are less affected. The CreCr pair correlation function analysis shows that matrix inhomogeneity decreases under irradiation. Irradiation leads to a decrease in the number density of diffuse clusters, whereas in the case of well-developed precipitates it remains unchanged.

  13. Microstructural evolution of Fesbnd 22%Cr model alloy under thermal ageing and ion irradiation conditions studied by atom probe tomography

    Science.gov (United States)

    Korchuganova, Olesya A.; Thuvander, Mattias; Aleev, Andrey A.; Rogozhkin, Sergey V.; Boll, Torben; Kulevoy, Timur V.

    2016-08-01

    Nanostructure evolution during ion irradiation of two thermally aged binary Fee22Cr alloys has been investigated using atom probe tomography. Specimens aged at 500 °C for 50 and 200 h were irradiated by 5.6 MeV Fe ions at room temperature up to fluences of 0.3 × 1015 ions/cm2 and 1 × 1015 ions/cm2. The effect of irradiation on the material nanostructure was examined at a depth of 1 μm from the irradiated surface. The analysis of Cr radial concentration functions reveals that dense α‧-phase precipitates in the 200 h aged alloy become diffuse and thereby larger when subjected to irradiation. On the other hand, less Cr-enriched precipitates in the alloy aged for 50 h are less affected. The CreCr pair correlation function analysis shows that matrix inhomogeneity decreases under irradiation. Irradiation leads to a decrease in the number density of diffuse clusters, whereas in the case of well-developed precipitates it remains unchanged.

  14. Melting of size-selected gallium clusters with 60-183 atoms.

    Science.gov (United States)

    Pyfer, Katheryne L; Kafader, Jared O; Yalamanchali, Anirudh; Jarrold, Martin F

    2014-07-10

    Heat capacities have been measured as a function of temperature for size-selected gallium cluster cations with between 60 and 183 atoms. Almost all clusters studied show a single peak in the heat capacity that is attributed to a melting transition. The peaks can be fit by a two-state model incorporating only fully solid-like and fully liquid-like species, and hence no partially melted intermediates. The exceptions are Ga90(+), which does not show a peak, and Ga80(+) and Ga81(+), which show two peaks. For the clusters with two peaks, the lower temperature peak is attributed to a structural transition. The melting temperatures for clusters with less than 50 atoms have previously been shown to be hundreds of degrees above the bulk melting point. For clusters with more than 60 atoms the melting temperatures decrease, approaching the bulk value (303 K) at around 95 atoms, and then show several small upward excursions with increasing cluster size. A plot of the latent heat against the entropy change for melting reveals two groups of clusters: the latent heats and entropy changes for clusters with less than 94 atoms are distinct from those for clusters with more than 93 atoms. This observation suggests that a significant change in the nature of the bonding or the structure of the clusters occurs at 93-94 atoms. Even though the melting temperatures are close to the bulk value for the larger clusters studied here, the latent heats and entropies of melting are still far from the bulk values.

  15. Atomically precise arrays of fluorescent silver clusters: a modular approach for metal cluster photonics on DNA nanostructures.

    Science.gov (United States)

    Copp, Stacy M; Schultz, Danielle E; Swasey, Steven; Gwinn, Elisabeth G

    2015-03-24

    The remarkable precision that DNA scaffolds provide for arraying nanoscale optical elements enables optical phenomena that arise from interactions of metal nanoparticles, dye molecules, and quantum dots placed at nanoscale separations. However, control of ensemble optical properties has been limited by the difficulty of achieving uniform particle sizes and shapes. Ligand-stabilized metal clusters offer a route to atomically precise arrays that combine desirable attributes of both metals and molecules. Exploiting the unique advantages of the cluster regime requires techniques to realize controlled nanoscale placement of select cluster structures. Here we show that atomically monodisperse arrays of fluorescent, DNA-stabilized silver clusters can be realized on a prototypical scaffold, a DNA nanotube, with attachment sites separated by <10 nm. Cluster attachment is mediated by designed DNA linkers that enable isolation of specific clusters prior to assembly on nanotubes and preserve cluster structure and spectral purity after assembly. The modularity of this approach generalizes to silver clusters of diverse sizes and DNA scaffolds of many types. Thus, these silver cluster nano-optical elements, which themselves have colors selected by their particular DNA templating oligomer, bring unique dimensions of control and flexibility to the rapidly expanding field of nano-optics.

  16. Formation mechanism of solute clusters under neutron irradiation in ferritic model alloys and in a reactor pressure vessel steel: clusters of defects; Mecanismes de fragilisation sous irradiation aux neutrons d'alliages modeles ferritiques et d'un acier de cuve: amas de defauts

    Energy Technology Data Exchange (ETDEWEB)

    Meslin-Chiffon, E

    2007-11-15

    The embrittlement of reactor pressure vessel (RPV) under irradiation is partly due to the formation of point defects (PD) and solute clusters. The aim of this work was to gain more insight into the formation mechanisms of solute clusters in low copper ([Cu] = 0.1 wt%) FeCu and FeCuMnNi model alloys, in a copper free FeMnNi model alloy and in a low copper French RPV steel (16MND5). These materials were neutron-irradiated around 300 C in a test reactor. Solute clusters were characterized by tomographic atom probe whereas PD clusters were simulated with a rate theory numerical code calibrated under cascade damage conditions using transmission electron microscopy analysis. The confrontation between experiments and simulation reveals that a heterogeneous irradiation-induced solute precipitation/segregation probably occurs on PD clusters. (author)

  17. Quantum-statistical mechanics of an atom-dimer mixture: Lee-Yang cluster expansion approach

    International Nuclear Information System (INIS)

    Ohkuma, Takahiro; Ueda, Masahito

    2006-01-01

    We use the Lee-Yang cluster expansion method to study quantum-statistical properties of a mixture of interconvertible atoms and dimers, where the dimers form in a two-body bound state of the atoms. We point out an infinite series of cluster diagrams whose summation leads to the Bose-Einstein condensation of the dimers below a critical temperature. Our theory captures some important features of a cold atom-dimer mixture such as interconversion of atoms and dimers and properties of the mixture at the unitarity limit

  18. Scanning probe microscopy investigation of gold clusters deposited on atomically flat substrates

    International Nuclear Information System (INIS)

    Vandamme, N; Janssens, E; Vanhoutte, F; Lievens, P; Haesendonck, C van

    2003-01-01

    We systematically studied the influence of the substrate on the shape, mobility, and stability of deposited gold clusters. The Au n clusters were produced in a laser vaporization source and deposited with low kinetic energy (∼0.4 eV/atom) on atomically flat substrates (graphite, mica, and gold and silver films on mica) under UHV conditions. Their size distribution is probed with time-of-flight mass spectrometry and ranges from dimers to several hundreds of atoms. Scanning probe microscopy is used to characterize the deposited clusters and the formation of islands by cluster aggregation. On all substrates, Au n islands can be clearly distinguished and the islands are flattened despite the small impact energy. The shape and size of the island configurations are strongly system dependent. Gold clusters deposited on Au(111) and Ag(111) films grown on mica do not aggregate, but deform due to strong cluster-substrate interactions. The clusters tend to grow epitaxially on these surfaces. On graphite and on mica, deposited clusters do diffuse and aggregate. On the graphite surface, large ramified islands are formed by juxtaposition of small islands and trapping of the clusters at the step edges. On the other hand, the diffusion of the clusters on mica results in a total coalescence of the Au n clusters into compact islands

  19. Detecting and extracting clusters in atom probe data: A simple, automated method using Voronoi cells

    International Nuclear Information System (INIS)

    Felfer, P.; Ceguerra, A.V.; Ringer, S.P.; Cairney, J.M.

    2015-01-01

    The analysis of the formation of clusters in solid solutions is one of the most common uses of atom probe tomography. Here, we present a method where we use the Voronoi tessellation of the solute atoms and its geometric dual, the Delaunay triangulation to test for spatial/chemical randomness of the solid solution as well as extracting the clusters themselves. We show how the parameters necessary for cluster extraction can be determined automatically, i.e. without user interaction, making it an ideal tool for the screening of datasets and the pre-filtering of structures for other spatial analysis techniques. Since the Voronoi volumes are closely related to atomic concentrations, the parameters resulting from this analysis can also be used for other concentration based methods such as iso-surfaces. - Highlights: • Cluster analysis of atom probe data can be significantly simplified by using the Voronoi cell volumes of the atomic distribution. • Concentration fields are defined on a single atomic basis using Voronoi cells. • All parameters for the analysis are determined by optimizing the separation probability of bulk atoms vs clustered atoms

  20. Nano-structural changes in the RPV steels irradiated in MTR to high doses. 3D atom probe and positron annihilation study

    International Nuclear Information System (INIS)

    Dohi, Kenji; Soneda, Naoki; Nomoto, Akiyoshi; Ishino, Shiori

    2005-01-01

    Reactor pressure vessel (RPV) steels of life-extended light water reactors are to be exposed to higher neutron fluence. The understanding of radiation embrittlement of RPV steels is very important in order to improve prediction of the embrittlement. The radiation embrittlement is mainly cased by copper-enriched cluster (CEC) and matrix damage (MD) due to irradiation. The state-or-the art technique such as three dimensional atom probe (3DAP) and positron annihilation (PA) has enabled to observe these microstructural features. The effect of highly dose irradiation on the formation of clusters in a low copper base metal and a high copper weld metal is investigated by means of the 3DAP and PA observations in this paper. The materials were irradiated to a neutron fluence of 10 20 n/cm 2 at 290 degC in a test reactor. The 3DAP observation shows that high dense CRCs in size of about 2 nm are formed in the high Cu weld metal. The CRCs consist of Si in addition to Fe, Cu, Mn, and Ni. Solute atom clusters below 2 nm are also observed in low Cu base metal, but the clusters include a large amount of Si and free from Cu. These clusters may be peculiar to highly irradiated materials because of no literature reporting such the clusters in the similar steels irradiated at the lower fluence. The data of the positron annihilation coincidence Doppler broadening measurement for both materials also shows the formation of clusters containing Cu, Ni, Mn, and Si. This means the clusters observed by 3DAP are uniformly distributed in the materials. Hardness tests and PA measurement combined with isochronal annealing show that defects, e.g. dislocation loop etc., having a positron lifetime of about 140 psec influence on mechanical properties of the steels. (author)

  1. Hydrogen isotope dynamic effects on partially reduced paramagnetic six-atom Ag clusters in low-symmetry cage of zeolite A

    Directory of Open Access Journals (Sweden)

    Amgalanbaatar Baldansuren

    2016-12-01

    Full Text Available A well-defined, monodisperse Ag6+ cluster was prepared by mild chemical treatments including aqueous ion-exchange, dehydration, oxygen calcination at 673 K and hydrogen reduction 293 K, rather than autoreduction and irradiations with γ-ray and X-ray. H2 reduction was proved as a crucial step to form the nanosize cluster with six equivalent silver atoms. Hydrogen isotope exchange and dynamics were probed by EPR and HYSCORE to provide information relevant to the cluster geometry, size, charge state and spin state. Desorption experiments result in the deuterium desorption energy of 0.78 eV from the cluster, exceeding the experimental value of 0.38 eV for the single crystal Ag(111 surface. These experiments indicate that the EPR-active clusters are in delicate equilibrium with EPR-silent clusters.

  2. Atomic interaction with quantum fluid clusters: cross-jet deflection of 3He- and 4He-clusters

    International Nuclear Information System (INIS)

    Gspann, J.; Vollmar, H.

    1977-01-01

    The authors have studied earlier the velocity dependence of the total scattering of Cs atomic beams by 4 He-cluster beams, in comparison with corresponding experiments with N 2 - and Ne-cluster beams. Only with the 4 He-cluster beams a deficiency in the effective total scattering compared to the expected behaviour has been observed which was largest near 200 m/s of relative velocity. However, it is difficult to estimate, and therefore still a matter of investigation, to which extent this effect could be attributed to the presence of a small amount of uncondensed helium atoms in the cluster beam. In this paper a first account is given on an experimental study of the drag coefficients in free molecular flow of helium clusters of either isotope. The drag coefficients describe the respective efficiencies of linear momentum transfer onto the clusters and are found to be appreciably lower for helium than for nitrogen clusters which is ascribed to the fluidity of the helium clusters. (Auth.)

  3. An adaptive immune optimization algorithm with dynamic lattice searching operation for fast optimization of atomic clusters

    International Nuclear Information System (INIS)

    Wu, Xia; Wu, Genhua

    2014-01-01

    Highlights: • A high efficient method for optimization of atomic clusters is developed. • Its performance is studied by optimizing Lennard-Jones clusters and Ag clusters. • The method is proved to be quite efficient. • A new Ag 61 cluster with stacking-fault face-centered cubic motif is found. - Abstract: Geometrical optimization of atomic clusters is performed by a development of adaptive immune optimization algorithm (AIOA) with dynamic lattice searching (DLS) operation (AIOA-DLS method). By a cycle of construction and searching of the dynamic lattice (DL), DLS algorithm rapidly makes the clusters more regular and greatly reduces the potential energy. DLS can thus be used as an operation acting on the new individuals after mutation operation in AIOA to improve the performance of the AIOA. The AIOA-DLS method combines the merit of evolutionary algorithm and idea of dynamic lattice. The performance of the proposed method is investigated in the optimization of Lennard-Jones clusters within 250 atoms and silver clusters described by many-body Gupta potential within 150 atoms. Results reported in the literature are reproduced, and the motif of Ag 61 cluster is found to be stacking-fault face-centered cubic, whose energy is lower than that of previously obtained icosahedron

  4. Irradiation-induced precipitates in a neutron irradiated 304 stainless steel studied by three-dimensional atom probe

    Energy Technology Data Exchange (ETDEWEB)

    Toyama, T., E-mail: ttoyama@imr.tohoku.ac.jp [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, Narita-cho 2145-2, Oarai, Ibaraki 311-1313 (Japan); Nozawa, Y. [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, Narita-cho 2145-2, Oarai, Ibaraki 311-1313 (Japan); Van Renterghem, W. [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, 2400 Mol (Belgium); Matsukawa, Y.; Hatakeyama, M.; Nagai, Y. [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, Narita-cho 2145-2, Oarai, Ibaraki 311-1313 (Japan); Al Mazouzi, A. [EDF R and D, Avenue des Renardieres Ecuelles, 77818 Moret sur Loing Cedex (France); Van Dyck, S. [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, 2400 Mol (Belgium)

    2011-11-15

    Highlights: > Irradiation-induced precipitates in a 304 stainless steel were investigated by three-dimensional atom probe. > The precipitates were found to be {gamma}' precipitates (Ni{sub 3}Si). > Post-irradiation annealing was performed to discuss the contribution of the precipitates to irradiation-hardening. - Abstract: Irradiation-induced precipitates in a 304 stainless steel, neutron-irradiated to a dose of 24 dpa at 300 deg. C in the fuel wrapper plates of a commercial pressurized water reactor, were investigated by laser-assisted three-dimensional atom probe. A high number density of 4 x 10{sup 23} m{sup -3} of Ni-Si rich precipitates was observed, which is one order of magnitude higher than that of Frank loops. The average diameter was {approx}10 nm and the average chemical composition was 40% Ni, 14% Si, 11% Cr and 32% Fe in atomic percent. Over a range of Si concentrations, the ratio of Ni to Si was {approx}3, close to that of {gamma}' precipitate (Ni{sub 3}Si). In some precipitates, Mn enrichment inside the precipitate and P segregation at the interface were observed. Post-irradiation annealing was performed to discuss the contribution of the precipitates to irradiation-hardening.

  5. Electrodeposition of Isolated Platinum Atoms and Clusters on Bismuth-Characterization and Electrocatalysis.

    Science.gov (United States)

    Zhou, Min; Dick, Jeffrey E; Bard, Allen J

    2017-12-06

    We describe a method for the electrodeposition of an isolated single Pt atom or small cluster, up to 9 atoms, on a bismuth ultramicroelectrode (UME). This deposition was immediately followed by electrochemical characterization via the hydrogen evolution reaction (HER) that occurs readily on the electrodeposited Pt but not on Bi. The observed voltammetric current plateau, even for a single atom, which behaves as an electrode, allows the estimation of deposit size. Pt was plated from solutions of femtomolar PtCl 6 2- , which allowed precise control of the arrival of ions and thus the plating rate on the Bi UME, to one ion every few seconds. This allowed the atom-by-atom fabrication of isolated platinum deposits, ranging from single atoms to 9-atom clusters. The limiting currents in voltammetry gave the size and number of atoms of the clusters. Given the stochasticity of the plating process, we show that the number of atoms plated over a given time (10 and 20 s) follows a Poisson distribution. Taking the potential at a certain current density as a measure of the relative rate of the HER, we found that the potential shifted positively as the size increased, with single atoms showing the largest overpotentials compared to bulk Pt.

  6. Helium clusters as cold, liquid matrix for the laser spectroscopy of silver atoms, silver clusters and C60 fullerenes

    International Nuclear Information System (INIS)

    Hoffmann, K.

    1999-01-01

    One of the main obstacles in the study of gas phase metal clusters is their high temperature. Even cooling in a seeded beam is only of limited used, since the condensation continuously releases energy into the system. As a consequence, spectroscopic studies of free metal clusters typically yield broad structures, which are interpreted as plasma resonances of a free electron gas. An experiment on ionic sodium clusters has shown that low temperatures lead to a narrowing of the absorption bands and the appearance of additional structure, that can not be explained within the free electron model. Thus the need for cold clusters is evident. In principle the deposition of metal clusters into inert matrices eliminates the temperature problem but it can also inflict strong changes on the electronic spectra. Droplets of liquid helium serve as a much more gentle matrix that avoids many of the above problems. In this thesis the new technique of helium droplet spectroscopy is presented as a tool for the study of extremely cold metal clusters. Clusters of silver up to a mass greater than 7000 amu have been produced by pickup of single atoms by a beam of helium droplets. The droplets are formed in a supersonic expansion. The cluster's binding energy is removed by evaporative cooling and the system remains at 0.4 K. The doped droplets are probed by laser spectroscopy with a depletion technique or resonant two photon ionization. We were able to measure the first UV absorption spectrum of metal atoms (silver) inside helium droplets. Another experiment shows that a small fraction of the captured silver atoms resides on the surface of the droplet like alkali atoms. In a two photon process previously unobserved s- and d-Rydberg states of the free silver atom (20 left angle n left angle 80) were excited. The silver atoms, initially embedded in the helium droplets, are found to move to the surface and desorb when excited to the broadened 5p level. This is the first result showing laser

  7. Fragmentation of neutral carbon clusters formed by high velocity atomic collision

    International Nuclear Information System (INIS)

    Martinet, G.

    2004-05-01

    The aim of this work is to understand the fragmentation of small neutral carbon clusters formed by high velocity atomic collision on atomic gas. In this experiment, the main way of deexcitation of neutral clusters formed by electron capture with ionic species is the fragmentation. To measure the channels of fragmentation, a new detection tool based on shape analysis of current pulse delivered by semiconductor detectors has been developed. For the first time, all branching ratios of neutral carbon clusters are measured in an unambiguous way for clusters size up to 10 atoms. The measurements have been compared to a statistical model in microcanonical ensemble (Microcanonical Metropolis Monte Carlo). In this model, various structural properties of carbon clusters are required. These data have been calculated with Density Functional Theory (DFT-B3LYP) to find the geometries of the clusters and then with Coupled Clusters (CCSD(T)) formalism to obtain dissociation energies and other quantities needed to compute fragmentation calculations. The experimental branching ratios have been compared to the fragmentation model which has allowed to find an energy distribution deposited in the collision. Finally, specific cluster effect has been found namely a large population of excited states. This behaviour is completely different of the atomic carbon case for which the electron capture in the ground states predominates. (author)

  8. Application of Delaunay tessellation for the characterization of solute-rich clusters in atom probe tomography

    International Nuclear Information System (INIS)

    Lefebvre, W.; Philippe, T.; Vurpillot, F.

    2011-01-01

    This work presents an original method for cluster selection in Atom Probe Tomography designed to be applied to large datasets. It is based on the calculation of the Delaunay tessellation generated by the distribution of atoms of a selected element. It requires a single input parameter from the user. Furthermore, no prior knowledge of the material is needed. The sensitivity of the proposed Delaunay cluster selection is demonstrated by its application on simulated APT datasets. A strong advantage of the proposed methodology is that it is reinforced by the availability of an analytical model for the distribution of Delaunay cells circumspheres, which is used to control the accuracy of the cluster selection procedure. Another advantage of the Delaunay cluster selection is the direct calculation of a sharp envelope for each identified cluster or precipitate, which leads to the more appropriate morphology of the objects as they are reconstructed in the APT dataset. -- Research Highligthts: →Original method for cluster selection in Atom Probe Tomography. →Delaunay tessellation generated by the distribution of solute atoms. →Direct calculation of a sharp envelope for each identified cluster or precipitate. →Delaunay cluster selection demonstrated by its application on simulated APT datasets.

  9. A new apparatus at hyper irradiation research facility at the Atomic Research Center, University of Tokyo

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, Hiromi; Iwai, Takeo; Narui, Makoto; Omata, Takao [Tokyo Univ. (Japan). Research Center for Nuclear Science and Technology

    1996-12-01

    In the hyper irradiation research facility at the Atomic Research Center, the University of Tokyo, following apparatuses were newly installed for accelerator relating apparatus on 1995 fiscal year; (1) Hyper ion microbeam analysis apparatus, (2) Fourier conversion infrared microscopy, (3) Pico second two-dimensional fluorescence measuring apparatus, (4) Femto second wave-length reversible pulse laser radiation apparatus, and others. In addition to double irradiation, pulse beam irradiation experiment and so forth characteristic in conventional hyper irradiation research apparatus, upgrading of material irradiation experiments using these new apparatuses are intended. (G.K.)

  10. A new apparatus at hyper irradiation research facility at the Atomic Research Center, University of Tokyo

    International Nuclear Information System (INIS)

    Shibata, Hiromi; Iwai, Takeo; Narui, Makoto; Omata, Takao

    1996-01-01

    In the hyper irradiation research facility at the Atomic Research Center, the University of Tokyo, following apparatuses were newly installed for accelerator relating apparatus on 1995 fiscal year; 1) Hyper ion microbeam analysis apparatus, 2) Fourier conversion infrared microscopy, 3) Pico second two-dimensional fluorescence measuring apparatus, 4) Femto second wave-length reversible pulse laser radiation apparatus, and others. In addition to double irradiation, pulse beam irradiation experiment and so forth characteristic in conventional hyper irradiation research apparatus, upgrading of material irradiation experiments using these new apparatuses are intended. (G.K.)

  11. Picosecond multiphoton ionization of atomic and molecular clusters

    International Nuclear Information System (INIS)

    Miller, J.C.; Smith, D.B.

    1990-01-01

    High peak-power picosecond laser pulses have been used for the first time to effect nonresonant or resonant multiphoton ionization (MPI) of clusters generated in a supersonic nozzle expansion. The resulting ions are subsequently detected and characterized by time-of-flight mass spectroscopy. Specifically, we present results involving MPI of clusters of xenon and nitric oxide. Previous MPI studies of many molecular clusters using nanosecond lasers have not been successful in observing the parent ion, presumably due to fast dissociation channels. It is proposed that the present technique is a new and rather general ionization source for cluster studies which is complementary to electron impact but may, in addition, provide unique spectroscopic or dynamical information. 23 refs., 5 figs

  12. Novel phenomena in clusters irradiated by short-wavelength free-electron lasers

    International Nuclear Information System (INIS)

    Fukuzawa, Hironobu; Ueda, Kiyoshi

    2017-01-01

    By electron spectroscopy, we investigated various phenomena that are caused by the irradiation of extreme ultraviolet (EUV) and X-ray free-electron laser (FEL) pulses on rare-gas clusters. The results for the Ne clusters, which were irradiated by EUVFEL pulses at a photon energy of 20.3 eV below the ionization threshold, illustrate that novel interatomic processes yield low-energy electrons. The results for the Xe clusters, irradiated by EUVFEL pulses at a photon energy of 24.3 eV above the threshold, illustrate that nanoplasma is formed as a result of trapping the photoelectrons and consequently emits low-energy thermal electrons. The results for the Ar clusters irradiated by 5 keV XFEL pulses illustrate that nanoplasma is formed by trapping low-energy Auger electrons and secondary electrons in the tens of fs range, and continuous thermal emission from the plasma occurs in the ps range. (author)

  13. Genetic effects of prolonged combined irradiation of laboratory animals in Chernobyl Atomic Power Plant alienation zone

    International Nuclear Information System (INIS)

    Savtsova, Z.D.; Vojejkova, Yi.M.; Dzhaman, N.Yi.; Yudyina, O.Yu.; Yindik, V.M.; Kovbasyuk, S.A.

    2000-01-01

    Prolonged combined (external and internal) irradiation of mice in the r zone of the Chernobyl Atomic Power Plant caused hereditary disturbances physiological defects in the posterity irrespective of the fact if one or both parents were irradiated. The most favourable indices were observed in F2 posterity of the both exposed parents

  14. Model of defect reactions and the influence of clustering in pulse-neutron-irradiated Si

    International Nuclear Information System (INIS)

    Myers, S. M.; Cooper, P. J.; Wampler, W. R.

    2008-01-01

    Transient reactions among irradiation defects, dopants, impurities, and carriers in pulse-neutron-irradiated Si were modeled taking into account the clustering of the primal defects in recoil cascades. Continuum equations describing the diffusion, field drift, and reactions of relevant species were numerically solved for a submicrometer spherical volume, within which the starting radial distributions of defects could be varied in accord with the degree of clustering. The radial profiles corresponding to neutron irradiation were chosen through pair-correlation-function analysis of vacancy and interstitial distributions obtained from the binary-collision code MARLOWE, using a spectrum of primary recoil energies computed for a fast-burst fission reactor. Model predictions of transient behavior were compared with a variety of experimental results from irradiated bulk Si, solar cells, and bipolar-junction transistors. The influence of defect clustering during neutron bombardment was further distinguished through contrast with electron irradiation, where the primal point defects are more uniformly dispersed

  15. The annealing of interstitial carbon atoms in high-resistivity n-type silicon after proton irradiation

    CERN Document Server

    Kuhnke, M; Lindström, G

    2002-01-01

    The annealing of interstitial carbon C sub i after 7-10 MeV and 23 GeV proton irradiations at room temperature in high-resistivity n-type silicon is investigated. Deep level transient spectroscopy is used to determine the defect parameters. The annealing characteristics of the impurity defects C sub i , C sub i C sub s , C sub i O sub i and VO sub i suggest that the mobile C sub i atoms are also captured at divacancy VV sites at the cluster peripheries and not only at C sub s and O sub i sites in the silicon bulk. The deviation of the electrical filling characteristic of C sub i from the characteristic of a homogeneously distributed defect can be explained by an aggregation of C sub i atoms in the environment of the clusters. The capture rate of electrons into defects located in the cluster environment is reduced due to a positive space charge region surrounding the negatively charged cluster core. The optical filling characteristic of C sub i suggests that the change of the triangle-shaped electric field dis...

  16. A study of defect cluster formation in vanadium by heavy ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Sekimura, Naoto; Shirao, Yasuyuki; Morishita, Kazunori [Tokyo Univ. (Japan)

    1996-10-01

    Formation of defect clusters in thin foils of vanadium was investigated by heavy ion irradiation. In the very thin region of the specimens less than 20 nm, vacancy clusters were formed under gold ion irradiation, while very few clusters were detected in the specimens irradiated with 200 and 400 keV self-ions up to 1 x 10{sup 16} ions/m{sup 2}. The density of vacancy clusters were found to be strongly dependent on ion energy. Only above the critical value of kinetic energy transfer density in vanadium, vacancy clusters are considered to be formed in the cascade damage from which interstitials can escape to the specimen surface in the very thin region. (author)

  17. Giant metal sputtering yields induced by 20-5000 keV/atom gold clusters

    International Nuclear Information System (INIS)

    Andersen, H.H.; Brunelle, A.; Della-Negra, S.; Depauw, J.; Jacquet, D.; Le Beyec, Y.

    1997-01-01

    Very large non-linear effects have been found in cluster-induced metal sputtering over a broad projectile energy interval for the first time. Recently available cluster beams from tandem accelerators have allowed sputtering yield measurements to be made with Au 1 to Au 5 from 20 keV/atom to 5 MeV/atom. The cluster-sputtering yield maxima were found at the same total energy but not at the same energy/atom as expected. For Au 5 a yield as high as 3000 was reached at 150 keV/atom while the Au 1 yield was only 55 at the same velocity. The Sigmund-Claussen thermal spike theory, which fits published data at low energy, cannot reproduce our extended new data set. (author)

  18. Migration mechanisms of self-interstitial atoms and their clusters in Fe-Cr alloys

    International Nuclear Information System (INIS)

    Terentyev, D.; Malerba, L.

    2006-06-01

    The mobility of self-interstitial atoms (SIAs) and their clusters in pure iron and iron-chromium alloys was studied by atomic scale modelling techniques. Molecular dynamics (MD) was used to simulate thermally activated motion, i.e. diffusion, and its mechanisms whereas molecular statics was used to estimate energies of interactions of SIA and SIA clusters with Cr-impurities. It is shown that the presence of Cr atoms reduces the diffusivity of SIAs and their clusters in a non monotonic way with increasing Cr concentration. The main reason for this reduction is the presence of a long-range attractive interaction between self-interstitials in the crowdion configuration and Cr atoms. The migration mechanisms behind this effect are discussed relying on the results obtained from the MD simulations. (author)

  19. Optical properties of an atom in the presence of a two-nanosphere cluster

    International Nuclear Information System (INIS)

    Klimov, Vasilii V; Guzatov, D V

    2007-01-01

    The optical properties of an atom located near a cluster of two arbitrarily arranged nanospheres of an arbitrary composition are studied. Changes in the spontaneous decay rates of excited states and emission frequency shifts are considered for different orientations of the dipole moment and different positions of the atom with respect to the cluster. It is shown that a two-nanosphere cluster can be used to control efficiently the spontaneous decay rates of excited states of the atom by changing the distance between spheres. It is found that spontaneous decay rates of the excited states of an atom located between silver nanospheres and having the dipole moment directed along the axis connecting the centres of spheres can increase by a factor of 10 5 and more when nanospheres are brought closer together. (invited paper)

  20. Self-diffusion dynamic behavior of atomic clusters on Re(0 0 0 1) surface

    Energy Technology Data Exchange (ETDEWEB)

    Liu Fusheng [Department of Applied Physics, Hunan University, Changsha 410082 (China); Hu Wangyu, E-mail: wangyuhu2001cn@yahoo.com.cn [Department of Applied Physics, Hunan University, Changsha 410082 (China); Deng Huiqiu; Luo Wenhua; Xiao Shifang [Department of Applied Physics, Hunan University, Changsha 410082 (China); Yang Jianyu [Department of Maths and Physics, Hunan Institute of Engineering, Xiangtan 411104 (China)

    2009-08-15

    Using molecular dynamics simulations and a modified analytic embedded atom potential, the self-diffusion dynamics of rhenium atomic clusters up to seven atoms on Re(0 0 0 1) surface have been studied in the temperature ranges from 600 K to 1900 K. The simulation time varies from 20 ns to 200 ns according to the cluster sizes and the temperature. The heptamer and trimer are more stable comparing to other neighboring non-compact clusters. The diffusion coefficients of clusters are derived from the mean square displacement of cluster's mass-center, and diffusion prefactors D{sub 0} and activation energies E{sub a} are derived from the Arrhenius relation. It is found that the Arrhenius relation of the adatom can be divided into two parts at different temperature range. The activation energy of clusters increases with the increasing of the atom number in clusters. The prefactor of the heptamer is 2-3 orders of magnitude higher than a usual prefactor because of a large number of nonequivalent diffusion processes. The trimer and heptamer are the nuclei at different temperature range according to the nucleation theory.

  1. A channeling investigation of the interaction between solute atoms and irradiation-produced defects in magnesium

    International Nuclear Information System (INIS)

    Howe, L.M.; Swanson, M.L.; Quenneville, A.F.

    1978-01-01

    The trapping of irradiation-produced defects by solute atoms in Mg crystals was monitored by measuring the displacement of the solute atoms from lattice sites using the backscattering-channeling technique. In Mg-0.2 at.% Ag crystals, irradiation at 30 K with 1 MeVHe + ions resulted in a very large fraction of Ag atoms being displaced from their lattice sites. The Ag atom displacement appeared to be along directions and is attributed to the trapping of migrating Mg interstitial atoms by Ag atoms to form Mg-Ag mixed dumbbells. Recovery of the Ag atom displacements and the irradiation-induced dechanneling increment occurred principally in two stages, 80-160 K (stage III) and 200-280 K (stage IV). Stage III is attributed mainly to some type of interstitial migration and stage IV is attributed to the migration of single vacancies. In contrast to the Mg-Ag results, a very small displaced fraction of Bi atoms occurred in an irradiated Mg-0.08 at.% Bi crystal; hence Mg-Bi mixed dumbbells do not appear to be formed. (author)

  2. Kr atoms and their clustering in zeolite A

    CERN Document Server

    Lim, W T; Jung, K J; Heo, N H

    2001-01-01

    The positions of Kr atoms encapsulated in the molecular-dimensioned cavities of fully dehydrated zeolite A of unit-cell composition Cs sub 3 Na sub 8 HSi sub 1 sub 2 Al sub 1 sub 2 O sub 4 sub 8 (Cs sub 3 -A) have been determined. Cs sub 3 -A was exposed to 1025 atm of krypton gas at 400 .deg. C for four days, followed by cooling at pressure to encapsulate Kr atoms. The resulting crystal structure of Cs sub 3 -A(6Kr) (a=12.247(2) A, R sub 1 =0.078, and R sub 2 =0.085) has been determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3m at 21(1) .deg. C and 1 atm. In the crystal structure of Cs sub 3 -A(6Kr), six Kr atoms per unit cell are distributed over three crystallographically distinct positions: each unit cell contains one Kr atom at Kr(1) on a threefold axis in the sodalite unit, three at Kr(2) opposite four-rings in the large cavity , and two at Kr(3) on threefold axes in the large cavity . Relatively strong interactions of Kr atoms at Kr(1) and Kr(3) with Na sup + ions of ...

  3. Atomic and electronic structure of clusters from car-Parrinello method

    International Nuclear Information System (INIS)

    Kumar, V.

    1994-06-01

    With the development of ab-initio molecular dynamics method, it has now become possible to study the static and dynamical properties of clusters containing up to a few tens of atoms. Here I present a review of the method within the framework of the density functional theory and pseudopotential approach to represent the electron-ion interaction and discuss some of its applications to clusters. Particular attention is focussed on the structure and bonding properties of clusters as a function of their size. Applications to clusters of alkali metals and Al, non-metal - metal transition in divalent metal clusters, molecular clusters of carbon and Sb are discussed in detail. Some results are also presented on mixed clusters. (author). 121 refs, 24 ifigs

  4. MD simulation of atomic displacement cascades near chromium-rich clusters in FeCr alloy

    International Nuclear Information System (INIS)

    Tikhonchev, M.; Svetukhin, V.; Gaganidze, E.

    2013-01-01

    The paper reports simulation of cascades in Fe–9 at.%Cr binary alloy containing chromium-rich clusters. The simulation is performed by the molecular dynamics method at the initial temperature of 300 K and primary knock-on atom energy of 15 and 20 keV. Spherical clusters containing 95 at.% of Cr with diameter of 1–5 nm have been considered. The properties of cascade evolution in the presence of chromium-rich cluster are studied. It is shown that these clusters tend to dissolve in collision cascades. However, clusters with diameter of ⩾3 nm exhibit only slight modifications and can be considered stable. Parameters of small (1–2 nm) clusters can change significantly and, in some cases, a 1 nm cluster can be totally dissolved

  5. MD simulation of atomic displacement cascades near chromium-rich clusters in FeCr alloy

    Energy Technology Data Exchange (ETDEWEB)

    Tikhonchev, M., E-mail: tikhonchev@sv.ulsu.ru [Ulyanovsk State University, Research Institute of Technology, 42 Leo Tolstoy St., 432970 Ulyanovsk (Russian Federation); Svetukhin, V. [Ulyanovsk State University, Research Institute of Technology, 42 Leo Tolstoy St., 432970 Ulyanovsk (Russian Federation); Gaganidze, E. [Karlsruhe Institute of Technology, Institute for Applied Materials, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Karlsruhe (Germany)

    2013-11-15

    The paper reports simulation of cascades in Fe–9 at.%Cr binary alloy containing chromium-rich clusters. The simulation is performed by the molecular dynamics method at the initial temperature of 300 K and primary knock-on atom energy of 15 and 20 keV. Spherical clusters containing 95 at.% of Cr with diameter of 1–5 nm have been considered. The properties of cascade evolution in the presence of chromium-rich cluster are studied. It is shown that these clusters tend to dissolve in collision cascades. However, clusters with diameter of ⩾3 nm exhibit only slight modifications and can be considered stable. Parameters of small (1–2 nm) clusters can change significantly and, in some cases, a 1 nm cluster can be totally dissolved.

  6. Motion of Defect Clusters and Dislocations at a Crack Tip of Irradiated Material

    International Nuclear Information System (INIS)

    Moon, Won Jin; Kwon, Sang Chul; Kim, Whung Whoe

    2007-01-01

    Effects of defect clusters on mechanical properties of irradiated materials have not been clarified until now. Two radiation hardening models have been proposed. One is a dispersed barrier hardening mechanism based on the Orowan hardening model. This explains defect clusters as barriers to a dislocation motion. Generally the dislocation would rather shear or remove the defect clusters than make so-called Orowan loops. And the other is a cascade induced source hardening mechanism, which explains defect clusters as a Cottrell atmosphere for dislocation motions. However, the above mechanisms can not explain the microstructure of deformed material after irradiation and the phenomenon of yield softening. These mechanisms are based on an immobility of clusters. But we observed defect clusters could move into a specific crystallographic direction easily. Through 3 times of High Voltage Electron Microscope analysis, defect clusters have been observed to make one dimensional motion without applied external stress. If very small defect clusters could move under a stress gradient due to interactions between clusters, we can suggest that the clusters will move more actively when a stress gradient is applied externally. In-situ tensile test at TEM, we confirmed that kind of motion. We suggest defect clusters can move into crack tip, a stress-concentrated area due to tensile stress gradient and dislocations move out from the area by shear stress. Therefore radiation hardening can be explained agglomeration of defect clusters at stress concentrated area prohibits a generation of dislocation and make an increase of yield point

  7. Ab initio calculations and modelling of atomic cluster structure

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Lyalin, Andrey G.; Solov'yov, Andrey V.

    2004-01-01

    The optimized structure and electronic properties of small sodium and magnesium clusters have been investigated using it ab initio theoretical methods based on density-functional theory and post-Hartree-Fock many-body perturbation theory accounting for all electrons in the system. A new theoretical...

  8. Atomic Cluster Ionization and Attosecond Generation at Long Wavelengths

    Science.gov (United States)

    2015-10-31

    fellowships for further studies in science, mathematics, engineering or technology fields: Student Metrics This section only applies to graduating...order to investigate this we use a modified Lewenstein quantum model in which the cluster is represented by a 1D Coulomb potential for the parent ion

  9. Dynamics of atomic clusters in intense optical fields of ultrashort ...

    Indian Academy of Sciences (India)

    J. Chem. Sci. Vol. 124, No. 1, January 2012, pp. 75–81. c Indian Academy of Sciences. ... Consequently, exposure of atoms and molecules to such intense pulses inevitably leads to single and multiple ... Coulomb explosion, giving rise to ejection of fast Ar-ions. .... intense laser pulses of only a few femtoseconds dura-.

  10. Detection of helium atoms in irradiated metals using positron annihilation radiation

    International Nuclear Information System (INIS)

    Xu, Q.; Sato, K.; Yoshiie, T.; Ishizaki, T.; Nagata, S.

    2007-01-01

    Iron alloys are used widely in the nuclear industry. The production of He atoms induced by nuclear reaction increases with increasing neutron energy, and the interaction between He and defects becomes important in the fusion reactor. A new composition analysis method, coincidence Doppler broadening (CDB) of positron annihilation radiation, was employed to detect He atoms in ion irradiated Fe. The results of positron lifetime showed that the microvoids and voids were formed in ion irradiated Fe. The results of CDB measurement indicated that He atoms exited in the microvoids, and they exited in the microvoids even after annealing at 1223 K in ion irradiated Fe. CDB measurement, which is a nondestructive technique for testing materials, is an available method to detect He atoms. (authors)

  11. Improved calculation of displacements per atom cross section in solids by gamma and electron irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Piñera, Ibrahin, E-mail: ipinera@ceaden.edu.cu [Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear, CEADEN, 30 St. 502, Playa 11300, Havana (Cuba); Cruz, Carlos M.; Leyva, Antonio; Abreu, Yamiel; Cabal, Ana E. [Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear, CEADEN, 30 St. 502, Playa 11300, Havana (Cuba); Espen, Piet Van; Remortel, Nick Van [University of Antwerp, CGB, Groenenborgerlaan 171, 2020 Antwerpen (Belgium)

    2014-11-15

    Highlights: • We present a calculation procedure for dpa cross section in solids under irradiation. • Improvement about 10–90% for the gamma irradiation induced dpa cross section. • Improvement about 5–50% for the electron irradiation induced dpa cross section. • More precise results (20–70%) for thin samples irradiated with electrons. - Abstract: Several authors had estimated the displacements per atom cross sections under different approximations and models, including most of the main gamma- and electron-material interaction processes. These previous works used numerical approximation formulas which are applicable for limited energy ranges. We proposed the Monte Carlo assisted Classical Method (MCCM), which relates the established theories about atom displacements to the electron and positron secondary fluence distributions calculated from the Monte Carlo simulation. In this study the MCCM procedure is adapted in order to estimate the displacements per atom cross sections for gamma and electron irradiation. The results obtained through this procedure are compared with previous theoretical calculations. An improvement in about 10–90% for the gamma irradiation induced dpa cross section is observed in our results on regard to the previous evaluations for the studied incident energies. On the other hand, the dpa cross section values produced by irradiation with electrons are improved by our calculations in about 5–50% when compared with the theoretical approximations. When thin samples are irradiated with electrons, more precise results are obtained through the MCCM (in about 20–70%) with respect to the previous studies.

  12. Effects of atomic oxygen irradiation on the surface properties of phenolphthalein poly(ether sulfone)

    International Nuclear Information System (INIS)

    Pei Xianqiang; Li Yan; Wang Qihua; Sun Xiaojun

    2009-01-01

    To study the effects of low earth orbit environment on the surface properties of polymers, phenolphthalein poly(ether sulfone) (PES-C) blocks were irradiated by atomic oxygen in a ground-based simulation system. The surface properties of the pristine and irradiated blocks were studied by attenuated total-reflection FTIR (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM). It was found that atomic oxygen irradiation induced the destruction of PES-C molecular chains, including the scission and oxidation of PES-C molecular chains, as evidenced by FTIR and XPS results. The scission of PES-C molecular chains decreased the relative concentration of C in the surface, while the oxidation increased the relative concentration of O in the surface. The changes in surface chemical structure and composition also changed the surface morphology of the block, which shifted from smooth structure before irradiation to 'carpet-like' structure after irradiation

  13. Changes in cluster magnetism and suppression of local superconductivity in amorphous FeCrB alloy irradiated by Ar"+ ions

    International Nuclear Information System (INIS)

    Okunev, V.D.; Samoilenko, Z.A.; Szymczak, H.; Szewczyk, A.; Szymczak, R.; Lewandowski, S.J.; Aleshkevych, P.; Malinowski, A.; Gierłowski, P.; Więckowski, J.; Wolny-Marszałek, M.; Jeżabek, M.; Varyukhin, V.N.; Antoshina, I.A.

    2016-01-01

    We show that cluster magnetism in ferromagnetic amorphous Fe_6_7Cr_1_8B_1_5 alloy is related to the presence of large, D=150–250 Å, α-(Fe Cr) clusters responsible for basic changes in cluster magnetism, small, D=30–100 Å, α-(Fe, Cr) and Fe_3B clusters and subcluster atomic α-(Fe, Cr, B) groupings, D=10–20 Å, in disordered intercluster medium. For initial sample and irradiated one (Φ=1.5×10"1"8 ions/cm"2) superconductivity exists in the cluster shells of metallic α-(Fe, Cr) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ=3×10"1"8 ions/cm"2, the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ(T)~T"2 is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ=1.5×10"1"8 ions/cm"2, the transition to a dependence ρ(T)~T"1"/"2 is caused by the effects of weak localization. In more homogeneous samples, at Φ=3×10"1"8 ions/cm"2, a return to the dependence ρ(T)~T"2 is observed. - Highlights: • The samples at high dose of ion irradiation become more homogeneous. • Gigantic increase in density of the samples (twice as much) is observed. • Ferromagnetism in large Fe–Cr clusters is restored. • Ferromagnetism of Fe–Cr clusters suppresses local superconductivity in them. • The participation of quantum defects in scattering of electrons is returned.

  14. Effect of impurities on the growth of {113} interstitial clusters in silicon under electron irradiation

    OpenAIRE

    Nakai, K.; Hamada, K.; Satoh, Y.; Yoshiie, T.

    2011-01-01

    The growth and shrinkage of interstitial clusters on {113} planes were investigated in electron irradiated Czochralski grown silicon (Cz-Si), floating-zone silicon (Fz-Si), and impurity-doped Fz-Si (HT-Fz-Si) using a high voltage electron microscope. In Fz-Si, {113} interstitial clusters were formed only near the beam incident surface after a long incubation period, and shrank on subsequent irradiation from the backside of the specimen. In Cz-Si and HT-Fz-Si, {113} interstitial clusters nucle...

  15. Atomic and electronic structure of neutral and charged SinOm clusters

    International Nuclear Information System (INIS)

    Nayak, S.K.; Rao, B.K.; Khanna, S.N.; Jena, P.

    1998-01-01

    Using molecular orbital approach and the generalized gradient approximation in the density functional theory, we have calculated the equilibrium geometries, binding energies, ionization potentials, and vertical and adiabatic electron affinities of Si n O m clusters (n≤6,m≤12). The calculations were carried out using both Gaussian and numerical form for the atomic basis functions. Both procedures yield very similar results. The bonding in Si n O m clusters is characterized by a significant charge transfer between the Si and O atoms and is stronger than in conventional semiconductor clusters. The bond distances are much less sensitive to cluster size than seen for metallic clusters. Similarly, calculated energy gaps between the highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) of (SiO 2 ) n clusters increase with size while the reverse is the norm in most clusters. The HOMO-LUMO gap decreases as the oxygen content of a Si n O m cluster is lowered eventually approaching the visible range. The photoluminescence and strong size dependence of optical properties of small silica clusters could thus be attributed to oxygen defects. copyright 1998 American Institute of Physics

  16. Density functional calculations for atoms, molecules and clusters

    International Nuclear Information System (INIS)

    Gunnarsson, O.; Jones, R.O.

    1980-01-01

    The density functional formalism provides a framework for including exchange and correlation effects in the calculation of ground state properties of many-electron systems. The reduction of the problem to the solution of single-particle equations leads to important numerical advantages over other ab initio methods of incorporating correlation effects. The essential features of the scheme are outlined and results obtained for atomic and molecular systems are surveyed. The local spin density (LSD) approximation gives generally good results for systems where the bonding involves s and p electrons, but results are less satisfactory for d-bonded systems. Non-local modifications to the LSD approximation have been tested on atomic systems yielding much improved total energies. (Auth.)

  17. In vivo UVB irradiation induces clustering of Fas (CD95) on human epidermal cells

    DEFF Research Database (Denmark)

    Bang, Bo; Gniadecki, Robert; Larsen, Jørgen K

    2003-01-01

    In vitro studies with human cell lines have demonstrated that the death receptor Fas plays a role in ultraviolet (UV)-induced apoptosis. The purpose of the present study was to investigate the relation between Fas expression and apoptosis as well as clustering of Fas in human epidermis after...... a single dose of UVB irradiation. Normal healthy individuals were irradiated with three minimal erythema doses (MED) of UVB on forearm or buttock skin. Suction blisters from unirradiated and irradiated skin were raised, and Fas, FasL, and apoptosis of epidermal cells quantified by flow cytometry....... Clustering of Fas was from skin biopsied. Soluble FasL in suction blister fluid was quantified by ELISA. Flow cytometric analysis demonstrated increased expression intensity of Fas after irradiation, with 1.6-,2.2- and 2.7-fold increased median expression at 24, 48 and 72 h after irradiation, respectively (n...

  18. A numerical study of spin-dependent organization of alkali-metal atomic clusters using density-functional method

    International Nuclear Information System (INIS)

    Liu Xuan; Ito, Haruhiko; Torikai, Eiko

    2012-01-01

    We calculate the different geometric isomers of spin clusters composed of a small number of alkali-metal atoms using the UB3LYP density-functional method. The electron density distribution of clusters changes according to the value of total spin. Steric structures as well as planar structures arise when the number of atoms increases. The lowest spin state is the most stable and Li n , Na n , K n , Rb n , and Cs n with n = 2–8 can be formed in higher spin states. In the highest spin state, the preparation of clusters depends on the kind and the number of constituent atoms. The interaction energy between alkali-metal atoms and rare-gas atoms is smaller than the binding energy of spin clusters. Consequently, it is possible to self-organize the alkali-metal-atom clusters on a non-wetting substrate coated with rare-gas atoms.

  19. Observation of isolated carbon atoms and the study of their mobility on Pt clusters by NMR

    International Nuclear Information System (INIS)

    Wang, P.; Ansermet, J.; Slichter, C.P.; Sinfelt, J.H.

    1985-01-01

    The authors have used NMR to determine the structure of surface species after the C-C bond scission of adsorbed acetylene and ethylene on Pt clusters produced by heating the samples to 690 K. They have found the species to be predominantly isolated carbon atoms adsorbed on Pt surfaces. They have studied the mobility of adsorbed carbon atoms from motional narrowing of the 13 C line shapes and motion-induced shortening of the spin-lattice relaxation times. They have found that the carbon atoms on Pt clusters are very mobile, their activation energy of 7 +- 1 kcal/mole for translational motion being less than half that of CO on Pt clusters

  20. Localization and orientation of heavy-atom cluster compounds in protein crystals using molecular replacement.

    Science.gov (United States)

    Dahms, Sven O; Kuester, Miriam; Streb, Carsten; Roth, Christian; Sträter, Norbert; Than, Manuel E

    2013-02-01

    Heavy-atom clusters (HA clusters) containing a large number of specifically arranged electron-dense scatterers are especially useful for experimental phase determination of large complex structures, weakly diffracting crystals or structures with large unit cells. Often, the determination of the exact orientation of the HA cluster and hence of the individual heavy-atom positions proves to be the critical step in successful phasing and subsequent structure solution. Here, it is demonstrated that molecular replacement (MR) with either anomalous or isomorphous differences is a useful strategy for the correct placement of HA cluster compounds. The polyoxometallate cluster hexasodium α-metatungstate (HMT) was applied in phasing the structure of death receptor 6. Even though the HA cluster is bound in alternate partially occupied orientations and is located at a special position, its correct localization and orientation could be determined at resolutions as low as 4.9 Å. The broad applicability of this approach was demonstrated for five different derivative crystals that included the compounds tantalum tetradecabromide and trisodium phosphotungstate in addition to HMT. The correct placement of the HA cluster depends on the length of the intramolecular vectors chosen for MR, such that both a larger cluster size and the optimal choice of the wavelength used for anomalous data collection strongly affect the outcome.

  1. Correlation between the resistivity and the atomic clusters in liquid Cu-Sn alloys

    Science.gov (United States)

    Jia, Peng; Zhang, Jinyang; Hu, Xun; Li, Cancan; Zhao, Degang; Teng, XinYing; Yang, Cheng

    2018-05-01

    The liquid structure of CuxSn100-x (x = 0, 10, 20, 33, 40, 50, 60, 75, 80 and 100) alloys with atom percentage were investigated with resistivity and viscosity methods. It can be found from the resistivity data that the liquid Cu75Sn25 and Cu80Sn20 alloys had a negative temperature coefficient of resistivity (TCR), and liquid Cu75Sn25 alloy had a minimum value of -9.24 μΩ cm K-1. While the rest of liquid Cu-Sn alloys had a positive TCR. The results indicated that the Cu75Sn25 atomic clusters existed in Cu-Sn alloys. In addition, the method of calculating the percentage of Cu75Sn25 atomic clusters was established on the basis of resistivity theory and the law of conservation of mass. The Cu75Sn25 alloy had a maximum volume of the atomic clusters and a highest activation energy. The results further proved the existence of Cu75Sn25 atomic clusters. Furthermore, the correlation between the liquid structure and the resistivity was established. These results provide a useful reference for the investigation of liquid structure via the sensitive physical properties to the liquid structure.

  2. Dependence of irradiation creep on temperature and atom displacements in 20% cold worked type 316 stainless steel

    International Nuclear Information System (INIS)

    Gilbert, E.R.

    1976-04-01

    Irradiation creep studies with pressurized tubes of 20 percent cold worked Type 316 stainless steel were conducted in EBR-2. Results showed that as atom displacements are extended above 5 dpa and temperatures are increased above 375 0 C, the irradiation induced creep rate increases with both increasing atom displacements and increasing temperature. The stress exponent for irradiation induced creep remained near unity. Irradiation-induced effective creep strains up to 1.8 percent were observed without specimen failure. 13 figures

  3. Effect of impurities on the growth of {113} interstitial clusters in silicon under electron irradiation

    Science.gov (United States)

    Nakai, K.; Hamada, K.; Satoh, Y.; Yoshiie, T.

    2011-01-01

    The growth and shrinkage of interstitial clusters on {113} planes were investigated in electron irradiated Czochralski grown silicon (Cz-Si), floating-zone silicon (Fz-Si), and impurity-doped Fz-Si (HT-Fz-Si) using a high voltage electron microscope. In Fz-Si, {113} interstitial clusters were formed only near the beam incident surface after a long incubation period, and shrank on subsequent irradiation from the backside of the specimen. In Cz-Si and HT-Fz-Si, {113} interstitial clusters nucleated uniformly throughout the specimen without incubation, and began to shrink under prolonged irradiation at higher electron beam intensity. At lower beam intensity, however, the {113} interstitial cluster grew stably. These results demonstrate that the {113} interstitial cluster cannot grow without a continuous supply of impurities during electron irradiation. Detailed kinetics of {113} interstitial cluster growth and shrinkage in silicon, including the effects of impurities, are proposed. Then, experimental results are analyzed using rate equations based on these kinetics.

  4. Localization and orientation of heavy-atom cluster compounds in protein crystals using molecular replacement

    International Nuclear Information System (INIS)

    Dahms, Sven O.; Kuester, Miriam; Streb, Carsten; Roth, Christian; Sträter, Norbert; Than, Manuel E.

    2013-01-01

    A new approach is presented that allows the efficient localization and orientation of heavy-atom cluster compounds used in experimental phasing by a molecular replacement procedure. This permits the calculation of meaningful phases up to the highest resolution of the diffraction data. Heavy-atom clusters (HA clusters) containing a large number of specifically arranged electron-dense scatterers are especially useful for experimental phase determination of large complex structures, weakly diffracting crystals or structures with large unit cells. Often, the determination of the exact orientation of the HA cluster and hence of the individual heavy-atom positions proves to be the critical step in successful phasing and subsequent structure solution. Here, it is demonstrated that molecular replacement (MR) with either anomalous or isomorphous differences is a useful strategy for the correct placement of HA cluster compounds. The polyoxometallate cluster hexasodium α-metatungstate (HMT) was applied in phasing the structure of death receptor 6. Even though the HA cluster is bound in alternate partially occupied orientations and is located at a special position, its correct localization and orientation could be determined at resolutions as low as 4.9 Å. The broad applicability of this approach was demonstrated for five different derivative crystals that included the compounds tantalum tetradecabromide and trisodium phosphotungstate in addition to HMT. The correct placement of the HA cluster depends on the length of the intramolecular vectors chosen for MR, such that both a larger cluster size and the optimal choice of the wavelength used for anomalous data collection strongly affect the outcome

  5. Atomic structures and covalent-to-metallic transition of lead clusters Pbn (n=2-22)

    International Nuclear Information System (INIS)

    Wang Baolin; Zhao Jijun; Chen Xiaoshuang; Shi Daning; Wang Guanghou

    2005-01-01

    The lowest-energy structures and electronic properties of the lead clusters are studied by density-functional-theory calculations with Becke-Lee-Yang-Parr gradient correction. The lowest-energy structures of Pb n (n=2-22) clusters are determined from a number of structural isomers, which are generated from empirical genetic algorithm simulations. The competition between atom-centered compact structures and layered stacking structures leads to the alternative appearance of the two types of structures as global minimum. The size evolution of geometric and electronic properties from covalent bonding towards bulk metallic behavior in Pb clusters is discussed

  6. Behaviors of transmutation elements Re and Os and their effects on energetics and clustering of vacancy and self-interstitial atoms in W

    Science.gov (United States)

    Li, Yu-Hao; Zhou, Hong-Bo; Jin, Shuo; Zhang, Ying; Deng, Huiqiu; Lu, Guang-Hong

    2017-04-01

    We investigate the behaviors of rhenium (Re) and osmium (Os) and their interactions with point defects in tungsten (W) using a first-principles method. We show that Re atoms are energetically favorable to disperse separately in bulk W due to the Re-Re repulsive interaction. Despite the attractive interaction between Os atoms, there is still a large activation energy barrier of 1.10 eV at the critical number of 10 for the formation of Os clusters in bulk W based on the results of the total nucleation free energy change. Interestingly, the presence of vacancy can significantly reduce the total nucleation free energy change of Re/Os clusters, suggesting that vacancy can facilitate the nucleation of Re/Os in W. Re/Os in turn has an effect on the stability of the vacancy clusters (V n ) in W, especially for small vacancy clusters. A single Re/Os atom can raise the total binding energies of V2 and V3 obviously, thus enhancing their formation. Further, we demonstrate that there is a strong attractive interaction between Re/Os and self-interstitial atoms (SIAs). Re/Os could increase the diffusion barrier of SIAs and decrease their rotation barrier, while the interstitial-mediated path may be the optimal diffusion path of Re/Os in W. Consequently, the synergistic effect between Re/Os and point defects plays a key role in Re/Os precipitation and the evolution of defects in irradiated W.

  7. Deuterium trapping at vacancy clusters in electron/neutron-irradiated tungsten studied by positron annihilation spectroscopy

    Science.gov (United States)

    Toyama, T.; Ami, K.; Inoue, K.; Nagai, Y.; Sato, K.; Xu, Q.; Hatano, Y.

    2018-02-01

    Deuterium trapping at irradiation-induced defects in tungsten, a candidate material for plasma facing components in fusion reactors, was revealed by positron annihilation spectroscopy. Pure tungsten was electron-irradiated (8.5 MeV at ∼373 K and to a dose of ∼1 × 10-3 dpa) or neutron-irradiated (at 573 K to a dose of ∼0.3 dpa), followed by post-irradiation annealing at 573 K for 100 h in deuterium gas of ∼0.1 MPa. In both cases of electron- or neutron-irradiation, vacancy clusters were found by positron lifetime measurements. In addition, positron annihilation with deuterium electrons was demonstrated by coincidence Doppler broadening measurements, directly indicating deuterium trapping at vacancy-type defects. This is expected to cause significant increase in deuterium retention in irradiated-tungsten.

  8. Irradiated foodstuff: atom, junk-food and globalization

    International Nuclear Information System (INIS)

    Azam, Genevieve; Berlan, Jean-Pierre; Desbordes, Roland; Dufour, Francois; Fievet, Yann; Folliard, Thierry; Gallais, Veronique; Hauter, Wenonah; Jacquiau, Christian; Kastler, Guy; Lannoye, Paul; Le Goff, Lylian; Le Rohellec, Catherine; Louchard, Olivier; Marechal, Gilles; Nicolas, Yveline; Remesy, Christian; Trouve, Aurelie; Veillerette, Francois

    2008-01-01

    Food irradiation is officially presented as an ideal technology at the service of worldwide health safety and as an alternative to chemical processing of foodstuff. It is first of all a multi-usage technology for the preservation, disinfestation, ripening slowing down, and germination inhibition of products which serves the interests of multinational companies of the agriculture and food industry. According to the authors, it is also an instrument for the globalization of foodstuff trade encouraged by the international institutions and by some governments. The book stresses on the health, socio-economic and environmental risks of this technology: vitamins loss, carcinogenesis, mutagenesis, impact on local employment and economy, risks linked with the use of irradiation devices etc

  9. Atom probe study of the microstructural evolution induced by irradiation in Fe-Cu ferritic alloys and pressure vessel steels

    International Nuclear Information System (INIS)

    Pareige, P.

    1996-04-01

    Pressure vessel steels used in pressurized water reactors are low alloyed ferritic steels. They may be prone to hardening and embrittlement under neutron irradiation. The changes in mechanical properties are generally supposed to result from the formation of point defects, dislocation loops, voids and/or copper rich clusters. However, the real nature of the irradiation induced-damage in these steels has not been clearly identified yet. In order to improve our vision of this damage, we have characterized the microstructure of several steels and model alloys irradiated with electrons and neutrons. The study was performed with conventional and tomographic atom probes. The well known importance of the effects of copper upon pressure vessel steel embrittlement has led us to study Fe-Cu binary alloys. We have considered chemical aging as well as aging under electron and neutron irradiations. The resulting effects depend on whether electron or neutron irradiations ar used for thus. We carried out both kinds of irradiation concurrently so as to compare their effects. We have more particularly considered alloys with a low copper supersaturation representative of that met with the French vessel alloys (0.1% Cu). Then, we have examined steels used on French nuclear reactor pressure vessels. To characterize the microstructure of CHOOZ A steel and its evolution when exposed to neutrons, we have studied samples from the reactor surveillance program. The results achieved, especially the characterization of neutron-induced defects have been compared with those for another steel from the surveillance program of Dampierre 2. All the experiment results obtained on model and industrial steels have allowed us to consider an explanation of the way how the defects appear and grow, and to propose reasons for their influence upon steel embrittlement. (author). 3 appends

  10. Diffusion of interstitial atoms in FCC metals after irradiation with 2 MeV electrons

    International Nuclear Information System (INIS)

    Kornmann, H.

    1980-01-01

    Selfdiffusion in nickel after electron irradiation has been restudied. The diffusion velocity near the surface and the diffusion constant in the interior of the crystal have been determined as a function of radiation flux and temperature. A special method for the measurement of diffusion has been improved, which is based on radioactive tracer atoms for indication and on ion etching for the removal of thin films. To improve additionally the accuracy of the technique tracer atoms are induced into the crystal by thermal diffusion and then irradiated with 2 MeV electrons. (orig./GSCH) [de

  11. The kinetics of formation and transformation of silver atoms on solid surfaces subjected to ionizing irradiation

    International Nuclear Information System (INIS)

    Popovich, G.M.

    1988-01-01

    The paper discusses the results obtained in ESR-assisted studies of the kinetics of formation and transformation of silver atoms generated by γ-irradiation of silver-containing carriers. Three types of dependences have been established: (1) extreme; (2) saturation curves and (3) step-like. All the kinetic curves display, after a definite period of time, stable concentrations of adsorbed silver atoms per unit of the surface at a given temperature. Depending on the temperature of the experiment, the composition and nature of the carrier, the number of adsorbed silver ions, the irradiation dose and conditions of the experiment, a stable concentration of silver atoms at a given temperature may be equal to, higher or lower than the number of silver atoms measured immediately after γ-irradiation at a temperature of liquid nitrogen. A kinetic scheme is proposed to explain the obtained curves. The model suggests that the silver atoms adsorbed on the surface, as well as those formed after γ-irradiation, are bonded to the surface by various energies, which are related to heterogeneity of the carrier surface. (author)

  12. Terrestrial irradiation-sunshine duration clustering and prediction

    International Nuclear Information System (INIS)

    Sen, Zekai; Oeztopal, Ahmet

    2003-01-01

    The relationship between terrestrial irradiance and sunshine duration is not crisp and there are scatters around a general trend, which most often is expressed to occur in the form of a linear expression. This study presents a way of grouping the solar irradiation-sunshine duration data into convenient seasonal subgroups and then makes predictions within each of the groups quantitatively. In the classical Angstroem or other approaches, the seasonal variations are not considered, and therefore, rather global parameter estimations are obtained. However, the seasonal methodology of this paper provides more detailed interpretations in addition to seasonal effects and parameter estimations

  13. Effect of solute atoms on collision cascades in copper and molybdenum irradiated with self-ions

    International Nuclear Information System (INIS)

    English, C.A.; Eyre, B.L.; Wadley, H.; Stathopoulos, A.Y.

    1975-01-01

    An examination of the effect material purity has on the numbers and sizes of the vacancy loops formed in collision cascades produced by self-ion irradiation of copper and molybdenum is reported. It is shown that substitutional and interstitial impurities both markedly reduce the damage generated in molybdenum by 60 keV Mo + ions but little effect is seen in copper irradiated by 30 keV Cu + ions. These results are compared with recent observations of vacancy defects in type 316 stainless steel following irradiation with 40-200 keV Cr + . The comparison highlights the much lower vacancy concentration retained in visible clusters in the complex alloy

  14. Direct atomic imaging and density functional theory study of the Au24Pd1 cluster catalyst.

    Science.gov (United States)

    Bruma, A; Negreiros, F R; Xie, S; Tsukuda, T; Johnston, R L; Fortunelli, A; Li, Z Y

    2013-10-21

    In this study we report a direct, atomic-resolution imaging of calcined Au24Pd1 clusters supported on multiwall carbon nanotubes by employing aberration-corrected scanning transmission electron microscopy. Using gold atoms as mass standards, we confirm the cluster size to be 25 ± 2, in agreement with the Au24Pd1(SR)18 precursor used in the synthesis. Concurrently, a Density-Functional/Basin-Hopping computational algorithm is employed to locate the low-energy configurations of free Au24Pd1 cluster. Cage structures surrounding a single core atom are found to be favored, with a slight preference for Pd to occupy the core site. The cluster shows a tendency toward elongated arrangements, consistent with experimental data. The degree of electron transfer from the Pd dopant to Au is quantified through a Löwdin charge analysis, suggesting that Pd may act as an electron promoter to the surrounding Au atoms when they are involved in catalytic reactions.

  15. Recombination radius of a Frenkel pair and capture radius of a self-interstitial atom by vacancy clusters in bcc Fe

    International Nuclear Information System (INIS)

    Nakashima, Kenichi; Stoller, Roger E; Xu, Haixuan

    2015-01-01

    The recombination radius of a Frenkel pair is a fundamental parameter for the object kinetic Monte Carlo (OKMC) and mean field rate theory (RT) methods that are used to investigate irradiation damage accumulation in irradiated materials. The recombination radius in bcc Fe has been studied both experimentally and numerically, however there is no general consensus about its value. The detailed atomistic processes of recombination also remain uncertain. Values from 1.0a 0 to 3.3a 0 have been employed as a recombination radius in previous studies using OKMC and RT. The recombination process of a Frenkel pair is investigated at the atomic level using the self-evolved atomistic kinetic Monte Carlo (SEAKMC) method in this paper. SEAKMC calculations reveal that a self-interstitial atom recombines with a vacancy in a spontaneous reaction from several nearby sites following characteristic pathways. The recombination radius of a Frenkel pair is estimated to be 2.26a 0 by taking the average of the recombination distances from 80 simulation cases. In addition, we apply these procedures to the capture radius of a self-interstitial atom by a vacancy cluster. The capture radius is found to gradually increase with the size of the vacancy cluster. The fitting curve for the capture radius is obtained as a function of the number of vacancies in the cluster. (paper)

  16. The use of atomic energy for the irradiation of foods

    International Nuclear Information System (INIS)

    Wills, P.A.

    1982-01-01

    Radiation processing is a highly versatile preservation technique for the food industry. It is a cold treatment which can inhibit sprouting, eliminate insects and food pathogens, extend shelf life, decontaminate raw materials, and pasteurise or sterilise food and packaging materials. Recent developments, such as an International Standard for Irradiated Foods and a Code of Practice for the Operation of Radiation Facilities for the Treatment of Foods, are expected to stimulate and facilitate trade in radiation processed foods. These developments and prospects for commercialisation of this new technology in Australia are discussed

  17. Electronic and atomic structure of the AlnHn+2 clusters

    DEFF Research Database (Denmark)

    Martinez, Jose Ignacio; Alonso, J.A.

    2008-01-01

    The electronic and atomic structure of the family of hydrogenated Al clusters AlnHn+2 with n=4-11 has been studied using the density functional theory with the generalized gradient approximation (GGA) for exchange and correlation. All these clusters have substantial gaps between the highest...... a polyhedron of n vertices and n H atoms form strong H-Al terminal bonds; one pair of electrons is involved in each of those bonds. The remaining n+1 electron pairs form a delocalized cloud over the surface of the Al cage. The clusters fulfilling the Wade-Mingos rule have wider HOMO-LUMO gaps...... and are chemically more stable. The trends in the gap have some reflections in the form of the photoabsorption spectra, calculated in the framework of time-dependent density functional theory using the GGA single-particle energies and orbitals and a local density approximation exchange-correlation kernel....

  18. Displacement rate and temperature equivalence in stochastic cluster dynamics simulations of irradiated pure α-Fe

    Energy Technology Data Exchange (ETDEWEB)

    Dunn, Aaron [Sandia National Laboratories, Albuquerque, 87185 NM (United States); George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, 30332 GA (United States); Muntifering, Brittany [Sandia National Laboratories, Albuquerque, 87185 NM (United States); Northwestern University, Chicago, 60208 IL (United States); Dingreville, Rémi; Hattar, Khalid [Sandia National Laboratories, Albuquerque, 87185 NM (United States); Capolungo, Laurent, E-mail: laurent@lanl.gov [George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, 30332 GA (United States); Material Science and Technology Division, MST-8, Los Alamos National Laboratory, Los Alamos, 87545 NM (United States)

    2016-11-15

    Charged particle irradiation is a frequently used experimental tool to study damage accumulation in metals expected during neutron irradiation. Understanding the correspondence between displacement rate and temperature during such studies is one of several factors that must be taken into account in order to design experiments that produce equivalent damage accumulation to neutron damage conditions. In this study, spatially resolved stochastic cluster dynamics (SRSCD) is used to simulate damage evolution in α-Fe and find displacement rate/temperature pairs under ‘target’ and ‘proxy’ conditions for which the local distribution of vacancies and vacancy clusters is the same as a function of displacement damage. The SRSCD methodology is chosen for this study due to its computational efficiency and ability to simulate damage accumulation in spatially inhomogeneous materials such as thin films. Results are presented for Frenkel pair irradiation and displacement cascade damage in thin films and bulk α-Fe. Holding all other material and irradiation conditions constant, temperature adjustments are shown to successfully make up for changes in displacement rate such that defect concentrations and cluster sizes remain relatively constant. The methodology presented in this study allows for a first-order prediction of the temperature at which ion irradiation experiments (‘proxy’ conditions) should take place in order to approximate neutron irradiation (‘target’ conditions).

  19. Atomic level simulations of interaction between edge dislocations and irradiation induced ellipsoidal voids in alpha-iron

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Bida [Department of Mechanics, Huazhong University of Science and Technology, Wuhan 430074 (China); Huang, Minsheng, E-mail: mshuang@hust.edu.cn [Department of Mechanics, Huazhong University of Science and Technology, Wuhan 430074 (China); Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment, Luoyu Road 1037, Wuhan 430074 (China); Li, Zhenhuan [Department of Mechanics, Huazhong University of Science and Technology, Wuhan 430074 (China); Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment, Luoyu Road 1037, Wuhan 430074 (China)

    2017-04-15

    High concentrations of vacancies tend to be formed inside the metal materials under irradiation, and then accumulate and cluster together gradually to promote the formation of nanovoids. Generally, these voids act as obstacles for dislocation glide and thereby change/degrade the mechanical behavior of irradiated materials. In this work, the interaction between ellipsoidal nanovoids with edge dislocations in alpha-iron has been studied by atomic simulations. The results illuminate that the ellipsoidal void’s semi-major axis on the slip plane and parallel to the dislocation line is the dominant factor controlling the obstacle strength of ellipsoidal nanovoids. Two other semi-major axes, which are perpendicular to the glide plane and parallel to the Burgers vector, respectively, can also influence the critical resolved shear stress (CRSS) for dislocation shearing the ellipsoidal void. The intrinsic atomic mechanisms controlling above phenomena, such as nanovoid-geometry spatial constraint and nanovoid-surface curvature on dislocation evolution, have been discussed carefully. The classical continuum model has been amended to describe the dislocation-ellipsoidal nanovoid interaction base on current results. In addition, the influence of temperature on the CRSS of ellipsoidal nanovoids has also been investigated.

  20. Displacement per atom profile in carbon nanotube bulk material under gamma irradiation

    International Nuclear Information System (INIS)

    Leyva, A.; Pinnera, I.; Leyva, D.; Cruz, C.; Abreu, Y.

    2011-01-01

    Taking into account the physical properties and the displacement threshold energy values reported in literature for C atoms in single and multiple walled carbon nanotubes, the effective atomic displacement cross-section in carbon nanotube bulk materials exposed to the gamma rays were calculated. Then, using the mathematical simulation of photons and particles transport in the matter, energy fluxes distribution of electrons and positrons within the irradiated object were also calculated. Finally, considering both results, the atomic displacement damage profiles inside the analyzed carbon nanotube bulk materials were determined. (Author)

  1. Ab initio random structure search for 13-atom clusters of fcc elements

    International Nuclear Information System (INIS)

    Chou, J P; Hsing, C R; Wei, C M; Cheng, C; Chang, C M

    2013-01-01

    The 13-atom metal clusters of fcc elements (Al, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) were studied by density functional theory calculations. The global minima were searched for by the ab initio random structure searching method. In addition to some new lowest-energy structures for Pd 13 and Au 13 , we found that the effective coordination numbers of the lowest-energy clusters would increase with the ratio of the dimer-to-bulk bond length. This correlation, together with the electronic structures of the lowest-energy clusters, divides the 13-atom clusters of these fcc elements into two groups (except for Au 13 , which prefers a two-dimensional structure due to the relativistic effect). Compact-like clusters that are composed exclusively of triangular motifs are preferred for elements without d-electrons (Al) or with (nearly) filled d-band electrons (Ni, Pd, Cu, Ag). Non-compact clusters composed mainly of square motifs connected by some triangular motifs (Rh, Ir, Pt) are favored for elements with unfilled d-band electrons. (paper)

  2. Living Colloidal Metal Particles from Solvated Metal Atoms. Clustering of Metal Atoms in Organic Media 15.

    Science.gov (United States)

    1986-09-23

    attributed to these solutions, especially toward heart disease. And in 1618 Antoni published Panacea Aurea : Auro Potabile 4 which centered on the...probably a slow process (discussed next under the electrophoresis section ). Electrophoresis: Electrophoresis, the movement of charged particles in...electrical properties. Experimental Section Preparation of a Typical Au-Acetone Colloid The metal atom reactor has been described previo sly. 3 9 ’ 5 9 ’ 6 0

  3. Nuclear prehistory influence on transfer velocity of 54Mn impurity 'hot' atoms in irradiated metallic iron

    International Nuclear Information System (INIS)

    Alekseev, I.E.

    2007-01-01

    Influence of nuclear prehistory on transfer velocity of 54 Mn impurity 'hot'-atoms - got by different nuclear channels: 56 Fe(d, α), 54 Fe(n,p) in irradiated metallic iron - is studied. Irradiation of targets were carried out in U-120 accelerator (energy range 7.3/5.3 MeV, deuteron beam current makes up 5 μA). Mean density of thermal neutron (WWR-M reactor) makes up 8.6·10 13 neutron·cm -2 ·s -1 . It is shown, that transfer velocity of 54 Mn 'hot' atoms is defining by rate of radiation damage of targets in the irradiation process at that a key importance has a bombarding particles type applied for radioactive label getting

  4. Observation of He bubbles in ion irradiated fusion materials by conductive atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Hongyu [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); Li, Ruihuan [School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024 (China); Yang, Deming [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); School of Science, Changchun University of Science and Technology, Changchun, Jilin 130022 (China); Wu, Yunfeng; Niu, Jinhai; Yang, Qi [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); Zhao, Jijun [School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024 (China); Liu, Dongping, E-mail: dongping.liu@dlnu.edu.cn [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600 (China); Fujian Key Laboratory for Plasma and Magnetic Resonance, Department of Electronic Science, Aeronautics, School of Physics and Mechanical and Electrical Engineering, Xiamen University, Xiamen, Fujian 361005 (China)

    2013-10-15

    Using a non-destructive conductive atomic force microscope combined with the Ar{sup +} etching technique, we demonstrate that nanoscale and conductive He bubbles are formed in the implanted layer of single-crystalline 6H-SiC irradiated with 100 keV He{sup +}. We find that the surface swelling of irradiated SiC samples is well correlated with the growth of elliptic He bubbles in the implanted layer. First-principle calculations are performed to estimate the internal pressure of the He bubble in the void of SiC. Analysis indicates that nanoscale He bubbles acting as a captor capture the He atoms diffusing along the implanted layer at an evaluated temperature and result in the surface swelling of irradiated SiC materials.

  5. Grain boundary segregation in neutron-irradiated 304 stainless steel studied by atom probe tomography

    Energy Technology Data Exchange (ETDEWEB)

    Toyama, T., E-mail: ttoyama@imr.tohoku.ac.jp [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Nozawa, Y. [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Van Renterghem, W. [SCK Bullet CEN, Nuclear Materials Science Institute, Boeretang 200, 2400 Mol (Belgium); Matsukawa, Y.; Hatakeyama, M.; Nagai, Y. [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Al Mazouzi, A. [EDF R and D, Avenue des Renardieres Ecuelles, 77818 Moret sur Loing Cedex (France); Van Dyck, S. [SCK Bullet CEN, Nuclear Materials Science Institute, Boeretang 200, 2400 Mol (Belgium)

    2012-06-15

    Radiation-induced segregation (RIS) of solute atoms at a grain boundary (GB) in 304 stainless steel (SS), neutron-irradiated to a dose of 24 dpa at 300 Degree-Sign C in the fuel wrapper plates of a commercial pressurized water reactor, was investigated using laser-assisted atom probe tomography (APT). Ni, Si, and P enrichment and Cr and Fe depletion at the GB were evident. The full-width at half-maximum of the RIS region was {approx}3 nm for the concentration profile peaks of Ni and Si. The atomic percentages of Ni, Si, and Cr at the GB were {approx}19%, {approx}7%, and {approx}14%, respectively, in agreement with previously-reported values for neutron-irradiated SS. A high number density of intra-granular Ni-Si rich precipitates formed in the matrix. A precipitate-denuded zone with a width of {approx}10 nm appeared on both sides of the GB.

  6. Fabrication of MOX fuel element clusters for irradiation in PWL, CIRUS

    International Nuclear Information System (INIS)

    Roy, P.R.; Purushotham, D.S.C.; Majumdar, S.

    1983-01-01

    Three clusters, each containing 6 zircaloy-2 clad short length fuel elements of either MOX or UO 2 fuel pellets were fabricated for irradiation in pressurized water loop of CIRUS. The major objectives of the programme were: (a) to optimize the various fabrication parameters for developing a flow sheet for MOX fuel element fabrication; (b) to study the performance of the MOX fuel elements at a peak heat flux of 110 W/cm 2 ; and (c) to study the effect of various fuel pellet design changes on the behaviour of the fuel element under irradiation. Two clusters, one each of UO 2 and MOX, have been successfully irradiated to the required burn-up level and are now awaiting post irradiation examinations. The third MOX cluster is still undergoing irradiation. Fabrication of these fuel elements involved considerable amount of developing work related to the fabrication of the MOX fuel pellets and the element welding technique and is reported in detail in this report. (author)

  7. Electronic relaxation dynamics of a metal atom deposited on argon cluster

    International Nuclear Information System (INIS)

    Awali, Slim

    2014-01-01

    This thesis is a study on the interaction between electronically excited atomic states and a non-reactive environment. We have theoretically and experimentally studied situations where a metal atom (Ba or K) is placed in a finite size environment (argon cluster). The presence of the medium affects the electronic levels of the atom. On the other side, the excitation of the atom induces a relaxation dynamics of the electronic energy through the deformation of the cluster. The experimental part of this work focuses on two aspects: the spectroscopy and the dynamics. In both cases a first laser electronically excites the metal atom and the second ionizes the excited system. The observable is the photoelectron spectrum recorded after photoionization and possibly information on the photoion which are also produced. This pump/probe technique, with also two lasers, provide the ultrafast dynamic when the lasers pulses used are of ultrashort (60 fs). The use of nanosecond lasers leads to resonance spectroscopic measurement, unresolved temporally, which give information on the position of the energy levels of the studied system. From a theoretical point-of-view, the excited states of M-Ar n were calculated at the ab initio level, using large core pseudo-potential to limit the active electrons of the metal to valence electrons. The study of alkali metals (potassium) is especially well adapted to this method since only one electron is active. The ab-initio calculation and a Monte-Carlo simulation where coupled to optimize the geometry of the KAr n (n = 1-10) cluster when K is in the ground state of the neutral and the ion, or excited in the 4p or 5s state. Calculations were also conducted in collaboration with B. Gervais (CIMAP, Caen) on KAr n clusters having several tens of argon atoms. Absorption spectra were also calculated. From an experimental point-of-view, we were able to characterize the excited states of potassium and barium perturbed by the clusters. In both cases a

  8. A cluster expansion model for predicting activation barrier of atomic processes

    International Nuclear Information System (INIS)

    Rehman, Tafizur; Jaipal, M.; Chatterjee, Abhijit

    2013-01-01

    We introduce a procedure based on cluster expansion models for predicting the activation barrier of atomic processes encountered while studying the dynamics of a material system using the kinetic Monte Carlo (KMC) method. Starting with an interatomic potential description, a mathematical derivation is presented to show that the local environment dependence of the activation barrier can be captured using cluster interaction models. Next, we develop a systematic procedure for training the cluster interaction model on-the-fly, which involves: (i) obtaining activation barriers for handful local environments using nudged elastic band (NEB) calculations, (ii) identifying the local environment by analyzing the NEB results, and (iii) estimating the cluster interaction model parameters from the activation barrier data. Once a cluster expansion model has been trained, it is used to predict activation barriers without requiring any additional NEB calculations. Numerical studies are performed to validate the cluster expansion model by studying hop processes in Ag/Ag(100). We show that the use of cluster expansion model with KMC enables efficient generation of an accurate process rate catalog

  9. Investigation of energy thresholds of atomic and cluster sputtering of some elements under ion bombardment

    CERN Document Server

    Atabaev, B G; Lifanova, L F

    2002-01-01

    Threshold energies of sputtering of negative cluster ions from the Si(111) surface were measured at bombardment by Cs sup + , Rb sup + , and Na sup + ions with energy of 0.1-3.0 keV. These results are compared with the calculations of the similar thresholds by Bohdansky etc. formulas (3) for clusters Si sub n sup - and Cu sub n sup - with n=(1-5) and also for B, C, Al, Si, Fe, Cu atoms. Threshold energies of sputtering for the above elements were also estimated using the data from (5). Satisfactory agreement between the experimental and theoretical results was obtained. (author)

  10. Atomic rearrangements in ordered fcc alloys during neutron irradiation

    International Nuclear Information System (INIS)

    Kirk, M.A.; Blewitt, T.H.

    1978-01-01

    Three sets of experiments performed at Argonne National Laboratory over the past few years are described. These experiments deal with atomic rearrangements in the ordered alloys Ni 3 Mn and Cu 3 Au during fast and thermal neutron bombardment. The unique magnetic properties of ordered Ni 3 Mn are utilized to investigate radiation damage production mechanisms at low temperature (5 K) where defect migration is not possible and only disordering is observed. In the case of thermal neutron bombardment, the average recoil energy is about 450 eV and significant disordering due to [110] replacement collision sequences is observed. For fast neutron bombardment where typical recoil energies are 20 keV, significant random disordering is observed but no evidence for sizable replacement sequences is found. The bombardment of ordered Cu 3 Au by fast and thermal neutrons at higher temperature (approx. 150 0 C) is studied by electrical resistance techniques. Both ordering and disordering are observed and related to the number of migrating vacancies escaping from the high energy collision cascade

  11. An investigation on the irradiation behavior of atomized U-Mo/Al dispersion rod fuels

    International Nuclear Information System (INIS)

    Park, J.M.; Ryu, H.J.; Lee, Y.S.; Lee, D.B.; Oh, S.J.; Yoo, B.O.; Jung, Y.H.; Sohn, D.S.; Kim, C.K.

    2005-01-01

    The second irradiation fuel experiment, KOMO-2, for the qualification test of atomized U-Mo dispersion rod fuels with U-loadings of 4-4.5 gU/cc at KAERI was finished after an irradiation up to 70 at% U 235 peak burn-up and subjected to the IMEF (Irradiation material Examination Facility) for a post-irradiation analysis in order to understand the fuel irradiation performance of the U-Mo dispersion fuel. Current results for PIE of KOMO-2 revealed that the U-Mo/Al dispersion fuel rods exhibited a sound performance without any break-away swelling, but most of the fuel rods irradiated at a high linear power showed an extensive formation of the interaction phase between the U-Mo particle and the Al matrix. In this paper, the analysis of the PIE results, which focused on the diffusion related microstructures obtained from the optical and EPMA (Electron Probe Micro Analysis) observations, will be presented in detail. And a thermal modeling will be carried out to calculate the temperature of the fuel rod during an irradiation. (author)

  12. 2nd International Symposium "Atomic Cluster Collisions : Structure and Dynamics from the Nuclear to the Biological Scale"

    CERN Document Server

    Solov'yov, Andrey; ISACC 2007; Latest advances in atomic cluster collisions

    2008-01-01

    This book presents a 'snapshot' of the most recent and significant advances in the field of cluster physics. It is a comprehensive review based on contributions by the participants of the 2nd International Symposium on Atomic Cluster Collisions (ISACC 2007) held in July 19-23, 2007 at GSI, Darmstadt, Germany. The purpose of the Symposium is to promote the growth and exchange of scientific information on the structure and properties of nuclear, atomic, molecular, biological and complex cluster systems studied by means of photonic, electronic, heavy particle and atomic collisions. Particular attention is devoted to dynamic phenomena, many-body effects taking place in cluster systems of a different nature - these include problems of fusion and fission, fragmentation, collective electron excitations, phase transitions, etc.Both the experimental and theoretical aspects of cluster physics, uniquely placed between nuclear physics on the one hand and atomic, molecular and solid state physics on the other, are discuss...

  13. The fifth international symposium ''atomic cluster collisions''. ISACC 2011. Book of Abstracts

    International Nuclear Information System (INIS)

    2011-01-01

    The Fifth International Symposium ''Atomic Cluster Collisions'' (ISACC 2011) will take place in July 21-25, 2011 in Berlin, Germany. The venue of the meeting will be the St.-Michaels-Heim a lovely place located within a garden area of Berlin-Grunewald. The ISACC 2011 is organized by the Fritz-Haber-Institute of the Max- Planck Society along with the King Saud University, Rhiyadh and by the Frankfurt Institute for Advanced Studies (FIAS), Frankfurt am Main, Germany. ISACC started as the international symposium on atomic cluster collisions in St. Petersburg, Russia in 2003. The second ISACC was held at the GSI, Darmstadt, Germany in 2007. Both first and second symposia were satellites of the International Conferences on Photonic Electronic and Atomic Collisions (ICPEAC). The third ISACC has returned to St. Petersburg, Russia in 2008. The last ISACC took place in Ann Arbor, again as a satellite meeting of the ICPEAC. Initially the symposium was mainly focused on dynamics of atomic clusters, especially in atomic cluster collisions, but since then its scope has been widened significantly to include dynamics of nanosystems, biomolecules, and macromolecules with the emphasis on the similarity of numerous essential clustering phenomena arising in different branches of physics, chemistry, and biology. After the four ISACC meetings it has become clear that there is a need for an interdisciplinary conference covering a broad range of topics related to the Dynamics of Systems on a Nanoscale. Therefore in 2010 it was decided to expand upon this series of meetings with a new conference organized under the new title ''Dynamics of Systems on the Nanoscale'', the DySoN Conference, since this title better reflects the interdisciplinary character of the earlier ISACC meetings embracing all the topics of interest under a common theme. The first DySoN Conference took place in Rome, Italy in 2010. The fifth ISACC symposium will be again a satellite of the ICPEAC. The ISACC 2011 will

  14. Ab initio study of neutral (TiO2)n clusters and their interactions with water and transition metal atoms

    International Nuclear Information System (INIS)

    Çakır, D; Gülseren, O

    2012-01-01

    We have systematically investigated the growth behavior and stability of small stoichiometric (TiO 2 ) n (n = 1-10) clusters as well as their structural, electronic and magnetic properties by using the first-principles plane wave pseudopotential method within density functional theory. In order to find out the ground state geometries, a large number of initial cluster structures for each n has been searched via total energy calculations. Generally, the ground state structures for the case of n = 1-9 clusters have at least one monovalent O atom, which only binds to a single Ti atom. However, the most stable structure of the n = 10 cluster does not have any monovalent O atom. On the other hand, Ti atoms are at least fourfold coordinated for the ground state structures for n ≥ 4 clusters. Our calculations have revealed that clusters prefer to form three-dimensional structures. Furthermore, all these stoichiometric clusters have nonmagnetic ground state. The formation energy and the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap for the most stable structure of (TiO 2 ) n clusters for each n have also been calculated. The formation energy and hence the stability increases as the cluster size grows. In addition, the interactions between the ground state structure of the (TiO 2 ) n cluster and a single water molecule have been studied. The binding energy (E b ) of the H 2 O molecule exhibits an oscillatory behavior with the size of the clusters. A single water molecule preferably binds to the cluster Ti atom through its oxygen atom, resulting an average binding energy of 1.1 eV. We have also reported the interaction of the selected clusters (n = 3, 4, 10) with multiple water molecules. We have found that additional water molecules lead to a decrease in the binding energy of these molecules to the (TiO 2 ) n clusters. Finally, the adsorption of transition metal (TM) atoms (V, Co and Pt) on the n = 10 cluster has been

  15. Exploring the atomic structure of 1.8 nm monolayer-protected gold clusters with aberration-corrected STEM

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jian; Jian, Nan; Ornelas, Isabel; Pattison, Alexander J. [Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Lahtinen, Tanja; Salorinne, Kirsi [Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä (Finland); Häkkinen, Hannu [Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä (Finland); Department of Physics, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä (Finland); Palmer, Richard E., E-mail: richardepalmerwork@yahoo.com [Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom)

    2017-05-15

    Monolayer-protected (MP) Au clusters present attractive quantum systems with a range of potential applications e.g. in catalysis. Knowledge of the atomic structure is needed to obtain a full understanding of their intriguing physical and chemical properties. Here we employed aberration-corrected scanning transmission electron microscopy (ac-STEM), combined with multislice simulations, to make a round-robin investigation of the atomic structure of chemically synthesised clusters with nominal composition Au{sub 144}(SCH{sub 2}CH{sub 2}Ph){sub 60} provided by two different research groups. The MP Au clusters were “weighed” by the atom counting method, based on their integrated intensities in the high angle annular dark field (HAADF) regime and calibrated exponent of the Z dependence. For atomic structure analysis, we compared experimental images of hundreds of clusters, with atomic resolution, against a variety of structural models. Across the size range 123–151 atoms, only 3% of clusters matched the theoretically predicted Au{sub 144}(SR){sub 60} structure, while a large proportion of the clusters were amorphous (i.e. did not match any model structure). However, a distinct ring-dot feature, characteristic of local icosahedral symmetry, was observed in about 20% of the clusters. - Highlights: • Chemically synthesised gold clusters were “weighed” by atom counting to get true size. • Image simulations show a few percent of clusters have the predicted atomic structure. • But a specific ring-dot feature indicates local icosahedral order in many clusters.

  16. Roles of dynamical symmetry breaking in driving oblate-prolate transitions of atomic clusters

    International Nuclear Information System (INIS)

    Oka, Yurie; Yanao, Tomohiro; Koon, Wang Sang

    2015-01-01

    This paper explores the driving mechanisms for structural transitions of atomic clusters between oblate and prolate isomers. We employ the hyperspherical coordinates to investigate structural dynamics of a seven-atom cluster at a coarse-grained level in terms of the dynamics of three gyration radii and three principal axes, which characterize overall mass distributions of the cluster. Dynamics of gyration radii is governed by two kinds of forces. One is the potential force originating from the interactions between atoms. The other is the dynamical forces called the internal centrifugal forces, which originate from twisting and shearing motions of the system. The internal centrifugal force arising from twisting motions has an effect of breaking the symmetry between two gyration radii. As a result, in an oblate isomer, activation of the internal centrifugal force that has the effect of breaking the symmetry between the two largest gyration radii is crucial in triggering structural transitions into prolate isomers. In a prolate isomer, on the other hand, activation of the internal centrifugal force that has the effect of breaking the symmetry between the two smallest gyration radii is crucial in triggering structural transitions into oblate isomers. Activation of a twisting motion that switches the movement patterns of three principal axes is also important for the onset of structural transitions between oblate and prolate isomers. Based on these trigger mechanisms, we finally show that selective activations of specific gyration radii and twisting motions, depending on the isomer of the cluster, can effectively induce structural transitions of the cluster. The results presented here could provide further insights into the control of molecular reactions

  17. Transport, dissociation and rotation of small self-interstitial atom clusters in tungsten

    International Nuclear Information System (INIS)

    Zhou, W.H.; Zhang, C.G.; Li, Y.G.; Zeng, Z.

    2014-01-01

    Numerical calculations have been performed to study the thermal motion of self-interstitial atom (SIA) clusters in tungsten (W). Molecular dynamics simulations show that SIA clusters exhibit a fast one-dimensional (1D) motion along the close packed 〈1 1 1〉 direction accompanied by a significant mass transport in this direction. A low frequency vibration mode is identified and considered to assist the motion of SIAs. The migration energy of SIA clusters are weakly dependent on their size in the average value of 0.019 eV, which is due to the strong interaction between SIAs revealed by calculating the potential energy curve of artificially moving the SIAs along 〈1 1 1〉 direction as well as nudged elastic band (NEB) method. The rotation process of SIA cluster is studied by activation–relaxation technique and the results show that SIA cluster presents complex rotation process. Our results on the motion SIA cluster may provide updated understanding on the performance decay of materials related to SIA defects

  18. Reaction of the H atom in gamma-irradiated ferrous sulphate solutions

    International Nuclear Information System (INIS)

    Mathews, R.W.

    1977-10-01

    The effect of sulphuric acid, ferrous and ferric ion, and oxygen concentrations on G(Fe 3+ ) values from cobalt-60 gamma-irradiated soltuions has been studied. Kinetic expressions were derived for reaction models involving reactions of various forms of the H atom and additional reactions postulated to be of importance at high solute concentration. Three models were assumed invoking the additional reactions: (1) an independent yield of an excited water species; (2) increasing contributions from interspur reactions of well established species at increasing solute concentration; (3) inhibition of charge pair recombination by acid and scavenger species. The calculated G(Fe 3+ ) values from the various models were compared by the least squares method with experimental G(Fe 3+ ) values from over 600 irradiations. Model 3 provided the best fit to the data for the least number of adjustable parameters. No evidence for more than one form of H atom was found with this model. (J.R.)

  19. The irradiation behavior of atomized U-Mo alloy fuels at high temperature

    Science.gov (United States)

    Park, Jong-Man; Kim, Ki-Hwan; Kim, Chang-Kyu; Meyer, M. K.; Hofman, G. L.; Strain, R. V.

    2001-04-01

    Post-irradiation examinations of atomized U-10Mo, U-6Mo, and U-6Mo-1.7Os dispersion fuels from the RERTR-3 experiment irradiated in the Advanced Test Reactor (ATR) were carried out in order to investigate the fuel behavior of high uranium loading (8 gU/cc) at a high temperature (higher than 200°C). It was observed after about 40 at% BU that the U-Mo alloy fuels at a high temperature showed similar irradiation bubble morphologies compared to those at a lower temperature found in the RERTR-1 irradiation result, but there was a thick reaction layer with the aluminum matrix which was found to be greatly affected by the irradiation temperature and to a lesser degree by the fuel composition. In addition, the chemical analysis for the irradiated U-Mo fuels using the Electron Probe Micro Analysis (EPMA) method were conducted to investigate the compositional changes during the formation of the reaction product.

  20. Irradiation damage in boron carbide: point defects, clusters and helium bubbles

    International Nuclear Information System (INIS)

    Stoto, T.; Zuppiroli, L.

    1986-06-01

    Boron carbide is a refractory hard and light material of interest in nuclear technology (fission and also fusion). Transmission electron microscopy was used to examine the properties of radiation induced damage. Firstly, the production of point defects and their clustering was studied in samples irradiated by 1 MeV electron in a high voltage electron microscope at selected temperatures from 12 K to 1000 K. Secondly, conventional transmission electron microscopy was used to understand the production of helium bubbles in neutron irradiated boron carbide and their role in the generation of microcracks. Finally, the interaction between point defects and bubbles was also examined

  1. Oligomeric rare-earth metal cluster complexes with endohedral transition metal atoms

    Energy Technology Data Exchange (ETDEWEB)

    Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd, E-mail: gerd.meyer@uni-koeln.de

    2014-11-15

    Comproportionation reactions of rare-earth metal trihalides (RX{sub 3}) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ((T{sub 3}R{sub 11})X{sub 15}-type, P6{sub 3}/m), tetramers ((T{sub 4}R{sub 16})X{sub 28}(R{sub 4}) (P-43m), (T{sub 4}R{sub 16})X{sub 20} (P4{sub 2}/nnm), (T{sub 4}R{sub 16})X{sub 24}(RX{sub 3}){sub 4} (I4{sub 1}/a) and (T{sub 4}R{sub 16})X{sub 23} (C2/m) types of structure) and pentamers ((Ru{sub 5}La{sub 14}){sub 2}Br{sub 39}, Cc) of (TR{sub r}){sub n} (n=2–5) clusters. These oligomers are further enveloped by inner (X{sup i}) as well as outer (X{sup a}) halido ligands, which possess diverse functionalities and interconnect like oligomers through i–i, i–a and/or a–i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of (TR{sub 6}) octahedra via common edges are more frequent than trimers and pentamers, in which the (TR{sub r}) clusters share common faces. - Graphical abstract: Rare earth-metal cluster complexes with endohedral transition metal atoms (TR{sub 6}) may connect via common edges or faces to form dimers, trimers, tetramers and pentamers of which the tetramers are the most prolific. Packing effects and electron counts play an important role. - Highlights: • Rare-earth metal cluster complexes encapsulate transition metal atoms. • Oligomers are built via connection of octahedral clusters via common edges or faces. • Dimers through pentamers with closed structures are known. • Tetramers including a tetrahedron of endohedral atoms are the most prolific.

  2. Comparative study of energy of particles ejected from coulomb explosion of rare gas and metallic clusters irradiated by intense femtosecond laser field

    Science.gov (United States)

    Boucerredj, N.; Beggas, K.

    2016-10-01

    We present our study of high intensity femtosecond laser field interaction with large cluster of Kr and Na (contained 2.103 to 2.107 atoms). When laser intensity is above a critical value, it blows off all of electrons from the cluster and forms a non neutral ion cloud. The irradiation of these clusters by the intense laser field leads to highly excitation energy which can be the source of energetic electrons, electronic emission, highly charge, energetic ions and fragmentation process. During the Coulomb explosion of the resulting highly ionized, high temperature nanoplasma, ions acquire again their energy. It is shown that ultra fast ions are produced. The goal of our study is to investigate in detail a comparative study of the expansion and explosion then the ion energy of metallic and rare gas clusters irradiated by an intense femtosecond laser field. We have found that ions have a kinetic energy up to 105 eV and the Coulomb pressure is little than the hydrodynamic pressure. The Coulomb explosion of a cluster may provide a new high energy ion source.

  3. On the importance of damping phenomena in clusters irradiated by intense laser fields

    International Nuclear Information System (INIS)

    Megi, F; Belkacem, M; Bouchene, M A; Suraud, E; Zwicknagel, G

    2003-01-01

    We study the dynamics of large clusters irradiated by intense and short laser pulses, within the framework of the nanoplasma model. Particular attention is paid to the influence of electron-surface collisions, which have not been considered in previous versions of the model. We show that they dominate inverse bremsstrahlung collisions when plasmon resonance occurs. The dynamics of the cluster changes considerably and the predictions of the model are significantly modified. Moreover, there is no evidence for the presence of highly charged ions and the hydrodynamic pressure is found to be smaller than the Coulomb one

  4. Status Summary of FY16 Atom Probe Tomography Studies on UCSB ATR-2 Irradiated RPV Steels

    Energy Technology Data Exchange (ETDEWEB)

    Wells, Peter [Idaho National Lab. (INL), Idaho Falls, ID (United States); Odette, G. Robert [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2016-05-01

    The University of California Santa Barbara-2 RPV Steel Irradiation experiment was awarded in 2010 by the Nuclear Science User Facility (formerly ATR NSUF) through a competitive peer review proposal process. The experiment involved irradiation of nearly 1300 samples distributed over 13 capsules. The major objective of this experiment was to better understand embrittlement behavior of reactor pressure steels at doses beyond which available data exists yet may be achieved if reactor operating licenses are extended beyond 60 years. The experiment was instrumented during irradiation and active temperature control was used to maintain the temperature at the design temperature. Six samples were selected from a large matrix of materials to perform atom probe tomography (APT) to look at formation of high dose phases. The nature and formation behavior of these phases is discussed.

  5. Resistance–temperature relation and atom cluster estimation of In–Bi system melts

    International Nuclear Information System (INIS)

    Geng, Haoran; Wang Zhiming; Zhou Yongzhi; Li Cancan

    2012-01-01

    Highlights: ► A testing device was adopted to measure the electrical resistivity of In–Bi system melts. ► A basically linear relation exists between the resistivity and temperature of In x Bi 100−x melts in measured temperature range. ► Based on Novakovic's assumption, the content of InBi atomic cluster in In x Bi 100−x melt is estimated with ρ ≈ ρ InBi x InBi + ρ m (1 − x InBi ) equation. - Abstract: A testing device for the resistivity of high-temperature melt was adopted to measure the l resistivity of In–Bi system melts at different temperatures. It can be concluded from the analysis and calculation of the experimental results that the resistivity of In x Bi 100−x (x = 0–100) melt is in linear relationship with temperature within the experiment temperature range. The resistivity of the melt decreases with the increasing content of In. The fair consistency of resistivity of In–Bi system melt is found in the heating and cooling processes. On the basis of Novakovic's assumption, we approximately estimated the content of InBi atom clusters in In x Bi 100−x melts with the resistivity data by equation ρ ≈ ρ InBi x InBi + ρ m (1 − x InBi ). In the whole components interval, the content corresponds well with the mole fraction of InBi clusters calculated by Novakovic in the thermodynamic approach. The mole fraction of InBi type atom clusters in the melts reaches the maximum at the point of stoichiometric composition In 50 Bi 50 .

  6. Long term simulation of point defect cluster size distributions from atomic displacement cascades in Fe70Cr20Ni10

    International Nuclear Information System (INIS)

    Souidi, A.; Hou, M.; Becquart, C.S.; Domain, C.; De Backer, A.

    2015-01-01

    We have used an Object Kinetic Monte Carlo (OKMC) model to simulate the long term evolution of the primary damage in Fe 70 Cr 20 Ni 10 alloys. The mean number of Frenkel pairs created by different Primary Knocked on Atoms (PKA) was estimated by Molecular Dynamics using a ternary EAM potential developed in the framework of the PERFORM-60 European project. This number was then used to obtain the vacancy–interstitial recombination distance required in the calculation of displacement cascades in the Binary Collision Approximation (BCA) with code MARLOWE (Robinson, 1989). The BCA cascades have been generated in the 10–100 keV range with the MARLOWE code and two different screened Coulomb potentials, namely, the Molière approximation to the Thomas–Fermi potential and the so-called “Universal” potential by Ziegler, Biersack and Littmark (ZBL). These cascades have been used as input to the OKMC code LAKIMOCA (Domain et al., 2004), with a set of parameters for describing the mobility of point defect clusters based on ab initio calculations and experimental data. The cluster size distributions have been estimated for irradiation doses of 0.1 and 1 dpa, and a dose rate of 10 −7 dpa/s at 600 K. We demonstrate that, like in the case of BCC iron, cluster size distributions in the long term are independent of the cascade energy and that the recursive cascade model suggested for BCC iron in Souidi et al. (2011) also applies to FCC Fe 70 Cr 20 Ni 10. The results also show that the influence of the BCA potential is sizeable but the qualitative correspondence in the predicted long term evolution is excellent

  7. Bond formation in hafnium atom implantation into SiC induced by high-energy electron irradiation

    International Nuclear Information System (INIS)

    Yasuda, H.; Mori, H.; Sakata, T.; Naka, M.; Fujita, H.

    1992-01-01

    Bilayer films of Hf (target atoms)/α-SiC (substrate) were irradiated with 2 MeV electrons in an ultra-high voltage electron microscope (UHVEM), with the electron beam incident on the hafnium layer. As a result of the irradiation, hafnium atoms were implanted into the SiC substrate. Changes in the microstructure and valence electronic states associated with the implantation were studied by a combination of UHVEM and Auger valence electron spectroscopy. The implantation process is summarized as follows. (1) Irradiation with 2 MeV electrons first induces a crystalline-to-amorphous transition in α-SiC. (2) Hafnium atoms which have been knocked-off from the hafnium layer by collision with the 2 MeV electrons are implanted into the resultant amorphous SiC. (3) The implanted hafnium atoms make preferential bonding to carbon atoms. (4) With continued irradiation, the hafnium atoms repeat the displacement along the beam direction and the subsequent bonding with the dangling hybrids of carbon and silicon. The repetition of the displacement and subsequent bonding lead to the deep implantation of hafnium atoms into the SiC substrate. It is concluded that implantation successfully occurs when the bond strength between a constituent atom of a substrate and an injected atom is stronger than that between constituent atoms of a substrate. (Author)

  8. Atomic force microscopy and mechanical testing of bovine pericardium irradiated to radiotherapy doses

    International Nuclear Information System (INIS)

    Daar, Eman; Kaabar, W.; Woods, E.; Lei, C.; Nisbet, A.; Bradley, D.A.

    2014-01-01

    Within the context of radiotherapy our work investigates the feasibility of identifying changes in structural and biomechanical properties of pericardium resulting from exposure to penetrating photon irradiation. Collagen fibres extracted from bovine pericardium were chosen as a model of pericardium extracellular matrix as these form the main fibrous component of the medium. Tests of mechanical properties, controlled by the various structural elements of the tissues, were performed on frontal pericardium, including uni-axial tests and atomic force microscopy (AFM). While the irradiated collagen fibres showed no significant change in D-band spacing up to doses of 80 Gy, the fibre width was found to increase by 34±9% at 80 Gy when compared with that for un-irradiated samples. - Highlights: • Methods for identifying changes in tissue biophysical properties following photon irradiation. • Tests made using collagen fibres extracted from bovine pericardium. • Sensitivity of uni-axial tests and atomic force microscopy (AFM) investigated. • Radiotherapy doses investigated up to 80 Gy, delivered by 6 MV photons

  9. Ultrahigh-sensitive detection of molecules produced in catalytic reactions by uni-atomic-composition bi-element clusters supported on solid substrate

    International Nuclear Information System (INIS)

    Yasumatsu, H; Fukui, N

    2013-01-01

    An apparatus has been developed for measuring catalytic activities of uni-atomic-composition bi-element clusters supported on a solid substrate. The cluster sample is prepared by irradiating a cluster-ion beam having the uni-atomic composition onto the substrate on a soft-landing condition in an ultra-high vacuum. The catalytic activity is measured by temperature-programmed desorption (TPD) mass analysis. Molecules at a density as low as 3 cm −3 have been detected with an ultrahigh-sensitive TPD mass spectrometer consisting of a cylindrical electron gun, a quadrupole mass filter and a micro-channel-plate ion-detector. The high reproducibility has been achieved by careful calibration of the TPD mass spectrometer. As a benchmark example, thermal oxidation of CO catalysed on Pt 30 disks supported on a silicon surface was studied. The CO 2 products have been successfully observed at the Pt 30 density as low as 3 × 10 12 clusters in a circular area of 8 mm in diameter at the ramping rate of the sample temperature as low as 0.3 K s −1 .

  10. Effect of solute atoms on swelling in Ni alloys and pure Ni under He + ion irradiation

    Science.gov (United States)

    Wakai, E.; Ezawa, T.; Imamura, J.; Takenaka, T.; Tanabe, T.; Oshima, R.

    2002-12-01

    The effects of solute atoms on microstructural evolutions have been investigated using Ni alloys under 25 keV He + irradiation at 500 °C. The specimens used were pure Ni, Ni-Si, Ni-Co, Ni-Cu, Ni-Mn and Ni-Pd alloys with different volume size factors. The high number densities of dislocation loops about 1.5×10 22 m -3 were formed in the specimens irradiated to 1×10 19 ions/m 2, and they were approximately equivalent, except for Ni-Si. The mean size of loops tended to increase with the volume size factor of solute atoms. In a dose of 4×10 20 ions/m 2, the swelling was changed from 0.2% to 4.5%, depending on the volume size factors. The number densities of bubbles tended to increase with the absolute values of the volume size factor, and the swelling increased with the volume size factors. This suggests that the mobility of helium and vacancy atoms may be influenced by the interaction of solute atoms with them.

  11. Irradiation-induced precipitation in a SUS316 stainless steel using three-dimensional atom probe

    International Nuclear Information System (INIS)

    Hatakeyama, M.; Yamagata, I.

    2013-01-01

    Precipitation and segregation were investigated in a compositionally modified 316 austenitic stainless steel, neutron-irradiated at 862 K using a three-dimensional atom probe. In the solution-annealed specimen, Mo, Ti, Nb, C and P enrichment were observed in a silicide, with nominal composition Fe 3 Cr 2 Ni 2 Mo 2 Si 2 . In a Ti-rich carbide, nominaling Fe 5 Cr 8 Ni 10 Mo 2 Ti 11 Si 2 C 6 , enrichment of Mo, Si, O, and Nb was observed. Radiation-induced segregation (RIS) at the precipitate–matrix interface was also investigated at an atomic scale. RIS of Ni and P atoms, which are undersized in Fe, was also analyzed around the interface of the Ti-rich carbide and matrix. Results suggest that the carbide–matrix interface is a sink with an interstitial bias. In the cold-worked specimen, complex-precipitates consisting of silicide and carbide were formed

  12. Transformation dynamics of Ni clusters into NiO rings under electron beam irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Knez, Daniel, E-mail: daniel.knez@felmi-zfe.at [Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz (Austria); Graz Centre for Electron Microscopy, Steyrergasse 17, 8010 Graz (Austria); Thaler, Philipp; Volk, Alexander [Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria); Kothleitner, Gerald [Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz (Austria); Graz Centre for Electron Microscopy, Steyrergasse 17, 8010 Graz (Austria); Ernst, Wolfgang E. [Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria); Hofer, Ferdinand [Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz (Austria); Graz Centre for Electron Microscopy, Steyrergasse 17, 8010 Graz (Austria)

    2017-05-15

    We report the transformation of nickel clusters into NiO rings by an electron beam induced nanoscale Kirkendall effect. High-purity nickel clusters consisting of a few thousand atoms have been used as precursors and were synthesized with the superfluid helium droplet technique. Aberration-corrected, analytical scanning transmission electron microscopy was applied to oxidise and simultaneously analyse the nanostructures. The transient dynamics of the oxidation could be documented by time lapse series using high-angle annular dark-field imaging and electron energy-loss spectroscopy. A two-step Cabrera-Mott oxidation mechanism was identified. It was found that water adsorbed adjacent to the clusters acts as oxygen source for the electron beam induced oxidation. The size-dependent oxidation rate was estimated by quantitative EELS measurements combined with molecular dynamics simulations. Our findings could serve to better control sample changes during examination in an electron microscope, and might provide a methodology to generate other metal oxide nanostructures. - Highlights: • Beam induced conversion of Ni clusters into crystalline NiO rings has been observed. • Ni clusters were grown with the superfluid He-droplet technique. • oxidizeSTEM was utilized to investigate and simultaneously oxidize these clusters. • Oxidation dynamics was captured in real-time. • Cluster sizes and the oxidation rate were estimated via EELS and molecular dynamics.

  13. The multi-scattering-Xα method for analysis of the electronic structure of atomic clusters

    International Nuclear Information System (INIS)

    Bahurmuz, A.A.; Woo, C.H.

    1984-12-01

    A computer program, MSXALPHA, has been developed to carry out a quantum-mechanical analysis of the electronic structure of molecules and atomic clusters using the Multi-Scattering-Xα (MSXα) method. The MSXALPHA program is based on a code obtained from the University of Alberta; several improvements and new features were incorporated to increase generality and efficiency. The major ones are: (1) minimization of core memory usage, (2) reduction of execution time, (3) introduction of a dynamic core allocation scheme for a large number of arrays, (4) incorporation of an atomic program to generate numerical orbitals used to construct the initial molecular potential, and (5) inclusion of a routine to evaluate total energy. This report is divided into three parts. The first discusses the theory of the MSXα method. The second gives a detailed description of the program, MSXALPHA. The third discusses the results of calculations carried out for the methane molecule (CH 4 ) and a four-atom zirconium cluster (Zr 4 )

  14. Cluster dynamics models of irradiation damage accumulation in ferritic iron. II. Effects of reaction dimensionality

    Energy Technology Data Exchange (ETDEWEB)

    Kohnert, Aaron A.; Wirth, Brian D. [University of Tennessee, Knoxville, Tennessee 37996-2300 (United States)

    2015-04-21

    The black dot damage features which develop in iron at low temperatures exhibit significant mobility during in situ irradiation experiments via a series of discrete, intermittent, long range hops. By incorporating this mobility into cluster dynamics models, the temperature dependence of such damage structures can be explained with a surprising degree of accuracy. Such motion, however, is one dimensional in nature. This aspect of the physics has not been fully considered in prior models. This article describes one dimensional reaction kinetics in the context of cluster dynamics and applies them to the black dot problem. This allows both a more detailed description of the mechanisms by which defects execute irradiation-induced hops while allowing a full examination of the importance of kinetic assumptions in accurately assessing the development of this irradiation microstructure. Results are presented to demonstrate whether one dimensional diffusion alters the dependence of the defect population on factors such as temperature and defect hop length. Finally, the size of interstitial loops that develop is shown to depend on the extent of the reaction volumes between interstitial clusters, as well as the dimensionality of these interactions.

  15. A numerical study of spin-dependent organization of alkali-metal atomic clusters using density-functional method

    Energy Technology Data Exchange (ETDEWEB)

    Liu Xuan, E-mail: liu.x.ad@m.titech.ac.jp; Ito, Haruhiko [Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology (Japan); Torikai, Eiko [Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi (Japan)

    2012-08-15

    We calculate the different geometric isomers of spin clusters composed of a small number of alkali-metal atoms using the UB3LYP density-functional method. The electron density distribution of clusters changes according to the value of total spin. Steric structures as well as planar structures arise when the number of atoms increases. The lowest spin state is the most stable and Li{sub n}, Na{sub n}, K{sub n}, Rb{sub n}, and Cs{sub n} with n = 2-8 can be formed in higher spin states. In the highest spin state, the preparation of clusters depends on the kind and the number of constituent atoms. The interaction energy between alkali-metal atoms and rare-gas atoms is smaller than the binding energy of spin clusters. Consequently, it is possible to self-organize the alkali-metal-atom clusters on a non-wetting substrate coated with rare-gas atoms.

  16. Influence of a transition metal atom on the geometry and electronic structure of Mg and Mg-H clusters

    International Nuclear Information System (INIS)

    Siretskiy, M.Yu.; Shelyapina, M.G.; Fruchart, D.; Miraglia, S.; Skryabina, N.E.

    2009-01-01

    We report on the study of (MgH 2 ) n + M complexes (M = Ti or Ni) carried out within the framework of the cluster density functional theory (DFT) method. The influence of such transition metal atoms on the cluster geometry and electronic structure is discussed considering the stability of MgH 2 hydride.

  17. Efficient Decarbonylation of Furfural to Furan Catalyzed by Zirconia-Supported Palladium Clusters with Low Atomicity.

    Science.gov (United States)

    Ishida, Tamao; Kume, Kurumi; Kinjo, Kota; Honma, Tetsuo; Nakada, Kengo; Ohashi, Hironori; Yokoyama, Takushi; Hamasaki, Akiyuki; Murayama, Haruno; Izawa, Yusuke; Utsunomiya, Masaru; Tokunaga, Makoto

    2016-12-20

    Decarbonylation of furfural to furan was efficiently catalyzed by ZrO 2 -supported Pd clusters in the liquid phase under a N 2 atmosphere without additives. Although Pd/C and Pd/Al 2 O 3 have frequently been used for decarbonylation, Pd/ZrO 2 exhibited superior catalytic performance compared with these conventional catalysts. Transmission electron microscopy and X-ray absorption fine structure measurements revealed that the size of the Pd particles decreased with an increase in the specific surface area of ZrO 2 . ZrO 2 with a high surface area immobilized Pd as clusters consisting of several (three to five) Pd atoms, whereas Pd aggregated to form nanoparticles on other supports such as carbon and Al 2 O 3 despite their high surface areas. The catalytic activity of Pd/ZrO 2 was enhanced with a decrease in particle size, and the smallest Pd/ZrO 2 was the most active catalyst for decarbonylation. When CeO 2 was used as the support, a decrease in Pd particle size with an increase in surface area was also observed. Single Pd atoms were deposited on CeO 2 with a high surface area, with a strong interaction through the formation of a Pd-O-Ce bond, which led to a lower catalytic activity than that of Pd/ZrO 2 . This result suggests that zero-valent small Pd clusters consisting of more than one Pd atom are the active species for the decarbonylation reaction. Recycling tests proved that Pd/ZrO 2 maintained its catalytic activity until its sixth use. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Asymptotical approximation of interconnection of nucleons' quadrupole and cluster motion in atomic nucleus

    International Nuclear Information System (INIS)

    Kabulov, A.B.

    2003-01-01

    Atomic nuclei display different kinds of collective motion. The well known example - is the collective model arising from valent nucleons motion. The other a special kind of collective motion is cluster mode. If a collective model has quadrupole character, then cluster one has dipole character. In the boson formalism this model is describing by dynamic symmetry U(6) direct X U(4). The common Hamiltonian symmetrical to U(6) direct X U(4) group has a form H=H d +H p +V pd . In the paper the asymptotical wave function for dipole states connected with (N-1) bosons of s- and d-types is presented. In this case the problem for Hamiltonian eigenvalues is solving by analytical way. With use Elliot method and wave functions asymptotical form the operators for matrix elements of E2-, E1-, M1-transitions are cited

  19. Room-temperature current blockade in atomically defined single-cluster junctions

    Science.gov (United States)

    Lovat, Giacomo; Choi, Bonnie; Paley, Daniel W.; Steigerwald, Michael L.; Venkataraman, Latha; Roy, Xavier

    2017-11-01

    Fabricating nanoscopic devices capable of manipulating and processing single units of charge is an essential step towards creating functional devices where quantum effects dominate transport characteristics. The archetypal single-electron transistor comprises a small conducting or semiconducting island separated from two metallic reservoirs by insulating barriers. By enabling the transfer of a well-defined number of charge carriers between the island and the reservoirs, such a device may enable discrete single-electron operations. Here, we describe a single-molecule junction comprising a redox-active, atomically precise cobalt chalcogenide cluster wired between two nanoscopic electrodes. We observe current blockade at room temperature in thousands of single-cluster junctions. Below a threshold voltage, charge transfer across the junction is suppressed. The device is turned on when the temporary occupation of the core states by a transiting carrier is energetically enabled, resulting in a sequential tunnelling process and an increase in current by a factor of ∼600. We perform in situ and ex situ cyclic voltammetry as well as density functional theory calculations to unveil a two-step process mediated by an orbital localized on the core of the cluster in which charge carriers reside before tunnelling to the collector reservoir. As the bias window of the junction is opened wide enough to include one of the cluster frontier orbitals, the current blockade is lifted and charge carriers can tunnel sequentially across the junction.

  20. Quadripartite cluster and Greenberger–Horne–Zeilinger entangled light via cascade interactions with separated atomic ensembles

    International Nuclear Information System (INIS)

    Li Xing; Hu Xiangming

    2012-01-01

    It has been known that two-mode entangled light can possibly be generated by employing near-resonant interaction with an ensemble of two-level atoms. The responsible mechanism is the absorption of two photons from the strong driving field and the emission of two new photons into the cavity field. Here, we generalize such a mechanism to three separated atomic ensembles and establish cascade interactions for four nondegenerate fields. It is shown that the quadripartite cluster and Greenberger–Horne–Zeilinger entangled states occur for continuous variables. The advantage of the present scheme for the multipartite entanglement lies in that the coupling strengths are much larger due to the near resonances than for far-off-resonance-based parametric processes. (paper)

  1. Monte Carlo simulation of atomic short range order and cluster formation in two dimensional model alloys

    International Nuclear Information System (INIS)

    Rojas T, J.; Instituto Peruano de Energia Nuclear, Lima; Manrique C, E.; Torres T, E.

    2002-01-01

    Using monte Carlo simulation have been carried out an atomistic description of the structure and ordering processes in the system Cu-Au in a two-dimensional model. The ABV model of the alloy is a system of N atoms A and B, located in rigid lattice with some vacant sites. In the model we assume pair wise interactions between nearest neighbors with constant ordering energy J = 0,03 eV. The dynamics was introduced by means of a vacancy that exchanges of place with any atom of its neighbors. The simulations were carried out in a square lattice with 1024 and 4096 particles, using periodic boundary conditions to avoid border effects. We calculate the first two parameters of short range order of Warren-Cowley as function of the concentration and temperature. It was also studied the probabilities of formation of different atomic clusters that consist of 9 atoms as function of the concentration of the alloy and temperatures in a wide range of values. In some regions of temperature and concentration it was observed compositional and thermal polymorphism

  2. Atomic-resolution study of homogeneous radiation-induced precipitation in a neutron-irradiated W-10 at. % Re alloy. MSC report No. 5014

    International Nuclear Information System (INIS)

    Herschitz, R.; Seidman, D.N.

    1983-06-01

    The phenomenon of radiation-induced precipitation has been investigated in a W-10 at. % Re alloy using the atom-probe field-ion microscope. Results show a significant alteration of the microstructure of this alloy as a result of the fast-neutron irradiation. Precipitates with the composition approx. WRe (sigma phase) were detected at a density of 10 16 cm -3 . Coherent, semicoherent and possibly incoherent precipitates of the sigma phase have been observed. They were not associated with either linear or planar defects, or with any impurity atoms; i.e. a true homogeneous radiation-induced precipitation occurs in this alloy. A physical argument is presented for the nucleation of the sigma phase precipitates in the vicinity of displacement cascades produced by primary knock-on atoms. It is suggested that the nucleation of the sigma phase is due to the formation of tightly-bound mobil mixed dumbells which react to form an immobile rhenium cluster. The growth of this cluster into a precipitate is most likely driven by the irreversible vacancy: self-interstitial atom (SIA) annihilation reaction, as suggested recently by Cauvin and Martin. A mechanism for the suppression of voids, in this alloy, is presented which is self-consistent with the homogeneous radiation-induced precipitation mechanism

  3. Point defects and irradiation in oxides: simulations at the atomic scale

    International Nuclear Information System (INIS)

    Crocombette, J.P.

    2005-12-01

    The studies done by Jean-Paul Crocombette between 1996 and 2005 in the Service de Recherches de Metallurgie Physique of the Direction de l'Energie Nucleaire in Saclay are presented in this Habilitation thesis. These works were part of the material science researches on the ageing, especially under irradiation, of oxides of interest for the nuclear industry. In this context simulation studies at the atomic scale were performed on two elementary components of ageing under irradiation : point defects and displacement cascades ; using two complementary simulation techniques : ab initio electronic structure calculations and empirical potential molecular dynamics. The first part deals with point defects : self defects (vacancies or interstitials) or hetero-atomic dopants. One first recalls the energetics of such defects in oxides, the specific features of defects calculations and the expected accuracy of these calculations. Then one presents the results obtained on uranium dioxide, oxygen in silver and amorphous silica. The second part tackles the modelling of disintegration recoil nuclei in various?displacement cascades created by crystalline matrices for actinide waste disposal. Cascade calculations give access to the amorphization mechanisms under irradiation of these materials. One thus predicts that the amorphization in zircon takes place directly in the tracks whereas in lanthanum zirconate, the amorphization proceeds through the accumulation of point defects. Finally the prospects of these studies are discussed. (author)

  4. Calculation of the number of atoms displaced during the irradiation of monolayer graphene

    International Nuclear Information System (INIS)

    Daniel Codorniu Pujals; Yuri Aguilera Corrales; Francesco Baldassarre

    2011-01-01

    The irradiation of monolayer graphene, combined with chemical functionalization, could be an effective method for modifying its electronic structure and for achieving specific physical properties adjusted to different applications. A difficulty arising during planning and studying the irradiation in this system is that many of the models of interaction of the radiation with the substance cannot be applied to the two-dimensional structure of graphene. In particular, the mathematical expressions available to calculate the number of atoms displaced during the bombardment with particles can be applied only to 3D isotropic solids. In the present work, an alternative analytic expression is presented for the irradiation of graphene with heavy ions or with protons and other light charged particles. The expression was obtained on the basis of the classic theory of dispersion, using a Coulomb potential for the light charged particles and one of Inverse Square for heavy ions. For medium values of the energy of the incident particle a decreasing dependence of the number of displaced atoms with energy is obtained. This behavior, related with the two-dimensional structure of the target, had been observed in other authors' works using computational simulation. (author)

  5. Irradiation of tungsten with metallic diatomic molecular ions: atomic-resolution observations of depleted zones

    International Nuclear Information System (INIS)

    Pramanik, D.; Seidman, D.N.

    1982-08-01

    Direct evidence, on an atomic scale, is presented for the enhancement of damage production per projectile ion in diatomic metallic molecular ion (dimer) irradiations of tungsten as compared to monatomic metallic ion (monomer) irradiations. Irradiations were performed in situ at less than or equal to 10 K, in a field-ion microscope, employing 20 keV Ag + or W + monomer ions and the results are compared with 40 keV W 2 + or Ag 2 + dimer ion bombardments; the average energy per ion was 20 keV. First, in the near-surface region the depleted zones produced by the W 2 + dimer ions give rise to void-like contrast effects. The W + monomer ions do not produce this void-like damage. The existence of voids was explained employing a nucleation and diffusion-limited growth model which suggests that the growth can occur on a time scale -9 s, if the effective diffusivity of an atom in the fully-developed collision cascade is > 3 x 10 -4 cm 2 s -1 . Second, by counting the number of vacancies in individual depleted zones, produced by the different ions, it was demonstrated that the number of vacancies produced per incoming ion of the dimer is 1.55 times greater than the number of vacancies produced per monomer ion

  6. Characterization of ion-irradiation-induced nanodot structures on InP surfaces by atom probe tomography.

    Science.gov (United States)

    Gnaser, Hubert; Radny, Tobias

    2015-12-01

    Surfaces of InP were bombarded by 1.9 keV Ar(+) ions under normal incidence. The total accumulated ion fluence the samples were exposed to was varied from 1 × 10(17) cm(-2) to 3 × 10(18)cm(-2) and ion flux densities f of (0.4-2) × 10(14) cm(-2) s(-1) were used. Nanodot structures were found to evolve on the surface from these ion irradiations, their dimensions however, depend on the specific bombardment conditions. The resulting surface morphology was examined by atomic force microscopy (AFM). As a function of ion fluence, the mean radius, height, and spacing of the dots can be fitted by power-law dependences. In order to determine possible local compositional changes in these nanostructures induced by ion impact, selected samples were prepared for atom probe tomography (APT). The results indicate that by APT the composition of individual InP nanodots evolving under ion bombardment could be examined with atomic spatial resolution. At the InP surface, the values of the In/P concentration ratio are distinctly higher over a distance of ~1 nm and amount to 1.3-1.8. However, several aspects critical for the analyses were identified: (i) because of the small dimensions of these nanostructures a successful tip preparation proved very challenging. (ii) The elemental compositions obtained from APT were found to be influenced pronouncedly by the laser pulse energy; typically, low energies result in the correct stoichiometry whereas high ones lead to an inhomogeneous evaporation from the tips and deviations from the nominal composition. (iii) Depending again on the laser energy, a prolific emission of Pn cluster ions was observed, with n ≤ 11. Copyright © 2015. Published by Elsevier B.V.

  7. Ag clustering investigation in laser irradiated ion-exchanged glasses by optical and vibrational spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Trave, E., E-mail: enrico.trave@unive.it [Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venezia, Dorsoduro 2137, I-30123 Venezia (Italy); Cattaruzza, E.; Gonella, F.; Calvelli, P. [Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venezia, Dorsoduro 2137, I-30123 Venezia (Italy); Quaranta, A. [Department of Materials Engineering and Industrial Technologies, University of Trento, via Mesiano 77, I-38050 Povo (Italy); Rahman, A.; Mariotto, G. [Department of Computer Science, University of Verona, Strada le Grazie 15, 37134 Verona (Italy)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer We modify the properties of Ag{sup +} exchanged glasses by thermal and laser treatment. Black-Right-Pointing-Pointer The induced microstructural changes are analyzed by optical and Raman spectroscopy. Black-Right-Pointing-Pointer Ag-based species in the glass show a peculiar PL activity in the UV-Vis range. Black-Right-Pointing-Pointer Raman and OA analysis allow for determining the Ag cluster size evolution. Black-Right-Pointing-Pointer Laser processing leads to different cluster formation and fragmentation mechanisms. - Abstract: Ion exchange process is widely used to dope silicate glass layers with silver for several applications, ranging from light waveguide to nanostructured composite glass fabrication. The silver-doped structure and its physical properties depend on the preparation parameters as well as on subsequent treatments. In particular, laser irradiation of the ion exchanged glasses has been demonstrated to be an effective tool to control cluster size and size distribution. Nevertheless, a complete comprehension of the basic phenomena and a systematic characterization of these systems are still lacking. In this paper, an extended optical characterization is presented for soda-lime glass slides, doped with silver by Ag{sup +}-Na{sup +} ion exchange, thermally treated and irradiated with a Nd:YAG laser beam at different wavelengths, and for different energy density. The samples were characterized by various spectroscopic techniques, namely, optical absorption, photoluminescence and micro-Raman analysis. The availability of all these characterization techniques allowed pointing out a suitable scenario for the Ag clustering evolution as a function of the ion exchange, annealing and laser irradiation parameters.

  8. Energetics and self-diffusion behavior of Zr atomic clusters on a Zr(0 0 0 1) surface

    Energy Technology Data Exchange (ETDEWEB)

    Liu Fusheng [Department of Applied Physics, Hunan University, Changsha 410082 (China); Hu Wangyu [Department of Applied Physics, Hunan University, Changsha 410082 (China)], E-mail: wangyuhu2001cn@yahoo.com.cn; Deng Huiqiu; Luo Wenhua; Xiao Shifang [Department of Applied Physics, Hunan University, Changsha 410082 (China); Yang Jianyu [Department of Maths and Physics, Hunan Institute of Engineering, Xiangtan 411104 (China)

    2009-09-15

    Using a molecular dynamics method and a modified analytic embedded atom potential, the energetic and the self-diffusion dynamics of Zr atomic clusters up to eight atoms on {alpha}-Zr(0 0 0 1) surface have been studied. The simulation temperature ranges from 300 to 1100 K and the simulation time varies from 20 to 40 ns. It's found that the heptamer and trimer are more stable comparing to other neighboring non-compact clusters. The diffusion coefficients of clusters are derived from the mean square displacement of cluster's mass-center and the present diffusion coefficients for clusters exhibit an Arrhenius behavior. The Arrhenius relation of the single adatom can be divided into two parts in different temperature range because of their different diffusion mechanisms. The migration energies of clusters increase with increasing the number of atoms in cluster. The differences of the prefactors also come from the diverse diffusion mechanisms. On the facet of 60 nm, the heptamer can be the nuclei in the crystal growth below 370 K.

  9. A history of study on safety of irradiated foods (2). Clostridium botulinum in irradiated seafood from the reports by the United States Atomic Energy Commission

    International Nuclear Information System (INIS)

    Miyahara, Makoto

    2004-01-01

    This review is a part of ''history of study on the wholesomeness of irradiated foods''. Clostridium botulinum in irradiated seafood have been of great concern at the beginning of development of irradiated food. This review describes the studies on Clostridium botulinum by US. Atomic Energy Commission in 1960's with their data and what they recognized it as a risk factor of irradiated foods. In 1999 FAO/IAEA/WHO reported that Clostridium botulinum type A and B spors are apparently the most resistant and thus of great concern in the radiation sterilization of food, whereas the less radiation-resistant type E spores are important in low dose irradiation of foods, particularly fishery products. This review also describes current break-through application by NASA and Canadian irradiator. (author)

  10. Tuning the electronic properties of LaAlO3/SrTiO3 interfaces by irradiating the LaAlO3 surface with low-energy cluster ion beams

    Science.gov (United States)

    Ridier, Karl; Aureau, Damien; Bérini, Bruno; Dumont, Yves; Keller, Niels; Vigneron, Jackie; Etcheberry, Arnaud; Domengès, Bernadette; Fouchet, Arnaud

    2018-01-01

    We have investigated the effects of low-energy ion beam irradiations using argon clusters on the chemical and electronic properties of LaAlO3/SrTiO3 (LAO/STO) heterointerfaces by combining x-ray photoelectron spectroscopy (XPS) and electrical transport measurements. Due to its unique features, we demonstrate that a short-time cluster ion irradiation of the LAO surface induces significant modifications in the chemical properties of the buried STO substrate with (1) a lowering of Ti atoms oxidation states (from Ti4 + to Ti3 + and Ti2 +) correlated to the formation of oxygen vacancies at the LAO surface and (2) the creation of new surface states for Sr atoms. Contrary to what is generally observed by using higher energy ion beam techniques, this leads to an increase of the electrical conductivity at the LAO/STO interface. Our XPS data clearly reveal the existence of dynamical processes on the titanium and strontium atoms, which compete with the effect of the cluster ion beam irradiation. These relaxation effects are in part attributed to the diffusion of the ion-induced oxygen vacancies in the entire heterostructure since an increase of the interfacial metallicity is also evidenced far from the irradiated area. This paper highlights the possibility of tuning the electrical properties of LAO/STO interfaces by surface engineering, confirming experimentally the intimate connection between LAO chemistry and electronic properties of LAO/STO interfaces.

  11. Post-irradiation examination of fuel elements of Tarapur Atomic Power Station (Report-I)

    International Nuclear Information System (INIS)

    Bahl, J.K.; Sah, D.N.; Chatterjee, S.; Sivaramkrishnan, K.S.

    1979-01-01

    Detailed post-irradiation examination of three initial load fuel elements of the Tarapur Atomic Power Station (TAPS) has been carried out. The causes of the element failures have been analysed. It was observed that almost 90% of the length of the elements exoerienced nodular corrosion. It has been estimated that nodular corrosion would seriously affect the wall thickness and surface temperature of higher rated elements. Lunar shaped fret marks have also been observed at some spacer grid locations in the elements. The depth of the largest fret mark was measured to be 16.9% clad wall thickness. Detailed metallographic examination of the clad and fuel in the three elements has been done. The temperatures at different structural regions of the fuel cross-sections have been estimated. The change in fuel density during irradiation has been evaluated by comparing the irradiated fuel diameter with the mean pellet design diameter. The performance of the end plug welds and spacer grid sites in the elements has been assessed. The burnup distribution along the length of the elements has been evaluated by gamma scanning. The redistribution of fission products in the fuel has been examined by gamma scanning and beta-gamma autoradiography. Mechanical properties of the irradiated cladding have been examined by ring tensile testing. (auth.)

  12. Electron ionization and spin polarization control of Fe atom adsorbed graphene irradiated by a femtosecond laser

    International Nuclear Information System (INIS)

    Yu, Dong; Jiang, Lan; Wang, Feng; Li, Xin; Qu, Liangti; Lu, Yongfeng

    2015-01-01

    We investigate the structural properties and ionized spin electrons of an Fe–graphene system, in which the time-dependent density functional theory (TDDFT) within the generalized gradient approximation is used. The electron dynamics, including electron ionization and ionized electron spin polarization, is described for Fe atom adsorbed graphene under femtosecond laser irradiation. The theoretical results show that the electron ionization and ionized electron spin polarization are sensitive to the laser parameters, such as the incident angle and the peak intensity. The spin polarization presents the maximum value under certain laser parameters, which may be used as a source of spin-polarized electrons. - Highlights: • The structural properties of Fe–graphene system are investigated. • The electron dynamics of Fe–graphene system under laser irradiation are described. • The Fe–graphene system may be used as a source of spin-polarized electrons

  13. Gold atomic cluster mediated electrochemical aptasensor for the detection of lipopolysaccharide.

    Science.gov (United States)

    Posha, Biyas; Nambiar, Sindhu R; Sandhyarani, N

    2018-03-15

    We have constructed an aptamer immobilized gold atomic cluster mediated, ultrasensitive electrochemical biosensor (Apt/AuAC/Au) for LPS detection without any additional signal amplification strategy. The aptamer self-assemble onto the gold atomic clusters makes Apt/AuAC/Au an excellent platform for the LPS detection. Differential pulse voltammetry and EIS were used for the quantitative LPS detection. The Apt/AuAC/Au sensor offers an ultrasensitive and selective detection of LPS down to 7.94 × 10 -21 M level with a wide dynamic range from 0.01 attomolar to 1pM. The sensor exhibited excellent selectivity and stability. The real sample analysis was performed by spiking the diluted insulin sample with various concentration of LPS and obtained recovery within 2% error value. The sensor is found to be more sensitive than most of the literature reports. The simple and easy way of construction of this sensor provides an efficient and promising detection of an even trace amount of LPS. Copyright © 2017 Elsevier B.V. All rights reserved.

  14. Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains.

    Science.gov (United States)

    Liu, Chun-Sheng; An, Hui; Guo, Ling-Ju; Zeng, Zhi; Ju, Xin

    2011-01-14

    The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ∼10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.

  15. Atomic kinetic Monte Carlo model based on ab initio data: Simulation of microstructural evolution under irradiation of dilute Fe-CuNiMnSi alloys

    International Nuclear Information System (INIS)

    Vincent, E.; Becquart, C.S.; Domain, C.

    2007-01-01

    The embrittlement of pressure vessel steels under radiation has been long ago correlated with the presence of Cu solutes. Other solutes such as Ni, Mn and Si are now suspected to contribute also to the embrittlement. The interactions of these solutes with radiation induced point defects thus need to be characterized properly in order to understand the elementary mechanisms behind the formation of the clusters formed upon radiation. Ab initio calculations based on the density functional theory have been performed to determine the interactions of point defects with solute atoms in dilute FeX alloys (X = Cu, Mn, Ni or Si) in order to build a database used to parameterise an atomic kinetic Monte Carlo model. Some results of irradiation damage in dilute Fe-CuNiMnSi alloys obtained with this model are presented

  16. Atomic kinetic Monte Carlo model based on ab initio data: Simulation of microstructural evolution under irradiation of dilute Fe CuNiMnSi alloys

    Science.gov (United States)

    Vincent, E.; Becquart, C. S.; Domain, C.

    2007-02-01

    The embrittlement of pressure vessel steels under radiation has been long ago correlated with the presence of Cu solutes. Other solutes such as Ni, Mn and Si are now suspected to contribute also to the embrittlement. The interactions of these solutes with radiation induced point defects thus need to be characterized properly in order to understand the elementary mechanisms behind the formation of the clusters formed upon radiation. Ab initio calculations based on the density functional theory have been performed to determine the interactions of point defects with solute atoms in dilute FeX alloys (X = Cu, Mn, Ni or Si) in order to build a database used to parameterise an atomic kinetic Monte Carlo model. Some results of irradiation damage in dilute Fe-CuNiMnSi alloys obtained with this model are presented.

  17. Simulation of the microstructural evolution under irradiation of dilute Fe-CuNiMnSi alloys by atomic kinetic monte Carlo model based on ab initio data

    International Nuclear Information System (INIS)

    Vincent, E.; Domain, C.; Vincent, E.; Becquart, C.S.

    2008-01-01

    Full text of publication follows. The embrittlement and the hardening of pressure vessel steels under radiation has been correlated with the presence solutes such as Cu, Ni, Mn and Si. Indeed it has been observed that under irradiation, these solutes tend to gather to form more or less dilute clusters. The interactions of these solutes with radiation induced point defects thus need to be characterised properly in order to understand the elementary mechanisms behind the formation of these clusters. Ab initio calculations based on the density functional theory have been performed to determine the interactions of point defects (vacancies as well as interstitials) with solute atoms in dilute FeX alloys (X Cu, Mn, Ni or Si) in order to build a database used to parameterize an atomic kinetic Monte Carlo model. The model has been applied to simulate thermal ageing as well as irradiation conditions in dilute Fe-CuNiMnSi alloys. Results obtained with this model will be presented. (authors)

  18. Formation of nanostructures on HOPG surface in presence of surfactant atom during low energy ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Ranjan, M., E-mail: ranjanm@ipr.res.in; Joshi, P.; Mukherjee, S.

    2016-07-15

    Low energy ions beam often develop periodic patterns on surfaces under normal or off-normal incidence. Formation of such periodic patterns depends on the substrate material, the ion beam parameters, and the processing conditions. Processing conditions introduce unwanted contaminant atoms, which also play strong role in pattern formation by changing the effective sputtering yield of the material. In this work we have analysed the effect of Cu, Fe and Al impurities introduced during low energy Ar{sup +} ion irradiation on HOPG substrate. It is observed that by changing the species of foreign atoms the surface topography changes drastically. The observed surface topography is co-related with the modified sputtering yield of HOPG. Presence of Cu and Fe amplify the effective sputtering yield of HOPG, so that the required threshold for the pattern formation is achieved with the given fluence, whereas Al does not lead to any significant change in the effective yield and hence no pattern formation occurs.

  19. Radiation clusters formation and evolution in FCC metals at low-temperature neutron irradiation up to small damage fluences

    International Nuclear Information System (INIS)

    Kozlov, A.V.; Shcherbakov, E.N.; Asiptsov, O.I.; Skryabin, L.A.; Portnykh, I.A.

    2006-01-01

    Methods of transmission electron microscopy and precision size measurements are used to study the formation of radiation-induced clusters in FCC metals (Ni, Pt, austenitic steels EhI-844, ChS-68) irradiated with fast neutron (E>0.1 MeV) fluences from 7 x 10 21 up to 3.5 x 10 22 m -2 at a temperature of 310 K. Using statistical thermodynamic methods the process of radiation clusters formation and evolution is described quantitatively. The change in the concentration of point defects under irradiation as well as size variations of irradiated specimens on annealing are calculated [ru

  20. Formation of atomic clusters through the laser ablation of refractory materials in a supersonic molecular beam source

    International Nuclear Information System (INIS)

    Haufler, R.E.; Puretzky, A.A.; Compton, R.N.

    1993-01-01

    Concepts which guide the design of atomic cluster supersonic beam sources have been developed. These ideas are founded on the knowledge of laser ablation dynamics and are structured in order to take advantage of certain features of the ablation event. Some of the drawbacks of previous cluster source designs become apparent when the sequence of events following laser ablation are clarified. Key features of the new cluster source design include control of the cluster size distribution, uniform performance with a variety of solid materials and elements, high beam intensity, and significant removal of internal energy during the supersonic expansion

  1. Changes in cluster magnetism and suppression of local superconductivity in amorphous FeCrB alloy irradiated by Ar{sup +} ions

    Energy Technology Data Exchange (ETDEWEB)

    Okunev, V.D., E-mail: okunev@mail.fti.ac.donetsk.ua [Donetsk Physiko-Technical Institute, Ukrainian Academy of Sciences, av. Nauki 46, 03028 Kiev (Ukraine); Samoilenko, Z.A. [Donetsk Physiko-Technical Institute, Ukrainian Academy of Sciences, av. Nauki 46, 03028 Kiev (Ukraine); Szymczak, H.; Szewczyk, A.; Szymczak, R.; Lewandowski, S.J.; Aleshkevych, P.; Malinowski, A.; Gierłowski, P.; Więckowski, J. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Wolny-Marszałek, M.; Jeżabek, M. [Institute of Nuclear Physics, Polish Academy of Sciences, Krakow (Poland); Varyukhin, V.N. [Donetsk Physiko-Technical Institute, Ukrainian Academy of Sciences, av. Nauki 46, 03028 Kiev (Ukraine); Antoshina, I.A. [Obninsk State Technical University of Atomic Energy, 249020 Obninsk (Russian Federation)

    2016-02-01

    We show that cluster magnetism in ferromagnetic amorphous Fe{sub 67}Cr{sub 18}B{sub 15} alloy is related to the presence of large, D=150–250 Å, α-(Fe Cr) clusters responsible for basic changes in cluster magnetism, small, D=30–100 Å, α-(Fe, Cr) and Fe{sub 3}B clusters and subcluster atomic α-(Fe, Cr, B) groupings, D=10–20 Å, in disordered intercluster medium. For initial sample and irradiated one (Φ=1.5×10{sup 18} ions/cm{sup 2}) superconductivity exists in the cluster shells of metallic α-(Fe, Cr) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ=3×10{sup 18} ions/cm{sup 2}, the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ(T)~T{sup 2} is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ=1.5×10{sup 18} ions/cm{sup 2}, the transition to a dependence ρ(T)~T{sup 1/2} is caused by the effects of weak localization. In more homogeneous samples, at Φ=3×10{sup 18} ions/cm{sup 2}, a return to the dependence ρ(T)~T{sup 2} is observed. - Highlights: • The samples at high dose of ion irradiation become more homogeneous. • Gigantic increase in density of the samples (twice as much) is observed. • Ferromagnetism in large Fe–Cr clusters is restored. • Ferromagnetism of Fe–Cr clusters suppresses local superconductivity in them. • The participation of quantum defects in scattering of electrons is returned.

  2. Barrier mechanism of multilayers graphene coated copper against atomic oxygen irradiation

    Science.gov (United States)

    Zhang, Haijing; Ren, Siming; Pu, Jibin; Xue, Qunji

    2018-06-01

    Graphene has been demonstrated as a protective coating for Cu under ambient condition because of its high impermeability and light-weight oxidation barrier. However, it lacks the research of graphene as a protective coating in space environment. Here, we experimentally and theoretically study the oxidation behavior of graphene-coated Cu in vacuum atomic oxygen (AO) condition. After AO irradiation, the experimental results show multilayer graphene has better anti-oxidation than monolayer graphene. Meanwhile, the calculation results show the oxidation appeared on the graphene's grain boundaries or the film's vacancy defects for the monolayer graphene coated Cu foil. Moreover, the calculation results show the oxidation process proceeds slowly in multilayers because of the matched defects overlaps each other to form a steric hindrance to suppress the O atom diffusion in the vertical direction, and the mismatched defects generates potential energy barriers for interlayer to suppress the O atom diffusion in the horizontal direction. Hence, multilayer graphene films could serve as protection coatings to prevent diffusion of O atom.

  3. Study of point defect clustering in electron and ion irradiated zirconium alloys

    International Nuclear Information System (INIS)

    Hellio, C.; Boulanger, L.

    1986-09-01

    Dislocation loops created by 500 keV Zr + ions and 1 MeV electrons in zirconium have a/3 type Burgers vectors, and in ion irradiated samples, loops lie preferentially on planes close to (1010). From in-situ observations of loop growth under 1 MeV electron irradiation in zirconium and dilute Zr (Nb,O) alloys, a strong increase of the vacancy migration energy with oxygen concentration was observed, from 0.72 eV for pure zirconium to 1.7 eV for Zr and Zr-1% Nb doped with 1800 ppm weight oxygen, indicating large trapping of vacancies by O single interstitials or clusters

  4. Atomic scale modeling of defect production and microstructure evolution in irradiated metals

    Energy Technology Data Exchange (ETDEWEB)

    Diaz de la Rubia, T.; Soneda, N.; Shimomura, Y. [Lawrence Livermore National Lab., CA (United States)] [and others

    1997-04-01

    Irradiation effects in materials depend in a complex way on the form of the as-produced primary damage state and its spatial and temporal evolution. Thus, while collision cascades produce defects on a time scale of tens of picosecond, diffusion occurs over much longer time scales, of the order of seconds, and microstructure evolution over even longer time scales. In this report the authors present work aimed at describing damage production and evolution in metals across all the relevant time and length scales. They discuss results of molecular dynamics simulations of displacement cascades in Fe and V. They show that interstitial clusters are produced in cascades above 5 keV, but not vacancy clusters. Next, they discuss the development of a kinetic Monte Carlo model that enables calculations of damage evolution over much longer time scales (1000`s of s) than the picosecond lifetime of the cascade. They demonstrate the applicability of the method by presenting predictions on the fraction of freely migrating defects in {alpha}Fe during irradiation at 600 K.

  5. Atomic scale modeling of defect production and microstructure evolution in irradiated metals

    International Nuclear Information System (INIS)

    Diaz de la Rubia, T.; Soneda, N.; Shimomura, Y.

    1997-01-01

    Irradiation effects in materials depend in a complex way on the form of the as-produced primary damage state and its spatial and temporal evolution. Thus, while collision cascades produce defects on a time scale of tens of picosecond, diffusion occurs over much longer time scales, of the order of seconds, and microstructure evolution over even longer time scales. In this report the authors present work aimed at describing damage production and evolution in metals across all the relevant time and length scales. They discuss results of molecular dynamics simulations of displacement cascades in Fe and V. They show that interstitial clusters are produced in cascades above 5 keV, but not vacancy clusters. Next, they discuss the development of a kinetic Monte Carlo model that enables calculations of damage evolution over much longer time scales (1000's of s) than the picosecond lifetime of the cascade. They demonstrate the applicability of the method by presenting predictions on the fraction of freely migrating defects in αFe during irradiation at 600 K

  6. Electron irradiation effects in amorphous antimony thin films obtained by cluster-beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Fuchs, G.; Treilleux, M.; Santos Aires, F.; Cabaud, B.; Melinon, P.; Hoareau, A. (Lyon-1 Univ., 69 - Villeurbanne (France))

    1991-03-01

    In order to understand the differences existing between films obtained with a classical molecular beam deposition (MBD) and the new low-energy cluster beam deposition (LECBD), transmission electron microscopy has been used to characterize the first stages of antimony LECBD. Antimony deposits are discontinuous and amorphous up to 2 nm in thickness. They are formed with isolated amorphous antimony particles surrounded by an amorphous antimony oxide shell. Moreover, under electron beam exposure in the microscope, an amorphous-crystal transformation has been observed in the oxide shell. Electron irradiation induces the formation of a crystallized antimony oxide (Sb{sub 2}O{sub 3}) around the amorphous antimony core. (author).

  7. Resistivity recovery simulations of electron-irradiated iron: Kinetic Monte Carlo versus cluster dynamics

    International Nuclear Information System (INIS)

    Dalla Torre, J.; Fu, C.-C.; Willaime, F.; Barbu, A.; Bocquet, J.-L.

    2006-01-01

    The isochronal resistivity recovery in high purity α-iron irradiated by electrons was successfully reproduced by a multiscale modelling approach. The stability and mobility of small self-defect clusters determined by ab initio methods were used as input data for an event based Kinetic Monte Carlo (KMC) model, used to explore the defect population evolution during the annealing and to extract the resistivity recovery peaks. In this paper, we investigate the possibility of using an efficient mesoscale model, the Cluster Dynamics (CD), instead of KMC in this approach. The comparison between the two methods for various CD initial conditions shows the importance of spatial correlations between defects, which are neglected in the CD model. However, using appropriate initial conditions, e.g. starting from the concentration of Frenkel pairs after the uncorrelated stage I E , the CD model captures the main characteristics of subsequent defect population evolution, and it can therefore be used for fast and semi-quantitative investigations

  8. Carbon/hydrogen clusters [CnHx+] formation from laser irradiation of coronene

    International Nuclear Information System (INIS)

    Betancourt, F; Alvarez, I; Guerrero, A; Cisneros, C; Poveda, J C

    2015-01-01

    This article presents the photo induced dehydrogenation of a cooled molecular jet of coronene, exposed to 266 nm laser radiation. Using unfocused laser radiation of 1064 nm, synchronously coupled with the ionization laser pulses, a system recently developed. Molecular beams were produced by laser desorption of coronene. Analysis of the photoproducts made by time-of flight mass spectrometer showed that a wide variety of ionic species were formed; more than 300 different species were observed. The results showed carbon clusters C + n with n up to 24 as well as carbon/hydrogen clusters C + n H + x with masses higher than 300 m/z. The effect on the laser irradiance on the formation of different ions, in the rage from 10 9 W/cm2 to 10 10 W/cm2, is discussed as it is reflected on the evolution from the big ions to the smaller ones. (paper)

  9. Role of isolated and clustered DNA damage and the post-irradiating repair process in the effects of heavy ion beam irradiation

    International Nuclear Information System (INIS)

    Tokuyama, Yuka; Terato, Hiroaki; Furusawa, Yoshiya; Ide, Hiroshi; Yasui, Akira

    2015-01-01

    Clustered DNA damage is a specific type of DNA damage induced by ionizing radiation. Any type of ionizing radiation traverses the target DNA molecule as a beam, inducing damage along its track. Our previous study showed that clustered DNA damage yields decreased with increased linear energy transfer (LET), leading us to investigate the importance of clustered DNA damage in the biological effects of heavy ion beam radiation. In this study, we analyzed the yield of clustered base damage (comprising multiple base lesions) in cultured cells irradiated with various heavy ion beams, and investigated isolated base damage and the repair process in post-irradiation cultured cells. Chinese hamster ovary (CHO) cells were irradiated by carbon, silicon, argon and iron ion beams with LETs of 13, 55, 90 and 200 keV µm -1 , respectively. Agarose gel electrophoresis of the cells with enzymatic treatments indicated that clustered base damage yields decreased as the LET increased. The aldehyde reactive probe procedure showed that isolated base damage yields in the irradiated cells followed the same pattern. To analyze the cellular base damage process, clustered DNA damage repair was investigated using DNA repair mutant cells. DNA double-strand breaks accumulated in CHO mutant cells lacking Xrcc1 after irradiation, and the cell viability decreased. On the other hand, mouse embryonic fibroblast (Mef) cells lacking both Nth1 and Ogg1 became more resistant than the wild type Mef. Thus, clustered base damage seems to be involved in the expression of heavy ion beam biological effects via the repair process. (author)

  10. Photoelectron imaging, probe of the dynamics: from atoms... to clusters; Imagerie de photoelectrons, sonde de la dynamique: des atomes... aux agregats

    Energy Technology Data Exchange (ETDEWEB)

    Lepine, F

    2003-06-15

    This thesis concerns the study of the deexcitation of clusters and atoms by photoelectron imaging. The first part is dedicated to thermionic emission of a finite size system. A 3-dimensional imaging setup allows us to measure the time evolution of the kinetic energy spectrum of electrons emitted from different clusters (W{sub n}{sup -}, C{sub n}{sup -}, C{sub 60}). Then we have a direct access to the fundamental quantities which characterize this statistical emission: the temperature of the finite heat bath and the decay rate. The second part concerns the ionization of atomic Rydberg states placed in a static electric field. We performed the first experiment of photoionization microscopy which allows us to obtain a picture which is the macroscopic projection of the electronic wave function. Then we have access to the detail of the photoionization and particularly to the quantum properties of the electron usually confined at the atomic scale. (author)

  11. Irradiation induced defects containing oxygen atoms in germanium crystal as studied by deep level transient spectroscopy

    International Nuclear Information System (INIS)

    Fukuoka, Noboru; Kambe, Yoshiyuki; Saito, Haruo; Matsuda, Koji.

    1984-05-01

    Deep level transient spectroscopy was applied to the electron trapping levels which are associated with the irradiation induced lattice defects in germanium crystals. The germanium crystals used in the study were doped with oxygen, antimony or arsenic and the defects were formed by electron irradiation of 1.5MeV or 10MeV. The nature of so called ''thermal defect'' formed by heat treatment at about 670K was also studied. The trapping levels at Esub(c)-0.13eV, Esub(c)-0.25eV and Esub(c)-0.29eV were found to be associated with defects containing oxygen atoms. From the experimental results the Esub(c)-0.25eV level was attributed to the germanium A-center (interstitial oxygen atom-vacancy pair). Another defect associated with the 715cm -1 infrared absorption band was found to have a trapping level at the same position at Esub(c)-0.25eV. The Esub(c)-0.23eV and Esub(c)-0.1eV levels were revealed to be associated with thermal donors formed by heat treatment at about 670K. Additional two peaks (levels) were observed in the DLTS spectrum. The annealing behavior of the levels suggests that the thermal donors originate from not a single type but several types of defects. (author)

  12. Positron states and nanoobjects in proton-irradiated quartz single crystals: Positronium atom in quartz

    International Nuclear Information System (INIS)

    Grafutin, V. I.; Zaluzhnyi, A. G.; Timoshenkov, S. P.; Britkov, O. M.; Ilyukhina, O. V.; Myasishcheva, G. G.; Prokop'ev, E. P.; Funtikov, Yu. V.

    2008-01-01

    The influence of proton bombardment and metal atom impurities on the structure of quartz single crystals has been studied. The related defects have been studied using positron annihilation spectroscopy (angular correlation of positron-annihilation photons), acoustic absorption, and optical absorption measurements. It is shown that the presence of a narrow component f in the angular distribution of annihilation photons (ADAP), which is related to the formation of parapositronium, determines a high sensitivity of this method with respect to features of the crystal structure of quartz. It is established that the defectness of the structure of irradiated quartz crystals can be characterized by the ratio f/f 0 of the relative intensities of narrow components in the ADAP curves measured before (f 0 ) and after (f) irradiation. Any process leading to a decrease in the probability of positronium formation (e.g., positron loss as a result of the trapping on defects and the interaction with impurity atoms and lattice distortions) decreases the intensity of the narrow component. Based on the ADAP data, estimates of the radii and concentrations of nanodefects in quartz have been obtained and their variation upon annealing at temperatures up to T = 873 K has been studied

  13. Atomistic simulation of damage production by atomic and molecular ion irradiation in GaN

    International Nuclear Information System (INIS)

    Ullah, M. W.; Kuronen, A.; Nordlund, K.; Djurabekova, F.; Karaseov, P. A.; Titov, A. I.

    2012-01-01

    We have studied defect production during single atomic and molecular ion irradiation having an energy of 50 eV/amu in GaN by molecular dynamics simulations. Enhanced defect recombination is found in GaN, in accordance with experimental data. Instantaneous damage shows non-linearity with different molecular projectile and increasing molecular mass. Number of instantaneous defects produced by the PF 4 molecule close to target surface is four times higher than that for PF 2 molecule and three times higher than that calculated as a sum of the damage produced by one P and four F ion irradiation (P+4×F). We explain this non-linearity by energy spike due to molecular effects. On the contrary, final damage created by PF 4 and PF 2 shows a linear pattern when the sample cools down. Total numbers of defects produced by Ag and PF 4 having similar atomic masses are comparable. However, defect-depth distributions produced by these species are quite different, also indicating molecular effect.

  14. An easy-to-use method for measuring the flux of free atoms in a cluster beam

    International Nuclear Information System (INIS)

    Cuvellier, J.; Binet, A.

    1988-01-01

    A method is proposed to measure the flux of free atoms remaining in a beam of clusters. The time-of-flight (TOF) of an Ar beam containing clusters was analysed for this purpose using an electron impact + quadrupole mass spectrometer as detector. When considering TOF's with mass settings at Ar + , a double mode structure was observed. The slow component was interpreted as coming from Ar clusters that fragment as Ar + in the ionization chamber of the detector. The rapid mode in the TOF's was linked to the free atoms remaining in the Ar beam. Evaluating the area of this mode allowed one to measure the flux of free atoms in the Ar beam. The method is not restricted to measurements on Ar beams

  15. Collective-field-corrected strong field approximation for laser-irradiated metal clusters

    International Nuclear Information System (INIS)

    Keil, Th; Bauer, D

    2014-01-01

    The strong field approximation (SFA) formulated in terms of so-called ‘quantum orbits’ led to much insight into intense-laser driven ionization dynamics. In plain SFA, the emitted electron is treated as a free electron in the laser field alone. However, with improving experimental techniques and more advanced numerical simulations, it becomes more and more obvious that the plain SFA misses interesting effects even on a qualitative level. Examples are holographic side lobes, the low-energy structure, radial patterns in photoelectron spectra at low kinetic energies and strongly rotated angular distributions. For this reason, increasing efforts have been recently devoted to Coulomb corrections of the SFA. In the current paper, we follow a similar line but consider ionization of metal clusters. It is known that photoelectrons from clusters can be much more energetic than those emitted from atoms or small molecules, especially if the Mie resonance of the expanding cluster is evoked. We develop a SFA that takes the collective field inside the cluster via the simple rigid-sphere model into account. Our approach is based on field-corrected quantum orbits so that the acceleration process (or any other spectral feature of interest) can be investigated in detail. (paper)

  16. Computer-simulated images of icosahedral, pentagonal and decagonal clusters of atoms

    International Nuclear Information System (INIS)

    Peng JuLin; Bursill, L.A.

    1989-01-01

    The aim of this work was to assess, by computer-simulation the sensitivity of high-resolution electron microscopy (HREM) images for a set of icosahedral and decagonal clusters, containing 50-400 atoms. An experimental study of both crystalline and quasy-crystalline alloys of A1(Si)Mn is presented, in which carefully-chosen electron optical conditions were established by computer simulation then used to obtain high quality images. It was concluded that while there is a very significant degree of model sensitiveness available, direct inversion from image to structure is not at realistic possibility. A reasonable procedure would be to record experimental images of known complex icosahedral alloys, in a crystalline phase, then use the computer-simulations to identify fingerprint imaging conditions whereby certain structural elements could be identified in images of quasi-crystalline or amorphous specimens. 27 refs., 12 figs., 1 tab

  17. Irradiation-induced precipitation in a SUS316 stainless steel using three-dimensional atom probe

    Energy Technology Data Exchange (ETDEWEB)

    Hatakeyama, M., E-mail: hatake@imr.tohoku.ac.jp [International Research Center for Nuclear Materials Science, IMR/Tohoku University, Narita, Oarai, Ibaraki 311-1313 (Japan); Yamagata, I. [Japan Atom Energy Agency, Narita, Oarai, Ibaraki 311-1393 (Japan)

    2013-11-15

    Precipitation and segregation were investigated in a compositionally modified 316 austenitic stainless steel, neutron-irradiated at 862 K using a three-dimensional atom probe. In the solution-annealed specimen, Mo, Ti, Nb, C and P enrichment were observed in a silicide, with nominal composition Fe{sub 3}Cr{sub 2}Ni{sub 2}Mo{sub 2}Si{sub 2}. In a Ti-rich carbide, nominaling Fe{sub 5}Cr{sub 8}Ni{sub 10}Mo{sub 2}Ti{sub 11}Si{sub 2}C{sub 6}, enrichment of Mo, Si, O, and Nb was observed. Radiation-induced segregation (RIS) at the precipitate–matrix interface was also investigated at an atomic scale. RIS of Ni and P atoms, which are undersized in Fe, was also analyzed around the interface of the Ti-rich carbide and matrix. Results suggest that the carbide–matrix interface is a sink with an interstitial bias. In the cold-worked specimen, complex-precipitates consisting of silicide and carbide were formed.

  18. Determining the field emitter temperature during laser irradiation in the pulsed laser atom probe

    International Nuclear Information System (INIS)

    Kellogg, G.L.

    1981-01-01

    Three methods are discussed for determining the field emitter temperature during laser irradiation in the recently developed Pulsed Laser Atom Probe. A procedure based on the reduction of the lattice evaporation field with increasing emitter temperature is found to be the most convenient and reliable method between 60 and 500 K. Calibration curves (plots of the evaporation field versus temperature) are presented for dc and pulsed field evaporation of W, Mo, and Rh. These results show directly the important influence of the evaporation rate on the temperature dependence of the evaporation field. The possibility of a temperature calibration based on the ionic charge state distribution of field evaporated lattice atoms is also discussed. The shift in the charge state distributions which occurs when the emitter temperature is increased and the applied field strength is decreased at a constant rate of evaporation is shown to be due to the changing field and not the changing temperature. Nevertheless, the emitter temperature can be deduced from the charge state distribution for a specified evaporation rate. Charge state distributions as a function of field strength and temperature are presented for the same three materials. Finally, a preliminary experiment is reported which shows that the emitter temperature can be determined from field ion microscope observations of single atom surface diffusion over low index crystal planes. This last calibration procedure is shown to be very useful at higher temperatures (>600 K) where the other two methods become unreliable

  19. Quantitative atom probe analysis of nanostructure containing clusters and precipitates with multiple length scales

    International Nuclear Information System (INIS)

    Marceau, R.K.W.; Stephenson, L.T.; Hutchinson, C.R.; Ringer, S.P.

    2011-01-01

    A model Al-3Cu-(0.05 Sn) (wt%) alloy containing a bimodal distribution of relatively shear-resistant θ' precipitates and shearable GP zones is considered in this study. It has recently been shown that the addition of the GP zones to such microstructures can lead to significant increases in strength without a decrease in the uniform elongation. In this study, atom probe tomography (APT) has been used to quantitatively characterise the evolution of the GP zones and the solute distribution in the bimodal microstructure as a function of applied plastic strain. Recent nuclear magnetic resonance (NMR) analysis has clearly shown strain-induced dissolution of the GP zones, which is supported by the current APT data with additional spatial information. There is significant repartitioning of Cu from the GP zones into the solid solution during deformation. A new approach for cluster finding in APT data has been used to quantitatively characterise the evolution of the sizes and shapes of the Cu containing features in the solid solution solute as a function of applied strain. -- Research highlights: → A new approach for cluster finding in atom probe tomography (APT) data has been used to quantitatively characterise the evolution of the sizes and shapes of the Cu containing features with multiple length scales. → In this study, a model Al-3Cu-(0.05 Sn) (wt%) alloy containing a bimodal distribution of relatively shear-resistant θ' precipitates and shearable GP zones is considered. → APT has been used to quantitatively characterise the evolution of the GP zones and the solute distribution in the bimodal microstructure as a function of applied plastic strain. → It is clearly shown that there is strain-induced dissolution of the GP zones with significant repartitioning of Cu from the GP zones into the solid solution during deformation.

  20. PREFACE: International Conference on Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces (MPS2014)

    Science.gov (United States)

    Ancarani, Lorenzo Ugo

    2015-04-01

    This volume contains a collection of contributions from the invited speakers at the 2014 edition of the International Conference on Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces held in Metz, France, from 15th to 18th July 2014. This biennial conference alternates with the ICPEAC satellite International Symposium on (e,2e), Double Photoionization and Related Topics, and is concerned with experimental and theoretical studies of radiation interactions with matter. These include many-body and electron-electron correlation effects in excitation, and in single and multiple ionization of atoms, molecules, clusters and surfaces with various projectiles: electrons, photons and ions. More than 80 scientists, from 19 different countries around the world, came together to discuss the most recent progress on these topics. The scientific programme included 28 invited talks and a poster session extending over the three days of the meeting. Amongst the 51 posters, 11 have been selected and were advertised through short talks. Besides, Professor Nora Berrah gave a talk in memory of Professor Uwe Becker who sadly passed away shortly after co-chairing the previous edition of this conference. Financial support from the Institut Jean Barriol, Laboratoire SRSMC, Groupement de Recherche THEMS (CNRS), Ville de Metz, Metz Métropole, Conseil Général de la Moselle and Région Lorraine is gratefully acknowledged. Finally, I would like to thank the members of the local committee and the staff of the Université de Lorraine for making the conference run smoothly, the International Advisory Board for building up the scientific programme, the sessions chairpersons, those who gave their valuable time in carefully refereeing the articles of this volume and last, but not least, all participants for contributing to lively and fruitful discussions throughout the meeting.

  1. Monte-Carlo simulation of defect-cluster nucleation in metals during irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Nakasuji, Toshiki, E-mail: t-nakasuji@iae.kyoto-u.ac.jp [Graduate School of Energy Science, Kyoto University, Uji, Kyoto 611-0011 (Japan); Morishita, Kazunori [Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011 (Japan); Ruan, Xiaoyong [Graduate School of Energy Science, Kyoto University, Uji, Kyoto 611-0011 (Japan)

    2017-02-15

    Highlights: • Monte-Carlo simulations were performed to investigate the nucleation process of copper-vacancy clusters in Fe. • Nucleation paths were obtained as a function of temperature and the damage rate. - Abstract: A multiscale modeling approach was applied to investigate the nucleation process of CRPs (copper rich precipitates, i.e., copper-vacancy clusters) in α-Fe containing 1 at.% Cu during irradiation. Monte-Carlo simulations were performed to investigate the nucleation process, with the rate theory equation analysis to evaluate the concentration of displacement defects, along with the molecular dynamics technique to know CRP thermal stabilities in advance. Our MC simulations showed that there is long incubation period at first, followed by a rapid growth of CRPs. The incubation period depends on irradiation conditions such as the damage rate and temperature. CRP’s composition during nucleation varies with time. The copper content of CRPs shows relatively rich at first, and then becomes poorer as the precipitate size increases. A widely-accepted model of CRP nucleation process is finally proposed.

  2. Monte-Carlo simulation of defect-cluster nucleation in metals during irradiation

    International Nuclear Information System (INIS)

    Nakasuji, Toshiki; Morishita, Kazunori; Ruan, Xiaoyong

    2017-01-01

    Highlights: • Monte-Carlo simulations were performed to investigate the nucleation process of copper-vacancy clusters in Fe. • Nucleation paths were obtained as a function of temperature and the damage rate. - Abstract: A multiscale modeling approach was applied to investigate the nucleation process of CRPs (copper rich precipitates, i.e., copper-vacancy clusters) in α-Fe containing 1 at.% Cu during irradiation. Monte-Carlo simulations were performed to investigate the nucleation process, with the rate theory equation analysis to evaluate the concentration of displacement defects, along with the molecular dynamics technique to know CRP thermal stabilities in advance. Our MC simulations showed that there is long incubation period at first, followed by a rapid growth of CRPs. The incubation period depends on irradiation conditions such as the damage rate and temperature. CRP’s composition during nucleation varies with time. The copper content of CRPs shows relatively rich at first, and then becomes poorer as the precipitate size increases. A widely-accepted model of CRP nucleation process is finally proposed.

  3. Relativistic Normal Coupled-Cluster Theory for Accurate Determination of Electric Dipole Moments of Atoms: First Application to the ^{199}Hg Atom.

    Science.gov (United States)

    Sahoo, B K; Das, B P

    2018-05-18

    Recent relativistic coupled-cluster (RCC) calculations of electric dipole moments (EDMs) of diamagnetic atoms due to parity and time-reversal violating (P,T-odd) interactions, which are essential ingredients for probing new physics beyond the standard model of particle interactions, differ substantially from the previous theoretical results. It is therefore necessary to perform an independent test of the validity of these results. In view of this, the normal coupled-cluster method has been extended to the relativistic regime [relativistic normal coupled-cluster (RNCC) method] to calculate the EDMs of atoms by simultaneously incorporating the electrostatic and P,T-odd interactions in order to overcome the shortcomings of the ordinary RCC method. This new relativistic method has been applied to ^{199}Hg, which currently has a lower EDM limit than that of any other system. The results of our RNCC and self-consistent RCC calculations of the EDM of this atom are found to be close. The discrepancies between these two results on the one hand and those of previous calculations on the other are elucidated. Furthermore, the electric dipole polarizability of this atom, which has computational similarities with the EDM, is evaluated and it is in very good agreement with its measured value.

  4. Relativistic Normal Coupled-Cluster Theory for Accurate Determination of Electric Dipole Moments of Atoms: First Application to the 199Hg Atom

    Science.gov (United States)

    Sahoo, B. K.; Das, B. P.

    2018-05-01

    Recent relativistic coupled-cluster (RCC) calculations of electric dipole moments (EDMs) of diamagnetic atoms due to parity and time-reversal violating (P ,T -odd) interactions, which are essential ingredients for probing new physics beyond the standard model of particle interactions, differ substantially from the previous theoretical results. It is therefore necessary to perform an independent test of the validity of these results. In view of this, the normal coupled-cluster method has been extended to the relativistic regime [relativistic normal coupled-cluster (RNCC) method] to calculate the EDMs of atoms by simultaneously incorporating the electrostatic and P ,T -odd interactions in order to overcome the shortcomings of the ordinary RCC method. This new relativistic method has been applied to 199Hg, which currently has a lower EDM limit than that of any other system. The results of our RNCC and self-consistent RCC calculations of the EDM of this atom are found to be close. The discrepancies between these two results on the one hand and those of previous calculations on the other are elucidated. Furthermore, the electric dipole polarizability of this atom, which has computational similarities with the EDM, is evaluated and it is in very good agreement with its measured value.

  5. Cluster protein structures using recurrence quantification analysis on coordinates of alpha-carbon atoms of proteins

    International Nuclear Information System (INIS)

    Zhou Yu; Yu Zuguo; Anh, Vo

    2007-01-01

    The 3-dimensional coordinates of alpha-carbon atoms of proteins are used to distinguish the protein structural classes based on recurrence quantification analysis (RQA). We consider two independent variables from RQA of coordinates of alpha-carbon atoms, %determ1 and %determ2, which were defined by Webber et al. [C.L. Webber Jr., A. Giuliani, J.P. Zbilut, A. Colosimo, Proteins Struct. Funct. Genet. 44 (2001) 292]. The variable %determ2 is used to define two new variables, %determ2 1 and %determ2 2 . Then three variables %determ1, %determ2 1 and %determ2 2 are used to construct a 3-dimensional variable space. Each protein is represented by a point in this variable space. The points corresponding to proteins from the α, β, α+β and α/β structural classes position into different areas in this variable space. In order to give a quantitative assessment of our clustering on the selected proteins, Fisher's discriminant algorithm is used. Numerical results indicate that the discriminant accuracies are very high and satisfactory

  6. Clustered atom-replaced structure in single-crystal-like metal oxide

    Science.gov (United States)

    Araki, Takeshi; Hayashi, Mariko; Ishii, Hirotaka; Yokoe, Daisaku; Yoshida, Ryuji; Kato, Takeharu; Nishijima, Gen; Matsumoto, Akiyoshi

    2018-06-01

    By means of metal organic deposition using trifluoroacetates (TFA-MOD), we replaced and localized two or more atoms in a single-crystalline structure having almost perfect orientation. Thus, we created a new functional structure, namely, clustered atom-replaced structure (CARS), having single-crystal-like metal oxide. We replaced metals in the oxide with Sm and Lu and localized them. Energy dispersive x-ray spectroscopy results, where the Sm signal increases with the Lu signal in the single-crystalline structure, confirm evidence of CARS. We also form other CARS with three additional metals, including Pr. The valence number of Pr might change from 3+ to approximately 4+, thereby reducing the Pr–Ba distance. We directly observed the structure by a high-angle annular dark-field image, which provided further evidence of CARS. The key to establishing CARS is an equilibrium chemical reaction and a combination of additional larger and smaller unit cells to matrix cells. We made a new functional metal oxide with CARS and expect to realize CARS in other metal oxide structures in the future by using the above-mentioned process.

  7. Polarizabilities and hyperpolarizabilities for the atoms Al, Si, P, S, Cl, and Ar: Coupled cluster calculations.

    Science.gov (United States)

    Lupinetti, Concetta; Thakkar, Ajit J

    2005-01-22

    Accurate static dipole polarizabilities and hyperpolarizabilities are calculated for the ground states of the Al, Si, P, S, Cl, and Ar atoms. The finite-field computations use energies obtained with various ab initio methods including Moller-Plesset perturbation theory and the coupled cluster approach. Excellent agreement with experiment is found for argon. The experimental alpha for Al is likely to be in error. Only limited comparisons are possible for the other atoms because hyperpolarizabilities have not been reported previously for most of these atoms. Our recommended values of the mean dipole polarizability (in the order Al-Ar) are alpha/e(2)a(0) (2)E(h) (-1)=57.74, 37.17, 24.93, 19.37, 14.57, and 11.085 with an error estimate of +/-0.5%. The recommended values of the mean second dipole hyperpolarizability (in the order Al-Ar) are gamma/e(4)a(0) (4)E(h) (-3)=2.02 x 10(5), 4.31 x 10(4), 1.14 x 10(4), 6.51 x 10(3), 2.73 x 10(3), and 1.18 x 10(3) with an error estimate of +/-2%. Our recommended polarizability anisotropy values are Deltaalpha/e(2)a(0) (2)E(h) (-1)=-25.60, 8.41, -3.63, and 1.71 for Al, Si, S, and Cl respectively, with an error estimate of +/-1%. The recommended hyperpolarizability anisotropies are Deltagamma/e(4)a(0) (4)E(h) (-3)=-3.88 x 10(5), 4.16 x 10(4), -7.00 x 10(3), and 1.65 x 10(3) for Al, Si, S, and Cl, respectively, with an error estimate of +/-4%. (c) 2005 American Institute of Physics.

  8. Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO2.

    Science.gov (United States)

    DeRita, Leo; Dai, Sheng; Lopez-Zepeda, Kimberly; Pham, Nicholas; Graham, George W; Pan, Xiaoqing; Christopher, Phillip

    2017-10-11

    Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO 2 . In these structures, isolated Pt atoms, Pt iso , remain stable through various conditions, and spectroscopic evidence suggests Pt iso species exist in homogeneous local environments. Comparing Pt iso to ∼1 nm preoxidized (Pt ox ) and prereduced (Pt metal ) Pt clusters on TiO 2 , we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Pt iso ≪ Pt metal atoms bonded to TiO 2 and that Pt iso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO 2 . This approach should be generally useful for studying the behavior of supported precious metal atoms.

  9. Microarray Cluster Analysis of Irradiated Growth Plate Zones Following Laser Microdissection

    International Nuclear Information System (INIS)

    Damron, Timothy A.; Zhang Mingliang; Pritchard, Meredith R.; Middleton, Frank A.; Horton, Jason A.; Margulies, Bryan M.; Strauss, Judith A.; Farnum, Cornelia E.; Spadaro, Joseph A.

    2009-01-01

    Purpose: Genes and pathways involved in early growth plate chondrocyte recovery after fractionated irradiation were sought as potential targets for selective radiorecovery modulation. Materials and Methods: Three groups of six 5-week male Sprague-Dawley rats underwent fractionated irradiation to the right tibiae over 5 days, totaling 17.5 Gy, and then were killed at 7, 11, and 16 days after the first radiotherapy fraction. The growth plates were collected from the proximal tibiae bilaterally and subsequently underwent laser microdissection to separate reserve, perichondral, proliferative, and hypertrophic zones. Differential gene expression was analyzed between irradiated right and nonirradiated left tibia using RAE230 2.0 GeneChip microarray, compared between zones and time points and subjected to functional pathway cluster analysis with real-time polymerase chain reaction to confirm selected results. Results: Each zone had a number of pathways showing enrichment after the pattern of hypothesized importance to growth plate recovery, yet few met the strictest criteria. The proliferative and hypertrophic zones showed both the greatest number of genes with a 10-fold right/left change at 7 days after initiation of irradiation and enrichment of the most functional pathways involved in bone, cartilage, matrix, or skeletal development. Six genes confirmed by real-time polymerase chain reaction to have early upregulation included insulin-like growth factor 2, procollagen type I alpha 2, matrix metallopeptidase 9, parathyroid hormone receptor 1, fibromodulin, and aggrecan 1. Conclusions: Nine overlapping pathways in the proliferative and hypertrophic zones (skeletal development, ossification, bone remodeling, cartilage development, extracellular matrix structural constituent, proteinaceous extracellular matrix, collagen, extracellular matrix, and extracellular matrix part) may play key roles in early growth plate radiorecovery.

  10. Atom Probe Tomography Characterization of the Solute Distributions in a Neutron-Irradiated and Annealed Pressure Vessel Steel Weld

    Energy Technology Data Exchange (ETDEWEB)

    Miller, M.K.

    2001-01-30

    A combined atom probe tomography and atom probe field ion microscopy study has been performed on a submerged arc weld irradiated to high fluence in the Heavy-Section Steel irradiation (HSSI) fifth irradiation series (Weld 73W). The composition of this weld is Fe - 0.27 at. % Cu, 1.58% Mn, 0.57% Ni, 0.34% MO, 0.27% Cr, 0.58% Si, 0.003% V, 0.45% C, 0.009% P, and 0.009% S. The material was examined after five conditions: after a typical stress relief treatment of 40 h at 607 C, after neutron irradiation to a fluence of 2 x 10{sup 23} n m{sup {minus}2} (E > 1 MeV), and after irradiation and isothermal anneals of 0.5, 1, and 168 h at 454 C. This report describes the matrix composition and the size, composition, and number density of the ultrafine copper-enriched precipitates that formed under neutron irradiation and the change in these parameters with post-irradiation annealing treatments.

  11. Dose control in semi industrial irradiation plant at the Ezeiza Atomic Center

    International Nuclear Information System (INIS)

    Dorda, E.M.

    1987-01-01

    In 1975 a study was initiated at the Division of Dosimetry to develop a technique and a system of dosimetry to be applied to the radiosterilization processes in the semi industrial irradiation plant of Ezeiza Atomic Center. The result of this study was the potassium nitrate/nitrite dosimeter used as routine dosimeter for control processes in food conservation, with a dose range of 0.2 kGy-1 kGy and in radiosterilization processes of disposable medical products of 1 kGy-150kGy. The potassium nitrate crystals undergo a radiolytic reduction. A linear correlation between the dose applied to the solid and the production of potassium nitrite was observed. After the irradiation of solid, the produced nitrite solution is colorimetrically titrated by measuring the absorbency in a spectrophotometer at 504 nm. The color is due to the formation of a diazonium salt and its later copulation with N-1 naphtylethylendiamine hydrochloride in acid medium. In 1980 a postal survey was organized presenting this dosimeter to standardize the irradiation dose in industrial process for Latin America. This dosimeter was presented in 1984 at the International Symposium on High Doses of the IAEA that took place in Vienna. Since them, comparative studies were performed between this dosimeter and those internationally considered and accepted: cerium(IV)/cerium(III) sulphate, ionization chamber of parallel plates, alanine. The results of comparison with the alanine dosimeter, which was used by Dr. Regula of the GSF of Munich, were the following: February 1985: 0% deviation; February 1986: 0.43% deviation. (Author)

  12. Coordination-resolved local bond contraction and electron binding-energy entrapment of Si atomic clusters and solid skins

    Energy Technology Data Exchange (ETDEWEB)

    Bo, Maolin; Huang, Yongli; Zhang, Ting [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); Wang, Yan, E-mail: ywang8@hnust.edu.cn, E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Zhang, Xi [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Li, Can [Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University, Hangzhou 330018 (China); Sun, Chang Q., E-mail: ywang8@hnust.edu.cn, E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University, Hangzhou 330018 (China)

    2014-04-14

    Consistency between x-ray photoelectron spectroscopy measurements and density-function theory calculations confirms our bond order-length-strength notation-incorporated tight-binding theory predictions on the quantum entrapment of Si solid skin and atomic clusters. It has been revealed that bond-order deficiency shortens and strengthens the Si-Si bond, which results in the local densification and quantum entrapment of the core and valence electrons. Unifying Si clusters and Si(001) and (111) skins, this mechanism has led to quantification of the 2p binding energy of 96.089 eV for an isolated Si atom, and their bulk shifts of 2.461 eV. Findings evidence the significance of atomic undercoordination that is of great importance to device performance.

  13. Electron correlation in the interacting quantum atoms partition via coupled-cluster lagrangian densities.

    Science.gov (United States)

    Holguín-Gallego, Fernando José; Chávez-Calvillo, Rodrigo; García-Revilla, Marco; Francisco, Evelio; Pendás, Ángel Martín; Rocha-Rinza, Tomás

    2016-07-15

    The electronic energy partition established by the Interacting Quantum Atoms (IQA) approach is an important method of wavefunction analyses which has yielded valuable insights about different phenomena in physical chemistry. Most of the IQA applications have relied upon approximations, which do not include either dynamical correlation (DC) such as Hartree-Fock (HF) or external DC like CASSCF theory. Recently, DC was included in the IQA method by means of HF/Coupled-Cluster (CC) transition densities (Chávez-Calvillo et al., Comput. Theory Chem. 2015, 1053, 90). Despite the potential utility of this approach, it has a few drawbacks, for example, it is not consistent with the calculation of CC properties different from the total electronic energy. To improve this situation, we have implemented the IQA energy partition based on CC Lagrangian one- and two-electron orbital density matrices. The development presented in this article is tested and illustrated with the H2 , LiH, H2 O, H2 S, N2 , and CO molecules for which the IQA results obtained under the consideration of (i) the CC Lagrangian, (ii) HF/CC transition densities, and (iii) HF are critically analyzed and compared. Additionally, the effect of the DC in the different components of the electronic energy in the formation of the T-shaped (H2 )2 van der Waals cluster and the bimolecular nucleophilic substitution between F(-) and CH3 F is examined. We anticipate that the approach put forward in this article will provide new understandings on subjects in physical chemistry wherein DC plays a crucial role like molecular interactions along with chemical bonding and reactivity. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  14. In-reactor behaviour of centrifugally atomized U3Si dispersion fuel irradiated at high temperature in HANARO

    International Nuclear Information System (INIS)

    Kim, Ki Hwan; Park, Jong Man; Yoo, Byeong Ok; Park, Dae Kyu; Lee, Choong Sung; Kim, Chang Kyu

    2002-01-01

    The irradiation test on full-size U 3 Si dispersion fuel elements, prepared by centrifugal atomization and conventional comminution method, has been performed up to about 77 at.% U-235 in maximum burn-up at CT hole position having the highest power condition in the HANARO reactor, in order to examine the irradiation performance of the atomized U 3 Si for the driver fuels of HANARO. The in-reactor interaction of the atomized U 3 Si dispersion fuel meats is generally assumed to be acceptable with the range of 5-15 μm in average thickness. The atomized spherical particles have more uniform and thinner reaction layer than the comminuted irregular particles. The U 3 Si particles have relatively fine and uniform size distribution of fission gas bubbles, irrespective of the powdering method. The bubble population in the atomized particles appears to be finer and more homogeneous with the characteristics of narrower bubble size distribution than that of the comminuted fuel. The atomized U 3 Si dispersion fuel elements exhibit sound swelling behaviours of 5 % in ΔV/V m even at ∼77 at.% U-235 burn-up, which meets with the safety criterion of the fuel rod, 20vol.% for HANARO. The atomized U3Si dispersion fuel elements show smaller swelling than the comminuted fuel elements

  15. Stable structures of Al510–800 clusters and lowest energy sequence of truncated octahedral Al clusters up to 10,000 atoms

    International Nuclear Information System (INIS)

    Wu, Xia; He, Chengdong

    2012-01-01

    Highlights: ► The stable structures of Al 510–800 clusters are obtained with the NP-B potential. ► Al 510–800 clusters adopt truncated octahedral (TO) growth pattern based on complete TOs at Al 405 , Al 586 , and Al 711 . ► The lowest energy sequence of complete TOs up to the size 10,000 is proposed. -- Abstract: The stable structures of Al 510–800 clusters are obtained using dynamic lattice searching with constructed cores (DLSc) method by the NP-B potential. According to the structural growth rule, octahedra and truncated octahedra (TO) configurations are adopted as the inner cores in DLSc method. The results show that in the optimized structures two complete TO structures are found at Al 586 and Al 711 . Furthermore, Al 510–800 clusters adopt TO growth pattern on complete TOs at Al 405 , Al 586 , and Al 711 , and the configurations of the surface atoms are investigated. On the other hand, Al clusters with complete TO motifs are studied up to the size 10,000 by the geometrical construction method. The structural characteristics of complete TOs are denoted by the term “family”, and the growth sequence of Al clusters is investigated. The lowest energy sequence of complete TOs is proposed.

  16. Application of pulsed multi-ion irradiations in radiation damage research: A stochastic cluster dynamics simulation study

    Science.gov (United States)

    Hoang, Tuan L.; Nazarov, Roman; Kang, Changwoo; Fan, Jiangyuan

    2018-07-01

    Under the multi-ion irradiation conditions present in accelerated material-testing facilities or fission/fusion nuclear reactors, the combined effects of atomic displacements with radiation products may induce complex synergies in the structural materials. However, limited access to multi-ion irradiation facilities and the lack of computational models capable of simulating the evolution of complex defects and their synergies make it difficult to understand the actual physical processes taking place in the materials under these extreme conditions. In this paper, we propose the application of pulsed single/dual-beam irradiation as replacements for the expensive steady triple-beam irradiation to study radiation damages in materials under multi-ion irradiation.

  17. Current mapping of low-energy (120 eV) helium and hydrogen irradiated tungsten by conductive atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Hongyu [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian (China); Endo, Takashi [Nano-micro Materials Analysis Laboratory, Hokkaido University, Sapporo (Japan); Bi, Zhenghua; Yan, Weibin [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian (China); Ohnuki, Somei [Nano-micro Materials Analysis Laboratory, Hokkaido University, Sapporo (Japan); Yang, Qi; Ni, Weiyuan [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian (China); Liu, Dongping, E-mail: dongping.liu@dlnu.edu.cn [School of Physics and Materials Engineering, Dalian Nationalities University, Dalian (China)

    2017-04-01

    Both conductive atomic force microscopy (CAFM) and transmission electron microscopy have been used to characterize the defects or He bubbles in low-energy (120 eV) H and He irradiated tungsten (W). By a comparative study, we find that the current mapping from CAFM is very sensitive in the detection of nanometer-sized defects in low-energy H and He irradiated W. Our calculation confirms that the resistance change in H and He irradiated W is strongly affected by the distance between atomic force microscopy tip and defects/He bubbles. CAFM can accurately detect defects/He bubbles in the W surface layer, however, it is infeasible to measure them in the deep layer (>20 nm), especially due to the existence of defects in the surface layer.

  18. Ab initio study of the structural, magnetic, and electronic properties of copper and silver clusters and their alloys with one palladium atom

    Directory of Open Access Journals (Sweden)

    S. J Hashemifar

    2015-01-01

    Full Text Available In this paper, the structural, magnetic, and electronic properties of two- to nine-atom copper and silver clusters and their alloys with one palladium atom are investigated by using full-potential all-electron density functional computations. After calculating minimized energy of several structural isomers of every nanocluster, it is argued that the small size nanoclusters (up to size of 6, ‎ prefer planar structures, while by increasing size a 2D-3D structural transformation is observed. The structural transformation of pure and copper-palladium clusters occurs in the size of seven and that of silver-palladium cluster in happens at the size of six. The calculated second difference and dissociation energies confirm that the two- and eight- atom pure clusters and three- and seven- atom alloyed clusters are magic clusters. The electronic and magnetic properties of stable isomers are calculated and considered after applying many body based GW correction.

  19. Atoms

    International Nuclear Information System (INIS)

    Fuchs, Alain; Villani, Cedric; Guthleben, Denis; Leduc, Michele; Brenner, Anastasios; Pouthas, Joel; Perrin, Jean

    2014-01-01

    Completed by recent contributions on various topics (atoms and the Brownian motion, the career of Jean Perrin, the evolution of atomic physics since Jean Perrin, relationship between scientific atomism and philosophical atomism), this book is a reprint of a book published at the beginning of the twentieth century in which the author addressed the relationship between atomic theory and chemistry (molecules, atoms, the Avogadro hypothesis, molecule structures, solutes, upper limits of molecular quantities), molecular agitation (molecule velocity, molecule rotation or vibration, molecular free range), the Brownian motion and emulsions (history and general features, statistical equilibrium of emulsions), the laws of the Brownian motion (Einstein's theory, experimental control), fluctuations (the theory of Smoluchowski), light and quanta (black body, extension of quantum theory), the electricity atom, the atom genesis and destruction (transmutations, atom counting)

  20. Atom-atom collision cascades localization

    International Nuclear Information System (INIS)

    Kirsanov, V.V.

    1980-01-01

    The presence of an impurity and thermal vibration influence on the atom-atom collision cascade development is analysed by the computer simulation method (the modificated dynamic model). It is discovered that the relatively low energetic cascades are localized with the temperature increase of an irradiated crystal. On the basis of the given effect the mechanism of splitting of the high energetic cascades into subcascades is proposed. It accounts for two factors: the primary knocked atom energy and the irradiated crystal temperature. Introduction of an impurity also localizes the cascades independently from the impurity atom mass. The cascades localization leads to intensification of the process of annealing in the cascades and reduction of the post-cascade vacancy cluster sizes. (author)

  1. The role of electron localization in the atomic structure of transition-metal 13-atom clusters: the example of Co13, Rh13, and Hf13.

    Science.gov (United States)

    Piotrowski, Maurício J; Piquini, Paulo; Cândido, Ladir; Da Silva, Juarez L F

    2011-10-14

    The crystalline structure of transition-metals (TM) has been widely known for several decades, however, our knowledge on the atomic structure of TM clusters is still far from satisfactory, which compromises an atomistic understanding of the reactivity of TM clusters. For example, almost all density functional theory (DFT) calculations for TM clusters have been based on local (local density approximation--LDA) and semilocal (generalized gradient approximation--GGA) exchange-correlation functionals, however, it is well known that plain DFT fails to correct the self-interaction error, which affects the properties of several systems. To improve our basic understanding of the atomic and electronic properties of TM clusters, we report a DFT study within two nonlocal functionals, namely, the hybrid HSE (Heyd, Scuseria, and Ernzerhof) and GGA+U functionals, of the structural and electronic properties of the Co(13), Rh(13), and Hf(13) clusters. For Co(13) and Rh(13), we found that improved exchange-correlation functionals decrease the stability of open structures such as the hexagonal bilayer (HBL) and double simple-cubic (DSC) compared with the compact icosahedron (ICO) structure, however, DFT-GGA, DFT-GGA+U, and DFT-HSE yield very similar results for Hf(13). Thus, our results suggest that the DSC structure obtained by several plain DFT calculations for Rh(13) can be improved by the use of improved functionals. Using the sd hybridization analysis, we found that a strong hybridization favors compact structures, and hence, a correct description of the sd hybridization is crucial for the relative energy stability. For example, the sd hybridization decreases for HBL and DSC and increases for ICO in the case of Co(13) and Rh(13), while for Hf(13), the sd hybridization decreases for all configurations, and hence, it does not affect the relative stability among open and compact configurations.

  2. Hall effect measurements of Frenkel defect clustering in aluminium during high-dose reactor irradiation at 4.6 K

    International Nuclear Information System (INIS)

    Boening, K.; Mauer, W.; Pfaendner, K.; Rosner, P.

    1976-01-01

    The low-field Hall coefficient R 0 of irradiated aluminium at 4.6 K is independent of the Frenkel defect (FD) concentration, however sensitively dependent of their configuration. Since measurement of R 0 is not too difficult, rather extensive investigations of FD clustering during irradiation can be performed, but only qualitative interpretations are possible. Several pure Al samples have been irradiated with reactor neutrons at 4.6 K up to very high doses phit resp. resistivity increments Δrho 0 (maximum 91% of extrapolated saturation value Δrho 0 sup(sat) approximately 980 nΩcm). The main results are 1.FD clustering within a single displacement cascade is not a very strong effect in Al, since the R 0 values are essentially the same after reactor and after electron irradiation. Rough cascade averages are: volume Vsub(c) approximately 2.1 x 10 5 at.vol. and FD concentration csub(c) approximately 1100 ppm. 2. There is practically no dose-dependent FD clustering up to Δrho 0 approximately 350 nΩcm, since R 0 remains essentially constant there. It follows that dose-dependent FD clustering can only occur for high-order overlap of cascade volumes. The differential dose curve dΔrho 0 /dphit is perfectly linear in Δrho 0 as long as R 0 = const. 3. For Δrho 0 > 350 nΩcm FD clustering becomes increasingly important and R 0 changes strongly. Surprisingly dR 0 /dphit approximately const whence there is a constant rate of cluster size increase in spite of the vanishing rate of FD production, evidence of the continuous regrouping of the lattice and its defects. (author)

  3. Interaction between solute atoms and radiation defects in Fe-Ni-Si and Fe-Mn-Si alloys under irradiation with proton ions at low-temperature

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, Kenta, E-mail: murakami@tokai.t.u-tokyo.ac.jp [Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakata-Shirane, Tokai-mura, Ibaraki, 319-1188 (Japan); Iwai, Takeo, E-mail: iwai@med.id.yamagata-u.ac.jp [Faculty of Medicine, Yamagata University, 2-2-2 Iida-Nishi, Yamagata, Yamagata-shi, 990-9585 (Japan); Abe, Hiroaki [Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakata-Shirane, Tokai-mura, Ibaraki, 319-1188 (Japan); Sekimura, Naoto, E-mail: sekimura@n.t.u-tokyo.ac.jp [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1, Tokyo, Hongo, Bunkyo, 113-8656 (Japan)

    2016-12-15

    Isochronal annealing followed by residual resistivity measurements at 12 K was performed in Fe-0.6Ni-0.6Si and Fe-1.5Mn-0.6Si alloys irradiated with 1 MeV proton ions below 70 K, and recovery stages were compared with those of Fe–0.6Ni and Fe–1.5Mn. The effects of silicon addition in the Fe-Ni alloy was observed as the appearance of a new recovery stage at 282–372 K, presumably corresponding to clustering of solute atoms in matrix, and as a change in mixed dumbbell migration at 122–142 K. Silicon addition mitigated the manganese effect in Fe–Mn alloy that is obstructing the recovery of radiation defects. Reduction of resistivity in Fe-Mn-Si alloy also suggested formation of small solute atom clusters.

  4. Differential effects of atomic bomb irradiation in inducing major leukemia types

    International Nuclear Information System (INIS)

    Tomonaga, Masao; Matsuo, Tatsuki; Carter, R.L.

    1993-05-01

    In this report we utilize data from the additional 517 cases from the leukemia registry together with the Life Span Study (LSS) cohort data to study the effects of atomic bomb irradiation on major leukemia types. The French-American-British classification and other improved diagnostic methods were used to reclassify cases into 21 categories, including new disease entities such as adult T-cell leukemia (ATL). These categories were then grouped into four major types for analysis: (1) acute lymphocytic leukemia (ALL), (2) acute myeloid leukemia (AML) including myelodysplastic syndromes (MDS), (3) chronic myeloid leukemia (CML), and (4) OTHER types including ATL. Analyses of radiation effects were based on the updated Dosimetry System 1986(DS86). Incidence rates of all four leukemia types increased with increasing exposure level. The effects of radiation were significantly greater on the incidence of ALL and CML than on that of AML and OTHER. In the two lowest dose categories (1-49 and 50-499 mGy), estimated incidence either remained constant or increased slightly as the population of survivors aged. In the two highest dose categories (500-1,499 and ≥ 1,500 mGy). Among unexposed persons, the estimated risk of CML in Nagasaki relative to Hiroshima was significantly less than that of AML, whereas that of OTHER types was significantly greater. The time to onset of ALL, AML, and CML declined with increasing dose. The rate of decline, however, was greater for ALL and CML than for AML. The resulting differences at high doses reflect shorter incubation times for atomic-bomb-induced ALL and CML than for AML. (J.P.N.)

  5. Topological and morphological analysis of gamma rays irradiated chitosan-poly (vinyl alcohol) blends using atomic force microscopy

    International Nuclear Information System (INIS)

    Bhatt, Rinkesh; Bisen, D.S.; Bajpai, R.; Bajpai, A.K.

    2017-01-01

    In the present communication, binary blends of poly (vinyl alcohol) (PVA) and chitosan (CS) were prepared by solution cast method and the roughness parameters of PVA, native CS and CS-PVA blend films were determined using atomic force microscopy (AFM). Moreover, the changes in the morphology of the samples were also investigated after irradiation of gamma rays at absorbed dose of 1 Mrad and 10 Mrad for the scanning areas of 5×5 µm 2 , 10×10 µm 2 and 20×20 µm 2 . Amplitude, statistical and spatial parameters, including line, 3D and 2D image profiles of the experimental surfaces were examined and compared to un-irradiated samples. For gamma irradiated CS-PVA blends the larger waviness over the surface was found as compared to un-irradiated CS-PVA blends but the values of average roughness for both the films were found almost same. The coefficient of skewness was positive for gamma irradiated CS-PVA blends which revealed the presence of more peaks than valleys on the blend surfaces. - Highlights: • Binary polymer blends of chitosan and PVA were prepared. • Irradiation by gamma rays exhibited a significant change in surface morphology. • Various topographical and morphological parameters were investigated. • The prepared irradiated blends may find biomedical applications.

  6. The fifth international symposium ''atomic cluster collisions''. ISACC 2011. Book of Abstracts

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2011-07-01

    The Fifth International Symposium ''Atomic Cluster Collisions'' (ISACC 2011) will take place in July 21-25, 2011 in Berlin, Germany. The venue of the meeting will be the St.-Michaels-Heim a lovely place located within a garden area of Berlin-Grunewald. The ISACC 2011 is organized by the Fritz-Haber-Institute of the Max- Planck Society along with the King Saud University, Rhiyadh and by the Frankfurt Institute for Advanced Studies (FIAS), Frankfurt am Main, Germany. ISACC started as the international symposium on atomic cluster collisions in St. Petersburg, Russia in 2003. The second ISACC was held at the GSI, Darmstadt, Germany in 2007. Both first and second symposia were satellites of the International Conferences on Photonic Electronic and Atomic Collisions (ICPEAC). The third ISACC has returned to St. Petersburg, Russia in 2008. The last ISACC took place in Ann Arbor, again as a satellite meeting of the ICPEAC. Initially the symposium was mainly focused on dynamics of atomic clusters, especially in atomic cluster collisions, but since then its scope has been widened significantly to include dynamics of nanosystems, biomolecules, and macromolecules with the emphasis on the similarity of numerous essential clustering phenomena arising in different branches of physics, chemistry, and biology. After the four ISACC meetings it has become clear that there is a need for an interdisciplinary conference covering a broad range of topics related to the Dynamics of Systems on a Nanoscale. Therefore in 2010 it was decided to expand upon this series of meetings with a new conference organized under the new title ''Dynamics of Systems on the Nanoscale'', the DySoN Conference, since this title better reflects the interdisciplinary character of the earlier ISACC meetings embracing all the topics of interest under a common theme. The first DySoN Conference took place in Rome, Italy in 2010. The fifth ISACC symposium will be again a

  7. Light emission from sputtered or backscattered atoms on tungsten surfaces under ion irradiation

    International Nuclear Information System (INIS)

    Sakai, Yasuhiro; Nogami, Keisuke; Kato, Daiji; Sakaue, Hiroyuki A.; Kenmotsu, Takahiko; Furuya, Kenji; Motohashi, Kenji

    2013-01-01

    We measured the intensity of light emission from sputtered atoms on tungsten surfaces under the irradiations of Kr"+ ion and Ar"+ ion, as a function of the perpendicular distance from the surface. Using the analysis of decay curve, we estimated the mean vertical velocity component in direction normal to the surface. We found that the estimated mean velocity had much differences according to the excited state. For example, although the estimated mean vertical velocity component normal to the surface from the 400.9 nm line((5d"5(6S)6p "7p_4→(5d"5(6S)6s "7S_3 transition) was 5.6±1.7 km/sec, that from the 386.8 nm line((5d"4(6S)6p "7D_4→(5d"5(6S)6s "7S_4 transition) was 2.8±1.0 km/sec. However, for different projectiles and energies, we found no remarkable changes in the velocity. (author)

  8. The features of the atomic structure of the impurities complexes in the irradiated materials doped by the elements with a large atomic radii

    International Nuclear Information System (INIS)

    Neklyudov, I.M.; Sleptsov, A.N.; Marchenko, I.G.; Sleptsov, S.N.

    1995-01-01

    The interaction between impurity atoms and radiation-induced defects in Ni(Sc), Ni(Ti), Ni(Pr) and Ni(Y) alloys irradiated with 5 and 30 MeV electrons were studied by the residual resistivity measurements, and the methods of reciprocal damage rate and positron annihilation. The activation energies of the main recovery stages in pure nickel (I D+E - 54 K, II 4 -250 K, III 2 - 390 K) and dilute alloys (up to 700 K) were determined. The radii trapping, r t , of self-interstitial atoms (SIA) by the Sc and Ti atoms were calculated in the temperature range 45-300 K.It is found that the scandium atoms (among all large atomic size elements) are effective traps for SIA and vacancies and form compound complexes. The binding energy of vacancy-impurity complexes are about 0.25, 0.30 and 0.6 - 0.8 eV in Ni(Ti), Ni(Y) and Ni(Sc) alloys, respectively. The solubilities of Sc, Ti, Y and Pr in nickel were deduced from the analysis of dependence of the specific residual resistivity (ρ t ) and the lattice parameter (Δa/a) on concentration. 38 refs., 3 tab., 10 figs

  9. Kinetics of cluster-related defects in silicon sensors irradiated with monoenergetic electrons

    Science.gov (United States)

    Radu, R.; Pintilie, I.; Makarenko, L. F.; Fretwurst, E.; Lindstroem, G.

    2018-04-01

    This work focuses on the kinetic mechanisms responsible for the annealing behavior of radiation cluster-related defects with impact on the electrical performance of silicon sensors. Such sensors were manufactured on high resistivity n-type standard float-zone (STFZ) and oxygen enriched float-zone (DOFZ) material and had been irradiated with mono-energetic electrons of 3.5 MeV energy and fluences of 3 × 1014 cm-2 and 6 × 1014 cm-2. After irradiation, the samples were subjected either to isochronal or isothermal heat treatments in the temperature range from 80 °C to 300 °C. The specific investigated defects are a group of three deep acceptors [H(116 K), H(140 K), and H(152 K)] with energy levels in the lower half of the band gap and a shallow donor E(30 K) with a level at 0.1 eV below the conduction band. The stability and kinetics of these defects at high temperatures are discussed on the basis of the extracted activation energies and frequency factors. The annealing of the H defects takes place similarly in both types of materials, suggesting a migration rather than a dissociation mechanism. On the contrary, the E(30 K) defect shows a very different annealing behavior, being stable in STFZ even at 300 °C, but annealing-out quickly in DOFZ material at temperatures higher than 200 °C , with a high frequency factor of the order of 1013 s-1. Such a behavior rules out a dissociation process, and the different annealing behavior is suggested to be related to a bistable behavior of the defect.

  10. Antimicrobial photodynamic activity and cytocompatibility of Au25(Capt18 clusters photoexcited by blue LED light irradiation

    Directory of Open Access Journals (Sweden)

    Miyata S

    2017-04-01

    Full Text Available Saori Miyata,1 Hirofumi Miyaji,1 Hideya Kawasaki,2 Masaki Yamamoto,2 Erika Nishida,1 Hiroko Takita,3 Tsukasa Akasaka,4 Natsumi Ushijima,3 Toshihiko Iwanaga,5 Tsutomu Sugaya1 1Department of Periodontology and Endodontology, Hokkaido University Graduate School of Dental Medicine, Kita-ku, Sapporo, 2Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita-shi, Osaka, 3Support Section for Education and Research, Hokkaido University Graduate School of Dental Medicine, 4Department of Biomedical, Dental Materials and Engineering, Graduate School of Dental Medicine, Hokkaido University, 5Department of Anatomy, Laboratory of Histology and Cytology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo, Japan Abstract: Antimicrobial photodynamic therapy (aPDT has beneficial effects in dental treatment. We applied captopril-protected gold (Au25(Capt18 clusters as a novel photosensitizer for aPDT. Photoexcited Au clusters under light irradiation generated singlet oxygen (1O2. Accordingly, the antimicrobial and cytotoxic effects of Au25(Capt18 clusters under dental blue light-emitting diode (LED irradiation were evaluated. 1O2 generation of Au25(Capt18 clusters under blue LED irradiation (420–460 nm was detected by a methotrexate (MTX probe. The antimicrobial effects of photoexcited Au clusters (0, 5, 50, and 500 µg/mL on oral bacterial cells, such as Streptococcus mutans, Aggregatibacter actinomycetemcomitans, and Porphyromonas gingivalis, were assessed by morphological observations and bacterial growth experiments. Cytotoxicity testing of Au clusters and blue LED irradiation was then performed against NIH3T3 and MC3T3-E1 cells. In addition, the biological performance of Au clusters (500 µg/mL was compared to an organic dye photosensitizer, methylene blue (MB; 10 and 100 µg/mL. We confirmed the 1O2 generation ability of Au25(Capt18 clusters through the fluorescence

  11. Combining in situ transmission electron microscopy irradiation experiments with cluster dynamics modeling to study nanoscale defect agglomeration in structural metals

    International Nuclear Information System (INIS)

    Xu Donghua; Wirth, Brian D.; Li Meimei; Kirk, Marquis A.

    2012-01-01

    We present a combinatorial approach that integrates state-of-the-art transmission electron microscopy (TEM) in situ irradiation experiments and high-performance computing techniques to study irradiation defect dynamics in metals. Here, we have studied the evolution of visible defect clusters in nanometer-thick molybdenum foils under 1 MeV krypton ion irradiation at 80 °C through both cluster dynamics modeling and in situ TEM experiments. The experimental details are reported elsewhere; we focus here on the details of model construction and comparing the model with the experiments. The model incorporates continuous production of point defects and/or small clusters, and the accompanying interactions, which include clustering, recombination and loss to the surfaces that result from the diffusion of the mobile defects. To account for the strong surface effect in thin TEM foils, the model includes one-dimensional spatial dependence along the foil depth, and explicitly treats the surfaces as black sinks. The rich amount of data (cluster number density and size distribution at a variety of foil thickness, irradiation dose and dose rate) offered by the advanced in situ experiments has allowed close comparisons with computer modeling and permitted significant validation and optimization of the model in terms of both physical model construct (damage production mode, identities of mobile defects) and parameterization (diffusivities of mobile defects). The optimized model exhibits good qualitative and quantitative agreement with the in situ TEM experiments. The combinatorial approach is expected to bring a unique opportunity for the study of radiation damage in structural materials.

  12. Generalized vibrating potential model for collective excitations in spherical, deformed and superdeformed systems: (1) atomic nuclei, (2) metal clusters

    International Nuclear Information System (INIS)

    Nesterenko, V.O.; Kleinig, W.

    1995-01-01

    The self-consistent vibrating potential model (VPM) is extended for description of Eλ collective excitations in atomic nuclei and metal clusters with practically any kind of static deformation. The model is convenient for a qualitative analysis and provides the RPA accuracy of numerical calculations. The VPM is applied to study Eλ giant resonances in spherical metal clusters and deformed and superdeformed nuclei. It is shown that the deformation splitting of superdeformed nuclei results in a very complicated (''jungle-like'') structure of the resonances, which makes the experimental observation of E2 and E3 giant resonances in superdeformed nuclei quite problematic. Calculations of E1 giant resonance in spherical sodium clusters Na 8 , Na 20 and Na 40 are presented, as a test of the VPM in this field. The results are in qualitative agreement with the experimental data. (orig.)

  13. Discrete Visible Luminescence of Helium Atoms and Molecules Desorbing from Helium Clusters: The Role of Electronic, Vibrational, and Rotational Energy Transfer

    International Nuclear Information System (INIS)

    von Haeften, K.; von Pietrowski, R.; Moeller, T.; Joppien, M.; Moussavizadeh, L.; de Castro, A.R.

    1997-01-01

    Discrete visible and near-infrared luminescence of a beam of photoexcited helium clusters is reported. The emission lines are attributed to free helium atoms and molecules desorbing from clusters in electronically excited states. Depending on the excitation energy, various atomic and molecular singlet and triplet states are involved in the relaxation process. With increasing cluster size the intensity of molecular transitions becomes dominant. The temperature of ejected molecules could be estimated to T vib ∼2500 K and T rot ∼450 K and is much higher than that of the cluster itself. copyright 1997 The American Physical Society

  14. Atom

    International Nuclear Information System (INIS)

    Auffray, J.P.

    1997-01-01

    The atom through centuries, has been imagined, described, explored, then accelerated, combined...But what happens truly inside the atom? And what are mechanisms who allow its stability? Physicist and historian of sciences, Jean-Paul Auffray explains that these questions are to the heart of the modern physics and it brings them a new lighting. (N.C.)

  15. Point defects and irradiation in oxides: simulations at the atomic scale; Defauts ponctuels et irradiation dans les oxydes: simulation a l'echelle atomique

    Energy Technology Data Exchange (ETDEWEB)

    Crocombette, J.P

    2005-12-15

    The studies done by Jean-Paul Crocombette between 1996 and 2005 in the Service de Recherches de Metallurgie Physique of the Direction de l'Energie Nucleaire in Saclay are presented in this Habilitation thesis. These works were part of the material science researches on the ageing, especially under irradiation, of oxides of interest for the nuclear industry. In this context simulation studies at the atomic scale were performed on two elementary components of ageing under irradiation : point defects and displacement cascades ; using two complementary simulation techniques : ab initio electronic structure calculations and empirical potential molecular dynamics. The first part deals with point defects : self defects (vacancies or interstitials) or hetero-atomic dopants. One first recalls the energetics of such defects in oxides, the specific features of defects calculations and the expected accuracy of these calculations. Then one presents the results obtained on uranium dioxide, oxygen in silver and amorphous silica. The second part tackles the modelling of disintegration recoil nuclei in various?displacement cascades created by crystalline matrices for actinide waste disposal. Cascade calculations give access to the amorphization mechanisms under irradiation of these materials. One thus predicts that the amorphization in zircon takes place directly in the tracks whereas in lanthanum zirconate, the amorphization proceeds through the accumulation of point defects. Finally the prospects of these studies are discussed. (author)

  16. Texture variations and atomic dislocations by Ar-irradiation in Au and NbN sputtered layers

    International Nuclear Information System (INIS)

    Jung, V.

    1988-02-01

    Irradiation of Au and NbN sputtered layers with Ar ++ ions of 600 keV leads to a narrower orientation distribution of the [111] direction of the Au layers from 12 0 FWHM to 6 0 and to only very small FWHM changes in texture distributions of the NbN layers. But the FWHM of the reflex distribution of the irradiated NbN layers is increased significantly from ΔΘ = 0.65 0 to 1.17 0 for one sample position. This is caused by small atomic dislocations in the NbN lattice. The FWHM of reflex distribution of the Au layers increased only from ΔΘ = 0.60 0 to 0.65 0 after irradiation. Oblique incidence of Ar ++ ions causes, by absence of channeling, stronger distortions than perpendicular incidence. (orig.) [de

  17. A first-principles study of structure, orbital interactions and atomic oxygen and OH adsorption on Mo-, Sc- and Y-doped nickel bimetallic clusters

    International Nuclear Information System (INIS)

    Das, Nishith Kumar; Shoji, Tetsuo

    2013-01-01

    Highlights: •Mo-doped nickel clusters are energetically more stable than the Sc and Y-doped clusters (n ⩾ 10). •Mo atom exhibits center at the cluster rather than edge, while Sc and Y atom sit at the edge. •The metallic s, d orbitals are mainly dominated on the stability of nanoclusters. •The oxygen and OH adsorption energy of Mo-doped cluster are higher than those of other nanoclusters. •2p Orbitals are strongly bonds with Mo 4d, and a weakly interacts with Ni 3d, 4s and Mo 5s orbitals. -- Abstract: Density functional theory (DFT) has been used to study the stability, orbitals interactions and oxygen and hydroxyl chemisorption properties of Ni n M (1 ⩽ n ⩽ 12) clusters. A single atom doped-nickel clusters increase the stability, and icosahedral Ni 12 Mo cluster is the most stable structure. Molybdenum atom prefers to exhibit center at the cluster (n ⩾ 10) rather than edge, while Sc and Y atom remain at the edge. The Ni–Mo bond lengths are smaller than the Ni–Sc and Ni–Y. The pDOS results show that the d–d orbitals interactions are mainly dominating on the stability of clusters, while p orbitals have a small effect on the stability. The Mo-doped nanoclusters have the highest oxygen and OH chemisorption energy, and the most favorable adsorption site is on the top Mo site. The larger cluster distortion is found for the Sc- and Y-doped structures compared to other clusters. The oxygen 2p orbitals are strongly hybridizing with the Mo 4d orbitals (n < 9) and a little interaction between oxygen 2p and Ni 3d, 4s and Mo 5s orbitals. The Mo-doped clusters are significantly increased the chemisorption energies that might improve the passive film adherence of nanoalloys

  18. Electron irradiation effects and recovery of defect clusters in TiC through high voltage electron microscope

    International Nuclear Information System (INIS)

    Iseki, Michio; Kirihara, Tomoo; Ushijima, Susumu; Ohashi, Hideki.

    1984-01-01

    Titanium carbide(TiCsub(0.8)) prepared by plasma-jet melting was irradiated to an electron dose less than 6x10 26 e/m 2 from room temperature to 800 0 C. The number density and average size of the defect clusters formed at irradiation temperatures below 400 0 C were less than those formed above 600 0 C. Since TiCsub(0.8) has an order structure of carbon below around 600 0 C, the ordered phase is more resistant to radiation than the disordered one in higher temperatures. The clusters decrease in number density and develop to dislocation loops during post irradiation annealing above 1,000 0 C. The burgers vector of the loops was determined as a/2 . There were two temperature region for the recovery of the defect clusters. It is conceivable that the first one appeared in the temperature region around 600 0 C caused by migration of carbon vacancies, and the second one appeared above 1,000 0 C by migration of titanium vacancies. (author)

  19. Density functional calculations on 13-atom Pd12M (M = Sc—Ni) bimetallic clusters

    International Nuclear Information System (INIS)

    Tang Chun-Mei; Chen Sheng-Wei; Zhu Wei-Hua; Tao Cheng-Jun; Zhang Ai-Mei; Gong Jiang-Feng; Zou Hua; Liu Ming-Yi; Zhu Feng

    2012-01-01

    The geometric structures, electronic and magnetic properties of the 3d transition metal doped clusters Pd 12 M (M = Sc—Ni) are studied using the semi-core pseudopots density functional theory. The groundstate geometric structure of the Pd 12 M cluster is probably of pseudoicosahedron. The I h -Pd 12 M cluster has the most thermodynamic stability in five different symmetric isomers. The energy gap shows that Pd 12 M cluster is partly metallic. Both the absolutely predominant metal bond and very weak covalent bond might exist in the Pd 12 M cluster. The magnetic moment of Pd 12 M varies from 0 to 5 μ B , implying that it has a potential application in new nanomaterials with tunable magnetic properties

  20. Topological and morphological analysis of gamma rays irradiated chitosan-poly (vinyl alcohol) blends using atomic force microscopy

    Science.gov (United States)

    Bhatt, Rinkesh; Bisen, D. S.; Bajpai, R.; Bajpai, A. K.

    2017-04-01

    In the present communication, binary blends of poly (vinyl alcohol) (PVA) and chitosan (CS) were prepared by solution cast method and the roughness parameters of PVA, native CS and CS-PVA blend films were determined using atomic force microscopy (AFM). Moreover, the changes in the morphology of the samples were also investigated after irradiation of gamma rays at absorbed dose of 1 Mrad and 10 Mrad for the scanning areas of 5×5 μm2, 10×10 μm2 and 20×20 μm2. Amplitude, statistical and spatial parameters, including line, 3D and 2D image profiles of the experimental surfaces were examined and compared to un-irradiated samples. For gamma irradiated CS-PVA blends the larger waviness over the surface was found as compared to un-irradiated CS-PVA blends but the values of average roughness for both the films were found almost same. The coefficient of skewness was positive for gamma irradiated CS-PVA blends which revealed the presence of more peaks than valleys on the blend surfaces.

  1. In vivo UVB irradiation induces clustering of Fas (CD95) on human epidermal cells

    DEFF Research Database (Denmark)

    Bang, Bo; Gniadecki, Robert; Larsen, Jørgen K

    2003-01-01

    a single dose of UVB irradiation. Normal healthy individuals were irradiated with three minimal erythema doses (MED) of UVB on forearm or buttock skin. Suction blisters from unirradiated and irradiated skin were raised, and Fas, FasL, and apoptosis of epidermal cells quantified by flow cytometry...

  2. An intrinsic representation of atomic structure: From clusters to periodic systems

    Science.gov (United States)

    Li, Xiao-Tian; Xu, Shao-Gang; Yang, Xiao-Bao; Zhao, Yu-Jun

    2017-10-01

    We have improved our distance matrix and eigen-subspace projection function (EPF) [X.-T. Li et al., J. Chem. Phys. 146, 154108 (2017)] to describe the atomic structure for periodic systems. Depicting the local structure of an atom, the EPF turns out to be invariant with respect to the choices of the unit cell and coordinate frame, leading to an intrinsic representation of the crystal with a set of EPFs of the nontrivial atoms. The difference of EPFs reveals the difference of atoms in local structure, while the accumulated difference between two sets of EPFs can be taken as the distance between configurations. Exemplified with the cases of carbon allotropes and boron sheets, our EPF approach shows exceptional rationality and efficiency to distinguish the atomic structures, which is crucial in structure recognition, comparison, and analysis.

  3. Multiple H3+ fragment production in single collision of fast Hn+ clusters with He atoms

    International Nuclear Information System (INIS)

    Farizon, B.; Farizon, M.; Gaillard, M.J.; Gerlic, E.; Ouaskit, S.

    1994-09-01

    The production of H 3 + ions resulting from single collisions of mass-selected ionic hydrogen clusters, H n + (n=9,25,31), with helium at high velocity (1.55 times the Bohr velocity) has been studied. A strong double H 3 + ion production resulting from one incident cluster is observed. Moreover, evidence for a triple H 3 + fragment production is presented for n=25 and 31. Thus, in this energy range, the collision gives rise to multifragmentation processes. The formation of H 3 + ions takes place in the fragmentation of the multicharged cluster resulting from the collision. (authors)

  4. Fragmentation of neutral carbon clusters formed by high velocity atomic collision; Fragmentation d'agregats de carbone neutres formes par collision atomique a haute vitesse

    Energy Technology Data Exchange (ETDEWEB)

    Martinet, G

    2004-05-01

    The aim of this work is to understand the fragmentation of small neutral carbon clusters formed by high velocity atomic collision on atomic gas. In this experiment, the main way of deexcitation of neutral clusters formed by electron capture with ionic species is the fragmentation. To measure the channels of fragmentation, a new detection tool based on shape analysis of current pulse delivered by semiconductor detectors has been developed. For the first time, all branching ratios of neutral carbon clusters are measured in an unambiguous way for clusters size up to 10 atoms. The measurements have been compared to a statistical model in microcanonical ensemble (Microcanonical Metropolis Monte Carlo). In this model, various structural properties of carbon clusters are required. These data have been calculated with Density Functional Theory (DFT-B3LYP) to find the geometries of the clusters and then with Coupled Clusters (CCSD(T)) formalism to obtain dissociation energies and other quantities needed to compute fragmentation calculations. The experimental branching ratios have been compared to the fragmentation model which has allowed to find an energy distribution deposited in the collision. Finally, specific cluster effect has been found namely a large population of excited states. This behaviour is completely different of the atomic carbon case for which the electron capture in the ground states predominates. (author)

  5. Ambient-temperature diffusion and gettering of Pt atoms in GaN with surface defect region under 60Co gamma or MeV electron irradiation

    Science.gov (United States)

    Hou, Ruixiang; Li, Lei; Fang, Xin; Xie, Ziang; Li, Shuti; Song, Weidong; Huang, Rong; Zhang, Jicai; Huang, Zengli; Li, Qiangjie; Xu, Wanjing; Fu, Engang; Qin, G. G.

    2018-01-01

    Generally, the diffusion and gettering of impurities in GaN needs high temperature. Calculated with the ambient-temperature extrapolation value of the high temperature diffusivity of Pt atoms in GaN reported in literature, the time required for Pt atoms diffusing 1 nm in GaN at ambient temperature is about 19 years. Therefore, the ambient-temperature diffusion and gettering of Pt atoms in GaN can hardly be observed. In this work, the ambient-temperature diffusion and gettering of Pt atoms in GaN is reported for the first time. It is demonstrated by use of secondary ion mass spectroscopy that in the condition of introducing a defect region on the GaN film surface by plasma, and subsequently, irradiated by 60Co gamma-ray or 3 MeV electrons, the ambient-temperature diffusion and gettering of Pt atoms in GaN can be detected. It is more obvious with larger irradiation dose and higher plasma power. With a similar surface defect region, the ambient-temperature diffusion and gettering of Pt atoms in GaN stimulated by 3 MeV electron irradiation is more marked than that stimulated by gamma irradiation. The physical mechanism of ambient-temperature diffusion and gettering of Pt atoms in a GaN film with a surface defect region stimulated by gamma or MeV electron irradiation is discussed.

  6. First-principles real-space tight-binding LMTO calculation of electronic structures for atomic clusters

    International Nuclear Information System (INIS)

    Xie, Z.L.; Dy, K.S.; Wu, S.Y.

    1997-01-01

    A real-space scheme has been developed for a first-principles calculation of electronic structures and total energies of atomic clusters. The scheme is based on the combination of the tight-binding linear muffin-tin orbital (TBLMTO) method and the method of real-space Green close-quote s function. With this approach, the local electronic density of states can be conveniently determined from the real-space Green close-quote s function. Furthermore, the full electron density of a cluster can be directly calculated in real space. The scheme has been shown to be very efficient due to the incorporation of the method of real-space Green close-quote s function and Delley close-quote s method of evaluating multicenter integrals. copyright 1996 The American Physical Society

  7. Adsorption of beryllium atoms and clusters both on graphene and in a bilayer of graphite investigated by DFT.

    Science.gov (United States)

    Ferro, Yves; Fernandez, Nicolas; Allouche, Alain; Linsmeier, Christian

    2013-01-09

    We herein investigate the interaction of beryllium with a graphene sheet and in a bilayer of graphite by means of periodic DFT calculations. In all cases, we find the beryllium atoms to be more weakly bonded on graphene than in the bilayer. Be(2) forms both magnetic and non-magnetic structures on graphene depending on the geometrical configuration of adsorption. We find that the stability of the Be/bilayer system increases with the size of the beryllium clusters inserted into the bilayer of graphite. We also find a charge transfer from beryllium to the graphite layers. All these results are analysed in terms of electronic structure.

  8. Intense deuterium nuclear fusion of pycnodeuterium-lumps coagulated locally within highly deuterated atom clusters

    CERN Document Server

    Yoshiaki, A; Zhang, Y C

    2002-01-01

    Embedded nano-Pd particles of 5 nm in size instantly abundant D-atoms more than 250% in the atomic ratio against Pd-atoms at room temperature when they are kept in D sub 2 gas pressurized to less than 10 atm. In such ultrahigh densities, 2-4 D-atoms can be coagulated inside each octahedral space of Pd lattice (pycnodeuterium-lump). When a stimulation energy such as latticequake causing by ultrasonic wave was supplied to those highly deuterated Pd particles, intense deuterium nuclear fusion (''solid fusion'') was generated there and both excess heat and sup 4 He gas were abundantly produced. Naturally, these facts can not be realized at all in bulk Pd. The results show that the nuclear fusion occurs without any hazardous rays in pycnodeuterium-lumps coagulated locally inside the each cell of the host metal lattice. These unit cells correspond to minimum unit of the solid fusion reactor as a ''Lattice Reactor''. (author)

  9. Influence of interstitial impurity atoms on point defect relaxation in neutron irradiated iron

    International Nuclear Information System (INIS)

    Weller, M.; Diehl, J.

    1975-01-01

    The aim of the investigation was to study the combined influence of neutron irradiation and interstitial impurities on the low temperature internal friction peaks as well as on those appearing at higher temperatures after annealing, in a more systematic manner, using irradiations at [de

  10. Observation of oscillatory radiation induced segregation profiles at grain boundaries in neutron irradiated 316 stainless steel using atom probe tomography

    Science.gov (United States)

    Barr, Christopher M.; Felfer, Peter J.; Cole, James I.; Taheri, Mitra L.

    2018-06-01

    Radiation induced segregation in austenitic Fe-Ni-Cr stainless steels is a key detrimental microstructural modification experienced in the current generation of light water reactors. In particular, Cr depletion at grain boundaries can be a significant factor in irradiation-assisted stress corrosion cracking. Therefore, having a complete knowledge and mechanistic understanding of radiation induced segregation at high dose and after a long thermal history is desired for continued sustainability of existing reactors. Here, we examine a 12% cold worked AISI 316 stainless steel hexagonal duct exposed in the lower dose, outer blanket region of the EBR-II reactor, by using advanced characterization and analysis techniques including atom probe tomography and analytical scanning transmission electron microscopy. Contrary to existing literature, we observe an oscillatory w-shape Cr and M-shape Ni concentration profile at 31 dpa. The presence and characterization through advanced atom probe tomography analysis of the w-shape Cr RIS profile is discussed in the context of the localized GB plane interfacial excess of the other major and minor alloying elements. The key finding of a co-segregation phenomena coupling Cr, Mo, and C is discussed in the context of the existing solute segregation literature under irradiation with emphasis on improved spatial and chemical resolution of atom probe tomography.

  11. Probing potential Li-ion battery electrolyte through first principles simulation of atomic clusters

    Science.gov (United States)

    Kushwaha, Anoop Kumar; Sahoo, Mihir Ranjan; Nayak, Saroj

    2018-04-01

    Li-ion battery has wide area of application starting from low power consumer electronics to high power electric vehicles. However, their large scale application in electric vehicles requires further improvement due to their low specific power density which is an essential parameter and is closely related to the working potential windows of the battery system. Several studies have found that these parameters can be taken care of by considering different cathode/anode materials and electrolytes. Recently, a unique approach has been reported on the basis of cluster size in which the use of Li3 cluster has been suggested as a potential component of the battery electrode material. The cluster based approach significantly enhances the working electrode potential up to 0.6V in the acetonitrile solvent. In the present work, using ab-initio quantum chemical calculation and the dielectric continuum model, we have investigated various dielectric solvent medium for the suitable electrolyte for the potential component Li3 cluster. This study suggests that high dielectric electrolytic solvent (ethylene carbonate and propylene carbonate) could be better for lithium cluster due to improvement in the total electrode potential in comparison to the other dielectric solvent.

  12. Atomic-scale structure of irradiated GaN compared to amorphised GaP and GaAs

    International Nuclear Information System (INIS)

    Ridgway, M.C.; Everett, S.E.; Glover, C.J.; Kluth, S.M.; Kluth, P.; Johannessen, B.; Hussain, Z.S.; Llewellyn, D.J.; Foran, G.J.; Azevedo, G. de M.

    2006-01-01

    We have compared the atomic-scale structure of ion irradiated GaN to that of amorphised GaP and GaAs. While continuous and homogenous amorphised layers were easily achieved in GaP and GaAs, ion irradiation of GaN yielded both structural and chemical inhomogeneities. Transmission electron microscopy revealed GaN crystallites and N 2 bubbles were interspersed within an amorphous GaN matrix. The crystallite orientation was random relative to the unirradiated epitaxial structure, suggesting their formation was irradiation-induced, while the crystallite fraction was approximately constant for all ion fluences beyond the amorphisation threshold, consistent with a balance between amorphisation and recrystallisation processes. Extended X-ray absorption fine structure measurements at the Ga K-edge showed short-range order was retained in the amorphous phase for all three binary compounds. For ion irradiated GaN, the stoichiometric imbalance due to N 2 bubble formation was not accommodated by Ga-Ga bonding in the amorphous phase or precipitation of metallic Ga but instead by a greater reduction in Ga coordination number

  13. Atomic bonding between metal and graphene

    KAUST Repository

    Wang, Hongtao

    2013-03-07

    To understand structural and chemical properties of metal-graphene composites, it is crucial to unveil the chemical bonding along the interface. We provide direct experimental evidence of atomic bonding between typical metal nano structures and graphene, agreeing well with density functional theory studies. Single Cr atoms are located in the valleys of a zigzag edge, and few-atom ensembles preferentially form atomic chains by self-assembly. Low migration barriers lead to rich dynamics of metal atoms and clusters under electron irradiation. We demonstrate no electron-instigated interaction between Cr clusters and pristine graphene, though Cr has been reported to be highly reactive to graphene. The metal-mediated etching is a dynamic effect between metal clusters and pre-existing defects. The resolved atomic configurations of typical nano metal structures on graphene offer insight into modeling and simulations on properties of metal-decorated graphene for both catalysis and future carbon-based electronics. © 2013 American Chemical Society.

  14. Atomic- and void-species nanostructures in chalcogenide glasses modified by high-energy γ-irradiation

    International Nuclear Information System (INIS)

    Kavetskyy, T.; Shpotyuk, O.; Kaban, I.; Hoyer, W.

    2007-01-01

    Atomic- and void-species nanostructures are studied in As 2 S 3 glass in unmodified and γ-modified states using a combination of conventional X-ray diffraction with respect to the first sharp diffraction peak, synchrotron-based high-energy X-ray diffraction and extended X-ray absorption fine structure spectroscopy. The experimental data are analyzed taking into account radiation-induced changes in the parameters of the first sharp diffraction peak (position, full width at half maximum, intensity), packing factor, structural disordering, atomic and void topology, coordination number and mean square deviation in bond length. The origin of the structural modification effect induced by γ-irradiation is explained in terms of coordination topological defects model. (authors)

  15. Effect of Pt:Sn atomic ratio on the preparation of PtSn/C electrocatalysts using electron beam irradiation

    International Nuclear Information System (INIS)

    Silva, Dionisio F.; Oliveira Neto, Almir; Pino, Eddy S.; Linardi, Marcelo; Spinace, Estevam V.

    2009-01-01

    PtSn/C electrocatalysts were prepared with Pt:Sn atomic ratios of 3:1, 1:1 and 1:3 in water/2-propanol using electron beam irradiation. The obtained materials were characterized by EDX, XRD and cyclic voltammetry. The ethanol electro-oxidation was studied by chronoamperometry. The XRD diffractograms of the PtSn/C electrocatalysts showed typical face-centered cubic (fcc) structure of platinum and the presence of a SnO 2 phase (cassiterite). The mean crystallite sizes of Pt fcc phase was in the range of 3.0-3.5 nm. The PtSn/C electrocatalysts were active for ethanol electro-oxidation at room temperature and the material prepared with Pt:Sn atomic ratio of 1:1 showed the best activity. (author)

  16. Effect of Pt:Sn atomic ratio on the preparation of PtSn/C electrocatalysts using electron beam irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Dionisio F.; Oliveira Neto, Almir; Pino, Eddy S.; Linardi, Marcelo; Spinace, Estevam V., E-mail: dfsilva@ipen.b, E-mail: espinace@ipen.b [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2009-07-01

    PtSn/C electrocatalysts were prepared with Pt:Sn atomic ratios of 3:1, 1:1 and 1:3 in water/2-propanol using electron beam irradiation. The obtained materials were characterized by EDX, XRD and cyclic voltammetry. The ethanol electro-oxidation was studied by chronoamperometry. The XRD diffractograms of the PtSn/C electrocatalysts showed typical face-centered cubic (fcc) structure of platinum and the presence of a SnO{sub 2} phase (cassiterite). The mean crystallite sizes of Pt fcc phase was in the range of 3.0-3.5 nm. The PtSn/C electrocatalysts were active for ethanol electro-oxidation at room temperature and the material prepared with Pt:Sn atomic ratio of 1:1 showed the best activity. (author)

  17. Trapping of self-interstitials at manganese atoms in electron-irradiated dilute AlMn alloys

    International Nuclear Information System (INIS)

    Bartels, A.; Dworschak, F.

    1985-01-01

    Dilute AlMn alloys were irradiated isothermally at different temperatures in stage II with 1.8 MeV electrons and the resistivity damage rates were measured as a function of the residual resistivity increase. The results demonstrate that Mn atoms provide deep traps at least up to 150 K for mobile interstitials. A quantitative evaluation of the data with respect to trapping radii is somewhat handicapped by the fact that the resistivity contribution of a Mn-Al interstitial complex was found to be considerably less than the sum of the resistivity contributions of an isolated solute Mn atom and an Al self-interstitial. The results can be explained by a model which assumes that both the trapping radius and the resistivity contribution of solute-self-interstitial complexes increase with the number of trapped interstitials. (author)

  18. Indium clustering in a-plane InGaN quantum wells as evidenced by atom probe tomography

    International Nuclear Information System (INIS)

    Tang, Fengzai; Zhu, Tongtong; Oehler, Fabrice; Fu, Wai Yuen; Griffiths, James T.; Massabuau, Fabien C.-P.; Kappers, Menno J.; Oliver, Rachel A.; Martin, Tomas L.; Bagot, Paul A. J.; Moody, Michael P.

    2015-01-01

    Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown sample. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane sample pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering

  19. Indium clustering in a-plane InGaN quantum wells as evidenced by atom probe tomography

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Fengzai; Zhu, Tongtong; Oehler, Fabrice; Fu, Wai Yuen; Griffiths, James T.; Massabuau, Fabien C.-P.; Kappers, Menno J.; Oliver, Rachel A., E-mail: rao28@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Martin, Tomas L.; Bagot, Paul A. J.; Moody, Michael P., E-mail: michael.moody@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom)

    2015-02-16

    Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown sample. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane sample pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering.

  20. The mechanism of solute-enriched clusters formation in neutron-irradiated pressure vessel steels: The case of Fe-Cu model alloys

    Energy Technology Data Exchange (ETDEWEB)

    Subbotin, A.V., E-mail: Alexey.V.Subbotin@gmail.com [Scientific and Production Complex Atomtechnoprom, Moscow 119180 (Russian Federation); Panyukov, S.V., E-mail: panyukov@lpi.ru [PN Lebedev Physics Institute, Russian Academy of Sciences, Moscow 117924 (Russian Federation)

    2016-08-15

    Mechanism of solute-enriched clusters formation in neutron-irradiated pressure vessel steels is proposed and developed in case of Fe-Cu model alloys. The suggested solute-drag mechanism is analogous to the well-known zone-refining process. We show that the obtained results are in good agreement with available experimental data on the parameters of clusters enriched with the alloying elements. Our model explains why the formation of solute-enriched clusters does not happen in austenitic stainless steels with fcc lattice structure. It also allows to quantify the method of evaluation of neutron irradiation dose for the process of RPV steels hardening.

  1. Irradiation of four pencils fuel element clusters in the periphery of OSIRIS. Qualification of the calculation method by dosimetry

    International Nuclear Information System (INIS)

    Alberman, A.; Morin, C.

    1983-09-01

    The programs of qualification of PWR fuels required many irradiations in research reactors. In the periphery of the OSIRIS reactor (70 MW), two devices (IRENE and ISABELLE loops) recreating the environment of the fuel rods in power reactors have been put into service. In each device a fuel element cluster including four pencils was irradiated. The problem set by dosimetry was to calculate the enrichments of the pencils to obtain the required power level and to compensate the neutron flux gradient (in front of/behind) to obtain the same power on each one of the four pencils. The required accuracy is about 5%. Fuels dosimetry achieved on loops mockups in the ISIS reactor allowed to test the validity of the calculations and to calibrate the probes according to the nuclear power [fr

  2. Gold atoms and clusters on MgO(100) films; an EPR and IRAS study

    Science.gov (United States)

    Yulikov, M.; Sterrer, M.; Risse, T.; Freund, H.-J.

    2009-06-01

    Single gold atoms deposited on single crystalline MgO(1 0 0) films grown on Mo(1 0 0) are characterized by electron paramagnetic resonance spectroscopy as well as IR spectroscopy using CO as probe molecules. In this article we describe the first angular dependent measurements to determine the principal hyperfine components of a secondary hyperfine interaction, namely, with 17O of the MgO. The values determined here are in perfect agreement with theoretical expectations and corroborate the previously reported binding mechanism of Au atoms on the oxygen anions of the MgO terrace. The temperature dependent EPR data reveal an onset of Au atom mobility at about 80 K while the formation of Au particles occurs only above 125 K. By an analysis of the EPR line width in combination with STM measurements it is possible to deduce an increase of the interatomic distance above 80 K. The Au/CO complexes show a somewhat smaller temperature stability as compared to the Au atoms. The observed thermal stability is in perfect agreement with theoretical predictions for CO desorption.

  3. Reactivity of chemisorbed oxygen atoms and their catalytic consequences during CH4-O2 catalysis on supported Pt clusters.

    Science.gov (United States)

    Chin, Ya-Huei Cathy; Buda, Corneliu; Neurock, Matthew; Iglesia, Enrique

    2011-10-12

    absence of CH(4) show that O(2) activation steps are quasi-equilibrated during catalysis. Measured and DFT-derived C-H bond activation barriers are large, because of the weak stabilization of the CH(3) fragments at transition states, but are compensated by the high entropy of these radical-like species. Turnover rates in this regime decrease with increasing Pt dispersion, because low-coordination exposed Pt atoms on small clusters bind O* more strongly than those that reside at low-index facets on large clusters, thus making O* less effective in H-abstraction. As vacancies (*, also exposed Pt atoms) become available on O*-covered surfaces, O*-* site pairs activate C-H bonds via concerted oxidative addition and H-abstraction in transition states effectively stabilized by CH(3) interactions with the vacancies, which lead to much higher turnover rates than on O*-O* pairs. In this regime, O(2) activation becomes irreversible, because fast C-H bond activation steps scavenge O* as it forms. Thus, O* coverages are set by the prevalent O(2)/CH(4) ratios instead of the O(2) pressures. CH(4)/CD(4) kinetic isotope effects are much larger for turnovers mediated by O*-* than by O*-O* site pairs, because C-H (and C-D) activation steps are required to form the * sites involved in C-H bond activation. Turnover rates for CH(4)-O(2) reactions mediated by O*-* pairs decrease with increasing Pt dispersion, as in the case of O*-O* active structures, because stronger O* binding on small clusters leads not only to less reactive O* atoms, but also to lower vacancy concentrations at cluster surfaces. As O(2)/CH(4) ratios and O* coverages become smaller, O(2) activation on bare Pt clusters becomes the sole kinetically relevant step; turnover rates are proportional to O(2) pressures and independent of CH(4) pressure and no CH(4)/CD(4) kinetic isotope effects are observed. In this regime, turnover rates become nearly independent of Pt dispersion, because the O(2) activation step is essentially

  4. Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study.

    Science.gov (United States)

    Jendrzej, Sandra; Gökce, Bilal; Amendola, Vincenzo; Barcikowski, Stephan

    2016-02-01

    Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz-Slyozov-Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. Copyright © 2015. Published by Elsevier Inc.

  5. From atoms to layers: in situ gold cluster growth kinetics during sputter deposition

    Science.gov (United States)

    Schwartzkopf, Matthias; Buffet, Adeline; Körstgens, Volker; Metwalli, Ezzeldin; Schlage, Kai; Benecke, Gunthard; Perlich, Jan; Rawolle, Monika; Rothkirch, André; Heidmann, Berit; Herzog, Gerd; Müller-Buschbaum, Peter; Röhlsberger, Ralf; Gehrke, Rainer; Stribeck, Norbert; Roth, Stephan V.

    2013-05-01

    The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction of morphological real space parameters, such as cluster size and shape, correlation distance, layer porosity and surface coverage, directly from reciprocal space scattering data. This approach enables a large variety of future investigations of the influence of different process parameters on the thin metal film morphology. Furthermore, our study allows for deducing the wetting behavior of gold cluster films on solid substrates and provides a better understanding of the growth kinetics in general, which is essential for optimization of manufacturing parameters, saving energy and resources.The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction

  6. Point defects and irradiation in oxides: simulations at the atomic scale

    International Nuclear Information System (INIS)

    Crocombette, J.P.

    2005-11-01

    The author gives an overview of his research activity since 1995. This activity concerns research in materials science, and more particularly the ageing of oxides present in the nuclear industry, or more generally, the evolution of these materials under irradiation. The first part deals with the investigation of point defects, and more particularly of the structures and energies of these defects. The author discusses results obtained on uranium dioxide, on amorphous silica, and on the solution of oxygen in silver. The second part deals with irradiation-induced damages in crystalline matrices storing radioactive actinides, and more particularly with the effect of alpha disintegration decay nuclei which are the main sources of long term irradiation in these materials

  7. Quantum Monte-Carlo programming for atoms, molecules, clusters, and solids

    International Nuclear Information System (INIS)

    Schattke, Wolfgang; Diez Muino, Ricardo

    2013-01-01

    This is a book that initiates the reader into the basic concepts and practical applications of Quantum Monte Carlo. Because of the simplicity of its theoretical concept, the authors focus on the variational Quantum Monte Carlo scheme. The reader is enabled to proceed from simple examples as the hydrogen atom to advanced ones as the Lithium solid. In between, several intermediate steps are introduced, including the Hydrogen molecule (2 electrons), the Lithium atom (3 electrons) and expanding to an arbitrary number of electrons to finally treat the three-dimensional periodic array of Lithium atoms in a crystal. The book is unique, because it provides both theory and numerical programs. It pedagogically explains how to transfer into computational tools what is usually described in a theoretical textbook. It also includes the detailed physical understanding of methodology that cannot be found in a code manual. The combination of both aspects allows the reader to assimilate the fundamentals of Quantum Monte Carlo not only by reading but also by practice.

  8. clusters

    Indian Academy of Sciences (India)

    2017-09-27

    Sep 27, 2017 ... Author for correspondence (zh4403701@126.com). MS received 15 ... lic clusters using density functional theory (DFT)-GGA of the DMOL3 package. ... In the process of geometric optimization, con- vergence thresholds ..... and Postgraduate Research & Practice Innovation Program of. Jiangsu Province ...

  9. clusters

    Indian Academy of Sciences (India)

    environmental as well as technical problems during fuel gas utilization. ... adsorption on some alloys of Pd, namely PdAu, PdAg ... ried out on small neutral and charged Au24,26,27, Cu,28 ... study of Zanti et al.29 on Pdn (n = 1–9) clusters.

  10. Coupled electronic and atomic effects on defect evolution in silicon carbide under ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yanwen [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Xue, Haizhou [Univ. of Tennessee, Knoxville, TN (United States); Zarkadoula, Eva [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Sachan, Ritesh [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Army Research Office, Triangle Park, NC (United States); Ostrouchov, Christopher [Univ. of Tennessee, Knoxville, TN (United States); Liu, Peng [Univ. of Tennessee, Knoxville, TN (United States); Shandong Univ., Jinan (China); Wang, Xue -lin [Shandong Univ., Jinan (China); Zhang, Shuo [Lanzhou Univ., Gansu Province (China); Wang, Tie Shan [Lanzhou Univ., Gansu Province (China); Weber, William J. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2017-10-16

    Understanding energy dissipation processes in electronic/atomic subsystems and subsequent non-equilibrium defect evolution is a long-standing challenge in materials science. In the intermediate energy regime, energetic particles simultaneously deposit a significant amount of energy to both electronic and atomic subsystems of silicon carbide (SiC). Here we show that defect evolution in SiC closely depends on the electronic-to-nuclear energy loss ratio (Se/Sn), nuclear stopping powers (dE/dxnucl), electronic stopping powers (dE/dxele), and the temporal and spatial coupling of electronic and atomic subsystem for energy dissipation. The integrated experiments and simulations reveal that: (1) increasing Se/Sn slows damage accumulation; (2) the transient temperatures during the ionization-induced thermal spike increase with dE/dxele, which causes efficient damage annealing along the ion trajectory; and (3) for more condensed displacement damage within the thermal spike, damage production is suppressed due to the coupled electronic and atomic dynamics. Ionization effects are expected to be more significant in materials with covalent/ionic bonding involving predominantly well-localized electrons. Here, insights into the complex electronic and atomic correlations may pave the way to better control and predict SiC response to extreme energy deposition

  11. Self-interstitial atom clusters as obstacles to glide of 1/3{11-bar 00} edge dislocations in α-zirconium

    International Nuclear Information System (INIS)

    Voskoboynikov, R.E.; Osetsky, Yu.N.; Bacon, D.J.

    2005-01-01

    Atomic-scale details of interaction of a 1/3 {11-bar 00} edge dislocation with clusters of self-interstitial atoms (SIAs) in α-zirconium has been studied by computer simulation. Four typical clusters are considered. A triangular cluster of five SIAs lying within a basal plane bisected by the dislocation glide plane is not absorbed by the dislocation but acts as a moderately strong obstacle. A 3-D SIA cluster lying across the glide plane is completely absorbed by the dislocation by creation of super-jogs, and is a weak obstacle. Interaction of the dislocation with glissile SIA loops with perfect Burgers vector inclined at 60 deg. to the dislocation glide plane shows that the process depends on the vector orientation. Defects of the two orientations are strong obstacles, and one, which initially forms a sessile segment on the dislocation line, is particularly so

  12. Lattice site occupation of insoluble impurity atoms in aluminium after implantation and irradiation

    International Nuclear Information System (INIS)

    Kloska, M.K.

    1987-03-01

    Several elements, whose atoms are oversized and insoluble in aluminium, were implanted in aluminium single crystals at different temperatures. The substitutional fraction and the lattice site location were determined using the ion-channeling technique. The substitutional fractions obtained by in situ analyses are strongly dependent on the implantation temperature. At implantation and analysis temperatures below the temperature of stage III the substitutional fraction is significant larger than at temperatures above. With increasing heat of solution the substitutional fraction decreases for all implantation temperatures. The nonsubstitutional component consists of impurity atom-vacancy complexes. These complexes are formed in the cooling phase of the cascade. At temperatures above the temperature of stage III additional free mobile vacancies were captured by the impurity atoms. The capture radius is correlated with the heat of solution and the size mismatch energy. The results constitute for the first time an experimental confirmation of molecular dynamics calculations of cascade evolution. (orig./BHO)

  13. Inner-shell spectroscopy and exchange interaction of Rydberg electrons bound by singly and doubly charged Kr and Xe atoms in small clusters

    International Nuclear Information System (INIS)

    Nagasaka, Masanari; Hatsui, Takaki; Setoyama, Hiroyuki; Ruehl, Eckart; Kosugi, Nobuhiro

    2011-01-01

    Surface-site resolved Kr 3d 5/2 -1 5p and 3d 5/2 -1 6p and Xe 4d 5/2 -1 6p and 4d 5/2 -1 7p Rydberg excited states in small van der Waals Kr and Xe clusters with a mean size of = 15 are investigated by X-ray absorption spectroscopy. Furthermore, surface-site resolved Kr 4s -2 5p, 4s -2 6p, and 4s -1 4p -1 5p shakeup-like Rydberg states in small Kr clusters are investigated by resonant Auger electron spectroscopy. The exchange interaction of the Rydberg electron with the surrounding atoms and the induced polarization of the surrounding atoms in the singly and doubly ionized atoms are deduced from the experimental spectra to analyze different surface-site contributions in small clusters, assuming that the corner, edge, face, and bulk sites have 3, 5-6, 8, and 12 nearest neighbor atoms. These energies are almost proportional to the number of the nearest neighbor atoms. The present analysis indicates that small Kr and Xe clusters with = 15 have an average or mixture structure between the fcc-like cubic and icosahedron-like spherical structures.

  14. A novel stibacarbaborane cluster with adjacent antimony atoms exhibiting unique pnictogen bond formation that dominates its crystal packing.

    Science.gov (United States)

    Holub, Josef; Melichar, Petr; Růžičková, Zdeňka; Vrána, Jan; Wann, Derek A; Fanfrlík, Jindřich; Hnyk, Drahomír; Růžička, Aleš

    2017-10-17

    We have prepared nido-7,8,9,11-Sb 2 C 2 B 7 H 9 , the first cluster with simultaneous Sb-B, Sb-C and Sb-Sb atom pairs with interatomic separations with magnitudes that approach the respective sums of covalent radii. However, the length of the Sb-Sb separation in this cluster is slightly less than the sum of the covalent radii. Quantum chemical analysis has revealed that the crystal packing of nido-7,8,9,11-Sb 2 C 2 B 7 H 9 is predominantly dictated by pnictogen (Pn) bonding, an unconventional σ-hole interaction. Indeed, the interaction energy of a very strong Sb 2 H-B Pn-bond in the nido-7,8,9,11-Sb 2 C 2 B 7 H 9 dimer exceeds -6.0 kcal mol -1 . This is a very large value and is comparable to the strengths of known Pn-bonds in Cl 3 Pnπ complexes (Pn = As, Sb).

  15. A valence-universal coupled-cluster single- and double-excitations method for atoms: Pt. 3

    International Nuclear Information System (INIS)

    Jankowski, K.; Malinowski, P.

    1994-01-01

    To better understand the problems met when solving the equations of VU-CC approaches in the presence of intruder states, we are concerned with the following aspects of the solvability problem for sets of non-linear equations: the existence and properties of multiple solutions and the attainability of these solutions by means of various numerical methods. Our study is concentrated on the equations obtained for Be within the framework of the recently formulated atomically oriented form of the valence-universal coupled-cluster theory accounting for one- and two-electron excitations (VU-CCSD/R) and based on the complete model space (2s 2 , 2p 2 ). Six pairs of multiple solutions representing four 1 S states are found and discussed. Three of these solutions provide amplitudes describing the 2p 2 1 S state for which the intruder state problem has been considered as extremely serious. Several known numerical methods have been applied to solve the same set of non-linear equations for the two-valence cluster amplitudes. It is shown that these methods perform quite differently in the presence of intruder states, which seems to indicate that the intruder state problem for VU-CC methods is partly caused by the commonly used methods of solving the non-linear equations. (author)

  16. Van der Waals potentials between metal clusters and helium atoms obtained with density functional theory and linear response methods

    International Nuclear Information System (INIS)

    Liebrecht, M.

    2014-01-01

    The importance of van der Waals interactions in many diverse research fields such as, e. g., polymer science, nano--materials, structural biology, surface science and condensed matter physics created a high demand for efficient and accurate methods that can describe van der Waals interactions from first principles. These methods should be able to deal with large and complex systems to predict functions and properties of materials that are technologically and biologically relevant. Van der Waals interactions arise due to quantum mechanical correlation effects and finding appropriate models an numerical techniques to describe this type of interaction is still an ongoing challenge in electronic structure and condensed matter theory. This thesis introduces a new variational approach to obtain intermolecular interaction potentials between clusters and helium atoms by means of density functional theory and linear response methods. It scales almost linearly with the number of electrons and can therefore be applied to much larger systems than standard quantum chemistry techniques. The main focus of this work is the development of an ab-initio method to account for London dispersion forces, which are purely attractive and dominate the interaction of non--polar atoms and molecules at large distances. (author) [de

  17. Photoelectron angular distributions for states of any mixed character: An experiment-friendly model for atomic, molecular, and cluster anions

    International Nuclear Information System (INIS)

    Khuseynov, Dmitry; Blackstone, Christopher C.; Culberson, Lori M.; Sanov, Andrei

    2014-01-01

    We present a model for laboratory-frame photoelectron angular distributions in direct photodetachment from (in principle) any molecular orbital using linearly polarized light. A transparent mathematical approach is used to generalize the Cooper-Zare central-potential model to anionic states of any mixed character. In the limit of atomic-anion photodetachment, the model reproduces the Cooper-Zare formula. In the case of an initial orbital described as a superposition of s and p-type functions, the model yields the previously obtained s-p mixing formula. The formalism is further advanced using the Hanstorp approximation, whereas the relative scaling of the partial-wave cross-sections is assumed to follow the Wigner threshold law. The resulting model describes the energy dependence of photoelectron anisotropy for any atomic, molecular, or cluster anions, usually without requiring a direct calculation of the transition dipole matrix elements. As a benchmark case, we apply the p-d variant of the model to the experimental results for NO − photodetachment and show that the observed anisotropy trend is described well using physically meaningful values of the model parameters. Overall, the presented formalism delivers insight into the photodetachment process and affords a new quantitative strategy for analyzing the photoelectron angular distributions and characterizing mixed-character molecular orbitals using photoelectron imaging spectroscopy of negative ions

  18. Photoelectron angular distributions for states of any mixed character: An experiment-friendly model for atomic, molecular, and cluster anions

    Science.gov (United States)

    Khuseynov, Dmitry; Blackstone, Christopher C.; Culberson, Lori M.; Sanov, Andrei

    2014-09-01

    We present a model for laboratory-frame photoelectron angular distributions in direct photodetachment from (in principle) any molecular orbital using linearly polarized light. A transparent mathematical approach is used to generalize the Cooper-Zare central-potential model to anionic states of any mixed character. In the limit of atomic-anion photodetachment, the model reproduces the Cooper-Zare formula. In the case of an initial orbital described as a superposition of s and p-type functions, the model yields the previously obtained s-p mixing formula. The formalism is further advanced using the Hanstorp approximation, whereas the relative scaling of the partial-wave cross-sections is assumed to follow the Wigner threshold law. The resulting model describes the energy dependence of photoelectron anisotropy for any atomic, molecular, or cluster anions, usually without requiring a direct calculation of the transition dipole matrix elements. As a benchmark case, we apply the p-d variant of the model to the experimental results for NO- photodetachment and show that the observed anisotropy trend is described well using physically meaningful values of the model parameters. Overall, the presented formalism delivers insight into the photodetachment process and affords a new quantitative strategy for analyzing the photoelectron angular distributions and characterizing mixed-character molecular orbitals using photoelectron imaging spectroscopy of negative ions.

  19. Metals on graphene and carbon nanotube surfaces: From mobile atoms to atomtronics to bulk metals to clusters and catalysts

    KAUST Repository

    Sarkar, Santanu C.

    2014-01-14

    In this Perspective, we present an overview of recent fundamental studies on the nature of the interaction between individual metal atoms and metal clusters and the conjugated surfaces of graphene and carbon nanotube with a particular focus on the electronic structure and chemical bonding at the metal-graphene interface. We discuss the relevance of organometallic complexes of graphitic materials to the development of a fundamental understanding of these interactions and their application in atomtronics as atomic interconnects, high mobility organometallic transistor devices, high-frequency electronic devices, organometallic catalysis (hydrogen fuel generation by photocatalytic water splitting, fuel cells, hydrogenation), spintronics, memory devices, and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight some of the latest advances in understanding the nature of interactions between metals and graphene surfaces from the standpoint of metal overlayers deposited on graphene and SWNT thin films. Finally, we comment on the major challenges facing the field and the opportunities for technological applications. © 2013 American Chemical Society.

  20. Lateral manipulation of small clusters on the Cu and Ag(1 1 1) surfaces with the single-atom and trimer-apex tips: Reliability study

    International Nuclear Information System (INIS)

    Xie Yiqun; Liu Fen; Huang Lei

    2010-01-01

    We study the reliability of the lateral manipulation of small Cu clusters (dimer and trimer) on the flat Cu(1 1 1) surface with both the single-atom and trimer-apex tips and that for the Ag/Ag(1 1 1) system, and compare the results between the two systems as well as with the single-atom manipulation on these surfaces. Manipulations are simulated using molecular statics method with semi-empirical potentials. The dependence of the manipulation reliability on the tip height and tip orientation are investigated. Overall, the manipulation reliability increases with decreasing tip height although it depends obviously on the tip orientation. For the Cu/Cu(1 1 1) system, the manipulation of the dimmer and trimer can be successful with both tips. The manipulation reliability can be improved by the trimer-apex tip, and the tip-height range for the successful manipulation is also broader, as compared to the single-atom apex tip. Differently from the single-atom manipulation, the tip orientation has a noticeable influence on the manipulation reliability even for the single-atom tip due to the stronger tip-cluster and surface-adatom interactions in cluster manipulation. For the Ag/Ag(1 1 1) system, successful manipulations only be achieved with the trimer-apex tip, and the manipulation reliability is worse than that of the Cu/Cu(1 1 1) system, indicating the difference in mechanic properties between the two surfaces at the atomic level.

  1. Irradiation characteristics of metal-cluster-complex ions containing diverse multi-elements with large mass differences

    International Nuclear Information System (INIS)

    Fujiwara, Yukio; Kondou, Kouji; Teranishi, Yoshikazu; Nonaka, Hidehiko; Saito, Naoaki; Fujimoto, Toshiyuki; Kurokawa, Akira; Ichimura, Shingo; Tomita, Mitsuhiro

    2007-01-01

    Tetrairidium dodecacarbonyl, Ir 4 (CO) 12 , is a metal cluster complex which has a molecular weight of 1104.9. Using a metal-cluster-complex ion source, the interaction between Ir 4 (CO) n + ions (n=0-12) and silicon substrates was studied at a beam energy ranging from 2keV to 10keV at normal incidence. By adjusting Wien-filter voltage, the influence of CO ligands was investigated. Experimental results showed that sputtering yield of silicon bombarded with Ir 4 (CO) n + ions at 10keV decreased with the number of CO ligands. In the case of 2keV, deposition tended to be suppressed by removing CO ligands from the impinging cluster ions. The influence of CO ligands was explained by considering changes in surface properties caused by the irradiation of Ir 4 (CO) n + ions. It was also found that the bombardment with Ir 4 (CO) 7 + ions at 2.5keV caused deposition on silicon target

  2. Irradiation-induced displacement of Ag atoms from lattice sites in an Al-0.2% Mg-0.1% Ag crystal

    International Nuclear Information System (INIS)

    Swanson, M.L.; Howe, L.M.; Quenneville, A.F.

    1976-01-01

    In irradiated alloys of Al containing approximately 0.1 at% Ag, the backscattering - channelling method shows that Al-Ag dumbells are created by the trapping of Al interstitial atoms at Ag solute atoms. The present results demonstrate that the addition of 0.2 at% Mg to such irradiated alloys retards not only the formation of Al-Ag dumbells during annealing from 30 to 100 K but also their annihilation during annealing from 180 to 240 K. Al interstitials are released from Mg traps at 100 to 160 K, causing further trapping at Ag atoms. Approximately 70% of the Ag atoms return to lattice sites at approximately 200 K (stage III) (compared with 100% in the Al-0.1% Ag alloys) and the remainder return to lattice sites at approximately 260 K. These results favour migration of Al-Ag dumbells rather than vacancies during stage III annealing. (author)

  3. Structure and physical properties of silicon clusters and of vacancy clusters in bulk silicon

    International Nuclear Information System (INIS)

    Sieck, A.

    2000-01-01

    In this thesis the growth-pattern of free silicon clusters and vacancy clusters in bulk silicon is investigated. The aim is to describe and to better understand the cluster to bulk transition. Silicon structures in between clusters and solids feature new interesting physical properties. The structure and physical properties of silicon clusters can be revealed by a combination of theory and experiment, only. Low-energy clusters are determined with different optimization techniques and a density-functional based tight-binding method. Additionally, infrared and Raman spectra, and polarizabilities calculated within self-consistent field density-functional theory are provided for the smaller clusters. For clusters with 25 to 35 atoms an analysis of the shape of the clusters and the related mobilities in a buffer gas is given. Finally, the clusters observed in low-temperature experiments are identified via the best match between calculated properties and experimental data. Silicon clusters with 10 to 15 atoms have a tricapped trigonal prism as a common subunit. Clusters with up to about 25 atoms follow a prolate growth-path. In the range from 24 to 30 atoms the geometry of the clusters undergoes a transition towards compact spherical structures. Low-energy clusters with up to 240 atoms feature a bonding pattern strikingly different from the tetrahedral bonding in the solid. It follows that structures with dimensions of several Angstroem have electrical and optical properties different from the solid. The calculated stabilities and positron-lifetimes of vacancy clusters in bulk silicon indicate the positron-lifetimes of about 435 ps detected in irradiated silicon to be related to clusters of 9 or 10 vacancies. The vacancies in these clusters form neighboring hexa-rings and, therefore, minimize the number of dangling bonds. (orig.)

  4. DFT study of the structures and energetics of 98-atom AuPd clusters.

    Science.gov (United States)

    Bruma, Alina; Ismail, Ramli; Paz-Borbón, L Oliver; Arslan, Haydar; Barcaro, Giovanni; Fortunelli, Alessandro; Li, Z Y; Johnston, Roy L

    2013-01-21

    The energetics, structures and segregation of 98-atom AuPd nanoclusters are investigated using a genetic algorithm global optimization technique with the Gupta empirical potential (comparing three different potential parameterisations) followed by local minimizations using Density Functional Theory (DFT) calculations. A shell optimization program algorithm is employed in order to study the energetics of the highly symmetric Leary Tetrahedron (LT) structure and optimization of the chemical ordering of a number of structural motifs is carried out using the Basin Hopping Monte Carlo approach. Although one of the empirical potentials is found to favour the LT structure, it is shown that Marks Decahedral and mixed FCC-HCP motifs are lowest in energy at the DFT level.

  5. Direct determination of a radiation-damage profile with atomic resolution in ion-irradiated platinum. MSC report No. 5030

    International Nuclear Information System (INIS)

    Pramanik, D.; Seidman, D.N.

    1983-05-01

    The field-ion microscope (FIM) technique has been employed to determine directly a radiation damage profile, with atomic resolution, in a platinum specimen which had been irradiated at 80 0 K with 20-keV Kr + ions to a fluence of 5 x 10 12 cm - 2 . It is shown that the microscopic spatial-vacancy distribution (radiation-damage profile) is directly related to the elastically-deposited-energy profile. The experimentally constructed radiation-damage profile is compared with a theoretical damage profile - calculated employing the TRIM Monte Carlo code - and excellent agreement is obtained between the two, thus demonstrating that it is possible to go directly from a microscopic spatial distribution of vacancies to a continuous radiation-damage profile

  6. Assessment of current atomic scale modelling methods for the investigation of nuclear fuels under irradiation: Example of uranium dioxide

    International Nuclear Information System (INIS)

    Bertolus, M.; Freyss, M.; Krack, M.; Devanathan, R.

    2015-01-01

    We focus here on the assessment of the description of interatomic interactions in uranium dioxide using, on the one hand, electronic structure methods, in particular in the Density Functional Theory (DFT) framework, and on the other hand, empirical potential methods. These two types of methods are complementary, the former enabling results to be obtained from a minimal amount of input data and further insight into the electronic and magnetic properties to be achieved, while the latter are irreplaceable for studies where a large number of atoms need to be considered. We consider basic properties as well as specific ones, which are important for the description of nuclear fuel under irradiation. These are especially energies, which are the main data passed on to higher scale models. For this exercise, we limit ourselves to uranium dioxide (UO 2 ) because of the extensive amount of studies available on this system. (authors)

  7. An improved model of fission gas atom transport in irradiated uranium dioxide

    Science.gov (United States)

    Shea, J. H.

    2018-04-01

    The hitherto standard approach to predicting fission gas release has been a pure diffusion gas atom transport model based upon Fick's law. An additional mechanism has subsequently been identified from experimental data at high burnup and has been summarised in an empirical model that is considered to embody a so-called fuel matrix 'saturation' phenomenon whereby the fuel matrix has become saturated with fission gas so that the continued addition of extra fission gas atoms results in their expulsion from the fuel matrix into the fuel rod plenum. The present paper proposes a different approach by constructing an enhanced fission gas transport law consisting of two components: 1) Fick's law and 2) a so-called drift term. The new transport law can be shown to be effectively identical in its predictions to the 'saturation' approach and is more readily physically justifiable. The method introduces a generalisation of the standard diffusion equation which is dubbed the Drift Diffusion Equation. According to the magnitude of a dimensionless Péclet number, P, the new equation can vary from pure diffusion to pure drift, which latter represents a collective motion of the fission gas atoms through the fuel matrix at a translational velocity. Comparison is made between the saturation and enhanced transport approaches. Because of its dependence on P, the Drift Diffusion Equation is shown to be more effective at managing the transition from one type of limiting transport phenomenon to the other. Thus it can adapt appropriately according to the reactor operation.

  8. Microscopic solvation of a lithium atom in water-ammonia mixed clusters: solvent coordination and electron localization in presence of a counterion.

    Science.gov (United States)

    Pratihar, Subha; Chandra, Amalendu

    2008-07-14

    The microsolvation structures and energetics of water-ammonia mixed clusters containing a lithium atom, i.e., Li(H(2)O)(n)(NH(3)), n = 1-5, are investigated by means of ab initio theoretical calculations. Several structural aspects such as the solvent coordination to the metal ion and binding motifs of the free valence electron of the metal are investigated. We also study the energetics aspects such as the dependence of vertical ionization energies on the cluster size, and all these structural and energetics aspects are compared to the corresponding results of previously studied anionic water-ammonia clusters without a metal ion. It is found that the Li-O and Li-N interactions play a very important role in stabilizing the lithium-water-ammonia clusters, and the presence of these metal ion-solvent interactions also affect the characteristics of electron solvation in these clusters. This is seen from the spatial distribution of the singly occupied molecular orbital (SOMO) which holds the ejected valence electron of the Li atom. For very small clusters, SOMO electron density is found to exist mainly at the vicinity of the Li atom, whereas for larger clusters, it is distributed outside the first solvation shell. The free dangling hydrogens of water and ammonia molecules are involved in capturing the SOMO electron density. In some of the conformers, OH{e}HO and OH{e}HN types of interactions are found to be present. The presence of the metal ion at the center of the cluster ensures that the ejected electron is solvated at a surface state only, whereas both surface and interiorlike states were found for the free electron in the corresponding anionic clusters without a metal ion. The vertical ionization energies of the present clusters are found to be higher than the vertical detachment energies of the corresponding anionic clusters which signify a relatively stronger binding of the free electron in the presence of the positive metal counterion. The shifts in different

  9. Small interstitial clusters as opposite defect recombinators in decomposing solid solutions under irradiation

    International Nuclear Information System (INIS)

    Orlov, A.N.; Trushin, Yu.V.

    1988-01-01

    An attempt was made to make allowance for the role of binary and ternary interstitials in the kinetics of radiation point defects both in the presence and in the absence of coherent preseparation. It is shown that in solid solutions, decomposing under irradiation, recombination with binary and ternary interstitials proceeds more quickly than directly, and this difference is more pronounced (from 2 up to 20 time growth) due to defect flow for preseparation at the stage of coherent preseparation formation

  10. Displaying of formation of atomic clusters in radioactive lutetium oxide films

    International Nuclear Information System (INIS)

    Kartashov, V.M.; Troitskata, A.G.

    2002-01-01

    We earlier reported the results of our investigations of electron spectra of radioactive lutetium oxide films on the magnetic β-spectrometer π√2 with momentum resolution 0.04-0.1 %. The researches were conducted many times during ≅15 years, and a lot of the data has resulted us in the conclusion about possible formation of toroidal structures in these films. It is impossible to consider a radioactive oxide layer, deposited on metallic foil support having the electric potential of its foil support on all its depth because of its high dielectric properties. There is the potential gradient (≅10 6 -10 7 V/c) on its depth because of constant outflow of electrons from its surface. Our experiments included in itself also giving a potential, accelerating for electrons, to the metallic foil support. In this case we received a capability to watch the segments of auto emission and low energy Auger electrons. The analysis of the threshold relations and behavior (in time) of the M 4 NN and M 5 NN Auger electron intensities have resulted us in the conclusion that the greatest contribution to structure formations of these oxide films is introduced by electrons of M 4 -, M 5 - and N-sub-shell of ytterbium atoms (being formed as the result of radioactive decay of the lutetium fraction with half-times from 140 to 1200 days). The auto emission electron spectrum testifies to composite scission of M4 and M5 stationary states of the atom. It is possible to offer as the explanation a quantum flat rotator. If the particle orbit un-compresses the solenoid with a magnetic flux Φ, power condition of a rotator E m =h 2 (m-Φ/Φ 0 ) 2 /(8πm e R 0 2 ), where m e - electron mass, R 0 - an electron orbit radius; m - a magnetic quantum number, a Φ 0 =h c/e - a quantum of magnetic flux. At a quantum flow Φ=nΦ 0 (n - integer) and the power spectrum does not differ from a spectrum without the solenoid. The behavior (in time) of the experimental auto emission electron spectrum responds

  11. Specimen preparation of irradiated materials for examination in the atom probe field ion microscope

    International Nuclear Information System (INIS)

    Russell, K.F.; Miller, M.K.

    1994-01-01

    The atom probe field ion microscope (APFIM) requires specimens in the form of ultrasharp needles. Basic protective measures used to reduce exposure druing specimen preparation are discussed. The low-level radioactive specimen blanks may be made using a two-stage electropolishing process using a thin layer of electrolyte floating on a denser inert liquid; this produces a necked region and eventually two specimens from each single blank. The amount of material handled may also be reduced using a micropolishing technique to repolish blunt or fractured specimens. Control of contamination and possible spills is discussed

  12. Algorithms for solving atomic structures of nanodimensional clusters in single crystals based on X-ray and neutron diffuse scattering data

    International Nuclear Information System (INIS)

    Andrushevskii, N.M.; Shchedrin, B.M.; Simonov, V.I.

    2004-01-01

    New algorithms for solving the atomic structure of equivalent nanodimensional clusters of the same orientations randomly distributed over the initial single crystal (crystal matrix) have been suggested. A cluster is a compact group of substitutional, interstitial or other atoms displaced from their positions in the crystal matrix. The structure is solved based on X-ray or neutron diffuse scattering data obtained from such objects. The use of the mathematical apparatus of Fourier transformations of finite functions showed that the appropriate sampling of the intensities of continuous diffuse scattering allows one to synthesize multiperiodic difference Patterson functions that reveal the systems of the interatomic vectors of an individual cluster. The suggested algorithms are tested on a model one-dimensional structure

  13. Study of Pair and many-body interactions in rare-gas halide atom clusters using negative ion zero electron kinetic energy (ZEKE) and threshold photodetachment spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Yourshaw, Ivan [Univ. of California, Berkeley, CA (United States)

    1998-07-09

    The diatomic halogen atom-rare gas diatomic complexes KrBr-, XeBr-, and KrCl- are studied in this work by zero electron kinetic energy (ZEKE) spectroscopy in order to characterize the weak intermolecular diatomic potentials of these species. Also, the ZEKE and threshold photodetachment spectra of the polyatomic clusters ArnBr- (n = 2-9) and ArnI- (n = 2-19) are studied to obtain information about the non-additive effects on the interactions among the atoms. This work is part of an ongoing effort to characterize the pair and many-body potentials of the complete series of rare gas halide clusters. In these studies we obtain information about both the anionic and neutral clusters.

  14. Prediction of the transition energies of atomic No and Lr by the intermediate Hamiltonian coupled cluster method

    International Nuclear Information System (INIS)

    Borschevsky, A.; Eliav, E.; Kaldor, U.; Vilkas, M.J.; Ishikawa, Y.

    2007-01-01

    Complete text of publication follows: Measurements of the spectroscopic properties of the superheavy elements present a serious challenge to the experimentalist. Their short lifetimes and the low quantities of their production necessitate reliable prediction of transition energies to avoid the need for broad wavelength scans and to assist in identifying the lines. Thus, reliable high-accuracy calculations are necessary prior and parallel to experimental research. Nobelium and Lawrencium are at present the two most likely candidates for spectroscopic measurements, with the first experiments planned at GSI, Darmstadt. The intermediate Hamiltonian (IH) coupled cluster method is applied to the ionization potentials, electron affinities, and excitation energies of atomic nobelium and lawrencium. Large basis sets are used (37s31p26d21f16g11h6i). All levels of a particular atom are obtained simultaneously by diagonalizing the IH matrix. The matrix elements correspond to all excitations from correlated occupied orbitals to virtual orbitals in a large P space, and are 'dressed' by folding in excitations to higher virtual orbitals (Q space) at the coupled cluster singles-and-doubles level. Lamb-shift corrections are included. The same approach was applied to the lighter homologues of Lr and No, lutetium and ytterbium, for which many transition energies are experimentally known, in order to assess the accuracy of the calculation. The average absolute error of 20 excitation energies of Lu is 423 cm -1 , and the error limits for Lr are therefore put at 700 cm -1 . Predicted Lr excitations with large transition moments in the prime range for the planned experiment, 20,000-30,000 cm -1 , are 7p → 8s at 20,100 cm -1 and 7p →p 7d at 28,100 cm -1 . In case of Yb, the calculated ionization potential was within 20 cm -1 of the experiment, and the average error of the 20 lowest calculated excitations was about 300 cm -1 . Hence, the error limits of nobelium are set to 800 cm -1

  15. Investigation of modulus hardening of various co-clusters in aged Al-Cu-Mg-Ag alloy by atom probe tomography

    International Nuclear Information System (INIS)

    Bai, Song; Liu, Zhiyi; Ying, Puyou; Wang, Jian; Li, Junlin

    2016-01-01

    The modulus hardening capability of various co-clusters in a low Cu/Mg ratio Al-Cu-Mg-Ag alloy aged at 165 °C is investigated by quantitative atom probe tomography analysis. Prolonged aging from 5 min to 2 h leads to the simultaneous increase in the critical shear stress of both Mg-Ag and Cu-Mg co-clusters. Regardless of the higher shear modulus of Cu-Mg co-clusters, calculation results show that Mg-Ag co-clusters possess a greater modulus hardening capability than Cu-Mg co-clusters, suggesting its primary contribution to the rapid hardening at the early aging stage. As aging extends from 30 min to 2 h, the increment in the critical shear stress of Mg-Ag co-clusters is lower than that of Cu-Mg co-clusters due to the precipitation of high density Ω phase. In addition, the shear modulus of Mg-Ag co-clusters is generally independent on its size at each investigated condition.

  16. Investigation of modulus hardening of various co-clusters in aged Al-Cu-Mg-Ag alloy by atom probe tomography

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Song [Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083 (China); School of Material Science and Engineering, Central South University, Changsha 410083 (China); Liu, Zhiyi, E-mail: liuzhiyi@csu.edu.cn [Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083 (China); School of Material Science and Engineering, Central South University, Changsha 410083 (China); Ying, Puyou; Wang, Jian; Li, Junlin [Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083 (China); School of Material Science and Engineering, Central South University, Changsha 410083 (China)

    2016-06-21

    The modulus hardening capability of various co-clusters in a low Cu/Mg ratio Al-Cu-Mg-Ag alloy aged at 165 °C is investigated by quantitative atom probe tomography analysis. Prolonged aging from 5 min to 2 h leads to the simultaneous increase in the critical shear stress of both Mg-Ag and Cu-Mg co-clusters. Regardless of the higher shear modulus of Cu-Mg co-clusters, calculation results show that Mg-Ag co-clusters possess a greater modulus hardening capability than Cu-Mg co-clusters, suggesting its primary contribution to the rapid hardening at the early aging stage. As aging extends from 30 min to 2 h, the increment in the critical shear stress of Mg-Ag co-clusters is lower than that of Cu-Mg co-clusters due to the precipitation of high density Ω phase. In addition, the shear modulus of Mg-Ag co-clusters is generally independent on its size at each investigated condition.

  17. Mechanism of cluster DNA damage repair in response to high-atomic number and energy particles radiation

    Energy Technology Data Exchange (ETDEWEB)

    Asaithamby, Aroumougame, E-mail: Aroumougame.Asaithamy@UTsouthwestern.edu [Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390 (United States); Chen, David J., E-mail: David.Chen@UTsouthwestern.edu [Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390 (United States)

    2011-06-03

    Low-linear energy transfer (LET) radiation (i.e., {gamma}- and X-rays) induces DNA double-strand breaks (DSBs) that are rapidly repaired (rejoined). In contrast, DNA damage induced by the dense ionizing track of high-atomic number and energy (HZE) particles is slowly repaired or is irreparable. These unrepaired and/or misrepaired DNA lesions may contribute to the observed higher relative biological effectiveness for cell killing, chromosomal aberrations, mutagenesis, and carcinogenesis in HZE particle irradiated cells compared to those treated with low-LET radiation. The types of DNA lesions induced by HZE particles have been characterized in vitro and usually consist of two or more closely spaced strand breaks, abasic sites, or oxidized bases on opposing strands. It is unclear why these lesions are difficult to repair. In this review, we highlight the potential of a new technology allowing direct visualization of different types of DNA lesions in human cells and document the emerging significance of live-cell imaging for elucidation of the spatio-temporal characterization of complex DNA damage. We focus on the recent insights into the molecular pathways that participate in the repair of HZE particle-induced DSBs. We also discuss recent advances in our understanding of how different end-processing nucleases aid in repair of DSBs with complicated ends generated by HZE particles. Understanding the mechanism underlying the repair of DNA damage induced by HZE particles will have important implications for estimating the risks to human health associated with HZE particle exposure.

  18. Mechanism of cluster DNA damage repair in response to high-atomic number and energy particles radiation

    International Nuclear Information System (INIS)

    Asaithamby, Aroumougame; Chen, David J.

    2011-01-01

    Low-linear energy transfer (LET) radiation (i.e., γ- and X-rays) induces DNA double-strand breaks (DSBs) that are rapidly repaired (rejoined). In contrast, DNA damage induced by the dense ionizing track of high-atomic number and energy (HZE) particles is slowly repaired or is irreparable. These unrepaired and/or misrepaired DNA lesions may contribute to the observed higher relative biological effectiveness for cell killing, chromosomal aberrations, mutagenesis, and carcinogenesis in HZE particle irradiated cells compared to those treated with low-LET radiation. The types of DNA lesions induced by HZE particles have been characterized in vitro and usually consist of two or more closely spaced strand breaks, abasic sites, or oxidized bases on opposing strands. It is unclear why these lesions are difficult to repair. In this review, we highlight the potential of a new technology allowing direct visualization of different types of DNA lesions in human cells and document the emerging significance of live-cell imaging for elucidation of the spatio-temporal characterization of complex DNA damage. We focus on the recent insights into the molecular pathways that participate in the repair of HZE particle-induced DSBs. We also discuss recent advances in our understanding of how different end-processing nucleases aid in repair of DSBs with complicated ends generated by HZE particles. Understanding the mechanism underlying the repair of DNA damage induced by HZE particles will have important implications for estimating the risks to human health associated with HZE particle exposure.

  19. Enhanced atomic mobility due to low dose neutron irradiation as measured in a 30Ag at % Zn alloy by Zener relaxation methods

    International Nuclear Information System (INIS)

    Halbwachs, M.; Hillairet, J.; Gonzalez, H.; Cost, J.

    1975-01-01

    Mean atomic jump rates were measured during and after short-time neutron irradiations of a fcc Ag-30 at. percent Zn alloy by monitoring the rate of the Zener relaxation. Measurements made at 40 0 C immediately after rapid suppression of the flux showed significant enhancement of the atomic mobility for a flux of approximately 10 11 fast n/cm 2 .sec and an irradiation time of only 30 sec. The subsequent decrease of the atomic mobility to the thermal equilibrium value was studied and found to follow simple exponential decay. The results are discussed in terms of the nature and concentration of mobile defects created by cascades, the mechanism for defect annihilation and the concentration of sinks

  20. Atom probe study of the microstructural evolution induced by irradiation in Fe-Cu ferritic alloys and pressure vessel steels; Etude a la sonde atomique de l`evolution microstructurale sous irradiation d`alliages ferritiques Fe-Cu et d`aciers de cuve REP

    Energy Technology Data Exchange (ETDEWEB)

    Pareige, P

    1996-04-01

    Pressure vessel steels used in pressurized water reactors are low alloyed ferritic steels. They may be prone to hardening and embrittlement under neutron irradiation. The changes in mechanical properties are generally supposed to result from the formation of point defects, dislocation loops, voids and/or copper rich clusters. However, the real nature of the irradiation induced-damage in these steels has not been clearly identified yet. In order to improve our vision of this damage, we have characterized the microstructure of several steels and model alloys irradiated with electrons and neutrons. The study was performed with conventional and tomographic atom probes. The well known importance of the effects of copper upon pressure vessel steel embrittlement has led us to study Fe-Cu binary alloys. We have considered chemical aging as well as aging under electron and neutron irradiations. The resulting effects depend on whether electron or neutron irradiations ar used for thus. We carried out both kinds of irradiation concurrently so as to compare their effects. We have more particularly considered alloys with a low copper supersaturation representative of that met with the French vessel alloys (0.1% Cu). Then, we have examined steels used on French nuclear reactor pressure vessels. To characterize the microstructure of CHOOZ A steel and its evolution when exposed to neutrons, we have studied samples from the reactor surveillance program. The results achieved, especially the characterization of neutron-induced defects have been compared with those for another steel from the surveillance program of Dampierre 2. All the experiment results obtained on model and industrial steels have allowed us to consider an explanation of the way how the defects appear and grow, and to propose reasons for their influence upon steel embrittlement. (author). 3 appends.

  1. Surface processing with ionized cluster beams: computer simulation

    International Nuclear Information System (INIS)

    Insepov, Z.; Yamada, I.

    1999-01-01

    Molecular Dynamics (MD) and Monte Carlo (MC) models of energetic gas cluster irradiation of a solid surface have been developed to investigate the phenomena of crater formation, sputtering, surface treatment, and the material hardness evaluation by irradiation with cluster ions. Theoretical estimation of crater dimensions formed with Ar gas cluster ion irradiation of different substrates, based on hydrodynamics and MD simulation, are presented. The atomic scale shock waves arising from cluster impact were obtained by calculating the pressure, temperature and mass-velocity of the target atoms. The crater depth is given as a unique 1/3 dependence on the cluster energy and on the cold material Brinell hardness number (BHN). A new 'true material hardness' scale which can be very useful for example for thin film coatings deposited on a soft substrate, is defined. This finding could be used as a new technique for measuring of a material hardness. Evolution of surface morphology under cluster ion irradiation was described by the surface relaxation equation which contains a term of crater formation at cluster impact. The formation of ripples on a surface irradiated with oblique cluster ion beams was predicted. MD and MC models of Decaborane ion (B 10 H 14 ) implantation into Si and the following rapid thermal annealing (RTA) have been developed

  2. Radiation hardening: study of production velocity and post-irradiation recovery of defect clusters produced by neutron irradiation at 77 K

    International Nuclear Information System (INIS)

    Gonzalez, Hector C.; Miralles, Monica T.

    1999-01-01

    This work includes three basic studies using radiation hardening of Cu single crystals irradiated at 77 K in the RA-1-reactor of CNEA: 1) The initial of a production curve of defect clusters originated during radiation until 5.2 x 10 20 n m 2 . The shape of the curve is compared with those obtained from measurement of resistivity increased (Δρ) with neutronic doses (φt) and the acceptance of the linear dependency of Δρ with Frenkel Pairs concentration (PFs); 2) The isochronal hardening recovery in the temperature interval of stage V (T > 450 K). The existence of the sub-stages Vb (∼ 550 K) and Vc (∼ 587 K), determined for the first time from hardening measurements, are shown and compared with results obtained by other techniques; 3) Isothermal recoveries performed in the temperature interval of the sub-stage Vc to determine phenomenologically the apparent activation energy of the sub-stage. The value obtained was in agreement with the energy for Cu vacancies auto diffusion. (author)

  3. The study of the irradiation-induced embrittlement of reactor pressure vessels. Analysis of surveillance test specimens of a commercial nuclear reactor pressure vessel studied by three-dimensional atom probe and positron annihilation

    International Nuclear Information System (INIS)

    Nagai, Yasuyoshi; Toyama, Takeshi; Hasegawa, Masayuki

    2007-01-01

    The study of embrittlement of nuclear power reactor pressure vessels (RPVs) is of critical importance for the safety assessment in the nuclear industry. Some origins of embrittlement are attributed to fine Cu precipitates, matrix defects, grain boundary segregation of P and late blooming phase. This review article described nanostructural observation by three-dimensional atom probe (3DAP) and positron annihilation spectroscopy (PAS). The density and sizes of Cu-rich nanoprecipitates and grain boundary segregation are sensitively detected by 3DAP, and vacancies are probed by PAS. Element analysis around vacancies and fine microstructural Cu precipitates not containing vacancies are successfully observed by a coincidence doppler broadening method. The nanostructural evolution of irradiation-induced Cu-rich nanoprecipitates (CRNPs) and vacancy clusters in surveillance test specimens of commercial nuclear reactor pressure vessel steel welds of Doel-2 in Belgium were revealed by combining 3DAP and PAS. In both medium (0.13 wt%) and high (0.30 wt%) Cu welds, the CRNPs were found to form readily at the very beginning of the reactor lifetime. On the other hand, small vacancy clusters start appearing after the initial Cu precipitates and accumulate steadily with increasing neutron dose. The CRNPs were also observed at very low dose rate of neutrons in the test specimen of Calder Hall Reactor of Japan Atomic Power Company. The significant enhancement of these Cu precipitates results in the embrittlement in practical RPVs. At very high dose of 2.2x10 18 n/cm 2 by JMTR, the Cu precipitates were scarcely observed, and the irradiation-induced embrittlement was primarily caused from vacancy-impurity complexes and dislocation loops. (author)

  4. On the use of big-bang method to generate low-energy structures of atomic clusters modeled with pair potentials of different ranges.

    Science.gov (United States)

    Marques, J M C; Pais, A A C C; Abreu, P E

    2012-02-05

    The efficiency of the so-called big-bang method for the optimization of atomic clusters is analysed in detail for Morse pair potentials with different ranges; here, we have used Morse potentials with four different ranges, from long- ρ = 3) to short-ranged ρ = 14) interactions. Specifically, we study the efficacy of the method in discovering low-energy structures, including the putative global minimum, as a function of the potential range and the cluster size. A new global minimum structure for long-ranged ρ = 3) Morse potential at the cluster size of n= 240 is reported. The present results are useful to assess the maximum cluster size for each type of interaction where the global minimum can be discovered with a limited number of big-bang trials. Copyright © 2011 Wiley Periodicals, Inc.

  5. Vicinage forces between molecular and atomic fragments dissociated from small hydrogen clusters and their effects on energy distributions

    International Nuclear Information System (INIS)

    Barriga-Carrasco, Manuel D.; Garcia-Molina, Rafael

    2003-01-01

    In this paper we analyze the dynamic evolution of molecular and atomic fragments of small hydrogen clusters interacting with thin solid foils. We compare the vicinage forces, calculated within the dielectric formalism, for H + , H 0 , and H 2 + fragments. Using a molecular dynamics numerical code we determine the energy distribution of the fragments after interacting with the target. This distribution is compared to experimental results for protons coming from the fragmentation of v=2.02 a.u. H 2 + ions impinging on an aluminum foil; a fraction of neutral H 0 is needed to be included in the simulation to get a good agreement with the experimental results. The H 2 + energy spectra for v=5.42 a.u. H 3 + interacting with amorphous carbon is also determined. The asymmetry in the Coulomb peaks appearing in the energy spectra both experimentally and in our calculation is opposite for H 2 + than in H + ; kinematic effects and differences in the electronic stopping are enough to reproduce the difference in the alignment of H 2 + and H + fragments

  6. Analysis and evaluation of atom level composition variation and property change due to materials irradiation damage

    International Nuclear Information System (INIS)

    Furuya, Kazuo; Takeguchi, Masaki; Mitsuishi, Kazuki; Song Menhi; Saito, Tetsuya

    2000-01-01

    This study aims at general elucidation of atom level composition variation due to radiation damage and property change accompanied with this under intending to stressing application of the in-situ analysis and evaluation apparatus on material radiation damage. Then, by using the electron energy loss spectroscopy (EELS) capable of showing a power in composition analysis at microscopic region, measurement of EELS on crystal structure change after heat treatment of Xe precipitation was carried out under parallel of its high resolution observation. As a result, a precipitation with less than 30 nm in diameter was observed on a specimen inserted at 473 K. Xe precipitates in crystalline state began to change at 623 K, to be perfectly gassy state at 773 K. In an energy filter image (EFI) using low loss of Xe, distribution of crystalline and non-crystalline Xe was observed. In EELS, peaks at 14.6 and 15.3 eV were observed in 300 and 773 K, respectively, which were thought to be plasmon. And, difference of peak position at the core loss was thought to reflex difference of Xe state at 300 and 773 K. (G.K.)

  7. Interaction of atomic and low-energy deuterium with tungsten pre-irradiated with self-ions

    International Nuclear Information System (INIS)

    Ogorodnikova, O. V.; Markelj, S.; Toussaint, U. von

    2016-01-01

    Polycrystalline tungsten (W) specimens were pre-irradiated with self-ions to create identical samples with high density of defects up to ∼2.5 μm near the surface. Then, W specimens were exposed to either thermal atomic deuterium (D) beam with an incident energy of ∼0.2 eV or low energy D plasma with the incident energy varied between 5 and 200 eV at different sample temperatures. Each sample was exposed once at certain temperature and fluence. The D migration and accumulation in W were studied post-mortem by nuclear reaction method. It was shown that the rate of the D to occupy radiation-induced defects increases with increasing the incident energy, ion flux, and temperature. Experimental investigation was accompanied by modelling using the rate-equation model. Moreover, the analytical model was developed and benchmarked against numerical model. The calculations of the deuterium diffusion with trapping at radiation-induced defects in tungsten by analytical model are consistent with numerical calculations using rate-equation model. The data of reflection and penetration of atomic and low-energy D were taking from calculations using molecular dynamics (MD) with Juslin interatomic potentials and a binary collision code TRIM. MD calculations show an agreement with a binary collision code TRIM only in a very narrow range of deuterium energies between 1 and 20 eV. Incorporation of the data of reflection and penetration of deuterium in the macroscopic modelling has been done to verify the range of validity of calculations using MD and binary collision code TRIM by comparison of modelling results with experimental data. Modelling results are consistent with experiments using reflection and penetration data of D obtained from TRIM code for incident ion energy above 1 eV. Otherwise, the parameters obtained from MD should be incorporated in the rate-equation model to have a good agreement with the experiments

  8. Vacancy defects in electron irradiated RPV steels studied by positron lifetime

    Energy Technology Data Exchange (ETDEWEB)

    Moser, P; Li, X H [CEA Centre d` Etudes de Grenoble, 38 (France). Dept. de Recherche Fondamentale sur la Matiere Condensee; Akamatsu, M; Van Duysen, J C [Electricite de France (EDF), 77 - Ecuelles (France)

    1994-12-31

    Specimens of French RPV (reactor pressure vessels) steels at different rates of segregation have been irradiated at 150 and 288 deg C with 3 MeV electrons (irradiation dose: 4*10{sup 19} e-/cm{sup 2}). Vacancy defects are studied by positron lifetime measurements before and after irradiation and at each step of isochronal annealing. After 150 deg C irradiation, a recovery step is observed in both specimens, for annealing treatments in the range 220-370 deg C and is attributed to the dissociation of vacancy-impurity complexes. The size of vacancy clusters never overcome 10 empty atomic volumes. If ``fresh`` dislocations are created just before irradiation, big vacancy clusters could be formed. After 288 deg C irradiation, small vacancy cluster of 4-10 empty atomic volumes are observed. (authors). 3 figs., 7 refs.

  9. DAMAGE IN MOLYBDENUM ASSOCIATED WITH NEUTRON IRRADIATION AND SUBSEQUENT POST-IRRADIATION ANNEALING

    Energy Technology Data Exchange (ETDEWEB)

    Mastel, B.

    1963-07-23

    Molybdemum containing carbon was studied in an attempt to establish the combined effect of impurity content and neutron irradiation on the properties and structure of specific metals. Molybdenum foils were punched into discs and heat treated in vacuum. They were then slow-cooled and irradiated. After irradiation and subsequent decay of radioactivity to a low level the foils were subjected to x-ray diffraction measurements. Cold-worked foils with less than 10 ppm carbon showed no change in microstructure due to irradiation. Molybdenum foils that were annealed prior to irradiation showed spot defects. In foils containing up to 500 ppm carbon, it was concluded that the small loops present after irradiation are due to the clustering of point defects at interstitial carbon atoms, followed by collapse to form a dislocation loop. The amount of lattice expansion after irradiation was strongly dependent on impurity content. Neutron irradiation was found to reduce the number of active slip systems. (M.C.G.)

  10. Annealing and cluster formation of defects in a cascade

    International Nuclear Information System (INIS)

    Martynenko, Yu.V.

    1975-01-01

    The behaviour of radiative defects after a dynamic cascade of atomic collisions caused by irradiation by neutrons or accelerated heavy ions if theoretically investigated. In investig.ation, apart from processes of vacancy recombination, cluster formation and interstitial atoms the diffusive ''spreading'' of point defects from the initial region is taken into account. Since interstitial atoms are more mobile, all the processes are divided into two stages: at the first stage only interstitial atoms diffuse, and vacancies are stationary; at the second stage vacancies are mobile, and interstitial atoms are either ''spread'' over the whole volume, or are united into stable clusters. The number of defects and clusters is calculated depending on energy of cascade, atomic number of the material and temperature

  11. Photo-irradiation effects on GaAs atomic layer epitaxial growth. GaAs no genshiso epitaxial seicho ni okeru hikari reiki koka

    Energy Technology Data Exchange (ETDEWEB)

    Mashita, M.; Kawakyu, Y.; Sasaki, M.; Ishikawa, H. (Toshiba Corp., Kawasaki (Japan). Research and Development Center)

    1990-08-10

    Single atomic layer epitaxy (ALE) aims at controlling a growing film at a precision of single molecular layer. In this article, it is reported that the growth temperature range of ALE was expanded by the vertical irradiation of KrF exima laser (248 nm) onto the substrate for the ALE growth of GaAs using the metalorganic chemical vapor deposition (MOCVD) method. Thanks for the results of the above experiment, it was demonstrated that the irradiation effect was not thermal, but photochemical. In addition, this article studies the possibility of adsorption layer irradiation and surface irradiation as the photo-irradiation mechanism, and points out that coexistence of both irradiation mechanisms can be considered and, in case of exima laser, strong possibility of direct irradiation of the adsorption layer because of its high power density. Hereinafter, by using both optical growth ALE and thermal growth ALE jointly, the degree of freedom of combination of hetero ALE increases and its application to various material systems becomes possible. 16 refs., 6 figs.

  12. Clustering of DSB in DNA by X-Ray and a-particle irradiation in MCF-7 cells studied with anti γ-H2AX

    International Nuclear Information System (INIS)

    Tapia, O.; Soto, J.; Castro, F.A.; Berciano, Ma T; Lafarga, M.; Cos, S.; Sanchez-Barcelo, E.

    2007-01-01

    Among the effects produced by the ionizing radiations in cellular DNA, double strand breaks (DSB) are considered particularly important. These ruptures and their grouping in certain points, clustering, are acknowledged as the cause for mutagenic effects and cellular death. In this work we present the methodology and the results of the application of the DSB - DNA marking technique by using anti γ-H2AX, taking human cancerous cells MCF-7 as model and X-rays and a particles as irradiation agents. The obtained results are showed in a qualitative way like a set of figures. Are shows the effects of a dose of 2 Gy X-rays in the DSB - DNA after 30 minutes of the irradiation that responds to a certain pattern in which a spatially homogenous irradiation interacts with the DNA. As in previous case, the effects of X-rays in the DSB - DNA shows a different pattern affecting the cells that are in mitosis. Also, the effects of a dose of 2 Gy X-rays obtained after 24 hours of irradiation shows a number of DSB smaller, which is indicative of the repairing process. The results of the irradiation with a dose of 0.1 Gy originated from a particles cause a smaller number of DSB. Nevertheless, the existence of a bigger clustering with the appearance of clearly more intense points is appraised. Also, the effect of the irradiation is showed as an aligned trace of clusters that is possible to attribute to the passing of a a particle through the cellular nucleus. (Author)

  13. Long-term irradiation effects on reactor-pressure vessel steels. Investigations on the nanometer scale

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Arne

    2017-06-01

    The exposure of reactor pressure vessel (RPV) steels to neutron irradiation gives rise to irradiation-enhanced diffusion, a rearrangement of solute atoms and, consequently, a degradation of the mechanical properties. The increasing age of existing nuclear power plants raises new questions specific to long-term operation. Two of them are addressed in this thesis: flux effects and the late-blooming effect. Can low-flux irradiations up to a given fluence be reproduced by more rapid high-flux irradiations up to the same fluence? Can the irradiation response of RPV steels be extrapolated to higher fluences or are there unexpected ''late-blooming'' effects. Small-angle neutron scattering (SANS), atom-probe tomography (APT) and Vickers-hardness testing were applied. A novel Monte-Carlo based fitting algorithm for SANS data was implemented in order to derive statistically reliable characteristics of irradiation-induced solute-atom clusters. APT was applied in selected cases to gain additional information on the composition and the shape of clusters. Vickers hardness testing was performed on the SANS samples to link the nanometer-scale changes to irradiation hardening. The investigations on flux effects show that clusters forming upon high-flux irradiation are smaller and tend to have a higher number density compared to low-flux irradiations at a given neutron fluence. The measured flux dependence of the cluster-size distribution is consistent with the framework of deterministic growth (but not with coarsening) in combination with radiation-enhanced diffusion. Since the two effects on cluster-size and volume fraction partly cancel each other out, no significant effect on the hardening is observed. The investigations of a possible late-blooming effect indicate that the very existence (yes or no) of such an effect depends on the irradiation conditions. Irradiations at lower fluxes and a lower temperature (255 C) give rise to a significant increase of the

  14. The Effect of Indium Content on the Atomic Environment and Cluster Stability of GeSe4Inx=10,15 Glasses

    Directory of Open Access Journals (Sweden)

    Georgios S. E. Antipas

    2015-01-01

    Full Text Available The atomic environments of two chalcogenide glasses, with compositions GeSe4In10 and GeSe4In15, were studied via Reverse Monte Carlo and Density Functional Theory. Indium content demoted Ge–Se bonding in favor of Se-In while the contribution of Se–Se in the first coordination shell order was faint. Upon transition to the richer In glass, there was formation of rich Ge-centered clusters at radial distances further than 4 Å from the RMC box center, which was taken to signify a reduction of Ge–Se interactions. Cluster coordination by Se promoted stability while, very conclusively, In coordination lowered cluster stability by intervening in the Ge–Se and Se–Se networks.

  15. Ligand-free gold atom clusters adsorbed on graphene nano sheets generated by oxidative laser fragmentation in water

    Science.gov (United States)

    Lau, Marcus; Haxhiaj, Ina; Wagener, Philipp; Intartaglia, Romuald; Brandi, Fernando; Nakamura, Junji; Barcikowski, Stephan

    2014-08-01

    Over three decades after the first synthesis of stabilized Au55-clusters many scientific questions about gold cluster properties are still unsolved and ligand-free colloidal clusters are difficult to fabricate. Here we present a novel route to produce ultra-small gold particles by using a green technique, the laser ablation and fragmentation in water, without using reductive or stabilizing agents at any step of the synthesis. For fabrication only a pulsed laser, a gold-target, pure water, sodium hydroxide and hydrogen peroxide are deployed. The particles are exemplarily hybridized to graphene supports showing that these carbon-free colloidal clusters might serve as versatile building blocks.

  16. Food irradiation

    International Nuclear Information System (INIS)

    Anon.

    1985-01-01

    The article explains what radiation does to food to preserve it. Food irradiation is of economic importance to Canada because Atomic Energy of Canada Limited is the leading world supplier of industrial irradiators. Progress is being made towards changing regulations which have restricted the irradiation of food in the United States and Canada. Examples are given of applications in other countries. Opposition to food irradiation by antinuclear groups is addressed

  17. Computational evaluation of sub-nanometer cluster activity of singly exposed copper atom with various coordinative environment in catalytic CO2 transformation

    Science.gov (United States)

    Shanmugam, Ramasamy; Thamaraichelvan, Arunachalam; Ganesan, Tharumeya Kuppusamy; Viswanathan, Balasubramanian

    2017-02-01

    Metal cluster, at sub-nanometer level has a unique property in the activation of small molecules, in contrast to that of bulk surface. In the present work, singly exposed active site of copper metal cluster at sub-nanometer level was designed to arrive at the energy minimised configurations, binding energy, electrostatic potential map, frontier molecular orbitals and partial density of states. The ab initio molecular dynamics was carried out to probe the catalytic nature of the cluster. Further, the stability of the metal cluster and its catalytic activity in the electrochemical reduction of CO2 to CO were evaluated by means of computational hydrogen electrode via calculation of the free energy profile using DFT/B3LYP level of theory in vacuum. The activity of the cluster is ascertained from the fact that the copper atom, present in a two coordinative environment, performs a more selective conversion of CO2 to CO at an applied potential of -0.35 V which is comparatively lower than that of higher coordinative sites. The present study helps to design any sub-nano level metal catalyst for electrochemical reduction of CO2 to various value added chemicals.

  18. The effects of oxide evolution on mechanical properties in proton- and neutron-irradiated Fe-9%Cr ODS steel

    Energy Technology Data Exchange (ETDEWEB)

    Swenson, M.J., E-mail: matthewswenson1@u.boisestate.edu [Boise State University, 1910 University Drive, Boise, ID 83725 (United States); Dolph, C.K. [Boise State University, 1910 University Drive, Boise, ID 83725 (United States); Wharry, J.P. [Boise State University, 1910 University Drive, Boise, ID 83725 (United States); Purdue University, 400 Central Drive, West Lafayette, IN 47907 (United States)

    2016-10-15

    The objective of this study is to evaluate the effect of irradiation on the strengthening mechanisms of a model Fe-9%Cr oxide dispersion strengthened steel. The alloy was irradiated with protons or neutrons to a dose of 3 displacements per atoms at 500 °C. Nanoindentation was used to measure strengthening due to irradiation, with neutron irradiation causing a greater increase in yield strength than proton irradiation. The irradiated microstructures were characterized using transmission electron microscopy and atom probe tomography (APT). Cluster analysis reveals solute migration from the Y-Ti-O-rich nanoclusters to the surrounding matrix after both irradiations, though the effect is more pronounced in the neutron-irradiated specimen. Because the dissolved oxygen atoms occupy interstitial sites in the iron matrix, they contribute significantly to solid solution strengthening. The dispersed barrier hardening model relates microstructure evolution to the change in yield strength, but is only accurate if solid solution contributions to strengthening are considered simultaneously.

  19. Computer simulation of defect cluster

    Energy Technology Data Exchange (ETDEWEB)

    Kuramoto, Eiichi [Kyushu Univ., Kasuga, Fukuoka (Japan). Research Inst. for Applied Mechanics

    1996-04-01

    In order to elucidate individual element process of various defects and defect clusters of used materials under irradiation environments, interatomic potential with reliability was investigated. And for comparison with experimental results, it is often required to adopt the temperature effect and to investigate in details mechanism of one dimensional motion of micro conversion loop and so forth using the molecular dynamic (MD) method. Furthermore, temperature effect is also supposed for stable structure of defects and defect clusters, and many problems relating to alloy element are also remained. And, simulation on photon life at the defects and defect clusters thought to be important under comparison with equipment can also be supposed an improvement of effectiveness due to relation to theses products. In this paper, some topics in such flow was extracted to explain them. In particular, future important problems will be potential preparation of alloy, structure, dynamic behavior and limited temperature of intralattice atomic cluster. (G.K.)

  20. Chemical inhomogeneity in In{sub x}Ga{sub 1-x}N and ZnO. A HRTEM study on atomic scale clustering

    Energy Technology Data Exchange (ETDEWEB)

    Bartel, T.P.

    2008-10-08

    Nanostructuration as well as the nucleation and growth of nanoparticles pervades the development of modern materials and devices. Quantitative high resolution transmission electron microscopy (HRTEM) is currently being developed for a structural and chemical analysis at an atomic scale. It is used in this thesis to study the chemical inhomogeneity and clustering in In{sub x}Ga{sub 1-x}N, InN and ZnO. A methodology for reliable quantitative HRTEM is rst de ned: it necessitates a damage free sample, the avoidance of electron beam damage and the control of microscope instabilities. With these conditions satis ed, the reliability of quantitative HRTEM is demonstrated by an accurate measurement of lattice relaxation in a thin TEM sample. Clustering in an alloy can then be distinguished from a random distribution of atoms. In In{sub x}Ga{sub 1-x}N for instance, clustering is detected for concentrations x>0.1. The sensitivity is insufficient to determine whether clustering is present for lower concentrations. HRTEM allows to identify the amplitude and the spatial distribution of the decomposition which is attributed to a spinodal decomposition. In InN, nanometer scale metallic indium inclusions are detected. With decreasing size of the metallic clusters, the photoluminescence of the sample shifts towards the infrared. This indicates that the inclusions may be responsible for the infrared activity of InN. Finally, ZnO grown homoepitaxially on zinc-face and oxygen-face substrates is studied. The O-face epilayer is strained whereas the Zn-face epilayer is almost strain free and has a higher crystalline quality. Quantitative analysis of exit wave phases is in good agreement with simulations, but the signal to noise ratio needs to be improved for the detection of single point defects. (orig.)

  1. Chemical inhomogeneity in InxGa1-xN and ZnO. A HRTEM study on atomic scale clustering

    International Nuclear Information System (INIS)

    Bartel, T.P.

    2008-01-01

    Nanostructuration as well as the nucleation and growth of nanoparticles pervades the development of modern materials and devices. Quantitative high resolution transmission electron microscopy (HRTEM) is currently being developed for a structural and chemical analysis at an atomic scale. It is used in this thesis to study the chemical inhomogeneity and clustering in In x Ga 1-x N, InN and ZnO. A methodology for reliable quantitative HRTEM is rst de ned: it necessitates a damage free sample, the avoidance of electron beam damage and the control of microscope instabilities. With these conditions satis ed, the reliability of quantitative HRTEM is demonstrated by an accurate measurement of lattice relaxation in a thin TEM sample. Clustering in an alloy can then be distinguished from a random distribution of atoms. In In x Ga 1-x N for instance, clustering is detected for concentrations x>0.1. The sensitivity is insufficient to determine whether clustering is present for lower concentrations. HRTEM allows to identify the amplitude and the spatial distribution of the decomposition which is attributed to a spinodal decomposition. In InN, nanometer scale metallic indium inclusions are detected. With decreasing size of the metallic clusters, the photoluminescence of the sample shifts towards the infrared. This indicates that the inclusions may be responsible for the infrared activity of InN. Finally, ZnO grown homoepitaxially on zinc-face and oxygen-face substrates is studied. The O-face epilayer is strained whereas the Zn-face epilayer is almost strain free and has a higher crystalline quality. Quantitative analysis of exit wave phases is in good agreement with simulations, but the signal to noise ratio needs to be improved for the detection of single point defects. (orig.)

  2. Contributions of Cu-rich clusters, dislocation loops and nanovoids to the irradiation-induced hardening of Cu-bearing low-Ni reactor pressure vessel steels

    Energy Technology Data Exchange (ETDEWEB)

    Bergner, F., E-mail: f.bergner@hzdr.de [Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden (Germany); Gillemot, F. [Centre for Energy Research of the Hungarian Academy of Sciences, 29-33 Konkoly-Thege street, 1121 Budapest XII (Hungary); Hernández-Mayoral, M.; Serrano, M. [Division of Materials, CIEMAT, Avenida Complutense 22, 28040 Madrid (Spain); Török, G. [Wigner Research Center for Physics of the Hungarian Academy of Sciences, 29-33 Konkoly-Thege street, 1121 Budapest XII (Hungary); Ulbricht, A.; Altstadt, E. [Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden (Germany)

    2015-06-15

    Highlights: • TEM and SANS were applied to estimate mean size and number density of loops, nanovoids and Cu-rich clusters. • A three-feature dispersed-barrier hardening model was applied to estimate the yield stress increase. • The values and errors of the dimensionless obstacle strength were estimated in a consistent way. • Nanovoids are stronger obstacles for dislocation glide than dislocation loops, loops are stronger than Cu-rich clusters. • For reactor-relevant conditions, Cu-rich clusters contribute most to hardening due to their high number density. - Abstract: Dislocation loops, nanovoids and Cu-rich clusters (CRPs) are known to represent obstacles for dislocation glide in neutron-irradiated reactor pressure vessel (RPV) steels, but a consistent experimental determination of the respective obstacle strengths is still missing. A set of Cu-bearing low-Ni RPV steels and model alloys was characterized by means of SANS and TEM in order to specify mean size and number density of loops, nanovoids and CRPs. The obstacle strengths of these families were estimated by solving an over-determined set of linear equations. We have found that nanovoids are stronger than loops and loops are stronger than CRPs. Nevertheless, CRPs contribute most to irradiation hardening because of their high number density. Nanovoids were only observed for neutron fluences beyond typical end-of-life conditions of RPVs. The estimates of the obstacle strength are critically compared with reported literature data.

  3. Atomic polarizabilities

    International Nuclear Information System (INIS)

    Safronova, M. S.; Mitroy, J.; Clark, Charles W.; Kozlov, M. G.

    2015-01-01

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed

  4. Atomic polarizabilities

    Energy Technology Data Exchange (ETDEWEB)

    Safronova, M. S. [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Mitroy, J. [School of Engineering, Charles Darwin University, Darwin NT 0909 (Australia); Clark, Charles W. [Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, Gaithersburg, Maryland 20899-8410 (United States); Kozlov, M. G. [Petersburg Nuclear Physics Institute, Gatchina 188300 (Russian Federation)

    2015-01-22

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed.

  5. Irradiation and various cytotoxic drugs enhance tyrosine phosphorylation and β1-integrin clustering in human A549 lung cancer cells in a substratum-dependent manner in vitro

    International Nuclear Information System (INIS)

    Cordes, N.; Beinke, C.; Beuningen, D. van; Plasswilm, L.

    2004-01-01

    Background and purpose: interactions of cells with a substratum, especially extracellular matrix proteins, initiate clustering of integrin receptors in the cell membrane. This process represents the initial step for the activation of signaling pathways regulating survival, proliferation, differentiation, adhesion, and migration, and could, furthermore, be important for cellular resistance-mediating mechanisms against radiation or cytotoxic drugs. The lack of data elucidating the impact of irradiation or cytotoxic drugs on this important phenomenon led to this study on human A549 lung cancer cells in vitro. Material and methods: the human lung carcinoma cell line A549 grown on polystyrene or fibronectin (FN) was irradiated with 0-8 Gy or treated with cisplatin (0.1-50 μM), paclitaxel (0.1-50 nM), or mitomycin (0.1-50 μM). Colony formation assays, immunofluorescence staining in combination with activation of integrin clustering using anti-β 1 -integrin antibodies (K20), and Western blotting for tyrosine phosphorylation under treatment of cells with the IC 50 for irradiation (2 Gy; IC 50 = 2.2 Gy), cisplatin (2 μM), paclitaxel (5 nM), or mitomycin (7 μM) were performed. Results: attachment of cells to FN resulted in a significantly reduced radio- and chemosensitivity compared to polystyrene. The clustering of β 1 -integrins examined by immunofluorescence staining was only stimulated by irradiation, cisplatin, paclitaxel, or mitomycin in case of cell attachment to FN. By contrast, tyrosine phosphorylation, as one of the major events following β 1 -integrin clustering, showed a 3.7-fold, FN-related enhancement, and treatment of cells with the IC 50 of radiation, cisplatin, paclitaxel, or mitomycin showed a substratum-dependent induction. Conclusion: for the first time, a strong influence of irradiation and a variety of cytotoxic drugs on the clustering of β 1 -integrins could be shown. This event is a prerequisite for tyrosine phosphorylation and, thus, the

  6. The emergence of nonbulk properties in supported metal clusters: negative thermal expansion and atomic disorder in Pt nanoclusters supported on gamma-Al2O3.

    Science.gov (United States)

    Sanchez, Sergio I; Menard, Laurent D; Bram, Ariella; Kang, Joo H; Small, Matthew W; Nuzzo, Ralph G; Frenkel, Anatoly I

    2009-05-27

    The structural dynamics-cluster size and adsorbate-dependent thermal behaviors of the metal-metal (M-M) bond distances and interatomic order-of Pt nanoclusters supported on a gamma-Al(2)O(3) are described. Data from scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) studies reveal that these materials possess a dramatically nonbulklike nature. Under an inert atmosphere small, subnanometer Pt/gamma-Al(2)O(3) clusters exhibit marked relaxations of the M-M bond distances, negative thermal expansion (NTE) with an average linear thermal expansion coefficient alpha = (-2.4 +/- 0.4) x 10(-5) K(-1), large static disorder and dynamical bond (interatomic) disorder that is poorly modeled within the constraints of classical theory. The data further demonstrate a significant temperature-dependence to the electronic structure of the Pt clusters, thereby suggesting the necessity of an active model to describe the cluster/support interactions mediating the cluster's dynamical structure. The quantitative dependences of these nonbulklike behaviors on cluster size (0.9 to 2.9 nm), ambient atmosphere (He, 4% H(2) in He or 20% O(2) in He) and support identity (gamma-Al(2)O(3) or carbon black) are systematically investigated. We show that the nonbulk structural, electronic and dynamical perturbations are most dramatically evidenced for the smallest clusters. The adsorption of hydrogen on the clusters leads to an increase of the Pt-Pt bondlengths (due to a lifting of the surface relaxation) and significant attenuation of the disorder present in the system. Oxidation of these same clusters has the opposite effect, leading to an increase in Pt-Pt bond strain and subsequent enhancement in nonbulklike thermal properties. The structural and electronic properties of Pt nanoclusters supported on carbon black contrast markedly with those of the Pt/gamma-Al(2)O(3) samples in that neither NTE nor comparable levels of atomic disorder are observed. The Pt

  7. Cluster generator

    Science.gov (United States)

    Donchev, Todor I [Urbana, IL; Petrov, Ivan G [Champaign, IL

    2011-05-31

    Described herein is an apparatus and a method for producing atom clusters based on a gas discharge within a hollow cathode. The hollow cathode includes one or more walls. The one or more walls define a sputtering chamber within the hollow cathode and include a material to be sputtered. A hollow anode is positioned at an end of the sputtering chamber, and atom clusters are formed when a gas discharge is generated between the hollow anode and the hollow cathode.

  8. Cross section measurements of the processes occurring in the fragmentation of Hn+ (3 ≤ n ≤ 35) hydrogen clusters induced by high speed (60 keV/u) collisions on helium atoms

    International Nuclear Information System (INIS)

    Louc, Sandrine

    1997-01-01

    Different processes involved in the fragmentation of ionised hydrogen clusters H 3 + (H 2 ) (n-3)/2 (n = 5-35) have been studied in the same experiment: the fragmentation of the cluster is induced by the collision with an helium atom at high velocity (≅ c/100). The collision is realised in reversed kinematic - clusters are accelerated - which allows the detection of neutral and charged fragments. The different channels of fragmentation are identified by using coincidence techniques. For all the cluster sizes studied the capture cross sections of one electron of the target by the cluster is equal to the capture cross section of the H 3 + ion. In the same way, the dissociation cross section of the H 3 + core of the cluster does not depend on cluster size. These fragmentation processes are due to the interaction of H 3 + core of the cluster and the helium atom without ionization of another component of the cluster. On the contrary, the cross sections of loss of one, two and three molecules by the cluster and the dissociation cross section of the cluster in all its molecular components depends strongly on the cluster size. This dependence is different from the one measured for the metastable decay of the cluster. Thus, the process of loss of molecules induced by a collision should correspond to a different dissociation mechanism. In regard of the singularities observed for the size dependence, the H 9 + , H 15 + , H 19 + and H 29 + clusters could be the 'core' of the biggest clusters. These observation are in agreement with the size effects of smaller magnitude observed for the dissociation cross section (all the processes). The values of the cross section for the process of at least one ionization of the cluster indicate that about 80% of the fragmentation events result from this process. (author)

  9. Coupled cluster and density functional theory calculations of atomic hydrogen chemisorption on pyrene and coronene as model systems for graphene hydrogenation.

    Science.gov (United States)

    Wang, Ying; Qian, Hu-Jun; Morokuma, Keiji; Irle, Stephan

    2012-07-05

    Ab initio coupled cluster and density functional theory studies of atomic hydrogen addition to the central region of pyrene and coronene as molecular models for graphene hydrogenation were performed. Fully relaxed potential energy curves (PECs) were computed at the spin-unrestricted B3LYP/cc-pVDZ level of theory for the atomic hydrogen attack of a center carbon atom (site A), the midpoint of a neighboring carbon bond (site B), and the center of a central hexagon (site C). Using the B3LYP/cc-pVDZ PEC geometries, we evaluated energies at the PBE density functional, as well as ab initio restricted open-shell ROMP2, ROCCSD, and ROCCSD(T) levels of theory, employing cc-pVDZ and cc-pVTZ basis sets, and performed a G2MS extrapolation to the ROCCSD(T)/cc-pVTZ level of theory. In agreement with earlier studies, we find that only site A attack leads to chemisorption. The G2MS entrance channel barrier heights, binding energies, and PEC profiles are found to agree well with a recent ab initio multireference wave function theory study (Bonfanti et al. J. Chem. Phys.2011, 135, 164701), indicating that single-reference open-shell methods including B3LYP are sufficient for the theoretical treatment of the interaction of graphene with a single hydrogen atom.

  10. Beams of mass-selected clusters: realization and first experiments

    International Nuclear Information System (INIS)

    Kamalou, O.

    2007-04-01

    The main objective of this work concerns the production of beams of mass-selected clusters of metallic and semiconductor materials. Clusters are produced in magnetron sputtering source combined with a gas aggregation chamber, cooled by liquid nitrogen circulation. Downstream of the cluster source, a Wiley-McLaren time-of-flight setup allows to select a given cluster size or a narrow size range. The pulsed mass-selected cluster ion beam is separated from the continuous neutral one by an electrostatic 90-quadrupole deflector. After the deflector, the density of the pulsed beam amounts to about 10 3 particles/cm 3 . Preliminary deposition experiments of mass-selected copper clusters with a deposition energy of about 0.5 eV/atom have ben performed on highly oriented pyrolytic graphite (HOPG) substrates, indicating that copper clusters are evidently mobile on the HOPG-surface until they reach cleavage steps, dislocation lines or other surface defects. In order to lower the cluster mobility on the HOPG-surface, we have first irradiated HOPG samples with slow highly charged ions (high dose) in order to create superficial defects. In a second step we have deposited mass-selected copper clusters on these pre-irradiated samples. The first analysis by AFM (Atomic Force Microscopy) techniques showed that the copper clusters are trapped on the defects produced by the highly charged ions. (author)

  11. Conductivity of γ-irradiated LiF

    International Nuclear Information System (INIS)

    Guckelsberger, K.

    1974-01-01

    The conductivity of pure monocrystalline LiF, γ-irradiated, was measured in the temperature range 0.3-100 deg K. The F centers produced by irradiation disperse phonons like point defects, the corresponding fluorine atoms on inter-lattice sites appear as clusters of about 10 A diameter, and high irradiation doses (above 10 8 R) give rise to extensive perturbation zones. Each of these 3 defects influences heat conduction in a characteristic temperature range and may thus be analyzed during irradiation and consecutive recovery [fr

  12. Indium tin oxide surface smoothing by gas cluster ion beam

    CERN Document Server

    Song, J H; Choi, W K

    2002-01-01

    CO sub 2 cluster ions are irradiated at the acceleration voltage of 25 kV to remove hillocks on indium tin oxide (ITO) surfaces and thus to attain highly smooth surfaces. CO sub 2 monomer ions are also bombarded on the ITO surfaces at the same acceleration voltage to compare sputtering phenomena. From the atomic force microscope results, the irradiation of monomer ions makes the hillocks sharper and the surfaces rougher from 1.31 to 1.6 nm in roughness. On the other hand, the irradiation of CO sub 2 cluster ions reduces the height of hillocks and planarize the ITO surfaces as smooth as 0.92 nm in roughness. This discrepancy could be explained by large lateral sputtering yield of the cluster ions and re-deposition of sputtered particles by the impact of the cluster ions on surfaces.

  13. On the size and structure of helium snowballs formed around charged atoms and clusters of noble gases.

    Science.gov (United States)

    Bartl, Peter; Leidlmair, Christian; Denifl, Stephan; Scheier, Paul; Echt, Olof

    2014-09-18

    Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx(+) ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He20(84)Kr2(+) and the isobaric, nonmagic He41(84)Kr(+). Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr(+), which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa(+) [J. Phys. Chem. A 2011, 115, 7300] that reveal three shells of icosahedral symmetry. HenArx(+) (2 ≤ x ≤ 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx(+) suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr(+) to Kr3(+). Previously reported strong anomalies at He12Kr2(+) and He12Kr3(+) [Kim , J. H.; et al. J. Chem. Phys. 2006, 124, 214301] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex(+) (x ≤ 3). The distributions of HenKr(+) and HenXe(+) show strikingly similar, broad features that are absent from the distribution of HenAr(+); differences are tentatively ascribed to the very different fragmentation dynamics of these ions.

  14. In situ atomic-level observation of the formation of platinum silicide at platinum-silicon oxide interfaces under electron irradiation

    Directory of Open Access Journals (Sweden)

    Takeshi Nagase

    2018-05-01

    Full Text Available In situ atomic-level observation of the formation of Pt2Si at Pt/SiOx interface by electronic excitation under electron irradiation was performed by using scanning transmission electron microscopy. Scanning of an electron-beam probe stimulates silicide formation at the Pt/SiOx interface; the change in the Pt column corresponding to Pt2Si formation with a crystallographic orientation of (001Pt//(001Pt2Si and [110]Pt//[110]Pt2Si was observed in high-angle annular dark-field images.

  15. Radiation situation and irradiation level in forest workers in places of timber works in alienation zone of Chernobyl Atomic Power Plant

    International Nuclear Information System (INIS)

    Kalashnikova, Z.V.; Karachov, Yi.Yi.; Berezhna, T.Yi.; Kuchma, M.D.

    1997-01-01

    The radiation hygienic situation in the forest plots and dose load of the personnel at timber works in the alienation zone of the Chernobyl Atomic Power Plant was evaluated.It has been revealed that the density of contamination of the forest soil at the areas of timber works was 155.4-447.3 kBq centre dot m 2 . Maximum year equivalent dose on the lungs and total dose of external and internal irradiation in the forest workers in the zone of alienation during the work at the areas were about 40% of the values of the respective dose limits for the population of B category

  16. Elastic atomic displacements and color center creation in LiF crystals irradiated with 3-, 9- and 12-MeV Au ions

    International Nuclear Information System (INIS)

    Sorokin, M.V.; Papaleo, R.M.; Schwartz, K.

    2009-01-01

    Creation of color centers in LiF under irradiation with 3-12-MeV Au ions was studied. Comparison of experimental data of color center creation with computer simulation of the energy deposition and elastic atomic displacements reveals the role of elastic collisions in defect creation by these ions, which have comparable magnitudes of electronic and elastic stopping. The experimentally measured efficiency of color center creation and that predicted by the simulation of elastic displacements have a similar dependence on the projectile energy. Thus, the color center creation is mainly associated with the elastic collisions, despite the relatively large values of the electronic stopping power for these ions. (orig.)

  17. Computational evaluation of sub-nanometer cluster activity of singly exposed copper atom with various coordinative environment in catalytic CO{sub 2} transformation

    Energy Technology Data Exchange (ETDEWEB)

    Shanmugam, Ramasamy [Department of Chemistry, Thiagarajar College, Madurai, Tamilnadu 625 009 (India); National Center for Catalysis Research, Indian Institute of Technology Madras, Chennai, Tamilnadu 600 036 (India); Thamaraichelvan, Arunachalam [Faculty of Allied Health Sciences, Chettinad Hospital & Research Institute, Kelambakkam, Tamilnadu 603 103 (India); Ganesan, Tharumeya Kuppusamy [Department of Chemistry, The American College, Madurai, Tamilnadu 625 002 (India); Viswanathan, Balasubramanian, E-mail: bvnathan@iitm.ac.in [National Center for Catalysis Research, Indian Institute of Technology Madras, Chennai, Tamilnadu 600 036 (India)

    2017-02-28

    Highlights: • On interaction with adsorbate CO{sub 2,} the adsorbent changes its configuration around the metal. • Electron transfer is faster in low coordinative environment of Cu. • CO formation is more favorable on Cu sites with even coordination number. • Cu at coordination number two has a over potential of −0.35 V. - Abstract: Metal cluster, at sub-nanometer level has a unique property in the activation of small molecules, in contrast to that of bulk surface. In the present work, singly exposed active site of copper metal cluster at sub-nanometer level was designed to arrive at the energy minimised configurations, binding energy, electrostatic potential map, frontier molecular orbitals and partial density of states. The ab initio molecular dynamics was carried out to probe the catalytic nature of the cluster. Further, the stability of the metal cluster and its catalytic activity in the electrochemical reduction of CO{sub 2} to CO were evaluated by means of computational hydrogen electrode via calculation of the free energy profile using DFT/B3LYP level of theory in vacuum. The activity of the cluster is ascertained from the fact that the copper atom, present in a two coordinative environment, performs a more selective conversion of CO{sub 2} to CO at an applied potential of −0.35 V which is comparatively lower than that of higher coordinative sites. The present study helps to design any sub-nano level metal catalyst for electrochemical reduction of CO{sub 2} to various value added chemicals.

  18. A combination method for simulation of secondary knock-on atoms of boron carbide induced by neutron irradiation in SPRR-300

    International Nuclear Information System (INIS)

    Wu, Jian-Chun; Feng, Qi-Jie; Liu, Xian-Kun; Zhan, Chang-Yong; Zou, Yu; Liu, Yao-Guang

    2016-01-01

    A multiscale sequence of simulation should be used to predict properties of materials under irradiation. Binary collision theory and molecular dynamics (MDs) method are commonly used to characterize the displacement cascades induced by neutrons in a material. In order to reduce the clock time spent for the MD simulation of damages induced by high-energy primary knock-on atoms (PKAs), the damage zones were split into sub-cascade according to the sub-cascade formation criteria. Two well-known codes, Geant4 and TRIM, were used to simulate high-energy PKA-induced cascades in B_4C and then produce the secondary knock-on atom (SKA) energy spectrum. It has been found that both high-energy primary knock-on B and C atoms move a long range in the boron carbide. These atoms produce sub-cascades at the tip of trajectory. The energy received by most of the SKAs is <10 keV, which can be used as input to reduce the clock time spent for MD simulation.

  19. Benchmark calculations of excess electrons in water cluster cavities: balancing the addition of atom-centered diffuse functions versus floating diffuse functions.

    Science.gov (United States)

    Zhang, Changzhe; Bu, Yuxiang

    2016-09-14

    Diffuse functions have been proved to be especially crucial for the accurate characterization of excess electrons which are usually bound weakly in intermolecular zones far away from the nuclei. To examine the effects of diffuse functions on the nature of the cavity-shaped excess electrons in water cluster surroundings, both the HOMO and LUMO distributions, vertical detachment energies (VDEs) and visible absorption spectra of two selected (H2O)24(-) isomers are investigated in the present work. Two main types of diffuse functions are considered in calculations including the Pople-style atom-centered diffuse functions and the ghost-atom-based floating diffuse functions. It is found that augmentation of atom-centered diffuse functions contributes to a better description of the HOMO (corresponding to the VDE convergence), in agreement with previous studies, but also leads to unreasonable diffuse characters of the LUMO with significant red-shifts in the visible spectra, which is against the conventional point of view that the more the diffuse functions, the better the results. The issue of designing extra floating functions for excess electrons has also been systematically discussed, which indicates that the floating diffuse functions are necessary not only for reducing the computational cost but also for improving both the HOMO and LUMO accuracy. Thus, the basis sets with a combination of partial atom-centered diffuse functions and floating diffuse functions are recommended for a reliable description of the weakly bound electrons. This work presents an efficient way for characterizing the electronic properties of weakly bound electrons accurately by balancing the addition of atom-centered diffuse functions and floating diffuse functions and also by balancing the computational cost and accuracy of the calculated results, and thus is very useful in the relevant calculations of various solvated electron systems and weakly bound anionic systems.

  20. Contributions of Cu-rich clusters, dislocation loops and nanovoids to the irradiation-induced hardening of Cu-bearing low-Ni reactor pressure vessel steels

    Science.gov (United States)

    Bergner, F.; Gillemot, F.; Hernández-Mayoral, M.; Serrano, M.; Török, G.; Ulbricht, A.; Altstadt, E.

    2015-06-01

    Dislocation loops, nanovoids and Cu-rich clusters (CRPs) are known to represent obstacles for dislocation glide in neutron-irradiated reactor pressure vessel (RPV) steels, but a consistent experimental determination of the respective obstacle strengths is still missing. A set of Cu-bearing low-Ni RPV steels and model alloys was characterized by means of SANS and TEM in order to specify mean size and number density of loops, nanovoids and CRPs. The obstacle strengths of these families were estimated by solving an over-determined set of linear equations. We have found that nanovoids are stronger than loops and loops are stronger than CRPs. Nevertheless, CRPs contribute most to irradiation hardening because of their high number density. Nanovoids were only observed for neutron fluences beyond typical end-of-life conditions of RPVs. The estimates of the obstacle strength are critically compared with reported literature data.

  1. Cluster-cluster clustering

    International Nuclear Information System (INIS)

    Barnes, J.; Dekel, A.; Efstathiou, G.; Frenk, C.S.; Yale Univ., New Haven, CT; California Univ., Santa Barbara; Cambridge Univ., England; Sussex Univ., Brighton, England)

    1985-01-01

    The cluster correlation function xi sub c(r) is compared with the particle correlation function, xi(r) in cosmological N-body simulations with a wide range of initial conditions. The experiments include scale-free initial conditions, pancake models with a coherence length in the initial density field, and hybrid models. Three N-body techniques and two cluster-finding algorithms are used. In scale-free models with white noise initial conditions, xi sub c and xi are essentially identical. In scale-free models with more power on large scales, it is found that the amplitude of xi sub c increases with cluster richness; in this case the clusters give a biased estimate of the particle correlations. In the pancake and hybrid models (with n = 0 or 1), xi sub c is steeper than xi, but the cluster correlation length exceeds that of the points by less than a factor of 2, independent of cluster richness. Thus the high amplitude of xi sub c found in studies of rich clusters of galaxies is inconsistent with white noise and pancake models and may indicate a primordial fluctuation spectrum with substantial power on large scales. 30 references

  2. Modeling of DNA damage-cluster, cell-cycle and repair pathway dependent radiosensitivity after low- and high-LET irradiation

    International Nuclear Information System (INIS)

    Guenther, Paul

    2017-01-01

    irradiation. This method is able to qualitatively predict the influence of the cell-cycle and the radiation quality on radiosensitivity. Based on this, two approaches for the LEM prediction of the Relative Biological Effectiveness (RBE) are compared. The first approach predicts the RBE based on the survival of asynchronous cells. The second approach predicts the RBE from the sum of survival curves of the subpopulations, which contribute to the asynchronous cell population. Both approaches lead to qualitatively similar results. In the context of describing the microscopic dose deposition of ion irradiation by the amorphous track structure, two questions are addressed: 1. Is it possible to improve the prediction of cell survival after ion irradiation by a more sophisticated composition of the direct and indirect effect? 2. is the amorphous track structure an appropriate model of the dose deposition regarding the DNA damage clustering on the nm-scale or is it necessary to evaluate single ionizations on the molecular level? Regarding the first question, it is shown that a more detailed evaluation of the direct and indirect effect improves the agreement of the LEM predictions to data. Concerning the second question, it is shown that the amorphous track structure can be used for the prediction of DNA damage induction on the nm-scale similar to an ab initio Monte Carlo simulation. In the context of cell-survival modeling, the relevant length scale for DNA damage-clustering is often discussed. The iDSBs und cDSBs used in the GLOBLE and LEM are referring to DNA damage clustering on the μm-scale. There are also models which predict the cell survival after ion irradiation based on complex DNA-damage-clusters on the nm-scale. This work shows, that complex DNA damage-clusters on the μm-scale are correlated to damage clusters on the nm-scale. Therefore, it is possible to predict the cell survival after ion irradiation based on both scales. However, the cell survival after photon

  3. Characterisation of the early stages of solute clustering in 1Ni-1.3Mn welds containing Cu

    Energy Technology Data Exchange (ETDEWEB)

    Hyde, J.M., E-mail: jonathan.hyde@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); National Nuclear Laboratory Ltd, B168 Harwell, Didcot, Oxon OX11 0QJ (United Kingdom); Burke, M.G. [Bechtel Bettis Inc., 814 Pittsburgh-McKeesport Blvd, West Mifflin, Pittsburgh 15122-0079 (United States); Boothby, R.M.; English, C.A. [National Nuclear Laboratory Ltd, B168 Harwell, Didcot, Oxon OX11 0QJ (United Kingdom)

    2009-04-15

    Microstructural characterisation of neutron irradiated low alloy steels is important for developing mechanistic understanding of irradiation embrittlement. This work is focused on the early stages of irradiation-induced clustering in a low Cu (0.03 wt%), high Ni ({approx}1 wt%) weld. The weld was irradiated at a very high dose rate and then examined by atom probe (energy-compensated position-sensitive atom probe (ECOPoSAP) and local electrode atom probe (LEAP)) with supporting microstructural information obtained by small angle neutron scattering (SANS) and positron annihilation (PALA). It was demonstrated that extreme care must be taken optimising parameters used to characterise the extent of clustering. This is particularly important during the early stages of irradiation-damage when the clusters are poorly defined and significant compositional variations are present in what is traditionally described as matrix. Analysis of the irradiated materials showed increasing clustering of Cu, Mn, Ni and Si with dose. In the low Cu steel the results showed that initially the irradiation damage results in clustering of Mn, Ni and Si, but at very high doses, at very high dose rates, redistribution of Si is significantly more advanced than that for Mn and Ni.

  4. The behavior of interstitials in irradiated graphite

    International Nuclear Information System (INIS)

    Pedraza, D.F.

    1991-01-01

    A computer model is developed to simulate the behavior of self-interstitials with particular attention to clustering. Owing to the layer structure of graphite, atomistic simulations can be performed using a large parallelepipedic supercell containing a few layers. In particular, interstitial clustering is studied here using a supercell that contains two basal planes only. Frenkel pairs are randomly produced. Interstitials are placed at sites between the crystal planes while vacancies are distributed in the two crystal planes. The size of the computational cell is 20000 atoms and periodic boundary conditions are used in two dimensions. Vacancies are assumed immobile whereas interstitials are given a certain mobility. Two point defect sinks are considered, direct recombination of Frenkel pairs and interstitial clusters. The clusters are assumed to be mobile up to a certain size where they are presumed to become loop nuclei. Clusters can shrink by emission of singly bonded interstitials or by recombination of a peripheral interstitial with a neighboring vacancy. The conditions under which interstitial clustering occurs are reported. It is shown that when clustering occurs the cluster size population gradually shifts towards the largest size cluster. The implications of the present results for irradiation growth and irradiation-induced amorphization are discussed

  5. Effects of neutron irradiation on microstructure and deformation behaviour of mono- and polycrystalline molybdenum and its alloys

    DEFF Research Database (Denmark)

    Singh, B.N.; Evans, J.H.; Horsewell, A.

    1998-01-01

    The influence of neutron irradiation on microstructural evolution and mechanical properties of mono- and polycrystalline molybdenum and its alloys has been investigated. Tensile specimens and 3 mm diameter discs of monocrystals of pure molybdenum and Mo-5%Re were irradiated with fission neutrons...... microscopy are presented and discussed in terms of intracascade clustering of self-interstitial atoms and the role of one-dimensional glide of these clusters in controlling microstructural evolution and the resulting mechanical properties....

  6. Evolution of precipitation in reactor pressure vessel steel welds under neutron irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Lindgren, Kristina, E-mail: kristina.lindgren@chalmers.se [Department of Physics, Chalmers University of Technology, SE-412 96 Göteborg (Sweden); Boåsen, Magnus [Department of Solid Mechanics, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Stiller, Krystyna [Department of Physics, Chalmers University of Technology, SE-412 96 Göteborg (Sweden); Efsing, Pål [Department of Solid Mechanics, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Vattenfall Ringhals AB, SE-430 22 Väröbacka (Sweden); Thuvander, Mattias [Department of Physics, Chalmers University of Technology, SE-412 96 Göteborg (Sweden)

    2017-05-15

    Reactor pressure vessel steel welds are affected by irradiation during operation. The irradiation results in nanometre cluster formation, which in turn affects the mechanical properties of the material, e.g. the ductile-to-brittle transition temperature is shifted to higher levels. In this study, cluster formation is characterised in high Ni (1.58%) low Cu (0.04%) steel welds identical to Ringhals R4 welds, using atom probe tomography in both surveillance material and in material irradiated at accelerated dose rates. Clusters containing mainly Ni and Mn, but also some Si and Cu were observed in all of the irradiated materials. Their evolution did not change drastically during irradiation; the clusters grew and new clusters were nucleated. Hence, both the cluster number density and the average size increased with irradiation time. Some flux effects were observed when comparing the high flux material and the surveillance material. The surveillance material has a lower cluster number density, but larger clusters. The resulting impact on the mechanical properties of these two effects cancel out, resulting in a measured hardness that seems to be on the same trend as the high flux material. The dispersed barrier hardening model with an obstacle strength factor of 0.15 was found to reproduce the increase in hardness. In the investigated high flux materials, the clusters' Cu content was higher. - Highlights: •Clustering in a low Cu, high Ni reactor pressure vessel steel weld is studied. •The clusters nucleate and grow during irradiation, and consist of Ni, Mn, Si, and Cu. •High flux neutron irradiated material is compared to surveillance material. •High flux was found to result in smaller clusters with a larger number density. •Hardness follows the same dependence on fluence, independent of flux.

  7. SCF MS Xα determination of ionization energies and atomic populations of octaedral TiO6-8 cluster

    International Nuclear Information System (INIS)

    Michel-Calendini, F.M.; Chermette, H.; Pertosa, P.

    1979-02-01

    The ionization energies of titanium and oxygen states in BaTiO 3 crystal have been investigated through the self-consistent-field-Xα-scattered-wave (SCF MS Xα) method, with the Slater transition state model, applied to a TiO 6 -8 cluster of octaedral symmetry. Ionization energies and electronic charge distribution are compared to XPS data and related to results obtained from tight-binding band computations

  8. Preparation and electrical-property characterization of poly(vinyl chloride)-derived carbon nanosheet by ion beam irradiation-induced carbon clustering and carbonization

    Science.gov (United States)

    Jung, Chan-Hee; Sohn, Joon-Yong; Kim, Hyo-Sub; Hwang, In-Tae; Lee, Hong-Joon; Shin, Junhwa; Choi, Jae-Hak

    2018-05-01

    In this work, we demonstrated that carbon nanosheet (CNS) can easily be produced by a room-temperature, solid-state proton irradiation-induced clustering of poly(vinyl chloride) (PVC) films followed by carbonization. The results of the optical, chemical, and structural analyses revealed that oxidized and sp2-hybridized carbon clusters were effectively created in the PVC thin film by combined dehydrochlorination and inter-coupling reactions during proton irradiation. This was further converted to pseudo-hexagonally-structured nano-crystalline CNS with 2-D symmetry and metallic transporting character by high-temperature treatment. As a result, the CNS exhibited a very high electrical conductivity (587 S/cm) without a significant change in their thickness, a low surface roughness (0.36 nm), and a high work function (5.11 eV). These findings demonstrate that the radiation-based approach opens new avenues for the design and development of 2-D CNS as a graphene allotrope for the application of electronic devices, including field-effect transistors, electric heating devices, biosensors, supercapacitors, and fuel cells.

  9. On the application of the weak-beam technique to the determination of the sizes of small point-defect clusters in ion-irradiated copper

    International Nuclear Information System (INIS)

    Jenkins, M. L.

    1998-01-01

    We have made an analysis of the conditions necessary for the successful use of the weak-beam technique for identifying and characterizing small point-defect clusters in ion-irradiated copper. The visibility of small defects was found to depend only weakly on the magnitude of the beam-convergence. In general, the image sizes of small clusters were found to be most sensitive to the magnitude of Sa with the image sizes of some individual defects changing by large amounts with changes as small as 0.025 nm -1 . The most reliable information on the true defect size is likely to be obtained by taking a series of 5-9 micrographs with a systematic variation of deviation parameter from 0.2-0.3 nm -1 . This procedure allows size information to be obtained down to a resolution limit of about 0.5 nm for defects situated throughout a foil thickness of 60 nm. The technique has been applied to the determination of changes in the sizes of small defects produced by a low-temperature in-situ irradiation and annealing experiment

  10. Hematologic studies of irradiated survivors in Hiroshima, Japan. Refractory anemia occurring in survivors of the atomic bombing in Nagasaki, Japan

    Energy Technology Data Exchange (ETDEWEB)

    Yamasowa, Yoshimichi; Lange, R D; Wright, S W; Tomonaga, Masanobu; Kurasaki, Hirotami; Matsuoka, Shigeru; Matsunaga, Haruji

    1959-01-01

    This document contains 2 reports on the effects of radiation on the survivors of the atomic explosions in Hiroshima and Nagasaki. The first report is a hematologic survey conducted 33 to 44 months after the detonation of the atomic bomb in Hiroshima, Japan. The hematologic findings on a total of 824 survivors are compared with those on a control group of 1145 residents of Kure. Although statistical differences are apparent in the two groups, when one takes into account errors inherent in the hematologic methods themselves and differences in the possible incidence of parasitism and nutrition it would be unwarranted to attribute the slight changes found to radiation effect. The data presented here seem to indicate that radiation resulting from the explosion of the atomic bomb in Hiroshima, on August 6, 1945, has not significantly varied the hematologic values as analyzed in this report over a three-to four-year period. In the second report, the case histories of six Nagasaki atomic bomb survivors who developed refractory anemia are presented. Four of these individuals received undoubted radiation injury. The fact that refractory anemia may occur as a late manifestation of exposure to atomic radiation is pointed out. 15 references, 5 figures, 2 tables.

  11. Electron and positron contributions to the displacement per atom profile in bulk multi-walled carbon nanotube material irradiated with gamma rays

    International Nuclear Information System (INIS)

    Leyva Fabelo, Antonio; Pinnera Hernandez, Ibrahin; Leyva Pernia, Diana

    2013-01-01

    The electron and positron contributions to the effective atom displacement cross-section in multi-walled carbon nanotube bulk materials exposed to gamma rays were calculated. The physical properties and the displacement threshold energy value reported in literature for this material were taken into account. Then, using the mathematical simulation of photon and particle transport in matter, the electron and positron energy flux distributions within the irradiated object were also calculated. Finally, considering both results, the atom displacement damage profiles inside the analyzed bulk carbon nanotube material were determined. The individual contribution from each type of secondary particles generated by the photon interactions was specified. An increasing behavior of the displacement cross-sections for all the studied particles energy range was observed. The particles minimum kinetic energy values that make probabilistically possible the single and multiple atom displacement processes were determined. The positrons contribution importance to the total number of point defects generated during the interaction of gamma rays with the studied materials was confirmed

  12. Basic Equations Interrelate Atomic and Nuclear Properties to Patterns at the Size Scales of the Cosmos, Extended Clusters of Galaxies, Galaxies, and Nebulae

    Science.gov (United States)

    Allen, Rob

    2016-09-01

    Structures within molecules and nuclei have relationships to astronomical patterns. The COBE cosmic scale plots, and large scale surveys of galaxy clusters have patterns also repeating and well known at atomic scales. The Induction, Strong Force, and Nuclear Binding Energy Periods within the Big Bang are revealed to have played roles in the formation of these large scale distributions. Equations related to the enormous patterns also model chemical bonds and likely nucleus and nucleon substructures. ratios of the forces that include gravity are accurately calculated from the distributions and shapes. In addition, particle masses and a great many physical constants can be derived with precision and accuracy from astrophysical shapes. A few very basic numbers can do modelling from nucleon internals to molecules to super novae, and up to the Visible Universe. Equations are also provided along with possible structural configurations for some Cold Dark Matter and Dark Energy.

  13. Clustering of germanium atoms in silica glass responsible for the 3.1 eV emission band studied by optical absorption and X-ray absorption fine structure analysis

    International Nuclear Information System (INIS)

    Yoshida, Tomoko; Muto, Shunsuke; Yuliati, Leny; Yoshida, Hisao; Inada, Yasuhiro

    2009-01-01

    Correlation between the 3.1 eV emission band and local atomic configuration was systematically examined for Ge + implanted silica glass by UV-vis optical absorption spectroscopy and X-ray absorption fine structure (XAFS) analysis. The 2.7 eV emission band, commonly observed in defective silica, was replaced by the sharp and intense 3.1 eV emission band for the Ge + fluence > 2 x 10 16 cm -2 , in which UV-vis absorption spectra suggested clustering of Ge atoms with the size ∼1 nm. XAFS spectroscopy indicated that the Ge atoms were under coordinated with oxygen atoms nearly at a neutral valence state on average. The present results are consistent with the previous ESR study but imply that the small Ge clusters rather than the O=Ge: complexes (point defects) are responsible for the 3.1 eV emission band.

  14. Stacking and Branching in Self-Aggregation of Caffeine in Aqueous Solution: From the Supramolecular to Atomic Scale Clustering.

    Science.gov (United States)

    Tavagnacco, Letizia; Gerelli, Yuri; Cesàro, Attilio; Brady, John W

    2016-09-22

    The dynamical and structural properties of caffeine solutions at the solubility limit have been investigated as a function of temperature by means of MD simulations, static and dynamic light scattering, and small angle neutron scattering experiments. A clear picture unambiguously supported by both experiment and simulation emerges: caffeine self-aggregation promotes the formation of two distinct types of clusters: linear aggregates of stacked molecules, formed by 2-14 caffeine molecules depending on the thermodynamic conditions and disordered branched aggregates with a size in the range 1000-3000 Å. While the first type of association is well-known to occur under room temperature conditions for both caffeine and other purine systems, such as nucleotides, the presence of the supramolecular aggregates has not been reported previously. MD simulations indicate that branched structures are formed by caffeine molecules in a T-shaped arrangement. An increase of the solubility limit (higher temperature but also higher concentration) broadens the distribution of cluster sizes, promoting the formation of stacked aggregates composed by a larger number of caffeine molecules. Surprisingly, the effect on the branched aggregates is rather limited. Their internal structure and size do not change considerably in the range of solubility limits investigated.

  15. Disintegration of C60 by Xe ion irradiation

    International Nuclear Information System (INIS)

    Kalish, R.; Samoiloff, A.; Hoffman, A.; Uzan-Saguy, C.

    1993-01-01

    The Changes in resistivity of fullerene (C 60 ) films subject to 320 keV Xe ion irradiation are investigated as a function of ion dose. From a comparison of this dependence with similar data on other Xe irradiated C containing insulating materials and with data on C implanted fused quartz, it is concluded that upon ion impact C 60 clusters completely disintegrate. This disintegration releases about 60 C atoms which disperse amongst the remaining intact C 60 spheres giving rise to hopping conductivity between isolated C atoms. 16 refs., 3 figs

  16. Positron annihilation lifetime measurements of austenitic stainless and ferritic/martensitic steels irradiated in the SINQ target irradiation program

    Science.gov (United States)

    Sato, K.; Xu, Q.; Yoshiie, T.; Dai, Y.; Kikuchi, K.

    2012-12-01

    Titanium-doped austenitic stainless steel (JPCA) and reduced activated ferritic/martensitic steel (F82H) irradiated with high-energy protons and spallation neutrons were investigated by positron annihilation lifetime measurements. Subnanometer-sized (steel, the positron annihilation lifetime of the bubbles decreased with increasing irradiation dose and annealing temperature because the bubbles absorb additional He atoms. In the case of JPCA steel, the positron annihilation lifetime increased with increasing annealing temperature above 773 K, in which case the dissociation of complexes of vacancy clusters with He atoms and the growth of He bubbles was detected. He bubble size and density were also discussed.

  17. Concurrent irradiation effects with ionization and displacement on the formation of defect clusters in magnesium aluminate spinel

    Energy Technology Data Exchange (ETDEWEB)

    Yasuda, Kazuhiro; Morisaki, Rieko; Kinoshita, Chiken [Kyushu Univ., Fukuoka (Japan). Faculty of Engineering; Abe, Hiroaki; Naramoto, Hiroshi

    1997-03-01

    Single crystals of MgAl{sub 2}O{sub 4} were irradiated concurrently with a homogeneous ion beam and a focused electron beam in TEM-accelerator facilities to get insight into the concurrent irradiation effects with ionization and displacements. Various kinds of 30 or 300 keV ions (He{sup +}, O{sup +}, Mg{sup +}, Ar{sup +} and Xe{sup +}) and 200 keV or 1 MeV electrons were used to provide a wide range of nuclear (S{sub n}) and ionizing (S{sub e}) stopping powers. Dislocation loops were formed both inside and outside the electron beam at 870 K under concurrent irradiation with 30 keV ions (He{sup +}, Ar{sup +} and Xe{sup +}) and 1 MeV electrons. In the case of irradiation with 300 keV ions and 200 keV electrons, on the other hand, a preferential formation of voids or bubbles and a suppressive formation of dislocation loops were observed inside the electron beam. On the basis of these results, we pointed out the importance of the nuclear stopping power which causes the diffusion of cations toward the outside of the focused electron beam. (author)

  18. Cluster-assistant generation of multiply charged atomic ions in nanosecond laser ionization of seeded methyl iodide beam

    International Nuclear Information System (INIS)

    Luo Xiaolin; Niu Dongmei; Kong Xianglei; Wen Lihua; Liang Feng; Pei Kemei; Wang Bin; Li Haiyang

    2005-01-01

    The photoionization of methyl iodide beam seeded in argon and helium is studied by time-of-flight mass spectrometry using a 25 ns, 532 nm Nd-YAG laser with intensities in the range of 2 x 10 10 -2 x 10 11 W/cm 2 . Multiply charged ions of I q+ (q = 2-3) and C 2+ with tens of eV kinetic energies have been observed when laser interacts with the middle part of the pulsed molecular beam, whose peak profiles are independent on the laser polarization directions. Strong evidences show that these ions are coming from the Coulomb explosion of multiply charged CH 3 I clusters, and laser induced inverse bremsstrahlung absorption of caged electrons plays a key role in the formation of multiply charged ions

  19. Monitoring of the morphologic reconstruction of deposited ablation products in laser irradiation of silicon

    Directory of Open Access Journals (Sweden)

    Vlasova M.

    2008-01-01

    Full Text Available Using electron microscopy, atomic force microscopy, X-ray microanalysis, and IR spectroscopy, it was established that, in the regime of continuous laser irradiation of silicon at P = 170 W in different gaseous atmospheres with an oxygen impurity, SiOx composite films with a complex morphology form. The main components of ablation products are clusters that form during flight of ablation products and as a result of separation of SiOx-clusters from the zone of the irradiation channel. The roughness and density of the films depend on the heating temperature of the target surface and the type of deposited clusters.

  20. Atomic diffusion in laser irradiated Ge rich GeSbTe thin films for phase change memory applications

    Science.gov (United States)

    Privitera, S. M. S.; Sousa, V.; Bongiorno, C.; Navarro, G.; Sabbione, C.; Carria, E.; Rimini, E.

    2018-04-01

    The atomic diffusion and compositional variations upon melting have been studied by transmission electron microscopy and electron energy loss spectroscopy in Ge rich GeSbTe films, with a composition optimized for memory applications. Melting and quenching has been achieved by laser pulses, in order to study pure thermal diffusion without electric field induced electromigration. The effect of different laser energy densities has been investigated. The diffusion of Ge atoms in the molten phase is found to be a prominent mechanism and, by employing finite elements computational analysis, a diffusion coefficient of Ge on the order of 5  ×  10-5 cm2 s-1 has been estimated.

  1. An extended formula for the energy spectrum of sputtered atoms from a material irradiated by light ions

    International Nuclear Information System (INIS)

    Ono, T.; Aoki, Y.; Yamamura, Y.; Kawamura, T.; Kenmotsu, T.

    2004-10-01

    We extend a formula proposed by Kenmotsu et al. (hereafter Paper I), which fits with the energy spectrum of atoms sputtered from a heavy material hit by low-energy light ions (H + , D + , T + , He + ) by taking into account an inelastic energy loss neglected in Paper I. We assume that primary knock-on atoms produced by ions backscattered at large angles do not lose energy while penetrating the material up to the surface, instead of the energy-loss model used in Paper I. The extended formula is expressed in terms of a normalized energy-distribution function and is compared with the data calculated with the ACAT code for 50 eV, 100 eV and 1 keV D + ions impinging on a Fe target. Our formula fits well with the data in a wide range of incident energy. (author)

  2. Effect of random inhomogeneities in the spatial distribution of radiation-induced defect clusters on carrier transport through the thin base of a heterojunction bipolar transistor upon neutron irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Puzanov, A. S.; Obolenskiy, S. V., E-mail: obolensk@rf.unn.ru; Kozlov, V. A. [Lobachevsky State University of Nizhny Novgorod (NNSU) (Russian Federation)

    2016-12-15

    We analyze the electron transport through the thin base of a GaAs heterojunction bipolar transistor with regard to fluctuations in the spatial distribution of defect clusters induced by irradiation with a fissionspectrum fast neutron flux. We theoretically demonstrate that the homogeneous filling of the working region with radiation-induced defect clusters causes minimum degradation of the dc gain of the heterojunction bipolar transistor.

  3. Cluster fusion algorithm: application to Lennard-Jones clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2006-01-01

    paths up to the cluster size of 150 atoms. We demonstrate that in this way all known global minima structures of the Lennard-Jones clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic number sequence......We present a new general theoretical framework for modelling the cluster structure and apply it to description of the Lennard-Jones clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing...... for the clusters of noble gas atoms and compare it with experimental observations. We report the striking correspondence of the peaks in the dependence of the second derivative of the binding energy per atom on cluster size calculated for the chain of the Lennard-Jones clusters based on the icosahedral symmetry...

  4. Cluster fusion algorithm: application to Lennard-Jones clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2008-01-01

    paths up to the cluster size of 150 atoms. We demonstrate that in this way all known global minima structures of the Lennard-Jones clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic number sequence......We present a new general theoretical framework for modelling the cluster structure and apply it to description of the Lennard-Jones clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing...... for the clusters of noble gas atoms and compare it with experimental observations. We report the striking correspondence of the peaks in the dependence of the second derivative of the binding energy per atom on cluster size calculated for the chain of the Lennard-Jones clusters based on the icosahedral symmetry...

  5. Distribution and evolution of electrons in a cluster plasma created by a laser pulse

    International Nuclear Information System (INIS)

    Smirnov, M.B.

    2003-01-01

    We analyze the properties and the character of the evolution of an electron subsystem of a large cluster (with a number of atoms n ∼ 10 4 -10 6 ) interacting with a short laser pulse of high intensity (10 17 -10 19 W/cm 2 ). As a result of ionization in a strong laser field, cluster atoms are converted into multicharged ions, part of the electrons being formed leaves the cluster, and the other electrons move in a self-consistent field of the charged cluster and the laser wave. It is shown that electron-electron collisions are inessential both during the cluster irradiation by the laser pulse and in the course of cluster expansion; the electron distribution in the cluster therefore does not transform into the Maxwell distribution even during cluster expansion. During cluster expansion, the Coulomb field of a cluster charge acts on cluster ions more strongly than the pressure resulting from electron-ion collisions. In addition, bound electrons remain inside the cluster in the course of its expansion, and cluster expansion therefore does not lead to additional cluster ionization

  6. Study of irradiation effects in austenitic stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    Etienne, A. [GPM UMR CNRS 6634, Universite et INSA de Rouen (France); Material Department, University of California, Santa Barbara (United States); Pareige, P.; Radiguet, B. [GPM UMR CNRS 6634, Universite et INSA de Rouen (France); Cunningham, N.J.; Odette, G.O. [Material Department, University of California, Santa Barbara (United States); Pokor, C. [EDF RD, departement MMC, site des Renardieres, Moret-sur-Loing (France)

    2011-07-01

    Chemical analyses using Atom Probe Tomography were performed on a bolt made of cold worked 316 austenitic stainless steel, extracted from the internal structures of a pressurized water reactor after seventeen years of reactor service. The irradiation temperature of these samples was 633 K and the irradiation dose was estimated to 12 dpa. These analyses have shown that neutron irradiation has a strong effect on the intragranular distribution of solute atoms. A very high number density (6.10{sup 23} m{sup -3}) of Ni-Si enriched and Cr-Fe depleted clusters was detected after irradiation. In order to bring complementary experimental results and to determine the mechanism of formation of these Ni-Si nano-clusters, Fe{sup 5+} ion irradiations have been performed on a 316 austenitic stainless steel. As after neutron irradiation, the formation of solute enriched features is observed. Linear features and two kinds of clusters, rounded and torus shaped, are present. Considering that solute enriched features are probably formed by radiation induced segregation on point defect sinks, these different shapes are due to the nature of the sinks where segregation occurs. (authors)

  7. Irradiation-induced microchemical changes in highly irradiated 316 stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, K., E-mail: fujiik@inss.co.jp; Fukuya, K.

    2016-02-15

    Cold-worked 316 stainless steel specimens irradiated to 74 dpa in a pressurized water reactor (PWR) were analyzed by atom probe tomography (APT) to extend knowledge of solute clusters and segregation at higher doses. The analyses confirmed that those clusters mainly enriched in Ni–Si or Ni–Si–Mn were formed at high number density. The clusters were divided into three types based on their size and Mn content; small Ni–Si clusters (3–4 nm in diameter), and large Ni–Si and Ni–Si–Mn clusters (8–10 nm in diameter). The total cluster number density was 7.7 × 10{sup 23} m{sup −3}. The fraction of large clusters was almost 1/10 of the total density. The average composition (in at%) for small clusters was: Fe, 54; Cr, 12; Mn, 1; Ni, 22; Si, 11; Mo, 1, and for large clusters it was: Fe, 44; Cr, 9; Mn, 2; Ni, 29; Si, 14; Mo,1. It was likely that some of the Ni–Si clusters correspond to γ′ phase precipitates while the Ni–Si–Mn clusters were precursors of G phase precipitates. The APT analyses at grain boundaries confirmed enrichment of Ni, Si, P and Cu and depletion of Fe, Cr, Mo and Mn. The segregation behavior was consistent with previous knowledge of radiation induced segregation.

  8. Irradiation-induced microchemical changes in highly irradiated 316 stainless steel

    International Nuclear Information System (INIS)

    Fujii, K.; Fukuya, K.

    2016-01-01

    Cold-worked 316 stainless steel specimens irradiated to 74 dpa in a pressurized water reactor (PWR) were analyzed by atom probe tomography (APT) to extend knowledge of solute clusters and segregation at higher doses. The analyses confirmed that those clusters mainly enriched in Ni–Si or Ni–Si–Mn were formed at high number density. The clusters were divided into three types based on their size and Mn content; small Ni–Si clusters (3–4 nm in diameter), and large Ni–Si and Ni–Si–Mn clusters (8–10 nm in diameter). The total cluster number density was 7.7 × 10"2"3 m"−"3. The fraction of large clusters was almost 1/10 of the total density. The average composition (in at%) for small clusters was: Fe, 54; Cr, 12; Mn, 1; Ni, 22; Si, 11; Mo, 1, and for large clusters it was: Fe, 44; Cr, 9; Mn, 2; Ni, 29; Si, 14; Mo,1. It was likely that some of the Ni–Si clusters correspond to γ′ phase precipitates while the Ni–Si–Mn clusters were precursors of G phase precipitates. The APT analyses at grain boundaries confirmed enrichment of Ni, Si, P and Cu and depletion of Fe, Cr, Mo and Mn. The segregation behavior was consistent with previous knowledge of radiation induced segregation.

  9. The influence of P solutes on an irradiated α-Fe matrix

    International Nuclear Information System (INIS)

    Hurchand, H.; Kenny, S.D.; Sanz-Navarro, C.F.; Smith, R.; Flewitt, P.E.J.

    2005-01-01

    Atomistic simulations of collision cascades in a Fe-0.04at.%P matrix and a pure Fe matrix are compared to investigate the interaction of the phosphorus atoms with the radiation. The simulations were performed for a primary knock-on atom having an energy in the range 1-16 keV. It is observed that the P atom in the Fe matrix does not increase significantly the damage induced to the lattice post irradiation. The density of vacancies and the morphology of the clusters formed in the Fe-0.04at.%P system are indistinguishable from residual defects produced in a pure irradiated Fe matrix. There are two mechanisms by which the Fe interstitials interact with the P atoms. The first occurs when a P atom is dislodged from its substitutional position by a recoil atom and combines with an Fe interstitial to form a mixed dumbbell. The second is one in which the Fe interstitial is attracted to a substitutional P atom due to the lattice strain region in the vicinity of the P atom. In this case the P atom acts as an attractive centre for interstitial Fe atoms and stabilises them into Fe-P nano-clusters. Nearly 35% of the atoms which are ejected from the core region of the cascade during the ballistic phase form such solute-defect clusters which remain pinned over the period of several hundred picoseconds. Finally, the radiation induced mobility of the P atom is reported. Substitutional P atoms whether isolated or as part of the larger defect clusters have a high energy barrier for diffusion but the P atoms displaced from substitutional sites can diffuse through the lattice by hopping between dumbbell and tetrahedral sites

  10. Formation of clusters (ions solvated with products of radiolysis) during irradiation of certain chloralkanes in the condensed phase

    International Nuclear Information System (INIS)

    Sukhov, F.F.; Karatun, A.A.; Slovokhotova, N.A.

    1983-01-01

    Using the infrared spectroscopy method, the radiolysis of the 2-chloropropane and 2-chloro-2-methylpropane was investigated in various phase states and in argon matrix at 15 and 77 K. A conclusion is drawn that the reaction of the radiation dehydrochlorination in the chloralkanes investigated occurs under certain conditions in the vicinity of ions, mostly; as this takes place, unique clusters composed of radiolysis products, i.e. ions solvated with complexes of alkane and hydrogen chloride are being formed. (author)

  11. Evaluation of the energetics of copper-vacancy clusters in Fe

    Energy Technology Data Exchange (ETDEWEB)

    Morishita, Kazunori, E-mail: morishita@iae.kyoto-u.ac.jp; Nakasuji, Toshiki; Ruan, Xiaoyong

    2017-02-15

    Highlights: • Thermodynamics evaluation of the nucleation process of copper-vacancy clusters in Fe is performed. • Nucleation free energy of copper-vacancy clusters in Fe is formulated. • With this energetics, two different nucleation paths of clusters are found as a function of the damage rate. - Abstract: A theoretical study is conducted to evaluate the nucleation free energy of copper-vacancy clusters in Fe as a function of the numbers of copper atoms and of vacancies in a cluster. Using this free energy value, cluster nucleation processes during irradiation are investigated. The results clearly show that there are two different types of cluster nucleation paths on the free energy surface; one is the formation of empty voids by jumping over the ridge of the free energy surface, and the other corresponds to a path for the formation of copper clusters by going around the ridge. The dependence of easy nucleation paths on the damage rate is discussed.

  12. Analysis of interrelationship between the protein fractions content and blood serum immunoglobulins with irradiation of atomic industry enterprises workers

    International Nuclear Information System (INIS)

    Tel'nov, V.I.

    1996-01-01

    989 workers of atomic industry at the age from 35 to 78 years old subjected to the general external gamma radiation and incorporation of plutonium 239 in a wide range of doses about 17-40 years ago have been examined for the protein indices with the radiation effect bearing in mind nine non-radiation factors. The step-by-step regression analysis revealed a positive linear link for the total protein level, absolute content of alpha-1-globulins with the total dose of external gamma radiation. Increasing of serum proteins entropy, correlated with external radiation by protein shifts effect, had not coincided with its age increasing. The influence of plutonium-239 incorporation on the examined protein parameters was not found

  13. Phasing and structure of bestrophin-1: a case study in the use of heavy-atom cluster compounds with multi-subunit transmembrane proteins

    Energy Technology Data Exchange (ETDEWEB)

    Dickson, Veronica Kane (Cambridge)

    2016-03-01

    The purification and three-dimensional crystallization of membrane proteins are commonly affected by a cumulation of pathologies that are less prevalent in their soluble counterparts. This may include severe anisotropy, poor spot shape, poor to moderate-resolution diffraction, crystal twinning, translational pseudo-symmetry and poor uptake of heavy atoms for derivatization. Such challenges must be circumvented by adaptations in the approach to crystallization and/or phasing. Here, an example of a protein that exhibited all of the above-mentioned complications is presented. Bestrophin-1 is a eukaryotic calcium-activated chloride channel, the structure of which was recently determined in complex with monoclonal antibody fragments using SAD phasing with tantalum bromide clusters (Ta6Br12·Br2). Some of the obstacles to obtaining improved diffraction and phasing for this particular channel are discussed, as well as the approach and adaptations that were key to determining the structure.

  14. ion irradiation

    Indian Academy of Sciences (India)

    Swift heavy ions interact predominantly through inelastic scattering while traversing any polymer medium and produce excited/ionized atoms. Here samples of the polycarbonate Makrofol of approximate thickness 20 m, spin coated on GaAs substrate were irradiated with 50 MeV Li ion (+3 charge state). Build-in ...

  15. Impact of Coulomb potential on peak structures arising in momentum and low-energy photoelectron spectra produced in strong-field ionization of laser-irradiated atoms

    Science.gov (United States)

    Pyak, P. E.; Usachenko, V. I.

    2018-03-01

    The phenomenon of pronounced peak structure(s) of longitudinal momentum distributions as well as a spike-like structure of low-energy spectra of photoelectrons emitted from laser-irradiated Ar and Ne atoms in a single ionization process is theoretically studied in the tunneling and multiphoton regimes of ionization. The problem is addressed assuming only the direct above-threshold ionization (ATI) as a physical mechanism underlying the phenomenon under consideration (viz. solely contributing to observed photoelectron momentum distributions (PMD)) and using the Coulomb-Volkov (CV) ansatz within the frame of conventional strong-field approximation (SFA) applied in the length-gauge formulation. The developed CV-SFA approach also incorporates the density functional theory essentially exploited for numerical composition of initial (laser-free) atomic state(s) constructed from atomic orbitals of Gaussian type. Our presented CV-SFA based (and laser focal-volume averaged) calculation results proved to be well reproducing both the pronounced double-peak and/or ATI-like multi-peak structure(s) experimentally observed in longitudinal PMD under conditions of tunneling and/or multiphoton regime, respectively. In addition, our CV-SFA results presented for tunneling regime also suggest and remarkably reproduce a pronounced structure observed in relevant experiments as a ‘spike-like’ enhanced maximum arising in low-energy region (around the value of about 1 eV) of photoelectron spectra. The latter consistency allows to identify and interpret these results as the so-called low-energy structure (LES) since the phenomenon proved to appear as the most prominent if the influence of Coulomb potential on photoelectron continuum states is maximally taken into account under calculations (viz. if the parameter Z in CV’s functions is put equal to 1). Moreover, the calculated LES proved to correspond (viz., established as closely related) to the mentioned double-peak structure arising

  16. Self-irradiation study of plutonium alloys

    International Nuclear Information System (INIS)

    Oudot, B.

    2005-02-01

    The plutonium is unstable and produces α or β decays depending on the isotope. These decays generate americium, uranium, helium and different kinds of structural defects. The effects of self-irradiation damage are observed at macroscopic scale, the mechanism occurs from atomic scale. In order to improve our understanding of the self-irradiation effects in PuGa alloys, a technique sensitive to the vacancies and vacancies clusters has been developed: the Positron Annihilation Spectroscopy (PAS). The swelling has been characterized by XRD at a microscopic scale and by dilatometry at a macroscopic scale. Swelling starts just after melting and reaches a saturation between 6 and 36 months depending on the degree of gallium homogeneity in the alloy. Swelling at saturation increases with the gallium content, but the absolute change in the cell parameters is constant during time. PAS showed that vacancies clusters develop immediately. Their concentration increase with time. A part of these clusters is stabilized by helium atoms and leads to the creation of bubbles, which contribution to swelling is negligible. The vacancies and vacancies clusters which are not stabilized by helium contribute to the swelling increase by mechanisms known for other materials. These mechanisms are based on a 'dislocation bias'. The presence of these dislocations can furthermore explain the low mean life time value of positrons at the saturation point. (author)

  17. Preconcentration, speciation and determination of ultra trace amounts of mercury by modified octadecyl silica membrane disk/electron beam irradiation and cold vapor atomic absorption spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Ashkenani, Hamid [Department of Chemistry, Yazd University, Yazd (Iran, Islamic Republic of); Dadfarnia, Shayessteh [Department of Chemistry, Yazd University, Yazd (Iran, Islamic Republic of)], E-mail: sdadfarnia@yazduni.ac.ir; Shabani, Ali Mohammad Haji; Jaffari, Abbas Ali [Department of Chemistry, Yazd University, Yazd (Iran, Islamic Republic of); Behjat, Abbas [Department of physics, Yazd University, Yazd (Iran, Islamic Republic of)

    2009-01-15

    Mercury (II) and methyl mercury cations at the Sub-ppb level were adsorbed quantitatively from aqueous solution onto an octadecyl-bonded silica membrane disk modified by 2-[(2-mercaptophyenylimino)methyl] phenol (MPMP). The trapped mercury was then eluted with 3 ml ethanol and Hg{sup 2+} ion was directly measured by cold vapor atomic absorption spectrometry, utilizing tin (II) chloride. Total mercury (Hgt) was determined after conversion of MeHg{sup +} into Hg{sup 2+} ion by electron beam irradiation. A sample volume of 1500 ml resulted in a preconcentration factor of 500 and the precision for a sampling volume of 500 ml at a concentration of 2.5 {mu}g l{sup -1} (n = 7) was 3.1%. The limit of detection of the proposed method is 3.8 ng l{sup -1}. The method was successfully applied to analysis of water samples, and the accuracy was assessed via recovery experiment.

  18. Interaction of point intrinsic defects in n-type indium phosphide with acceptor clusters

    International Nuclear Information System (INIS)

    Vitovskij, N.A.; Lagunova, T.S.; Rakhimov, O.

    1984-01-01

    The rates of implanting defects of donor- and acceptor type stable at room temperature in n-InP during gamma irradiation are found to vary versus the compensating impurity type. Zinc atoms interact with defects most actively. Irradiation also brings about the growth of acceptor clusters, this growth being most markedly expressed in InP . The presence of an additional mechanism of charge-carriers scattering associated with the existence of clusters of compensating centres is verified, the temperature dependence of the effectiveness of this mechanism μ approximately Tsup(-1.2) is found

  19. Photochemistry in rare gas clusters

    International Nuclear Information System (INIS)

    Moeller, T.; Haeften, K. von; Pietrowski, R. von

    1999-01-01

    In this contribution photochemical processes in pure rare gas clusters will be discussed. The relaxation dynamics of electronically excited He clusters is investigated with luminescence spectroscopy. After electronic excitation of He clusters many sharp lines are observed in the visible and infrared spectral range which can be attributed to He atoms and molecules desorbing from the cluster. It turns out that the desorption of electronically excited He atoms and molecules is an important decay channel. The findings for He clusters are compared with results for Ar clusters. While desorption of electronically excited He atoms is observed for all clusters containing up to several thousand atoms a corresponding process in Ar clusters is only observed for very small clusters (N<10). (orig.)

  20. Photochemistry in rare gas clusters

    Energy Technology Data Exchange (ETDEWEB)

    Moeller, T.; Haeften, K. von; Pietrowski, R. von [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany). Hamburger Synchrotronstrahlungslabor; Laarman, T. [Universitaet Hamburg, II. Institut fuer Experimentalphysik, Luruper Chaussee 149, D-22761 Hamburg (Germany)

    1999-12-01

    In this contribution photochemical processes in pure rare gas clusters will be discussed. The relaxation dynamics of electronically excited He clusters is investigated with luminescence spectroscopy. After electronic excitation of He clusters many sharp lines are observed in the visible and infrared spectral range which can be attributed to He atoms and molecules desorbing from the cluster. It turns out that the desorption of electronically excited He atoms and molecules is an important decay channel. The findings for He clusters are compared with results for Ar clusters. While desorption of electronically excited He atoms is observed for all clusters containing up to several thousand atoms a corresponding process in Ar clusters is only observed for very small clusters (N<10). (orig.)

  1. The influence of a nuclear prehistory on transport rate of impurity ''hot'' atoms 111In, 114mIn and 115mIn in the irradiated metal cadmium

    International Nuclear Information System (INIS)

    Alekseev, I.E.; Lazarev, V.V.; Orlov, S.P.

    2004-01-01

    In our previous publications it was shown, that the velocity of migration of radioactive microimpurities (formed as a result of a nuclear change) in irradiated in metals is instituted by a nuclear prehistory. In the present work this problem was explored in detail. The selected system '' cadmium - impurity atoms of indium '' is unique for such experiments: it is possible to gain the same impurity ''hot'' atoms ( 111 In, 114m In and 115m In) via different ''nuclear channels'' and to explore their behavior depending on a nuclear prehistory. (orig.)

  2. Food irradiation

    International Nuclear Information System (INIS)

    Anon.

    1984-01-01

    Food preservation by irradiation is one part of Eisenhower's Atoms for Peace program that is enjoying renewed interest. Classified as a food additive by the Food, Drug, and Cosmetic Act of 1958 instead of a processing technique, irradiation lost public acceptance. Experiments have not been done to prove that there are no health hazards from gamma radiation, but there are new pressures to get Food and Drug Administration approval for testing in order to make commercial use of some radioactive wastes. Irradiation causes chemical reactions and nutritional changes, including the destruction of several vitamins, as well as the production of radiolytic products not normally found in food that could have adverse effects. The author concludes that, lacking epidemiological evidence, willing buyers should be able to purchase irradiated food as long as it is properly labeled

  3. Defect microstructure in copper alloys irradiated with 750 MeV protons

    DEFF Research Database (Denmark)

    Zinkle, S.J.; Horsewell, A.; Singh, B.N.

    1994-01-01

    Transmission electron microscopy (TEM) disks of pure copper and solid solution copper alloys containing 5 at% of Al, Mn, or Ni were irradiated with 750 MeV protons to damage levels between 0.4 and 2 displacements per atom (dpa) at irradiation temperatures between 60 and 200 degrees C. The defect...... significant effect on the total density of small defect clusters, but they did cause a significant decrease in the fraction of defect clusters resolvable as SFT to similar to 20 to 25%. In addition, the dislocation loop density (> 5 nm diameter) was more than an order of magnitude higher in the alloys...

  4. Microstructural evolution under high flux irradiation of dilute Fe-CuNiMnSi alloys studied by an atomic kinetic Monte Carlo model accounting for both vacancies and self interstitials

    International Nuclear Information System (INIS)

    Vincent, E.; Becquart, C.S.; Domain, C.

    2008-01-01

    Under neutron irradiation, a large amount of point defects (vacancies and interstitials) are created. In the irradiated pressure vessel steels, weakly alloyed, these point defects are responsible for the diffusion of the solute atoms, leading to the formation of solute rich precipitates within the matrix. Ab initio calculations based on the density functional theory have been performed to determine the interactions of point defects with solute atoms in dilute FeX alloys (X = Cu, Mn, Ni or Si). For Mn, the results of these calculations lead to think that solute transport in α-Fe can very likely take place through an interstitial mechanism as well as via vacancies while the other solutes (Cu, Ni and Si) which establish strong bonds with vacancies diffuse more likely via vacancies only. The database thus created has been used to parameterize an atomic kinetic Monte Carlo model taking into account both vacancies and interstitials. Some results of irradiation damage in dilute Fe-CuNiMnSi alloys obtained with this model will be presented

  5. Microstructural evolution under high flux irradiation of dilute Fe CuNiMnSi alloys studied by an atomic kinetic Monte Carlo model accounting for both vacancies and self interstitials

    Science.gov (United States)

    Vincent, E.; Becquart, C. S.; Domain, C.

    2008-12-01

    Under neutron irradiation, a large amount of point defects (vacancies and interstitials) are created. In the irradiated pressure vessel steels, weakly alloyed, these point defects are responsible for the diffusion of the solute atoms, leading to the formation of solute rich precipitates within the matrix. Ab initio calculations based on the density functional theory have been performed to determine the interactions of point defects with solute atoms in dilute FeX alloys (X = Cu, Mn, Ni or Si). For Mn, the results of these calculations lead to think that solute transport in α-Fe can very likely take place through an interstitial mechanism as well as via vacancies while the other solutes (Cu, Ni and Si) which establish strong bonds with vacancies diffuse more likely via vacancies only. The database thus created has been used to parameterize an atomic kinetic Monte Carlo model taking into account both vacancies and interstitials. Some results of irradiation damage in dilute Fe-CuNiMnSi alloys obtained with this model will be presented.

  6. Food irradiation: fiction and reality

    International Nuclear Information System (INIS)

    1991-01-01

    The International Consultative Group on Food Irradiation (IGCFI), sponsored by World Health Organization (WHO), Food and Agriculture Organization (FAO) and the International Atomic Energy Agency (IAEA), with the intention to provide to governments, especially those of developing countries, scientifically correct information about food irradiation, decided to organize a file and questions of general public interest. The document is composed by descriptive files related with the actual situation and future prospective, technical and scientific terms, food irradiation and the radioactivity, chemical transformations in irradiated food, genetic studies, microbiological safety of irradiated food, irradiation and harmlessness, irradiation and additives, packing, irradiation facilities control, process control, irradiation costs and benefits as well as consumers reaction

  7. Angular distributions of particles sputtered from multicomponent targets with gas cluster ions

    Energy Technology Data Exchange (ETDEWEB)

    Ieshkin, A.E. [Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Ermakov, Yu.A., E-mail: yuriermak@yandex.ru [Skobeltsyn Nuclear Physics Research Institute, Lomonosov Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Chernysh, V.S. [Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation)

    2015-07-01

    The experimental angular distributions of atoms sputtered from polycrystalline W, Cd and Ni based alloys with 10 keV Ar cluster ions are presented. RBS was used to analyze a material deposited on a collector. It has been found that the mechanism of sputtering, connected with elastic properties of materials, has a significant influence on the angular distributions of sputtered components. The effect of non-stoichiometric sputtering at different emission angles has been found for the alloys under cluster ion bombardment. Substantial smoothing of the surface relief was observed for all targets irradiated with cluster ions.

  8. Cluster dynamics at different cluster size and incident laser wavelengths

    International Nuclear Information System (INIS)

    Desai, Tara; Bernardinello, Andrea

    2002-01-01

    X-ray emission spectra from aluminum clusters of diameter -0.4 μm and gold clusters of dia. ∼1.25 μm are experimentally studied by irradiating the cluster foil targets with 1.06 μm laser, 10 ns (FWHM) at an intensity ∼10 12 W/cm 2 . Aluminum clusters show a different spectra compared to bulk material whereas gold cluster evolve towards bulk gold. Experimental data are analyzed on the basis of cluster dimension, laser wavelength and pulse duration. PIC simulations are performed to study the behavior of clusters at higher intensity I≥10 17 W/cm 2 for different size of the clusters irradiated at different laser wavelengths. Results indicate the dependence of cluster dynamics on cluster size and incident laser wavelength

  9. Microstructural evolution of pure tungsten neutron irradiated with a mixed energy spectrum

    Energy Technology Data Exchange (ETDEWEB)

    Koyanagi, Takaaki, E-mail: koyanagit@ornl.gov [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Kumar, N.A.P. Kiran [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Hwang, Taehyun [Tohoku University, Sendai, 980-8579 (Japan); Garrison, Lauren M.; Hu, Xunxiang [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Snead, Lance L. [Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Katoh, Yutai [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)

    2017-07-15

    Microstructures of single-crystal bulk tungsten (W) and polycrystalline W foil with a strong grain texture were investigated using transmission electron microscopy following neutron irradiation at ∼90–800 °C to 0.03–4.6 displacements per atom (dpa) in the High Flux Isotope Reactor with a mixed energy spectrum. The dominant irradiation defects were dislocation loops and small clusters at ∼90 °C. Additional voids were formed in W irradiated at above 460 °C. Voids and precipitates involving transmutation rhenium and osmium were the dominant defects at more than ∼1 dpa. We found a new phenomenon of microstructural evolution in irradiated polycrystalline W: Re- and Os-rich precipitation along grain boundaries. Comparison of results between this study and previous studies using different irradiation facilities revealed that the microstructural evolution of pure W is highly dependent on the neutron energy spectrum in addition to the irradiation temperature and dose.

  10. Simulation of the dynamics of laser-cluster interaction

    International Nuclear Information System (INIS)

    Deiss, C.

    2009-01-01

    Ranging in size from a few atoms to several million atoms, clusters form a link between gases and solids. When irradiating clusters with intense femtosecond laser pulses, the production of energetic and highly charged ions, hot electrons, and extreme UV and X-ray photons, gives evidence of a very efficient energy conversion. The size of the system and the multitude of mechanisms at play provide a considerable challenge for the theoretical treatment of the interaction. In this thesis, we have developed a Classical Trajectory Monte Carlo simulation that gives insight into the particle dynamics during the interaction of laser pulses with large argon clusters (with more than 10000 atoms per cluster). Elastic electron-ion scattering, electron-electron scattering, electron-impact ionization and excitation, as well as three-body recombination and Auger decay are included via stochastic events. In a strongly simplified picture, the dynamics of the laser-cluster interaction can be summarized as follows: the intense laser field ionizes the cluster atoms and drives the population of quasi-free electrons. In collision events, further free electrons and high ionic charge states are created. As some electrons leave the cluster, the ions feel a net positive charge, and the cluster ultimately disintegrates in a Coulomb explosion. Even at moderate laser intensities (approx. 10 15 W/cm 2 ), impact ionization produces inner-shell vacancies in the cluster ions that decay by emitting characteristic X-ray radiation. The small population of fast electrons responsible for these ionization events is produced near the cluster poles, where the combination of polarization and charging of the cluster leads to strongly enhanced field strengths. We achieve a good agreement over large parameter ranges between the simulation and X-ray spectroscopy experiments. We also investigate the dependence of X-ray emission on laser intensity, pulse duration and cluster size. We find that in order to

  11. Interaction of rare gas clusters in intense laser field

    International Nuclear Information System (INIS)

    Dobosz, Sandrine

    1998-01-01

    Rare gas cluster jet targets have only been scarcely studied in strong laser fields. This is surprising since their properties are particularly appealing. Although considered as a gas phase target, the local density within clusters is comparable to that of the bulk. Intense irradiation of clusters produces a plasma thereby giving rise to strong collisional heating. This explains, in particular, the observation of very high fragment charge states and the generation of X-rays in the keV energy range. The complete set of our experimental results shows that the intra-cluster atoms are first ionised by tunnel ionisation followed by massive electron impact ionisation. Thus, for Xenon clusters, we have observed up to 30-fold charged. The most energetic electrons leave the cluster which contributes to a positive charge build-up on the cluster surface. The plasma expands under the combined action of the Coulomb and kinetic pressures. The contribution of each pressure depends on the cluster size and we show that the Coulomb pressure is prevailing for the smallest sizes. This scenario explains the ejection of fragments with energies of up to lMeV. We have also performed a high resolution X-ray study to explore in situ the properties of the plasma. These studies underline the importance of electron-ion collisions and allow to deterrnine the mean charge states of the emitting ions. Finally, we have developed a model, describing the cluster expansion, which confirms our experimental observations. (author) [fr

  12. Effect of the energy of recoil atoms on conductivity compensation in moderately doped n-Si and n-SiC under irradiation with MeV electrons and protons

    Energy Technology Data Exchange (ETDEWEB)

    Kozlovski, V.V. [St. Petersburg State Polytechnic University, St. Petersburg 195251 (Russian Federation); Lebedev, A.A., E-mail: shura.lebe@mail.ioffe.ru [Ioffe Physical Technical Institute, Russian Academy of Sciences, St. Petersburg 194021 (Russian Federation); National Research University of Information Technologies, Mechanics, and Optics, St. Petersburg 197101 (Russian Federation); Emtsev, V.V.; Oganesyan, G.A. [Ioffe Physical Technical Institute, Russian Academy of Sciences, St. Petersburg 194021 (Russian Federation)

    2016-10-01

    Processes of radiation defect formation and conductivity compensation in silicon and silicon carbide irradiated with 0.9 MeV electrons are considered in comparison with the electron irradiation at higher energies. The experimental values of the carrier removal rate at the electron energy of 0.9 MeV are nearly an order of magnitude smaller than the similar values of the parameter for higher energy electrons (6–9 MeV). At the same time, the formation cross-section of primary radiation defects (Frenkel pairs, FPs) is nearly energy-independent in this range. It is assumed that these differences are due to the influence exerted by the energy of primary knocked-on atoms (PKAs). As the PKA energy increases, the average distance between the genetically related FPs grows and, as a consequence, the fraction of FPs unrecombined under irradiation becomes larger. The FP recombination radius is estimated (∼1.1 nm), which makes it possible to ascertain the charge state of the recombining components. Second, the increase in the PKA energy enables formation of new, more complex secondary radiation defects. At electron energies exceeding 15 MeV, the average PKA energies are closer to the values obtained under irradiation with 1 MeV protons, compared with an electron irradiation at the same energy. As for the radiation-induced defect formation, the irradiation of silicon with MeV protons can be, in principle, regarded as a superposition of the irradiation with 1 MeV electrons and that with silicon ions having energy of ∼1 keV, with the “source” of silicon ions generating these ions uniformly across the sample thickness.

  13. Thermal conductivity of electron-irradiated graphene

    Science.gov (United States)

    Weerasinghe, Asanka; Ramasubramaniam, Ashwin; Maroudas, Dimitrios

    2017-10-01

    We report results of a systematic analysis of thermal transport in electron-irradiated, including irradiation-induced amorphous, graphene sheets based on nonequilibrium molecular-dynamics simulations. We focus on the dependence of the thermal conductivity, k, of the irradiated graphene sheets on the inserted irradiation defect density, c, as well as the extent of defect passivation with hydrogen atoms. While the thermal conductivity of irradiated graphene decreases precipitously from that of pristine graphene, k0, upon introducing a low vacancy concentration, c reduction of the thermal conductivity with the increasing vacancy concentration exhibits a weaker dependence on c until the amorphization threshold. Beyond the onset of amorphization, the dependence of thermal conductivity on the vacancy concentration becomes significantly weaker, and k practically reaches a plateau value. Throughout the range of c and at all hydrogenation levels examined, the correlation k = k0(1 + αc)-1 gives an excellent description of the simulation results. The value of the coefficient α captures the overall strength of the numerous phonon scattering centers in the irradiated graphene sheets, which include monovacancies, vacancy clusters, carbon ring reconstructions, disorder, and a rough nonplanar sheet morphology. Hydrogen passivation increases the value of α, but the effect becomes very minor beyond the amorphization threshold.

  14. Investigation of neutron irradiated reactor vessel steels using post-irradiation annealing techniques

    Energy Technology Data Exchange (ETDEWEB)

    Nakata, Hayato; Fukuya, Koji [Institute of Nuclear Safety System Inc., Mihama, Fukui (Japan)

    2001-09-01

    The matrix damage is known to be a major factor that contributes to embrittlement and hardening of irradiated reactor vessel steels, and is assumed to be composed of the point defect clusters. However field emission gun scanning transmission electron microscopy (FEGSTEM) and atom probe (AP) could not detect any evidence of the matrix damage. In this study, post irradiation annealing experiments combining positron annihilation lineshape analysis (PALA) and hardness experiments were applied to an actual surveillance test specimen and a sample of reactor vessel steel irradiated in a material test reactor (MTR), in order to investigate the matrix damage recovery behavior and its contribution to hardening. It was confirmed that higher fluence increased the hardness and the volume fraction of open volume defects and that higher flux decreased the thermal stability of matrix damage and the effect on hardening. The contribution of matrix damage to hardening could be estimated to be below 30%. (author)

  15. Blood irradiation

    International Nuclear Information System (INIS)

    Chandy, Mammen

    1998-01-01

    Viable lymphocytes are present in blood and cellular blood components used for transfusion. If the patient who receives a blood transfusion is immunocompetent these lymphocytes are destroyed immediately. However if the patient is immunodefficient or immunosuppressed the transfused lymphocytes survive, recognize the recipient as foreign and react producing a devastating and most often fatal syndrome of transfusion graft versus host disease [T-GVHD]. Even immunocompetent individuals can develop T-GVHD if the donor is a first degree relative since like the Trojan horse the transfused lymphocytes escape detection by the recipient's immune system, multiply and attack recipient tissues. T-GVHD can be prevented by irradiating the blood and different centers use doses ranging from 1.5 to 4.5 Gy. All transfusions where the donor is a first degree relative and transfusions to neonates, immunosuppressed patients and bone marrow transplant recipients need to be irradiated. Commercial irradiators specifically designed for irradiation of blood and cellular blood components are available: however they are expensive. India needs to have blood irradiation facilities available in all large tertiary institutions where immunosuppressed patients are treated. The Atomic Energy Commission of India needs to develop a blood irradiator which meets international standards for use in tertiary medical institutions in the country. (author)

  16. The comparison of microstructure and nanocluster evolution in proton and neutron irradiated Fe–9%Cr ODS steel to 3 dpa at 500 °C

    Energy Technology Data Exchange (ETDEWEB)

    Swenson, M.J., E-mail: matthewswenson1@u.boisestate.edu; Wharry, J.P.

    2015-12-15

    A model Fe–9%Cr oxide dispersion strengthened (ODS) steel was irradiated with protons or neutrons to a dose of 3 displacements per atom (dpa) at a temperature of 500 °C, enabling a direct comparison of ion to neutron irradiation effects at otherwise fixed irradiation conditions. The irradiated microstructures were characterized using transmission electron microscopy and atom probe tomography including cluster analysis. Both proton and neutron irradiations produced a comparable void and dislocation loop microstructure. However, the irradiation response of the Ti–Y–O oxide nanoclusters varied. Oxides remained stable under proton irradiation, but exhibited dissolution and an increase in Y:Ti composition ratio under neutron irradiation. Both proton and neutron irradiation also induced varying extents of Si, Ni, and Mn clustering at existing oxide nanoclusters. Protons are able to reproduce the void and loop microstructure of neutron irradiation carried out to the same dose and temperature. However, since nanocluster evolution is controlled by both diffusion and ballistic impacts, protons are rendered unable to reproduce the nanocluster evolution of neutron irradiation at the same dose and temperature. - Highlights: • Fe–9% Cr ODS was irradiated with protons and neutrons to 3 dpa at 500 °C. • Dislocation loop size and density were similar upon proton and neutron irradiation. • Oxide nanocluster size and density decreased more with neutron irradiation. • Oxide Y:Ti ratio increased from 0.54 to 0.97 upon neutron irradiation. • Irradiation induced enrichment of Si, Mn, and Ni at oxide locations.

  17. Formation of stable products from cluster-cluster collisions

    International Nuclear Information System (INIS)

    Alamanova, Denitsa; Grigoryan, Valeri G; Springborg, Michael

    2007-01-01

    The formation of stable products from copper cluster-cluster collisions is investigated by using classical molecular-dynamics simulations in combination with an embedded-atom potential. The dependence of the product clusters on impact energy, relative orientation of the clusters, and size of the clusters is studied. The structures and total energies of the product clusters are analysed and compared with those of the colliding clusters before impact. These results, together with the internal temperature, are used in obtaining an increased understanding of cluster fusion processes

  18. Coordination of the Ser2056 and Thr2609 Clusters of DNA-PKcs in Regulating Gamma Rays and Extremely Low Fluencies of Alpha-Particle Irradiation to G0/G1 Phase Cells.

    Science.gov (United States)

    Nagasawa, Hatsumi; Lin, Yu-Fen; Kato, Takamitsu A; Brogan, John R; Shih, Hung-Ying; Kurimasa, Akihiro; Bedford, Joel S; Chen, Benjamin P C; Little, John B

    2017-02-01

    The catalytic subunit of DNA dependent protein kinase (DNA-PKcs) and its kinase activity are critical for mediation of non-homologous end-joining (NHEJ) of DNA double-strand breaks (DSB) in mammalian cells after gamma-ray irradiation. Additionally, DNA-PKcs phosphorylations at the T2609 cluster and the S2056 cluster also affect DSB repair and cellular sensitivity to gamma radiation. Previously we reported that phosphorylations within these two regions affect not only NHEJ but also homologous recombination repair (HRR) dependent DSB repair. In this study, we further examine phenotypic effects on cells bearing various combinations of mutations within either or both regions. Effects studied included cell killing as well as chromosomal aberration induction after 0.5-8 Gy gamma-ray irradiation delivered to synchronized cells during the G 0 /G 1 phase of the cell cycle. Blocking phosphorylation within the T2609 cluster was most critical regarding sensitization and depended on the number of available phosphorylation sites. It was also especially interesting that only one substitution of alanine in each of the two clusters separately abolished the restoration of wild-type sensitivity by DNA-PKcs. Similar patterns were seen for induction of chromosomal aberrations, reflecting their connection to cell killing. To study possible change in coordination between HRR and NHEJ directed repair in these DNA-PKcs mutant cell lines, we compared the induction of sister chromatid exchanges (SCEs) by very low fluencies of alpha particles with mutant cells defective in the HRR pathway that is required for induction of SCEs. Levels of true SCEs induced by very low fluence of alpha-particle irradiation normally seen in wild-type cells were only slightly decreased in the S2056 cluster mutants, but were completely abolished in the T2609 cluster mutants and were indistinguishable from levels seen in HRR deficient cells. Again, a single substitution in the S2056 together with a single

  19. The effect of alloying elements on the vacancy defect evolution in electron-irradiated austenitic Fe-Ni alloys studied by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Druzhkov, A.P. [Institute of Metal Physics, Ural Branch RAS, 18 Kovalevskaya St., 620041 Ekaterinburg (Russian Federation)], E-mail: druzhkov@imp.uran.ru; Perminov, D.A.; Davletshin, A.E. [Institute of Metal Physics, Ural Branch RAS, 18 Kovalevskaya St., 620041 Ekaterinburg (Russian Federation)

    2009-01-31

    The vacancy defect evolution under electron irradiation in austenitic Fe-34.2 wt% Ni alloys containing oversized (aluminum) and undersized (silicon) alloying elements was investigated by positron annihilation spectroscopy at temperatures between 300 and 573 K. It is found that the accumulation of vacancy defects is considerably suppressed in the silicon-doped alloy. This effect is observed at all the irradiation temperatures. The obtained results provide evidence that the silicon-doped alloy forms stable low-mobility clusters involving several Si and interstitial atoms, which are centers of the enhanced recombination of migrating vacancies. The clusters of Si-interstitial atoms also modify the annealing of vacancy defects in the Fe-Ni-Si alloy. The interaction between small vacancy agglomerates and solute Al atoms is observed in the Fe-Ni-Al alloy under irradiation at 300-423 K.

  20. Effect of thermal friction on the generation and transport of interstitial defects in irradiated metals

    CERN Document Server

    Dudarev, S L

    2002-01-01

    Generation of interstitial and vacancy defects under 14.1 MeV neutron irradiation is expected to drive the evolution of microstructure of materials in a future fusion power station. We investigate effects of thermal friction associated with the interaction between mobile clusters of interstitial atoms produced in collision cascades and phonon excitations. Phonons give rise to the random Brownian motion of clusters in the crystal lattice. Phonon excitations are also responsible for the dissipation of energy of rapidly moving clusters formed at the periphery of collision cascades. We investigate how the coefficient of thermal friction depends on the structure of clusters. We also discuss implications of our findings for understanding the origin of higher resistance of bcc metals to irradiation and the connection between this phenomenon and the long-range effect observed in experiments on ion implantation.

  1. Clustering of transmutation elements tantalum, rhenium and osmium in tungsten in a fusion environment

    Science.gov (United States)

    You, Yu-Wei; Kong, Xiang-Shan; Wu, Xuebang; Liu, C. S.; Fang, Q. F.; Chen, J. L.; Luo, G.-N.

    2017-08-01

    The formation of transmutation solute-rich precipitates has been reported to seriously degrade the mechanical properties of tungsten in a fusion environment. However, the underlying mechanisms controlling the formation of the precipitates are still unknown. In this study, first-principles calculations are therefore performed to systemically determine the stable structures and binding energies of solute clusters in tungsten consisting of tantalum, rhenium and osmium atoms as well as irradiation-induced vacancies. These clusters are known to act as precursors for the formation of precipitates. We find that osmium can easily segregate to form clusters even in defect-free tungsten alloys, whereas extremely high tantalum and rhenium concentrations are required for the formation of clusters. Vacancies greatly facilitate the clustering of rhenium and osmium, while tantalum is an exception. The binding energies of vacancy-osmium clusters are found to be much higher than those of vacancy-tantalum and vacancy-rhenium clusters. Osmium is observed to strongly promote the formation of vacancy-rhenium clusters, while tantalum can suppress the formation of vacancy-rhenium and vacancy-osmium clusters. The local strain and electronic structure are analyzed to reveal the underlying mechanisms governing the cluster formation. Employing the law of mass action, we predict the evolution of the relative concentration of vacancy-rhenium clusters. This work presents a microscopic picture describing the nucleation and growth of solute clusters in tungsten alloys in a fusion reactor environment, and thereby explains recent experimental phenomena.

  2. Clustering of near clusters versus cluster compactness

    International Nuclear Information System (INIS)

    Yu Gao; Yipeng Jing

    1989-01-01

    The clustering properties of near Zwicky clusters are studied by using the two-point angular correlation function. The angular correlation functions for compact and medium compact clusters, for open clusters, and for all near Zwicky clusters are estimated. The results show much stronger clustering for compact and medium compact clusters than for open clusters, and that open clusters have nearly the same clustering strength as galaxies. A detailed study of the compactness-dependence of correlation function strength is worth investigating. (author)

  3. Nanostructure evolution of neutron-irradiated reactor pressure vessel steels: Revised Object kinetic Monte Carlo model

    Energy Technology Data Exchange (ETDEWEB)

    Chiapetto, M., E-mail: mchiapet@sckcen.be [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, B-2400 Mol (Belgium); Unité Matériaux Et Transformations (UMET), UMR 8207, Université de Lille 1, ENSCL, F-59600 Villeneuve d’Ascq Cedex (France); Messina, L. [DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette (France); KTH Royal Institute of Technology, Roslagstullsbacken 21, SE-114 21 Stockholm (Sweden); Becquart, C.S. [Unité Matériaux Et Transformations (UMET), UMR 8207, Université de Lille 1, ENSCL, F-59600 Villeneuve d’Ascq Cedex (France); Olsson, P. [KTH Royal Institute of Technology, Roslagstullsbacken 21, SE-114 21 Stockholm (Sweden); Malerba, L. [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, B-2400 Mol (Belgium)

    2017-02-15

    This work presents a revised set of parameters to be used in an Object kinetic Monte Carlo model to simulate the microstructure evolution under neutron irradiation of reactor pressure vessel steels at the operational temperature of light water reactors (∼300 °C). Within a “grey-alloy” approach, a more physical description than in a previous work is used to translate the effect of Mn and Ni solute atoms on the defect cluster diffusivity reduction. The slowing down of self-interstitial clusters, due to the interaction between solutes and crowdions in Fe is now parameterized using binding energies from the latest DFT calculations and the solute concentration in the matrix from atom-probe experiments. The mobility of vacancy clusters in the presence of Mn and Ni solute atoms was also modified on the basis of recent DFT results, thereby removing some previous approximations. The same set of parameters was seen to predict the correct microstructure evolution for two different types of alloys, under very different irradiation conditions: an Fe-C-MnNi model alloy, neutron irradiated at a relatively high flux, and a high-Mn, high-Ni RPV steel from the Swedish Ringhals reactor surveillance program. In both cases, the predicted self-interstitial loop density matches the experimental solute cluster density, further corroborating the surmise that the MnNi-rich nanofeatures form by solute enrichment of immobilized small interstitial loops, which are invisible to the electron microscope.

  4. Gamma radiation effect on n-InP crystals with impurity clusters

    International Nuclear Information System (INIS)

    Vitovskij, N.A.; Dakhno, A.N.; Emel'yanenko, O.V.; Lagunova, T.S.; Mashovets, T.V.

    1982-01-01

    Parameters of acceptor-impurity atom clusters have been investigated for the cases of nonirradiated and gamma-irradiated n-InP crystals. Temperature dependences of electric conductivity, the Hall coefficient and the longitudinal magnetoresistance have been measured both in darkness and in lighting, the kinetics of the photoconductivity drop has also been studied. It is shown that in nonirradiated n-InP:Cu and n-InP-Zn the number of atoms in the cluster may be about 25-30. The concentration of the clusters may reach 10 11 cm -3 . Gamma-radiation increases the number of atoms in the cluster up to approximately equal to 40 with the insignificant change of the radius. In the nonirradiated material, the potential barrier heights created by the cluster are 0.15 eV and 0.4 eV at 78 and 300 K, respectively. The irradiation increases the barrier and the fraction of the volume occupied by the space-charge regions which overlap if the dose is sufficiently high

  5. Atomic hydrogen reactor

    International Nuclear Information System (INIS)

    Massip de Turville, C.M.D.

    1982-01-01

    Methods are discussed of generating heat in an atomic hydrogen reactor which involve; the production of atomic hydrogen by an electrical discharge, the capture of nascent neutrons from atomic hydrogen in a number of surrounding steel alloy tubes having a high manganese content to produce 56 Mn, the irradiation of atomic hydrogen by the high energy antineutrinos from the beta decay of 56 Mn to yield nascent neutrons, and the removal of the heat generated by the capture of nascent neutrons by 55 Mn and the beta decay of 56 Mn. (U.K.)

  6. The influence of non-equilibrium fluctuations on radiation damage and recovery of metals under irradiation

    International Nuclear Information System (INIS)

    Dubinko, V.I.; Klepikov, V.F.

    2007-01-01

    In the conventional theory of radiation damage, it is assumed that the main effect of irradiation is due to formation of Frenkel pairs of vacancies and self-interstitial atoms (SIAs) and their clusters. The difference in absorption of vacancies and SIAs by primary or radiation-induced extended defects (EDs) is thought to be the main reason of microstructural evolution under irradiation. On the other hand, the recovery of radiation damage is thought to be driven exclusively by thermal fluctuations resulting in the vacancy evaporation from voids (void annealing) or dislocations (thermal creep) and in the fluctuation-driven overcoming of obstacles by gliding dislocations (plastic strain). However, these recovery mechanisms can be efficient only at sufficiently high temperatures. At lower irradiation temperatures, the main driving force of the recovery processes may be due to nonequilibrium fluctuations of energy states of the atoms surrounding EDs arising as a result of scattering of radiation-induced excitations of atomic and electronic structure at EDs. In the present paper, the mechanisms of nonequilibrium fluctuations that result in such phenomena as the void shrinkage under irradiation at low temperatures (or high dose rates), irradiation creep and irradiation-induced increase of plasticity under sub-threshold irradiation was considered

  7. A comparison of the risk of stillbirth associated with paternal pre-conception irradiation in the Sellafield workforce with that of stillbirth and untoward pregnancy outcome among Japanese atomic bomb survivors

    International Nuclear Information System (INIS)

    Little, M.P.

    1999-01-01

    A comparison is made of the relative risks associated with paternal pre-conception irradiation of stillbirth and untoward pregnancy outcome (stillbirths, congenital malformations, neonatal deaths) in the offspring of the Japanese atomic bomb survivors and of stillbirth in the offspring of Sellafield workers. It is concluded that the pre-conception exposure risks of stillbirth in the offspring of Sellafield workers are statistically incompatible with the Japanese data at the 5% level. Other human and experimental data relating to the induction of congenital abnormalities are briefly reviewed. (author)

  8. Anelastic relaxation of interstitial foreign atoms and their complexes with intrinsic defects in B.C.C. metals

    International Nuclear Information System (INIS)

    Weller, M.

    1985-01-01

    In body-centred cubic metals, heavy interstitial foreign atoms (IFA) O, N and C give rise to relaxations of Snoek type. For dilute alloys, relaxation parameters are summarized. In concentrated alloys (group Va metals containing O or N) Snoek relaxations are influenced by the interaction of IFA. The recent controversy is discussed as to whether this interaction is based on clustering or anticlustering. In irradiated metals complexes of IFA with intrinsic atomic defects (vacancies or self interstitial atoms) also give rise to relaxations

  9. Kinetic Monte Carlo simulation of nanostructural evolution under post-irradiation annealing in dilute FeMnNi

    Energy Technology Data Exchange (ETDEWEB)

    Chiapetto, M. [SCK-CEN, Nuclear Materials Science Institute, Mol (Belgium); Unite Materiaux et Transformations (UMET), UMR 8207, Universite de Lille 1, ENSCL, Villeneuve d' Ascq (France); Becquart, C.S. [Unite Materiaux et Transformations (UMET), UMR 8207, Universite de Lille 1, ENSCL, Villeneuve d' Ascq (France); Laboratoire commun EDF-CNRS, Etude et Modelisation des Microstructures pour le Vieillissement des Materiaux (EM2VM) (France); Domain, C. [EDF R and D, Departement Materiaux et Mecanique des Composants, Les Renardieres, Moret sur Loing (France); Laboratoire commun EDF-CNRS, Etude et Modelisation des Microstructures pour le Vieillissement des Materiaux (EM2VM) (France); Malerba, L. [SCK-CEN, Nuclear Materials Science Institute, Mol (Belgium)

    2015-01-01

    Post-irradiation annealing experiments are often used to obtain clearer information on the nature of defects produced by irradiation. However, their interpretation is not always straightforward without the support of physical models. We apply here a physically-based set of parameters for object kinetic Monte Carlo (OKMC) simulations of the nanostructural evolution of FeMnNi alloys under irradiation to the simulation of their post-irradiation isochronal annealing, from 290 to 600 C. The model adopts a ''grey alloy'' scheme, i.e. the solute atoms are not introduced explicitly, only their effect on the properties of point-defect clusters is. Namely, it is assumed that both vacancy and SIA clusters are significantly slowed down by the solutes. The slowing down increases with size until the clusters become immobile. Specifically, the slowing down of SIA clusters by Mn and Ni can be justified in terms of the interaction between these atoms and crowdions in Fe. The results of the model compare quantitatively well with post-irradiation isochronal annealing experimental data, providing clear insight into the mechanisms that determine the disappearance or re-arrangement of defects as functions of annealing time and temperature. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Introduction to cluster dynamics

    CERN Document Server

    Reinhard, Paul-Gerhard

    2008-01-01

    Clusters as mesoscopic particles represent an intermediate state of matter between single atoms and solid material. The tendency to miniaturise technical objects requires knowledge about systems which contain a ""small"" number of atoms or molecules only. This is all the more true for dynamical aspects, particularly in relation to the qick development of laser technology and femtosecond spectroscopy. Here, for the first time is a highly qualitative introduction to cluster physics. With its emphasis on cluster dynamics, this will be vital to everyone involved in this interdisciplinary subje

  11. Modeling of DNA damage-cluster, cell-cycle and repair pathway dependent radiosensitivity after low- and high-LET irradiation; Modellierung der DNA-Schadenscluster-, Zellzyklus- und Reparaturweg-abhaengigen Strahlenempfindlichkeit nach niedrig- und hoch-LET-Bestrahlung

    Energy Technology Data Exchange (ETDEWEB)

    Guenther, Paul

    2017-07-17

    irradiation. This method is able to qualitatively predict the influence of the cell-cycle and the radiation quality on radiosensitivity. Based on this, two approaches for the LEM prediction of the Relative Biological Effectiveness (RBE) are compared. The first approach predicts the RBE based on the survival of asynchronous cells. The second approach predicts the RBE from the sum of survival curves of the subpopulations, which contribute to the asynchronous cell population. Both approaches lead to qualitatively similar results. In the context of describing the microscopic dose deposition of ion irradiation by the amorphous track structure, two questions are addressed: 1. Is it possible to improve the prediction of cell survival after ion irradiation by a more sophisticated composition of the direct and indirect effect? 2. is the amorphous track structure an appropriate model of the dose deposition regarding the DNA damage clustering on the nm-scale or is it necessary to evaluate single ionizations on the molecular level? Regarding the first question, it is shown that a more detailed evaluation of the direct and indirect effect improves the agreement of the LEM predictions to data. Concerning the second question, it is shown that the amorphous track structure can be used for the prediction of DNA damage induction on the nm-scale similar to an ab initio Monte Carlo simulation. In the context of cell-survival modeling, the relevant length scale for DNA damage-clustering is often discussed. The iDSBs und cDSBs used in the GLOBLE and LEM are referring to DNA damage clustering on the μm-scale. There are also models which predict the cell survival after ion irradiation based on complex DNA-damage-clusters on the nm-scale. This work shows, that complex DNA damage-clusters on the μm-scale are correlated to damage clusters on the nm-scale. Therefore, it is possible to predict the cell survival after ion irradiation based on both scales. However, the cell survival after photon

  12. Modelling irradiation effect of EUROFER

    International Nuclear Information System (INIS)

    Boutard, J.-L.; Dudarev, S.; Victoria, M.

    2006-01-01

    In fusion power reactor, the properties that controlled the behaviour of materials are affected at the atom scale: (i) the crystalline structure is locally destroyed where a displacement cascade occurs, (ii) the chemical bond is affected by transmutation products such as He and H, (iii) an radiation induced microstructure will take place due the diffusion of these point defects and impurities EFDA has launched a programme since 2002 to develop and validate modelling tools to predict the radiation effects in the reference ferritic martensitic steel Eurofer. Up to now, the effort has been devoted (i) to validate the multi-scale modelling approach based on ab-initio energetics map of point defects and He, (iii) to develop inter-atomic potentials for Molecular Dynamics simulation of displacement cascades and dislocation dynamics. Formation and migration energies and diffusion mechanisms of small vacancy (n< ) and interstitial clusters (n< ) were computed with the ab-initio code SIESTA and used to successfully predict via Kinetic Monte Carlo the experimental recovery stages of radiation damage in ultra high purity Fe. A complete He and point defect energetics mapping was ab-initio determined in Fe-C and used to reproduce via Rate Theory He-desorption from pre-implanted specimens. A developed '' magnetic '' potential is capable of transferring the magnetic properties of Fe due to the 3d-electron correlation to the scale of the Molecular Dynamics. An inter-atomic potential is being developed to reproduce the thermodynamics of the Fe-Cr system. The program will now be devoted (i) to develop atom-scale reference kinetic methods to predict the phase - stability of the Fe-Cr thermally and under irradiation (ii) to predict at the atom scale the core structure and dynamics of screw dislocation and their collective behaviour at the meso-scale, using Discrete Dislocation Dynamics (iii) to validate at the relevant scale using the multi-beam CEA-CNRS facility JANNUS. JANNUS allows

  13. Influence of impurities on the evolution of vacancy-type defects in neutron-irradiated nickel

    International Nuclear Information System (INIS)

    Druzhkov, A.P.; Perminov, D.A.; Arbuzov, V.L.

    2012-01-01

    Highlights: ► We study, by means of PAS, the effects of purity on damage evolution in neutron-irradiated Ni at 330 K. ► Impurity carbon atoms in solution decrease the cascade efficiency during irradiation. ► C–V complexes are formed on the recovery stage III in impure Ni irradiated with 10 −4 dpa. ► The formation of V-loops and SFTs dominate on stage III with increasing dose level. ► The thermal stability of SFTs in impure Ni is similar to that in pure Ni. - Abstract: In order to investigate the effect of impurities on vacancy defect evolution in nickel, specimens with high (5N) and technical (3N) purity were neutron-irradiated at ∼330 K in the IVV-2M reactor (Russia) to fluencies in the range of 1 × 10 21 –1 × 10 23 n/m 2 (E > 0.1 MeV) corresponding to displacement dose levels in the range of about 0.0001–0.01 dpa and subsequently stepwise annealed to about 900 K. The specimens of Ni with different purities were characterized both in as-irradiated state as well as after post-irradiation annealing by positron annihilation spectroscopy. The formation of three-dimensional vacancy clusters (3D-VCs) in cascades was observed under neutron irradiation. The density and size of 3D-VCs depended not only on dose level, but also on purity. The population of 3D-VCs in the technical Ni is lower than that in the high-purity Ni. 3D-VCs collapse into secondary-type clusters (stacking fault tetrahedra (SFTs) and vacancy loops) during stepwise annealing at 350–450 K (stage III in Ni). The suppression of secondary cluster formation in 3N Ni is attributed to an effective vacancy interaction with impurity carbon atoms, which based on a relatively large vacancy–carbon atom binding energy (0.32–0.35 eV). The trapping of vacancies released at the collapse of 3D-VCs by the interstitial impurity atoms dominates at low irradiation dose level (10 −4 dpa). Thus, we found that carbon impurity atoms have strong effects both on the primary vacancy-type defect

  14. Cross section measurements of the processes occurring in the fragmentation of H{sub n}{sup +} (3 {<=} n {<=} 35) hydrogen clusters induced by high speed (60 keV/u) collisions on helium atoms; Mesure des sections efficaces des differents processus intervenant dans la fragmentation d`agregats d`hydrogene H{sub n}{sup +} (3 {<=} n {<=} 35) induite par collision a haute vitesse (60 keV/u) sur un atome d`helium

    Energy Technology Data Exchange (ETDEWEB)

    Louc, Sandrine [Inst. de Physique Nucleaire, Lyon-1 Univ., 69 - Villeurbanne (France)

    1997-09-15

    Different processes involved in the fragmentation of ionised hydrogen clusters H{sub 3} + (H{sub 2}){sub (n-3)/2} (n = 5-35) have been studied in the same experiment: the fragmentation of the cluster is induced by the collision with an helium atom at high velocity ({approx_equal} c/100). The collision is realised in reversed kinematic - clusters are accelerated - which allows the detection of neutral and charged fragments. The different channels of fragmentation are identified by using coincidence techniques. For all the cluster sizes studied the capture cross sections of one electron of the target by the cluster is equal to the capture cross section of the H{sub 3}{sup +} ion. In the same way, the dissociation cross section of the H{sub 3}{sup +} core of the cluster does not depend on cluster size. These fragmentation processes are due to the interaction of H{sub 3}{sup +} core of the cluster and the helium atom without ionization of another component of the cluster. On the contrary, the cross sections of loss of one, two and three molecules by the cluster and the dissociation cross section of the cluster in all its molecular components depends strongly on the cluster size. This dependence is different from the one measured for the metastable decay of the cluster. Thus, the process of loss of molecules induced by a collision should correspond to a different dissociation mechanism. In regard of the singularities observed for the size dependence, the H{sub 9}{sup +}, H{sub 15}{sup +}, H{sub 19}{sup +} and H{sub 29}{sup +} clusters could be the `core` of the biggest clusters. These observation are in agreement with the size effects of smaller magnitude observed for the dissociation cross section (all the processes). The values of the cross section for the process of at least one ionization of the cluster indicate that about 80% of the fragmentation events result from this process. (author) 114 refs., 74 figs., 9 tabs.

  15. Numerical simulation of physicochemical interactions between oxygen atom and phosphatidylcholine due to direct irradiation of atmospheric pressure nonequilibrium plasma to biological membrane with quantum mechanical molecular dynamics

    Science.gov (United States)

    Uchida, Satoshi; Yoshida, Taketo; Tochikubo, Fumiyoshi

    2017-10-01

    Plasma medicine is one of the most attractive applications using atmospheric pressure nonequilibrium plasma. With respect to direct contact of the discharge plasma with a biological membrane, reactive oxygen species play an important role in induction of medical effects. However, complicated interactions between the plasma radicals and membrane have not been understood well. In the present work, we simulated elemental processes at the first stage of physicochemical interactions between oxygen atom and phosphatidylcholine using the quantum mechanical molecular dynamics code in a general software AMBER. The change in the above processes was classified according to the incident energy of oxygen atom. At an energy of 1 eV, the abstraction of a hydrogen atom and recombination to phosphatidylcholine were simultaneously occurred in chemical attachment of incident oxygen atom. The exothermal energy of the reaction was about 80% of estimated one based on the bond energies of ethane. An oxygen atom over 10 eV separated phosphatidylcholine partially. The behaviour became increasingly similar to physical sputtering. The reaction probability of oxygen atom was remarkably high in comparison with that of hydrogen peroxide. These results suggest that we can uniformly estimate various physicochemical dynamics of reactive oxygen species against membrane lipids.

  16. Simulating irradiation hardening in tungsten under fast neutron irradiation including Re production by transmutation

    Science.gov (United States)

    Huang, Chen-Hsi; Gilbert, Mark R.; Marian, Jaime

    2018-02-01

    Simulations of neutron damage under fusion energy conditions must capture the effects of transmutation, both in terms of accurate chemical inventory buildup as well as the physics of the interactions between transmutation elements and irradiation defect clusters. In this work, we integrate neutronics, primary damage calculations, molecular dynamics results, Re transmutation calculations, and stochastic cluster dynamics simulations to study neutron damage in single-crystal tungsten to mimic divertor materials. To gauge the accuracy and validity of the simulations, we first study the material response under experimental conditions at the JOYO fast reactor in Japan and the High Flux Isotope Reactor at Oak Ridge National Laboratory, for which measurements of cluster densities and hardening levels up to 2 dpa exist. We then provide calculations under expected DEMO fusion conditions. Several key mechanisms involving Re atoms and defect clusters are found to govern the accumulation of irradiation damage in each case. We use established correlations to translate damage accumulation into hardening increases and compare our results to the experimental measurements. We find hardening increases in excess of 5000 MPa in all cases, which casts doubts about the integrity of W-based materials under long-term fusion exposure.

  17. Positron annihilation lifetime measurements of austenitic stainless and ferritic/martensitic steels irradiated in the SINQ target irradiation program

    Energy Technology Data Exchange (ETDEWEB)

    Sato, K., E-mail: ksato@rri.kyoto-u.ac.jp [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Xu, Q.; Yoshiie, T. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Dai, Y. [Spallation Neutron Source Division, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Kikuchi, K. [Frontier Research Center for Applied Atomic Sciences, Ibaraki University, Tokai-mura, Naka-gun, Ibaraki 319-1106 (Japan)

    2012-12-15

    Titanium-doped austenitic stainless steel (JPCA) and reduced activated ferritic/martensitic steel (F82H) irradiated with high-energy protons and spallation neutrons were investigated by positron annihilation lifetime measurements. Subnanometer-sized (<{approx}0.8 nm) helium bubbles, which cannot be observed by transmission electron microscopy, were detected by positron annihilation lifetime measurements for the first time. For the F82H steel, the positron annihilation lifetime of the bubbles decreased with increasing irradiation dose and annealing temperature because the bubbles absorb additional He atoms. In the case of JPCA steel, the positron annihilation lifetime increased with increasing annealing temperature above 773 K, in which case the dissociation of complexes of vacancy clusters with He atoms and the growth of He bubbles was detected. He bubble size and density were also discussed.

  18. Positron annihilation lifetime measurements of austenitic stainless and ferritic/martensitic steels irradiated in the SINQ target irradiation program

    International Nuclear Information System (INIS)

    Sato, K.; Xu, Q.; Yoshiie, T.; Dai, Y.; Kikuchi, K.

    2012-01-01

    Titanium-doped austenitic stainless steel (JPCA) and reduced activated ferritic/martensitic steel (F82H) irradiated with high-energy protons and spallation neutrons were investigated by positron annihilation lifetime measurements. Subnanometer-sized (<∼0.8 nm) helium bubbles, which cannot be observed by transmission electron microscopy, were detected by positron annihilation lifetime measurements for the first time. For the F82H steel, the positron annihilation lifetime of the bubbles decreased with increasing irradiation dose and annealing temperature because the bubbles absorb additional He atoms. In the case of JPCA steel, the positron annihilation lifetime increased with increasing annealing temperature above 773 K, in which case the dissociation of complexes of vacancy clusters with He atoms and the growth of He bubbles was detected. He bubble size and density were also discussed.

  19. Ceramic coatings by ion irradiation of polycarbosilanes and polysiloxanes. Pt. 1: Conversion mechanism

    International Nuclear Information System (INIS)

    Pivin, J.C.; Colombo, P.

    1997-01-01

    Changes of composition and structure of various types of polysiloxanes and polycarbosilanes when submitted to irradiation with ions of increasing mass, were analysed by means of several ion-beam analytical techniques, Raman and Fourier transform-infrared spectroscopes. Ion irradiations is as efficient as annealing at temperatures above 1000 o C for releasing hydrogen from these organic-inorganic polymers, and the radiolytic evolution of hydrogen is selective, whereas methane, silanes and carbon monoxide are also evolved during heat treatments. The kinetics of the polymer conversion into amorphous ceramics depends strongly on the linear density of energy transferred by ions to electron shells of target atoms, according to the ion energy per nucleon and to the nature of the side groups. Some of the carbon atoms segregate in clusters exhibiting a diamond-like hybridization state, in contrast to the clusters of turbostatic graphite formed in pyrolysed films. (Author)

  20. Stability and mobility of defect clusters and dislocation loops in metals

    DEFF Research Database (Denmark)

    Osetsky, Y.N.; Bacon, D.J.; Serra, A.

    2000-01-01

    has been observed in the computer simulation of small vacancy loops in alpha-Fe. In the present paper we summarise results obtained by molecular dynamics simulations of defect clusters and small dislocation loops in alpha-Fe(bcc) and Cu(fcc). The structure and stability of vacancy and interstitial......According to the production bias model, glissile defect clusters and small dislocation loops play an important role in the microstructural evolution during irradiation under cascade damage conditions. The atomic scale computer simulations carried out in recent years have clarified many questions...... loops are reviewed, and the dynamics of glissile clusters assessed. The relevance and importance of these results in establishing a better understanding of the observed differences in the damage accumulation behaviour between bcc and fee metals irradiated under cascade damage conditions are pointed out...

  1. Ion-channeling analysis of As relocation in heavily doped Si:As irradiated with high-energy ions

    International Nuclear Information System (INIS)

    Lulli, G.; Albertazzi, E.; Bianconi, M.; Ferri, M.

    2003-01-01

    Silicon on insulator layers doped with 8x10 20 As cm -3 and thermally equilibrated at 1100 deg. C, have been irradiated with 2 MeV Si + ions. Rutherford backscattering-channeling analysis shows an increase in As disorder upon irradiation significantly larger than the increase in Si disorder, while electrical measurements show a large decrease in electrical activation. Monte Carlo simulation of channeling angular scans suggests that the enhanced As disorder effect is due to the preferential relocation of dopant atoms slightly displaced from lattice sites, which appear the main reason responsible for the electrical deactivation in the unirradiated sample and are believed to be in the form of As-vacancy clusters. Upon 600 deg. C 15 s annealing, the As atoms randomly relocated by ion irradiation almost completely recover their original configuration, probably capturing vacancies and forming, again, the complexes dissociated by ion irradiation

  2. Spontaneous nano-clustering of ZrO2 in atomic layer deposited LayZr1-yOx thin films: Part 1 - Material characterization

    NARCIS (Netherlands)

    Klootwijk, J.H.; Jinesh, K.B.; Wolters, R.A.M.; Roozeboom, F.; Besling, W.

    2008-01-01

    During atomic layer deposition (ALD) of uniform LayZr1-yOx thin films, spontaneous segregation of ZrO2 nanocrystals takes place that are embedded in an amorphous La2O3 matrix. This occurs if the Zr content in the LayZr1-yOx film is above 30% i.e. if the pulse ratio between the lanthanum precursor

  3. Defect production and formation of helium-vacancy clusters due to cascades in α-iron

    International Nuclear Information System (INIS)

    Yang, L.; Zu, X.T.; Xiao, H.Y.; Gao, F.; Heinisch, H.L.; Kurtz, R.J.

    2007-01-01

    Displacement cascades are simulated by molecular dynamics methods in α-Fe containing different concentrations of substitutional He atoms. Primary knock-on atom (PKA) energies, E p , from 0.5 to 5 keV are considered at the irradiation temperature of 100 K. The concentration of He in Fe varies from 1 to 5 at%, and the results are compared with the simulations performed in pure α-Fe. We find that the total number of point defects increases with increasing He concentration. The present studies reveal the formation and the configurations of He-vacancy clusters in the cascades of α-Fe. Furthermore, the production efficiency of He-vacancy clusters increases with increasing He concentration and PKA energy. The nucleation mechanisms of He-vacancy clusters in displacement cascades are discussed in detail

  4. Molecular dynamics simulations of sputtering of organic overlayers by slow, large clusters

    International Nuclear Information System (INIS)

    Rzeznik, L.; Czerwinski, B.; Garrison, B.J.; Winograd, N.; Postawa, Z.

    2008-01-01

    The ion-stimulated desorption of organic molecules by impact of large and slow clusters is examined using molecular dynamics (MDs) computer simulations. The investigated system, represented by a monolayer of benzene deposited on Ag{1 1 1}, is irradiated with projectiles composed of thousands of noble gas atoms having a kinetic energy of 0.1-20 eV/atom. The sputtering yield of molecular species and the kinetic energy distributions are analyzed and compared to the results obtain for PS4 overlayer. The simulations demonstrate quite clearly that the physics of ejection by large and slow clusters is distinct from the ejection events stimulated by the popular SIMS clusters, like C 60 , Au 3 and SF 5 at tens of keV energies.

  5. An in situ study of the enhancement of atomic mobility under neutron irradiation in a Ag-30at%Zn alloy, using the Zener relaxation

    International Nuclear Information System (INIS)

    Halbwachs, M.; Hillairet, J.; Gonzalez, H.; Cost, J.

    1975-01-01

    An application of the Zener relaxation to the study of fast neutron effects on a Ag-Zn alloy is presented. The temperature dependence of the relaxation time is shown. It can be seen that the measured relaxation time at a given temperature increases with the irradiation doses [fr

  6. Self-organization processes and nanocluster formation in crystal lattices by low-energy ion irradiation

    International Nuclear Information System (INIS)

    Tereshko, I.; Abidzina, V.; Tereshko, A.; Glushchenko, V.; Elkin, I.

    2007-01-01

    The goal of this paper is to study self-organization processes that cause nanostructural evolution in nonlinear crystal media. The subjects of the investigation were nonlinear homogeneous and heterogeneous atom chains. The method of computer simulation was used to investigate the interaction between low-energy ions and crystal lattices. It was based on the conception of three-dimensional lattice as a nonlinear atom chain system. We showed that that in homogeneous atom chains critical energy needed for self-organization processes development is less than for nonlinear atom chain with already embedded clusters. The possibility of nanostructure formation was studied by a molecular dynamics method of nonlinear oscillations in atomic oscillator systems of crystal lattices after their low-energy ion irradiation. (authors)

  7. From solid solution to cluster formation of Fe and Cr in α-Zr

    International Nuclear Information System (INIS)

    Burr, P.A.; Wenman, M.R.; Gault, B.; Moody, M.P.; Ivermark, M.; Rushton, M.J.D.; Preuss, M.; Edwards, L.; Grimes, R.W.

    2015-01-01

    To understand the mechanisms by which the re-solution of Fe and Cr additions increase the corrosion rate of irradiated Zr alloys, the solubility and clustering of Fe and Cr in model binary Zr alloys was investigated using a combination of experimental and modelling techniques — atom probe tomography (APT), x-ray diffraction (XRD), thermoelectric power (TEP) and density functional theory (DFT). Cr occupies both interstitial and substitutional sites in the α-Zr lattice; Fe favours interstitial sites, and a low-symmetry site that was not previously modelled is found to be the most favourable for Fe. Lattice expansion as a function of Fe and Cr content in the α-Zr matrix deviates from Vegard's law and is strongly anisotropic for Fe additions, expanding the c-axis while contracting the a-axis. Matrix content of solutes cannot be reliably estimated from lattice parameter measurements, instead a combination of TEP and APT was employed. Defect clusters form at higher solution concentrations, which induce a smaller lattice strain compared to the dilute defects. In the presence of a Zr vacancy, all two-atom clusters are more soluble than individual point defects and as many as four Fe or three Cr atoms could be accommodated in a single Zr vacancy. The Zr vacancy is critical for the increased apparent solubility of defect clusters; the implications for irradiation induced microstructure changes in Zr alloys are discussed.

  8. From solid solution to cluster formation of Fe and Cr in α-Zr

    Energy Technology Data Exchange (ETDEWEB)

    Burr, P.A., E-mail: burr.patrick@gmail.com [Centre for Nuclear Engineering and Department of Materials, Imperial College London, London, SW7 2AZ (United Kingdom); Institute of Materials Engineering, Australian Nuclear Science & Technology Organisation, Menai, New South Wales 2234 (Australia); Wenman, M.R. [Centre for Nuclear Engineering and Department of Materials, Imperial College London, London, SW7 2AZ (United Kingdom); Gault, B.; Moody, M.P. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom); Ivermark, M. [High Temperature Materials, Sandvik Materials Technology, 734 27 Hallstahammar (Sweden); University of Manchester, School of Materials, M13 9PL (United Kingdom); Rushton, M.J.D. [Centre for Nuclear Engineering and Department of Materials, Imperial College London, London, SW7 2AZ (United Kingdom); Preuss, M. [University of Manchester, School of Materials, M13 9PL (United Kingdom); Edwards, L. [Institute of Materials Engineering, Australian Nuclear Science & Technology Organisation, Menai, New South Wales 2234 (Australia); Grimes, R.W. [Centre for Nuclear Engineering and Department of Materials, Imperial College London, London, SW7 2AZ (United Kingdom)

    2015-12-15

    To understand the mechanisms by which the re-solution of Fe and Cr additions increase the corrosion rate of irradiated Zr alloys, the solubility and clustering of Fe and Cr in model binary Zr alloys was investigated using a combination of experimental and modelling techniques — atom probe tomography (APT), x-ray diffraction (XRD), thermoelectric power (TEP) and density functional theory (DFT). Cr occupies both interstitial and substitutional sites in the α-Zr lattice; Fe favours interstitial sites, and a low-symmetry site that was not previously modelled is found to be the most favourable for Fe. Lattice expansion as a function of Fe and Cr content in the α-Zr matrix deviates from Vegard's law and is strongly anisotropic for Fe additions, expanding the c-axis while contracting the a-axis. Matrix content of solutes cannot be reliably estimated from lattice parameter measurements, instead a combination of TEP and APT was employed. Defect clusters form at higher solution concentrations, which induce a smaller lattice strain compared to the dilute defects. In the presence of a Zr vacancy, all two-atom clusters are more soluble than individual point defects and as many as four Fe or three Cr atoms could be accommodated in a single Zr vacancy. The Zr vacancy is critical for the increased apparent solubility of defect clusters; the implications for irradiation induced microstructure changes in Zr alloys are discussed.

  9. Cluster growing process and a sequence of magic numbers

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2003-01-01

    demonstrate that in this way all known global minimum structures of the Lennard-Jones (LJ) clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic