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Sample records for analysing positron lifetime

  1. Mining the bulk positron lifetime

    Energy Technology Data Exchange (ETDEWEB)

    Aourag, H.; Guittom, A. [Centre de Recherche Nucleaire d' Alger (CRNA), Alger Gare - Algiers (Algeria)

    2009-02-15

    We introduce a new approach to investigate the bulk positron lifetimes of new systems based on data-mining techniques. Through data mining of bulk positron lifetimes, we demonstrate the ability to predict the positron lifetimes of new semiconductors on the basis of available semiconductor data already studied. Informatics techniques have been applied to bulk positron lifetimes for different tetrahedrally bounded semiconductors in order to discover computational design rules. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Mining the bulk positron lifetime

    International Nuclear Information System (INIS)

    We introduce a new approach to investigate the bulk positron lifetimes of new systems based on data-mining techniques. Through data mining of bulk positron lifetimes, we demonstrate the ability to predict the positron lifetimes of new semiconductors on the basis of available semiconductor data already studied. Informatics techniques have been applied to bulk positron lifetimes for different tetrahedrally bounded semiconductors in order to discover computational design rules. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Deconvolution of Positrons' Lifetime spectra

    International Nuclear Information System (INIS)

    In this paper, we explain the iterative method previously develop for the deconvolution of Doppler broadening spectra using the mathematical optimization theory. Also, we start the adaptation and application of this method to the deconvolution of positrons' lifetime annihilation spectra

  4. Positron lifetime calculation for the elements of the periodic table

    International Nuclear Information System (INIS)

    Theoretical positron lifetime values have been calculated systematically for most of the elements of the periodic table. Self-consistent and non-self-consistent schemes have been used for the calculation of the electronic structure in the solid, as well as different parametrizations for the positron enhancement factor and correlation energy. The results obtained have been studied and compared with experimental data, confirming the theoretical trends. As is known, positron lifetimes in bulk show a periodic behaviour with atomic number. These calculations also confirm that monovacancy lifetimes follow the same behaviour. The effects of enhancement factors used in calculations have been commented upon. Finally, we have analysed the effects that f and d electrons have on positron lifetimes

  5. Positron Annihilation Lifetimes in Compacted Iron Powder

    International Nuclear Information System (INIS)

    The positron annihilation lifetime (PAL) spectroscopy has been performed on iron powder as a function of compacted powder load. The ortho-positronium lifetime increases from 1.45 to 2.55 ns with compaction load increment from 30 to 50 tons. By increasing the compaction load, the ultimate stress and hardness increases and the ductlity decreases. The result shows that there is a direct correlation between the void size and the load decrement. These results will be presented and discussed

  6. A compact positron annihilation lifetime spectrometer

    Institute of Scientific and Technical Information of China (English)

    李道武; 刘军辉; 章志明; 王宝义; 张天保; 魏龙

    2011-01-01

    Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size γ-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the co

  7. Digital positron lifetime spectroscopy at EPOS

    International Nuclear Information System (INIS)

    As the digital equipment to measure positron lifetimes gets cheaper and more widely used, it is decided that EPOS, the ELBE positron source will sample the signals from the photomultipliers directly and evaluate it online or offline by digital means. Still using isotope sources, the EPOS lifetime spectrometer results in a timing resolution of around 170 ps (with 60Co), which compares good to analog equipment. A distinct improvement is expected when a coincidence setup will be used at ELBE. However, also the software needs further improvement: while one of the goals is of course to achieve the best time resolution, there is also the aspect of runtime and expandability. Results of evaluations will be presented and compared with results from other groups

  8. Application of positron annihilation lifetime technique for {gamma}-irradiation stresses study in chalcogenide vitreous semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, O.; Golovchak, R.; Kovalskiy, A. [Scientific Research Company ' ' Carat' ' , Stryjska str. 20279031 Lviv (Ukraine); Filipecki, J.; Hyla, M. [Physics Institute, Pedagogical University, Al. Armii Krajowej 13/1542201 Czestochowa (Poland)

    2002-08-01

    The influence of {gamma}-irradiation on the positron annihilation lifetime spectra in chalcogenide vitreous semiconductors of As-Ge-S system has been analysed. The correlations between lifetime data, structural features and chemical compositions of glasses have been discussed. The observed lifetime components are connected with bulk positron annihilation and positron annihilation on various native and {gamma}-induced open volume defects. It is concluded that after {gamma}-irradiation of investigated materials the {gamma}-induced microvoids based on S{sub 1}{sup -}, As{sub 2}{sup -}, and Ge{sub 3}{sup -} coordination defects play the major role in positron annihilation processes. (Abstract Copyright[2002], Wiley Periodicals, Inc.)

  9. Discrete and continuous analysis of positron lifetime spectra: A comparison

    International Nuclear Information System (INIS)

    Positron lifetime spectra in poly[1-(trimethylsilyl)]propine membranes were collected at different temperatures and various number of accumulated counts, in order to compare the results from analyses obtained by different decay models: discrete (that is, purely exponential or continuous (with at least one distribution of lifetimes). Analysis into four discrete components is un adequate, unless a low number of counts (1 to 2 millions) is accumulated. Conversely, deconvolutions which allow to ortho-positronium lifetime to be distributed give satisfactory fits, even at highest statistics (60 millions). An equivalent good fit in terms of Χ2 test is obtained with a five discrete components analysis, from which it is possible to extract information on the first moments (centroid and standard deviation) of ortho-positronium lifetime distribution. (author)

  10. Positron annihilation lifetime study of polyvinylpyrrolidone for nanoparticle-stabilizing pharmaceuticals.

    Science.gov (United States)

    Shpotyuk, O; Bujňáková, Z; Baláž, P; Ingram, A; Shpotyuk, Y

    2016-01-01

    Positron annihilation lifetime spectroscopy was applied to characterize free-volume structure of polyvinylpyrrolidone used as nonionic stabilizer in the production of many nanocomposite pharmaceuticals. The polymer samples with an average molecular weight of 40,000 g mol(-1) were pelletized in a single-punch tableting machine under an applied pressure of 0.7 GPa. Strong mixing in channels of positron and positronium trapping were revealed in the polyvinylpyrrolidone pellets. The positron lifetime spectra accumulated under normal measuring statistics were analysed in terms of unconstrained three- and four-term decomposition, the latter being also realized under fixed 0.125 ns lifetime proper to para-positronium self-annihilation in a vacuum. It was shown that average positron lifetime extracted from each decomposition was primary defined by long-lived ortho-positronium component. The positron lifetime spectra treated within unconstrained three-term fitting were in obvious preference, giving third positron lifetime dominated by ortho-positronium pick-off annihilation in a polymer matrix. This fitting procedure was most meaningful, when analysing expected positron trapping sites in polyvinylpyrrolidone-stabilized nanocomposite pharmaceuticals. PMID:26444751

  11. Positron lifetime technique with applications in materials science

    International Nuclear Information System (INIS)

    This thesis deals with the positron lifetime technique as a method to measure extremely low concentrations of extremely small cavities in materials. The method is based upon the fact that the positron lieftime decreases as the electron density increases and upon the fact that a positron preferably annihilates in cavity-like defects in lattices. The theory of positron behaviour in materials and technical aspects of measuring positron liefetimes are described in ch.'s 2 and 3 respectively. Three methods for increasing the time resolution are discussed and some positron sources are described (ch.4). Some applications of the positron lifetime technique and experimental results are shown in chapter 5. 125 refs.; 61 figs.; 18 tabs

  12. Positron Lifetimes in Pure and Doped Ice and in Water

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Mogensen, O.; Trumpy, Georg

    1972-01-01

    Positron lifetime spectra were measured in mono- and polycrystalline light ice, polycrystalline heavy ice, doped light ice, as well as in light and heavy water. All spectra were resolved into three components. At temperatures between −196° and −100°C the lifetimes and relative intensities are vir...

  13. Positron annihilation lifetime study of low temperature irradiated metals

    Energy Technology Data Exchange (ETDEWEB)

    Kuramoto, Eiichi [Kyushu Univ., Kasuga, Fukuoka (Japan). Research Inst. for Applied Mechanics

    1997-11-01

    Positron annihilation lifetime measurements have been made for electron and neutron irradiated Fe, Fe-Cr, Fe-Cu, Fe-Si, Fe-16Cr-17Ni specimens, and isochronal annealing behaviors were obtained for these metals and alloys. It was found that vacancies start to migrate at about 200 K in Fe and form microvoids, but by the addition of small amount of alloying elements this behavior was changed depending on the alloying elements. Positron lifetime calculations were made to explain the experimental results using EAM (embedded atom method) type potential for the lattice relaxation and the atomic superposition method for the lifetime calculation. Fairly good agreements were obtained for the positron lifetime in a vacancy in Fe and other alloys. (author)

  14. Positron annihilation lifetime study of oxide dispersion strengthened steels

    Science.gov (United States)

    Krsjak, V.; Szaraz, Z.; Hähner, P.

    2012-09-01

    A comparative positron annihilation lifetime study has been performed on various commercial ferritic and ferritic/martensitic oxide dispersion strengthened (ODS) steels. Both as-extruded and recrystallized materials were investigated. In the materials with recrystallized coarse-grained microstructures, only the positron trapping at small vacancy clusters and yttria nanofeatures was observed. Materials which had not undergone recrystallization treatment clearly showed additional positron trapping which is associated with dislocations. Dislocation densities were calculated from a two-component decomposition of the positron lifetime spectra by assuming the first component to be a superposition of the bulk controlled annihilation rate and the dislocation controlled trapping rate. The second component (which translates into lifetimes of 240-260 ps) was found to be well separated in all those ODS materials. This paper presents the potentialities and limitations of the positron annihilation lifetime spectroscopy, and discusses the results of the experimental determination of the defect concentrations and sensitivity of this technique to the material degradation due to thermally induced precipitation of chromium-rich α' phases.

  15. Positron lifetime studies in vinyl polymers of medical importance

    International Nuclear Information System (INIS)

    Vinyl polymers used as artificial lens implants in ophthalmology were investigated by positron lifetime spectroscopy. The structure of these polymers with free volumes offers the possibility of charging them with anti-inflammatory drugs for sustained release. A correlation between the amount of normalised free volume and the ratio of the methyl methacrylate to ethyl-hexyl-acrylate, used as polymerisation monomers, was found

  16. Positron lifetime studies in vinyl polymers of medical importance

    OpenAIRE

    Marques, M. F. Ferreira; Gordo, P. M.; Gil, C. Lopes; Kajcsos, Zs.; Gil, M. H.; Mariz, M. J.; Lima, A.P.

    2003-01-01

    Vinyl polymers used as artificial lens implants in ophthalmology were investigated by positron lifetime spectroscopy. The structure of these polymers with free volumes offers the possibility of charging them with anti-inflammatory drugs for sustained release. A correlation between the amount of normalised free volume and the ratio of the methyl methacrylate to ethyl-hexyl-acrylate, used as polymerisation monomers, was found.

  17. Positron and Positronium Annihilation Lifetime, and Free Volume in Polymers.

    Science.gov (United States)

    Yu, Zhibin

    1995-01-01

    Positron annihilation lifetime measurements were carried out for six polycarbonates of different structures and four polystyrenes of different molecular weight over a wide temperature range covering the glass transition region. The o-Ps mean lifetime is very sensitive to the changes of free volume in those polymers which occur due to change of molecular structure, chain length, and temperature. The influence of the unavoidable e^{+} irradiation and physical aging on the mean lifetime and the intensity of o-Ps annihilation were studied by conducting time dependent measurements on both very aged and rejuvenated samples. Both irradiation and physical aging reduce the formation of positronium, but have no effect on the mean lifetime of Ps atoms. The free volume fraction h obtained from the positron lifetime measurements was compared with the prediction of the statistical mechanical theory of Simha and Somcynsky; good agreement was found in the melt state though clear deviations were observed in the glassy state. A free volume quantity, computed from the bulk volume, which is in a good numerical agreement with the Simha-Somcynsky h-function in the melt, gives improved agreement with the h value calculated from the positron lifetime measurements. To investigate certain anomalies observed in the computer analysis of the positron annihilation lifetime spectra on polymers, we developed a computer simulation of the experimental data, which then was used to test the accuracy of the fitting results in the different circumstances. The influence caused by a possible distribution of the o-Ps mean lifetimes and the width of the spectrometer time resolution function were studied. The theoretical connection between the o-Ps mean lifetime and the free volume hole size was reviewed based on a finite spherical potential well model, and the status of the localized Ps atom in polymers was evaluated by calculation of the barrier transmission probability and the escaping probability of the

  18. Accurate theoretical prediction on positron lifetime of bulk materials

    CERN Document Server

    Zhang, Wenshuai; Liu, Jiandang; Ye, Bangjiao

    2015-01-01

    Based on the first-principles calculations, we perform an initiatory statistical assessment on the reliability level of theoretical positron lifetime of bulk material. We found the original generalized gradient approximation (GGA) form of the enhancement factor and correlation potentials overestimates the effect of the gradient factor. Furthermore, an excellent agreement between model and data with the difference being the noise level of the data is found in this work. In addition, we suggest a new GGA form of the correlation scheme which gives the best performance. This work demonstrates that a brand-new reliability level is achieved for the theoretical prediction on positron lifetime of bulk material and the accuracy of the best theoretical scheme can be independent on the type of materials.

  19. Positron lifetime study of electron-irradiated epoxy resins

    International Nuclear Information System (INIS)

    Two bisphenol-A type epoxy resins were irradiated by electron beam and studied afterwards by positron lifetime spectroscopy. An interesting result is that despite of the considerable amount of free-radicals, no inhibition of positronium formation was observed in the two epoxies. Nevertheless, several serious differences were detected between the studied polymers. The results suggest that the radiation-resistant properties of epoxies depend strongly on the amount of the curing agent. (author) 8 refs.; 2 figs

  20. Positron lifetime calculation of the elements of the periodic table

    International Nuclear Information System (INIS)

    The classification of the elements has been one of the major achievements of Science. Since then the resulting periodic order has been most strikingly reflected in a quantitative manner by most of the physical properties of the elements. The aim of this paper is to show the strong relation between the atomic volume and the positron lifetime of the elements of the periodic table. The differences between the BN, LDA and GGA schemes of calculations are pointed out too. (orig.)

  1. Positron lifetime spectroscopy of vitreous B2O3

    International Nuclear Information System (INIS)

    A comparison is made of the structural data obtained by positron lifetime spectroscopy (PLS) for vitreous B2O3 (v-B2O3) and crystalline B2O3 (c-B2O3). Samples of v-B2O3 were dried by holding the melt at 1350K to reduce residual OH groups. Fast quenching and slow cooling were used to obtain glasses having different fictive structures. According to the literature, B3O6 rings are thought to be formed during slow cooling of v-B2O3. PLS measurements show that both the intensity value and the long lifetime component (t3) associated with positron decay in cavities and lifetime component (t1) associated with the positron annihilation in the bulk are different for v-B2O3 and c-B2O3. The low intensity of t3 for c-B2O3 and its high value for v-B2O3 is argued to be due to the presence of different structural units in the two states of B2O3

  2. Investigation on the porosity of zeolite NU-88 by means of positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Seven well characterized zeolites were investigated by positron annihilation lifetime spectroscopy. The lifetime spectra were analysed in four discrete components. The third one was associated with ortho-positronium annihilation in the channels, framed in terms of infinite cylinders. Differences between the radii determined from the positron annihilation technique and X-ray diffraction data were found and explained in terms of the physical structure of the channel. An analogous study on a high-silica NU-88 zeolite gave a value of 0.33 nm for the corresponding radius, in agreement with Ar and N2 adsorption data as well as with the catalytic behaviour of this zeolite in several acid catalyzed reactions. The longest lifetime component in NU-88 reveals the existence of mesopores, with average radius of about 1.8 nm, which could explain the importance of hydrogen transfer reactions in this zeolite.

  3. Single-shot positron annihilation lifetime spectroscopy with LYSO scintillators

    Science.gov (United States)

    Alonso, A. M.; Cooper, B. S.; Deller, A.; Cassidy, D. B.

    2016-08-01

    We have evaluated the application of a lutetium yttrium oxyorthosilicate (LYSO) based detector to single-shot positron annihilation lifetime spectroscopy. We compare this detector directly with a similarly configured PbWO4 scintillator, which is the usual choice for such measurements. We find that the signal to noise ratio obtained using LYSO is around three times higher than that obtained using PbWO4 for measurements of Ps excited to longer-lived (Rydberg) levels, or when they are ionized soon after production. This is due to the much higher light output for LYSO (75% and 1% of NaI for LYSO and PbWO4 respectively). We conclude that LYSO is an ideal scintillator for single-shot measurements of positronium production and excitation performed using a low-intensity pulsed positron beam.

  4. A positron lifetime study of properties of light particles in liquids

    International Nuclear Information System (INIS)

    The positron lifetime technique has been used for studying the behaviour of the three light particles: the positron, positronium (Ps) (a bound state of an electron and positron), and excess electron in non-polar liquids. A brief introduction to the subject and a short description of the experimental techniques are given. Further, the principles of the data analyses are discussed in some detail. Positron lifetime measurements have been performed on the liquids: SF6, neopentane, hexane, and two viscoelastic organic liquids. The experiments have been performed as function of temperature, e.g., from just above the melting point to above the critical point in the cases of liquid SF6 and neopentane. In all of the liquids the experimental results show that Ps is formed. The analyses of the lifetime spectra show that the Ps yields as well as the state of Ps in these liquids change with temperature. A detailed discussion of the state of Ps in liquids is given. The present results can be explained fairly well in terms of the Ps bubble model. In liquid SF6 the experimental results strongly indicate that ortho-Ps can annihilate from two different states. The longest-lived ortho-Ps state seems to be similar to that observed in most liquids while the shortest-lived state seems not to have been observed in any other liquids before. A detailed discussion of the measured Ps yield in liquid neopentane and hexane is given. The Ps yield is interpreted by means of the positron spur model. (author)

  5. Photon-induced positron annihilation lifetime spectroscopy using an S-band compact electron linac

    International Nuclear Information System (INIS)

    A new photon-induced positron annihilation lifetime spectroscopy approach has been developed using an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). The high energy (5 photons pulse−1), and ultra-short pulse (3 ps pulse width) photon beam creates positrons throughout an entire sample via pair production. A positron lifetime spectrum can be obtained by measuring the time difference between the accelerator's RF frequency and the detection time of the annihilation gamma rays. The positron lifetimes for lead and yttria-stabilized zirconia samples have been successfully measured. - Highlights: ► Photon-induced positron annihilation lifetime spectrometer has been developed. ► Defect analysis for thick materials is possible by using our spectrometer. ► The positron lifetime for a lead and a YSZ has been successfully measured

  6. Design, simulation and performance of a slow positron beam with secondary electron tagging for positron annihilation lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Marinov, H. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia (Bulgaria); Djourelov, N., E-mail: nikdjour@inrne.bas.bg [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia (Bulgaria); Nédélec, P. [Université de Lyon, Laboratoire IPNL, UCB Lyon 1, Bâtiment Paul Dirac, 4 rue Enrico Fermi, 69622 Villeurbanne Cedex (France); Petrov, L. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia (Bulgaria)

    2013-11-21

    A positron annihilation lifetime spectrometer using a magnetically guided continuous positron beam and the signal from secondary electrons (SE) emitted from the sample is presented. The positron and secondary electrons trajectories as well as the physics of SE were simulated using GEANT4 program. A special attention was paid to the consequences of positron backscattering, in particular on the shape of the lifetime spectrum. A very good agreement was obtained between simulation and measurements concerning the time resolution (∼300–400 ps FWHM) for the studied range of incident positron energies. Due to the complex shape of the resolution function, the present design of the spectrometer is not suited to study of short lifetimes, but can be used for depth profiling porosimetry of materials with Ps formation with the an excellent peak to background ratio of ∼10{sup 5}.

  7. Positron annihilation lifetime study of radiation-damaged natural zircons

    Science.gov (United States)

    Roberts, J.; Gaugliardo, P.; Farnan, I.; Zhang, M.; Vance, E. R.; Davis, J.; Karatchevtseva, I.; Knott, R. B.; Mudie, S.; Buckman, S. J.; Sullivan, J. P.

    2016-04-01

    Zircons are a well-known candidate waste form for actinides and their radiation damage behaviour has been widely studied by a range of techniques. In this study, well-characterised natural single crystal zircons have been studied using Positron Annihilation Lifetime Spectroscopy (PALS). In some, but not all, of the crystals that had incurred at least half of the alpha-event damage of ∼1019 α/g required to render them structurally amorphous, PALS spectra displayed long lifetimes corresponding to voids of ∼0.5 nm in diameter. The long lifetimes corresponded to expectations from published Small-Angle X-ray Scattering data on similar samples. However, the non-observation by PALS of such voids in some of the heavily damaged samples may reflect large size variations among the voids such that no singular size can be distinguished or. Characterisation of a range of samples was also performed using scanning electron microscopy, optical absorption spectroscopy, Raman scattering and X-ray scattering/diffraction, with the degree of alpha damage being inferred mainly from the Raman technique and X-ray diffraction. The observed void diameters and intensities of the long lifetime components were changed somewhat by annealing at 700 °C; annealing at 1200 °C removed the voids entirely. The voids themselves may derive from He gas bubbles or voids created by the inclusion of small quantities of organic and hydrous matter, notwithstanding the observation that no voidage was evidenced by PALS in two samples containing hydrous and organic matter.

  8. Positron annihilation lifetime study of interfaces in ternary polymer blends

    Science.gov (United States)

    Meghala, D.; Ramya, P.; Pasang, T.; Raj, J. M.; Ranganathaiah, C.; Williams, J. F.

    2013-06-01

    A new method based on positron lifetime spectroscopy is developed to characterize individual interfaces in ternary polymer blends and hence determine the composition dependent miscibility level. The method owes its origin to the Kirkwood-Risemann-Zimm (KRZ) model for the evaluation of the hydrodynamic interaction parameters (αij) which was used successfully for a binary blend with a single interface. The model was revised for the present work for ternary polymer blends to account for three interfaces. The efficacy of this method is shown for two ternary blends namely poly(styrene-co-acrylonitrile)/poly (ethylene-co-vinylacetate)/poly(vinyl chloride) (SAN/EVA/PVC) and polycaprolactone /poly(styrene-co-acrylonitrile)/poly(vinyl chloride) (PCL/SAN/PVC) at different compositions. An effective hydrodynamic interaction parameter, αeff, was introduced to predict the overall miscibility of ternary blends.

  9. Positron lifetime study in dilute electron irradiated lead based alloys

    Energy Technology Data Exchange (ETDEWEB)

    Moya, G. [Lab. de Physique des Materiaux, 13 Marseille (France); Li, X.H. [D.R.F.M., S.P.2.M., M.P., C.E.N.G., 38 Grenoble (France); Menai, A. [Lab. de Physique des Materiaux, 13 Marseille (France); Kherraz, M. [Lab. de Physique des Materiaux, 13 Marseille (France); Amenzou, H. [Lab. de Physique des Materiaux, 13 Marseille (France); Bernardini, J. [Lab. de Metallurgie, 13 Marseille (France); Moser, P. [D.R.F.M., S.P.2.M., M.P., C.E.N.G., 38 Grenoble (France)

    1995-06-01

    The recovery of defects in two dilute solute-lead based alloys (Pb-Au, Pb-Cd) has been followed by positron lifetime measurements after a 3 MeV electron irradiation at 20 K. Two distinct isochronal annealing stages, the first centred at about 150 K and the other around 275 K, are to be observed as exactly the same in both the pure Pb and dilute alloys but the vacancy clustering over the second stage seen in lead and Pb-Au is completely suppressed in the Pb-Cd alloy. The results are discussed in terms of a high interaction between the cadmium atoms and vacancies in agreement with a probable presence of atomic excitons. (orig.)

  10. Positron lifetime study in dilute electron irradiated lead based alloys

    International Nuclear Information System (INIS)

    The recovery of defects in two dilute solute-lead based alloys (Pb-Au, Pb-Cd) has been followed by positron lifetime measurements after a 3 MeV electron irradiation at 20 K. Two distinct isochronal annealing stages, the first centred at about 150 K and the other around 275 K, are to be observed as exactly the same in both the pure Pb and dilute alloys but the vacancy clustering over the second stage seen in lead and Pb-Au is completely suppressed in the Pb-Cd alloy. The results are discussed in terms of a high interaction between the cadmium atoms and vacancies in agreement with a probable presence of atomic excitons. (orig.)

  11. Positron lifetime study in dilute electron irradiated lead based alloys

    International Nuclear Information System (INIS)

    The recovery of defects in two dilute solute-lead based alloys (Pb-Au, Pb-Cd) has been followed by positron lifetime measurements after a 3 MeV electron irradiation at 20 K. Two distinct isochronal annealing stages, the first centered at about 150 K and the other around 275 K, are to be observed as exactly the same in both the pure Pb and dilute alloys but the vacancy clustering over the second stage seen in lead and Pb-Au is completely suppressed in the Pb-Cd alloy. The results are discussed in terms of a high interaction between the cadmium atoms and vacancies in agreement with a probable presence of atomic excitons. (authors). 3 figs., 9 refs

  12. Ab initio calculation of positron distribution, ACAR and lifetime in TTF-TCNQ

    International Nuclear Information System (INIS)

    We have performed ab initio calculations of positron distribution, ACAR and lifetime in the quasi-one-dimensional organic conductor TTF-TCNQ. The electronic structure is obtained within the LDA, while the positron state is calculated either with the LDA or with the GGA. Except the positron lifetime, differences between the LDA and GGA results are rather small. The obtained results are compared with our previous experiments and calculations.

  13. Ab initio calculation of positron distribution, ACAR and lifetime in TTF-TCNQ

    Science.gov (United States)

    Ishibashi, Shoji; Kohyama, Masanori

    2000-06-01

    We have performed ab initio calculations of positron distribution, ACAR and lifetime in the quasi-one-dimensional organic conductor TTF-TCNQ. The electronic structure is obtained within the LDA, while the positron state is calculated either with the LDA or with the GGA. Except the positron lifetime, differences between the LDA and GGA results are rather small. The obtained results are compared with our previous experiments and calculations.

  14. Permeability of gases in polyacetylenes and free volume obtained by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectra (PALS) of nine substituted polyacetylenes in vacuum and in air were analysed with aim to determine free volume and influence of the atmosphere. Studied glassy polymers in wide variation of permeability showed bimodal distribution of free volume elements. Good correlation between long-live component(s) of PALS spectra of trialkylsilyl-, denyl- and adamantyl-substituted polyacetylenes and permeability of oxygen and nitrogen is suitable for quickly and non-destructive evaluation of free volume of the polymers and for their screening of membranes. (author)

  15. Application of fast-digitizer card Acqiris DP-240 in positron lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Petriska, Martin; Slugen, Vladimir; Krsjak, Vladimir; Sojak, Stanislav [Slovak University of Technology, FEI, Bratislava (Slovakia); Zeman, Andrej; Debarberis, Luigi [European Commission, Joint Research Centre, Institute for Energy, Petten (Netherlands)

    2009-11-15

    Based on the available knowledge base in positron annihilation measurements, new software for digital positron lifetime spectrometry has been designed within the frame of joint activity between STU Bratislava and JRC Petten. The tests of the new positron digital-life time setup have been carried out. Detectors with BaF{sub 2} scintillators and fast-dynode outputs were chosen for such studies. As the digitiser unit, the card Acqiris DP240 was fully tested. Originally, start and stop timing signals were sampled to digital waveforms separately at a rate of 1 GS/s in 8 bit resolution. However, due to limited quality of collected waveforms which significantly affected post-processing of data, the joined delayed channel mode with 2 GS/s sampling rate was applied for further studies. The full setup was benchmarked by a series of calibration measurements of two high purity materials, specifically Si and Ni. The inter-comparison of conventional analogue- and digital-based processing are discussed in detail. Further, the optimisation of main parameters for waveform-processing are analysed too. Such a new approach in the digital life-time spectroscopy will help to improve the resolution of existing methodology which might enhance the capabilities of this technique for further applications, especially in materials science. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. A positron annihilation lifetime spectroscopy study of porous silicon using a continuous lifetime fitting algorithm

    International Nuclear Information System (INIS)

    In the present work we report on a positron annihilation lifetime spectroscopy (PALS) investigation of porous silicon using a continuous lifetime fitting algorithm. Our motivation lies in the underlying disadvantage in discrete lifetime fitting algorithms where the number of components must initially be assumed since in general a realistic spectrum does not uniquely determine this number. This becomes particularly apparent when looking at highly disordered systems where the notion of a discrete spectrum may be invalid and indeed crucial to an understanding of the optical absorption and photo-luminescence properties. Using the PALS data collected from different porous silicon samples in conjunction with other methods of characterisation, we have extended the findings of previous work. In particular we resolve three rather than two ortho-positronium components, suggesting that there may be an additional intermediary scale of porosity in which ortho-positronium annihilates. We also establish the existence of a very weak ortho-positronium component in the pre-anodised wafers at a time scale approximately equal to the longest time ortho-positronium component seen in porous silicon, suggesting that irregularities of a particular magnitude exist before anodisation and that these may, in part, be the catalyst for the initial pore formation process

  17. Positron lifetimes in voids and other defects in annealed, neutron-irradiated aluminum

    International Nuclear Information System (INIS)

    Positron lifetimes were measured in neutron-irradiated high-purity aluminum single crystals, and companion small-angle x-ray scattering experiments were performed to determine the radius of gyration and volume fraction of radiation-induced voids. The lifetime data are consistent with a model in which positrons are trapped both in voids and in other defects which are tentatively identified as vacancy clusters bound to transmutation-produced silicon. The lifetime in the latter defects increased from 230 to 430 ps as the voids annealed out (around 3060C), suggesting that the clusters grow in size as voids disappear. The lifetime in voids remained constant at (550 +- 30) ps

  18. Approximate method for calculating the lifetime of positrons trapped by lattice defects

    International Nuclear Information System (INIS)

    A method which takes account of core as well as valence electrons is presented for theoretically estimating the life-time of positrons trapped in lattice defects. The method is illustrated by calculations for vacancies and divacancies in aluminum

  19. Positron lifetime as a probe for the investigation of conducting polystyrene

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectroscopy is applied to study the microstructure and conducting mechanism of polystyrene conducting polymer. The positron lifetime spectra and electrical conductivity of the sample were measured as a function of temperature (30-145 C). The data clearly revealed the phase transition at about 62 C and the glass transition temperature (Tg) around 95 C. The dependence of the size and relative fractional of the ortho-positronium hole volume on the electrical conductivity has been obtained. (orig.)

  20. Positron lifetime study of native vacancy-like defects in chalcogenide glasses

    International Nuclear Information System (INIS)

    Modified model for positron annihilation in vitreous chalcogenide semiconductors is developed to explain a number of previously obtained results on positron lifetime measurements in glassy As-Ge-S of stoichiometric As2S3-GeS2 and non-stoichiometric As2S3-Ge2S3 cut-sections

  1. Vacancy clustering in pure metals: some first principle calculations of positron lifetimes and momentum distributions

    International Nuclear Information System (INIS)

    First results of a systematic study on the vacancy clustering process in Al, Cu, Mg and Nb are presented. To this aim first principle calculation of positron lifetimes and positron-electron momentum distributions were performed. We test the reliability of the computational scheme used by comparing some of the calculated results with experimental ones.

  2. Electronic structure calculations of positron lifetimes in nuclear materials: SiC and UO2

    International Nuclear Information System (INIS)

    We present first-principles calculations of positron lifetimes of vacancy-type defects in two nuclear materials: SiC and UO2. We use a self-consistent positron lifetime calculation scheme based on the two-component density functional theory (DFT). Full defect relaxation due to both the creation of the vacancy and the presence of the positron was taken into account. Our results for SiC differ strongly from those published in literature up to now [G. Brauer et al. Phys. Rev. B 54, 2512 (1996)]. This is mostly due to the effect of the relaxation, that was not taken into account before. We also present the first calculated positron lifetimes obtained for UO2 in the DFT+U approach. Results are compared with experimental data. (authors)

  3. Study of defects in electron irradiated CuInSe2 by positron lifetime spectroscopy

    International Nuclear Information System (INIS)

    CuInSe2 was studied in the as-grown state and after low-temperature (4 K) 2 MeV electron irradiation. The positron bulk lifetime of 235 ps was measured for the unirradiated sample. The positron bulk lifetime was theoretically calculated and is in good agreement with the experimental value. In addition, the defect-related lifetimes for mono-, di-, and trivacancies are theoretically determined. An increased average positron lifetime indicated after electron irradiation the appearance of open-volume defects, most probably of divacancy type. The disappearance of this defect was observed during annealing below 250 K. Other defects were formed leading to a divacancy signal at least stable up to 600 K in the temperature range above 450 K. copyright 1998 American Institute of Physics

  4. Digitized detection of gamma-ray signals concentrated in narrow time windows for transient positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    A pulsed slow-positron beam generated by an electron linear accelerator was directly used for positron annihilation lifetime spectroscopy without any positron storage devices. A waveform digitizer was introduced to simultaneously capture multiple gamma-ray signals originating from positron annihilation events during a single accelerator pulse. The positron pulse was chopped and bunched with the chopper signals also sent to the waveform digitizer. Time differences between the annihilation gamma-ray and chopper peaks were calculated and accumulated as lifetime spectra in a computer. The developed technique indicated that positron annihilation lifetime spectroscopy can be performed in a 20 μs time window at a pulse repetition rate synchronous with the linear accelerator. Lifetime spectra of a Kapton sheet and a thermally grown SiO2 layer on Si were successfully measured. Synchronization of positron lifetime measurements with pulsed ion irradiation was demonstrated by this technique

  5. The application of artificial neural networks to the inversion of the positron lifetime spectrum

    International Nuclear Information System (INIS)

    A new method of processing positron annihilation lifetime spectra is proposed. It is based on an artificial neural network (ANN)-back propagation network (BPN). By using data from simulated positron lifetime spectra which are generated by a simulation program and tested by other analysis programs, the BPN can be trained to extract lifetime and intensity from a positron annihilation lifetime spectrum as an input. In principle, the method has the potential to unfold an unknown number of lifetimes and their intensities from a measured spectrum. So far, only a proof-of-principle type preliminary investigation was made by unfolding three or four discrete lifetimes. The present study aims to design the network. Besides, the performance of this method requires both the accurate design of the BPN structure and a long training time. In addition, the performance of the method in practical applications is dependent on the quality of the simulation model. However, the chances of satisfying the above criteria appear to be high. When appropriately developed, a trained network could be a very efficient alternative to the existing methods, with a very short identification time. We have used the artificial neural network codes to analyze data such as the positron lifetime spectra for single crystal materials and monocrystalline silicon. Some meaningful results are obtained

  6. Temperature and phase dependence of positron lifetimes in solid cyclohexane

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard

    1985-01-01

    longer of these (≈ 2.5 ns), which is temperature dependent, is ascribed to ortho-Ps trapped at vacancies. The shorter lifetime (≈ 0.9 ns), shows little temperature dependence. In contrast to most other plastic crystals, no sigmoidal behaviour of the average ortho-Ps lifetime is observed. A possibility......The temperature dependence of position lifetimes in both the brittle and plastic phases of cyclohaxane has been examined. Long-lived components in both phases are associated with the formation of positronium (Ps). Two long lifetimes attributable to ortho-Ps are resolvable in the plastic phase. The...

  7. Temperature and phase dependence of positron lifetimes in solid cyclohexane

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard

    1985-01-01

    The temperature dependence of position lifetimes in both the brittle and plastic phases of cyclohaxane has been examined. Long-lived components in both phases are associated with the formation of positronium (Ps). Two long lifetimes attributable to ortho-Ps are resolvable in the plastic phase. The...

  8. A study of dye molecule diffusion in human hair using positron lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Chandrashekara, M.N.; Ranganathaiah, C. [Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore (India)

    2009-11-15

    The diffusion behavior of a commercial permanent liquid hair dye in human hair has been investigated using Positron Annihilation Lifetime Spectroscopy (PALS) and gravimetric sorption method. The o-Ps lifetime parameters {tau}{sub 3} and I{sub 3} decrease rapidly during the first 60 minutes of sorption time. This is understood in terms of dye molecules filling the free volume cavities in hair. The sorption results suggest that the dye molecule diffusion is essentially a Fickian process. In the latter part of the sorption, where positron parameters remain almost constant, mass increase might be due to surface adhesion. These two stages of sorption are well separated by the positron technique. The study shows that the free volume theory and positron technique, widely used in polymer research, may expediently be used to understand hair properties, more importantly diffusion of dye molecules. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Study of PRIMAVERA Steel Samples by Positron Annihilation Spectroscopy Technique II – Lifetime Measurements

    OpenAIRE

    KRSJAK VLADIMIR; GRAFUTIN V.; O.V. Ilyukhina; BURCL Rudolf; BALLESTEROS AVILA ANTONIO; Haehner, Peter

    2012-01-01

    In the present article, a positron annihilation lifetime technique was used for the study of VVER-440/230 weld materials, manufactured in the frame of the international PRIMAVERA project on microstructural investigation of the irradiated WWER-440 reactor pressure vessel steel. The present results complement our previous report of positron angular correlation experiments and provide in-depth characterization of vacancy type defects behavior under irradiation and thermal treatment. The results ...

  10. Positron lifetime study of native vacancy-like defects in chalcogenide glasses

    Energy Technology Data Exchange (ETDEWEB)

    Filipecki, J.; Shpotyuk, O.I. E-mail: shpotyuk@novas.lviv.ua; Kozdras, A.; Kovalskiy, A.P

    2003-11-01

    Modified model for positron annihilation in vitreous chalcogenide semiconductors is developed to explain a number of previously obtained results on positron lifetime measurements in glassy As-Ge-S of stoichiometric As{sub 2}S{sub 3}-GeS{sub 2} and non-stoichiometric As{sub 2}S{sub 3}-Ge{sub 2}S{sub 3} cut-sections.

  11. Development of a pico-second life-time spectrometer for positron annihilation studies

    International Nuclear Information System (INIS)

    Positron annihilation technique is a sensitive probe to investigate various physico-chemical phenomena due to the ability to provide information about the electron momentum and density in any medium. While measurements on the Doppler broadening and angular correlation of annihilation photons provide information about the electron momentum, the electron density at the annihilation site is obtained, by the positron life-time measurement. This report describes the development, optimization and calibration of a high resolution life-time spectrometer (FWHM=230 ps), based on fast-fast coincidence technique, a relatively new concept in nuclear timing spectroscopy. (author). 4 refs., 9 figs., 1 tab

  12. Low-temperature positron-lifetime studies of proton-irradiated silicon

    DEFF Research Database (Denmark)

    Mäkinen, S.; Rajainmäki, H.; Linderoth, Søren

    1990-01-01

    samples, the first starting at 100 K and the other at 400 K. The first is suggested to be a result of the migration of free, negatively charged monovacancies, and the second is connected to the annealing of some vacancy-impurity complexes, probably negatively charged vacancy-oxygen pairs. The specific...... trapping rate of positrons to both of these negatively charged monovacancy-type defects has been found to have a clear T-0.5 dependence. The positron lifetime in perfect Si is measured to be 217±1 ps, and the monovacancy lifetime is found to be 275±5 ps. Also the negatively charged vacancy-oxygen complexes...

  13. Positron annihilation lifetime spectroscopy study of thermal processing and rehydration of dry leek (Allium porrum L.)

    International Nuclear Information System (INIS)

    New application of positron annihilation lifetime spectroscopy (PALS) to development of food processing techniques is tested. Dehydrated leeks were an object of the study. Three experiments were performed consisting of evacuating air and volatile compounds from the sample, applying thermal treatment and rehydrating the sample. Distinct changes in positron lifetime spectra allowed the monitoring of alterations in the sample structure. The most likely origin of the particular components present in the spectra was able to be proposed from these data. Changes of the components were ascribed to the various processes occurring in the samples. (authors)

  14. Free volume investigation of imidazolium ionic liquids from positron lifetime spectroscopy

    OpenAIRE

    Yu, Yang; Bejan, Dana; Krause-Rehberg, Reinhard

    2014-01-01

    In this work, relationships between the free volume and various fundamental physical properties (density, surface tension and transport properties) of ionic liquids were investigated. Two imidazolium ionic liquids 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluoro phosphate ([C4MIM][FAP]) and 1-butyl-3-methylimidazolium bis[bis(pentafluoroethyl)phosphinyl]imide ([C4MIM][FPI]) were measured by positron annihilation lifetime spectroscopy (PALS). Changes of the ortho-positronium lifetim...

  15. Interlaboratory comparison of positron and positronium lifetimes in polymers

    DEFF Research Database (Denmark)

    Wastlund, C.; Eldrup, Morten Mostgaard; Maurer, F.H.J.

    1998-01-01

    used were a semi-crystalline linear polyethylene, an amorphous poly(methyl methacrylate) and an amorphous copolymer of styrene-acrylonitrile. The results show that the ortho-positronium lifetimes and intensities agree fairly well between different laboratories, despite large differences in experimental...

  16. Positron annihilation lifetime study of extended defects in semiconductor glasses and polymers

    International Nuclear Information System (INIS)

    The processes of atomic shrinkage in network-forming solids initiated by external influences are tested using technique of positron annihilation lifetime spectroscopy at the example of chalcogenide vitreous semiconductors of arsenic sulphide type and acrylic polymers for dental application. Two state positron trapping is shown to be responsible for atomic shrinkage in chalcogenide glasses, while mixed trapping and ortho-positronium decaying is character for volumetric densification and stress propagation in acrylic dental polymers. At the basis of the obtained results it is concluded that correct analysis of externally-induced shrinkage in polymer networks under consideration can be developed by using original positron lifetime data treatment algorithms to compensate defect-free bulk annihilation channel within two-state positron trapping model and account for an interbalance between simultaneously co-existing positron trapping and orth-positronium related decaying channels within mixed three-state positron annihilation model (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Positron annihilation lifetime study of extended defects in semiconductor glasses and polymers

    Energy Technology Data Exchange (ETDEWEB)

    Boyko, Olha [Department of Pediatric Dentistry, Danylo Halytsky Lviv National Medical University, Pekarska str. 69, 79010 Lviv (Ukraine); Shpotyuk, Yaroslav [Department of Optoelectronics and Information Technologies, Ivan Franko National University of Lviv, Dragomanova str. 50, 79005 Lviv (Ukraine); Lviv Scientific Research Institute of Materials, Scientific Research Company ' ' Carat' ' , Stryjska str. 202, 79031 Lviv (Ukraine); Filipecki, Jacek [Institute of Physics, Jan Dlugosz University in Czestochowa, Armii Krajowej al. 13/15, 42200 Czestochowa (Poland)

    2013-01-15

    The processes of atomic shrinkage in network-forming solids initiated by external influences are tested using technique of positron annihilation lifetime spectroscopy at the example of chalcogenide vitreous semiconductors of arsenic sulphide type and acrylic polymers for dental application. Two state positron trapping is shown to be responsible for atomic shrinkage in chalcogenide glasses, while mixed trapping and ortho-positronium decaying is character for volumetric densification and stress propagation in acrylic dental polymers. At the basis of the obtained results it is concluded that correct analysis of externally-induced shrinkage in polymer networks under consideration can be developed by using original positron lifetime data treatment algorithms to compensate defect-free bulk annihilation channel within two-state positron trapping model and account for an interbalance between simultaneously co-existing positron trapping and orth-positronium related decaying channels within mixed three-state positron annihilation model (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. A Review of Studies of Polymeric Membranes by Positron Annihilation Lifetime Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    A review is presented of studies of polymeric membranes by applying positron annihilation lifetime spectroscopy (PALS). PALS has been used to study subnanometer-sized holes, to determine their size distribution and free-volume fractions, and to probe molecular-sized vacancies in glassy polymers. At present, PALS is believed to be a highly effective physical method for the examination of polymeric membranes.

  19. Compositional dependences of average positron lifetime in binary As-S/Se glasses

    International Nuclear Information System (INIS)

    Compositional dependence of average positron lifetime is studied systematically in typical representatives of binary As-S and As-Se glasses. This dependence is shown to be in opposite with molar volume evolution. The origin of this anomaly is discussed in terms of bond free solid angle concept applied to different types of structurally-intrinsic nanovoids in a glass.

  20. Compositional dependences of average positron lifetime in binary As-S/Se glasses

    Energy Technology Data Exchange (ETDEWEB)

    Ingram, A. [Department of Physics of Opole University of Technology, 75 Ozimska str., Opole, PL-45370 (Poland); Golovchak, R., E-mail: roman_ya@yahoo.com [Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195 (United States); Kostrzewa, M.; Wacke, S. [Department of Physics of Opole University of Technology, 75 Ozimska str., Opole, PL-45370 (Poland); Shpotyuk, M. [Lviv Polytechnic National University, 12, Bandery str., Lviv, UA-79013 (Ukraine); Shpotyuk, O. [Institute of Physics of Jan Dlugosz University, 13/15al. Armii Krajowej, Czestochowa, PL-42201 (Poland)

    2012-02-15

    Compositional dependence of average positron lifetime is studied systematically in typical representatives of binary As-S and As-Se glasses. This dependence is shown to be in opposite with molar volume evolution. The origin of this anomaly is discussed in terms of bond free solid angle concept applied to different types of structurally-intrinsic nanovoids in a glass.

  1. PALSfit: A new program for the evaluation of positron lifetime spectra

    DEFF Research Database (Denmark)

    Olsen, Jens V.; Kirkegaard, Peter; Pedersen, Niels Jørgen;

    2007-01-01

    PALSfit is a new Windows program for the analysis of positron lifetime spectra. PALSfit combines into one interactive Windows program the features of our previous PATFIT program package, such as data input, least-squares fitting routines as well as graphical displays. A number of options...

  2. Positron lifetime studies on the Fe alloy coating sprayed by plasma and treated by compression

    International Nuclear Information System (INIS)

    The microstructure and defects of the plasma spraying Fe alloy coating that underwent a compression treatment were investigated by the positron lifetime analysis and hardness testing. A mechanism for increasing the density of the Fe alloy coating with compression techniques was suggested

  3. Positron lifetime and Mossbauer study on hydrogenized Zr/sub 75/Fe/sub 25/ alloy

    International Nuclear Information System (INIS)

    Zr/sub 3/FeH/sub 5.5/ sample was examined by positron lifetime and Mossbauer effect measurements. During the desorption process metastable Zr/sub 3/Fe is formed which transforms to stable orthorombic Zr/sub 3/Fe at higher temperatures. Effect of changes in the hydrogen concentration is discussed

  4. Positron annihilation lifetime study of Ag-ion exchanged and heat treated soda lime glass

    International Nuclear Information System (INIS)

    Slabs of soda lime silica glass (15% Na2O) were subjected to Ag+/Na+ ion exchange process and subsequent heat treatment. The change in glass structure and Ag states accompanied with these processes were studied using the positron annihilation lifetime spectroscopy. The positron annihilation lifetime measurements were performed with a fast-fast coincidence spectrometer employing a multi-parameter acquisition system. The lifetime parameters showed that the Ag+ ion reduction process takes place through two processes; the oxidation reduction reaction with Fe2+ impurities in the glass at heat treatment temperatures <500 deg. C, whereas at heat treatment ≥500 deg. C the reduction takes place through the polymerization reaction. The results also indicated that the heat treatment at 600 deg. C enhanced the formation of Ag metal nanoparticle crystals through the structural relaxation revealed by the free volume defects

  5. Positron lifetime study of polycarbonate/poly(styrene-co-acrylonitrile) blends

    Czech Academy of Sciences Publication Activity Database

    Čížek, J.; Motyčka, V.; Procházka, I.; Ilavský, Michal; Kolařík, Jan

    2001-01-01

    Roč. 363, č. 3 (2001), s. 340-342. ISSN 0255-5476. [International Conference on Positron Annihilation /12./. Munchen, 06.08.2000-12.08.2000] R&D Projects: GA ČR GA106/98/0700; GA AV ČR KSK2050602 Institutional research plan: CEZ:AV0Z4050913 Keywords : partial miscibility of polymers * polycarbonate/poly(styrene-co- acrylonitrile ) blends * positron lifetime spectroscopy Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.461, year: 2001

  6. Positron lifetime in vacancy clusters. Application to the study of vacancy-impurity interactions

    International Nuclear Information System (INIS)

    Positron lifetime measurements are used to study the vacancy recovery (77-650 K) in 20 K electron irradiated dilute gold or iron alloys in stainless steels. Positron lifetimes in clusters of various shapes and structures are calculated to precise the information obtained by measuring the positron lifetime in a vacancy cluster of unknown size and configuration. From the calculations, we have drawn the following conclusions: - the minimal size of an unknown cluster can be deduced from the measurement of the positron lifetime in the cluster; - a decrease of the positron lifetime when the structure of the cluster evolves, means either a decrease of the size of the cluster, or, the appearance of a relaxed configuration. - The positron lifetime is very useful to discriminate between a spatial planar or relaxed configuration and a tri-dimensional one. In AuGe, AuSb, AuTn alloys, vacancy clusters decorated by solute atoms appear at 250 K. Their configurations are different from those in pure Au. Mobile vacancy-solutes complexes are involved in the clustering process in AuGe, AuSb. The clusters are probably decorated by several solute atoms in AuGe and AuSb where the resistivity evidences a clustering of solute atoms. In AuFe, vacancy-single or multi-complexes stable up to 670 K prevent cluster formation. In FeTi, FeSb, FeAu, vacancy migration is hindered by the formation of vacancy-solute complexes up to 315 K (Ti), up to 670 K (Sb), up to 700 K (Au). In FeSi, FeCu, FeAg, tri-dimensional clusters grow less easily than Fe. This is likely due to the formation of several kinds of small decorated clusters with relaxed or planar configurations. They are peculiarly stable, surviving up to 700 K at least. In Si (resp. Ti) doped 59Fe25Ni16Cr, solute atoms retain the vacancies up to 300 K (resp. 320 K)

  7. Study of PRIMAVERA steel samples by positron annihilation spectroscopy technique II – Lifetime measurements

    International Nuclear Information System (INIS)

    In the present article, a positron annihilation lifetime technique was used for the study of VVER-440/230 weld materials, manufactured in the frame of the international PRIMAVERA project on microstructural investigation of the irradiated WWER-440 reactor pressure vessel steel. The present results complement our previous report of positron angular correlation experiments and provide in-depth characterization of vacancy type defects behavior under irradiation and thermal treatment. The results give new insight into the previously published atom probe tomography and angular correlation of annihilation radiation studies. The measurements do not show any association of phosphorus or its segregation to the open volume defects investigated by positron annihilation spectroscopy. The embrittlement effects related to the phosphorus seem to be effectively annealed-out during 475 °C thermal treatment and the post annealing microstructure and mechanical properties of the material are consequently affected mostly by agglomerations of vacancy clusters coarsened during thermal treatment.

  8. A fast detector for single-shot positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    When an intense sub-nanosecond positron pulse impinges upon a target, a pulse of γ-rays is created which can yield information concerning electron-positron pairs just prior to annihilation. Many conventional γ-ray detectors are unable to exploit the timing information contained within such pulses, and we describe here the development of a fast detector that is able to do so. Using a single-crystal PbF2 Cherenkov radiator coupled to a fast photomultiplier tube (PMT), we have produced a detector with a time response of ∼4 ns (primarily determined by the PMT response), as well as a low-efficiency detector with a sub-nanosecond response. Since 511 keV photons produce very little Cherenkov light, the problem of photomultiplier saturation is mitigated and this detector is therefore well suited to single-shot positron annihilation lifetime spectroscopy (SSPALS) measurements

  9. Nanoscopic properties of silica filled polydimethylsiloxane by means of positron annihilation lifetime spectroscopy

    DEFF Research Database (Denmark)

    Wiinberg, P.; Eldrup, Morten Mostgaard; Maurer, F.H.J.

    2004-01-01

    Positron annihilation lifetime spectroscopy (PALS) was performed on a series of polydimethylsiloxane (PDMS)/fumed silicon dioxide (SiO2) composites at temperatures between -185 and 100degreesC to study the effect of filler content and filler particle size on the free volume properties and the...... positron annihilation characteristics. The glass transition behavior of the PDMS/SiO2 composites was determined with differential scanning calorimetry. A clear influence on the o-Ps lifetime (73) in the polymer upon addition of nano-sized fumed SiO2 was observed at all temperatures. The observed o...... behavior of ordinary molecular liquids was observed in this temperature region. The o-Ps yield was strongly reduced in the crystallization region and by addition Of SiO2. The reduction due to filler addition did, however, in the case of nano-sized SiO2 not follow a linear relationship with filler weight...

  10. Study the effect of radiations on poly(ethylene naphthalate) using positron annihilation lifetime technique

    International Nuclear Information System (INIS)

    Poly(ethylene naphthalate), PEN, irradiated by gamma-rays has been by positron annihilation lifetime (PAL). The PAL measurements were performed in the temperature range between 25 to 150 degree C for three samples (non-, 1 and 5 Mrad gamma-irradiated). The ortho-positronium (o-ps) lifetime, T3, is varying depending upon the phase of the polymer. The data clearly revealed the glass transition temperature, Tg, which is shifted toward lower values upon irradiation with 5 mrad, which could be attributed to the decrease in the degree of crystallinity. This is in consistent with the wide angle X-ray scattering data. The thermal expansion coefficient values for the three samples indicate decrease in the crystallinity with increasing irradiation. To our knowledge no positron annihilation studies on PEN exist in the literature, so the results reported here may be considered new and important

  11. On irradiated poly(ethylene naphthalate) studied by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Poly(ethylene naphthalate), PEN, irradiated by γ-rays has been studied by positron annihilation lifetime (PAL). The PAL measurements were performed in the temperature range between 25 to 150 C for three samples (non-, 1 and 5 Mrad γ-irradiated). The ortho-positronium (o-Ps) lifetime, τ3, is varying depending upon the phase of the polymer. The data clearly revealed the glass transition temperature, Tg, which is shifted toward lower values upon irradiation 5 Mrad, which could be attributed to the decrease in the degree of crystallinity. This is in consistent with the wide-angle X-ray scattering data. The thermal expansion coefficient values for the three samples indicate decrease in the crystallinity with increasing irradiation. To our knowledge no positron annihilation studies on PEN exist in the literature, so the results reported here may be considered new and important. (orig.)

  12. Positron ACAR distributions and lifetimes in irradiated highly oriented pyrolytic graphite

    International Nuclear Information System (INIS)

    In this report, a combined experimental and theoretical study of positron annihilation for graphite are presented. We focus on two aspects of experiments, namely the one-dimensional ACAR (1D-ACAR) distribution along the p(parallel)c direction (perpendicular to the basal plane) and positron lifetime. A pronounced bimodal in the 1D-ACAR is observed before irradiation. This bimodal is found to be much suppressed after electron irradiations and to disappear completely after neutron irradiations. These dramatic changes are well reproduced by first-principles calculations based on the two-component density functional (TCDF) theory within the local density approximation (LDA): With the increase in vacancy size the shape of calculational 1D-ACAR varies from a bimodal in the bulk to a narrow single peak in the vacancy-clusters. Based on the present calculations, the physical origin of this sequential change is clarified to be unique density distributions (around the basal planes) of trapped positrons and consequent reduction of positron sampling for π band electrons. Combined with corresponding positron lifetime measurements, the vacancies in electron-irradiated graphite are identified to be monovacancies. On the other hand, the vacancy-clusters in the basal planes by neutron irradiation are unambiguously explored firstly by the present positron study, which have not been directly evident in previous experiments. In our present experiments, highly-oriented-pyrolytic graphite (HOPG) samples were irradiated with electron and fast neutrons. The irradiation conditions are summarized in Table I. The positron lifetime and 1D-ACAR measurements were performed on a fast-fast coincidence spectrometer and a usual long-slit ACAR machine, respectively. The general description for details of the experimental setups can be found in our previous papers. In ACAR experiments, the measurements yield a 1D-ACAR distribution proportional to the 1D projection of the three-dimensional (3D) two

  13. Positron lifetimes at the initial stage of pore formation in Vycor glass

    CERN Document Server

    Jasinska, B; Goworek, T

    2000-01-01

    The formation of narrow pores during leaching of Vycor glass by sulphuric acid was investigated using the positron lifetime technique. During the leaching process the pore diameter remained roughly constant (except for the case of cold leaching). The time of processing changed the total length of capillaries, but not their number; at the temperature 50 deg. C during 20 min of leaching the average leaching depth was 24 mu m.

  14. Monovacancy–As complexes in proton-irradiated Ge studied by positron lifetime spectroscopy

    International Nuclear Information System (INIS)

    We applied positron annihilation lifetime spectroscopy to study the proton-irradiation-induced defects in germanium and its annealing behavior. The n-doped Ge ([As] = 9 × 1017 cm−3) samples were irradiated at room temperature with a proton energy of 15 MeV at a dose of 1015 cm−2. We distinguished a complex containing a vacancy and arsenic atoms. In addition, we observed shallow positron traps, which are ascribed to the impurities in a Ge lattice crystal. Isochronal annealing experiments were carried out in the temperature interval 300–820 K. Temperature-dependent positron lifetime measurements were performed after each annealing step. During isochronal annealing of the proton-irradiated Ge, a vacancy–As complex was found to dissociate to its constituents and the single monovacancies eventually anneal out. Two annealing stages were observed: the first, at ∼450 K, was attributed to the dissociation of complexes and the second annealing stage, at 650 K, was assigned to annealing of vacancies. Shallow positron traps anneal in the temperature range 540–660 K

  15. A new positron lifetime spectrometer using a fast digital oscilloscope and BaF2 scintillators

    International Nuclear Information System (INIS)

    A new positron lifetime spectrometer has been constructed and tested. It consists of a state-of-the-art digital oscilloscope (LeCroy Wavepro 960) and scintillation detectors based on Hamamatsu H3378 (R2083Q) photomultiplier tubes and BaF2 scintillators. A very good time resolution is obtained with scintillators of commonly used sizes (28 mm in diameter, 10-20 mm thick) and wide energy window settings (40-50%). The time resolution of 144 ps full-width at half-maximum (FWHM) is achieved for the positron lifetime measurement, in which time differences are measured between the arrivals of a 1.27 MeV γ-ray from 22Na and one of the two positron annihilation γ-rays of 0.511 MeV. The time resolution is further improved with a 'double-stop' setup, where timing information carried by the positron annihilation γ-ray pair is combined to determine the time of the annihilation. The time resolution with this setup is 119 ps FWHM. This improvement is interpreted in terms of the energy deposit in the scintillation detectors by γ-rays. Applications of the new spectrometer to other scintillation timing measurements are also described

  16. A simplified digital positron lifetime spectrometer based on a fast digital oscilloscope

    International Nuclear Information System (INIS)

    A simplified digital positron lifetime spectrometer is presented and tested. This system is only composed of two scintillation detectors, a time delayer and a digital oscilloscope. Both online and offline analysis of the detector signals can be optionally chosen to construct positron lifetime spectrum by histogramming the time difference between the positron birth signal of 1.27 MeV γ-ray and one positron annihilation signal of 0.511 MeV γ-rays. Several pulse discrimination methods and timing numerical algorithms are proposed and well applied to perform pulse energy discrimination and digital constant fraction timing (DCFT). A combination discrimination of pulse amplitude, pulse risetime and ratio of pulse area to pulse amplitude with DCFT is found able to achieve the best time resolution of 208 ps full-width at half-maximum (FWHM), which is much better over the analog spectrometer using the same detectors. This newly developed apparatus except for having better performance is particularly easy to be constructed and implemented.

  17. Positron Annihilation Lifetime Study of Pure and Doped Polyvinyl Chloride with Al2O3

    International Nuclear Information System (INIS)

    Positron annihilation lifetime of pure and doped polyvinyl chloride (PVC) with Al2O3 reflect the effect of concentration as well as temperature on free volume. Therefore, variations of the ortho-positronium (o-Ps) lifetime and its intensity have been correlated with changes in the dielectric properties of the pure and doped PVC. The o-Ps lifetime and its intensity show a linear dependence with a discontinuity at 20 % concentration of Al2O3. The size and the fractional of the o-Ps hole volume were estimated from the positron annihilation parameters. Therefore, the temperature dependence of the electrical conductivity and the positron annihilation parameters on pure and doped PVC with 20 % Al2O3 were studied in the range from 20 to 140 degree C. The shift of the glass transition temperature to lower temperature for the 20 % Al2O3 doped PVC might explain the increase in the electrical conductivity with the concentration of the additive

  18. Positron lifetime spectroscopy of vitreous B{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Shivachev, B.L.; Kashchieva, E.P.; Dimitriev, Y.B. [Department of Physics, University of Chemical Technology and Metallurgy, 8, Kliment Ohridsky Blvd, 1756 Sofia (Bulgaria); Mincov, I.P.; Troev, T. [Institute for Nuclear Research and Nuclear Energy, BAS, 72, Tsarigradsko Shaussee Blvd, 1784 Sofia (Bulgaria); Smith, R. [US Borax Inc., 26877 Tourney Road, Valencia, CA 91355-1847 (United States)

    2004-10-15

    A comparison is made of the structural data obtained by positron lifetime spectroscopy (PLS) for vitreous B{sub 2}O{sub 3} (v-B{sub 2}O{sub 3}) and crystalline B{sub 2}O{sub 3} (c-B{sub 2}O{sub 3}). Samples of v-B{sub 2}O{sub 3} were dried by holding the melt at 1350K to reduce residual OH groups. Fast quenching and slow cooling were used to obtain glasses having different fictive structures. According to the literature, B{sub 3}O{sub 6} rings are thought to be formed during slow cooling of v-B{sub 2}O{sub 3}. PLS measurements show that both the intensity value and the long lifetime component (t{sub 3}) associated with positron decay in cavities and lifetime component (t{sub 1}) associated with the positron annihilation in the bulk are different for v-B{sub 2}O{sub 3} and c-B{sub 2}O{sub 3}. The low intensity of t{sub 3} for c-B{sub 2}O{sub 3} and its high value for v-B{sub 2}O{sub 3} is argued to be due to the presence of different structural units in the two states of B{sub 2}O{sub 3}.

  19. Free volumes studies in Thymoquinone and Carvone β-cyclodextrin nanoparticles by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectroscopy is used to study free volume in β-cyclodextrin with the encapsulation of thymoquinone and S-carvone, in samples covering the guest to host fraction range from 1:0.1 to 1:1. The results clearly indicate the presence of long lifetime components related to Ps-formation. Although the behavior of the two guests is different, in both cases the results indicate the formation of 1:1 cyclodextrin inclusion compounds. Data show that the addition of carvone to β-cyclodextrin results in a decrease of the o-Ps lifetime corresponding to a reduction of the average radius of cavities from 2.41 Å to 2.29 Å, whereas the addition of thymoquine decreases the radius from 2.57 Å to 2.35 Å. In turn, the intensity varied from 20.55 to 19.20% and from 20.83 to 0.41%, respectively.

  20. Characterization of control mesoporous glasses (CPGs) using positron annihilation lifetime spectroscopy (PALS)

    International Nuclear Information System (INIS)

    This thesis has two main goals. Firstly and for the first time, the positron annihilation lifetime technique (PALS) is used to characterize the control porous glasses (CPGs) media. All the positron annihilation spectroscopy (PAS) investigations have been interested in the commercial Vycor glass media of pores size ≤ 4 nm. Therefore, the PALS is used to establish basic correlations between the important physical properties of the CPG (pore size, surface area, and porosity) and the orthopositronium (o-Ps) lifetime. The second goal is to use these correlations to verify the validity of some suggested models and theories to discover possible deviations from the expected behaviour and to discuss the physical point of view for these deviations. Chapter 1 presents an overview of positron, positronium and their interaction with solid materials. Chapter 2 of this thesis is concerned with characterization of porous glass materials. This chapter discusses in detail the preparation methods of porous glasses specially control porous glass and Vycor glass. The gas adsorption phenomenon in porous glass and the related definitions are discussed. The most important terms of the porous glass such as pore size, shape, volume, pore size distribution, surface area, and porosity are discussed. Chapter 3 presents in detail the well known models and the derived equations which correlate between the lifetime of the o-Ps long-lived component and the pore size, pore shape and the temperature dependence of the porous media. Chapter 4 presents an overview of the main experimental techniques used in this thesis, namely positron annihilation lifetime spectroscopy. Chapter 5 explains the sample preparation for the measurements. The chapter represents also the experimental data for the correlation between the o-Ps lifetime and pore sizes for a system of CPG media (from 1 nm to 64 nm). I also studied the temperature dependence of the o-Ps long-lived component in different pore sizes. In this

  1. Characterization of control mesoporous glasses (CPGs) using positron annihilation lifetime spectroscopy (PALS)

    Energy Technology Data Exchange (ETDEWEB)

    Sayed Ahmed, Essmat Mahmoud Hassan

    2008-01-30

    This thesis has two main goals. Firstly and for the first time, the positron annihilation lifetime technique (PALS) is used to characterize the control porous glasses (CPGs) media. All the positron annihilation spectroscopy (PAS) investigations have been interested in the commercial Vycor glass media of pores size {<=} 4 nm. Therefore, the PALS is used to establish basic correlations between the important physical properties of the CPG (pore size, surface area, and porosity) and the orthopositronium (o-Ps) lifetime. The second goal is to use these correlations to verify the validity of some suggested models and theories to discover possible deviations from the expected behaviour and to discuss the physical point of view for these deviations. Chapter 1 presents an overview of positron, positronium and their interaction with solid materials. Chapter 2 of this thesis is concerned with characterization of porous glass materials. This chapter discusses in detail the preparation methods of porous glasses specially control porous glass and Vycor glass. The gas adsorption phenomenon in porous glass and the related definitions are discussed. The most important terms of the porous glass such as pore size, shape, volume, pore size distribution, surface area, and porosity are discussed. Chapter 3 presents in detail the well known models and the derived equations which correlate between the lifetime of the o-Ps long-lived component and the pore size, pore shape and the temperature dependence of the porous media. Chapter 4 presents an overview of the main experimental techniques used in this thesis, namely positron annihilation lifetime spectroscopy. Chapter 5 explains the sample preparation for the measurements. The chapter represents also the experimental data for the correlation between the o-Ps lifetime and pore sizes for a system of CPG media (from 1 nm to 64 nm). I also studied the temperature dependence of the o-Ps long-lived component in different pore sizes. In this

  2. Study of poly(methyl methacrylate) via positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    positron annihilation lifetimes (PAL) were measured for two different viscosity average molecular weight of poly(methyl methacrylate). PMMA. samples as a function of temperature. The measurements were performed under vacuum in the temperature range from 22 to 150 degree C with interval of 10 degrees. The lifetime spectra were analyzed using two methods; 1) average results of the ortho-positronium (o-ps) lifetime and its intensity obtained by PATFIT program, and 2) the p-ps lifetime and o-ps hole volume distributions given by bayes theorem and the maximum entropy principle using MELT program. The o-ps lifetime decreases by increasing the viscosity-average molecular weight while it increases with increasing temperature. On the hand, the o-ps intensity as well as the relative fractional of the o-ps hole volume shows behavior in contrast to the o-ps lifetime with the viscosity-average molecular weight weight . Within the temperature range, two different transitions are observed. The first transition temperature is due to the reduction of non equilibrium states that are frozen below this temperature. The other one is in accordance with the glass transition temperature of PMMA

  3. Positron annihilation lifetime in Fe-Rh alloys deformed by high-speed compression

    Energy Technology Data Exchange (ETDEWEB)

    Fukuzumi, M. [Graduate School of Engineering, Osaka Prefecture Univ., Sakai (Japan); Hori, F.; Oshima, R. [Research Inst. for Advanced Science and Technology, Osaka Prefecture Univ., Sakai (Japan); Komatsu, M.; Kiritani, M. [Research Center for Ultra-High-Speed Plastic Deformation, Hiroshima Inst. of Tech., Saekiku (Japan)

    2001-07-01

    In order to examine the role of structural vacancies in the stress-induced phase transitions of B2-type FeRh alloys, Fe-40, 45 and 50 at%Rh specimens were deformed at room temperature with a high-speed compression machine and were studied by X-ray diffractometry (XRD) and positron annihilation measurements. It was found from the positron lifetime results that vacancies or vacancy clusters were introduced into the alloy by deformation. The longer lifetime ({tau}{sub 2}) components were changed with the deformation momenta and Rh concentrations. In the case of Fe-50 at%Rh, they were 188 ps and 254 ps after deformation with small or large momenta, respectively. Taking the X-ray results into consideration, it is concluded that an atom movement mechanism forming large vacancy clusters is associated with the B2-A1 transition. The short lifetime ({tau}{sub 1}) of the alloy is accounted for by bulk annihilation in the transformed phases and a high density of dislocations. (orig.)

  4. Positron lifetime studies on the BiSrCaCuO(F) superconductors

    International Nuclear Information System (INIS)

    We have measured the positron lifetime and the transition temperature Tc as a function of doped F content for Bi2Sr2CaCu2Oy-xFx superconductors. The observed results are interpreted in terms of the change of the electron density in the Bi - O layers, which is the region probed by the positron, and the hole concentration in the Cu - O planes, which is correlated with the Tc of the sample. From this point of view, it is suggested that the F atom mainly substitutes the oxygen atom in the Bi - O layers, and it causes the electrons transfer from the Bi - O layers to the Sr - O planes; when x = 0.4, the F atom mainly substitues the oxygen atom in the Sr - O planes, it causes the electrons transfer from the Sr - O planes to the Bi - O layers and the Cu - O planes. (orig.)

  5. The Structure of the Free Volume in Poly(styrene-co-acrylonitrile) from Positron Lifetime and Pressure Volume Temperature (PVT) Experiments

    OpenAIRE

    Dlubek, Gunter; Bondarenko, Vladimir; Al-Qaradawi, Ilham Y.; Kilburn, Duncan; Krause-Rehberg, Reinhard

    2004-01-01

    Summary: The structure of the free volume and its temperature dependence between 25 and 190 °C of copolymers of styrene with acrylonitrile, SAN (0 to 50 mol-% AN), is studied by pressure volume temperature (PVT) experiments and positron annihilation lifetime spectroscopy (PALS). In this second part of the work, PALS data are reported from which the temperature dependence of the mean size and size distribution of local free volumes (subnanometer size holes) is analysed. The mean hole volume, v...

  6. Temperature dependence of free volume of polyacrylamide gels studied by positron lifetime measurements

    International Nuclear Information System (INIS)

    Changes of positronium (Ps) cavity radii in polyacrylamide and poly(N-isopropylacrylamide) gels were studied from 120 to 300 K by positron lifetime technique and it has been shown that the Ps cavity radius in the hydrogels changes by three or four stages. Temperature dependence of the Ps cavity radius exhibits variations similar to common polymers around the glass transition temperature. Hydrophilicity of the polymer chains significantly affects the Ps cavity radius just below 273 K. These results suggest an important role of free volume on the state of water in hydrogels.

  7. Application possibilities of Acqiris digital card DP240 for positron lifetime measurement

    Energy Technology Data Exchange (ETDEWEB)

    Petriska, M; Slugen, V [Department of Nuclear Physics and Technology, Slovak University of Technology, Ilkovicova 3, 81219 Bratislava (Slovakia); Krsjak, V [Institute for Energy, Joint Research Centre of the European Commission, PO Box 2, 1755ZG Petten (Netherlands); Zeman, A, E-mail: martin.petriska@stuba.sk [International Atomic Energy Agency, Department of Nuclear Sciences and Applications, Wagramer Strasse 5, A-1400, Vienna (Austria)

    2011-01-10

    Based on existing knowledge, a software for the digital positron lifetime (LT) spectrometer has been designed at the Slovak University of Technology. As a digitizer, Acqiris DP240 card was used. Start and stop timing signals have been digitised separately with sampling rate 1GS/s in 8 bit resolution. This sampling rate was not sufficient; therefore a joined delayed channel mode with 2GS/s sampling rate was used. Next applications for the study of advanced materials for nuclear industry are foreseen.

  8. Photo-degradation of Lexan polycarbonate studied using positron lifetime spectroscopy

    International Nuclear Information System (INIS)

    The free volume properties of pristine and UV irradiated Lexan polycarbonate have been investigated using Positron Lifetime Spectroscopy (PLS). The decrease in o-Ps life time and free volume size of irradiated sample is attributed to free volume modification and formation of more stable free radicals. These free radicals are formed due to the breakage of C-O bonds in Lexan polycarbonate after irradiation. This is also supported by the decrease in the intensity of C-O bond after exposure to UV-radiation as studied from Fourier Transform Infrared (FTIR) spectroscopy and it also shows that benzene ring does not undergo any changes after irradiation.

  9. Nanoporosity in a self-assembled drug delivery system detected by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Full text: We present a new drug carrier system that consists of silica hybrid gels having organic side groups. A major difference to existing formulations is that the matrix is generated in the presence of the drug molecule in a self-assembling process. The critical role of pore architecture (size and accessibility) in the tailored drug release is clearly revealed by positron annihilation lifetime spectroscopy (PALS), while the classical nitrogen adsorption technique (BET method) is not suitable here to indicate the internal void structure. Copyright (2005) Australian Institute of Physics

  10. Structural studies of spinel manganite ceramics with positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    The new transition-metal manganite Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics for temperature sensors with improved functional reliability are first proposed. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. This effect is well revealed only in ceramics having a character fine-grain microstructure, while the monolithization of ceramics caused by great amount of transferred thermal energy reveals an opposite influence. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy.

  11. Study of the ionic transport in polymer electrolyte using positron lifetime distribution method

    Science.gov (United States)

    Peng, Z. L.; Itoh, Y.; Li, S. Q.; Wang, S. J.

    1996-09-01

    Positron annihilation spectroscopy has been applied to measure the free-volume hole distribution in poly(ether urethane) as a function of temperature. The hole radius distribution determined from orthopositronium lifetime distribution is found to shift to a larger values with increasing temperature. This result, combined with the variation of ionic conductivity, suggests that carrier ions do not migrate naked but are bound to polymer segments through ion-dipole interaction forces, and the ion migration is controlled primarily by segmental motion of the polymer.

  12. The physical ageing mechanism in glassy polycarbonate studied by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectroscopy (PALS) is used to compare the free volume behaviour in as-extruded and aged polycarbonate. The lifetime and intensity of the orthoPositronium pickoff annihilation component are interpreted to represent mean free volume cavity size and free volume concentration, respectively. The PALS results indicate a lower mean free volume cavity size and quasi-equilibrium free volume concentration in the aged material than in the as-extruded polycarbonate. The physical ageing mechanism is discussed in terms of PALS studies and related studies of physical ageing by other researchers investigating secondary relaxations, local ordering phenomena and partial de-ageing phenomena in glassy polymers. A phenomenological description of the mechanism for physical ageing is developed based on the PALS results and literature survey. 74 refs., 2 tabs., 4 figs

  13. Positron lifetime measurements and positron-annihilation induced auger electron spectroscpy using slow positron beams; Teisoku yodenshi bimu wo mochiita yodenshi jumyo sokutei oyobi yodenshi shometsu reiki oje denshi bunko

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, R. [Electrotechnical Lab., Tsukuba (Japan)

    1996-02-20

    Slow positron beam with less than several eV can be controlled freely such as accelerating, throttling the beam size, shortening the pulse or making pulse with short time width and so forth. These low positron beams are applied to various measurements like Doppler broadening measurement of annihilation {gamma} rays or lifetime measurement of positron, and secondary particle measurements using positron microscope, positron electron ray diffraction, flight time method and so forth. In particular, these recent years, high intensity slow positron beams were possible using accelerators like electron linac and its application is increasing. In this report, pulse shortening method for high intensity slow positron beam, and incidence energy variable positron lifetime measurement method using this slow pulsed beam and flight time type positron-annihilation-induced auger electron spectroscopy are outlined. In future, these measurements can be possible to carry out with high resolution and also with high counting rate if higher intensity monochromatic excellent positron beam than present one is produced. 31 refs., 5 figs.

  14. POSITRON LIFETIME STUDY OF THERMALLY INDUCED MICROSTRUCTURAL CHANGES IN NISTARI SILK FIBER

    Institute of Scientific and Technical Information of China (English)

    C. Ranganathaiah

    2003-01-01

    Positron lifetime measurements have been made in natural polymer-Nistari silk fibers as a function of isochronal annealing temperature in the range of 27℃ to 280℃. The variations in the positron results indicate the structural changes occurring in the Nistari silk fibers and determine the glass transition temperature as 170℃. Activation energies were measured separately for the crystalline and amorphous regions indicating the versatility of the technique. These values are close to the N-H bond dissociation energy, suggesting N-H bond dissociation as the most probable process occurring during thermal treatment. As an extension of the positron results, the molecular weight of the Nistari silk fibers was determined to be 10.7 × 105 based on free volume, which lies within the range suggested for the silk fibers. There seems to be an indication that cross-linking changes the spiral structure of cotton fibers to network type. However, this needs to be validated by other techniques.

  15. Evaluation of a microchannel-plate PMT as a potential timing detector suitable for positron lifetime measurements

    International Nuclear Information System (INIS)

    This paper focuses on the evaluation of a microchannel-plate photomultiplier tube (MCP-PMT) as a candidate detector, suitable for positron lifetime studies. Several properties of MCP-PMTs, such as their fast time response, compact size, low susceptibility to magnetic fields, relatively high gain and the low power consumption make them attractive for positron lifetime spectroscopy. The preliminary tests were performed with a 85001-501 Burle PlanaconTM photomultiplier tube assembly. Initial measurements were conducted with a pulsed Picosecond Injection Laser (PiLas) system. The engineering sample of the 85001 exhibits a transit-time-spread (TTS) of 110 ps (FWHM). Further timing experiments showing the suitability of the device as Cherenkov detector are presented. For the first time, a conventional positron lifetime spectrum of a Cz-Si probe measured with a spectrometer, where an MCP-PMT detector is included, has been demonstrated.

  16. Free volume investigation of imidazolium ionic liquids from positron lifetime spectroscopy

    CERN Document Server

    Yu, Yang; Krause-Rehberg, Reinhard

    2014-01-01

    In this work, relationships between the free volume and various fundamental physical properties (density, surface tension and transport properties) of ionic liquids were investigated. Two imidazolium ionic liquids 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluoro phosphate ([C4MIM][FAP]) and 1-butyl-3-methylimidazolium bis[bis(pentafluoroethyl)phosphinyl]imide ([C4MIM][FPI]) were measured by positron annihilation lifetime spectroscopy (PALS). Changes of the ortho-positronium lifetime (o-Ps) with different states (amorphous and crystalline) were depicted as completely as possible. The mean local free (hole) volume was calculated from the o-Ps lifetime in amorphous state for the samples. Comparison between and specific volume obtained from the temperature dependent mass density gave the specific hole densities Nf and the occupied volumes Vocc. Thermal expansion of hole volume was compared with molecular volume VM of [C4MIM][FAP] and [C4MIM][FPI] as well as five other ionic liquids from our previous ...

  17. Vacancy defects in electron irradiated RPV steels studied by positron lifetime

    International Nuclear Information System (INIS)

    Specimens of RPV steels with different compositions are irradiated at 150 C and 288 C with 3MeV electrons (irradiation dose: 4*1019 e-/cm2). Vacancy defects are studied by positron lifetime measurements before and after irradiation and at each step of isochronal annealing (ΔT=50K, Δt=30min.). After 150 C irradiation, a recovery step is observed in both specimens, for annealing treatments in range 220 C - 370 C and attributed to the dissociation of vacancy-impurity complexes. The size of vacancy clusters never overcome 50 empty atomic volumes. If ''fresh'' dislocations are created just before irradiation, big vacancy clusters could be formed. After 288 C irradiation, small vacancy cluster of 4 - 10 empty atomic volumes are observed. (orig.)

  18. Change of free volume in polymer gels as studied by positron annihilation lifetimes

    International Nuclear Information System (INIS)

    Variations of free volume size of poly(N-isopropylacrylamide) gel and a polyacrylamide gel during a volume phase transition induced by a change of external environment - temperature, solvent composition, pH, and ion strength is described. The free volume size is probed by positron annihilation lifetime technique. Variations of the free volume size suggest that nanoscopic environment of the gels is affected by the free volume of the solvent phase and an interaction between the polymer chain and the solvent molecule in the swollen state, and by the aggregation of the polymer chain and a balance of the interaction among the polymer chain and the solvent molecules in the collapsed state. It is revealed that the free volume size reflects the essential change of the nanoscopic environment in the gels which could induce the macroscopic volume phase transition. (author)

  19. Structural studies of spinel manganite ceramics with positron annihilation lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Klym, H; Shpotyuk, O; Hadzaman, I [Institute of Materials of SRC ' Carat' , 202 Stryjska str., Lviv, 79031 (Ukraine); Ingram, A [Opole University of Technology, 75 Ozimska str., Opole, 45370 (Poland); Filipecki, J, E-mail: shpotyuk@novas.lviv.ua, E-mail: klymha@yahoo.com [Institute of Physics of Jan Dlugosz University, 13/15 Armii Krajowei, 42201, Czestochowa (Poland)

    2011-04-01

    The new transition-metal manganite Cu{sub 0.1}Ni{sub 0.8}Co{sub 0.2}Mn{sub 1.9}O{sub 4} ceramics for temperature sensors with improved functional reliability are first proposed. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. This effect is well revealed only in ceramics having a character fine-grain microstructure, while the monolithization of ceramics caused by great amount of transferred thermal energy reveals an opposite influence. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy.

  20. Prediction of free-volume-type correlations in glassy chalcogenides from positron annihilation lifetime measurements

    International Nuclear Information System (INIS)

    Highlights: • Decisive role of specific chemical environment in free-volume correlations in glass. • Realistic free volumes in As–S/Se glass are defined by newly modified τ2-R formula. • Overestimated void sizes in chalcogenide glass as compared with molecular polymers. - Abstract: A newly modified correlation equation between defect-related positron lifetime determined within two-state trapping model and radius of corresponding free-volume-type defects was proposed to describe compositional variations in atomic-deficient structure of covalent-bonded chalcogenides like binary As–S/Se glasses. Specific chemical environment of free-volume voids around neighboring network-forming polyhedrons was shown to play a decisive role in this correlation, leading to systematically enhanced volumes in comparison with typical molecular substrates, such as polymers

  1. Prediction of free-volume-type correlations in glassy chalcogenides from positron annihilation lifetime measurements

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, O., E-mail: shpotyuk@novas.lviv.ua [Institute of Materials of SRC “Carat”, 212 Stryjska Str., Lviv 79031 (Ukraine); Institute of Physics of Jan Dlugosz University, 13/15 al. Armii Krajowej, Czestcochowa 42200 (Poland); Ingram, A. [Opole University of Technology, 75 Ozimska Str., Opole 45370 (Poland); Shpotyuk, M. [Institute of Materials of SRC “Carat”, 212 Stryjska Str., Lviv 79031 (Ukraine); Lviv Polytechnic National University, 12 Bandery Str., Lviv 79013 (Ukraine); Filipecki, J. [Institute of Physics of Jan Dlugosz University, 13/15 al. Armii Krajowej, Czestcochowa 42200 (Poland)

    2014-11-01

    Highlights: • Decisive role of specific chemical environment in free-volume correlations in glass. • Realistic free volumes in As–S/Se glass are defined by newly modified τ{sub 2}-R formula. • Overestimated void sizes in chalcogenide glass as compared with molecular polymers. - Abstract: A newly modified correlation equation between defect-related positron lifetime determined within two-state trapping model and radius of corresponding free-volume-type defects was proposed to describe compositional variations in atomic-deficient structure of covalent-bonded chalcogenides like binary As–S/Se glasses. Specific chemical environment of free-volume voids around neighboring network-forming polyhedrons was shown to play a decisive role in this correlation, leading to systematically enhanced volumes in comparison with typical molecular substrates, such as polymers.

  2. Measurement of hydrodynamic interaction parameter for miscibility test of polymer blends by positron lifetime method

    International Nuclear Information System (INIS)

    Positron Annihilation Lifetime Spectroscopy is used to determine the free volume content in the blends of SAN/PMMA and PS/PVC. Though the free volume data indicate the miscible/immiscible nature of the blends, the extent of miscibility for different weight compositions is not forthcoming. Therefore the hydrodynamic interaction parameter α which accounts for the excess friction between the constituents of the blend system is evaluated for this purpose. The SAN/PMMA system produces a maximum α of -209 at 20% of PMMA concentration while PS/PVC almost zero. It appears sound that hydrodynamic interaction parameter, α, is a suitable parameter to understand the composition dependent miscibility level in polymer blends. (author)

  3. Vacancy defects in electron irradiated RPV steels studied by positron lifetime

    International Nuclear Information System (INIS)

    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*1019 e-/cm2). 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

  4. Estimation of free volumes of elastomer (polymerized siloxane rubber) by positron annihilation lifetime techniques

    International Nuclear Information System (INIS)

    In order to correlate size and content of free volumes present in amorphous region of these polymers and the mechanical and dynamical properties of elastomers, positron annihilation peak profile analysis and lifetime measurements were carried out from 30 K up to melting temperature for several poly(methyl-vinyl-siloxane) containing silica glass powders. S parameter and mean lifetime were adopted as a perspective measure for the rough estimation of the multiplied size and content of free volumes and proved that these parameters worked as a simple measure of the over-all free volumes. The free volume diameters of poly(methyl-vinyl-siloxane) (KE-931-B and KE-931) and poly(methyl-vinyl-siloxane) (KE-951 and KE-971) increased with the elevation of temperature from about 0.63 nm (30 K) to about 0.82 nm (Tm: 225 K) and from about 0.52 nm (30 K) to about 0.80 nm (Tm: 225 K), respectively. The free volume content (I3) of poly(methyl-vinyl-siloxane) (KE-951 and KE-971) is constant from 30 K (20.5% and 26.5%) to 150 K (Tg) and increased to about 29% and 37% at melting point (225 K), respectively, whereas those of poly(methyl-vinyl-siloxane) (KE-931-B and KE-931) increased from 28% and 20.5% (30 K) to 54% and 43% (225 K) monotonously. The presence of pseudo cross-linkage among silanol groups at the interface of elastomers and silica powders was suggested because both size and content of free volume were reduced by the increase of silica powder concentration in the elastomers. The Laplace inversion was applied to positron annihilation decay curve and obtained size distribution of free volume. (author)

  5. Hydrogen- and helium-implanted silicon: Low-temperature positron-lifetime studies

    DEFF Research Database (Denmark)

    Mäkinen, S.; Rajainmäki, H.; Linderoth, Søren

    1991-01-01

    High-purity single-crystal samples of float-zoned Si have been implanted with 6.95-MeV protons and with 25-MeV 3He2 ions at 15 K, and the positron-lifetime technique has been used to identify the defects created in the samples, and to study the effects of H and He on the annealing of point defects...... it is connected to annealing out of negatively charged divacancy-oxygen pairs. This stage was clearly longer than that for the p-irradiated Si, probably due to the breakup of Si-H bonds at about 550 K. The 100-K annealing stage was not seen with the He-implanted samples. This has been explained by...... assuming that almost all vacancies contained He after the irradiation with 3He. Helium is suggested to be released from vacancies at about 600 K, and small He bubbles seem to have grown at temperatures above 800 K. The specific positron-trapping rate for negatively charged monovacancy-type defects in H...

  6. Non-destructive evaluation of fatigue damage in type 316 stainless steel by using β+-γ coincidence positron lifetime spectrometer

    International Nuclear Information System (INIS)

    Newly developed β+-γ coincidence positron lifetime spectroscopy was applied to analysis of fatigue damage aiming at non-destructive evaluation of fatigue stored in type 316 stainless steel which is mostly used in primary water line of pressurized water reactor. Stress-controlled fatigue specimens and strain-controlled fatigue specimens were prepared and relations between fatigue life and positron lifetime were investigated. Mean positron lifetime increases with the fatigue life monotonically in both fatigue test modes. In the strain-controlled mode, mean positron lifetime increases faster at early stage than that in the stress-controlled mode; however, it converges to the same value at the end of the fatigue life in both conditions. Component analysis of positron lifetime spectra revealed that main defects are dislocations and their density increases with fatigue life to a critical value. With this non-destructive evaluation method, the fatigue damage can be analyzed precisely without destruction of the sample. (author)

  7. Study on positron annihilation lifetime spectrum of polysilicone rubber after proton radiation

    International Nuclear Information System (INIS)

    The positron annihilation lifetime spectrum (PALS) method was employed to study the effect of proton radiation on microstructure of the space grade KH-L-Y polysilicone rubber. The results show that both τ3 of I3 of the longest lifetime component and the free volume Vf decrease with the increasing of the radiation fluence at the beginning and become level off after 1015 cm-2 radiation fluence. The proton radiation causes decrease in both the free volume of polysilicone rubber, and the distance between the molecules when the radiation fluence is less than 1015 cm-2. However, the proton radiation makes the free volume of silicon rubber increase when the radiation fluence is greater than 1015 cm-2. Both the experimental results of the cross-linking density and DMA indicate that the cross-linking effect due to the proton radiation is predominant in the range of small proton radiation fluence, while the radiation degradation become superior when the proton radiation fluence is larger

  8. Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses

    Science.gov (United States)

    Taira, Y.; Toyokawa, H.; Kuroda, R.; Yamamoto, N.; Adachi, M.; Tanaka, S.; Katoh, M.

    2013-05-01

    High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

  9. Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses.

    Science.gov (United States)

    Taira, Y; Toyokawa, H; Kuroda, R; Yamamoto, N; Adachi, M; Tanaka, S; Katoh, M

    2013-05-01

    High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured. PMID:23742543

  10. Low energy positron flux generator for lifetime studies in thin films

    Science.gov (United States)

    Singh, Jag J.; St. Clair, Terry L.; Eftekhari, Abe

    1991-01-01

    A slow positron flux generator for positron annihilation spectroscopic measurements in thin polymer films is described. The advantages of this generator include operability at room temperature and atmospheric pressure without special test film preparaton requirements.

  11. Positron annihilation lifetime spectroscopy (PALS) application in metal barrier layer integrity for porous low- k materials

    CERN Document Server

    Simon, Lin; Gidley, D W; Wetzel, J T; Monnig, K A; Ryan, E T; Simon, Jang; Douglas, Yu; Liang, M S; En, W G; Jones, E C; Sturm, J C; Chan, M J; Tiwari, S C; Hirose, M

    2002-01-01

    Positron Annihilation Lifetime Spectroscopy (PALS) is a useful tool to pre-screen metal barrier integrity for Si-based porous low-k dielectrics. Pore size of low-k, thickness of metal barrier Ta, positronium (Ps) leakage from PALS, trench sidewall morphology, electrical test from one level metal (1LM) pattern wafer and Cu diffusion analysis were all correlated. Macro-porous low-k (pore size >=200 AA) and large scale meso-porous low-k (>50~200 AA) encounter both Ps leakage and Cu diffusion into low-k dielectric in the 0.25 mu mL/0.3 mu mS structures when using SEMATECH in-house PVD Ta 250 AA as barrier layer. For small scale meso-porous (>20~50 AA) and micro- porous (<=20 AA) low-k, no Ps leakage and no Cu diffusion into low-k were observed even with PVD Ta 50 AA, which is proved also owing to sidewall densification to seal all sidewall pores due to plasma etch and ash. For future technology, smaller pore size of porous Si-based low-k (=<50 AA) will be preferential for dense low-k like trench sidewall to...

  12. Studies on microdomain structure in segmented polyether polyurethaneureas by positron annihilation lifetime and small—angle X—ray scattering

    Institute of Scientific and Technical Information of China (English)

    YinChuan-Yuan; GuQing-Chao; 等

    1997-01-01

    The microdomain structure of segmented polyether polyurethaneureas is investigated by means of positron annihilation lifetime spectroscopy,small-angle X-ray scattering and differential scanning calorimetry.The experimental results show that the decrease in the domain volume and free volume results from the increase in the hard segment (polyurethaneurea segment)contents as the number-average molecular weight Mn of the soft segments (polyethylene glycol segments)is the same,and that the increase in domain volume and free volume result from the increase in the Mn of the soft segments when the hard segment content is the same or nearly the same.These results demonstrate that positron annihilation lifetime spectroscopy is a sensitive technique to probe the microdomain structure in polymers.

  13. Positron annihilation lifetime measurements of vanadium alloy and F82H irradiated with fission and fusion neutrons

    International Nuclear Information System (INIS)

    V-4Cr-4Ti, F82H, Ni and Cu were irradiated with fission and fusion neutrons at room temperature and 473 K. Defect structures were analyzed and compared using positron annihilation lifetime measurement, and microstructural evolution was discussed. The mean lifetime of positrons (the total amount of residual defects) increased with the irradiation dose. The effect of cascade impact was detected in Ni at room temperature. The size and the number of vacancy clusters were not affected by the displacement rate in the fission neutron irradiation at 473 K for the metals studied. The vacancy clusters were not formed in V-4Cr-4Ti irradiated at 473 K in the range of 10-6-10-3 dpa. In F82H irradiated at 473 K, the defect evolution was prevented by pre-existing defects. The mean lifetime of positrons in fission neutron irradiation was longer than that in fusion neutron irradiation in V-4Cr-4Ti at 473 K. It was interpreted that more closely situated subcascades were formed in the fusion neutron irradiation and subcascades interacted with each other, and consequently the vacancy clusters did not grow larger.

  14. The assessment of pore connectivity in hierarchical zeolites using positron annihilation lifetime spectroscopy: instrumental and morphological aspects.

    Science.gov (United States)

    Zubiaga, Asier; Warringham, Robbie; Boltz, Marilyne; Cooke, David; Crivelli, Paolo; Gidley, David; Pérez-Ramírez, Javier; Mitchell, Sharon

    2016-03-23

    Recent studies demonstrated the power of positron annihilation lifetime spectroscopy (PALS) to characterise the connectivity and corresponding effectiveness of hierarchical pore networks in zeolites. This was based on the fractional escape of ortho-positronium (Ps), formed within the micropore framework, to vacuum. To further develop this technique, here we assess the impact of the positron implantation energy and of the zeolite crystal size and the particle morphology. Conventional measurements using fast positrons and beam measurements applying moderated positrons both readily distinguish purely microporous ZSM-5 zeolites comprised of single crystals or crystal aggregates. Unlike beam measurements, however, conventional measurements fail to discriminate model hierarchical zeolites with open or constricted mesopore architectures. Several steps are taken to rationalise these observations. The dominant contribution of Ps diffusion to the PALS response is confirmed by capping the external surface of the zeolite crystals with tetraethylorthosilicate, which greatly enhances the sensitivity to the micropore network. A one-dimensional model is constructed to predict the out-diffusion of Ps from a zeolite crystal, which is validated experimentally by comparing coffin-shaped single crystals of varying size. Calculation of the trends expected on the application of fast or moderated positrons indicates that the distinctions in the initial distribution of Ps at the crystal level cannot explain the limited sensitivity of the former to the mesopore architecture. Instead, we propose that the greater penetration of fast positrons within the sample increases the probability of Ps re-entry from intercrystalline voids into mesopores connected with the external surface of zeolite crystals, thereby reducing their fractional escape. PMID:26975204

  15. Nano-crystallization of amorphous Fe75.5Cu1Nb3Si12.5B8 studied by the positron lifetime technique

    International Nuclear Information System (INIS)

    The crystallization process of amorphous Fe75.5Cu1Nb3Si12.5B8 into a nano-crystalline structure is investigated by the positron annihilation lifetime technique. Samples have been isothermally annealed at 643 K for times varying between 600 and 105 seconds. The positron lifetime spectra have been analyzed allowing for three lifetimes. The shortest and the longest lifetime, τ1 = 150 ± 2 ps and τ3 = 1500-2000 ps, respectively, are attributed to annihilation of positrons in the amorphous phase and to the formation and annihilation of ortho-positronium at the surface of the stacked foils and did not change significantly upon the annealing. The intermediate positron lifetime τ2 increased from 324 ps to 387 ps. The intensity of this component increased from 5 to 15%. Comparison with resistivity measurements indicates that the change of this lifetime component occurs at an early stage in the crystallisation process, i.e. when the fraction of crystalline material is on the order of 10-3. The increase of τ2 is attributed to positrons annihilating in a region with lower average density surrounding the small crystallite. (orig.)

  16. Constitutional and/or thermal vacancies in some B2 intermetallic compounds studied by positron lifetime spectroscopy

    International Nuclear Information System (INIS)

    Constitutional vacancies have been observed in some B2 intermetallics such as NiAl, CoAl, NiGa and CoGa by using positron lifetime spectroscopy. A large amount of non-thermal vacancies have been found not only on transition-element-poor compositions but also on transition-element-rich compositions of these intermetallics. B2 CuZn does not have such constitutional vacancies, but has a very low vacancy formation enthalpy. Intermetallic compounds with B2 structure are quite unique in the manner of vacancy formation. (orig.)

  17. Self-consistent field method and non-self-consistent field method for calculating the positron lifetime

    International Nuclear Information System (INIS)

    Many methods are used to calculate the positron lifetime, these methods could be divided into two main types. The first method is atomic superposition approximation method and the second one is the so called energy band calculation method. They are also known as the non-self-consistent field method and self-consistent field method respectively. In this paper, we first introduce the two basic methods and then, we take Si as an example and give our calculation results, these results coincide with our latest experimental results, finally, we discuss the advantages and disadvantages of the two methods

  18. 'Smart cut' silicon by proton implantation: lifetime studies with a pulsed positron beam

    International Nuclear Information System (INIS)

    High dose implantation of hydrogen into silicon and subsequent annealing induce a splitting of silicon. The state of hydrogen and the implantation induced defects are of scientific and technological interest. Samples implanted with 1 . 1016 and 5 . 1016 H+/cm2 at an energy of 60 keV were investigated after different thermal annealing treatments with the pulsed positron beam as a function of the positron energy and the specimen temperature (80 K to 500 K). There is clear evidence of growth of defect clusters with increasing annealing temperature which correspond in depth with the mean projected range of the implanted hydrogen atoms. In addition to the large defect agglomerates, there are most likely shallow positron traps which are effective only when the specimens are measured at low temperature. (orig.)

  19. Cold rolling induced amorphization and nanocrystallization processes studied by positron lifetime and 2-dimensional Doppler broadening measurements

    International Nuclear Information System (INIS)

    In order to contribute to an atomistic understanding of the interfacial structure and processes during amorphization and nanocrystallization, the present work deals with studies of interfacial free volumes by means of positron-annihilation-spectroscopy. In addition to positron lifetime spectroscopy, coincident Doppler broadening of the positron-electron annihilation photons is applied as novel technique for studying the chemistry of interfaces. To study the amorphization process, pure foils of Cu and Zr with a nominal composition of Cu60Zr40 were mechanically intermixed by cold rolling. Starting from the constituent pure metals, a nanoscale multilayer structure of elemental layers and amorphous interlayers develops in an intermediate state of folding and rolling, where free volumes with a Zr-rich environment occur that are presumably located in the hetero-interfaces between the various layers or in grain boundaries of the Cu-layers. To analyze the nanocrystallization reaction that occurs in marginal glass formers, pure foils of Al and Sm with a composition of Al92Sm8 were produced by the abovementioned synthesis route. Specific modifications of free volumes and their chemical environment could be observed for various strain levels

  20. A study of annealing stages in commercial pure Cu using mechanical measurements and positron annihilation lifetime technique

    International Nuclear Information System (INIS)

    Mechanical property measurements, positron annihilation lifetime (PAL) measurements and metallographic observations, have been performed to study the isochronal annealing of commercial pure Cu in the temperature range from 25 up to 850 deg. C. A positive correlation has been found between positron lifetime (τ) and both the tensile strain (ΔL/L0) and Vicker's microhardness (Hv). This correlation shows the presence of three annealing stages in commercial pure Cu which are attributed to recovery, recrystallization, and grain growth. These different stages were studied by both pure tensile and combined torsion-tension deformation for samples pre-annealed at the different annealing stages. Plastic instability behavior is observed in the case of combined torsion-tension deformation. It is observed that the onset and disappearance of this instability depend on some parameters such as mode of deformation, applied axial tensile stress and pre-annealing temperature. The activation energy is found to be 0.5 eV for the recovery stage which is attributed to the energy for dislocation annihilation by glide or cross-slip. The recrystallization stage is a multi-energy stage (1.35, 1.6, and 1.71 eV) which is attributed to lattice diffusion or boundary diffusion.

  1. Positron annihilation lifetime characterization of oxygen ion irradiated rutile TiO2

    Science.gov (United States)

    Luitel, Homnath; Sarkar, A.; Chakrabarti, Mahuya; Chattopadhyay, S.; Asokan, K.; Sanyal, D.

    2016-07-01

    Ferromagnetic ordering at room temperature has been induced in rutile phase of TiO2 polycrystalline sample by O ion irradiation. 96 MeV O ion induced defects in rutile TiO2 sample has been characterized by positron annihilation spectroscopic techniques. Positron annihilation results indicate the formation of cation vacancy (VTi, Ti vacancy) in these irradiated TiO2 samples. Ab initio density functional theoretical calculations indicate that in TiO2 magnetic moment can be induced either by creating Ti or O vacancies.

  2. Utility of positron annihilation lifetime technique for the assessment of spectroscopic data of some charge-transfer complexes derived from N-(1-Naphthyl)ethylenediamine dihydrochloride.

    Science.gov (United States)

    Refat, Moamen S; Adam, Abdel Majid A; Sharshar, T; Saad, Hosam A; Eldaroti, Hala H

    2014-03-25

    In this work, structural, thermal, morphological, pharmacological screening and positron annihilation lifetime measurements were performed on the interactions between a N-(1-Naphthyl)ethylenediamine dihydrochloride (NEDA·2HCl) donor and three types of acceptors to characterize these CT complexes. The three types of acceptors include π-acceptors (quinol and picric acid), σ-acceptors (iodine) and vacant orbital acceptors (tin(IV) tetrachloride and zinc chloride). The positron annihilation lifetime parameters were found to be dependent on the structure, electronic configuration, the power of acceptors and molecular weight of the CT complexes. The positron annihilation lifetime spectroscopy can be used as a probe for the formation of charge-transfer (CT) complexes. PMID:24291622

  3. Vacancy-like defects in doped Pb(Zr60Ti40)O3 observed by positron lifetime and coincident Doppler spectroscopy

    International Nuclear Information System (INIS)

    Ferroelectric Pb(Zr60Ti40)O3 ceramics sintered for 6 hours at 1050 C in air and doped with La or Nb in the range 0.5 to 6 mol% have been investigated by positron lifetime spectroscopy and two-dimensional coincident Doppler measurements. The undoped samples show two lifetime components with a defect lifetime of about 250 ps. After doping this defect lifetime increases to about 295 ps. The influence of the doping on the Doppler spectra is extremely small. Additional XRD pattern show a significant correlation between doping and lattice structure. (orig.)

  4. Per-fluorinated sulfonic acid/PTFE copolymer studied by positron annihilation lifetime and gas permeation techniques

    Science.gov (United States)

    Mohamed, Hamdy F. M.; Abdel-Hady, E. E.; Ohira, A.

    2015-06-01

    The mechanism of gas permeation in per-fluorinated sulfonic acid/PTFE copolymer Fumapem® membranes for polymer electrolyte fuel cells has been investigated from the viewpoint of free volume. Three different samples, Fumapem® F-950, F-1050 and F-14100 membranes with ion exchange capacity (IEC) = 1.05, 0.95 and 0.71 meq/g, respectively were used after drying. Free volume was quantified using the positron annihilation lifetime (PAL) technique and gas permeabilities were measured for O2 and H2 as function of temperature. Good linear correlation between the logarithm of the permeabilities at different temperatures and reciprocal free volume indicate that gas permeation in dry Fumapem® is governed by the free volume. Nevertheless permeabilities are much smaller than the corresponding flexible chain polymer with a similar free volume size due to stiff chains of the perfluoroethylene backbone.

  5. Positron Lifetime Study of the Transition from Glassy to Normal Liquid State for Two Phenyl Ethers

    DEFF Research Database (Denmark)

    Pethrick, R. A.; Jacobsen, F. M.; Mogensen, O. E.;

    1980-01-01

    at ≈ 233 K is associated with the glass transition for these liquids. A further change in the temperature dependence of the o-Ps lifetime was observed above 313 K where it becomes once more only weakly temperature dependent. Below the glass transition (Tg) Ps is probably trapped in pre-existing holes...

  6. Positron annihilation lifetime spectroscopy of carbon black- and silica-filled rubber

    International Nuclear Information System (INIS)

    Lifetime spectroscopy has been used to investigate different grades of carbon black (CB) and silica mixed into a variety of rubbers as a function of CB or silica loading. The spectra were analyzed into three lifetimes. The results show that: (1) The longest observed lifetime, τ3, attributed to ortho positronium formation depends on the rubber but not on filter loading or type of CB. The free volume size in the rubber is not affected by the addition of the filler. (2) The intensity, I3, of ortho positronium formation depends both on the loading and on the type of CB, but is less dependent on loading in the case of silica. (3) The intermediate lifetime, τ2, depends both on the loading of the filler and on the type of CB. For CB, this indicates that τ2 is not simply the additive result of bulk annihilation in the rubber and CB. Rather the CB loading creates new trapping sites at the CB-rubber interface that depend on the type of CB. (orig.)

  7. A positron lifetime study of lanthanum and niobium doped Pb(Zr0.6Ti0.4)O3

    International Nuclear Information System (INIS)

    A study of vacancy-related defects in lanthanum and niobium doped PbZr0.6Ti0.4O3 with dopant concentrations of 0-6 and 0-4 mol%, respectively has been performed using positron annihilation spectroscopy X-ray diffraction, and photoelectron spectroscopy. Positron lifetime as well as coincidence annihilation radiation Doppler line broadening measurements were carried out. It was found that the samples exhibit vacancylike defects that act as positron traps. Two main defect lifetime components were found in both sample sets one at ≅150 ps and one at ≅300 ps. These defect trapping sites can be attributed to single oxygen vacancies and A-site vacancies, respectively. Doppler line broadening measurements, however, do not show significant changes as a function of dopant concentrations in terms of shape S and wing W parameters

  8. Positron annihilation spectroscopy - a non-destructive method for lifetime prediction in the field of dynamical material testing

    International Nuclear Information System (INIS)

    The fatigue behavior of iron-based materials has been investigated by rotating bending testing, employing positron annihilation spectroscopy to probe defects on the atomic level. Positron annihilation spectra have been recorded at various stages of material fatigue. The defect density has been determined by analysing the line shape of the Doppler broadening of the annihilation radiation in the photo peak. The line shape parameter (S parameter), a measure of the defect density, showed a linear relation to the logarithm of the number of loadings, thus from only a small number of loadings it is possible to determine the remaining useful life of the sample. Furthermore, along the longitudinal sample axis spatially resolved line-scans are taken using the Bonn Positron Microprobe. Due to the special sample geometry, the stress gradient allows to obtain the S parameter for different values of the applied load using the very same sample. This leads to a way to determine a complete Woehler diagram using a non-destructive method for just one sample. (orig.)

  9. Dependence of alpha particle track diameter on the free volume holes size using positron annihilation lifetime technique

    Energy Technology Data Exchange (ETDEWEB)

    El-Gamal, S. [Physics Department, Faculty of Education, Ain Shams University, Roxy, 11711 Cairo (Egypt); Abdalla, Ayman M., E-mail: aymanabdalla62@hotmail.com [Physics Department, Faculty of Arts and Sciences, Najran University, Najran (Saudi Arabia); Centre for Advanced Materials and Nano-Engineering, Najran University, Najran 11001 (Saudi Arabia); Abdel-Hady, E.E. [Physics Department, Faculty of Science, Minia University, BO 61519, Minia (Egypt)

    2015-09-15

    The alpha particle track diameter dependence of the free volume holes size (V{sub f}) in DAM–ADC and CR-39 nuclear track detectors was investigated using positron annihilation lifetime technique. The effect of temperature on the alpha particle track diameter and free volume were also investigated in the T-range (RT-130 °C). The obtained results revealed that the values of ortho-positronium lifetime τ{sub 3} and V{sub f} increases while I{sub 3} slightly increases as T increases for the two detectors. The values of τ{sub 3}, V{sub f} and I{sub 3} are higher in CR-39 than DAM–ADC. The interpretation of obtained results is based on the fact that increasing T leads to significant enhancement of thermal expansion of the polymer matrix and consequently V{sub f} increases. The track diameter increases as T increases. This can be explained by the fact that the increase in T increases the crystal size and V{sub f} in the polymer. A relationship between V{sub f} and the alpha particle track diameter was obtained. Moreover results of detector irradiation, along with free volume evaluation are addressed and thoroughly discussed.

  10. Dependence of alpha particle track diameter on the free volume holes size using positron annihilation lifetime technique

    International Nuclear Information System (INIS)

    The alpha particle track diameter dependence of the free volume holes size (Vf) in DAM–ADC and CR-39 nuclear track detectors was investigated using positron annihilation lifetime technique. The effect of temperature on the alpha particle track diameter and free volume were also investigated in the T-range (RT-130 °C). The obtained results revealed that the values of ortho-positronium lifetime τ3 and Vf increases while I3 slightly increases as T increases for the two detectors. The values of τ3, Vf and I3 are higher in CR-39 than DAM–ADC. The interpretation of obtained results is based on the fact that increasing T leads to significant enhancement of thermal expansion of the polymer matrix and consequently Vf increases. The track diameter increases as T increases. This can be explained by the fact that the increase in T increases the crystal size and Vf in the polymer. A relationship between Vf and the alpha particle track diameter was obtained. Moreover results of detector irradiation, along with free volume evaluation are addressed and thoroughly discussed

  11. Bulk-volume behavior of pressure-densified amorphous polymers and free-volume behavior by positron annihilation lifetime measurement

    International Nuclear Information System (INIS)

    In order to study the nature of amorphous polymers, the free volume contribution on the bulk volume change was investigated on the basis of the relationship between the bulk volume behavior by PVT (pressure-volume-temperature) measurement and the free volume behavior by PALS (positron annihilation lifetime spectroscopy) measurement. A densified glass, prepared by cooling at constant rate from the melt state temperature to room temperature under 200 MPa, showed smaller bulk volume and free volume than non-densified glass. And the densified glass showed not only the same glass transition temperature (Tg) as non-densified glass but also another transition at lower temperature around (Tg-30 C). In this glass-glass transition, both the bulk volume and free volume of densified glass recovered to those of non-densified glass. Moreover the densified glass showed different thermal behavior from the glass which was enthalpy-relaxed under atmospheric pressure. From those results, it was considered that the free volume behavior largely related to the behavior of amorphous polymers. (orig.)

  12. Positron annihilation lifetime spectroscopy study on the structural relaxation of phenylmethylsiloxane-modified epoxy hybrids at different aging temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Hsu, Chia-Wen [Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan (China); Ma, Chen-Chi M., E-mail: ccma@che.nthu.edu.tw [Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Tan, Chung-Sung [Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Li, Hsun-Tien [Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan (China)

    2015-07-15

    The cured network conformations and structural relaxation behaviours of the diglycidyl ether of bisphenol A (DGEBA)-methylhexahydrophthalic anhydride (MHHPA) modified with phenylmethylsiloxane-modified epoxy (PMSE) at different aging temperatures were studied using dynamic mechanical analysis (DMA) and positron annihilation lifetime spectroscopy (PALS). The DMA results revealed that the cured PMSE network can insert into the cured DGEBA network to form interpenetrating polymer networks (IPNs). The structural relaxation behaviours of DGEBA–PMSE-0.4 produced using DGEBA, PMSE, and MHHPA at a ratio of 0.6:0.4:1 by equivalent weight were studied using PALS at 150 °C and 55 °C. The aging-induced free volume relaxation parameters of DGEBA–PMSE-0.4 at 150 °C and 55 °C were investigated using the double additive exponential model and the Kohlrausch–Williams–Watts exponential model. For double additive exponential model, only one relaxation time (ζ) of 584.5 h was found at 150 °C; By contrast, there were two separate relaxation times of 37.4 h (ζ{sub 1}) and 753.6 h (ζ{sub 2}) at 55 °C. The ζ{sub 1} of the IPNs hybrid can be attributed to the network relaxation of PMSE, and the ζ{sub 2} can be attributed to the network relaxation of DGEBA at 55 °C. The results suggested the double additive exponential model can effectively predict DGEBA–PMSE hybrid relaxation behaviours. - Highlights: • The cured network conformations of DGEBA–PMSE hybrids were studied using DMA. • The structural relaxation behaviours of DGEBA–PMSE hybrids were studied using PALS. • The cured DGEBA–PMSE hybrids were interpenetrating polymer networks (IPNs). • PALS studies provided a quantitative demonstration of relaxation behaviours. • Double additive exponential model effectively predicted the relaxation times of hybrids.

  13. Positron annihilation lifetime spectroscopy study on the structural relaxation of phenylmethylsiloxane-modified epoxy hybrids at different aging temperatures

    International Nuclear Information System (INIS)

    The cured network conformations and structural relaxation behaviours of the diglycidyl ether of bisphenol A (DGEBA)-methylhexahydrophthalic anhydride (MHHPA) modified with phenylmethylsiloxane-modified epoxy (PMSE) at different aging temperatures were studied using dynamic mechanical analysis (DMA) and positron annihilation lifetime spectroscopy (PALS). The DMA results revealed that the cured PMSE network can insert into the cured DGEBA network to form interpenetrating polymer networks (IPNs). The structural relaxation behaviours of DGEBA–PMSE-0.4 produced using DGEBA, PMSE, and MHHPA at a ratio of 0.6:0.4:1 by equivalent weight were studied using PALS at 150 °C and 55 °C. The aging-induced free volume relaxation parameters of DGEBA–PMSE-0.4 at 150 °C and 55 °C were investigated using the double additive exponential model and the Kohlrausch–Williams–Watts exponential model. For double additive exponential model, only one relaxation time (ζ) of 584.5 h was found at 150 °C; By contrast, there were two separate relaxation times of 37.4 h (ζ1) and 753.6 h (ζ2) at 55 °C. The ζ1 of the IPNs hybrid can be attributed to the network relaxation of PMSE, and the ζ2 can be attributed to the network relaxation of DGEBA at 55 °C. The results suggested the double additive exponential model can effectively predict DGEBA–PMSE hybrid relaxation behaviours. - Highlights: • The cured network conformations of DGEBA–PMSE hybrids were studied using DMA. • The structural relaxation behaviours of DGEBA–PMSE hybrids were studied using PALS. • The cured DGEBA–PMSE hybrids were interpenetrating polymer networks (IPNs). • PALS studies provided a quantitative demonstration of relaxation behaviours. • Double additive exponential model effectively predicted the relaxation times of hybrids

  14. Free volume in imidazolium triflimide ([C3MIM][NTf2]) ionic liquid from positron lifetime: amorphous, crystalline, and liquid states.

    Science.gov (United States)

    Dlubek, G; Yu, Yang; Krause-Rehberg, R; Beichel, W; Bulut, S; Pogodina, N; Krossing, I; Friedrich, Ch

    2010-09-28

    Positron annihilation lifetime spectroscopy (PALS) is used to study the ionic liquid 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide [C(3)MIM][NTf(2)] in the temperature range between 150 and 320 K. The positron decay spectra are analyzed using the routine LifeTime-9.0 and the size distribution of local free volumes (subnanometer-size holes) is calculated. This distribution is in good agreement with Fürth's classical hole theory of liquids when taking into account Fürth's hole coalescence hypothesis. During cooling, the liquid sample remains in a supercooled, amorphous state and shows the glass transition in the ortho-positronium (o-Ps) lifetime at 187 K. The mean hole volume varies between 70 Å(3) at 150 K and 250 Å(3) at 265-300 K. From a comparison with the macroscopic volume, the hole density is estimated to be constant at 0.20×10(21) g(-1) corresponding to 0.30 nm(-3) at 265 K. The hole free volume fraction varies from 0.023 at 185 K to 0.073 at T(m)+12 K=265 K and can be estimated to be 0.17 at 430 K. It is shown that the viscosity follows perfectly the Cohen-Turnbull free volume theory when using the free volume determined here. The heating run clearly shows crystallization at 200 K by an abrupt decrease in the mean and standard deviation σ(3) of the o-Ps lifetime distribution and an increase in the o-Ps intensity I(3). The parameters of the second lifetime component and σ(2) behave parallel to the o-Ps parameters, which also shows the positron's (e(+)) response to structural changes. During melting at 253 K, all lifetime parameters recover to the initial values of the liquid. An abrupt decrease in I(3) is attributed to the solvation of e(-) and e(+) particles. Different possible interpretations of the o-Ps lifetime in the crystalline state are briefly discussed. PMID:20886945

  15. Free volume in imidazolium triflimide ([C3MIM][NTf2]) ionic liquid from positron lifetime: Amorphous, crystalline, and liquid states

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectroscopy (PALS) is used to study the ionic liquid 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide [C3MIM][NTf2] in the temperature range between 150 and 320 K. The positron decay spectra are analyzed using the routine LifeTime-9.0 and the size distribution of local free volumes (subnanometer-size holes) is calculated. This distribution is in good agreement with Fuerth's classical hole theory of liquids when taking into account Fuerth's hole coalescence hypothesis. During cooling, the liquid sample remains in a supercooled, amorphous state and shows the glass transition in the ortho-positronium (o-Ps) lifetime at 187 K. The mean hole volume varies between 70 A3 at 150 K and 250 A3 at 265-300 K. From a comparison with the macroscopic volume, the hole density is estimated to be constant at 0.20x1021 g-1 corresponding to 0.30 nm-3 at 265 K. The hole free volume fraction varies from 0.023 at 185 K to 0.073 at Tm+12 K=265 K and can be estimated to be 0.17 at 430 K. It is shown that the viscosity follows perfectly the Cohen-Turnbull free volume theory when using the free volume determined here. The heating run clearly shows crystallization at 200 K by an abrupt decrease in the mean 3> and standard deviation σ3 of the o-Ps lifetime distribution and an increase in the o-Ps intensity I3. The parameters of the second lifetime component 2> and σ2 behave parallel to the o-Ps parameters, which also shows the positron's (e+) response to structural changes. During melting at 253 K, all lifetime parameters recover to the initial values of the liquid. An abrupt decrease in I3 is attributed to the solvation of e- and e+ particles. Different possible interpretations of the o-Ps lifetime in the crystalline state are briefly discussed.

  16. Investigations into the free-volume changes within starch/plasticizer/nanoclay systems using Positron Annihilation Lifetime Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Huihua, E-mail: h.liu@federation.edu.au [School of Health Sciences, Federation University Australia, Ballarat, Vic (Australia); Chaudhary, Deeptangshu, E-mail: deepc@ers.com.au [ERS Environmental Risk Solutions PTY LTD, Perth, WA (Australia); Campbell, Colin, E-mail: colin.campbell@anu.edu.au [ARC Centre of Excellence for Antimatter-Matter Studies (CAMS), Research School of Physics and Engineering, Australian National University, Canberra (Australia); Roberts, Jason, E-mail: jxr107@physics.anu.edu.au [ARC Centre of Excellence for Antimatter-Matter Studies (CAMS), Research School of Physics and Engineering, Australian National University, Canberra (Australia); Buckman, Stephen, E-mail: stephen.buckman@anu.edu.au [ARC Centre of Excellence for Antimatter-Matter Studies (CAMS), Research School of Physics and Engineering, Australian National University, Canberra (Australia); Sullivan, James, E-mail: james.sullivan@anu.edu.au [ARC Centre of Excellence for Antimatter-Matter Studies (CAMS), Research School of Physics and Engineering, Australian National University, Canberra (Australia)

    2014-11-14

    The free-volume of a matrix is a fundamental parameter that relates to its molecular and bulk characteristics, such as crystalline change and glass transition behavior. In starch-based bionanocomposite, we investigated the effect of the addition of montmorillonite nanoclay (MMT) and food plasticizers (glycerol and sorbitol) on changes of molecular pore size (including pore volume and pore distribution) using the Positron Annihilation Lifetime Spectroscopy (PALS) method. The results demonstrated counter-intuitive impact of MMT on the total free-volume where the total free-volume increased within the polymeric matrix. When compared to the pure matrix free-volume, the addition of MMT also resulted in the appearance of a broader distribution of the void sizes. The plasticizers, on the other hand, apparently occupied the void spaces, and therefore decreased the free-volume of the matrix. Further, together with the small angle X-ray scattering (SAXS) analysis, we concluded that this is a result of interplay between the plasticizer-plasticizer interactions and the polymer–plasticizer interactions. For example, in the starch/glycerol/MMT system, the pore radii slightly decrease upon the increasing of glycerol amount (OG210 = O.27 nm and OG220 = 0.26 nm), but the relative weight did increase with the increasing glycerol concentration. However, increasing the sorbitol amount increased the pore size from 0.23 nm(OS210) to 0.28 nm(OS220). Furthermore, the addition MMT in the OS010 system, promote the emergence of a new dateable pore radius(0.90 nm), and the total weight significantly increased from 13.70 (OS010) to 19.5% (OS210). We suggest that the pore variation (size and distribution) due to the MMT and plasticizers are reflected in the polymer glass transition and crystallinity because ultimately, the, total free-volume is a reflection of level of interactions existing within the bulk of these nanocomposites. - Highlights: • PALS is applied to explore the

  17. Variation of free volume size and content of shape memory polymer -polyurethane - upon temperature studied by positron annihilation lifetime techniques and infrared spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation lifetime measurement and Fourier transform infrared spectrometry were applied to the study of temperature dependencies of free volume parameters and hydrogen bonds in segmented polyurethane, specially fabricated as a shape memory polymer. The variation of free volumes in amorphous region were correlated to that of hydrogen bonding and the shape memory mechanism of polyurethane is elucidated from a microscopic point of view. The relationship between free volume contents and the formation of hydrogen bonds significantly suggests that the shape memory occurs due to the configurational recovery of the microscopic regulation around urethane bundles of hard segment and consequent restoration of soft-segment in polyurethane. (author)

  18. Neutronic Lifetime Analyses of Small and Medium Reactors with TRISO and Cermet Fuel. Annex III

    International Nuclear Information System (INIS)

    The Nuclear Physics Laboratory, Faculty of Sciences, University Mohammed V (Rabat, Morocco) have studied the innovative small and medium reactors (the AFPR from the USA, the FBNR from Brazil, the VKR-MT from the Russian Federation, and the PFPWR50 from Japan, performing independent neutronics and depletion analyses in confirmation of the results from the design teams. These innovative reactors are designed to have a long core lifetime and operate without on-site refuelling. Their main design objectives are to provide enhanced safety, proliferation resistance and cost reduction. This ANNEX presents calculation results of the depletion analyses performed for cells with the two types of micro fuel elements (cermet and TRISO). The results for the benchmark problems cover neutron spectrum, neutron multiplication factors versus fuel burn-up and other related parameters for all considered reactor concepts. The final results prove that all of the considered reactor concepts can achieve long refuelling interval. The focus of the calculations performed was on comparing cermet and TRISO fuel options. Specifically analyzed was an option to retain long-life core operation in direct transition from a TRISO based to the cermet based fuel. More details on the fuel and reactor design and the codes and data libraries used in the calculations can be found in Chapter 5 of the report

  19. Lifetime evaluation of first wall and divertor plate by crack analyses during plasma disruptions

    International Nuclear Information System (INIS)

    The first wall and divertor armor in fusion devices are subjected to high heat and particle fluxes. In particular, disruption heating is an intense thermal shock which may cause melting or vaporization of the armor surfaces. The behavior of the armor materials is one of the major factors limiting the lifetime of these components. Generally the surface temperature of armor due to disruption gets so high that the surface may become cracked. However, even if only the surface of the armor is cracked, the function of the armor will not be lost as long as the damage is limited to within a small depth of the surface. In this study, the lifetime of the armor is evaluated by two stages: crack initiation life and crack propagation life which are related to the fatigue life and the energy release rate, respectively. Materials are graphite and C/C composite (carbon fiber reinforced carbon composite) for the first wall, and tungsten for the dinertor. For disruption conditions of Fusion Experimental Reactor, the fatigue life and the energy release rates are calculated by thermal, and stress analyses. Results show that crack initiation is expected after only a few disruptions, and the energy release rate as a function of the crack length comes up to the maximum value at a small crack length, and decreases with increasing of the crack length. This decreasing means that a crack propagation rate reduces. An unstable fracture does not occur if the maximum energy release rate does not exceed the critical energy release rate which can be obtained from the fracture toughness. (author)

  20. Damage structure due to displacement cascades in 14 MeV neutron-irradiated metals studied by positron lifetime and TEM techniques

    International Nuclear Information System (INIS)

    Transmission electron microscopy (TEM) and positron lifetime measurements were performed for Au, Cu, Ni, Fe, SUS316 and Fe-9Cr irradiated with 14 MeV D-T neutrons to (2.9-12.0)x1019 nm-2 at 333 and 423 K. TEM observations for the specimens irradiated at 333 K showed visible defect clusters in Au, Cu and Ni. There were no visible defect clusters in Fe, SUS316 and Fe-9Cr. Positron lifetime analysis and the trapping model analysis suggested an important role of invisible defect clusters during cascade defect formation. In Fe, the depleted zone from a single cascade event rarely collapses to a dislocation loop, and preferentially forms a three-dimensional vacancy cluster. Three-dimensional vacancy clusters are formed in Cu, Ni, Fe, SUS316 and Fe-9Cr. The size of these clusters is very small (di- or tri-vacancies) in SUS316 and Fe-9Cr because of the trapping of vacancies by impurities or solute atoms. (orig.)

  1. Location and size of nanoscale free-volume holes in crosslinked- polytetrafluoroethylene-based graft-type polymer electrolyte membranes determined by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    The location and size of nanoscale free-volume holes (nanoholes) in graft-type polymer electrolyte membranes (PEMs), which were prepared by radiation-induced graft polymerization (grafting) of styrene into crosslinked-polytetrafluoroethylene (cPTFE) films and subsequent sulfonation, were investigated using positron annihilation lifetime (PAL) spectroscopy. The PAL spectra of the PEMs indicated the existence of two types of ortho-positronium (o-Ps) species, corresponding to nanoholes with volumes of 0.11 and 0.38 nm3. A comparison of the PAL data of the PEMs with that of the precursor original cPTFE and polystyrene-grafted films demonstrated the probability that the smaller holes were located in both the PTFE crystalline phases and the poly(styrene sulfonic acid) graft regions, whereas the larger holes are potentially localized in the PTFE amorphous phases. Taking into account both the size and the location of the nanoholes, it was concluded that gas transport through the larger holes in the amorphous PTFE phases was dominant over permeation through the smaller holes in the PTFE crystals and grafted regions. - Highlights: ► Positron annihilation lifetime measurement of graft-type electrolyte membrane. ► There were two types of free-volume holes with different sizes. ► The smaller holes were located in the PTFE crystalline phases and grafted regions. ► The larger holes were located in the PTFE amorphous phases

  2. Modeling of high homologous temperature deformation behavior for stress and life-time analyses

    Energy Technology Data Exchange (ETDEWEB)

    Krempl, E. [Rensselaer Polytechnic Institute, Troy, NY (United States)

    1997-12-31

    Stress and lifetime analyses need realistic and accurate constitutive models for the inelastic deformation behavior of engineering alloys at low and high temperatures. Conventional creep and plasticity models have fundamental difficulties in reproducing high homologous temperature behavior. To improve the modeling capabilities {open_quotes}unified{close_quotes} state variable theories were conceived. They consider all inelastic deformation rate-dependent and do not have separate repositories for creep and plasticity. The viscoplasticity theory based on overstress (VBO), one of the unified theories, is introduced and its properties are delineated. At high homologous temperature where secondary and tertiary creep are observed modeling is primarily accomplished by a static recovery term and a softening isotropic stress. At low temperatures creep is merely a manifestation of rate dependence. The primary creep modeled at low homologous temperature is due to the rate dependence of the flow law. The model is unaltered in the transition from low to high temperature except that the softening of the isotropic stress and the influence of the static recovery term increase with an increase of the temperature.

  3. Determination of the activation enthalpy for migration of dislocations in plastically deformed 8006 Al-alloy by positron annihilation lifetime technique

    Science.gov (United States)

    Salah, Mohammed; Abdel-Rahman, M.; Badawi, Emad A.; Abdel-Rahman, M. A.

    2016-06-01

    The activation enthalpy for migration of dislocations of plastically deformed 8006 Al-alloy was investigated by positron annihilation lifetime technique. Plastic deformation using a hydraulic press produces mainly dislocations and may produce point defects. The type of defect was studied by isochronal annealing which determines the temperature range of recovery of each type. Only one type of defect (dislocations) was observed for the investigated sample and was found to be recovered within the range 455-700 K. Isothermal annealing by slow cooling was performed through this range and used in determination of the activation enthalpy of migration of dislocations which was found to be 0.26 ± 0.01 eV.

  4. Nuclear Instruments and Methods in Physics Research. Section B; Microstructural Characterization of Semi-Interpenetrating Polymer Networks by Positron Lifetime Spectroscopy

    Science.gov (United States)

    Singh, Jag J.; Pater, Ruth H.; Eftekhari, Abe

    1998-01-01

    Thermoset and thermoplastic polyimides have complementary physical/mechanical properties. Whereas thermoset polyimides are brittle and generally easier to process, thermoplastic polyimides are tough but harder to process. It is expected that a combination of these two types of polyimides may help produce polymers more suitable for aerospace applications. Semi-Interpenetrating Polymer Networks (S-IPNs) of thermoset LaRC(Trademark)-RP46 and thermoplastic LARC(Trademark)-IA polyimides were prepared in weight percent ratios ranging from 100:0 to 0: 100. Positron lifetime measurements were made in these samples to correlate their free volume features with physical/mechanical properties. As expected, positronium atoms are not formed in these samples. The second life time component has been used to infer the positron trap dimensions. The "free volume" goes through a minimum at about 50:50 ratio, suggesting that S-IPN samples are not merely solid solutions of the two polymers. These data and related structural properties of the S-IPN samples have been discussed in this paper.

  5. Determination of the positron diffusion length in Kapton by analysing the positronium emission

    International Nuclear Information System (INIS)

    Doppler profile spectroscopy and Compton-to-peak ratio analysis have been used to study the positronium (Ps) emission from the Kapton surface as a function of the positron implantation energy E. Two different positions for the sample have been performed in the experiment. In the first case the sample and the Ge-detector are perpendicular to the positron beam. With this geometry the emission of para-positronium (p-Ps) is detected as a narrow central peak. In the second case, by rotating the sample 45 deg. with respect to the beam axis, the emission of p-Ps is detected as a blue-shifted fly away peak. The implantation of the positrons is described by the Makhov profile, where we used the modified median implantation for polymers as given by Algers et al. [J. Algers, P. Sperr, W. Egger, G. Koegel, F.H.J. Maurer, Phys. Rev. B 67 (2003) 125404]. Thermalised positrons can diffuse to the surface and may pick up an electron to be emitted as Ps. We found a thermal and or epithermal positron diffusion length L+ = 5.43 ± 0.71 nm and L+ = 5.51 ± 0.28 nm correspondingly for both cases, which is much more than the one found by Brusa et al. [R.S. Brusa, A. Dupasquier, E. Galvanetto, A. Zecca, Appl. Phys. A 54 (1992) 233]. The respective efficiency for the emission of Ps by picking up an electron from the surface is found to be fpu = 0.247 ± 0.012 and fpu = 0.156 ± 0.003

  6. Microstructural changes and effect of variation of lattice strain on positron annihilation lifetime parameters of zinc ferrite nanocomposites prepared by high enegy ball-milling

    Directory of Open Access Journals (Sweden)

    Abhijit Banerjee

    2012-12-01

    Full Text Available Zn-ferrite nanoparticles were synthesized at room temperature by mechanical alloying the stoichiometric (1:1 mol% mixture of ZnO and α-Fe2O3 powder under open air. Formation of both normal and inverse spinel ferrite phases was noticed after 30 minutes and 2.5 hours ball milling respectively and the content of inverse spinel phase increased with increasing milling time. The phase transformation kinetics towards formation of ferrite phases and microstructure characterization of ball milled ZnFe2O4 phases was primarily investigated by X-ray powder diffraction pattern analysis. The relative phase abundances of different phases, crystallite size, r.m.s. strain, lattice parameter change etc. were estimated from the Rietveld powder structure refinement analysis of XRD data. Positron annihilation lifetime spectra of all ball milled samples were deconvoluted with three lifetime parameters and their variation with milling time duration was explained with microstructural changes and formation of different phases with increase of milling time duration.

  7. OL1/OL2 License renewal for extended life-time: Class 1 piping load and strength analyses

    International Nuclear Information System (INIS)

    Teollisuuden Voima Oyj (TVO) operates two NPP units Olkiluoto 1 (OL1) and Olkiluoto 2 (OL2), that are identical 880 MWe BWRs. The units were originally designed for 40 years life-time. TVO is applying license renewal for extended life-time for 60 years plant life. Part of the license renewal project is to evaluate and update all Class 1 piping load and strength analyses. These analyses are done with the help of TVO's in-house Piping and Component Analysis and Monitoring System (PAMS). PAMS is basically a database system, consisting of separate geometry, material, loading, result and document databases. The thermo hydraulic analysis program RELAP5 is used to obtain temperature, pressure and mass flow for the piping loading areas. The piping strength analysis are carried out mainly with the Finnish FPIPE FEA program for all related thermal transient and dynamic load cases. The slides of the presentation have been added to the paper

  8. Thermal and Chemical Analyses of Silicone Polymers for Component Engineering Lifetime Assessments

    Energy Technology Data Exchange (ETDEWEB)

    Balazs, B; Maxwell, R S

    2002-05-14

    Accurate predictions of a polymer component's functional lifetime at best arc tenuous when one has only relatively short term chemical or mechanical property data to extrapolate. We have analyzed a series of silica-filled siloxanes to determine the chemical and microstructural signatures of aging, and we are incorporating these data into rational methodologies for assessing a component's lifetime measured against as-designed engineering properties. We are monitoring changes in mechanical properties, crystallization kinetics, cross-link density changes, and motional dynamics with a variety of analysis methods: Modulated DSC, Dynamic Mechanical Analysis, and Solid-state Nuclear Magnetic Resonance. Previous work has shown that the addition of phenyl side groups to polydimethylsiloxane (PDMS) polymer chains reduces the rate and extent of crystallization of the co-polymer compared to that of pure PDMS. Crystallization has been observed in copolymer systems up to 6.5 mol % phenyl composition by DSC and up to 8 mol % phenyl by XRD. The PDMS-PDPS-silica composite materials studied here are silica reinforced random block copolymers consisting of dimethyl and diphenyl monomer units with 11.2 mol. % polydiphenylsiloxane. Based on this previous work, it is not expected that this material would exhibit crystallization in the polymer network; however, these silicones do, in fact, exhibit crystallization phenomena. This report focuses primarily on our efforts to assess the information content of the crystallization phenomena with respect to aging signatures and mechanisms that may be limiting the functional lifetime of the composite materials.

  9. Consequences of changed nuclear power plant lifetimes in Germany. Scenario analyses until 2035

    International Nuclear Information System (INIS)

    The report is aimed to discuss the implications of changed NPP lifetimes in Germany on energy policy, environment, energy cost and macroeconomics. An extensive scenario analysis is used considering the effects on the German energy system in the frame of the European context. It is shown that a nuclear phase-out until 2017 is technically feasible, but needs adequate replacement options that will change the German energy system in the medium term. The study shows that the time of nuclear phase-out has no significant influence on the use of renewable energies.

  10. Positron Annihilation Lifetime Spectroscopy Study of Neutron Irradiated High Temperature Superconductors YBa2Cu3O7-δ for Application in Fusion Facilities

    Science.gov (United States)

    Veterníková, J.; Chudý, M.; Slugeň, V.; Eisterer, M.; Weber, H. W.; Sojak, S.; Petriska, M.; Hinca, R.; Degmová, J.; Sabelová, V.

    2012-02-01

    This study focuses on the crystallographic defects introduced by neutron irradiation and the resulting changes of the superconducting properties in the high temperature superconductor YBa2Cu3O7-δ. This material is considered to be most promising for magnet systems in future fusion reactors. Two different bulk samples, pure non-doped YBa2Cu3O7-δ (YBCO) and multi-seed YBa2Cu3O7-δ doped by platinum (MS2F) were studied prior to and after irradiation in the TRIGA MARK II reactor in Vienna. Neutron irradiation is responsible for a significant enhancement of the critical current densities as well as for a reduction in critical temperature. The accumulation of small open volume defects (<0.5 nm) partially causes those changes. These defects were studied by positron annihilation lifetime spectroscopy at room temperature. A high concentration of Cu-O di-vacancies was found in both samples, which increased with neutron fluence. The defect concentration was significantly reduced after a heat treatment.

  11. Lifetime and economic analyses of lithium-ion batteries for balancing wind power forecast error

    DEFF Research Database (Denmark)

    Swierczynski, Maciej Jozef; Stroe, Daniel Ioan; Stroe, Ana-Irina;

    2015-01-01

    Wind power plant operators are often faced with extra charges when their power production does not match the forecasted power. Because the accuracy of wind power forecasts is limited, the use of energy storage systems is an attractive alternative even when large-scale aggregation of wind power is...... considered. In this paper, the economic feasibility of lithium-ion batteries for balancing the wind power forecast error is analysed. In order to perform a reliable assessment, an ageing model of lithium-ion battery was developed considering both cycling and calendar life. The economic analysis considers two...... different energy management strategies for the storage systems and it is performed for the Danish market. Analyses have shown that the price of the Li-ion BESS needs to decrease by 6.7 times in order to obtain a positive net present value considering the present prices on the Danish energy market. Moreover...

  12. Recent development of positron annihilation methods

    CERN Document Server

    Doyama, M

    2002-01-01

    When positron comes into solid or liquid, it moves in the matter and emitted two gamma rays at the opposite direction, by pair annihilation with electron. Each gamma ray is about 511 keV. The experiments of positron annihilation has been developed by three methods such as angular correlation between two gamma rays, energy analysis of emission gamma ray and positron lifetime. The angular correlation between two gamma rays is determined by gamma ray position detector.The energy analysis was measured by S-W analysis and Coincidence Doppler Broadening (CDB) method. Positron lifetime are determined by gamma-gamma lifetime measurement method, beta sup + -gamma lifetime measurement method and other method using waveform of photomultiplier, and determination of time and frequency of gamma-ray. Positron beam is applied to positron scattering, positron diffraction, low energy positron diffraction (LEPD), PELS, LEPSD, PAES, positron re-emission imaging microscope (PRIM) and positron channeling. The example of CDB method...

  13. Effect of free volume and temperature on the structural relaxation in polymethylphenylsiloxane: a positron lifetime and pressure-volume-temperature study.

    Science.gov (United States)

    Dlubek, G; Shaikh, M Q; Krause-Rehberg, R; Paluch, M

    2007-01-14

    The microstructure of the free volume and its temperature dependence in polymethylphenylsiloxane (PMPS) have been examined using positron annihilation lifetime spectroscopy (PALS) and pressure-volume-temperature experiments. The hole-free volume fraction h and the specific hole-free and occupied volumes, Vf=hV and Vocc=(1-h)V, were estimated employing the Simha-Somcynsky (SS) lattice-hole theory. From the PALS spectra analyzed with the new routine LT9.0 the hole size distribution, its mean, , and mean dispersion, sigmah, were calculated. A comparison of with V and Vf delivered a constant specific hole number Nh'. Using a fluctuation approach the temperature dependency of the volume of the smallest representative freely fluctuating subsystem, , is estimated to vary from approximately 8.5 nm3 at Tg to approximately 3 nm3 at T/Tg>or=1.15. Unlike other polymers, the segmental relaxation from dielectric spectroscopy of PMPS follows the Cohen-Turnbull free volume theory almost perfectly in the temperature and pressure ranges between 243 and 279 K and 0 and approximately 100 MPa. This behavior correlates with the small mass of the SS lattice mer which indicates the high flexibility of the PMPS chain. Above 293 K and approximately 150 MPa, the free volume prediction gives relaxation times that are too small, which indicates that effects of thermal energy must be included in the analysis. To quantify the degree to which volume and thermal energy govern the structural dynamics the ratio of the activation enthalpies, Ei=R[(d ln taudT1)]i (tau-relaxation time of alpha relaxation), at constant volume V and constant pressure P, EV/EP, is frequently determined. The authors present arguments for necessity to substitute EV with EVf, the activation enthalpy at constant (hole) free volume, and show that EVf/EP changes as expected: increasing with increasing free volume, i.e., with increasing temperature and decreasing pressure. EVf/EP (=0.04-0.1) exhibits remarkably smaller values

  14. Increased brain amyloid deposition in patients with a lifetime history of major depression: evidenced on {sup 18}F-florbetapir (AV-45/Amyvid) positron emission tomography

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Kuan-Yi; Chen, Chia-Hsiang; Liu, Chia-Yih [Chang Gung Memorial Hospital and Chang Gung University, Department of Psychiatry, Tao-Yuan (China); Hsiao, Ing-Tsung; Hsieh, Chia-Ju [Chang Gung Memorial Hospital, Department of Nuclear Medicine and Molecular Imaging Center, Tao-Yuan (China); Chang Gung University, Department of Medical Imaging and Radiological Sciences and Healthy Aging Research Center, Tao-Yuan (China); Chen, Cheng-Sheng [Kaohsiung Medical University Hospital, Department of Psychiatry, Kaohsiung (China); Wai, Yau-Yau [Chang Gung Memorial Hospital, Department of Radiology, Tao-Yuan (China); Chang, Chee-Jen [Chang Gung University, Graduate Institute of Clinical Medical Science, Tao-Yuan (China); Chang Gung University, Clinical Informatics and Medical Statistics Research Center, Tao-Yuan (China); Chang Gung Memorial Hospital, Biostatistical Center for Clinical Research, Tao-Yuan (China); Tseng, Hsiao-Jung [Chang Gung Memorial Hospital, Biostatistical Center for Clinical Research, Tao-Yuan (China); Yen, Tzue-Chen; Lin, Kun-Ju [Chang Gung University, Department of Medical Imaging and Radiological Sciences and Healthy Aging Research Center, Tao-Yuan (China); Chang Gung Memorial Hospital, Department of Nuclear Medicine and Molecular Imaging Center, Tao-Yuan (China)

    2014-04-15

    The literature suggests that a history of depression is associated with an increased risk of developing Alzheimer's disease (AD). The aim of this study was to examine brain amyloid accumulation in patients with lifetime major depression using {sup 18}F-florbetapir (AV-45/Amyvid) PET imaging in comparison with that in nondepressed subjects. The study groups comprised 25 depressed patients and 11 comparison subjects who did not meet the diagnostic criteria for AD or amnestic mild cognitive impairment. Vascular risk factors, homocysteine and apolipoprotein E (ApoE) genotype were also examined. The standard uptake value ratio (SUVR) of each volume of interest was analysed using whole the cerebellum as the reference region. Patients with a lifetime history of major depression had higher {sup 18}F-florbetapir SUVRs in the precuneus (1.06 ± 0.08 vs. 1.00 ± 0.06, p = 0.045) and parietal region (1.05 ± 0.08 vs. 0.98 ± 0.07, p = 0.038) than the comparison subjects. Voxel-wise analysis revealed a significantly increased SUVR in depressed patients in the frontal, parietal, temporal and occipital areas (p < 0.01). There were no significant associations between global {sup 18}F-florbetapir SUVRs and prior depression episodes, age at onset of depression, or time since onset of first depression. Increased {sup 18}F-florbetapir binding values were found in patients with late-life major depression relative to comparison subjects in specific brain regions, despite no differences in age, sex, education, Mini Mental Status Examination score, vascular risk factor score, homocysteine and ApoE ε4 genotype between the two groups. A longitudinal follow-up study with a large sample size would be worthwhile. (orig.)

  15. Increased brain amyloid deposition in patients with a lifetime history of major depression: evidenced on 18F-florbetapir (AV-45/Amyvid) positron emission tomography

    International Nuclear Information System (INIS)

    The literature suggests that a history of depression is associated with an increased risk of developing Alzheimer's disease (AD). The aim of this study was to examine brain amyloid accumulation in patients with lifetime major depression using 18F-florbetapir (AV-45/Amyvid) PET imaging in comparison with that in nondepressed subjects. The study groups comprised 25 depressed patients and 11 comparison subjects who did not meet the diagnostic criteria for AD or amnestic mild cognitive impairment. Vascular risk factors, homocysteine and apolipoprotein E (ApoE) genotype were also examined. The standard uptake value ratio (SUVR) of each volume of interest was analysed using whole the cerebellum as the reference region. Patients with a lifetime history of major depression had higher 18F-florbetapir SUVRs in the precuneus (1.06 ± 0.08 vs. 1.00 ± 0.06, p = 0.045) and parietal region (1.05 ± 0.08 vs. 0.98 ± 0.07, p = 0.038) than the comparison subjects. Voxel-wise analysis revealed a significantly increased SUVR in depressed patients in the frontal, parietal, temporal and occipital areas (p 18F-florbetapir SUVRs and prior depression episodes, age at onset of depression, or time since onset of first depression. Increased 18F-florbetapir binding values were found in patients with late-life major depression relative to comparison subjects in specific brain regions, despite no differences in age, sex, education, Mini Mental Status Examination score, vascular risk factor score, homocysteine and ApoE ε4 genotype between the two groups. A longitudinal follow-up study with a large sample size would be worthwhile. (orig.)

  16. Digital positron annihilation spectrometer

    International Nuclear Information System (INIS)

    With the high speed development of digital signal process, the technique of the digitization and processing of signals was applied in the domain of a broad class of nuclear technique. The development of digital positron lifetime spectrometer (DPLS) is more promising than the conventional positron lifetime spectrometer equipped with nuclear instrument modules. And digital lifetime spectrometer has many advantages, such as low noise, long term stability, flexible online or offline digital processing, simple setup, low expense, easy to setting, and more physical information. Digital constant fraction discrimination is for timing. And a new method of optimizing energy windows setting for digital positron lifetime spectrometer is also developed employing the simulated annealing for the convenient use. The time resolution is 220ps and the count rate is 200cps. (authors)

  17. Simulations of 〈1 0 0〉 edge and 1/2〈1 1 1〉 screw dislocations in α-iron and tungsten and positron lifetime calculations

    International Nuclear Information System (INIS)

    Dislocations in BCC metals are of crucial importance for understanding behavior of fusion materials. In this study model positron lifetime quantum-mechanical calculations have been carried out in the two-component density functional theory (DFT) in local density approximation (LDA) for perfect iron and tungsten lattices, lattices with 〈1 0 0〉 edge and 1/2〈1 1 1〉 screw dislocations and several cases in which dislocations interact with a vacancy, bi-vacancy and vacancies containing hydrogen or helium atoms. The core structures of the dislocations have been obtained by MD-simulations using Mendelev and Ackland potentials for iron and Finnis–Sinclair potential for tungsten. The calculated values for iron are 153 ps for edge dislocation and 124 ps for screw dislocation, while for tungsten are 161 and 130 ps, respectively. We report new results for screw dislocation showing that minor dilation of the lattice volume associated with second-order elasticity theory influences the calculated positron lifetime

  18. Simulations of 〈1 0 0〉 edge and 1/2〈1 1 1〉 screw dislocations in α-iron and tungsten and positron lifetime calculations

    Energy Technology Data Exchange (ETDEWEB)

    Staikov, P., E-mail: staikovpavel@gmail.com [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko chaussee blvd, 1784 Sofia (Bulgaria); Djourelov, N. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko chaussee blvd, 1784 Sofia (Bulgaria)

    2013-03-15

    Dislocations in BCC metals are of crucial importance for understanding behavior of fusion materials. In this study model positron lifetime quantum-mechanical calculations have been carried out in the two-component density functional theory (DFT) in local density approximation (LDA) for perfect iron and tungsten lattices, lattices with 〈1 0 0〉 edge and 1/2〈1 1 1〉 screw dislocations and several cases in which dislocations interact with a vacancy, bi-vacancy and vacancies containing hydrogen or helium atoms. The core structures of the dislocations have been obtained by MD-simulations using Mendelev and Ackland potentials for iron and Finnis–Sinclair potential for tungsten. The calculated values for iron are 153 ps for edge dislocation and 124 ps for screw dislocation, while for tungsten are 161 and 130 ps, respectively. We report new results for screw dislocation showing that minor dilation of the lattice volume associated with second-order elasticity theory influences the calculated positron lifetime.

  19. Can the lifetime of the superheater tubes be predicted according to the fuel analyses? Assessment from field and laboratory data

    Energy Technology Data Exchange (ETDEWEB)

    Salmenoja, K. [Kvaerner Pulping Oy, Tampere (Finland)

    1998-12-31

    Lifetime of the superheaters in different power boilers is more or less still a mystery. This is especially true in firing biomass based fuels (biofuels), such as bark, forest residues, and straw. Due to the unhomogeneous nature of the biofuels, the lifetime of the superheaters may vary from case to case. Sometimes the lifetime is significantly shorter than originally expected, sometimes no corrosion even in the hottest tubes is observed. This is one of the main reasons why the boiler operators often demand for a better predictability on the corrosion resistance of the materials to avoid unscheduled shutdowns. (orig.) 9 refs.

  20. Study of plasma sprayed copper alloy using positron annihilation

    International Nuclear Information System (INIS)

    A positron annihilation technique has been employed to study the microdefects of copper alloy sprayed on a steel substrate by plasma after being compressed in different thickness. The positron lifetime in the alloy is varied with different amount of compression. It is found that the positron lifetime decreases with increasing of the compression deformation. On the contrary, the positron lifetime is increased for normal alloy after deformation

  1. Toward a European Network of Positron Laboratories

    Directory of Open Access Journals (Sweden)

    Karwasz Grzegorz P.

    2015-12-01

    Full Text Available Some applications of controlled-energy positron beams in material studies are discussed. In porous organic polysilicates, measurements of 3γ annihilation by Doppler broadening (DB method at the Trento University allowed to trace pore closing and filling by water vapor. In silicon coimplanted by He+ and H+, DB data combined with positron lifetime measurements at the München pulsed positron beam allowed to explain Si blistering. Presently measured samples of W for applications in thermonuclear reactors, irradiated by W+ and electrons, show vast changes of positron lifetimes, indicating complex dynamics of defects.

  2. Positron emission tomography study of pindolol occupancy of 5-HT1A receptors in humans: preliminary analyses

    International Nuclear Information System (INIS)

    Preclinical studies in rodents suggest that augmentation of serotonin reuptake inhibitors (SSRIs) therapy by the 5-hydroxytryptamine1A (5-HT1A) receptor agent pindolol might reduce the delay between initiation of treatment and antidepressant response. This hypothesis is based on the ability of pindolol to potentiate the increase in serotonin (5-HT) transmission induced by SSRIs, an effect achieved by blockade of the 5-HT1A autoreceptors in the dorsal raphe nuclei (DRN). However, placebo-controlled clinical studies of pindolol augmentation of antidepressant therapy have reported inconsistent results. Here, we evaluated the occupancy of 5-HT1A receptors following treatment with controlled release pindolol in nine healthy volunteers with positron-emission tomography (PET). Each subject was studied four times: at baseline (scan 1), following 1 week of oral administration of pindolol CR (7.5 mg/day) at peak level, 4 h after the dose (scan 2), and at 10 h following the dose (scan 3), and following one dose of pindolol CR (30 mg) (at peak level, 4 h) (scan 4). Pindolol occupancy of 5-HT1A receptors was evaluated in the DRN and cortical regions as the decrease in binding potential (BP) of the radiolabelled selective 5-HT1A antagonist [carbonyl-11C]WAY-100635 or [carbonyl-11C] N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide abbreviated as [11C]WAY-100635. Pindolol dose-dependently decreased [11C]WAY-100635 BP. Combining all the regions, occupancy was 20 ± 8% at scan 2, 14 ± 8% at scan 3, and 44 ± 8% at scan 4. The results of this study suggest that at doses used in clinical studies of augmentation of the SSRI effect by pindolol (2.5 mg t.i.d.), the occupancy of 5-HT1A receptors is moderate and highly variable between subjects. This factor might explain the variable results obtained in clinical studies. On the other hand, at each dose tested, pindolol occupancy of 5-HT1A receptors was higher in the DRN compared to cortical regions

  3. Positron emission tomography study of pindolol occupancy of 5-HT{sub 1A} receptors in humans: preliminary analyses

    Energy Technology Data Exchange (ETDEWEB)

    Martinez, Diana; Mawlawi, Osama; Hwang, Dah-Ren; Kent, Justine; Simpson, Norman; Parsey, Ramin V.; Hashimoto, Tomoki; Slifstein, Mark; Huang Yiyun; Heertum, Ronald van; Abi-Dargham, Anissa; Caltabiano, Stephen; Malizia, Andrea; Cowley, Hugh; Mann, J. John; Laruelle, Marc

    2000-07-01

    Preclinical studies in rodents suggest that augmentation of serotonin reuptake inhibitors (SSRIs) therapy by the 5-hydroxytryptamine{sub 1A} (5-HT{sub 1A}) receptor agent pindolol might reduce the delay between initiation of treatment and antidepressant response. This hypothesis is based on the ability of pindolol to potentiate the increase in serotonin (5-HT) transmission induced by SSRIs, an effect achieved by blockade of the 5-HT{sub 1A} autoreceptors in the dorsal raphe nuclei (DRN). However, placebo-controlled clinical studies of pindolol augmentation of antidepressant therapy have reported inconsistent results. Here, we evaluated the occupancy of 5-HT{sub 1A} receptors following treatment with controlled release pindolol in nine healthy volunteers with positron-emission tomography (PET). Each subject was studied four times: at baseline (scan 1), following 1 week of oral administration of pindolol CR (7.5 mg/day) at peak level, 4 h after the dose (scan 2), and at 10 h following the dose (scan 3), and following one dose of pindolol CR (30 mg) (at peak level, 4 h) (scan 4). Pindolol occupancy of 5-HT{sub 1A} receptors was evaluated in the DRN and cortical regions as the decrease in binding potential (BP) of the radiolabelled selective 5-HT{sub 1A} antagonist [carbonyl-{sup 11}C]WAY-100635 or [carbonyl-{sup 11}C] N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide abbreviated as [{sup 11}C]WAY-100635. Pindolol dose-dependently decreased [{sup 11}C]WAY-100635 BP. Combining all the regions, occupancy was 20 {+-} 8% at scan 2, 14 {+-} 8% at scan 3, and 44 {+-} 8% at scan 4. The results of this study suggest that at doses used in clinical studies of augmentation of the SSRI effect by pindolol (2.5 mg t.i.d.), the occupancy of 5-HT{sub 1A} receptors is moderate and highly variable between subjects. This factor might explain the variable results obtained in clinical studies. On the other hand, at each dose tested, pindolol occupancy of 5

  4. Modeling momentum distributions of positron annihilation radiation in solids

    OpenAIRE

    Makkonen, Ilja

    2007-01-01

    Positron annihilation spectroscopy is a materials characterization method especially applicable for studying vacancy defects in solids. In typical crystal lattices positrons get trapped at vacancy-type defects. By measuring positron lifetimes and momentum distributions of positron annihilation radiation one obtains information about the open volumes and the chemical environments of the defects. Computational tools can be used in the analysis of positron annihilation experiments. Calculate...

  5. Positron annihilation studies of organic superconductivity

    International Nuclear Information System (INIS)

    The positron lifetimes of two organic superconductors, κ-(ET)2Cu(NCS)2 and κ-(ET)2Cu[N(CN)2]Br, are measured as a function of temperature across Tc. A drop of positron lifetime below Tc is observed. Positron-electron momentum densities are measured by using 2D-ACAR to search for the Fermi surface in κ-(ET)2Cu[N(CN)2]Br. Positron density distributions and positron-electron overlaps are calculated by using the orthogonalized linear combination atomic orbital (OLCAO) method to interprete the temperature dependence due to the local charge transfer which is inferred to relate to the superconducting transition. 2D-ACAR results in κ-(ET)2Cu[N(CN)2]Br are compared with theoretical band calculations based on a first-principles local density approximation. Importance of performing accurate band calculations for the interpretation of positron annihilation data is emphasized

  6. Nanometer cavities studied by positron annihilation

    International Nuclear Information System (INIS)

    Positronium (Ps) is trapped in cavities in insulating solids, and the lifetime of ortho Ps is determined by the size of the cavity. The information on the properties of the cavities obtained by use of the standard slow positron beam and the 'normal' positron annihilation techniques is compared for several selected cases. (author)

  7. Gas Permeations Studied by Positron Annihilation

    Science.gov (United States)

    Yuan, Jen-Pwu; Cao, Huimin; Jean, X.; Yang, Y. C.

    1997-03-01

    The hole volumes and fractions of PC and PET polymers are measured by positron annihilation lifetime spectroscopy. Direct correlations between the measured hole properties and gas permeabilities are observed. Applications of positron annihilation spectroscopy to study gas transport and separation of polymeric materials will be discussed.

  8. Positron annihilation studies of mesoporous silica films using a slow positron beam

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectra were measured for mesoporous silica films, which were synthesized using triblock copolymer (EO106PO70EO106) as a structure-directing agent. Different positron lifetime spectra for the deposited and calcined films indicated the formation of meso-structure after calcination, which was confirmed by Fourier transform infrared (FTIR) spectra and field emission-scanning electron microscopy (FE-SEM) observation. Open porosity or pore interconnectivity of a silica film might be evaluated by a two-dimensional positron annihilation lifetime spectrum of an uncapped film. Pore sizes and their distributions in the silica films were found to be affected by thermal treatments

  9. Positron sources

    International Nuclear Information System (INIS)

    A tentative survey of positron sources is given. Physical processes on which positron generation is based are indicated and analyzed. Explanation of the general features of electromagnetic interactions and nuclear β+ decay makes it possible to predict the yield and emittance for a given optical matching system between the positron source and the accelerator. Some kinds of matching systems commonly used - mainly working with solenoidal fields - are studied and the acceptance volume calculated. Such knowledge is helpful in comparing different matching systems. Since for large machines, a significant distance exists between the positron source and the experimental facility, positron emittance has to be preserved during beam transfer over large distances and methods used for that purpose are indicated. Comparison of existing positron sources leads to extrapolation to sources for future linear colliders

  10. Positron sources

    International Nuclear Information System (INIS)

    A tentative survey of positron sources is given. Physical processes on which positron generation is based are indicated and analyzed. Explanation of the general features of electromagnetic interactions and nuclear β+ decay makes it possible to predict the yield and emittance for a given optical matching system between the positron source and the accelerator. Some kinds of matching systems commonly used - mainly working with solenoidal field - are studied and the acceptance volume calculated. Such knowledge is helpful in comparing different matching systems. Since for large machines, a significant distance exists between the positron source and the experimental facility, positron emittance has to be preserved during beam transfer over large distances and methods used for that purpose are indicated. Comparison of existing positron sources leads to extrapolation to sources for future linear colliders. Some new ideas associated with these sources are also presented. (orig.)

  11. A Study On Positron - Electron Annihilation In Multi-Wall Carbon Nabitan

    International Nuclear Information System (INIS)

    Positron annihilation in multi-wall carbon nanotube is studied using positron lifetime measurements and positron diffusion theory in nano material. Experimental measurements of positron lifetime were performed on multi-wall carbon nanotube samples having various average radiuses. A closed correlation between positron lifetime on tube surface and tube radius was found, which indicates that positron lifetime measurement could become a useful means for investigating average diameter of multi-wall carbon nanotubes. Furthermore, in this work the positron diffusion theory in nano material modifying from positron diffusion model in nanofilament was used for studying effects of rate of positron runaway k from a nanotube to positron annihilation characteristics. Result shows a strong influence of nanotube radius to the rate of positron runaway and positron lifetime. Beside, value of shape coefficient α for positron diffusion in multi-wall carbon nanotubes also was calculated from experimental data. A quite good agreement between experimental and calculated values of positron annihilation probability on tube surface was result of using average shape coefficient α. Results of study demonstrate that modified positron diffusion model in nanofilament can well apply for researching positron annihilation in multi-wall carbon nanotubes. (author)

  12. Direct evidence for positron annihilation from shallow traps

    DEFF Research Database (Denmark)

    Linderoth, Søren; Hidalgo, C.

    1987-01-01

    For deformed Ag the temperature dependence of the positron lifetime parameters is followed between 12 and 300 K. Clear direct evidence for positron trapping and annihilation at shallow traps, with a positron binding energy of 9±2 meV and annihilation characteristics very similar to those in the...

  13. Positron annihilation in Ni3Al: theory and experiment

    International Nuclear Information System (INIS)

    The results of positron lifetime and binding energy calculations for relaxed vacancy-type defects as well as for grain boundaries in Ni3Al are presented. For this purpose, the so-called atomic superposition method and linear-muffin-tin-orbital techniques are employed. The atomic configurations of defects considered are obtained using molecular dynamics based on an N-body empirical potential. The effect of atomic relaxations around defects on positron characteristics is discussed. Finally, positron lifetime experiments on an electron-irradiated polycrystalline Ni76Al24 sample are performed. The positron lifetimes extracted from these measurements are compared with theoretical calculations. (orig.)

  14. Generation and application of slow positrons based on a electron LINAC

    International Nuclear Information System (INIS)

    History of slow positron in Institute of Materials Structure Science High Energy Accelerator Research Organization is explained. The principle of generation and application of intense positron beam is mentioned. Two sources of intense positron are radioactive decay of radioactive isotopes emitting positron and electron-positron pair creation. The radioactive decay method uses 58Co, 64Cu, 11C, 13N, 15O and 18F. The electron-positron pair creation method uses nuclear reactor or electron linear accelerator (LINAC). The positron experimental facility in this organization consists of electron LINAC, slow positron beam source, positron transport and experimental station. The outline of this facility is started. The intense slow positron beam is applied to research positronium work function, electron structure of surface. New method such as combination of positron lifetime measurement and slow positron beam or Auger electron spectroscopy by positron annihilation excitation and positron reemission microscope are developed. (S.Y.)

  15. Tomography by positrons emission

    International Nuclear Information System (INIS)

    The tomography by positrons emission is a technology that allows to measure the concentration of positrons emission in a tri dimensional body through external measurements. Among the isotope emissions have carbon isotopes are (11C), of the oxygen (15O), of the nitrogen (13N) that are three the element that constitute the base of the organic chemistry. Theses have on of the PET's most important advantages, since many biological interesting organic molecules can be tracer with these isotopes for the metabolism studies 'in vivo' through PET, without using organic tracers that modify the metabolism. The mentioned isotopes, also possess the characteristic of having short lifetime, that constitute on of PET's advantages from the dosimetric point of view. Among 11C, 15O, and 13N, other isotopes that can be obtained of a generator as the 68Ga and 82Rb

  16. Comparison of meta-analyses among elastosonography (ES) and positron emission tomography/computed tomography (PET/CT) imaging techniques in the application of prostate cancer diagnosis.

    Science.gov (United States)

    Ouyang, Qiaohong; Duan, Zhongxiang; Lei, Jixiao; Jiao, Guangli

    2016-03-01

    The early diagnosis of prostate cancer (PCa) appears to be of vital significance for the provision of appropriate treatment programs. Even though several sophisticated imaging techniques such as positron emission tomography/computed tomography (PET/CT) and elastosonography (ES) have already been developed for PCa diagnosis, the diagnostic accuracy of these imaging techniques is still controversial to some extent. Therefore, a comprehensive meta-analysis in this study was performed to compare the accuracy of various diagnostic imaging methods for PCa, including 11C-choline PET/CT, 11C-acetate PET/CT, 18F-fluorocholine PET/CT, 18F-fluoroglucose PET/CT, transrectal real-time elastosonography (TRTE), and shear-wave elastosonography (SWE). The eligible studies were identified through systematical searching for the literature in electronic databases including PubMed, Cochrane, and Web of Science. On the basis of the fixed-effects model, the pooled sensitivity (SEN), specificity (SPE), and area under the receiver operating characteristics curve (AUC) were calculated to estimate the diagnostic accuracy of 11C-choline PET/CT, 11C-acetate PET/CT, 18F-fluorocholine (FCH) PET/CT, 18F-fluoroglucose (FDG) PET/CT, TRTE, and SWE. All the statistical analyses were conducted with R language Software. The present meta-analysis incorporating a total of 82 studies demonstrated that the pooled sensitivity of the six imaging techniques were sorted as follows: SWE > 18F-FCH PET/CT > 11C-choline PET/CT > TRTE > 11C-acetate PET/CT > 18F-FDG PET/CT; the pooled specificity were also compared: SWE > 18F-FCH PET/CT > 11C-choline PET/CT > TRTE > 18F-FDG PET/CT > 11C-acetate PET/CT; finally, the pooled diagnostic accuracy of the six imaging techniques based on AUC were ranked as below: SWE > 18F-FCH PET/CT > 11C-choline PET/CT > TRTE > 11C-acetate PET/CT > 18F-FDG PET/CT. SWE and 18F-FCH PET/CT imaging could offer more assistance in the

  17. Applications of slow positrons to cancer research: Search for selectivity of positron annihilation to skin cancer

    Energy Technology Data Exchange (ETDEWEB)

    Jean, Y.C. [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States)]. E-mail: jeany@umkc.edu; Li Ying [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States); Liu Gaung [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States); Chen, Hongmin [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States); Zhang Junjie [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States); Gadzia, Joseph E. [Dermatology, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, KS 66103 (United States); Kansas Medical Clinic, Topeka, KS 66614 (United States)

    2006-02-28

    Slow positrons and positron annihilation spectroscopy (PAS) have been applied to medical research in searching for positron annihilation selectivity to cancer cells. We report the results of positron lifetime and Doppler broadening energy spectroscopies in human skin samples with and without cancer as a function of positron incident energy (up to 8 {mu}m depth) and found that the positronium annihilates at a significantly lower rate and forms at a lower probability in the samples having either basal cell carcinoma (BCC) or squamous cell carcinoma (SCC) than in the normal skin. The significant selectivity of positron annihilation to skin cancer may open a new research area of developing positron annihilation spectroscopy as a novel medical tool to detect cancer formation externally and non-invasively at the early stages.

  18. Probing atomic-size defects and free volumes with positron and positronium

    International Nuclear Information System (INIS)

    The lifetime measurement of positrons injected in a metal allows to investigate defects of atomic dimension. Many crucial problems in metallurgy have found their solutions by the positron annihilation (PA) techniques for about three decades. Application to semiconductors research has been developed in recent years. Specific theory and analysing method can be used in the studies of the free-volume hole in polymers, the size of the empty spaces being between 0.3 and 1.5 nanometers. In many insulating materials, the diffusing positron can trap an electron and form a metastable positronium (Ps). Like a gas bubble, the Ps atom may diffuse and get trapped by the free-volume hole. When this mechanism is governing, lifetimes over the range of 1-10 ns are well observable and a correspondence exists between the positronium lifetime and minimum diameter of the trapping open space. Example of application is given in a study of polyimide membranes used for gas separation. A good correlation is revealed between the Ps lifetime and H2 and/or CH4 permeabilities. Recent progress in polymers research is also reviewed

  19. Positronium lifetime in porous VP-DVB copolymer

    Energy Technology Data Exchange (ETDEWEB)

    Zaleski, Radoslaw [Institute of Physics, Maria Curie-Sklodowska University, Lublin (Poland); Goworek, Jacek; Maciejewska, Malgorzata [Faculty of Chemistry, Maria Curie-Sklodowska University, Lublin (Poland)

    2009-11-15

    Porous 1-vinyl-2-pyrrolidone-divinylbenzene copolymer was studied using Positron Annihilation Lifetime Spectroscopy. A set of spectra measured at various temperatures was analysed using two methods: model parameters fitting and quantified maximum entropy. Similarity of the results obtained by entirely different methods ensure that distortion of the results arisen from inappropriate data processing was minimized. Temperature dependence of the experimental ortho-positronium lifetimes was compared to predictions of the Extended Tao-Eldrup model. Very good agreement in whole temperature range was found for empirical parameter {delta}=0.15 nm. Basing on PALS data and the Extended Tao-Eldrup model the distribution of free volume sizes was derived. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. KENO lifetimes

    International Nuclear Information System (INIS)

    When performing k-eigenvalue solutions with KENO-V.a, two different prompt neutron lifetimes are estimated - a system lifetime and a neutron generation time. The meaning of these two lifetimes has been ascertained by comparing values of various neutron lifespans/lifetimes predicted by MCNP and DANTSYS based on the neutron-balance theory. The system lifetime in KENO-Va corresponds to the unweighted removal lifetime calculated by both MCNP and DANTSYS. The unweighted removal lifetime is the average time between removal events resulting from a neutron absorption or a neutron leakage. The generation time in KENO-V.a corresponds to the fission lifespan calculated by MCNP, where the fission lifespan in MCNP represents the average time for a newly born neutron to cause another fission. As such, the generation time in KENO-Va does not represent the generation time that appears in the point kinetic model. The generation time in the point kinetic model is the adjoint-weighted removal lifetime divided by keff, which is identically equal to the adjoint-weighted neutron production rate. In small bare systems operating in the vicinity of delayed critical, the difference between the adjoint-weighted neutron generation time and the fission lifespan can be as small as a few percent. However, in reflected systems, the difference between these two quantities can be several orders of magnitude. In conclusion, the prompt neutron generation time predicted by KENO-Va corresponds to the fission lifespan of a prompt neutron in a given system. The fission lifespan is the average time from birth-to-fission and, in general, is not a good approximation for the adjoint-weighted neutron generation time that appears in the point-kinetic model

  1. Fluorine-18-labeled boronophenylalanine positron emission tomography for oral cancers: Qualitative and quantitative analyses of malignant tumors and normal structures in oral and maxillofacial regions

    OpenAIRE

    Ariyoshi, Yasunori; Shimahara, Masashi; Kimura,Yoshihiro; Ito, Yuichi; SHIMAHARA, TAKESHI; MIYATAKE, SHIN-ICHI; Kawabata, Shinji

    2011-01-01

    The present study aimed to demonstrate the features of fluorine-18-labeled boronophenylalanine positron emission tomography (18F-BPA-PET) to reveal oral cancer, as well as normal structures in the oral and maxillofacial regions. We analyzed 18F-BPA-PET findings from 8 patients with histologically confirmed recurrent and/or advanced oral cancer scheduled for boron neutron capture therapy. The capacity of 18F-BPA-PET to delineate tumor and normal structures was assessed qualitatively and quanti...

  2. Positron and positronium annihilation in silica-based thin films studied by a pulsed positron beam

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, R. E-mail: r-suzuki@aist.go.jp; Ohdaira, T.; Kobayashi, Y.; Ito, K.; Shioya, Y.; Ishimaru, T

    2003-11-01

    Positron and positronium annihilation in silica-based thin films has been investigated by means of measurement techniques with a monoenergetic pulsed positron beam. The age-momentum correlation study revealed that positron annihilation in thermally grown SiO{sub 2} is basically the same as that in bulk amorphous SiO{sub 2} while o-Ps in the PECVD grown SiCOH film predominantly annihilate with electrons of C and H at the microvoid surfaces. We also discuss time-dependent three-gamma annihilation in porous low-k films by two-dimensional positron annihilation lifetime spectroscopy.

  3. The Galactic 511 keV line: analysis and interpretation of Integral observations; L'annihilation des positrons galactiques: analyse et interpretation des donnees INTEGRAL

    Energy Technology Data Exchange (ETDEWEB)

    Lonjou, V

    2005-09-15

    Ever since the discovery of the 511 keV annihilation line emission from the galactic center region in the late seventies, the origin of galactic positrons has been the topic of a vivid scientific debate. It is also one of the prime scientific objectives of the imaging spectrometer SPI on board ESA's INTEGRAL observatory. In this thesis first a description of the most important SPI sub-system is given - the detector plane. Procedures for detector energy calibration and detector degradation analysis are developed. The determination of instrumental background models, a crucial aspect of data analysis, is elaborated. These background models are then applied to deriving sky maps and spectra of unprecedented quality of the Galactic positron annihilation radiation. The emission is centered on the galactic center with a spatial resolution of 8 degrees (FWHM), a second spatial component appears clearly: the galactic disc. The ray energy has been measured with unprecedented accuracy: 511.0 {+-} 0.03 keV for a full width at half maximum (FWHM) of 2.07 {+-} 0.1 keV. The total galactic flux ranges from 1.09 to 2.43 10{sup -3} ph.cm{sup -2}.s{sup -1} including uncertainties on spatial distribution. Finally, the implications of these observations for the production of positrons by various Galactic populations are discussed.

  4. Positron-trapping mechanism at dislocations in Zn

    DEFF Research Database (Denmark)

    Hidalgo, Carlos; Linderoth, Søren; Diego, Nieves de

    1987-01-01

    The evolution of the positron-lifetime parameters with the measuring temperature has been studied in deformed Zn in the temperature range 12–210 K. For two samples with different degrees of deformation the presence of a component with a lifetime close to that in a monovacancy is observed. Both the...... temperature dependence of the positron-lifetime spectra below 120 K is attributed to the temperature dependence of the trapping rate to the dislocation line. The experimental results have demonstrated that detrapping processes from the dislocation line take place above 120 K. The positron binding energy to...

  5. Confronting recent AMS-02 positron fraction and Fermi-LAT extragalactic γ-ray background measurements with gravitino dark matter

    Science.gov (United States)

    Carquín, Edson; Díaz, Marco A.; Gómez-Vargas, Germán A.; Panes, Boris; Viaux, Nicolás

    2016-03-01

    Recent positron flux fraction measurements in cosmic-rays (CR) made by the AMS-02 detector confirm and extend the evidence on the existence of a new (yet unknown) source of high energy electrons and positrons. We test the gravitino dark matter of bilinear R-parity violating supersymmetric models as this electrons/positrons source. Being a long lived weak-interacting and spin 3/2 particle, it offers several particularities which makes it an attractive dark matter candidate. We compute the electron, positron and γ-ray fluxes produced by each gravitino decay channel as it would be detected at the Earth's position. Combining the flux from the different decay modes we are able to reproduce AMS-02 measurements of the positron fraction, as well as the electron and positron fluxes, with a gravitino dark matter mass in the range 1-3 TeV and lifetime of ˜1.0-0.7×1026 s. The high statistics measurement of electron and positron fluxes, and the flattening in the behaviour of the positron fraction recently found by AMS-02 allow us to determine that the preferred gravitino decaying mode by the fit is W±τ∓, unlike previous analyses. Then we study the viability of these scenarios through their implication in γ-ray observations. For this we use the Extragalactic γ-ray Background recently reported by the Fermi-LAT Collaboration and a state-of-the-art model of its known contributors. Based on the γ-ray analysis we exclude the gravitino parameter space which provides an acceptable explanation of the AMS-02 data. Therefore, we conclude that the gravitino of bilinear R-parity violating models is ruled out as the unique primary source of electrons and positrons needed to explain the rise in the positron fraction.

  6. Double-positron decay, positron-emitting K capture, and double K capture

    International Nuclear Information System (INIS)

    We have calculated the lifetimes of the two-neutrino and neutrinoless double-positron decay, K-capture, and KK-capture processes for several nuclei. It is found that the two-neutrino KK-capture process is a dominant channel with a lifetime of 1023--1024 yr, whereas the neutrinoless processes have lifetimes greater than 1027yr if the currently accepted upper limits on the lepton-number-violation parameters are used

  7. High resolution time positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    The ORTEC conventional positron lifetime spectrometer (PLS) with 12.9 cm3 plastic scintillation detector (BC-148), mounted with photo-multiplier (8850PMT), CFD discriminator (583) has been installed at the laboratory of physics of Center for Nuclear Techniques (Vietnam Atomic Energy Commission). The technical features of this system were investigated. The results show that the resolution time is better than 195 ps, and peak to background ratio in the spectrum measured with 10 μCi Na-22 is greater than 4000 of this conventional positron lifetime spectroscopy. The results of research using this spectrometer to study the porosity of materials are presented. The positronium formation in the medium of meso- and macro-pores, the correlation of macro pore size, porosity and positron lifetime characteristics will be discussed. The application of the PLS for the purpose of research and training are also proposed. (author)

  8. Generation of a high-brightness pulsed positron beam for the Munich scanning positron microscope

    Energy Technology Data Exchange (ETDEWEB)

    Piochacz, Christian

    2009-11-20

    Within the present work the prerequisites for the operation of the Munich scanning positron microscope (SPM) at the high intense neutron induced positron source Munich (NEPOMUC) were established. This was accomplished in two steps: Firstly, a re-moderation device was installed at the positron beam facility NEPOMUC, which enhances the brightness of the positron beam for all connected experiments. The second step was the design, set up and initial operation of the SPM interface for the high efficient conversion of the continuous beam into a bunched beam. The in-pile positron source NEPOMUC creates a positron beam with a diameter of typically 7 mm, a kinetic energy of 1 keV and an energy spread of 50 eV. The NEPOMUC re-moderator generates from this beam a low energy positron beam (20 - 200 eV) with a diameter of less than 2 mm and an energy spread well below 2.5 eV. This was achieved with an excellent total efficiency of 6.55{+-}0.25 %. The re-moderator was not only the rst step to implement the SPM at NEPOMUc, it enables also the operation of the pulsed low energy positron beam system (PLEPS). Within the present work, at this spectrometer rst positron lifetime measurements were performed, which revealed the defect types of an ion irradiated uranium molybdenum alloy. Moreover, the instruments which were already connected to the positron beam facility bene ts considerably of the high brightness enhancement. In the new SPM interface an additional re-moderation stage enhances the brightness of the beam even more and will enable positron lifetime measurements at the SPM with a lateral resolution below 1 {mu}m. The efficiency of the re-moderation process in this second stage was 24.5{+-}4.5 %. In order to convert high efficiently the continuous positron beam into a pulsed beam with a repetition rate of 50 MHz and a pulse duration of less than 50 ps, a sub-harmonic pre-bucher was combined with two sine wave bunchers. Furthermore, the additional re-moderation stage of the

  9. Generation of a high-brightness pulsed positron beam for the Munich scanning positron microscope

    International Nuclear Information System (INIS)

    Within the present work the prerequisites for the operation of the Munich scanning positron microscope (SPM) at the high intense neutron induced positron source Munich (NEPOMUC) were established. This was accomplished in two steps: Firstly, a re-moderation device was installed at the positron beam facility NEPOMUC, which enhances the brightness of the positron beam for all connected experiments. The second step was the design, set up and initial operation of the SPM interface for the high efficient conversion of the continuous beam into a bunched beam. The in-pile positron source NEPOMUC creates a positron beam with a diameter of typically 7 mm, a kinetic energy of 1 keV and an energy spread of 50 eV. The NEPOMUC re-moderator generates from this beam a low energy positron beam (20 - 200 eV) with a diameter of less than 2 mm and an energy spread well below 2.5 eV. This was achieved with an excellent total efficiency of 6.55±0.25 %. The re-moderator was not only the rst step to implement the SPM at NEPOMUc, it enables also the operation of the pulsed low energy positron beam system (PLEPS). Within the present work, at this spectrometer rst positron lifetime measurements were performed, which revealed the defect types of an ion irradiated uranium molybdenum alloy. Moreover, the instruments which were already connected to the positron beam facility bene ts considerably of the high brightness enhancement. In the new SPM interface an additional re-moderation stage enhances the brightness of the beam even more and will enable positron lifetime measurements at the SPM with a lateral resolution below 1 μm. The efficiency of the re-moderation process in this second stage was 24.5±4.5 %. In order to convert high efficiently the continuous positron beam into a pulsed beam with a repetition rate of 50 MHz and a pulse duration of less than 50 ps, a sub-harmonic pre-bucher was combined with two sine wave bunchers. Furthermore, the additional re-moderation stage of the SPM

  10. Positron annihilation in AgBr microcrystals

    International Nuclear Information System (INIS)

    Positron decay rates have been measured in pure silver bromide microcrystals subjected to various surface treatments before and after exposure. Two distinct decay rates are observed in most samples. The results show no difference between the positron decay spectra in microcrystals exposed to uv light relative to unexposed samples, indicating that the chemical transitions induced on the surfaces of silver halide grains by the photographic process are in too low concentration to be detectable by the positron-lifetime technique. (4 figures, 2 tables, 12 references)

  11. Consequences of changed nuclear power plant lifetimes in Germany. Scenario analyses until 2035; Auswirkungen veraenderter Laufzeiten fuer Kernkraftwerke in Deutschland. Szenarioanalysen bis zum Jahre 2035

    Energy Technology Data Exchange (ETDEWEB)

    Blesl, Markus; Bruchof, David; Fahl, Ulrich; Kober, Tom; Kuder, Ralf; Beestermoeller, Robert; Goetz, Birgit; Voss, Alfred

    2011-06-01

    The report is aimed to discuss the implications of changed NPP lifetimes in Germany on energy policy, environment, energy cost and macroeconomics. An extensive scenario analysis is used considering the effects on the German energy system in the frame of the European context. It is shown that a nuclear phase-out until 2017 is technically feasible, but needs adequate replacement options that will change the German energy system in the medium term. The study shows that the time of nuclear phase-out has no significant influence on the use of renewable energies.

  12. Positron annihilation

    International Nuclear Information System (INIS)

    The main work in the annihilation of positrons at Harwell (UK) has been the application of the technique of technological problems to do with the effects of radiation damage and mechanical phenomena, such as fatigue and creep, on the properties of materials. Three experimental techniques for studying positron annihilation in solids are documented in this article. Nuclear pulse counting methods are being used, also angular correlation and the Doppler method. The irradiation of metals and alloys with fast neutrons at high temperatures in a reactor can cause voids to develop in the material. Defects are also produced by the plastic deformation of metals and alloys. It opens up the possibility of using positron annihilation as a practical non-destructive tool to assess mechanical damage in materials. Harwell has also been able to make measurements on the inside surface of a hole in a metal sample and on variously-shaped notched and cracked test pieces, which means that it is possible to apply the technique to engineering components

  13. Competitive positron and positronium trapping in porous media

    International Nuclear Information System (INIS)

    Positron annihilation acquired acceptance for structural investigation of solids but results in porous media-where positron lifetime spectroscopy (LT) reveals substantial Ps formation-were ambiguous. Data on zeolites lead to the conclusion that Ps trapping in competing 'extended free volume' sites, inhomogeneous regions and grain boundaries occurs. Furthermore, positron trapping must also be considered. Systematic errors due to incomplete time range selection are discussed, significance and importance of corrections for 3γ/2γ counting efficiency differences are shown in practice

  14. Precipitation Study in Inconel 625 Alloy by Positron Annihilation Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    M.Ahmad; W. Ahmad; M.A.Shaikh; Mahmud Ahmad; M.U. Rajput

    2003-01-01

    Precipitation in Inconel 625 alloy has been studied by positron annihilation spectroscopy and electron microscopy. The observeddependence of annihilation characteristics on aging time is attributed to the change of the positron state due to the increaseand decrease of the density and size of the γ″ precipitates. Hardness measurements and lifetime measurements are in goodagreement.

  15. Characterization of point defects in CdTe by positron annihilation spectroscopy

    Science.gov (United States)

    Elsharkawy, M. R. M.; Kanda, G. S.; Abdel-Hady, E. E.; Keeble, D. J.

    2016-06-01

    Positron lifetime measurements on CdTe 0.15% Zn-doped by weight are presented, trapping to monovacancy defects is observed. At low temperatures, localization at shallow binding energy positron traps dominates. To aid defect identification density functional theory, calculated positron lifetimes and momentum distributions are obtained using relaxed geometry configurations of the monovacancy defects and the Te antisite. These calculations provide evidence that combined positron lifetime and coincidence Doppler spectroscopy measurements have the capability to identify neutral or negative charge states of the monovacancies, the Te antisite, A-centers, and divacancy defects in CdTe.

  16. Positronics of subnanometer atomistic imperfections in solids as a high-informative structure characterization tool.

    Science.gov (United States)

    Shpotyuk, Oleh; Filipecki, Jacek; Ingram, Adam; Golovchak, Roman; Vakiv, Mykola; Klym, Halyna; Balitska, Valentyna; Shpotyuk, Mykhaylo; Kozdras, Andrzej

    2015-01-01

    Methodological possibilities of positron annihilation lifetime (PAL) spectroscopy applied to characterize different types of nanomaterials treated within three-term fitting procedure are critically reconsidered. In contrast to conventional three-term analysis based on admixed positron- and positronium-trapping modes, the process of nanostructurization is considered as substitutional positron-positronium trapping within the same host matrix. Developed formalism allows estimate interfacial void volumes responsible for positron trapping and characteristic bulk positron lifetimes in nanoparticle-affected inhomogeneous media. This algorithm was well justified at the example of thermally induced nanostructurization occurring in 80GeSe2-20Ga2Se3 glass. PMID:25852373

  17. PREFACE: The International Workshop on Positron Studies of Defects 2014

    Science.gov (United States)

    Sugita, Kazuki; Shirai, Yasuharu

    2016-01-01

    The International Workshop on Positron Studies of Defects 2014 (PSD-14) was held in Kyoto, Japan from 14-19 September, 2014. The PSD Workshop brought together positron scientists interested in studying defects to an international platform for presenting and discussing recent results and achievements, including new experimental and theoretical methods in the field. The workshop topics can be characterized as follows: • Positron studies of defects in semiconductors and oxides • Positron studies of defects in metals • New experimental methods and equipment • Theoretical calculations and simulations of momentum distributions, positron lifetimes and other characteristics for defects • Positron studies of defects in combination with complementary methods • Positron beam studies of defects at surfaces, interfaces, in sub-surface regions and thin films • Nanostructures and amorphous materials

  18. A positron annihilation study of hydrated DNA

    DEFF Research Database (Denmark)

    Warman, J. M.; Eldrup, Morten Mostgaard

    1986-01-01

    Positron annihilation measurements are reported for hydrated DNA as a function of water content and as a function of temperature (20 to -180.degree. C) for samples containing 10 and 50% wt of water. The ortho-positronium mean lifetime and its intensity show distinct variations with the degree of ...

  19. Positron Annihilation in Solid Charge-Transfer Complexes

    DEFF Research Database (Denmark)

    Lévay, B.; Jansen, P.

    1979-01-01

    Positron lifetime and angular correlation measurements have been carried out on 1:1 charge-transfer complexes, on their pure donor and acceptor components and on the 1:1 M mechanical mixtures of these components. Complex formation reduced the intensity of the long-lifetime component of the donor ...

  20. Polymeric membrane studied using slow positron beam

    International Nuclear Information System (INIS)

    A radioisotope slow positron beam has been built at the Chung Yuan Christian University in Taiwan for the research and development in membrane science and technology. Doppler broadening energy spectra and positron annihilation lifetime have been measured as a function of positron energy up to 30 keV in a polyamide membrane prepared by the interfacial polymerization between triethylenetetraamine (TETA) and trimesoyl chloride (TMC) on modified porous polyacrylonitrile (PAN) asymmetric membrane. The multilayer structures and free-volume depth profile for this asymmetric membrane system are obtained. Positron annihilation spectroscopy coupled with a slow beam could provide new information about size selectivity of transporting molecules and guidance for molecular designs in polymeric membranes

  1. Calculation of positron characteristics for elements of the periodic table

    International Nuclear Information System (INIS)

    Positron characteristics have been calculated in bulk and monovacancies for most of the elements of the periodic table. Self-consistent and non-self-consistent schemes have been used for the calculation of the electronic structure in the solid, and different parametrizations for the positron enhancement factor and correlation energy. As it is known, positron lifetimes in bulk show a periodic behaviour with atomic number. These calculations also confirm that monovacancy lifetimes follow the same behaviour. The results obtained have been compared with selected experimental lifetime data, which confirms the calculated theoretical trends. Positron binding energies to a monovacancy have been calculated also for most of the elements of the periodic table. The binding energy shows a periodic behaviour with atomic number too.

  2. Positron methods for the study of defects in bulk materials

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard

    The basic principles of positron annihilation physics are briefly discussed and the three most important experimental techniques used for bulk studies are described (i.e. positron lifetime, angular correlation, Doppler broadening). Several examples of the use of the positron methods are discussed...... for metals, ceramics and molecular materials, which illustrate the sensitivity of the positron annihilation techniques to vacancy type defects. For example it is shown how information can be obtained about vacancy formation energies, vacancy migration and clustering, vacancy-impurity interactions......, densities of rare gasses in bubbles in metals, and about free volume in molecular materials....

  3. Positron annihilation in transparent ceramics

    Science.gov (United States)

    Husband, P.; Bartošová, I.; Slugeň, V.; Selim, F. A.

    2016-01-01

    Transparent ceramics are emerging as excellent candidates for many photonic applications including laser, scintillation and illumination. However achieving perfect transparency is essential in these applications and requires high technology processing and complete understanding for the ceramic microstructure and its effect on the optical properties. Positron annihilation spectroscopy (PAS) is the perfect tool to study porosity and defects. It has been applied to investigate many ceramic structures; and transparent ceramics field may be greatly advanced by applying PAS. In this work positron lifetime (PLT) measurements were carried out in parallel with optical studies on yttrium aluminum garnet transparent ceramics in order to gain an understanding for their structure at the atomic level and its effect on the transparency and light scattering. The study confirmed that PAS can provide useful information on their microstructure and guide the technology of manufacturing and advancing transparent ceramics.

  4. Positron study of MCM-41 sieve formation

    Energy Technology Data Exchange (ETDEWEB)

    Zaleski, R. [Inst. of Physics, Maria Curie-Sklodowska Univ., Lublin (Poland); Borowka, A. [Faculty of Chemistry, Maria Curie-Sklodowska Univ., Lublin (Poland)

    2004-07-01

    The removal of alkyltrimethylammonium template from MCM-41 ordered silica was investigated, using positron annihilation lifetime spectroscopy (PALS). The lifetime spectra of positrons were measured as a function of temperature for several samples with different template alkyl chain length (different pore radius). At low temperatures the template interior behaves like a liquid, and the ''bubble model'' of positronium in liquid can be applied. The change of template structure starts at 380-400 K, and at 520 K the process of template removal is completed. Analysis of o-Ps lifetime components suggests the following stages: breaking long micelle cylinders, rise of the gaps between the fragments, and pore evacuation. (orig.)

  5. Positron annihilation spectroscopy of neon ion irradiated MgB2

    International Nuclear Information System (INIS)

    Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening Spectroscopy (CDBS) were carried out on Neon ion irradiated MgB2 superconductor. CDBS of unirradiated sample shows similarity to boron spectrum. In contrast, the spectrum of the irradiated sample shows similarity to Mg spectrum. The PALS spectra show that there is decrease in the lifetime of positron in irradiated sample. The decrease in the lifetime is due to neon ion implantation. (author)

  6. Positron annihilation in SiO2

    International Nuclear Information System (INIS)

    Defects in different types of crystalline and fused quartz have been studied by conventional coincidence positron annihilation and optical absorption technique before and after 60Co gamma irradiation with 500 krad, 2 Mrad and 15.8 Mrad. Samples of synthetic powdered quartz (SPQ), natural quartz (NQ), low-OH synthetic monocrystal quartz (LSMQ), high-OH-fused quartz (HFQ) and low-OH fused quartz (LFQ) have been investigated. Two- and three-component analysis of the positron lifetime spectra have been applied. Data on lifetime (τ), intensities (I) and mean lifetimes have been obtained by exponential fitting of spectra. In non-irradiated SPQ and LSMQ big differences in the values of I2 (1.53% vs. 16.0%) and τ2 (1460 ps vs. 478 ps) have been noticed. This is explained by an increased number of dislocations in the synthetic quartz. The τ2 is interpreted as apparent mixed lifetime of two pick-off annihilation of oPs and positron annihilation in micro cracks. The values of τ1 in HFQ (178 ps) and in LHQ (173 ps) are attributed to positron annihilation in small crystalline areas in the glass. Because of the sharp increase in Ps formation probability in amorphous state, the longest component intensity I3 in these samples is of the order of 50%. After gamma irradiation, a creation of coloured centres has been observed only in SPQ and LFQ., which is connected with Al substitutional impurity. The newly detected diffused band at 215 nm in UV-spectra of irradiated LFQ is attributed to a positively charged oxygen vacancy (E'1 centre) which explains the lack of difference between the parameters of irradiated and non irradiated LFQ. The increased mean positron lifetime of irradiated HFQ is ascribed to creation of negatively charged defects able to trap positrons. Except for HFQ, all samples have surprisingly shown a decrease, although slight, in their mean positron lifetime values after low dose irradiation. The authors ascribe this to possible self-annealing of some defects due

  7. Positron annihilation in non-simple liquids. Normal hexane

    International Nuclear Information System (INIS)

    Positron lifetime measurements were carried out in normal hexane vs. temperature in the range of 12.5 - 62.5 deg C. The evaluation of the lifetime spectra indicates the presence of four lifetime components, as published first by Jacobsen et al. An attempt is made to interpret the properties of the longest-living two components in terms of the microscopic structure of the liquid. (author) 11 refs.; 3 figs

  8. Positron tomographs

    International Nuclear Information System (INIS)

    Specifications of position emission tomographs used for examination of brain and internal organs of human beings are presented. The tomograph comprises a detecting system, devices for detector displacement, sighting, calibration, electronics units (discriminators-formers, coincidence circuits, coders, buffer memory), detectors for detecting system position, bed for patient. Spatial resolution of the tomograph is determined by sizes of the detectors and their dispositin relatively to the object of examination. Besides, it depends on positron path in the investigated medium, deflections of the angle of scatter of annihilation quanta from 180 deg, distribution of points of gamma-quantum interaction by depth of the detector, filter and algorithm of image reconstruction, motion of organs of a patient, motion of labelled pharm-preparation in the organism. Such factors as absorption of annihilation radiation by substance of an object, radiation scattering and registration of random coincidences essentially affect the quality of tomographic image. It is shown that use of asseblies of microchannel plates and a scintillator on the base of barium fluoride permits to produce a coordinate-sensitive detector for a tomograph complying with highest requirements

  9. Thermalized positrons in jellium: a GW investigation

    International Nuclear Information System (INIS)

    Full text: Since many decades, positron annihilation experiments (lifetime, angular correlation, and Doppler broadening spectroscopy) play an important role for investigations of the electronic structure of both crystalline and amorphous materials. In this context, the most important quantity to be investigated is the electron-positron annihilation rate including the momentum-dependence of electron-positron pairs in the moment of their mass annihilation. Theoretically, the quantity of interest is the two-particle Green's function Gep which describes the propagation of an electron-positron pair in the material. One can imagine that the calculation (perturbation expansion) of Gep is a rather complicated task, because one has to take into account two different kinds of correlation: at first, interactions between the electron and the positron of an annihilating pair with the surrounding electron gas, and secondly, the direct correlation between the annihilating fermions leading to the so-called enhancement of the annihilation probability. Both types of interactions are not easy to handle in theory, and it is due to these complications, that in the greatest part of the relevant literature, all dynamical effects of the electron-electron and electron-positron interactions are neglected and static approximations are used. In contrast to that, in the paper presented here, a fully dynamical theory of positron annihilation is described within a homogenous electron gas (jellium) on a GW level. This means that the two-particle Green's function Gep contains momentum- and frequency-dependent self-energy functions for both annihilating partners - the electron and the (thermalized) positron. This investigation clearly demonstrates that a static theory of the electron-positron interaction may indeed provide a rough first insight into the enhancement process, but the role of dynamical correlation effects is by no means negligible. The jellium results reported here represent the first

  10. Free volumes in glass bonded sodalite as probed by positrons

    International Nuclear Information System (INIS)

    Glass bonded sodalite is a promising waste form for immobilizing radioactive wastes, resulting from pyrometallurgical processing of the spent fuel. The synthesis procedure for the glass-bonded sodalite involves (a) incorporating the simulated chloride waste salt into dehydrated zeolite 4A by high temperature equilibration (b) blending the salt loaded zeolite with boroaluminosilicate glass and (c) sintering at high temperature and pressure to yield the glass-ceramic. This work is aimed at using positron lifetime spectroscopy to follow the changes in the free volume size as the zeolite is being transformed to the glass bonded sodalite. Positron lifetime measurements were carried out on various glass samples using lifetime spectrometer having a time resolution of 260 ps and the measured spectra were resolved into various lifetime components. Based on the Tao-Eldrup model, the longest positron lifetimes τ3 and τ4 (ns) which correspond to pick-off annihilation of o-Ps, are related to the average radii (R) of free volume holes. The variation in positron lifetime components and hence the deduced free volume radii for dehydrated zeolite 4A, pure sodalite, glass bonded sodalite and boroaluminosilicate glass are shown. The shortest lifetime component τ1 is attributed to positrons annihilating in the bulk and p-Ps annihilation. The intermediate component τ2, which is not listed in table, is due to positrons annihilating at the defect complexes. The longest lifetime components, τ3 and τ4, are attributed to o-Ps annihilation in the β and α cages, respectively. While dehydrated zeolite 4A exhibits 4 lifetime components, sodalite and glass bonded sodalite give rise to only three lifetime components. Absence of the fourth o-Ps lifetime component along with reduced average free volume radius from 2.56 Å to about 1.55 Å in sodalite implies that the chloride waste salt loaded in the zeolite has got incorporated possibly in both α and β cages. The fact that the o

  11. Cold positrons from decaying dark matter

    Science.gov (United States)

    Boubekeur, Lotfi; Dodelson, Scott; Vives, Oscar

    2012-11-01

    Many models of dark matter contain more than one new particle beyond those in the Standard Model. Often, heavier particles decay into the lightest dark matter particle as the Universe evolves. Here, we explore the possibilities which arise if one of the products in a (heavyparticle)→(darkmatter) decay is a positron, and the lifetime is shorter than the age of the Universe. The positrons cool down by scattering off the cosmic microwave background and eventually annihilate when they fall into Galactic potential wells. The resulting 511 keV flux not only places constraints on this class of models, but might even be consistent with that observed by the INTEGRAL satellite.

  12. Muon lifetime measurement

    International Nuclear Information System (INIS)

    A simple experimental setup to measure the muon lifetime is presented. The muon detector consists of a sealed container with liquid scintillator coupled to a 2.5'' photomultiplier (PMT). A home-made electronics module controlled by the parallel port of a personal computer (PC) digitizes the time interval between two consecutive PMT pulses in a time window of 25.6 μs. The muon lifetime is obtained by analysing thousands of double-pulse events in which the first pulse corresponds to a cosmic ray muon that stops inside the detector and the second to the decay electron coming from the weak decay of the muon. The background noise comes from random coincidences of pulses due to muons crossing the detector within the same time window. The PC is used as the data adquisition (DAQ) and data analysis computer. In addition to the muon lifetime, the charge ratio of cosmic ray muons and the capture rate of negative muons by carbon nuclei can be measured if the number of events is sufficiently high

  13. Study on positron annihilation spectroscopy of methanol synthesis catalyst CuO/ZnO

    International Nuclear Information System (INIS)

    A new method was developed for determining the solid solubility of a metal oxide series prepared by precipitation using the positron lifetime parameters. The positron lifetime spectra of a series of CuO/ZnO catalysts prepared by precipitation were measured, in which the CuO at % contents were different before and after reducing. The relations between the solid solubility of the catalysts and the positron lifetime parameters were obtained, from which a result of solid solubility of 12 CuO at% after reducing had been found. The viewpoint that the Cu+ ion acted as the active centre in the CuO/ZnO catalyst was supported

  14. Positron annihilation studies of Czochralski-grown silicon annealed under pressure

    International Nuclear Information System (INIS)

    Two positron techniques have been applied to study dynamics of oxygen precipitation in Czochralski-grown silicon, annealed under high (up to 1,4 GPa) pressure. Lifetime measurements were performed with 180 ps resolution; Doppler broadening with variable-energy slow-positron beam. Different thermal treatings rise the mean lifetime of positrons from 222 ps in as-grown samples up to 227 ps. in samples with a high (up to 85%) amount of oxygen precipitated, an intermediate (550-800 ps) lifetime is observed. (author)

  15. Positron Facilities in Europe

    OpenAIRE

    Triftshäuser, W.

    1995-01-01

    Positron annihilation is a well established method in solid state physics and material science. The positron being a very sensitive probe, can give very precise information on the momentum distribution of electrons in metals and alloys as well as on lattice defects in crystals. Starting with the energy distribution of positrons from a radioactive decay, the current development is directed more to monoenergetic positrons of variable energy and of high intensity. Pulsed and continuous beams of ...

  16. Positron annihilation study of graphite, glassy carbon and C60/C70 fullerene

    International Nuclear Information System (INIS)

    ACAR (Angular Correlation of Annihilation Radiation) and positron lifetime measurements have been made on, HOPG (Highly Oriented Pyrolytic Graphite), isotropic fine-grained graphite, glassy carbons and C60/C70 powder. HOPG showed marked bimodality along the c-axis and anisotropy in ACAR momentum distribution, which stem from characteristic annihilation between 'interlayer' positrons and π-electrons in graphite. ACAR curves of the isotropic graphite and glassy carbons are even narrower than that of HOPG perpendicular to the c-axis. Positron lifetime of 420 and 390 - 480 psec, much longer than that of 221 psec in HOPG, were observed for the isotropic graphite and glassy carbons respectively, which are due to positron trapping in structural voids in them. Positron lifetime and ACAR width (FWHM) can be well correlated to void sizes (1.7 to 5.0 nm) of glassy carbons which have been determined by small angle neutron (SAN) scattering measurements. ACAR curves and positron lifetime of C60/C70 powder agree well with those of glassy carbons. This shows that positron wave functions extend, as in the voids of glassy carbons, much wider than open spaces of the octahedral interstices of the face-centered cubic (FCC) structure of C60 crystal and strongly suggests positron trapping in the 'soccer ball' vacancy. Possible positron states in the carbon materials are discussed with a simple model of void volume-trapping. Preliminary results on neutron irradiation damage in HOPG are also presented. (author)

  17. Polymerization of epoxy resins studied by positron annihilation

    International Nuclear Information System (INIS)

    The polymerization process of epoxy resins (bisphenol-A dicyanate) was studied using positron-annihilation spectroscopy. The polymerization from monomer to polymer through a polymerization reaction was followed by positron-annihilation lifetime spectroscopy measurements. Resins kept at curing temperatures (120, 150 and 200 oC) changed form from of powder to a solid through a liquid. The size of the intermolecular spaces of the solid samples increased along with the progress of polymerization. (author)

  18. Migration Enthalpy of Thermal Vacancies by Positron Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    Emad A. Badawi

    2005-01-01

    @@ The trapping of positrons at vacancy site in some materials provide a new and sensitive method for the equilibrium determination of point defect migration enthalpy. Data are presented for commercial Al-Mg alloys and fitted to a model allowing presentation in the form of Arrhenius plots, hence the migration enthalpy H m iv can bedetermined by the positron annihilation lifetime technique. The results show that the value of Hm iv increases as the concentration of Mg increases.

  19. Structural defects in electrodeposited Ni studied by positron annihilation

    International Nuclear Information System (INIS)

    Structural investigation of electrodeposited Ni was carried out by positron annihilation (PA) technique. Additional Moessbauer effect and X-ray diffraction measurements were also performed. The samples were produced under different plating conditions resulting in stress in the range -100 to +600 N/mm2. From the positron lifetime measurements it seems that the defect pattern of electrodeposited Ni samples might be substantially different from sample to sample with different deposition and plating conditions. (Auth.)

  20. A positron annihilation study of hydrated DNA

    DEFF Research Database (Denmark)

    Warman, J. M.; Eldrup, Morten Mostgaard

    1986-01-01

    Positron annihilation measurements are reported for hydrated DNA as a function of water content and as a function of temperature (20 to -180.degree. C) for samples containing 10 and 50% wt of water. The ortho-positronium mean lifetime and its intensity show distinct variations with the degree of...... content until, for approximately 50% water, its properties resemble more those of a highly viscous fluid....

  1. Analysis of stress degradation of metals by positron annihilation

    International Nuclear Information System (INIS)

    Since the stress degradation of metals originates from the change of the microstructure induced by glide motion and multiplication of dislocations, fundamental features of this process have been investigated from the viewpoint of the dislocation - dislocation interaction and the consequent vacancy production by using positron technique and computer simulation. Corresponding to the positron trapping at deformation induced defects in metals such as Fe and Ni, positron lifetime calculation has been made for the configurations obtained in model Fe and Ni lattices which contain a dislocation and vacancies produced by dislocation cutting process. The important results are (1) straight dislocation lines usually behave as shallow traps for a positron and the corresponding positron lifetime is close to that at matrix, (2) complex defects consisting of a dislocation line and vacancies usually show intermediate positron lifetimes between matrix and a single vacancy. Vacancy production process by dislocation cutting is simulated in model Fe lattice and it has been clarified that a vacancy is produced at each step of a climbing jog dragged by a screw dislocation line on atomic row in the vicinity of a jog. Another topic of vacancy production process in a small Cu precipitate cut by a gliding dislocation has also been simulated in Fe model lattice, showing a conversion from a straight dislocation line to a jogged line after cutting the Cu precipitates. (author)

  2. Modeling of positron states and annihilation in solids

    International Nuclear Information System (INIS)

    Theoretical models and computational aspects to describe positron states and to predict positron annihilation characteristics in solids are discussed. The comparison of the calculated positron lifetimes, core annihilation lineshapes, and two-dimensional angular correlation maps with experimental results are used in identifying the structure (including the chemical composition) of vacancy-type defects and their development e.g. during thermal annealing. The basis of the modeling is the two-component density-functional theory. The ensuing approximations and the state-of-the-art electronic-structure computation methods enable practical schemes with a quantitative predicting power. (author)

  3. Charge accumulation in polycarbonate induced by positron irradiation

    OpenAIRE

    Cangialosi, D.; Schut, H.; Wübbenhorst, Michael; van Turnhout, J.; Veen, A.

    2002-01-01

    Positron annihilation lifetime spectroscopy (PALS) is a powerful technique for the study of free volume in polymers. The lifetime of ortho-positronium (o-Ps), a bound state of an electron and a positron, can be used to assess the cavity size, while the intensity can be used to characterize the number of cavities. In the past results have been published, which suffer from artifacts, whereby the drop in o-Ps intensity is not related to a decrease in the number of cavities. One of the possible a...

  4. Development of an electron gun for the KEK positron generator

    International Nuclear Information System (INIS)

    In the KEK Positron Generator, a semi-long pulsed beam (∼40ns) has turned out to be suitable for effective positron injection into the PF storage ring. However, to use the semi-long pulsed beam, there was a problem concerning the cathode lifetime of the gun. Thus, a new gun has been developed with a dispenser cathode, Y-796(EIMAC); the characteristics of this gun have been investigated. This new gun has been used since October 1988 and has continued to produce constant current of about 12A without having to exchange its cathode. Thus, the cathode lifetime has been remarkably improved. (author) 6 refs., 7 figs

  5. Computational Study of Positron-Monovacancy Interaction in d-Block Metals

    Science.gov (United States)

    Ishibashi, Shoji

    2015-08-01

    The positron-monovacancy interaction in d-block metals (except for Mn, Tc, and Hg) has been studied by the two-component density-functional-theory formalism [E. Boroński and R. M. Nieminen, Phys. Rev. B 34, 3820 (1986)]. On the unrelaxed structure, the positron lifetime calculated with the presence of a positron is generally longer than that obtained neglecting the positron effect. When the atomic positions are relaxed, the difference is widened, especially for the group V metals. The inward relaxation of the atoms surrounding the monovacancy is suppressed when the positron effect is taken into account. The difference in the positron lifetime can be also related to the bulk modulus and the cohesive energy.

  6. Surfaces of colloidal PbSe nanocrystals probed by thin-film positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectroscopy and positron-electron momentum density (PEMD) studies on multilayers of PbSe nanocrystals (NCs), supported by transmission electron microscopy, show that positrons are strongly trapped at NC surfaces, where they provide insight into the surface composition and electronic structure of PbSe NCs. Our analysis indicates abundant annihilation of positrons with Se electrons at the NC surfaces and with O electrons of the oleic ligands bound to Pb ad-atoms at the NC surfaces, which demonstrates that positrons can be used as a sensitive probe to investigate the surface physics and chemistry of nanocrystals inside multilayers. Ab initio electronic structure calculations provide detailed insight in the valence and semi-core electron contributions to the positron-electron momentum density of PbSe. Both lifetime and PEMD are found to correlate with changes in the particle morphology characteristic of partial ligand removal

  7. Surfaces of colloidal PbSe nanocrystals probed by thin-film positron annihilation spectroscopy

    Directory of Open Access Journals (Sweden)

    L. Chai

    2013-08-01

    Full Text Available Positron annihilation lifetime spectroscopy and positron-electron momentum density (PEMD studies on multilayers of PbSe nanocrystals (NCs, supported by transmission electron microscopy, show that positrons are strongly trapped at NC surfaces, where they provide insight into the surface composition and electronic structure of PbSe NCs. Our analysis indicates abundant annihilation of positrons with Se electrons at the NC surfaces and with O electrons of the oleic ligands bound to Pb ad-atoms at the NC surfaces, which demonstrates that positrons can be used as a sensitive probe to investigate the surface physics and chemistry of nanocrystals inside multilayers. Ab initio electronic structure calculations provide detailed insight in the valence and semi-core electron contributions to the positron-electron momentum density of PbSe. Both lifetime and PEMD are found to correlate with changes in the particle morphology characteristic of partial ligand removal.

  8. Positron sources for electron-positron colliders application to the ILC and CLIC

    CERN Document Server

    CERN. Geneva

    2008-01-01

    The increased demanding qualities for positron sources dedicated to e+e- colliders pushed on investigations oriented on new kinds of e+ sources. The different kinds of positron sources polarized and no polarized are considered. Their main features (intensity, emittance) are described and analysed. Comparison between the different sources is worked out. The characteristics of the positron beam available in the collision point are greatly depending on the capture device and on the positron accelerator. Different kinds of capture systems are considered and their qualities, compared. Intense positron sources which are necessary for the colliders require intense incident beams (electrons or photons). The large number of pairs created in the targets leads to important energy deposition and so, thermal heating, which associated to temperature gradients provoke mechanical stresses often destructive. Moreover, the important Coulomb collisions, can affect the atomic structure in crystal targets and the radiation resist...

  9. Positronics of subnanometer atomistic imperfections in solids as a high-informative structure characterization tool

    OpenAIRE

    Shpotyuk, Oleh; Filipecki, Jacek; Ingram, Adam; Golovchak, Roman; Vakiv, Mykola; Klym, Halyna; Balitska, Valentyna; Shpotyuk, Mykhaylo; Kozdras, Andrzej

    2015-01-01

    Methodological possibilities of positron annihilation lifetime (PAL) spectroscopy applied to characterize different types of nanomaterials treated within three-term fitting procedure are critically reconsidered. In contrast to conventional three-term analysis based on admixed positron- and positronium-trapping modes, the process of nanostructurization is considered as substitutional positron-positronium trapping within the same host matrix. Developed formalism allows estimate interfacial void...

  10. Study of Defects in GaAs by 2D-ACAR Positron Annihilation

    OpenAIRE

    Manuel, A; Ambigapathy, R.; Hautojärvi, P.; Saarinen, K.; Corbel, C.

    1995-01-01

    We describe the two dimensional angular correlation of positron annihilation radiation (2D-ACAR) method and show that it can be advantageously used to study the electronic structure of defects, in addition to standard positron lifetime and Doppler broadening measurements. Using annihilation fractions determined by lifetime measurements, we separate 2D-ACAR distributions for negatively charged and neutral arsenic vacancies in n-type GaAs. In electron-irradiated semi-insulating GaAs, we present...

  11. Characterization of radiation-induced defects in ZnO probed by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    In this study we discuss the microstructural changes after electron and proton irradiation and the thermal evolution of the radiation induced defects during isochronal annealing of single crystals irradiated either with 3 MeV protons or with 1 or 2 MeV electrons, respectively. The investigations were performed with positron lifetime and Doppler-broadening measurements. The differently grown ZnO single crystals show positron bulk lifetimes in the range of 159-173 ps. (orig.)

  12. Carbon-vacancy interaction in α iron: interpretation of positron annihilation results

    International Nuclear Information System (INIS)

    The tapped positron characteristics are calculated for the carbon-vacancy pair in α iron. The method used is based on superimposing free atom electron densities and solving the resulting three-dimensional Schroedinger equation by relaxation techniques. The results are used to interpret positron lifetime measurements in α iron doped with controlled amounts of carbon impurities. (author)

  13. Characterizing metal-oxide semiconductor structures consisting of HfSiOx as gate dielectrics using monoenergetic positron beams

    International Nuclear Information System (INIS)

    Metal-oxide-semiconductor structures consisting of HfSiOx as the gate dielectric were characterized by using monoenergetic positron beams. 200-nm-thick polycrystalline-Si (poly-Si) and 5-nm HfSiOx films were grown on Si substrates by chemical vapor deposition. Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons were measured as a function of incident positron energy for ion-implanted and unimplanted samples. For the unimplanted sample after rapid thermal annealing (RTA: 1030degC, 10s), the lifetime of positrons in the HfSiOx film was 448±2 ps. Since the obtained lifetime was longer than the lifetime of positrons trapped by point defects in metal oxides, the positrons in HfSiOx films were considered to annihilate from the trapped state by open spaces which exist intrinsically in their amorphous structure. After P+, As+ and BF+-implantation into the poly-Si film and RTA, the lifetime of positrons was 420-430 ps. This decrease in the lifetime was attributed to the shrinkage of the open spaces in the HfSiOx film due to the accumulation of implanted impurities in the film during RTA. The diffusion length of positrons in Si substrates was found to depend on the implanted species of ions. This fact was attributed to the electric field introduced by charged defects in the HfSiOx films. (author)

  14. Intense positron beams: linacs

    International Nuclear Information System (INIS)

    Beams of monoenergetic positrons with energies of a few eV to many keV have been used in experiments in atomic physics, solid-state physics and materials science. The production of positron beams from a new source, an electron linac, is described. Intense, pulsed beams of low-energy positrons were produced by a high-energy beam from an electron linac. The production efficiency, moderator geometry, beam spot size and other positron beam parameters were determined for electrons with energies from 60 to 120 MeV. Low-energy positron beams produced with a high-energy electron linac can be of much higher intensity than those beams currently derived from radioactive sources. These higher intensity beams will make possible positron experiments previously infeasible. 10 references, 1 figure

  15. Positron emission tomography.

    Science.gov (United States)

    Hoffman, E J; Phelps, M E

    1979-01-01

    Conventional nuclear imaging techniques utilizing lead collimation rely on radioactive tracers with little role in human physiology. The principles of imaging based on coincidence detection of the annihilation radiation produced in positron decay indicate that this mode of detection is uniquely suited for use in emission computed tomography. The only gamma-ray-emitting isotopes of carbon, nitrogen, and oxygen are positron emitters, which yield energies too high for conventional imaging techniques. Thus development of positron emitters in nuclear medicine imaging would make possible the use of a new class of physiologically active, positron-emitting radiopharmaceuticals. The application of these principles is described in the use of a physiologically active compound labeled with a positron emitter and positron-emission computed tomography to measure the local cerebral metabolic rate in humans. PMID:440173

  16. Monte Carlo modelling of positron transport in real world applications

    International Nuclear Information System (INIS)

    Due to the unstable nature of positrons and their short lifetime, it is difficult to obtain high positron particle densities. This is why the Monte Carlo simulation technique, as a swarm method, is very suitable for modelling most of the current positron applications involving gaseous and liquid media. The ongoing work on the measurements of cross-sections for positron interactions with atoms and molecules and swarm calculations for positrons in gasses led to the establishment of good cross-section sets for positron interaction with gasses commonly used in real-world applications. Using the standard Monte Carlo technique and codes that can follow both low- (down to thermal energy) and high- (up to keV) energy particles, we are able to model different systems directly applicable to existing experimental setups and techniques. This paper reviews the results on modelling Surko-type positron buffer gas traps, application of the rotating wall technique and simulation of positron tracks in water vapor as a substitute for human tissue, and pinpoints the challenges in and advantages of applying Monte Carlo simulations to these systems.

  17. Positron ionization mass spectrometry: An organic mass spectrometrist's view

    International Nuclear Information System (INIS)

    We are currently engaged in a research program to study the ionization of polyatomic molecules by positrons. We refer to the technique herein as positron ionization mass spectrometry which includes all of the possible ionization mechanisms. In the course of this work we will attempt to characterize each of the important ionization mechanisms. Our ultimate objective is to explore the use of positron ionization mass spectrometry for chemical analysis. Several other groups have also begun to pursue aspects of positron ionization in parallel with our efforts although with somewhat different approaches and, perhaps with slightly different emphases. Recently, for example, Passner et al. have acquired mass spectra in a Penning trap resulting from the ionization of several different polyatomic molecules by near thermal kinetics energy positrons. Our research involves studying the different types of ionizing interactions of positrons with organic molecules, as a function of positron kinetic energy. For ionization of polyatomic molecules by positrons, several possible mechanisms are apparent from lifetime and scattering cross-section data. These mechanisms are discussed

  18. Microstructural probing of ferritic/martensitic steels using internal transmutation-based positron source

    Science.gov (United States)

    Krsjak, Vladimir; Dai, Yong

    2015-10-01

    This paper presents the use of an internal 44Ti/44Sc radioisotope source for a direct microstructural characterization of ferritic/martensitic (f/m) steels after irradiation in targets of spallation neutron sources. Gamma spectroscopy measurements show a production of ∼1MBq of 44Ti per 1 g of f/m steels irradiated at 1 dpa (displaced per atom) in the mixed proton-neutron spectrum at the Swiss spallation neutron source (SINQ). In the decay chain 44Ti → 44Sc → 44Ca, positrons are produced together with prompt gamma rays which enable the application of different positron annihilation spectroscopy (PAS) analyses, including lifetime and Doppler broadening spectroscopy. Due to the high production yield, long half-life and relatively high energy of positrons of 44Ti, this methodology opens up new potential for simple, effective and inexpensive characterization of radiation induced defects in f/m steels irradiated in a spallation target.

  19. Determination of absolute defect concentrations for saturated positron trapping - deformed polycrystalline Ni as a case study

    International Nuclear Information System (INIS)

    Positrons may be used in many cases to determine defect densities of vacancies and dislocations. In case of saturated positron trapping, i.e. all positrons are getting trapped, only a lower-limit estimation can be given. However, a combination of positron back-diffusion measurements using a monoenergetic positron beam in combination with conventional lifetime spectroscopy can be used to overcome the problem of saturated positron trapping. As a case study, this combination was used for the determination of dislocation densities in polycrystalline nickel samples of highly varying dislocation density. Saturated positron trapping into dislocations and small voids was observed. The total positron trapping rate was calculated from the positron diffusion length obtained by back-diffusion experiments. The trapping rates of the two defects were finally obtained using the decomposition of lifetime spectra. The results were found in good agreement with those determined by the analysis of synchrotron Bragg-diffraction profiles, measured on the same set of samples. From the comparison of both techniques, the positron trapping coefficient was found to be μ disl = 3.9 ± 0.3 cm2/s for a high density of dislocations in Ni

  20. Positron Annihilation in a Rubber Modified Epoxy Resin

    DEFF Research Database (Denmark)

    Mogensen, O. E.; Jacobsen, F. M.; Pethrick, R. A.

    1979-01-01

    Positron annihilation data is reported on a rubber-modified epoxy resin. Studies of the temperature dependence of the o-positronium lifetime indicated the existence of three distinct regions; the associated transition temperatures by comparison with dilatometric data can be ascribed respectively ...... be glass transition of the epoxy phase and to that of a mixed acrylonitrile—epoxy—butadiene interfacial region....

  1. Positronium Yields in Liquids Determined by Lifetime and Angular Correlation Measurements

    DEFF Research Database (Denmark)

    Mogensen, O. E.; Jacobsen, F. M.

    1982-01-01

    Positron lifetime and angular correlation spectra were measured for 36 pure liquids, CCl4 mixtures with hexane and diethylether, and C6F6 mixtures with hexane. Apparent ortho-Ps yields, I'3, were determined as the intensity of the long-lived component in the lifetime spectra, while the apparent...

  2. Defects in fine-grained and porous materials characterized by positron annihilation

    International Nuclear Information System (INIS)

    We investigate the annihilation parameters (lifetimes and intensities) for positrons becoming trapped at grain boundaries and at inner surfaces (pores), examining fine-grained nickel powder compacts (effective powder particle size 1 - 10 μm with grains in or even below the micron size). Furthermore, we can monitor grain growth and sintering (volume shrinkage) during successive heat treatment of powder compacts. To reach this aim, we correlate the annihilation parameters with results of a Monte-Carlo simulation and analytical solutions of the positron diffusion. We find that it is possible to determine an effective average powder particle size as well as grain sizes by positron lifetime spectroscopy. (author)

  3. Studies of iron exposed to heavy ion implantation using positron annihilation spectroscopy

    Science.gov (United States)

    Horodek, P.; Dryzek, J.; Skuratov, V. A.

    2016-05-01

    Variable energy positron beam and positron lifetime spectroscopy were used to study pure iron exposed to irradiation with 167 MeV Xe26+ heavy ions with different doses of 1012, 1013, 5×1013, 1014 ions/cm2. The positron lifetime spectroscopy revealed the presence of large cluster of about 15-27 vacancies and dislocations. The dislocations are distributed at the depth of about 18 μm i.e. almost twice deeper than the ion implantation range from the surface exposed to the heavy ions implantation. Possible explanation is the long-range effect attributed to the ion implantation into materials.

  4. Solvated Positron Chemistry. II

    DEFF Research Database (Denmark)

    Mogensen, O. E.

    1979-01-01

    The reaction of the hydrated positron, eaq+ with Cl−, Br−, and I− ions in aqueous solutions was studied by means of positron The measured angular correlation curves for [Cl−, e+], [Br−, e+, and [I−, e+] bound states were in good agreement with th Because of this agreement and the fact that the ca...

  5. Positron annihilation microprobe

    Energy Technology Data Exchange (ETDEWEB)

    Canter, K.F. [Brandeis Univ., Waltham, MA (United States)

    1997-03-01

    Advances in positron annihilation microprobe development are reviewed. The present resolution achievable is 3 {mu}m. The ultimate resolution is expected to be 0.1 {mu}m which will enable the positron microprobe to be a valuable tool in the development of 0.1 {mu}m scale electronic devices in the future. (author)

  6. γ-irradiation of polyethylene studied by positron annihilation

    International Nuclear Information System (INIS)

    In order to study the third positron lifetime component in γ-irradiated polyethylene samples the influence of different irradiation conditons (absorbed doses of 1, 10, 100, and 1000 KGy and dose rates of 0.1 and 12.5 KGy/h, respectively) on the properties of polyethylene in air has been tested by Doppler broadening and positron lifetime measurements. The effect of different radiation-induced reactions such as oxidic degradation, cross-linking, positronium formation and others has been discussed. It can be concluded that radiation-induced changes in the properties of polyethylene are demonstrable by positron annihilation and the influence of independent irradiation parameters as dose and dose rate can be described by logarithmic functions

  7. Positron annihilation spectroscopy in condensed matter

    International Nuclear Information System (INIS)

    The topic of positron annihilation spectroscopy (PAS) is the investigation of all aspects connected with the annihilation of slow positrons. This work deals with the application of PAS to different problems of materials science. The first chapter is an introduction to fundamental aspects of positron annihilation, as far as they are important to the different experimental techniques of PAS. Chapter 2 is concerned with the information obtainable by PAS. The three main experimental techniques of PAS (2γ-angular correlation, positron lifetime and Doppler broadening) are explained and problems in the application of these methods are discussed. Chapter 3 contains experimental results. According to the different fields of application it was subgrouped into: 1. Investigations of crystalline solids. Detection of structural defects in Cu, estimation of defect concentrations, study of the sintering of Cu powders as well as lattice defects in V3Si. 2. Chemical investigations. Structure of mixed solvents, selective solvation of mixed solvents by electrolytes as well as the micellization of sodium dodecylsulphate in aqueous solutions. 3. Investigations of glasses. Influence of heat treatment and production technology on the preorder of X-amorphous silica glass as well as preliminary measurements of pyrocerams. 4. Investigations of metallic glasses. Demonstration of the influence of production technology on parameters measurable by PAS. Chapter 4 contains a summary as well as an outlook of further applications of PAS to surface physics, medicine, biology and astrophysics. (author)

  8. Positron annihilation in silica aerogel UV-irradiated at low temperature

    International Nuclear Information System (INIS)

    Positron lifetime spectra for the silica aerogel heat-treated at various temperatures (373 K-673 K) have been measured following UV-irradiation at 30 K. It has been observed that positronium lifetime in the UV-irradiated silica aerogel depends on the heat-treatment temperature. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. TiCrV hydrogen storage alloy studied by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    We have studied the structural changes of Ti24Cr36V40 alloy prepared by arc-melting using positron annihilation spectroscopy and X-ray diffraction (XRD) as functions of the number of hydrogen pressure swing cycles and degassing temperature. As the hydrogen storage capacity decreased with the number of pressure swing cycles, both positron lifetime and XRD peak width increased. Upon hydriding, the crystal structure changed from bcc to bct with increased lattice constants. The increase in positron lifetime is due to the volume expansion caused by hydride formation. After degassing at 500 deg. C, the hydrogen storage capacity recovered to 95% of the initial level, and the XRD peak width and the lattice constants nearly completely returned to their initial values. However, the positron lifetime was still longer than the initial level suggesting the survival of dislocations. The degradation of hydrogen storage capacity is probably caused by both hydride formation and the generation of dislocations.

  10. A positron annihilation study of damage distribution in C+6 irradiated nickel

    International Nuclear Information System (INIS)

    Positron annihilation technique (PAT) is able to give a good quantitative result for both extended defects and simple defects. The sample thickness must fulfil the special requirement in positron annihilation measurement thus applications of PAT to study of damage distribution induced by heavy ion irradiation are seriously restricted. An attempt to tackle this problem has been made. A stack of samples of pure nickel was irradiated at ambient temperature under a vacuum of 1.33 x 10-4 Pa with 42.5 MeV/A C+6 ions at the Heavy Ion Research Facility of Lanzhou (HIRFL). The total dose was 1.33 x 1015 cm-2 at a current density of 2 x 109 cm-2s-1. Four adjacent samples as a grou whose thickness meets the requirement of PAT were successively taken out in the order of stacking and measured with a fast-fast coincidence system which had a resolution of 240 ps. By analysing the lifetime spectra with computer code, POSITRONFIT-EXTENDED, the distribution of reduced trapping rate, k, and mean lifetime, τ-bar, along the penetration depth of incident ions were obtained. The theoretical calculation of damage distribution was carried out with a computer program, HEDEP-1, that considered the nuclear force and extended the energy range of EDEP-1 to 100 MeV/A. The distribution of k, τ-bar, and calculated damage energy present similar trend but experimental damage peak was obviously widened. Furthermore the peak position is slightly shifted towards the incident direction of ions. These phenomena may be attributed to the average effect of four samples in positron annihilation measurement and some complicated factors introduced by irradiation with ions of such high energy in defect production

  11. Positron Annihilation Spectroscopy of High Performance Polymer Films under CO2 Pressure

    Energy Technology Data Exchange (ETDEWEB)

    C.A. Quarles; John R. Klaehn; Eric S. Peterson; Jagoda M. Urban-Klaehn

    2010-08-01

    Positron annihilation Lifetime and Doppler broadening measurements are reported for six polymer films as a function of carbon dioxide absolute pressure ranging from 0 to 45 psi. Since the polymer films were thin and did not absorb all positrons, corrections were made in the lifetime analysis for the absorption of positrons in the positron source and sample holder using the Monte Carlo transport code MCNP. Different polymers are found to behave differently. Some polymers studied form positronium and some, such as the polyimide structures, do not. For those samples that form positronium an interpretation in terms of free volume is possible; for those that don’t form positronium, further work is needed to determine how best to describe the behavior in terms of the bulk positron annihilation parameters. Some polymers exhibit changes in positron lifetime and intensity under CO2 pressure which may be described by the Henry or Langmuir sorption models, while the positron response of other polymers is rather insensitive to the CO2 pressure. The results demonstrate the usefulness of positron annihilation spectroscopy in investigating the sorption of CO2 into various polymers at pressures up to about 3 atm.

  12. Cold Positrons from Decaying Dark Matter

    Energy Technology Data Exchange (ETDEWEB)

    Boubekeur, Lotfi [Universitate de Valencia (Spain); Dodelson, Scott [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Vives, Oscar [Universitate de Valencia (Spain)

    2012-11-01

    Many models of dark matter contain more than one new particle beyond those in the Standard Model. Often heavier particles decay into the lightest dark matter particle as the Universe evolves. Here we explore the possibilities that arise if one of the products in a (Heavy Particle) $\\rightarrow$ (Dark Matter) decay is a positron, and the lifetime is shorter than the age of the Universe. The positrons cool down by scattering off the cosmic microwave background and eventually annihilate when they fall into Galactic potential wells. The resulting 511 keV flux not only places constraints on this class of models but might even be consistent with that observed by the INTEGRAL satellite.

  13. Positron annihilation studies of some charge transfer molecular complexes

    CERN Document Server

    El-Sayed, A; Boraei, A A A

    2000-01-01

    Positron annihilation lifetimes were measured for some solid charge transfer (CT) molecular complexes of quinoline compounds (2,6-dimethylquinoline, 6-methoxyquinoline, quinoline, 6-methylquinoline, 3-bromoquinoline and 2-chloro-4-methylquinoline) as electron donor and picric acid as an electron acceptor. The infrared spectra (IR) of the solid complexes clearly indicated the formation of the hydrogen-bonding CT-complexes. The annihilation spectra were analyzed into two lifetime components using PATFIT program. The values of the average and bulk lifetimes divide the complexes into two groups according to the non-bonding ionization potential of the donor (electron donating power) and the molecular weight of the complexes. Also, it is found that the ionization potential of the donors and molecular weight of the complexes have a conspicuous effect on the average and bulk lifetime values. The bulk lifetime values of the complexes are consistent with the formation of stable hydrogen-bonding CT-complexes as inferred...

  14. Positron-emission tomography

    International Nuclear Information System (INIS)

    Positron-emission tomography (PET) combines early biochemical assessment of pathology achieved by nuclear medicine with the precise localization achieved by computerized image reconstruction. In this technique a chemical compound with the desired biological activity is labeled with a radioactive isotope that decays by emitting a positron, or positive electron. With suitable interpretation PET images can provide a noninvasive, regional assessment of many biochemical processes that are essential to the functioning of the organ that is being visualized

  15. Lifetime of organic photovoltaics

    DEFF Research Database (Denmark)

    Corazza, Michael; Krebs, Frederik C; Gevorgyan, Suren A.

    2015-01-01

    tests. Comparison of the indoor and outdoor lifetimes was performed by means of the o-diagram, which constitutes the initial steps towards establishing a method for predicting the lifetime of an organic photovoltaic device under real operational conditions based on a selection of accelerated indoor...

  16. Computing Battery Lifetime Distributions

    NARCIS (Netherlands)

    Cloth, Lucia; Jongerden, Marijn R.; Haverkort, Boudewijn R.

    2007-01-01

    The usage of mobile devices like cell phones, navigation systems, or laptop computers, is limited by the lifetime of the included batteries. This lifetime depends naturally on the rate at which energy is consumed, however, it also depends on the usage pattern of the battery. Continuous drawing of a

  17. Study of Hg vacancies in (Hg,Cd)Te after THM growth and post-growth annealing by positron annihilation

    OpenAIRE

    Krause, R.; Klimakow, A.; Kießling, F. M.; Polity, A.; Gille, Peter; Schenk, M.

    1990-01-01

    Positron lifetime measurements have been performed to study vacancy defects in Hg0.78Cd0.22Te. Post-growth annealing under various Hg vapour pressure conditions have been used to create a well-defined number of Hg vacancies. The sensitivity range of the positron annihilation method was found to be 1015 < cHgvac

  18. Positronics of radiation-induced effects in chalcogenide glassy semiconductors

    International Nuclear Information System (INIS)

    Using As2S3 and AsS2 glasses as an example, the principal possibility of using positron annihilation spectroscopy methods for studying the evolution of the free volume of hollow nanoobjects in chalcogenide glassy semiconductors exposed to radiation is shown. The results obtained by measurements of the positron annihilation lifetime and Doppler broadening of the annihilation line in reverse chronological order are in full agreement with the optical spectroscopy data in the region of the fundamental absorption edge, being adequately described within coordination defect-formation and physical-aging models

  19. Positronics of radiation-induced effects in chalcogenide glassy semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, O. [Scientific Research Company “Carat” (Ukraine); Kozyukhin, S. A., E-mail: sergkoz@igic.ras.ru [Russian Academy of Sciences, Kurnakov Institute of General and Inorganic Chemistry (Russian Federation); Shpotyuk, M. [Scientific Research Company “Carat” (Ukraine); Ingram, A. [Opole Technical University (Poland); Szatanik, R. [Opole University (Poland)

    2015-03-15

    Using As{sub 2}S{sub 3} and AsS{sub 2} glasses as an example, the principal possibility of using positron annihilation spectroscopy methods for studying the evolution of the free volume of hollow nanoobjects in chalcogenide glassy semiconductors exposed to radiation is shown. The results obtained by measurements of the positron annihilation lifetime and Doppler broadening of the annihilation line in reverse chronological order are in full agreement with the optical spectroscopy data in the region of the fundamental absorption edge, being adequately described within coordination defect-formation and physical-aging models.

  20. Application of positron annihilation techniques in non-destructive testing

    International Nuclear Information System (INIS)

    Background: The investigation of the material damage state is very important for industrial application. Most mechanical damage starts with a change in the microstructure of the material. Positron annihilation techniques are very sensitive probes for detecting defects and damage on an atomic scale in materials, which are of great concern in the engineering applications. Additionally they are apparatus of non-destruction, high-sensitivity and easy-use. Purpose: Our goal is to develop a system to exploit new non-destructive testing (NDT) methods using positron annihilation spectroscopy, a powerful tool to detect vacancy-type defects and their chemical environment. Methods: A positron NDT system was designed and constructed by modifying the 'sandwich structure' of sample-source-sample in conventional Doppler broadening and positron lifetime spectrometers. Doppler broadening and positron lifetime spectra of a single sample can be measured and analyzed by subtracting the contribution of a reference sample. Results: The feasibility and reliability of positron NDT system have been tested by analyzing nondestructively deformation and damage caused by mechanical treatment or by irradiation of metal alloys. This system can be used for detecting defects and damage in thick or large-size samples, as well as for measuring the two-dimension distribution of defects in portable, sensitive, fast way. Conclusion: Positron NDT measurement shows changes in real atomic-scale defects prior to changes in the mechanical properties, which are detectable by other methods of NDT, such as ultrasonic testing and eddy current testing. This system can be developed for use in both the laboratory and field in the future. (authors)

  1. Effect of positron source irradiation on positronium annihilation in fine powdered alumina

    Science.gov (United States)

    Liu, Z. W.; Chen, Z. Q.

    2016-09-01

    Positron lifetime and Doppler broadening of positron annihilation radiation were measured as a function of time to study the irradiation effect by 22Na positron source in fine powdered alumina. The γ-Al2O3 samples were put in a vacuum chamber with a pressure of about 10-6 Torr and were cooled down to 10 K by a closed-cycle helium gas refrigerator. The irradiation of γ-Al2O3 samples by positron source was taken for a duration of about two days immediately after the sample was cooled down. After that, the sample was subjected to a warm up process from 10 K to 300 K with a step of 10 K. Positron lifetime and Doppler broadening spectra were measured simultaneously during these processes. Two long lifetime components corresponding to ortho-positronium annihilation were observed. A significant shortening of these long lifetime components and a large increase in S parameter is observed during irradiation. It is supposed that positron source irradiation creates a large number of paramagnetic centers on the surface of the γ-Al2O3 grains, which induce spin conversion quenching of positronium. The irradiation induced paramagnetic centers are unstable above 70 K and are nearly annealed out when the temperature rises to 190 K. After warming up of the sample to room temperature, the positron lifetime spectrum is identical to that before irradiation. It was also found that after irradiation, a medium long lifetime component of about 5 ns appears, of which the intensity increases with increasing irradiation time. This may be originated from the formation of the surface o-Ps state. This surface o-Ps state is also inhibited at elevated temperatures. Our results indicate that positronium is a very sensitive probe for the surface defects in porous materials.

  2. Micellar effects on positronium lifetime in aqueous SDS solutions

    International Nuclear Information System (INIS)

    Positron lifetime measurements have been performed in aqueous SDS (Sodium Dodecyl Sulphate) solutions. The lifetime distributions measured by fast-slow coincidence technique have been found to be influenced by surfactant concentration, which varied in the range of 1.25x10-3 - 3.2x10-1 mol/dm3 (i.e. 2.27x10-5 - 5.82x10-3 mole fractions). The lifetime of the long living component connected to positronium formation and decay increases with increasing surfactant concentration. Lifetime data suggest that a direct positronium-micelle electron-exchange reaction leading to pick-off annihilation is contraindicated. (author)

  3. Theory of Beauty Lifetimes

    OpenAIRE

    Neubert, Matthias(PRISMA Cluster of Excellence and Mainz Institut for Theoretical Physics, Johannes Gutenberg University, 55099, Mainz, Germany)

    1997-01-01

    A critical review of the theoretical understanding of the lifetimes of beauty hadrons is given. A model-independent analysis using the heavy-quark expansion allows for a description of the lifetime ratios tau(B-)/tau(B0) and tau(Lambda_b)/tau(B0) in a small region of parameter space. It is demonstrated that the lifetime ratio tau(B-)/tau(B0) cannot be used to extract the decay constant of the B meson. Implications for the semileptonic branching ratio and charm yield in B decays are pointed out.

  4. Customer Lifetime Value Measurement

    OpenAIRE

    Sharad Borle; Siddharth S. Singh; Dipak C. Jain

    2008-01-01

    The measurement of customer lifetime value is important because it is used as a metric in evaluating decisions in the context of customer relationship management. For a firm, it is important to form some expectations as to the lifetime value of each customer at the time a customer starts doing business with the firm, and at each purchase by the customer. In this paper, we use a hierarchical Bayes approach to estimate the lifetime value of each customer at each purchase occasion by jointly mod...

  5. 169Lu positron decay

    International Nuclear Information System (INIS)

    The object of the investigation is the positron decay spectrum of 169Lu. The isotope under study was obtained by irradiating a tantalum target with 660 MeV protons. The spectra of positrons and conversion electrons were investigated by means of an air-core toroidal β spectrometer. When processing the spectra coefficients were introduced, which took into account the efficiency of β particle detection, backscattering of β particles in a source substrate, and the shape of spectrometer lines. The Fermi-Curie plot obtained as a result of processing the experimental spectrum of 169Lu is presented. The ratio of the intensities of positron components to that of the K conversion line of the 199 keV transition is determined. The relative intensity of the 169Lu positron decay is Isub(β)sup(+)=0.56+-0.07% of the total number of decays. The mass difference 169Lu-169Yt is equal to 2293+-3 keV. The 169Lu positron spectrum served to determine the matrix element for the β transition (log ft=8.0+-0.1) and the intensity of electron capture into the ground state of 169Yb (11.4+-1.6%)

  6. Positron sensing of distribution of defects in depth materials

    Science.gov (United States)

    Kupchishin, A. I.; Kupchishin, A. A.; Voronova, N. A.; Kirdyashkin, V. I.

    2016-02-01

    It was developed a non-destructive method of positron sensing, which allows to determine the distribution of defects in the depth of the material. From the analysis we can conclude that the angular distribution curves of annihilation photons (well as and on the characteristics in experiments on the lifetime, 3γ - angular correlation, Doppler effect) is influenced by three main factors: a) The distribution of defects in the depth of the material, their dimensions as well as parameters of the interaction of positrons with defects. With increasing the concentration of defects the intensity Jγ(a, ξ) varies more; b) Modification of the energy spectrum of slow positrons due to the influence of defects, wherein the spectrum of positrons becomes softer, and the average energy of the positron annihilation is reduced; c) Deformation of the momentum distribution of the electrons in the region of defect. The energy spectrum of electrons is also becomes softer, and the average energy of the electrons (on which positrons annihilate) is less. The experimentally were measured spectra of photons in the zone of annihilation and were calculated the distribution of defects in depth for a number of metals.

  7. Positron spectroscopy and its applications

    International Nuclear Information System (INIS)

    Positrons are the antiparticles of electrons, and their mass is m (the stationary mass of an electron) and their charge is e (the charge of an electron is -e). Accordingly, in principle only by reversing the polarity of measuring systems, the positron version of the analysis methods utilizing electrons becomes feasible, such as low energy positron diffraction (LEPD), reflection high energy positron diffraction (RHEPD) and transmission positron microscope (TPM), and except the problem of beam intensity, there are much merits than electrons. Positrons are the stable particles that do not have peculiar life similarly to electrons, but since matters are composed of electrons and atomic nuclei in this world, the pair annihilation with electrons occurs. At the time of pair annihilation, gamma-ray is emitted, and this gamma-ray transmits the information on the life of positrons. The individual character and possibility of positrons as a physical property probe, the interaction of positrons with matters, the sources of positrons, the analysis method utilizing positrons, the concrete examples of utilizing positron beam and the future perspective of positron utilization as probes are reported. (K.I.) 83 refs

  8. Positron annihilation in medical substances of insulin

    International Nuclear Information System (INIS)

    Positrons lifetimes were measured in medical substances of insulin (human and animal), differing as far as the degree of purity and time of their activity in the organism are concerned. In all of the cases the spectrum of positron lifetime was distributed into three components, with the long-life component ranging from 1.8 to 2.08 ns and the intensity taking on values from 18% to 24%. Making use of Tao-Eldrup model, the average radius of the free volume, in which o-Ps annihilated, and the degree of filling in the volume were determined. It was found that the value of the long-life component for human insulin is higher than that of animal insulin. Moreover, the value of this component clearly depends on the manner of purification of the insulin. It was also noticed that there occurs a correlation between the value of this component and the time after which it begins to be active in the organism, as well as the total time of its activity. (author)

  9. Positron Annihilation in Medical Substances of Insulin

    Science.gov (United States)

    Pietrzak, R.; Szatanik, R.

    2005-05-01

    Positrons lifetimes were measured in medical substances of insulin (human and animal), differing as far as the degree of purity and time of their activity in the organism are concerned. In all of the cases the spectrum of positron lifetime was distributed into three components, with the long-life component ranging from 1.8 to 2.08 ns and the intensity taking on values from 18 to 24%. Making use of Tao-Eldrup model, the average radius of the free volume, in which o-Ps annihilated, and the degree of filling in the volume were determined. It was found that the value of the long-life component for human insulin is higher than that of animal insulin. Moreover, the value of this component clearly depends on the manner of purification of the insulin. It was also noticed that there occurs a correlation between the value of this component and the time after which it begins to be active in the organism, as well as the total time of its activity.

  10. Simulation of the annihilation emission of galactic positrons

    International Nuclear Information System (INIS)

    Positrons annihilate in the central region of our Galaxy. This has been known since the detection of a strong emission line centered on an energy of 511 keV in the direction of the Galactic center. This gamma-ray line is emitted during the annihilation of positrons with electrons from the interstellar medium. The spectrometer SPI, onboard the INTEGRAL observatory, performed spatial and spectral analyses of the positron annihilation emission. This thesis presents a study of the Galactic positron annihilation emission based on models of the different interactions undergone by positrons in the interstellar medium. The models are relied on our present knowledge of the properties of the interstellar medium in the Galactic bulge, where most of the positrons annihilate, and of the physics of positrons (production, propagation and annihilation processes). In order to obtain constraints on the positrons sources and physical characteristics of the annihilation medium, we compared the results of the models to measurements provided by the SPI spectrometer. (author)

  11. Positron emission tomography

    CERN Document Server

    Paans, A M J

    2006-01-01

    Positron Emission Tomography (PET) is a method for measuring biochemical and physiological processes in vivo in a quantitative way by using radiopharmaceuticals labelled with positron emitting radionuclides such as 11C, 13N, 15O and 18F and by measuring the annihilation radiation using a coincidence technique. This includes also the measurement of the pharmacokinetics of labelled drugs and the measurement of the effects of drugs on metabolism. Also deviations of normal metabolism can be measured and insight into biological processes responsible for diseases can be obtained. At present the combined PET/CT scanner is the most frequently used scanner for whole-body scanning in the field of oncology.

  12. 50 years of positrons

    International Nuclear Information System (INIS)

    This year marks the 50th anniversary of one of the major landmarks of modern physics - the discovery of the positron, the antimatter counterpart of the electron. This provided the first evidence for antimatter, and it was also unprecedented for the existence of a new particle to have been predicted by theory. The positron and the concepts behind it were to radically change our picture of Nature. It led to the rapid advancement or our understanding, culminating some fifteen years later with the formulation of quantum electrodynamics as we now know it. (orig./HSI).

  13. Positron annihilation as a tool in structural chemistry

    International Nuclear Information System (INIS)

    Complete text of publication follows. The paper will demonstrate that the positron annihilation spectroscopy (PAS) is an excellent tool to follow the structural changes in chemical species. After the presentation of the physical background and the techniques of the measurements of PAS we show four examples of applications. The sizes of defects in electrodeposited chromium layers were studied and estimated on the basis of positron lifetime spectra decomposed into two components. Vacancies, divacancies and vacancy-clusters could be identified in the electrodeposites. Positron lifetime measurements were performed to study the swelling dynamics of an amphiphilic polymer network (APN). Lifetime spectroscopy proved to be suitable to investigate APNs. Very quick structural changes were indicated by lifetime parameters at very low swelling ratios. On the basis of the results a possible mechanism is proposed for the hydration of the investigated materials. The ortho-para conversion of ortho-Ps was used to follow the partial spin-crossover in [Fe(1-alkyl-1H-tetrazole)6](BR4)2. If there are structural free volumes large enough (as for [Fe(1-ethyl-1H-tetrazole)6](BF4)2 and [Fe(1-propyl-1H-tetrazole)6](BF4)2), there is a significant intensity of positronium (Ps) and the lifetime of o-Ps is a detector of spin-crossover. A conformal structural transformation was found in [Zn(1-propyl-1H-tetrazole)6(BF4)2 between 170 and 90 K by positronium lifetime measurement and the role of (BF4)2- anion, in this transformation was proved by 19F NMR spectroscopy

  14. Irradiation-induced defects in ZnO studied by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    We have used positron annihilation spectroscopy to study the point defects induced by 2 MeV electron irradiation (fluence 6 x 1017 cm-2) in single crystal n-type ZnO samples. The positron lifetime measurements have shown that the zinc vacancies in their doubly negative charge state, which act as dominant compensating centers in the as-grown material, are produced in the irradiation and their contribution to the electrical compensation is important. The lifetime measurements reveal also the presence of competing positron traps with low binding energy and lifetime close to that of the bulk lattice. The analysis of the Doppler broadening of the 511 keV annihilation line indicates that these defects can be identified as neutral oxygen vacancies. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Moessbauer and positron annihilation studies of structural modifications of hemoglobin in solution

    International Nuclear Information System (INIS)

    Structural modifications of human adult oxyhemoglobin in concentrated solution were studied by Moessbauer and positron life-time spectroscopies. The effects of non-sterile degradation and irradiation by γ-rays were compared by both techniques. It was found that positron annihilation parameters were sensitive to the structural modifications of hemoglobin molecules in solution and could be related with the conformational states of hemoglobin. (author)15 refs.; 3 tabs

  16. Development of instrumentation and methods for positron spectroscopy of defects in semiconductors

    OpenAIRE

    Nissilä, Jaani

    2001-01-01

    Instrumentation and methods for positron annihilation spectroscopy of point defects in semiconductors have been developed. In particular, techniques to enhance the stability of positron lifetime spectrometers have been investigated. The ageing of the photomultiplier tubes (PMT) of the scintillation detectors can be slowed down by lowering the operating voltages over the PMTs and by compensating the lower gain with fast preamplifiers. The timing characteristics of the apparatus are preserved i...

  17. Structural transition of partially Ba-filled thermoelectric CoSb3 investigated by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Microstructure of unfilled and Ba-filled CoSb3 has been studied by positron lifetime measurements together with theoretical calculation. Positron trapping in intrinsic voids is observed in the CoSb3, which contributes a positron lifetime of 263 ± 2 ps. After filling Ba atoms with content up to x = 0.4, the positron lifetime shows continuous increase. By comparing the experimental results with calculation following the phase diagram of BaxCo4Sb12 with x in the range of 0–0.5, it is found that when the Ba content is lower than 0.16, the filling of Ba atoms is in a phase of solid solution. At x = 0.2, γ phase is formed, which is mixed with solid solution. At x > 0.25, transition from γ phase to a mixture of γ and α phases is confirmed

  18. Positron clouds within thunderstorms

    CERN Document Server

    Dwyer, Joseph R; Hazelton, Bryna J; Grefenstette, Brian W; Kelley, Nicole A; Lowell, Alexander W; Schaal, Meagan M; Rassoul, Hamid K

    2015-01-01

    We report the observation of two isolated clouds of positrons inside an active thunderstorm. These observations were made by the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of six gamma-ray detectors, which flew on a Gulfstream V jet aircraft through the top of an active thunderstorm in August 2009. ADELE recorded two 511 keV gamma-ray count rate enhancements, 35 seconds apart, each lasting approximately 0.2 seconds. The enhancements, which were about a factor of 12 above background, were both accompanied by electrical activity as measured by a flat-plate antenna on the underside of the aircraft. The energy spectra were consistent with a source mostly composed of positron annihilation gamma rays, with a prominent 511 keV line clearly visible in the data. Model fits to the data suggest that the aircraft was briefly immersed in clouds of positrons, more than a kilometer across. It is not clear how the positron clouds were created within the thunderstorm, but it is possible they were ca...

  19. Positron emission tomography

    International Nuclear Information System (INIS)

    The aim of this project is to provide a simple summary of new trends in positron emission tomography and its basic physical principles. It provides thereby compendious introduction of the trends of the present development in diagnostics using PET systems. A review of available literature was performed. (author)

  20. 151Tb positron decay

    International Nuclear Information System (INIS)

    The positron and (K251-β+)-coincidence spectra produced in the 151Tb are studied decay. The positron spectrum was detected by means of toroidal beta-spectrometers. The content of the 152Tb isotope impurity in 151Tb monoisotope sources was not more than 0.3 per cent. The β+-spectrum components and the Fermi-Curie diagram are shown. The ratio of positron intensity of that of K-conversion electrons of the 287.2 keV transition has been found Isub(β+)/Isub(K287.2)=0.36+-0.02. The 151Tb positron decay intensity has been determined: Isub(β+)=0.92+-0.12%. A fragment of the 1+H51Cd excited state scheme is shown. The experimental lg ft values for β-transitions in the 151Tb decay into excited states of 151Cd with the energies of 838.3 2 and 395.2 keV, equal to 6.46+-0.10 and 7.9+-0.1, are consistent with the ground state spin of 1/2 found for 151Tb by other authors

  1. Positron emission tomography

    International Nuclear Information System (INIS)

    Positron emission tomography (PET) is a method for quantitative imaging of regional physiological and biochemical parameters. Positron emitting radioactive isotopes can be produced by a cyclotron, eg. the biologically important carbon (11C), oxygen (15O), and nitrogen (13N) elements. With the tomographic principles of the PET scanner the quantitative distribution of the administered isotopes can be determined and images can be provided as well as dynamic information on blood flow, metabolism and receptor function. In neurology PET has been used for investigations on numerous physiological processes in the brain: circulation, metabolism and receptor studies. In Parkinson's disease PET studies have been able to localize the pathology specifically, and in early stroke PET technique can outline focal areas with living but non-functioning cells, and this could make it possible to intervene in this early state. With positron emission tomography a quantitative evaluation of myocardial blood flow, glucose and fatty acid metabolism can be made as well as combined assessments of blood flow and metabolism. Combined studies of blood flow and metabolism can determine whether myocardial segments with abnormal motility consist of necrotic or viable tissue, thereby delineating effects of revascularisation. In the future it will probably be possible to characterize the myocardial receptor status in different cardiac diseases. The PET technique is used in oncology for clinical as well as more basic research on tumor perfusion and metabolism. Further, tumor uptake of positron labelled cytotoxic drugs might predict the clinical benefit of treatment. (au) (19 refs.)

  2. A positron annihilation study on the hydration of cement pastes

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectroscopy experiments were carried out in various ordinary Portland cement pastes, in an attempt to monitor the porosity of the pastes. It is found that positronium intensity is well correlated to the time evolution of the total porosity and it is influenced by the water-to-cement ratio. This parameter is also sensitive to the delayed hydration process induced by adding methanol to the water-cement mixture

  3. Imaging optimizations with non-pure and high-energy positron emitters in small animal positron computed tomography

    International Nuclear Information System (INIS)

    The contribution on imaging optimizations with non-pure and high-energy positron emitters in small animal positron emission tomography (PET) covers the following topics: physical fundamentals of PET, mathematical image reconstruction and data analyses, Monte-Carlo simulations and implemented correction scheme, quantification of cascade gamma coincidences based on simulations and measurements, sinogram based corrections, restoration of the spatial resolution, implementation of full corrections.

  4. Positron trapping in vacancies in indium doped CdTe crystals

    Science.gov (United States)

    Gély-Sykes, C.; Corbel, C.; Triboulet, R.

    1991-10-01

    In weakly n-type CdTe(In) crystals grown by the travelling heater method, positrons annihilate in vacancy-type defects with a lifetime of 320 ± 4 ps. The concentration of these native defects varies with the concentration of indium and electron in agreement with the model of self-compensation where the indium donors are compensated by indium-vacancy complexes. These defects are assumed to be (V CdIn) - complexes. The positron trapping in these complexes disappears at low temperature. This phenomenon is attributed to competing trapping of positrons by negative ions which are either residual impurities or intrinsic defects.

  5. Application of positron beams to the study of positronium-forming solids

    International Nuclear Information System (INIS)

    Doppler broadening of annihilation radiation (DBAR) and positron annihilation lifetime spectroscopy (PALS) have been successfully applied to the study of positronium (Ps)-forming amorphous solids such as polymers and silicon oxide in the bulk. Implementing depth selectivity to DBAR and PALS by combining them with variable-energy positron beams considerably broadens their applicability. Variation of incident positron energy over a wide range enables depth-profiling, whereas tuning of the beam energy enables the studies of surfaces, interfaces and thin films. In this paper, we discuss fundamentals and applications of energy variable DBAR and PALS for Ps-forming polymers and silicon oxide

  6. Radiative lifetimes of Tb

    Energy Technology Data Exchange (ETDEWEB)

    Den Hartog, E. A.; Fedchak, J. A.; Lawler, J. E.

    2001-06-01

    Radiative lifetimes measured by time-resolved laser-induced fluorescence are reported for 40 odd-parity levels and 36 even-parity levels of singly ionized terbium. The odd-parity levels range in energy from 29000 to 40000 cm{minus}1 and those of even-parity from 21000 to 37000 cm{minus}1. These lifetimes, with one exception, are accurate to {+-}5%. They will provide an absolute scale for accurate atomic-transition probabilities in Tb II (the second spectrum of terbium). {copyright} 2001 Optical Society of America

  7. Radiative lifetimes of Tb

    International Nuclear Information System (INIS)

    Radiative lifetimes measured by time-resolved laser-induced fluorescence are reported for 40 odd-parity levels and 36 even-parity levels of singly ionized terbium. The odd-parity levels range in energy from 29000 to 40000 cm-1 and those of even-parity from 21000 to 37000 cm-1. These lifetimes, with one exception, are accurate to ±5%. They will provide an absolute scale for accurate atomic-transition probabilities in Tb II (the second spectrum of terbium). [copyright] 2001 Optical Society of America

  8. Nanohole formation in TEOS-HMDSO hybrid CVD films elucidated by positron beams

    International Nuclear Information System (INIS)

    Silicon-oxide-backboned hybrid thin films with thicknesses around 600 nm were fabricated through plasma enhanced chemical vapor deposition from tetraethyl orthosilicate mixed with hexamethyldisiloxane as precursors, and their subnano-scaled holes, generated by annealing at 560 °C, were investigated by means of the positron lifetime technique with a pulsed, low-energy positron beam. The hole dimension was quantified from the ortho-positronium lifetime for the as-prepared and annealed films with different compositions. The effect of the heat treatment and the precursor composition on the subnano holes was discussed.

  9. New system for a pulsed slow-positron beam using a radioisotope

    CERN Document Server

    Hamada, E; Suzuki, T; Kobayashi, H; Kondo, K; Kanazawa, I; Ito, Y

    2000-01-01

    To analyze the surface of polymers using positron-annihilation lifetime spectroscopy (PALS), a pulsed slow-positron beam system having both a high pulsing efficiency and a good time resolution is now under development. The time resolution, which is defined by the full width at half maximum (FWHM), and the pulsing efficiency of this system were achieved to be 0.54 ns and 50%, respectively. The lifetime of ortho-positronium (o-Ps) in low-density polyethylene (LDPE), obtained by PALS using our new pulsing system, agreed with that obtained by a conventional PALS.

  10. New system for a pulsed slow-positron beam using a radioisotope

    International Nuclear Information System (INIS)

    To analyze the surface of polymers using positron-annihilation lifetime spectroscopy (PALS), a pulsed slow-positron beam system having both a high pulsing efficiency and a good time resolution is now under development. The time resolution, which is defined by the full width at half maximum (FWHM), and the pulsing efficiency of this system were achieved to be 0.54 ns and 50%, respectively. The lifetime of ortho-positronium (o-Ps) in low-density polyethylene (LDPE), obtained by PALS using our new pulsing system, agreed with that obtained by a conventional PALS.

  11. Positron annihilation and thermally stimulated current of electron beam irradiated polyetheretherketone

    Energy Technology Data Exchange (ETDEWEB)

    Fujita, Shigetaka; Shinyama, Katsuyoshi; Baba, Makoto [Hachinohe Inst. of Tech., Hachinohe, Aomori (Japan); Suzuki, Takenori

    1997-03-01

    Positron lifetime measurements were applied to electron beam irradiated poly(ether-ether-ketone). The lifetime, {tau}{sub 3}, of the ortho-positronium of unirradiated and 5 MGy irradiated specimen became rapidly longer above about 150degC. {tau}{sub 3} of 50 MGy and 100 MGy irradiated specimen was shorter than that of unirradiated one. Thermally stimulated current (TSC) decreased with increasing the dose before voltage application. In the case of voltage application, a TSC peak appeared and the peak value decreased with increased the dose. The correlation between the results of positron annihilation and TSC was investigated. (author)

  12. Development of a sample chamber with humidity control for an atmospheric positron probe microanalyzer

    International Nuclear Information System (INIS)

    In order to perform positron lifetime measurements on thin films under atmospheric conditions, a slow positron microbeam was extracted into air using silicon nitride thin films (30 nm and 200 nm) as a vacuum window. Even the thinner window (30 nm) was found to reliably withstand a differential pressure of 1 atm under various stress tests. By placing the sample in an enclosed chamber through which gas with a fixed, controllable relative humidity (RH) was continuously passed, the RH dependence of the ortho-positronium lifetime for bulk fused silica was examined.

  13. Correlations between Positron Annihilation Parameters and Macroscopic Properties in Copolymers Belonging to Elastomers Group

    Science.gov (United States)

    Krzemień, K.; Kansy, J.

    2008-05-01

    The positron annihilation lifetime spectroscopy was used to study correlations between positron annihilation parameters and macroscopic properties in two kinds of polymers from elastomers group. Two kinds of material were investigated: three samples of ethylene octane copolymers (commercial name engage) of different densities and six samples of polybutylene terephtalate-polyether glycol copolymers (hytrel) having different densities. A correlation between intensity of ortho-positronium component and the density (d) of samples was observed for both kinds of material. From the ortho-positronium pick-off lifetime the mean radii (R) of free volume centers were determined. A good linear correlation between R and d was found.

  14. Positron annihilation study of Y-Ba-Cu-O high-T/sub c/ superconductors

    International Nuclear Information System (INIS)

    Detailed positron annihilation measurements are reported on high-T/sub c/ superconductors YBa2Cu3O/sub 7-//sub x/. The lifetime and Doppler-broadening spectra show a significant change at about 240 K indicating a structural change in the sample far above 90 K where the resistance falls to zero. An analysis of the lifetime spectra shows positron trapping without any sign of saturation, indicating low specific trapping rates. On this basis, the charge states of Cu-O structures and a possible local charge decomposition are discussed

  15. Slow positron beam study of corrosion-related defects in pure iron

    International Nuclear Information System (INIS)

    Corrosion-related defects of pure iron were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL). Defect profiles of the S-parameter from DBES as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) were analyzed. The DBES data show that S-parameter increases as a function of positron incident energy (mean depth) after corrosion, and the increase in the S-parameter is larger near the surface than in the bulk due to corrosion. Furthermore, information on defect size from PAL data as a function of positron incident energy up to 10 keV (i.e. ∼0.2 μm depth) was analyzed. In the two-state trapping model, the lifetime τ 2 = 500 ps is ascribed to annihilation of positrons in voids with a size of the order of nanometer. τ 1, which decreases with depth from the surface to the bulk, is ascribed to the annihilation of positrons in dislocations and three-dimensional vacancy clusters. The corroded samples show a significant increase in τ 1 and the intensity I 2, and near the surface the corroded iron introduces both voids and large-size three-dimensional vacancy clusters. The size of vacancy clusters decreases with depth

  16. Positron scattering from tetrahydrofuran

    Science.gov (United States)

    Brunger, M. J.; Chiari, L.; Tattersall, W.; Anderson, E.; Machacek, J.; Makochekanwa, C.; Sullivan, J.; Buckman, S. J.

    2012-10-01

    We present recent experimental results for positron scattering from tetrahydrofuran. Being a model for the deoxyribose sugar rings in the nucleic acids backbone, tetrahydrofuran is of particular interest for investigating radiation damage in biomolecular systems. The measurements on this species were carried out using the atomic and molecular trap-based positron beamline at The Australian National University with an energy resolution of ˜60 meV. Total cross sections and integral cross sections for the positronium formation, elastic and inelastic (direct ionization and electronic excitation) scattering channels are presented over the energy range of 1-190 eV. Low-energy elastic differential cross sections are also presented at selected energies between 1 eV and 25 eV. A fairly good agreement is found with the total cross section results from the only existing previous experimental investigation on this target species by the Trento group.

  17. Positrons as imaging agents and probes in nanotechnology

    Science.gov (United States)

    Smith, Suzanne V.

    2009-09-01

    Positron emission tomography (PET) tracks a positron emitting radiopharmaceutical injected into the body and generates a 3-dimensional image of its location. Introduced in the early 70s, it has now developed into a powerful medical diagnostic tool for routine clinical use as well as in drug development. Unrivalled as a highly sensitive, specific and non-invasive imaging tool, PET unfortunately lacks the resolution of Computer Tomography (CT) and Magnetic Resonance Imaging (MRI). As the resolution of PET depends significantly on the energy of the positron incorporated in the radiopharmaceutical and its interaction with its surrounding tissue, there is growing interest in expanding our understanding of how positrons interact at the atomic and molecular level. A better understanding of these interactions will contribute to improving the resolution of PET and assist in the design of better imaging agents. Positrons are also used in Positron Annihilation Lifetime Spectroscopy (PALS) to determine electron density and or presence and incidence of micro- and mesopores (0.1 to 10 nm) in materials. The control of porosity in engineered materials is crucial for applications such as controlled release or air and water resistant films. Equally important to the design of nano and microtechnologies, is our understanding of the microenvironments within these pores and on surfaces. Hence as radiopharmaceuticals are designed to track disease, nuclear probes (radioactive molecules) are synthesized to investigate the chemical properties within these pores. This article will give a brief overview of the present role of positrons in imaging as well as explore its potential to contribute in the engineering of new materials to the marketplace.

  18. New techniques of positron annihilation

    International Nuclear Information System (INIS)

    Studies on new techniques of positron annihilation and its application to various fields are presented. First, production of slow positron and its characteristic features are described. The slow positron can be obtained from radioisotopes by using a positron moderator, proton beam bombardment on a boron target, and pair production by using an electron linear accelerator. Bright enhancement of the slow positron beam is studied. Polarized positron beam can be used for the study of the momentum distribution of an electron in ferromagnetic substances. Production of polarized positrons and measurements of polarization are discussed. Various phases of interaction between slow positrons and atoms (or molecules) are described. A comparative study of electron scavenging effects on luminescence and on positronium formation in cyclohexane is presented. The positron annihilation phenomena are applicable for the surface study. The microscopic information on the surface of porous material may be obtained. The slow positrons are also useful for the surface study. Production and application of slow muon (positive and negative) are presented in this report. (Kato, T.)

  19. HI-positron production

    International Nuclear Information System (INIS)

    New results concerning the spectrum of positrons produced in U-U, U-Pb and Pb-Pb collisions - the inherent experimental problems and the initiative taken in overcoming these - are presented. The production probabilities obtained so far follow an interesting exponential behavior. The characteristic parameters, time and energy, describing these can be derived from a simplified picture for the monopole pair production which follows the theory of Greiner et al. (orig.)

  20. Review of positron annihilation spectroscopy studies of rubber with carbon black filler

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectra have been measured for rubber polymers with carbon black (CB) fillers as a function of temperature, sulfur concentration, type of CB fillers and type of polymer. The purpose of the study is to understand how the CB fillers and other components of the vulcanized composite affect the positron lifetime in polymer materials. The polymer samples to be studied include natural rubber (NR) with different sulfur concentration, Sn-SSBR either unloaded or loaded with CB N115 or N762, both vulcanized and unvulcanized Duradene 706 samples. The results show that CB fillers have no effect on the ortho-positronium lifetime but decrease the intensity of ortho-positronium; and the decrease in intensity depends on the type of CB. On the other hand both ortho-positronium lifetime and intensity decrease as a function of sulfur concentration

  1. 171Lu positron decay

    International Nuclear Information System (INIS)

    The purpose of the investigation is experimental and theoretical study of the 171Lu positron decay. 171Lu sources were prepared by two methods: chemical and chromatographic ones. In all the measurements a one-component positron spectrum was observed. The Fermi-Curie plot is a straight line within experimental errors. The intensity of positrons Isub(βsup(+)) with respect to the conversion electron spectrum Isub(c) was measured. The mean value of Isub(βsup(+))/Isub(c739)=0.074+-0.006. The mass difference 171Lu-171Yb was estimated from the β+-decay of 171Lu: Qsub(βsup(+))=1479+-3 keV. Mass differences of 171Lu - 171Yb, known from other investigations, are given for comparison. In the 171Lu β+- decay (ground state 7/2+[404]) the 95.26 keV (7/2+[633]) excited level of 171Yb is populated. The value of log ft for this β transition was found to be 8+-1. Theoretical calculations of log ft and the form factors of this transition were also made. Very good or satisfactory agreement between the theoretical and experimental values of log ft was obtained. The degree of agreement depends on the choice of wave functions in calculations. The experimental value of log ft for the 171Lu→171Yb β transition agrees well with the experimental values of log ft for the same type of β transitions in other nuclei

  2. Detection of non stoichiometric vacancy defects in CdTe, HgTe and Hg1-xCdxTe by positron annihilation

    International Nuclear Information System (INIS)

    Native vacancies are evidenced from positron lifetime measurements in as-grown CdTe, HgTe and Hg0.8Cd0.2Te. The positron lifetime depends on the conducting type of the materials rather than on the growing conditions. The native vacancies have two levels of ionisation and are identified as Cd-vacancies (VCd) in CdTe. (author) 2 figs., 2 tabs., 9 refs

  3. Positron annihilation and magnetic properties studies of copper substituted nickel ferrite nanoparticles

    Science.gov (United States)

    Kargar, Z.; Asgarian, S. M.; Mozaffari, M.

    2016-05-01

    Single phase copper substituted nickel ferrite Ni1-xCuxFe2O4 (x = 0.0, 0.1, 0.3 and 0.5) nanoparticles were synthesized by the sol-gel method. TEM images of the samples confirm formation of nano-sized particles. The Rietveld refinement of the X-ray diffraction patterns showed that lattice constant increase with increase in copper content from 8.331 for x = 0.0 to 8.355 Å in x = 0.5. Cation distribution of samples has been determined by the occupancy factor, using Rietveld refinement. The positron lifetime spectra of the samples were convoluted into three lifetime components. The shortest lifetime is due to the positrons that do not get trapped by the vacancy defects. The second lifetime is ascribed to annihilation of positrons in tetrahedral (A) and octahedral (B) sites in spinel structure. It is seen that for x = 0.1 and 0.3 samples, positron trapped within vacancies in A sites, but for x = 0.0 and 0.5, the positrons trapped and annihilated within occupied B sites. The longest lifetime component attributed to annihilation of positrons in the free volume between nanoparticles. The obtained results from coincidence Doppler broadening spectroscopy (CDBS) confirmed the results of positron annihilation lifetime spectroscopy (PALS) and also showed that the vacancy clusters concentration for x = 0.3 is more than those in other samples. Average defect density in the samples, determined from mean lifetime of annihilated positrons reflects that the vacancy concentration for x = 0.3 is maximum. The magnetic measurements showed that the saturation magnetization for x = 0.3 is maximum that can be explained by Néel's theory. The coercivity in nanoparticles increased with increase in copper content. This increase is ascribed to the change in anisotropy constant because of increase of the average defect density due to the substitution of Cu2+ cations and magnetocrystalline anisotropy of Cu2+ cations. Curie temperature of the samples reduces with increase in copper content which

  4. Irradiation-induced defects in silica glass studied by positron annihilation, ESR and optical absorption

    International Nuclear Information System (INIS)

    Fused and Synthetic silica glass samples were irradiated with fast neutrons up to a dose of 8.6 x 1018 n/cm2. Before and after irradiation, positron lifetime, angular correlation of positron annihilation radiation (ACAR), electron spin resonance (ESR) and optical absorption with photon energy ranging from 2 to 6.6 eV were measured. Positron lifetime spectra were decomposed into three components with the time constant τi (i=1,2,3) and their relative intensities Ii (I1+I2+I3=1). After irradiation, two kinds of defects which trap positrons were suggested by positron lifetime spectra: the type-1 defect gives a positron lifetime of about 0.3 ns for the τ1 component, while the type 2 gives about 0.5 ns of the τ2 lifetime. In ESR spectra of the irradiated samples, three kinds of paramagnetic defects were observed.: E' centers, peroxy radicals (POR) and non-bridging oxygen hole center (NBOHC). In optical absorption spectra, absorption bands around 4.8, 5.0, 5.4 and 5.8 eV were resolved. Photo-bleaching effects of ultraviolet rays with energy of 4.9 eV on E' center and POR in ESR spectra and on the 5.0, 5.4 and 5.8 absorption bands were observed, but no change was detected in the 4.8 band. No photo-bleaching effect, however, was obtained in the positron lifetime spectra. Positron lifetime and ESR measurements were also made after post-irradiation isochronal annealing. Detailed results from the photo-bleaching and the annealing experiments strongly suggest that the type 2 defect is not detected by ESR and hence a diamagnetic defect, while that the type 1 defect is a paramagnetic defect, possibly NBOHC. Both kinds of the defects, however, gave nearly the same ACAR momentum distribution, which reveals that the two kind defects are associated with the same valence electrons of oxygen related centers. (author)

  5. Annihilation Of Fast Channeled Positrons

    CERN Document Server

    Hunt, A W

    2000-01-01

    Energetic positrons propagating along low index directions in a crystal interact strongly with the periodic array of atoms via a process known as channeling. These channeled positrons are focused into the interstices of a crystal by a series of highly correlated small angle scattering events, thereby suppressing close nuclear collision processes and increasing interactions with valence electrons. Moreover, the positron trajectories can be manipulated to sample different spatial regions in the crystal, simply by changing the direction of the incident positron beam. As this direction deviates from that of the low index crystal direction the positron momentum transverse to this crystal direction increases, and the trajectories penetrate closer to the atomic nuclei of the crystal's atoms. Thus when observing the angular yield of close encounter events with the atomic nuclei, like wide angle Rutherford scattering, a characteristic channeling dip is obtained for positive ions and positrons traversing thin crystals[...

  6. QCD and electroweak analysis and first measurement of neutral and charged current cross section with the polarised positron beam at HERA 2; Premiere mesure des sections efficaces de courant charge et neutre avec le faisceau de positrons polarise a HERA 2 et analyses QCD-electrofaibles

    Energy Technology Data Exchange (ETDEWEB)

    Portheault, B

    2005-03-15

    In 2003-2004 the HERA collider delivered e{sup +}p collisions with a longitudinally polarised positron beam. We prescribe the measurement of inclusive Neutral and Charged Current DIS (deep inelastic scattering) cross section using the H1 detector. The total Charged Current cross section for Q{sup 2} > 400 GeV{sup 2}, y < 0,9 is measured with a Right-handed (P = 0,33) sample of 15,3 pb{sup -1} and a Left-handed (P = -0,40) sample of 21,7 pb{sup -1} yielding {sigma}cc (P = +0,33) = 34,67 pb {+-} 1,94 pb (stat) {+-} 1,66 pb (sys) C.20) {sigma}cc(P = -0,40) = 13,80 pb {+-} 1,04 pb (stat) {+-} 0,94 pb (sys). C.21) This result is consistent with the proportionality of the cross section with respect to the polarisation, in good agreement with the Standard Model expectations. The second part of this work is devoted to QCD analysis of the proton structure. The H1 data alone are used to extract flavor separated parton densities. This analysis is further used as a basis to extract various electroweak parameters, such as the W boson mass and the quarks couplings to the Z. Then a global QCD analysis of DIS and Drell Yan data is realized, focusing on the strange sea asymmetry which is found to be small: {integral}{sub 0}{sup 1} x(s - s-bar)dx = (1,8 {+-} 3,8) x 10{sup -4}. The impact of new E866 data on high x partons densities is discussed and the extraction of the strong coupling is realized {alpha}s = 0,1197 {+-} (+0,0005 - 0,0007)(mod) {+-}0,006 (th). (author)

  7. Applications of positron depth profiling

    International Nuclear Information System (INIS)

    In this thesis some contributions of the positron-depth profiling technique to materials science have been described. Following studies are carried out: Positron-annihilation measurements on neon-implanted steel; Void creation in silicon by helium implantation; Density of vacancy-type defects present in amorphous silicon prepared by ion implantation; Measurements of other types of amorphous silicon; Epitaxial cobalt disilicide prepared by cobalt outdiffusion. Positron-annihilation experiments on low-pressure CVD silicon-nitride films. (orig./MM)

  8. Positron emission tomography. Basic principles

    International Nuclear Information System (INIS)

    The basic principles of positron emission tomography (PET) technique are reviewed. lt allows to obtain functional images from gamma rays produced by annihilation of a positron, a positive beta particle. This paper analyzes positron emitters production in a cyclotron, its general mechanisms, and the various detection systems. The most important clinical applications are also mentioned, related to oncological uses of fluor-l8-deoxyglucose

  9. Applications of positron depth profiling

    Energy Technology Data Exchange (ETDEWEB)

    Hakvoort, R.A.

    1993-12-23

    In this thesis some contributions of the positron-depth profiling technique to materials science have been described. Following studies are carried out: Positron-annihilation measurements on neon-implanted steel; Void creation in silicon by helium implantation; Density of vacancy-type defects present in amorphous silicon prepared by ion implantation; Measurements of other types of amorphous silicon; Epitaxial cobalt disilicide prepared by cobalt outdiffusion. Positron-annihilation experiments on low-pressure CVD silicon-nitride films. (orig./MM).

  10. Positron Annihilation Studies of Mesoporous Silica MCM-41

    International Nuclear Information System (INIS)

    Positron annihilation has been used to study the mesoporous silica MCM-41. Lifetime spectra of evacuated MCM-41 indicate a significant contribution from 3γ annihilation events with τ4 = 116 ns and I4 = 24.5 %. This is supported by measurements of the full energy distribution, where MCM-41 shows enhanced counts in the low energy region (below 511 keV) relative to a pure 2γ sample. MCM-41 was also studied under air and oxygen atmospheres. The presence of atmosphere has a significant effect on both the lifetime and Doppler patterns, with both the lifetime data (τ4 and I4) and the 3γ-fraction decreasing with increasing oxygen concentration. This is indicative of paramagnetic quenching of o-Ps by oxygen.

  11. Atomic collisions involving pulsed positrons

    DEFF Research Database (Denmark)

    Merrison, J. P.; Bluhme, H.; Field, D.;

    2000-01-01

    Conventional slow positron beams have been widely and profitably used to study atomic collisions and have been instrumental in understanding the dynamics of ionization. The next generation of positron atomic collision studies are possible with the use of charged particle traps. Not only can large...... instantaneous intensities be achieved with in-beam accumulation, but more importantly many orders of magnitude improvement in energy and spatial resolution can be achieved using positron cooling. Atomic collisions can be studied on a new energy scale with unprecedented precion and control. The use of...... accelerators for producing intense positron pulses will be discussed in the context of atomic physics experiments....

  12. Measurement of the $\\tau$ lepton lifetime

    CERN Document Server

    Buskulic, Damir; De Bonis, I; Décamp, D; Ghez, P; Goy, C; Lees, J P; Lucotte, A; Minard, M N; Odier, P; Pietrzyk, B; Ariztizabal, F; Chmeissani, M; Crespo, J M; Efthymiopoulos, I; Fernández, E; Fernández-Bosman, M; Gaitan, V; Garrido, L; Martínez, M; Orteu, S; Pacheco, A; Padilla, C; Palla, Fabrizio; Pascual, A; Perlas, J A; Sánchez, F; Teubert, F; Colaleo, A; Creanza, D; De Palma, M; Farilla, A; Gelao, G; Girone, M; Iaselli, Giuseppe; Maggi, G; Maggi, M; Marinelli, N; Natali, S; Nuzzo, S; Ranieri, A; Raso, G; Romano, F; Ruggieri, F; Selvaggi, G; Silvestris, L; Tempesta, P; Zito, G; Huang, X; Lin, J; Ouyang, Q; Wang, T; Xie, Y; Xu, R; Xue, S; Zhang, J; Zhang, L; Zhao, W; Bonvicini, G; Cattaneo, M; Comas, P; Coyle, P; Drevermann, H; Engelhardt, A; Forty, Roger W; Frank, M; Hagelberg, R; Harvey, J; Jacobsen, R; Janot, P; Jost, B; Kneringer, E; Knobloch, J; Lehraus, Ivan; Markou, C; Martin, E B; Mato, P; Minten, Adolf G; Miquel, R; Oest, T; Palazzi, P; Pater, J R; Pusztaszeri, J F; Ranjard, F; Rensing, P E; Rolandi, Luigi; Schlatter, W D; Schmelling, M; Schneider, O; Tejessy, W; Tomalin, I R; Venturi, A; Wachsmuth, H W; Wiedenmann, W; Wildish, T; Witzeling, W; Wotschack, J; Ajaltouni, Ziad J; Bardadin-Otwinowska, Maria; Barrès, A; Boyer, C; Falvard, A; Gay, P; Guicheney, C; Henrard, P; Jousset, J; Michel, B; Monteil, S; Pallin, D; Perret, P; Podlyski, F; Proriol, J; Rossignol, J M; Saadi, F; Fearnley, Tom; Hansen, J B; Hansen, J D; Hansen, J R; Hansen, P H; Nilsson, B S; Kyriakis, A; Simopoulou, Errietta; Siotis, I; Vayaki, Anna; Zachariadou, K; Blondel, A; Bonneaud, G R; Brient, J C; Bourdon, P; Passalacqua, L; Rougé, A; Rumpf, M; Tanaka, R; Valassi, Andrea; Verderi, M; Videau, H L; Candlin, D J; Parsons, M I; Focardi, E; Parrini, G; Corden, M; Delfino, M C; Georgiopoulos, C H; Jaffe, D E; Antonelli, A; Bencivenni, G; Bologna, G; Bossi, F; Campana, P; Capon, G; Chiarella, V; Felici, G; Laurelli, P; Mannocchi, G; Murtas, F; Murtas, G P; Pepé-Altarelli, M; Dorris, S J; Halley, A W; ten Have, I; Knowles, I G; Lynch, J G; Morton, W T; O'Shea, V; Raine, C; Reeves, P; Scarr, J M; Smith, K; Smith, M G; Thompson, A S; Thomson, F; Thorn, S; Turnbull, R M; Becker, U; Braun, O; Geweniger, C; Graefe, G; Hanke, P; Hepp, V; Kluge, E E; Putzer, A; Rensch, B; Schmidt, M; Sommer, J; Stenzel, H; Tittel, K; Werner, S; Wunsch, M; Beuselinck, R; Binnie, David M; Cameron, W; Colling, D J; Dornan, Peter J; Konstantinidis, N P; Moneta, L; Moutoussi, A; Nash, J; San Martin, G; Sedgbeer, J K; Stacey, A M; Dissertori, G; Girtler, P; Kuhn, D; Rudolph, G; Bowdery, C K; Brodbeck, T J; Colrain, P; Crawford, G; Finch, A J; Foster, F; Hughes, G; Sloan, Terence; Whelan, E P; Williams, M I; Galla, A; Greene, A M; Kleinknecht, K; Quast, G; Raab, J; Renk, B; Sander, H G; Wanke, R; Van Gemmeren, P; Zeitnitz, C; Aubert, Jean-Jacques; Bencheikh, A M; Benchouk, C; Bonissent, A; Bujosa, G; Calvet, D; Carr, J; Diaconu, C A; Etienne, F; Thulasidas, M; Nicod, D; Payre, P; Rousseau, D; Talby, M; Abt, I; Assmann, R W; Bauer, C; Blum, Walter; Brown, D; Dietl, H; Dydak, Friedrich; Ganis, G; Gotzhein, C; Jakobs, K; Kroha, H; Lütjens, G; Lutz, Gerhard; Männer, W; Moser, H G; Richter, R H; Rosado-Schlosser, A; Schael, S; Settles, Ronald; Seywerd, H C J; Saint-Denis, R; Wolf, G; Alemany, R; Boucrot, J; Callot, O; Cordier, A; Courault, F; Davier, M; Duflot, L; Grivaz, J F; Heusse, P; Jacquet, M; Kim, D W; Le Diberder, F R; Lefrançois, J; Lutz, A M; Musolino, G; Nikolic, I A; Park, H J; Park, I C; Schune, M H; Simion, S; Veillet, J J; Videau, I; Abbaneo, D; Azzurri, P; Bagliesi, G; Batignani, G; Bettarini, S; Bozzi, C; Calderini, G; Carpinelli, M; Ciocci, M A; Ciulli, V; Dell'Orso, R; Fantechi, R; Ferrante, I; Fidecaro, F; Foà, L; Forti, F; Giassi, A; Giorgi, M A; Gregorio, A; Ligabue, F; Lusiani, A; Marrocchesi, P S; Messineo, A; Rizzo, G; Sanguinetti, G; Sciabà, A; Spagnolo, P; Steinberger, Jack; Tenchini, Roberto; Tonelli, G; Triggiani, G; Vannini, C; Verdini, P G; Walsh, J; Betteridge, A P; Blair, G A; Bryant, L M; Cerutti, F; Gao, Y; Green, M G; Johnson, D L; Medcalf, T; Mir, L M; Perrodo, P; Strong, J A; Bertin, V; Botterill, David R; Clifft, R W; Edgecock, T R; Haywood, S; Edwards, M; Maley, P; Norton, P R; Thompson, J C; Bloch-Devaux, B; Colas, P; Emery, S; Kozanecki, Witold; Lançon, E; Lemaire, M C; Locci, E; Marx, B; Pérez, P; Rander, J; Renardy, J F; Roussarie, A; Schuller, J P; Schwindling, J; Trabelsi, A; Vallage, B; Johnson, R P; Kim, H Y; Litke, A M; McNeil, M A; Taylor, G; Beddall, A; Booth, C N; Boswell, R; Cartwright, S L; Combley, F; Dawson, I; Köksal, A; Letho, M; Newton, W M; Rankin, C; Thompson, L F; Böhrer, A; Brandt, S; Cowan, G D; Feigl, E; Grupen, Claus; Lutters, G; Minguet-Rodríguez, J A; Rivera, F; Saraiva, P; Smolik, L; Stephan, F; Apollonio, M; Bosisio, L; Della Marina, R; Giannini, G; Gobbo, B; Ragusa, F; Rothberg, J E; Wasserbaech, S R; Armstrong, S R; Bellantoni, L; Elmer, P; Feng, Z; Ferguson, D P S; Gao, Y S; González, S; Grahl, J; Harton, J L; Hayes, O J; Hu, H; McNamara, P A; Nachtman, J M; Orejudos, W; Pan, Y B; Saadi, Y; Schmitt, M; Scott, I J; Sharma, V; Turk, J; Walsh, A M; Wu Sau Lan; Wu, X; Yamartino, J M; Zheng, M; Zobernig, G

    1996-01-01

    The mean lifetime of the \\tau lepton is measured in a sample of 25700 \\tau pairs collected in 1992 with the ALEPH detector at LEP. A new analysis of the 1-1 topology events is introduced. In this analysis, the dependence of the impact parameter sum distribution on the daughter track momenta is taken into account, yielding improved precision compared to other impact parameter sum methods. Three other analyses of the one- and three-prong \\tau decays are updated with increased statistics. The measured lifetime is 293.5 \\pm 3.1 \\pm 1.7 \\fs. Including previous (1989--1991) ALEPH measurements, the combined \\tau lifetime is 293.7 \\pm 2.7 \\pm 1.6 \\fs.

  13. Positron annihilation investigation of BaSrFBr:Eu by X-ray irradiation

    Science.gov (United States)

    Lee, C. Y.

    2014-12-01

    The mechanical property of the BaSrFBr:Eu phosphor layer of X-ray image plates was investigated by using resolution (LP/mm) and coincidence Doppler broadening (CDB) positron annihilation as well as positron annihilation lifetime (PAL). The image plate samples of BaSrFBr:Eu phosphors in this experiment were irradiated by using hospital X-rays. The LP/mm values of the irradiated BaSrFBr:Eu image plates varied from 3.35 to 1.25 for up to 20,000 exposures. CDB positron annihilation and lifetime spectroscopy were used to analyze defect structures in the phosphor layer. Even when the LP/mm values were greatly decreased due to exposures, the S parameter and the lifetime ( τ 1, τ 2) values were almost constant with increasing number of exposures. A positive relationship existed between the SEM images and positron annihilation spectroscopy (PAS). According to the SEM images and the positron annihilation spectroscopy (PAS) results, measurements of the defects with PAS indicate that the image-plate phosphor can be safely used for hospital X-rays in the course of diagnostic radiography at an average rate of 20,000 times for one year.

  14. Electron-positron interactions

    International Nuclear Information System (INIS)

    The experimental information available on e+e- interactions at the time of the Tbilisi Conference (Juli 1976) is reviewed. The topics of these lectures are: electron-positron storage rings, purely electromagnetic ee-interactions, phenomenology of hadron production, e+e- annihilation at low energies, nonresonant hadron production, the new particles psi-3105 and psi-3695, research for other vector states, radiative decays of psi-3105 and psi-3695, anti Q-Q model and predictions, the bound states of heavy quarks, data on new states with even charge conjugation, mesons with open charm, experimental evidence for charmed mesons and for a new lepton. (BJ)

  15. Positron scattering by potassium

    International Nuclear Information System (INIS)

    Coupled-state calculations in a K(4s, 4p, 5s, 5p, 3d) + Ps(1s, 2s, 2p, 3s, 3p, 3d) approximation are reported for positron scattering by ground-state potassium in the energy range 0.5-60.0 eV. Comparison is made with the earlier work of Hewitt et al (1993, 1994) in a K(4s, 4p, 5s, 5p) + Ps(1s, 2s, 2p) approximation. For the first time cross sections for positronium formation in n = 3 states are obtained. (author)

  16. Positron Emission Tomography (PET)

    International Nuclear Information System (INIS)

    Positron emission tomography (PET) assesses biochemical processes in the living subject, producing images of function rather than form. Using PET, physicians are able to obtain not the anatomical information provided by other medical imaging techniques, but pictures of physiological activity. In metaphoric terms, traditional imaging methods supply a map of the body's roadways, its, anatomy; PET shows the traffic along those paths, its biochemistry. This document discusses the principles of PET, the radiopharmaceuticals in PET, PET research, clinical applications of PET, the cost of PET, training of individuals for PET, the role of the United States Department of Energy in PET, and the futures of PET. 22 figs

  17. Lifetime measurements in 123Cs

    International Nuclear Information System (INIS)

    The aim of the present work was to measure the mean lifetimes of the excited states in the bands, which can be useful in understanding the shape co-existence phenomenon. The deformation parameter can be extracted from the mean lifetime of the excited states. The Doppler Shift Attenuation Method (DSAM) technique is used for the lifetime measurements

  18. Neutrino production of electron-positron pairs at excited Landau levels in a strong magnetic field

    CERN Document Server

    Kuznetsov, A V; Savin, V N

    2014-01-01

    The process of neutrino production of electron positron pairs in a magnetic field of arbitrary strength, where electrons and positrons can be created in the states corresponding to excited Landau levels, is analysed. The mean value of the neutrino energy loss due to the process $\

  19. Positron annihilation study of aluminum, titanium, and iron alloys surface after shot peening

    International Nuclear Information System (INIS)

    Shot peening influence on alloys based on iron, aluminum, and titanium was studied using positron annihilation lifetime spectroscopy (PALS) and residual stress measurements. The PALS spectra were analyzed assuming two lifetime components. While the residual stresses change in a similar way in all the samples, the PALS results show an opposite tendency of a component relative intensities change with the time of shot peening for the Ti alloy as compared to steel or the Al alloy. A comparison between the depth profiles of positron implantation and the residual stress distribution reveals that the positron range covers a whole depth where residual stress is observed only in the Ti alloy. Based on this observation, the evolution of the defect concentration is presumed, consisting in migration of large defects away from the surface, while only smaller ones remain close to the surface. Furthermore, the positron lifetime distribution in the Al alloy was determined using the MELT program. The results showed that the initial single, wide distribution of lifetime splits into two narrower ones with increasing shot peening time. (orig.)

  20. Positron annihilation studies in solid 2-aminopyridine, 3-aminopyridine, 4-aminopyridine and 2-aminopyrimidine

    Science.gov (United States)

    Netto, A. Marques; Bicalho, S. M. C. M.; Filgueiras, Ca. L.; Machado, J. C.

    1985-09-01

    Positron annihilation lifetimes and Doppler-broadened annihilation lines have been measured in solid 2-aminopyridine (2-APY), 3-aminopyridine (3-APY), 4-aminopyridine (4-APY) and 2-aminopyrimidine (2-APYM). The results point to the formation of positronium in the solid pyridines and the yields are discussed in terms of the structures and the electron donation character of the compounds.

  1. Positron annihilation study on Y-Ba-Cu-O high Tc superconductors

    International Nuclear Information System (INIS)

    First positron annihilation measurements are reported on high Tc superconductor YBa2Cu3O7-x. The lifetime and Doppler broadening spectra show a slight but significant change about 240K suggesting a deviation from the normal structure far above 90K where the resistance falls to zero. (author)

  2. Cyclotrons and positron emitting radiopharmaceuticals

    Energy Technology Data Exchange (ETDEWEB)

    Wolf, A.P.; Fowler, J.S.

    1984-01-01

    The state of the art of Positron Emission Tomography (PET) technology as related to cyclotron use and radiopharmaceutical production is reviewed. The paper discusses available small cyclotrons, the positron emitters which can be produced and the yields possible, target design, and radiopharmaceutical development and application. 97 refs., 12 tabs. (ACR)

  3. Positron production within our atmosphere

    Science.gov (United States)

    Dwyer, Joseph

    2016-04-01

    Positrons are commonly produced within our atmosphere by cosmic rays and the decay radioactive isotopes. Energetic positrons are also produced by pair production from the gamma rays generated by relativistic runaway electrons. Indeed, such positrons have been detected in Terrestrial Electron Beams (TEBs) in the inner magnetosphere by Fermi/GBM. In addition, positrons play an important role in relativistic feedback discharges (also known as dark lightning). Relativistic feedback models suggest that these discharges may be responsible for Terrestrial Gamma-ray Flashes (TGFs) and some gamma-ray glows. When producing TGFs, relativistic feedback discharges may generate large, lightning-like currents with current moments reaching hundreds of kA-km. In addition, relativistic feedback discharges also may limit the electric field that is possible in our atmosphere, affecting other mechanisms for generating runaway electrons. It is interesting that positrons, often thought of as exotic particles, may play an important role in thunderstorm processes. In this presentation, the role of positrons in high-energy atmospheric physics will be discussed. The unusual observation of positron clouds inside a thunderstorm by the ADELE instrument on an NCAR/NSF Gulfstream V aircraft will also be described. These observations illustrate that we still have much to learn about positron production within our atmosphere.

  4. Cyclotrons and positron emitting radiopharmaceuticals

    International Nuclear Information System (INIS)

    The state of the art of Positron Emission Tomography (PET) technology as related to cyclotron use and radiopharmaceutical production is reviewed. The paper discusses available small cyclotrons, the positron emitters which can be produced and the yields possible, target design, and radiopharmaceutical development and application. 97 refs., 12 tabs

  5. Statistical learning method in regression analysis of simulated positron spectral data

    International Nuclear Information System (INIS)

    Positron lifetime spectroscopy is a non-destructive tool for detection of radiation induced defects in nuclear reactor materials. This work concerns the applicability of the support vector machines method for the input data compression in the neural network analysis of positron lifetime spectra. It has been demonstrated that the SVM technique can be successfully applied to regression analysis of positron spectra. A substantial data compression of about 50 % and 8 % of the whole training set with two and three spectral components respectively has been achieved including a high accuracy of the spectra approximation. However, some parameters in the SVM approach such as the insensitivity zone e and the penalty parameter C have to be chosen carefully to obtain a good performance. (author)

  6. The study of defects in metallic alloys by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation spectroscopy (PAS) has become in a very useful non destructive testing to the study of condensed matter. Specially, in the last two decades, with the advent of solid state detectors and high-resolution time spectrometers. The basic information obtained with PAS in solid-state physics is on electronic structure in free defect materials. However, positron annihilation techniques (lifetime, angular correlation and Doppler broadening) have been succesfully applied to study crystal lattice defects with lower-than-average electron density, such as vacancies, small vacancy clusters, etc.. In this sense, information about: vacancy formation and migration energies, dislocations, grain boundaries, solid-solid phase transformation and radiation damage was obtained. In this work the application of the positron lifetime technique to study the thermal effects on a fine-grained superplastic Al-Ca-Zn alloy and the quenched-in defects in monocrystals of β Cu-Zn-Al alloy for several quenching temperatures is shown. (Author)

  7. Positron driven plasma wakefields

    Science.gov (United States)

    Pinkerton, S.; Shi, Y.; Huang, C.; An, W.; Mori, W. B.; Muggli, P.

    2010-11-01

    The LHC is producing high-energy, high-charge proton bunches (1e11 protons at 1-7 TeV each) that could be used to accelerate ``witness'' electron bunches to TeV range eneregies via a plasma wakefield accelerator (PWFA). Simulations [1] suggest that a proton ``drive'' bunch is able to excite large wakefields if the bunch size is on the order of 100 μm; however, the LHC paramters are currently on the 1 cm scale. SLAC'S FACET is able to supply positorn bunchs with the ideal parameters for driving a PWFA. Although at lower energy (2e10 positrons at 23 GeV each), initial simiulations in QuickPIC show that the physics of a positron drive bunch is very similar to that of a proton drive bunch. Differences in the physics arise from the mass difference: slower dephasing but faster transverse bunch evolution. Other considerations include driver head erosion and purity of the wakefield ion column. The physics of positive drivers for PWFA and the viability of this scheme for future high-energy colliders will be investigated at SLAC's FACET.[4pt] [1] Caldwell, et al. Nature Physics 5, 363 (2009).[0pt] [2] C.H. Huang, et al., J. Comp. Phys., 217(2), 658, (2006).

  8. Lifetimes of charmed mesons

    International Nuclear Information System (INIS)

    Using the ARGUS detector at the e+e- storage ring DORIS II at DESY, we have measured the lifetimes of the D0, D+ and Ds+ mesons. We find τsub(D0) = (4.8±0.4±0.3)x10-13 s, τsub(D+) = (10.5±0.8±0.7)x10-13 s and τsub(Ds+) = (5.6-1.2+1.3±0.8)x10.13s. (orig.)

  9. The influence of antioxidant on positron annihilation in polypropylene

    International Nuclear Information System (INIS)

    The purpose of this report is to check the influence of the carbonyl groups (CG), created by oxygen naturally dissolved in a polymer matrix and by the source irradiation, on annihilation characteristics of free positrons using the positron annihilation lifetime spectroscopy (PALS) and coincidence Doppler-broadening spectroscopy (CDBS). Positron annihilation in a pure polypropylene (PP) and in an antioxidant-containing polypropylene (PPA) sample at room and low temperatures has been studied by CDBS. PALS has been used as an o-Ps (orth-positronium) formation monitor. The momentum density distributions of electrons obtained by CDBS at the beginning of measurements have been compared to that at the o-Ps intensity saturation level. It has been shown that the initial concentration of carbonyl groups in a PP sample is high, while for an antioxidant-containing sample, PPA, carbonyl groups are not detected by CDBS. CDBS spectra for a PP can be explained by annihilation of free positrons with the oxygen contained in the carbonyl groups. For a PPA sample, no significant contribution of annihilation with oxygen core electrons can be concluded. (Y. Kazumata)

  10. Positron trapping and possible presence of SO3H clusters in dry fluorinated polymer electrolyte membranes

    Science.gov (United States)

    Mohamed, Hamdy F. M.; Kobayashi, Y.; Kuroda, S.; Ohira, A.

    2012-08-01

    The behavior of positrons that do not form positronium in dry fluorinated polymer electrolyte membranes (Nafion®, Fumapem® and Aquivion®) with various ion exchange capacities (IECs) was studied by the combined use of Doppler broadening of annihilation radiation (DBAR) and the positron lifetime technique. The drastic increase of the S parameter, measured by DBAR, with increasing IEC above 0.91 meq/g indicates that increasing numbers of positrons are trapped by oxygen atoms and annihilate with the electrons bound in them. Reversed micelle like SO3H nanoclusters to trap positrons possibly appear at IEC = 0.91 meq/g and their concentration increases with increasing IEC.

  11. Material evaluation technology by positron annihilation measurement and micro/nano-scopic stress measurement

    International Nuclear Information System (INIS)

    Two kinds of next generation nanotechnologies, positron annihilation measurement and micro/nano-scopic stress measurement are explained. The positron annihilation measurement is able to detect nano- or sub nanometer scale local structure such as atomic vacancy, void, dislocation, grain boundary and nanolack. The positron annihilation measurement method and some examples of measurement; fatigue of steel, creep behavior of heat-resistance steel and positron annihilation lifetime of polymer are stated. On the micro/nano-scopic stress measurement, the principle of method and measurement examples such as the emission and stress of sapphire (Cr3+), the stress distribution surrounding of crack and the crosslinking effect of Al2O3 compound materials and the stress of semiconductor SiC thin film base and the its future are ascribed. (S.Y.)

  12. Positron annihilation spectroscopy study on annealing effect of CuO nanoparticles

    International Nuclear Information System (INIS)

    The microstructure and defects of CuO nanoparticles under isochronal annealing were investigated by positron annihilation spectroscopy (PAS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD and SEM results indicated that the average grain sizes of CuO nanoparticles grew slowly below 800 °C, and then increased rapidly with the annealing temperature from 800 to 1000 °C. Positron lifetime analysis exhibited that positrons were mainly annihilated in mono-vacancies (VCu, VO) and vacancy clusters when annealing from 200 to 800 °C. Furthermore, W-S plot of Doppler broadening spectra at different annealing temperatures found that the (W, S) points distributed on two different defect species, which suggested that V−Cu - V+O complexes were produced when the grains grew to bigger size after annealing above 800 °C, and positrons might annihilate at these complexes. (author)

  13. Frontiers of positron and positronium chemistry in condensed media

    International Nuclear Information System (INIS)

    Positron annihilation spectroscopy is an excellent tool to follow the structural changes in chemical species. Four examples are presented to support the above statement. The sizes of defects in electrodeposited chromium layers were studied and estimated on the basis of positron lifetime spectra decomposed into two components. Vacancies, di-vacancies and vacancy-clusters could be identified in the electrodeposites. The changes of the size distribution of the free volume units in poly(methylmetacrylate) on the dependence of molecular weight and dispersity were described by the correlation between the lifetime of ortho-Ps and the free volume units in polymers. It was found that the free volume is affected by both the molecular weight and dispersity. The effect of dispersity was explained by the sample preparation technique, namely by the application of high pressure. The ortho-para conversion of ortho-Ps was used to follow the partial spin-crossover in [Fe(1-ethyl-1H-tetrazole)6](BF4)2. The spin-crossover temperature was identified to be 105 K. A conformal structural transformation was found in [Zn(1-propyl-1H-tetrazole)6](BF4)2 between 170 and 90 K by positronium lifetime measurement and the role of (BF4)2- anion, in this transformation, was proved by 19F NMR spectroscopy. (author)

  14. Positron annihilation in cardo-based polymer membranes.

    Science.gov (United States)

    Kobayashi, Y; Kazama, Shingo; Inoue, K; Toyama, T; Nagai, Y; Haraya, K; Mohamed, Hamdy F M; O'Rouke, B E; Oshima, N; Kinomura, A; Suzuki, R

    2014-06-01

    Positron annihilation lifetime spectroscopy (PALS) is applied to a series of bis(aniline)fluorene and bis(xylidine)fluorene-based cardo polyimide and bis(phenol)fluorene-based polysulfone membranes. It was found that favorable amounts of positronium (Ps, the positron-electron bound state) form in cardo polyimides with the 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) moiety and bis(phenol)fluorene-based cardo polysulfone, but no Ps forms in most of the polyimides with pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BTDA) moieties. A bis(xylidine)fluorene-based polyimide membrane containing PMDA and BTDA moieties exhibits a little Ps formation but the ortho-positronium (o-Ps, the triplet state of Ps) lifetime of this membrane anomalously shortens with increasing temperature, which we attribute to chemical reaction of o-Ps. Correlation between the hole size (V(h)) deduced from the o-Ps lifetime and diffusion coefficients of O2 and N2 for polyimides with the 6FDA moiety and cardo polysulfone showing favorable Ps formation is discussed based on free volume theory of gas diffusion. It is suggested that o-Ps has a strong tendency to probe larger holes in rigid chain polymers with wide hole size distributions such as those containing cardo moieties, resulting in deviations from the previously reported correlations for common polymers such as polystyrene, polycarbonate, polysulfone, and so forth. PMID:24815092

  15. Positron emission mammography imaging

    Energy Technology Data Exchange (ETDEWEB)

    Moses, William W.

    2003-10-02

    This paper examines current trends in Positron Emission Mammography (PEM) instrumentation and the performance tradeoffs inherent in them. The most common geometry is a pair of parallel planes of detector modules. They subtend a larger solid angle around the breast than conventional PET cameras, and so have both higher efficiency and lower cost. Extensions to this geometry include encircling the breast, measuring the depth of interaction (DOI), and dual-modality imaging (PEM and x-ray mammography, as well as PEM and x-ray guided biopsy). The ultimate utility of PEM may not be decided by instrument performance, but by biological and medical factors, such as the patient to patient variation in radiotracer uptake or the as yet undetermined role of PEM in breast cancer diagnosis and treatment.

  16. Ortho-positronium lifetime as a detector of spin crossover

    International Nuclear Information System (INIS)

    Positron lifetime parameters were measured for the spin-crossover complexes [Fe(R-1H-tetrazole)6](BF4)2 (R=1-ethyl, 1-n-propyl) and for the diamagnetic [Zn(1-n-propyl-1H-tetrazole)6](BF4)2. Positronium forms with significant intensity in the studied compounds. The ortho-para conversion of ortho-positronium was used to follow the spin-crossover. Changes of the dynamic structure were found in the propyl tetrazole complex between 150 K and 90 K. (author)

  17. Positron mobility in perylene

    International Nuclear Information System (INIS)

    Based on Doppler-shift measurements we have determined the positron drift velocity u in a high-purity monoclinic α-perylene single crystal as a function of applied electric field F and temperature. The electric field is applied as a triangular wave with a maximum field Fmax. At low fields the drift velocity displays a linear field dependence, while it assumes a sublinear field dependence above a characteristic velocity vs=50 km/s and finally tends to saturate at 110 km/s, presumably due to optical-phonon generation above a certain threshold kinetic energy. Unlike in the case of diamond, vs is much greater than the longitudinal sound velocity in the solid. By fitting the observed nonlinear electric-field dependence of u to a Shockley expression for acoustic deformation potential scattering of ''warm'' charge carriers we extract the zero-field limit of the positron mobility μ0 along the crystallographic c' axis (c'parallel axb). At 297 K μ0=(136±3±14) cm2 V-1 s-1, where the first error is statistical and the second is an estimated ±10% calibration uncertainty. Over the temperature range 100--350 K the mobility exhibits a Tn temperature dependence with n=-1.04±0.03, showing a clear departure from the T-3/2 dependence one might expect. Below 100 K μ0 still increases with decreasing temperature, but at a given temperature its value decreases as the maximum applied field Fmax increases, possibly indicating interference caused by the presence of a field-enhanced accumulation of trapped carriers that cause scattering at low temperatures

  18. Positron emitting pharmaceuticals

    International Nuclear Information System (INIS)

    Positron Emission Tomography (PET) imaging of physiology at the molecular level bridges the gap between laboratory science and clinical medicine by providing the most specific and sensitive means for imaging molecular pathways and interactions in tissues of man. PET-imaging requires the use Positron Emitting Radiopharmaceuticals (PRPs), which are radioactively labeled 'true metabolites' i.e., sugars, amino acids, fatty acids etc., essentially made of H, C, N and O which the cells in the body can metabolize. The PET-isotopes: 11C, 15O, 13N and 18F (instead of H) are cyclotron produced and are short-lived, which places several constraints on the synthesis time for the PRPs, quality control and their clinical use as compared to the conventional 99mTc- and other SPECT-RPs widely used in nuclear medicine. There are large number of published reports showing the utility of several PRPs labeled with 18F (T1/2 = 110 min) and 11C (T1/2 = 20 min). A few PRPs have been labeled with 13N (T1/2 = 10 min). 15O (T1/2 = 2min) is used mostly as H215O, C15 or C15O2. 18F-radiopharmaceuticals can be made at a medical cyclotron facility and sent to PET -imaging centres, which can be reached in a couple of hours. The sensitivity of PET -imaging has encouraged R and D in several other PRPs, labeled with viz., 68Ga (generator produced, T1/2 68 min), 124I (cyclotron, T1/2 4.2 d), 82Rb (generator, T1/2 75s), 64Cu (cyclotron, T1/2 12h), and 94mTc (cyclotron, T1/2 52 min). Due to its relevance in several diseases, particularly cancer, PET-imaging has made major scientific contribution to drug development, particularly for neurological diseases and cancer treatment. (author)

  19. Defect study on electron irradiated GaAs by means of positron annihilation

    International Nuclear Information System (INIS)

    Measurements of the positron lifetime and Doppler-broadened annihilation-radiation have been performed in electron-irradiated GaAs. The positron lifetime at the irradiation induced defects was ∝0.250 ns at 300 K. The defect clustering stage was found to occur at around 520-620 K, and the coarsening and annealing stage is believed to be above 620 K. Similar annealing stages were also observed in GaAs lightly doped with Si(0.2x1018 cm-3). Both the lifetime and the S-parameter in the irradiated GaAs were found to decrease with temperature from 300 K to 100 K, suggesting the coexistence of shallow traps in electron irradiated GaAs. (orig.)

  20. Fundamentals of positron emission tomography

    International Nuclear Information System (INIS)

    Positron emission tomography is a modern radionuclide method of measuring physiological quantities or metabolic parameters in vivo. The methods is based on: (1) Radioactive labelling with positron emitters; (2) the coincidence technique for the measurement of the annihilation radiation following positron decay; (3) analysis of the data measured using biological models. The basic aspects and problems of the method are discussed. The main fields of future research are the synthesis of new labelled compounds and the development of mathematical models of the biological processes to be investigated. (orig.)

  1. [Fundamentals of positron emission tomography].

    Science.gov (United States)

    Ostertag, H

    1989-07-01

    Positron emission tomography is a modern radionuclide method of measuring physiological quantities or metabolic parameters in vivo. The method is based on: (1) radioactive labelling with positron emitters; (2) the coincidence technique for the measurement of the annihilation radiation following positron decay; (3) analysis of the data measured using biological models. The basic aspects and problems of the method are discussed. The main fields of future research are the synthesis of new labelled compounds and the development of mathematical models of the biological processes to be investigated. PMID:2667029

  2. Ultrarelativistic Electron-Positron Plasma

    CERN Document Server

    Thoma, Markus H

    2008-01-01

    Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.

  3. 21 CFR 892.1110 - Positron camera.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Positron camera. 892.1110 Section 892.1110 Food... DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1110 Positron camera. (a) Identification. A positron camera is a device intended to image the distribution of positron-emitting radionuclides in the...

  4. Positron annihilation study of vacancy-type defects in Al single crystal foils with the tweed structures across the surface

    Energy Technology Data Exchange (ETDEWEB)

    Kuznetsov, Pavel, E-mail: kpv@ispms.tsc.ru [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Cizek, Jacub, E-mail: jcizek@mbox.troja.mff.cuni.cz; Hruska, Petr [Charles University in Prague, Praha, CZ-18000 Czech Republic (Czech Republic); Anwad, Wolfgang [Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, D-01314 Germany (Germany); Bordulev, Yuri; Lider, Andrei; Laptev, Roman [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Mironov, Yuri [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation)

    2015-10-27

    The vacancy-type defects in the aluminum single crystal foils after a series of the cyclic tensions were studied using positron annihilation. Two components were identified in the positron lifetime spectra associated with the annihilation of free positrons and positrons trapped by dislocations. With increasing number of cycles the dislocation density firstly increases and reaches a maximum value at N = 10 000 cycles but then it gradually decreases and at N = 70 000 cycles falls down to the level typical for the virgin samples. The direct evidence on the formation of a two-phase system “defective near-surface layer/base Al crystal” in aluminum foils at cyclic tension was obtained using a positron beam with the variable energy.

  5. Positron annihilation study of vacancy-type defects in Al single crystal foils with the tweed structures across the surface

    International Nuclear Information System (INIS)

    The vacancy-type defects in the aluminum single crystal foils after a series of the cyclic tensions were studied using positron annihilation. Two components were identified in the positron lifetime spectra associated with the annihilation of free positrons and positrons trapped by dislocations. With increasing number of cycles the dislocation density firstly increases and reaches a maximum value at N = 10 000 cycles but then it gradually decreases and at N = 70 000 cycles falls down to the level typical for the virgin samples. The direct evidence on the formation of a two-phase system “defective near-surface layer/base Al crystal” in aluminum foils at cyclic tension was obtained using a positron beam with the variable energy

  6. Positron injectors for high-luminosity storage-ring colliders

    International Nuclear Information System (INIS)

    This paper reports on high-luminosity B-factories utilizing storage rings operating at unequal energies which require high-energy, low-emittance sources of positrons, and electrons suitable to fill the storage rings. As an example, consider the proposed characteristics of a collider with a luminosity of 1034 cm-2s-1 using the PEP facility at SLAC as studied by LBL (Apiary-III) and summarized. The collider consists of two rings, a large 9-GeV ring (PEP or a modification thereof) plus a 3.1-GeV ring of one-third the circumference, each with a circulating current of 3 A. Ideally, the time to fill the positron ring should be much shorter than the luminosity lifetime (set by the size of the low-energy ring). Since the luminosity lifetime of the collider is not expected to be very high, the PEP-based B-factory should have a powerful, dedicated injector. In the estimate of the characteristics of the injection system the maximum time for a complete fill of the positron ring is taken as ∼100 seconds. In the design of the injection system several choices are possible: injection by linacs at full energy of the rings or use of an intermediate booster synchrotron; accelerating e+ and e- to high energy using conventional linacs or using high-gradient linacs plus gigawatt power RF-sources being developed for linear colliders; and using a conventional (warm magnet) damping ring for cooling the positron beam at an intermediate energy or a full energy ring with a radius equal to that of the low-energy ring

  7. Energy Savings Lifetimes and Persistence

    Energy Technology Data Exchange (ETDEWEB)

    Hoffman, Ian M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Schiller, Steven R. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Todd, Annika [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Billingsley, Megan A. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Goldman, Charles A. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Schwartz, Lisa C. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2016-02-01

    This technical brief explains the concepts of energy savings lifetimes and savings persistence and discusses how program administrators use these factors to calculate savings for efficiency measures, programs and portfolios. Savings lifetime is the length of time that one or more energy efficiency measures or activities save energy, and savings persistence is the change in savings throughout the functional life of a given efficiency measure or activity. Savings lifetimes are essential for assessing the lifecycle benefits and cost effectiveness of efficiency activities and for forecasting loads in resource planning. The brief also provides estimates of savings lifetimes derived from a national collection of costs and savings for electric efficiency programs and portfolios.

  8. Copulas Between Wealth and Lifetime

    Institute of Scientific and Technical Information of China (English)

    YE Dongyan

    2009-01-01

    The life insurance industry is very interested in how a person's lifetime is related to his wealth with financial advisors interested in how even a person's portfolio choice affects his lifetime. This paper presents a statistical analysis combined with intuitive relationships between lifetime and wealth. Key properties of this relationship are given and then various copulas are analyzed to see whether they have these properties. Other advantages and disadvantages of these copulas for describing the dependence are stated. The results show that some copulas are not appropriate for relating lifetime and wealth, including the Gaussian family.

  9. Parkinson disease and positron tomography

    International Nuclear Information System (INIS)

    Physiopathologic investigations of Parkinson disease and parkinsonian syndrome using positron tomography are briefly reviewed: study of cerebral blood flow and metabolism; effects of L-DOPA; study of dopaminergic receptors and of 18F-Fluoro-L-DOPA incorporation

  10. Resolvability of positron decay channels

    International Nuclear Information System (INIS)

    Many data analysis treatments of positron experiments attempt to resolve two or more positron decay or exist channels which may be open simultaneously. Examples of the need to employ such treatments of the experimental results can be found in the resolution of the constituents of a defect ensemble, or in the analysis of the complex spectra which arise from the interaction of slow positrons at or near the surfaces of solids. Experimental one- and two-dimensional angular correlation of annihilation radiation experiments in Al single crystals have shown that two defect species (mono- and divacancies) can be resolved under suitable conditions. Recent experiments at LLNL indicate that there are a variety of complex exit channels open to positrons interacting at surfaces, and ultimely these decay channels must also be suitably resolved from one another. 6 refs., 4 figs

  11. Personnel exposure from positron emitters

    International Nuclear Information System (INIS)

    Positron emitters may contribute considerably to the radiation from induced radioactivity in accelerator environments. In most cases of thick radiating objects (magnets, shielding walls) the dose rate from gamma emitters, including the 511 keV annihilation photons from positron emitters, dominates the radiation field. Direct positron interaction in skin tissue and in the lens of the eye may be an important contribution to absorbed dose in cases of thin targets and beam separating septa. Results of calculations and measurements show, however, that the dose to the lens of the eye is limited by limitations placed on whole-body doses. Irradiation from positron emitters gives rise to about the same absorbed doses as those experienced in the case of an electron exposure. (author)

  12. Simulation of the annihilation emission of galactic positrons; Modelisation de l'emission d'annihilation des positrons Galactiques

    Energy Technology Data Exchange (ETDEWEB)

    Gillard, W

    2008-01-15

    Positrons annihilate in the central region of our Galaxy. This has been known since the detection of a strong emission line centered on an energy of 511 keV in the direction of the Galactic center. This gamma-ray line is emitted during the annihilation of positrons with electrons from the interstellar medium. The spectrometer SPI, onboard the INTEGRAL observatory, performed spatial and spectral analyses of the positron annihilation emission. This thesis presents a study of the Galactic positron annihilation emission based on models of the different interactions undergone by positrons in the interstellar medium. The models are relied on our present knowledge of the properties of the interstellar medium in the Galactic bulge, where most of the positrons annihilate, and of the physics of positrons (production, propagation and annihilation processes). In order to obtain constraints on the positrons sources and physical characteristics of the annihilation medium, we compared the results of the models to measurements provided by the SPI spectrometer. (author)

  13. Probing Positron Gravitation at HERA

    CERN Document Server

    Gharibyan, Vahagn

    2015-01-01

    An equality of particle and antiparticle gravitational interactions holds in general relativity and is supported by indirect observations. Here I develop a method based on high energy Compton scattering to measure the gravitational interaction of accelerated charged particles. Within that formalism the Compton spectra measured at HERA rule out the positron's anti-gravity and hint for a positron's 1.3(0.2)\\% weaker coupling to the gravitational field relative to an electron.

  14. Probing Positron Gravitation at HERA

    Energy Technology Data Exchange (ETDEWEB)

    Gharibyan, Vahagn

    2015-07-15

    An equality of particle and antiparticle gravitational interactions holds in general relativity and is supported by indirect observations. Here I develop a method based on high energy Compton scattering to measure the gravitational interaction of accelerated charged particles. Within that formalism the Compton spectra measured at HERA rule out the positron's anti-gravity and hint for a positron's 1.3(0.2)% weaker coupling to the gravitational field relative to an electron.

  15. Photon correlations in positron annihilation

    OpenAIRE

    Gauthier, Isabelle; Hawton, Margaret

    2010-01-01

    The two-photon positron annihilation density matrix is found to separate into a diagonal center of energy factor implying maximally entangled momenta, and a relative factor describing decay. For unknown positron injection time, the distribution of the difference in photon arrival times is a double exponential at the para-Ps decay rate, consistent with experiment (V. D. Irby, Meas. Sci. Technol. 15, 1799 (2004)).

  16. Trapping of positron in gallium arsenide: evidencing of vacancies and of ions with a negative charge

    International Nuclear Information System (INIS)

    Vacancy type defects in Ga As as grown and irradiated by electrons are characterized by lifetime of positrons. Positron lifetime increases from 230 ps to 258 and 295 ps in presence of native vacancies in n type Ga As. Configuration of native vacancies changes when Fermi level crosses energy levels localized in the forbidden zone at 0.035eV and at 0.10eV from the bottom of the conduction band. Native vacancies are identified to arsenic vacancies with or without other point defects. Positron lifetime increases from 230 to 260 ps in presence of vacancies produced by low temperature irradiation negative ions are also produced. In irradiated Ga As, these ions trap positrons in competition with vacancies produced by irradiation, showing they have a negative charge. Two annealing zones between 180-300K and 300-600K are presented by vacancies. Ions do not anneal below ambient temperature. Vacancies and negative ions are identified respectively to gallium vacancies and gallium antisite

  17. Microstructure of thermally grown and deposited alumina films probed with positrons

    Science.gov (United States)

    Somieski, Bertram; Hulett, Lester D.; Xu, Jun; Pint, Bruce A.; Tortorelli, Peter F.; Nielsen, Bent; Asoka-Kumar, Palakkal; Suzuki, Ryoichi; Ohdaira, Toshiyuki

    1999-03-01

    Aluminum oxide films used for corrosion protection of iron and nickel aluminides were generated by substrate oxidation as well as plasma and physical vapor depositions. The films grown by oxidation were crystalline. The others were amorphous. Defect structures of the films were studied by positron spectroscopy techniques. Lifetimes of the positrons, and Doppler broadening of the γ photons generated by their annihilation, were measured as functions of the energies with which they were injected. In this manner, densities and sizes of the defects were determined as functions of depths from the outer surfaces of the films. Alumina films generated by oxidation had high densities of open volume defects, mainly consisting of a few aggregated vacancies. In the outer regions of the films the structures of the defects did not depend on substrate compositions. Positron lifetime measurements, and the S and W parameters extracted from Doppler broadening spectra, showed uniform distributions of defects in the crystalline Al2O3 films grown on nickel aluminide substrates, but these data indicated intermediate layers of higher defect contents at the film/substrate interfaces of oxides grown on iron aluminide substrates. Amorphous films generated by plasma and physical vapor deposition had much larger open volume defects, which caused the average lifetimes of the injected positrons to be significantly longer. The plasma deposited film exhibited a high density of large cavities.

  18. Alternative free volume models and positron cages for the characterisation of nanoporosity in materials

    International Nuclear Information System (INIS)

    Three semi-empirical positron stationary Quantum Models were developed for the study of nanoporosity in a wide range of solid porous materials. The cubic, conic and cylindrical well potentials were considered and their geometric parameters related to the Positron Annihilation LifeTime (PALT) measurements. If a conic or a cubic symmetry is assumed, a resonance lifetime phenomenon was found, which enables proposal of a technique to catch positrons in free volume sites. In the cylindrical case, an alternative method to determine free volume sizes in materials was developed. The free volume equations of these new models were then compared to the well-known and widely utilised Spherical Free Volume Model (SFVM) and remarkable differences were found. A strong variation of the free volume size-positron lifetime relation with the geometry involved was observed and a remarkable dependence of the electron layer thickness parameter ΔR with the hole-shape under study and with the nature of the material considered. The mathematical functions appearing in the conic and cylindrical cases are the superposition of Bessel functions of the first kind and trigonometric functions in the cubic case. Generalised free volume diagrams were constructed and a brief geometrical scheme of the diverse cases considered was obtained. (author)

  19. Effect of positron wave function on positron annihilation rates and electron-positron momentum densities in solids

    Energy Technology Data Exchange (ETDEWEB)

    Rubaszek, A. [Polska Akademia Nauk, Wroclaw (Poland). Inst. Niskich Temperatur i Badan Strukturalnych; Szotek, Z.; Temmerman, W.M. [Daresbury Lab. (United Kingdom)

    2001-07-01

    To interpret positron annihilation data in solids in terms of the electron momentum density and electron charge distribution, both the electron-positron interaction and positron wave function have to be considered explicitly. In the present work we discuss the effect of the shape of the positron wave function on the calculated positron annihilation rates in a variety of solids, for different types of electrons (core, s, p, d, f). We show that the form of the positron distribution in the Wigner-Seitz cell has a crucial effect on the resulting core electron contribution to the positron annihilation characteristics. The same is observed for the localised d and f electrons in transition metals Finally we study the influence of the positron wave function on the electron-positron momentum density in elemental Si. (orig.)

  20. Lifetime of Mechanical Equipment

    Energy Technology Data Exchange (ETDEWEB)

    Leland, K.

    1999-07-01

    The gas plant at Kaarstoe was built as part of the Statpipe gas transport system and went on stream in 1985. In 1993 another line was routed from the Sleipner field to carry condensate, and the plant was extended accordingly. Today heavy additional supply- and export lines are under construction, and the plant is extended more than ever. The main role of the factory is to separate the raw gas into commercial products and to pump or ship it to the markets. The site covers a large number of well-known mechanical equipment. This presentation deals with piping, mechanical and structural disciplines. The lifetime of mechanical equipment is often difficult to predict as it depends on many factors, and the subject is complex. Mechanical equipment has been kept in-house, which provides detailed knowledge of the stages from a new to a 14 years old plant. The production regularity has always been very high, as required. The standard of the equipment is well kept, support systems are efficient, and human improvisation is extremely valuable.

  1. Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

    Science.gov (United States)

    Milina, Maria; Mitchell, Sharon; Crivelli, Paolo; Cooke, David; Pérez-Ramírez, Javier

    2014-05-01

    Deactivation due to coking limits the lifetime of zeolite catalysts in the production of chemicals and fuels. Superior performance can be achieved through hierarchically structuring the zeolite porosity, yet no relation has been established between the mesopore architecture and the catalyst lifetime. Here we introduce a top-down demetallation strategy to locate mesopores in different regions of MFI-type crystals with identical bulk porous and acidic properties. In contrast, well-established bottom-up strategies as carbon templating and seed silanization fail to yield materials with matching characteristics. Advanced characterization tools capable of accurately discriminating the mesopore size, distribution and connectivity are applied to corroborate the concept of mesopore quality. Positron annihilation lifetime spectroscopy proves powerful to quantify the global connectivity of the intracrystalline pore network, which, as demonstrated in the conversions of methanol or of propanal to hydrocarbons, is closely linked to the lifetime of zeolite catalysts. The findings emphasize the need to aptly tailor hierarchical materials for maximal catalytic advantage.

  2. Positron annihilation investigations on poly(methyl methacrylate)

    International Nuclear Information System (INIS)

    Positron lifetime and Doppler broadened annihilation radiation were measured for seven different samples of poly(methyl methacrylate) at room temperature in vacuum. The polymerisation of methyl methacrylate was carried out as a bulk polymerisation in the presence of benzoyl peroxide as an initiator. The effect of the amount of the initiator on the viscosity-average molecular weight was studied. It was found that the viscosity-average molecular weight decreased with increasing amount of the initiator. The average lifetime and intensity of ortho-positronium (o-Ps) increased with increasing viscosity-average molecular weight up to 6.85x104 and remained constant after that. The S-parameter showed a similar behaviour as that of the o-Ps intensity.

  3. Applications of positron annihilation to dermatology and skin cancer

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Guang; Chen, Hongmin; Chakka, Lakshmi [Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110 (United States); Gadzia, Joseph E. [Dermatology, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, KS 66103 and Kansas Medical Clinic, Topeka, KS 66614 (United States); Jean, Y.C. [Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110 (United States); R and D Center for Membrane Technology, Chung Yuan Christian University, Chung-Li (China)

    2007-07-01

    Positronium annihilation lifetime experiments have been performed to investigate the interaction between skin cancer and positronium for human skin samples. Positronium annihilation lifetime is found to be shorter and intensity is found to be less for the samples with basal cell carcinoma and squamous cell carcinoma than the normal skin samples. These results indicate a reduction of free volume in the molecular level for the skin with cancer with respect to the skin without cancer. Positron annihilation spectroscopy may be potentially developed as a new noninvasive and external method for dermatology clinics, early detection of cancer, and nano-PET technology in the future. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Lifetime-based tomographic multiplexing

    Science.gov (United States)

    Raymond, Scott B.; Boas, David A.; Bacskai, Brian J.; Kumar, Anand T. N.

    2010-07-01

    Near-infrared (NIR) fluorescence tomography of multiple fluorophores has previously been limited by the bandwidth of the NIR spectral regime and the broad emission spectra of most NIR fluorophores. We describe in vivo tomography of three spectrally overlapping fluorophores using fluorescence lifetime-based separation. Time-domain images are acquired using a voltage-gated, intensified charge-coupled device (CCD) in free-space transmission geometry with 750 nm Ti:sapphire laser excitation. Lifetime components are fit from the asymptotic portion of fluorescence decay curve and reconstructed separately with a lifetime-adjusted forward model. We use this system to test the in vivo lifetime multiplexing suitability of commercially available fluorophores, and demonstrate lifetime multiplexing in solution mixtures and in nude mice. All of the fluorophores tested exhibit nearly monoexponential decays, with narrow in vivo lifetime distributions suitable for lifetime multiplexing. Quantitative separation of two fluorophores with lifetimes of 1.1 and 1.37 ns is demonstrated for relative concentrations of 1:5. Finally, we demonstrate tomographic imaging of two and three fluorophores in nude mice with fluorophores that localize to distinct organ systems. This technique should be widely applicable to imaging multiple NIR fluorophores in 3-D.

  5. Positron annihilation studies of SmS and (Smsub(0.8)Gdsub(0.2))S across valence transitions

    International Nuclear Information System (INIS)

    Positron life-time measurements have been made in SmS under pressure up to 15 kbar and in (Smsub(0.8)Gdsub(0.2))S at temperatures from 10 K to 300 K. A discontinuous change in life-time was observed at the valence transition. This is explained on the basis of the changes in the lattice parameter and the electronic structure of these compounds. (author)

  6. Lifetime Plots of N and $\\Delta$ Resonances

    CERN Document Server

    Kelkar, N G; Khemchandani, K P; Jain, S R; Jain, Sudhir R.

    2004-01-01

    We present a method for the determination of baryon resonances and their parameters using existing relations between the S-matrix and time delay in pion nucleon scattering. We draw attention to the fact that the existence of a positive maximum in time delay, which is related to the lifetime of a resonance is a necessary criterion for the existence of a resonance and should be used as a constraint in conventional analyses which locate resonances from poles of the S-matrix and Argand diagrams. The usefulness of the time delay or lifetime plots of resonances is demonstrated through a detailed analysis of the time delay in several partial waves of $\\pi N$ elastic scattering.

  7. Positron annihilation study of ageing and creep on inconel X750

    International Nuclear Information System (INIS)

    The correlation of positron annihilation characteristics with microstructrual changes occurring in a Ni-base alloy is experimentally studied using lifetime and angular-correlation methods. The samples are examined at room temperature after various ageing phases and after creep rupture; their structure is also investigated by differential chemical analysis, by electron microscopy and by small-angle neutron scattering. The comparison of the results obtained with the various techniques shows the field of applicability of the positron annihilation technique for material testing in cases of technological interest. (author)

  8. Positron annihilation studies of neutron irradiated and thermally treated reactor pressure vessel steels

    International Nuclear Information System (INIS)

    Positron annihilation lifetime measurements using the pulsed low energy positron system (PLEPS) were applied for the first time for the investigation of defects of irradiated and thermally treated reactor pressure vessel (RPV) steels. PLEPS results showed that the changes in the microstructure of the RPV-steel properties caused by neutron irradiation and post-irradiation thermal treatment can be detected. The samples originated from the Russian 15Kh2MFA and Sv10KhMFT steels, commercially used at WWER-440 reactors, were irradiated near the core at NPP Bohunice (Slovakia) to neutron fluences in the range from 7.8x1023 to 2.5x1024 m-2

  9. W-Co-C films on Ni substrate studied by positron annihilation

    International Nuclear Information System (INIS)

    Sputtered W-Co-C films were deposited on well annealed high purity nickel substrate by r.f. magnetron process. Film thicknesses of 3.6 and 7.0 μm were deposited on 125 and 500μm Ni foils after cleaning by argon bombardment. Chemical composition and crystallinity of the films were determined by EDXS and XRD techniques. Positron measurements were made, during isochronal annealing until 650degC, by Doppler broadening and lifetime techniques for positron incidences on the film side and on the substrate side of the samples. Evidence for defects inside the film and the substrate is discussed

  10. Polymeric coating degradation in accelerated weathering investigated by using positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Photo-degradation of a polyurethane-based topcoat induced by accelerated Xe-lamp irradiation is studied using Doppler broadened energy spectra (DBES) and positron annihilation lifetime (PAL) spectroscopy coupled with slow positron technique. Significant and similar variations of S-parameter and ortho-positronium intensity (I3) on the coating are observed as functions of depth and of exposure time. Cross-link densities have been measured by the solvent-swelling method. A correlation between the increase of crosslink density and a reduction of free-volume and hole fraction during the degradation is observed. (orig.)

  11. Early Stages of Precipitation Process in Al-(Mn-)Sc-Zr Alloy Characterized by Positron Annihilation

    KAUST Repository

    Vlach, Martin

    2015-01-29

    Thermal effects on the precipitation stages in as-cast Al-0.70 at. pct Mn-0.15 at. pct Sc-0.05 at. pct Zr alloy were studied. The role of lattice defects was elucidated by positron annihilation spectroscopy (lifetime and coincidence Doppler broadening) enabling investigation of solutes clustering at the atomic scale. This technique has never been used in the Al-Sc- and/or Al-Zr-based alloys so far. Studies by positron annihilation were combined with resistometry, hardness measurements, and microstructure observations. Positrons trapped at defects are preferentially annihilated by Sc electrons. Lifetime of trapped positrons indicates that Sc atoms segregate at dislocations. Maximum fraction of positrons annihilated by Sc electrons occurring at 453 K (180 °C) suggests that clustering of Sc bound with vacancies takes place. It is followed by peak of this fraction at 573 K (300 °C). A rise of the contribution of trapped positrons annihilated by Zr electrons starting at 513 K (240 °C) and attaining maximum also at 573 K (300 °C) confirms that Zr participates in precipitation of the Al3Sc particles already at these temperatures. The pronounced hardening at 573 K (300 °C) has its nature in the precipitation of the Al3Sc particles with a Zr-rich shell. The contribution of trapped positrons annihilated by Mn electrons was found to be negligible. © 2015, The Minerals, Metals & Materials Society and ASM International.

  12. Positron annihilation in the hydrogenated granular superconductor of YBa 2Cu 3O 7-δ

    Science.gov (United States)

    Lam, C. C.; Shao, L. W.; Jin, X.; Chen, W. M.; Xiong, H. Q.; Feng, J.; Qi, S. R.; Hung, K. C.

    1996-02-01

    In this paper, we have used the sputtering neutral-particles mass spectroscopy (SNMS) and positron-annihilation technique to investigate the effect of hydrogenation on the physical properties of different oxygenated YBa 2Cu 3O 7-δ superconductors. Under the same of hydrogenation treatment, the hydrogenation effects on the superconductors are compared to the non-superconductors. It was shown that the hydrogen concentration in the superconductors is about eight times of the non-superconductor's. It was proven that the long lifetime of positrons in the annihilation process is determined by the variation of the concentrations of monovacancies and microvoids, which takes place in both of intragrain and intergrain samples. The hydrogenation effect can be classified into four stages. At the first stage, the hydrogen atoms fill both monovacancy and microvoid. At the end of the first stage, the long lifetime τ2 reaches the maximum value which is determined by the lifetime of the positron in the monovacancy-free and nearly microvoid-exhausted YBCO sample. In the second stage, the hydrogen charging will lead to creation of new monovacancies; this will make the long lifetime τ2 drop monotonically to its minimum value. In the third stage, further hydrogen charging promotes the formation of microvoids, and leads to an increasing τ2 up to a saturation value, which indicates the equilibrium concentrations of monovacancy and microvoid at that temperature.

  13. Identification of open-volume defects in disordered and amorphized Si: A depth-resolved positron annihilation study

    International Nuclear Information System (INIS)

    Depth-resolved positron beam studies have been carried out on Ar-irradiated Si using Doppler S parameter and lifetime measurements. Si samples have been irradiated with 140-keV Ar ions to a dose of 2x1013 and 5x1016 Ar/cm2, respectively, so as to produce disordered and amorphous states in near-surface regions. The observed features of the defect sensitive line shape S parameter indicate the presence of small vacancylike defects in the disordered sample and higher-order vacancy clusters in an amorphous sample. Pulsed positron beam lifetime results indicate that the disordered Si sample exhibits lifetime distribution ascribable to mostly divacancies. In the case of an amorphous sample, the lifetime distribution is broad with larger lifetime values indicating the presence of a distribution of large vacancy clusters or nanovoids. By using theoretical lifetime values for Si reported in the literature, an empirical fit to the lifetime variation as a function of vacancy cluster size is obtained. By comparing the experimental lifetime distribution with this data, the vacancy cluster size distribution in disordered and amorphous Si is deduced. In disordered Si, divacancies are found to be the dominant defects species followed by small concentration of V3. In amorphous Si, nanovoids in the size range of four to seven vacancy clusters are present with V5 and V6 clusters being the dominant defect species. The implication of these results is discussed in light of recent computer-simulation studies

  14. Optical and microstructural characterization of porous silicon using photoluminescence, SEM and positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cheung, C K [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Nahid, F [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Cheng, C C [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Beling, C D [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Fung, S [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Ling, C C [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Djurisic, A B [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Pramanik, C [Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700032 (India); Saha, H [Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700032 (India); Sarkar, C K [Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700032 (India)

    2007-12-05

    We have studied the dependence of porous silicon morphology and porosity on fabrication conditions. N-type (100) silicon wafers with resistivity of 2-5 {omega} cm were electrochemically etched at various current densities and anodization times. Surface morphology and the thickness of the samples were examined by scanning electron microscopy (SEM). Detailed information of the porous silicon layer morphology with variation of preparation conditions was obtained by positron annihilation spectroscopy (PAS): the depth-defect profile and open pore interconnectivity on the sample surface has been studied using a slow positron beam. Coincidence Doppler broadening spectroscopy (CDBS) was used to study the chemical environment of the samples. The presence of silicon micropores with diameter varying from 1.37 to 1.51 nm was determined by positron lifetime spectroscopy (PALS). Visible luminescence from the samples was observed, which is considered to be a combination effect of quantum confinement and the effect of Si = O double bond formation near the SiO{sub 2}/Si interface according to the results from photoluminescence (PL) and positron annihilation spectroscopy measurements. The work shows that the study of the positronium formed when a positron is implanted into the porous surface provides valuable information on the pore distribution and open pore interconnectivity, which suggests that positron annihilation spectroscopy is a useful tool in the porous silicon micropores' characterization.

  15. Lifetime costs of cerebral palsy

    DEFF Research Database (Denmark)

    Kruse, Marie; Michelsen, Susan Ishøy; Flachs, Esben Meulengracht;

    2009-01-01

    This study quantified the lifetime costs of cerebral palsy (CP) in a register-based setting. It was the first study outside the US to assess the lifetime costs of CP. The lifetime costs attributable to CP were divided into three categories: health care costs, productivity costs, and social costs....... The population analyzed was retrieved from the Danish Cerebral Palsy Register, which covers the eastern part of the country and has registered about half of the Danish population of individuals with CP since 1950. For this study we analyzed 2367 individuals with CP, who were born in 1930 to 2000 and...

  16. Positron emitter labeled enzyme inhibitors

    International Nuclear Information System (INIS)

    This invention involves a new strategy for imagining and mapping enzyme activity in the living human and animal body using positron emitter-labeled suicide enzyme inactivators or inhibitors which become covalently bound to the enzyme as a result of enzymatic catalysis. Two such suicide inactivators for monoamine oxidase have been labeled with carbon-11 and used to map the enzyme subtypes in the living human and animal body using PET. By using positron emission tomography to image the distribution of radioactivity produced by the body penetrating radiation emitted by carbon-11, a map of functionally active monoamine oxidase activity is obtained. Clorgyline and L-deprenyl are suicide enzyme inhibitors and irreversibly inhibit monoamine oxidase. When these inhibitors are labeled with carbon-11 they provide selective probes for monoamine oxidase localization and reactivity in vivo using positron emission tomography

  17. Instrumentation in positron emission tomography

    International Nuclear Information System (INIS)

    Positron emission tomography (PET) is a three-dimensional medical imaging technique that noninvasively measures the concentration of radiopharmaceuticals in the body that are labeled with positron emitters. With the proper compounds, PET can be used to measure metabolism, blood flow, or other physiological values in vivo. The technique is based on the physics of positron annihilation and detection and the mathematical formulations developed for x-ray computed tomography. Modern PET systems can provide three-dimensional images of the brain, the heart, and other internal organs with resolutions on the order of 4 to 6 mm. With the selectivity provided by a choice of injected compounds, PET has the power to provide unique diagnostic information that is not available with any other imaging modality. This is the first five reports on the nature and uses of PET that have been prepared for the American Medical Association's Council on Scientific Affairs by an authoritative panel

  18. Gadolinium substitution induced defect restructuring in multiferroic BiFeO3: case study by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation spectroscopy (PAS) comprising of the measurements of positron lifetime and coincidence Doppler broadening spectra has been carried out to understand and monitor the evolution of the vacancy-type defects arising from the ionic deficiencies at lattice points of the multiferroic perovskite bismuth ferrite (BiFeO3) doped with 1, 5 and 10 at% gadolinium (Gd3+) ions. Negatively charged defects in the form of Bi3+ monovacancies (VBi3−) were present in the undoped nanocrystallites, which strongly trapped positrons. During the successive doping by Gd3+ ions, the positron trapping efficiency decreased while the doped ions combined with the vacancies to form complexes, which became neutral. A fraction of the positrons got annihilated at the crystallite surfaces too, being evident from the very large positron lifetimes obtained and confirming the nano-size-specific characteristics of the samples. Further, the intercrystallite regions provided favourable sites for orthopositronium formation, although in minute concentrations. The dopant ion-complex formation was also depicted clearly by the defect characteristic S–W plot. Also, the large change of electrical resistivity with Gd concentration has been explained nicely by invoking the defect information from the PAS study. The study has demonstrated the usefulness of an excellent method of defect identification in such a novel material system, which is vital information for exploiting them for further technological applications. (paper)

  19. The intense slow positron beam facility at the PULSTAR reactor and applications in nano-materials study

    International Nuclear Information System (INIS)

    An intense slow positron beam has been established at the PULSTAR nuclear research reactor of North Carolina State University. The slow positrons are generated by pair production in a tungsten moderator from gammarays produced in the reactor core and by neutron capture reactions in cadmium. The moderated positrons are electrostatically extracted and magnetically guided out of the region near the core. Subsequently, the positrons are used in two spectrometers that are capable of performing positron annihilation lifetime spectroscopy (PALS) and positron Doppler broadening spectroscopy (DBS) to probe the defect and free volume properties of materials. One of the spectrometers (e+-PALS) utilizes an rf buncher to produce a pulsed beam and has a timing resolution of 277 ps. The second spectrometer (Ps-PALS) uses a secondary electron timing technique and is dedicated to positronium lifetime measurements with an approximately 1 ns timing resolution. PALS measurements have been conducted in the e+-PALS spectrometer on a series of nano-materials including organic photovoltaic thin films, membranes for filtration, and polymeric fibers. These studies have resulted in understanding some critical issues related to the development of the examined nano-materials.

  20. Creation of electron-positron pairs at excited Landau levels by neutrino in a strong magnetic field

    CERN Document Server

    Kuznetsov, A V; Savin, V N

    2014-01-01

    The process of neutrino production of electron positron pairs in a magnetic field of arbitrary strength, where electrons and positrons can be created in the states corresponding to excited Landau levels, is analysed. The mean value of the neutrino energy loss due to the process $\

  1. Analytical positron range modelling in heterogeneous media for PET Monte Carlo simulation

    Energy Technology Data Exchange (ETDEWEB)

    Lehnert, Wencke; Meikle, Steven R [Discipline of Medical Radiation Sciences, Faculty of Health Sciences, University of Sydney, PO Box 170, Lidcombe NSW 1825 (Australia); Gregoire, Marie-Claude; Reilhac, Anthonin, E-mail: wlehnert@uni.sydney.edu.au [Australian Nuclear Science and Technology Organisation, Lucas Heights NSW 2234 (Australia)

    2011-06-07

    Monte Carlo simulation codes that model positron interactions along their tortuous path are expected to be accurate but are usually slow. A simpler and potentially faster approach is to model positron range from analytical annihilation density distributions. The aims of this paper were to efficiently implement and validate such a method, with the addition of medium heterogeneity representing a further challenge. The analytical positron range model was evaluated by comparing annihilation density distributions with those produced by the Monte Carlo simulator GATE and by quantitatively analysing the final reconstructed images of Monte Carlo simulated data. In addition, the influence of positronium formation on positron range and hence on the performance of Monte Carlo simulation was investigated. The results demonstrate that 1D annihilation density distributions for different isotope-media combinations can be fitted with Gaussian functions and hence be described by simple look-up-tables of fitting coefficients. Together with the method developed for simulating positron range in heterogeneous media, this allows for efficient modelling of positron range in Monte Carlo simulation. The level of agreement of the analytical model with GATE depends somewhat on the simulated scanner and the particular research task, but appears to be suitable for lower energy positron emitters, such as {sup 18}F or {sup 11}C. No reliable conclusion about the influence of positronium formation on positron range and simulation accuracy could be drawn.

  2. Radiative lifetimes of neutral erbium

    Energy Technology Data Exchange (ETDEWEB)

    Den Hartog, E A; Chisholm, J P; Lawler, J E, E-mail: eadenhar@wisc.ed, E-mail: chisholm@astro.wisc.ed, E-mail: jelawler@wisc.ed [Department of Physics, University of Wisconsin, 1150 University Ave., Madison, WI 53706 (United States)

    2010-08-14

    Radiative lifetimes have been measured for 123 levels of neutral erbium using time-resolved laser-induced fluorescence on a slow beam of erbium atoms. Of the 123 levels, 56 are even parity and range in energy from 26 993 to 40 440 cm{sup -1} and 67 are odd parity ranging from 16 070 to 38 401 cm{sup -1}. This set of Er i lifetimes is much more extensive than others published to date, with 90 of the 123 level lifetimes measured for the first time. These lifetimes will provide the absolute calibration for a large set of measured Er i transition probabilities. Spectroscopic studies of rare earth elements including erbium are motivated by research needs in both the astrophysics and lighting communities.

  3. Radiative lifetimes of neutral erbium

    International Nuclear Information System (INIS)

    Radiative lifetimes have been measured for 123 levels of neutral erbium using time-resolved laser-induced fluorescence on a slow beam of erbium atoms. Of the 123 levels, 56 are even parity and range in energy from 26 993 to 40 440 cm-1 and 67 are odd parity ranging from 16 070 to 38 401 cm-1. This set of Er i lifetimes is much more extensive than others published to date, with 90 of the 123 level lifetimes measured for the first time. These lifetimes will provide the absolute calibration for a large set of measured Er i transition probabilities. Spectroscopic studies of rare earth elements including erbium are motivated by research needs in both the astrophysics and lighting communities.

  4. Radiative lifetimes of neutral gadolinium

    Energy Technology Data Exchange (ETDEWEB)

    Den Hartog, E A; Bilty, K A; Lawler, J E, E-mail: eadenhar@wisc.edu, E-mail: biltyka@uwec.edu, E-mail: jelawler@wisc.edu [Department of Physics, University of Wisconsin, 1150 University Ave, Madison, WI 53706 (United States)

    2011-03-14

    The current work is part of an ongoing study of radiative properties of rare earth neutral atoms motivated by research needs in several disparate fields including astrophysics, laser chemistry and lighting technology. Time-resolved laser-induced fluorescence on a slow atomic beam has been used to measure radiative lifetimes, accurate to {+-}5%, for 136 levels of neutral gadolinium. Of the 136 levels, 6 are odd parity ranging in energy from 32 929 to 36 654 cm{sup -1}, and the remaining 130 are even parity ranging from 17 750 to 34 175 cm{sup -1}. This set of Gd i lifetimes represents a significant extension to the available published data, with 93 of the 136 level lifetimes measured for the first time. These lifetimes will provide the absolute normalization for a large set of measured Gd i transition probabilities.

  5. Radiative lifetimes of neutral gadolinium

    International Nuclear Information System (INIS)

    The current work is part of an ongoing study of radiative properties of rare earth neutral atoms motivated by research needs in several disparate fields including astrophysics, laser chemistry and lighting technology. Time-resolved laser-induced fluorescence on a slow atomic beam has been used to measure radiative lifetimes, accurate to ±5%, for 136 levels of neutral gadolinium. Of the 136 levels, 6 are odd parity ranging in energy from 32 929 to 36 654 cm-1, and the remaining 130 are even parity ranging from 17 750 to 34 175 cm-1. This set of Gd i lifetimes represents a significant extension to the available published data, with 93 of the 136 level lifetimes measured for the first time. These lifetimes will provide the absolute normalization for a large set of measured Gd i transition probabilities.

  6. Radiative lifetimes of neutral samarium

    International Nuclear Information System (INIS)

    Radiative lifetimes of 120 odd-parity levels of neutral samarium, ranging in energy from 17 190 to 33 507 cm−1, are measured using the technique of time-resolved laser-induced fluorescence on a slow atomic beam. This work is part of an ongoing study of radiative properties of rare earth neutral atoms, and is motivated by research needs in astrophysics and lighting technology. This set of Sm i lifetimes substantially increases the available published lifetime data, with 49 of the 120 level lifetimes measured for the first time. These data, most of which are accurate to ±5%, will be combined with branching fractions determined from Fourier transform spectroscopy to produce a large set of measured Sm i transition probabilities. (paper)

  7. Measurement of Charm Meson Lifetimes

    International Nuclear Information System (INIS)

    We report measurements of the D0 , D+ , and D+s meson lifetimes using 3.7 fb-1 of e+e- annihilation data collected near the Υ(4S) resonance with the CLEO detector. The measured lifetimes of the D0 , D+ , and D+s mesons are 408.5±4.1+3.5-3.4 fs , 1033.6±22.1+9.9-12.7 fs , and 486.3±15.0+4.9-5.1 fs . The precision of these lifetimes are comparable to those of the best previous measurements, and the systematic errors are very different. In a single experiment we find that the ratio of the D+s and D0 lifetimes is 1.19±0.04 . copyright 1999 The American Physical Society

  8. Final report on reliability and lifetime prediction.

    Energy Technology Data Exchange (ETDEWEB)

    Gillen, Kenneth Todd; Wise, Jonathan; Jones, Gary D.; Causa, Al G. [Goodyear Tire and Rubber Co., Akron, OH; Terrill, Edward R. [Goodyear Tire and Rubber Co., Akron, OH; Borowczak, Marc [Goodyear Tire and Rubber Co., Akron, OH

    2012-12-01

    This document highlights the important results obtained from the subtask of the Goodyear CRADA devoted to better understanding reliability of tires and to developing better lifetime prediction methods. The overall objective was to establish the chemical and physical basis for the degradation of tires using standard as well as unique models and experimental techniques. Of particular interest was the potential application of our unique modulus profiling apparatus for assessing tire properties and for following tire degradation. During the course of this complex investigation, extensive relevant information was generated, including experimental results, data analyses and development of models and instruments. Detailed descriptions of the findings are included in this report.

  9. Positrons trapped in polyethylene: Electric field effect

    International Nuclear Information System (INIS)

    The intensity of the iot2-component of positrons annihilated in polyethylene is found to increase with increasing electric field, while the formation probability of the positron state responsible for this component remains independent of the field. (orig.) 891 HPOE

  10. NMF on positron emission tomography

    DEFF Research Database (Denmark)

    Bödvarsson, Bjarni; Hansen, Lars Kai; Svarer, Claus;

    2007-01-01

    In positron emission tomography, kinetic modelling of brain tracer uptake, metabolism or binding requires knowledge of the cerebral input function. Traditionally, this is achieved with arterial blood sampling in the arm or as shown in (Liptrot, M, et al., 2004) by non-invasive K-means clustering....... We propose another method to estimate time-activity curves (TAC) extracted directly from dynamic positron emission tomography (PET) scans by non-negative matrix factorization (NMF). Since the scaling of the basis curves is lost in the NMF the estimated TAC is scaled by a vector alpha which is...

  11. Study on low-energy positron polarimetry

    Indian Academy of Sciences (India)

    A Schälicke; G Alexander; R Dollan; K Laihem; T Lohse; S Riemann; P Starovoitov; A Ushakov

    2007-12-01

    A polarised positron source has been proposed for the design of the international linear collider (ILC). In order to optimise the positron beam, a measurement of its degree of polarisation close to the positron creation point is desired. In this contribution, methods for determining the positron polarisation at low energies are reviewed. A newly developed polarisation extension to GEANT4 will provide the basis for further polarimeter investigations.

  12. Identification of cadmium vacancy complexes in CdTe(In), CdTe(Cl) and CdTe(I) by positron annihilation with core electrons

    International Nuclear Information System (INIS)

    Doppler-broadening of the 511 keV positron annihilation line was used for defect identification in CdTe materials. In electrically compensated lightly n-type CdTe(In) and lightly p-type or semi-insulating CdTe(Cl) crystals positron lifetime measurements show vacancy defects with characteristic positron lifetimes of 323 ps and 370 ps, respectively. The shapes of the high-momentum parts of the measured electron-momentum distributions indicate that both defects contain a cadmium vacancy VCd. The defects are assigned to vacancy-donor complexes VCd-In and VCd-Cl, respectively. A vacancy in MBE-grown CdTe(I) layers observed with a low-energy positron beam is also identified as a cadmium vacancy VCd which is most likely complexed with I-donors. (author)

  13. The Effect of Temperature on the Free Volume in Polytetrafluoroethylene Studied by Positron Annihilation Spectroscopy

    International Nuclear Information System (INIS)

    The positron annihilation techniques have been applied to investigate the free volume holes in pure and doped polytetrafluoroethylene (PTFE) with glass as a function of temperature. The measurements were performed from room temperature up to 250 degree C. The lifetime spectra were analyzed using two methods; 1) Finite-term analysis to determine the average values of the orthopositronium (o-Ps) lifetime and its intensity using PATFIT program, 2) Continuous lifetime analysis to obtain the o-Ps lifetime and o-Ps hole volume distributions using MELT program. The ortho-positronium (o-Ps) lifetimes, (T3 and T4) are found to be vary depending upon the phase of the polymer. Within the temperature range two transitions can be observed. The first one is related to the glass transition temperature, Tg (at 130 degree C for pure PTFE and at 110 degree C for doped PTFE with glass). The second one is the crystalline temperature at 210 degree C for the two samples. It was found that, Tg is shifted toward the lower values (110 degree C) for doped PTFE with glass, which could be attributed to the increase in the degree of crystallinity. This is in consistent with the wide-angle x-ray scattering data. A correlation between the positron annihilation parameters and the electrical conductivity was achieved

  14. Lifetime management and lifetime extension at PAKS nuclear power plant

    International Nuclear Information System (INIS)

    The Paks Nuclear Power Plant strategy is to extend the operational lifetime of the plant and renew the operational licence for 20 years over the designed and licensed lifetime. At Paks NPP the systematic ageing management activities were started eight years ago. It is now a deliberate and programmatic activity, which ensures the plant safety. The programme started with selection of equipment important from both lifetime and safety point of view. The systematic ageing management includes the definition of ageing processes, identification of sensitive parts of the components and the dominant ageing processes, and their control and monitoring. A computerized monitoring system supports the ageing management activity of the plant. The feasibility of plant lifetime extension has been investigated. The study includes a detailed plant assessment, ageing and lifetime prognosis of representative set of structures, systems and components, definition of necessary reconstructions and detailed business analysis. It has been found that a 20 years extension of operation is feasible from both technical and business point of view. Basic results of plant assessment and business analysis are discussed in the paper. A project has been launched by NPP Paks for preparation of plant life extension and licence renewal. The project tasks and conditions of success are presented and discussed in the paper. (author)

  15. Temperature Dependence of Free Volume in Cross-linked Polyurethane Studied by Positrons

    Institute of Scientific and Technical Information of China (English)

    何春清; 戴益群; 王波; 王少阶; 王贵友; 胡春圃

    2001-01-01

    Positron annihilation lifetime spectroscopy has been used to study the free volume properties of the cross-linked polyurethane network as a function of temperature in the range from 15K to 300K. The glass transition of polyurethane was observed and the thermal expansion coefficient of the free volume was calculated. Analysis of the ortho-positronium (o-Ps) lifetime distribution shows that the distribution of the free volume in polyurethane is slightly broadened with the increasing temperature in the glassy state, and then significantly broadened with the increasing temperature above the glass transition.

  16. Study of silica aerogel by the measurement of lifetime-momentum correlation

    International Nuclear Information System (INIS)

    Lifetime-momentum correlation measurements were applied to separate electron momentum distribution due to the first layer atoms at the surface of vacant space from that due to bulk in silica aerogel fine particles. Positroniums (Ps) solely interacted with the first layer atoms, and the momentum distribution of the electrons of the first layer atoms was obtained from the Doppler broadening of γ-rays due to the pickoff annihilation of orthopositroniums. The electron distribution of the bulk, on the other hand, was deduced from the annihilation γ-rays of positrons. The momentum of electron · positron pair was measured by a high purity Ge detector, and a β+-γ coincidence method was used for the lifetime measurements. Another coincidence method using photo-multiplier tubes was also applied to yield higher time resolution. The lifetime spectrum due to annihilation γ-rays in time range from 50 to 150 ns was attributed to the pickoff annihilation of orthopositroniums in the vacant spaces in the silica aerogel, and the spectrum in the time range from 0.7 to 2.2 ns was yielded from positrons without forming positroniums. The change of the pickoff annihilation spectrum after annealing above 200 degC for the aerogel was ascribed to the change from -OCH3 radicals to -OH radicals at the surface from the reference of measurements by infrared absorption. (Y. K.)

  17. Positron annihilation studies of Eu and Dy doped α'-Sr2SiO4

    Science.gov (United States)

    Gupta, S. K.; Sudarshan, K.; Sharma, S. K.; Pujari, P. K.; Natarajan, V.

    2015-06-01

    Sr2SiO4 is an important inorganic host for lanthanide doped white light emitting diodes (LEDs). Strontium silicate (Sr2SiO4) samples doped with 1.0 mol% of Eu3+ and Dy3+ content were prepared via sol-gel route and characterized by X-ray diffraction (XRD), Raman spectroscopy and positron annihilation spectroscopy (PAS). The concentration of the dopant ion and the temperature of annealing were optimized for maximum luminescence intensity. The positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements indicated that the local environment around the positron annihilation site is different in Eu+3 doped and Dy+3 doped samples. The results could be explained based on the different local site occupancy of Eu+3 and Dy+3 in the matrix.

  18. Positron annihilation spectroscopy and specific heat study of Neon ion irradiated MgB{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Talapatra, A. [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata 700064 (India); Bandyopadhyay, S.K. [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata 700064 (India)], E-mail: skband@veccal.ernet.in; Nambissan, P.M.G. [Saha Institute of Nuclear Physics, 1/AF, Bidhan Nagar, Kolkata 700064 (India); Sen, Pintu [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata 700064 (India); Ganesan, V. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452017 (India)

    2008-02-25

    Specific heat studies under magnetic field and positron annihilation spectroscopy were carried out on 160 MeV Ne ion irradiated polycrystalline MgB{sub 2} samples. There is an unusual decrease in positron lifetime in the irradiated sample which may be due to neon ion implantation. This was also indicated by change in cell volume. Coincidence Doppler Broadening Spectra of Mg, B, irradiated and unirradiated MgB{sub 2} show that positrons primarily annihilate in boron sublattice in the unirradiated sample whereas there is some similarity of the spectrum of the irradiated sample with that of Mg. There is Mg deficiency in the unirradiated sample whereas predominantly boron vacancies exist in Ne ion irradiated MgB{sub 2} sample. Specific heat measurements show that there is a small increase in electronic part of the specific heat and electron-phonon coupling constant.

  19. Positron annihilation spectroscopy and specific heat study of Neon ion irradiated MgB2

    International Nuclear Information System (INIS)

    Specific heat studies under magnetic field and positron annihilation spectroscopy were carried out on 160 MeV Ne ion irradiated polycrystalline MgB2 samples. There is an unusual decrease in positron lifetime in the irradiated sample which may be due to neon ion implantation. This was also indicated by change in cell volume. Coincidence Doppler Broadening Spectra of Mg, B, irradiated and unirradiated MgB2 show that positrons primarily annihilate in boron sublattice in the unirradiated sample whereas there is some similarity of the spectrum of the irradiated sample with that of Mg. There is Mg deficiency in the unirradiated sample whereas predominantly boron vacancies exist in Ne ion irradiated MgB2 sample. Specific heat measurements show that there is a small increase in electronic part of the specific heat and electron-phonon coupling constant

  20. Effect of epoxide equivalent on microstructure of epoxy/rectorite nanocomposite studied by positrons

    International Nuclear Information System (INIS)

    The epoxy/rectorite nanocomposites with different epoxide equivalent ranging from 188 to 1110 were prepared and the effects of epoxide equivalent on microstructure of materials were studied by X-ray diffraction (XRD) and positron annihilation lifetime spectroscope (PALS). In nanocomposites, the formation of exfoliated structure was observed from XRD pattern at epoxide equivalent >263. The PALS measurements reveal that the fractional free volume in nanocomposites was strongly affected by epoxide equivalent, in particular, the free-volume concentration was dramatically decreased with the increasing epoxide equivalent from 188 to 263, and the S parameter indicates the rectorite structure change and the high sensitivity of positron annihilation to the entry of rectorite into epoxy. These results indicate that positron annihilation characteristics are useful for study the microstructure of epoxy/rectorite nanocomposites

  1. Defect identification in semiconductors with positron annihilation: experiment and theory

    Science.gov (United States)

    Tuomisto, Filip

    2015-03-01

    Positron annihilation spectroscopy is a very powerful technique for the detection, identification and quantification of vacancy-type defects in semiconductors. In the past decades, it has been used to reveal the relationship between opto-electronic properties and specific defects in a wide variety of materials - examples include parasitic yellow luminescence in GaN, dominant acceptor defects in ZnO and broad-band absorption causing brown coloration in natural diamond. In typical binary compound semiconductors, the selective sensitivity of the technique is rather strongly limited to cation vacancies that possess significant open volume and suitable charge (negative of neutral). On the other hand, oxygen vacancies in oxide semiconductors are a widely debated topic. The properties attributed to oxygen vacancies include the inherent n-type conduction, poor p-type dopability, coloration (absorption), deep level luminescence and non-radiative recombination, while the only direct experimental evidence of their existence has been obtained on the crystal surface. We will present recent advances in combining state-of-the-art positron annihilation experiments and ab initio computational approaches. The latter can be used to model both the positron lifetime and the electron-positron momentum distribution - quantities that can be directly compared with experimental results. We have applied these methods to study vacancy-type defects in III-nitride semiconductors (GaN, AlN, InN) and oxides such as ZnO, SnO2, In2O3andGa2O3. We will show that cation-vacancy-related defects are important compensating centers in all these materials when they are n-type. In addition, we will show that anion (N, O) vacancies can be detected when they appear as complexes with cation vacancies.

  2. Solid state diffusion of NaCl into NaY zeolite studied by positron annihilation

    International Nuclear Information System (INIS)

    A series of samples, prepared from mechanical mixtures of NaCl with NaY zeolite and resulting in the dispersion of NaCl in NaY, was studied by position annihilation spectroscopy. We measured the positron lifetime spectroscopy as a function of the weight ratio of the NaCl-NaY zeolite heated at 500 degree C for 1 h, as a function of the heating temperature held for 1 h, and as a function of the heating duration at 500 degree C for NaCl/NaY (15%). All the lifetime spectra were resolved into five components, in which the third, fourth and fifth components are related to the positron annihilation in β cage, supercage and interface void respectively. The experimental results showed that position annihilation spectroscopy is sensitive to the change of the dispersion of NaCl in NaY zeolite

  3. Facility for positron computed tomography

    International Nuclear Information System (INIS)

    The positron computed tomography facility has got scintillator detector rings simultaneously recording more than one tomogrphic image of different cross-sections of the patient. The detectors in neighboring rings are staggered and can be rotated with respect to each other in order to increase the count rate without loss of efficiency. (DG)

  4. Clinical applications of positron scanning

    International Nuclear Information System (INIS)

    There are only a few ways in which the radiopharmaceuticals carrying the positron-emitting isotope can be applied. a. intravenous bolus injection, b. continuous intravenous injection until equilibrium is reached, c. inhalation of a bolus of radioactive gases, d. continuous inhalation until equilibrium is reached. (orig./VJ)

  5. Positron-acoustic shock waves associated with cold viscous positron fluid in superthermal electron-positron-ion plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Uddin, M. J., E-mail: josim.phys2007@gmail.com; Alam, M. S.; Mamun, A. A. [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh)

    2015-06-15

    A theoretical investigation is made on the positron-acoustic (PA) shock waves (SHWs) in an unmagnetized electron-positron-ion plasma containing immobile positive ions, cold mobile positrons, and hot positrons and electrons following the kappa (κ) distribution. The cold positron kinematic viscosity is taken into account, and the reductive perturbation method is used to derive the Burgers equation. It is found that the viscous force acting on cold mobile positron fluid is a source of dissipation and is responsible for the formation of the PA SHWs. It is also observed that the fundamental properties of the PA SHWs are significantly modified by the effects of different parameters associated with superthermal (κ distributed) hot positrons and electrons.

  6. Miscibility and Crystallization Behavior of Poly (3- Hydroxybutyrate) and Poly (Ethylene Glycol) Blends Studied by Positron Annihilation Spectroscopy

    International Nuclear Information System (INIS)

    Poly (3-hydroxybutyrate) (PHB) is linear stereo regular aliphatic polyester synthesized by some bacteria as a store of carbon and energy. Because of its high biocompatibility and the ability to be fully biodegraded, PHB is of special interest in medicine. To improve the physiochemical properties of PHB, Polyethylene glycol (PEG) was used for modifications of PHB. By using the chloroform as co-solvent a series of (PHB/PEG) blend with different ratio ranging from 100:0.0 (wt %) to 50:50 (wt %) was prepared by solution casting-technique. Positron Annihilation Lifetime (PAL) technique has been applied to study the effect of addition PEG on the structure of PHB. The positron annihilation lifetime measurements were performed with a conventional fast-fast coincidence system. The lifetime parameter, ι3 which represents the ortho-positronium atom (o-Ps) lifetime and I3 which reflects the (o-Ps) intensity, give indication of the free-volume size and concentration respectively. Positron annihilation lifetime measurements showed that, ι3 increases by increasing PEG ratio until the concentration (80:20 wt %) then start to decrease by increasing PEG ratio. The obtained results are in agreement with the results of X-ray diffraction.

  7. Electrochemical and positron annihilation studies of semicarbazones and thiosemicarbazones derived from ferrocene

    International Nuclear Information System (INIS)

    A series of six ferrocene derivates containing a semicarbazone or thiosemicarbazone side chain was investigated by cyclic voltammetry and positron annihilation lifetime measurements. Both the redox and the electron capture processes took place on the Fe atom. Correlations between the two methods were proposed. taking into account the substituents on the side chain of the compounds, their redox potentials and the probabilities of o-positronium (o-Ps), formation. (author)

  8. Digital Set-Ups for Positron Annihilation Spectroscopy at PAS Laboratory Fei Stu Bratislava

    International Nuclear Information System (INIS)

    Current status of the digitization in Positron Lifetime and Coincidence Doppler Broadening spectroscopy set-ups at the Slovak University of Technology in Bratislava is described in this paper. In PALS set-ups two digitizer cards Acqiris DP-240 and Ztec ZT4612 with different parameters and abilities were tested. The first results from the Coincidence Doppler Broadening set-up using Adlink PCI-9820 digitizer card are presented. (author)

  9. Elevated Brain Cannabinoid CB1 Receptor Availability in Posttraumatic Stress Disorder: A Positron Emission Tomography Study

    OpenAIRE

    Neumeister, Alexander; Normandin, Marc D.; Pietrzak, Robert H.; Piomelli, Daniele; Zheng, Ming-Qiang; Gujarro-Anton, Ana; Potenza, Marc N.; Bailey, Christopher R.; Lin, Shu-fei; Najafzadeh, Soheila; Ropchan, Jim; Henry, Shannan; Corsi-Travali, Stefani; Carson, Richard E; Huang, Yiyun

    2013-01-01

    Endocannabinoids and their attending cannabinoid type 1 receptor (CB1) have been implicated in animal models of posttraumatic stress disorder (PTSD). However, their specific role has not been studied in people with PTSD. Herein, we present an in vivo imaging study using positron emission tomography (PET) and the CB1-selective radioligand [11C]OMAR in individuals with PTSD, and healthy controls with lifetime histories of trauma (trauma controls [TC]) and those without such histories (healthy c...

  10. Texas Intense Positron Source (TIPS)

    Science.gov (United States)

    O'Kelly, D.

    2003-03-01

    The Texas Intense Positron Source (TIPS) is a state of the art variable energy positron beam under construction at the Nuclear Engineering Teaching Laboratory (NETL). Projected intensities on the order of the order of 10^7 e+/second using ^64Cu as the positron source are expected. Owing to is short half-life (t1/2 12.8 hrs), plans are to produce the ^64Cu isotope on-site using beam port 1 of NETL TRIGA Mark II reactor. Following tungsten moderation, the positrons will be electrostatically focused and accelerated from few 10's of eV up to 30 keV. This intensity and energy range should allow routine performance of several analytical techniques of interest to surface scientists (PALS, PADB and perhaps PAES and LEPD.) The TIPS project is being developed in parallel phases. Phase I of the project entails construction of the vacuum system, source chamber, main beam line, electrostatic/magnetic focusing and transport system as well as moderator design. Initial construction, testing and characterization of moderator and beam transport elements are underway and will use a commercially available 10 mCi ^22Na radioisotope as a source of positrons. Phase II of the project is concerned primarily with the Cu source geometry and thermal properties as well as production and physical handling of the radioisotope. Additional instrument optimizing based upon experience gained during Phase I will be incorporated in the final design. Current progress of both phases will be presented along with motivations and future directions.

  11. Positron transport studies at the Au-(InP:Fe) interface

    International Nuclear Information System (INIS)

    Positron mobility and lifetime measurements have been carried out on semi-insulating Fe-doped InP samples with Au contacts used for electric field application. The lifetime measurements, with electric fields directed towards the Au-InP:Fe interface, reveal no component associated with interfacial open-volume sites and thus give no evidence of any positron mobility. The mobility measurements, made using the Doppler-shifted annihilation radiation technique, however, reveal a temperature independent positron mobility of about 20 cm2 V-1 s-1 in the range 150 - 300 K. These observations, together with results from I-V analysis, are discussed with reference to two possible band-bending schemes. The first, which requires an ionized shallow donor region adjacent to the Au-InP interface, seems less plausible on a number of grounds. In the second, however, an Fe2+ negative space charge produces an adverse diffusion barrier for positrons approaching the interface together with a non-uniform electric field in the samples capable of explaining the observed mobility results. (author)

  12. Thermal Stability of MgyTi1-y Thin Films Investigated by Positron Annihilation Spectroscopy

    Science.gov (United States)

    Anastasopol, A.; Eijt, S. W. H.; Schut, H.; Mulder, F. M.; Plazaola, F.; Dam, B.

    Mg-Ti compounds are attractive candidates as hydrogen storage materials for their fast sorption kinetics and high storage capacity. In this context, an investigation of their thermal stability is of great importance. The thermal stability of MgyTi1-y thin films was investigated using positron annihilation spectroscopy. Despite the positive enthalpy of mixing of Mg and Ti, positron Doppler Broadening of Annihilation Radiation (DBAR) depth profiling showed that Mg0.9Ti0.1 films are stable up to 300°C. However, for Mg0.7Ti0.3 films, segregation of Mg and Ti was observed at 300oC by the appearance of a clear Ti signature in the S-W diagrams and in the Doppler broadening depth profiles analyzed using VEPFIT. The thickness of the 250-300 nm thin films remained unchanged during the heating treatments. We further present ab-initio calculations of positron lifetimes of the corresponding metal and metal hydride phases for comparison to our previous positron annihilation lifetime spectroscopy (PALS) study.

  13. Defect dynamics in P+ implanted 6H-SiC studied by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    We study P+-implanted 6H-SiC samples by means of a variable energy slow positron beam. In as-grown samples we observe a slow fall of the annihilation S-parameter from the surface to the bulk value, indicating a long diffusion length, i.e. absence of positron-trapping defects. This result is also confirmed by positron-lifetime measurements yielding essentially a single-component lifetime of 148 ps. In the implanted samples we detect a wide flat region of slightly risen defectiveness. However, we note that, in order to reproduce reasonably well the depth of the damaged layer, one has to assume the presence of strong electric fields in the implanted region. With annealing, S-curves show a rising maximum, moving towards surface - probably, in as-implanted samples the defects are decorated by P+ ions and do not trap positrons in effective way. After the highest temperature annealing a highly defected region extends for the first 50 nm depth. We perform also atomic force microscopy to monitor the evolution of the surface defects. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Determination of properties of high temperature superconductors and amorphous metallic alloys using positron annihilation techniques. Final report for the period 15 January 1992 - 15 July 1995

    International Nuclear Information System (INIS)

    The positron lifetime results obtained on amorphous thermally treated Ni25Zr55Al20 alloy indicate that positrons annihilate at places with different properties. The observed shifts of positron lifetime distribution were analyzed in the terms of a relaxation of free-volume, i.e. chemical (CSRO) and topological (TSRO) short range ordering. The upper limit of the activation energy of CSRO and TSRO relaxation was determined to be 2.2eV and 2.6eV, respectively. Positron lifetime τ and Doppler broadening of the annihilation line measurements on very pure C60 sample as a function of temperature between 120 and 300 K have been reported. A rapid change of τ was observed between 240 and 250 K. This results indicate that the lattice from C60 molecules is undergoing a phase transition and the phases coexist over an ∼ 10K range. The annihilation of positrons in amorphous tetramethylpoly-carbonate has been investigated in the temperature range from 30 to 300 K. The observed dependences of the mean lifetime of oPs and its relative intensity 1 on temperature were interpreted within the framework of the microstructural free-volume concept. The man radius of free space (hole) was deduced to be around 3,1.10-10m. Refs, figs, tabs

  15. Confronting recent AMS-02 positron fraction and Fermi-LAT Extragalactic Gamma-Ray Background measurements with gravitino dark matter

    CERN Document Server

    Carquin, Edson; Gomez-Vargas, German A; Panes, Boris; Viaux, Nicolas

    2015-01-01

    The positron fraction measured by the space-based detectors PAMELA, Fermi-LAT and AMS-02 presents anomalous behaviour as energy increase. In particular AMS-02 observations provide compelling evidence for a new source of positrons and electrons. Its origin is unknown, it can be non-exotic (e.g. pulsars), be dark matter or maybe a mixture. We prove the gravitino of R-parity violating supersymmetric models as this source. As the gravitino is a spin 3/2 particle, it offers particular decay channels. We compute the electron, positron and gamma-ray fluxes produced by each gravitino decay channel as it would be detected at the Earth's position. Combining the flux from the different decay modes we can fit AMS-02 measurements of the positron fraction, as well as the electron and positron fluxes, with a gravitino dark matter mass in the range $1-2$ TeV and lifetime of $\\sim 1.0-0.8\\times 10^{26}$ s. The high statistics measurement of electron and positron fluxes, and the flattering in the behaviour of the positron frac...

  16. Lifetime measurements in 180Pt

    Science.gov (United States)

    Chen, Q. M.; Wu, X. G.; Chen, Y. S.; Li, C. B.; Gao, Z. C.; Li, G. S.; Chen, F. Q.; He, C. Y.; Zheng, Y.; Hu, S. P.; Zhong, J.; Wu, Y. H.; Li, H. W.; Luo, P. W.

    2016-04-01

    Lifetimes of the yrast states in 180Pt have been measured from 4+ to 8+ using the recoil distance Doppler-shift technique in the coincidence mode. These states were populated by the reaction 156Gd(28Si,4 n )180Pt at a beam energy of 144 MeV. The differential decay curve method was applied to determine the lifetimes from experimental coincidence data. The B (E 2 ) values extracted from lifetimes increase with increasing spin, implying rotor behavior, but do not show the typical shape coexistence where the B (E 2 ) values present a rapid increase at very low spins. Calculations based on the triaxial projected shell model were performed for the yrast states in 180Pt and the results of both energies and E 2 transition probabilities reproduce the experimental data very well. The result also shows that a better description of the yrast band in 180Pt requires consideration of the γ degree of freedom.

  17. Radiative lifetimes of neutral neodymium

    International Nuclear Information System (INIS)

    This work is part of an on-going study of radiative properties of rare earth neutral atoms. This work is motivated by research needs in several disparate fields including astrophysics and lighting technology. Radiative lifetimes of 100 levels of neutral neodymium are measured using the technique of time-resolved laser-induced fluorescence on a slow atomic beam. Of the 100 levels, 3 are even parity ranging in energy from 25 746 to 26 835 cm-1, and the remaining 97 are odd parity ranging from 17 787 to 27 786 cm-1. This set of Nd i lifetimes represents a significant extension to the available published data, with 51 of the 100 level lifetimes measured for the first time. These data, which are accurate to ±5%, provide the absolute normalization for a large set of measured Nd i transition probabilities.

  18. Free-volume mean sizes of polymers probed by positron annihilation spectroscopy: a correlation of results obtained by PAL and by ACAR methods

    International Nuclear Information System (INIS)

    Positron annihilation spectroscopy (PAS) has been developed to analyze the microstructure of polymers. Both positron annihilation lifetime (PAL) and angular correlation of positron annihilation radiation (ACAR) measurements give direct information about the mean hole sizes of free-volume holes in amorhpous materials. Parallel experiments of PAL and ACAR have been performed in an epoxy polymer as a function of temperature. The free-volume mean hole radii ranging from 2.3 to 3.2 A are obtained. The results obtained by PAL and ACAR agree with each other very well. A correlation of mean free-volume hole sizes obtained by these two methods is established. (orig.)

  19. Cyclotron, positrons and PET [positron emission tomography]. An overview

    International Nuclear Information System (INIS)

    PET (positron emission tomography) is a powerful new scientific tool which is capable of revealing biochemical transformations while they are occurring in the brain and other organs in the living human body. The application of PET to problems in biology and medicine is dominated by the short half-life of the isotopes used to prepare the radiotracers. The most commonly used positron emitting isotopes are carbon-11, fluorine-18, nitrogen-13, and oxygen-15 which have half-lives of 20.4, 110, 10 and 2 minutes, respectively. Their incorporation into radiotracers having diverse chemical structures and biochemical specificities has allowed the study of blood flow, sugar metabolism, oxygen metabolism, neurotransmission, enzyme activity and binding sites for therapeutic drugs and substances of abuse. PET research is most commonly carried out at a Cyclotron-PET Center (cyclotron, positron emission tomography, chemistry laboratory) where the short-lived isotopes can be produced and used efficiently. The number of Cyclotron-PET Centers has grown from 4 in 1976 to several dozen in 1988 and the number is expected to double in the next five years attesting to the vitality of the field and the current and anticipated contributions to research in biology and medicine

  20. Photon induced positron annihilation spectroscopy: A nondestructive method for assay of defects in large engineering materials

    International Nuclear Information System (INIS)

    This paper describes a new methodology for volumetric assay of defects in large engineering materials nondestructively. It utilizes high energy photons produced by nuclear reaction to create positrons in situ whose fate is followed using conventional positron spectroscopic techniques. The photon induced positron annihilation (PIPA) spectroscopy system has been set-up using a Folded Tandem Ion Accelerator (FOTIA). Possibility of using prompt γ-rays produced in nuclear reactions 27Al(1H,γ)28Si and 19F(1H,αγ)16O has been examined. The reaction 19F(1H,αγ)16O is seen to provide higher photon flux (and positron yield) and measurements have been carried out in large samples of metals and polymers. We could establish good sensitivity of the technique as well as reproducibility in a number of measurements. This technique has been used to carry out defect studies in cold worked zircaloy-2 plates. The measured S-parameter, indicative of defect concentration, was seen to correlate well with the measured residual stress using X-ray technique. The results were validated by γ-induced positron annihilation lifetime measurements at ELBE LINAC based GiPS facility.

  1. Positron spectroscopy of defects in submicrocrystalline nickel after low-temperature annealing

    Science.gov (United States)

    Kuznetsov, P. V.; Mironov, Yu. P.; Tolmachev, A. I.; Bordulev, Yu. S.; Laptev, R. S.; Lider, A. M.; Korznikov, A. V.

    2015-02-01

    Using the method of measuring the positron lifetime spectra and Doppler broadening annihilation line spectroscopy, the annealing of defects in submicrocrystalline nickel produced by equal channel angular pressing has been studied. In as-prepared samples, the positrons are trapped by dislocation defects and vacancy complexes inside crystallites. The size of vacancy complexes decreases with increasing annealing temperature in the interval Δ T = 20-300°C. However, at T = 360°C, the complexes start growing again. The dependence of S-parameter on W-parameter derived from the Doppler broadening spectroscopy has two parts with different inclinations to axes that correspond to different types of primary centers of positron trapping in submicrocrystalline nickel. It has been elucidated that, at recovery stage in the temperature interval Δ T = 20-180°C, the main centers of positron trapping are low-angle boundaries enriched by impurities, while at in situ recrystallization stage in the temperature interval Δ T = 180-360°C, the primary centers of positron trapping are low-angle boundaries.

  2. Photon induced positron annihilation spectroscopy: A nondestructive method for assay of defects in large engineering materials

    Energy Technology Data Exchange (ETDEWEB)

    Pujari, P.K., E-mail: pujari@barc.gov.in [Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Sudarshan, K.; Tripathi, R.; Dutta, D.; Maheshwari, P.; Sharma, S.K. [Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Srivastava, D. [Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Krause-Rehberg, R. [Martin Luther University Halle, Dept. of Physics, 06099 Halle (Germany); Butterling, M.; Anwand, W.; Wagner, A. [Helmholtz-Zentrum Dresden-Rossendorf, Postfach 510119, 01314 Dresden (Germany)

    2012-01-01

    This paper describes a new methodology for volumetric assay of defects in large engineering materials nondestructively. It utilizes high energy photons produced by nuclear reaction to create positrons in situ whose fate is followed using conventional positron spectroscopic techniques. The photon induced positron annihilation (PIPA) spectroscopy system has been set-up using a Folded Tandem Ion Accelerator (FOTIA). Possibility of using prompt {gamma}-rays produced in nuclear reactions {sup 27}Al({sup 1}H,{gamma}){sup 28}Si and {sup 19}F({sup 1}H,{alpha}{gamma}){sup 16}O has been examined. The reaction {sup 19}F({sup 1}H,{alpha}{gamma}){sup 16}O is seen to provide higher photon flux (and positron yield) and measurements have been carried out in large samples of metals and polymers. We could establish good sensitivity of the technique as well as reproducibility in a number of measurements. This technique has been used to carry out defect studies in cold worked zircaloy-2 plates. The measured S-parameter, indicative of defect concentration, was seen to correlate well with the measured residual stress using X-ray technique. The results were validated by {gamma}-induced positron annihilation lifetime measurements at ELBE LINAC based GiPS facility.

  3. Photon induced positron annihilation spectroscopy: A nondestructive method for assay of defects in large engineering materials

    Science.gov (United States)

    Pujari, P. K.; Sudarshan, K.; Tripathi, R.; Dutta, D.; Maheshwari, P.; Sharma, S. K.; Srivastava, D.; Krause-Rehberg, R.; Butterling, M.; Anwand, W.; Wagner, A.

    2012-01-01

    This paper describes a new methodology for volumetric assay of defects in large engineering materials nondestructively. It utilizes high energy photons produced by nuclear reaction to create positrons in situ whose fate is followed using conventional positron spectroscopic techniques. The photon induced positron annihilation (PIPA) spectroscopy system has been set-up using a Folded Tandem Ion Accelerator (FOTIA). Possibility of using prompt γ-rays produced in nuclear reactions 27Al( 1H,γ) 28Si and 19F( 1H,αγ) 16O has been examined. The reaction 19F( 1H,αγ) 16O is seen to provide higher photon flux (and positron yield) and measurements have been carried out in large samples of metals and polymers. We could establish good sensitivity of the technique as well as reproducibility in a number of measurements. This technique has been used to carry out defect studies in cold worked zircaloy-2 plates. The measured S-parameter, indicative of defect concentration, was seen to correlate well with the measured residual stress using X-ray technique. The results were validated by γ-induced positron annihilation lifetime measurements at ELBE LINAC based GiPS facility.

  4. The 6 MV pelletron at Stuttgart - an accelerator for ions, positrons and electrons

    International Nuclear Information System (INIS)

    After a short introduction and a description of the accelerator facility the paper surveys the experiments which were performed with the ion and positron beams of this accelerator since its installation in Stuttgart. Selected examples are presented for either characteristic or novel applications in more detail. They comprise: (i) The ion beam analysis of solids by means of RBS (stoichiometry of high-Tc superconductors), NRA (trace analysis by a novel p-γ-coincidence technique), ion channeling (structure of quasicrystals), and high resolution RBS and ERDA of surfaces and near-surface layers with a recently set up electrostatic spectrometer for MeV ions (oxidation of metal surfaces, stoichiometry of multi-layers, high resolution ERDA of hydrogen). (ii) Measurement of the energy dependence of the elastic (Bhabha) scattering of positrons by electrons and of the annihilation-in-flight cross-section of positron-electron pairs (search for resonant neutral particle states), beam-based β+-γ-coincidence positron-lifetime measurements (high-temperature thermal-equilibrium studies on Ge in the solid and molten state and on Si up to the melting point), triple-coincidence β+γΔE Age - Momentum Correlation (AMOC) measurements (positronium formation in fused quartz, time-resolved observation of spin conversion of positronium in a paramagnetic solution (HTEMPO/methanol), trapping of positrons at defects in diamonds and at thermally generated vacancies in aluminium). (orig.)

  5. Lifetime health effects and costs of diabetes treatment

    OpenAIRE

    Niessen, Louis Wilhelmus; Dijkstra, R.; Hutubessy, Raymond; Rutten, Guy; Casparie, Anton

    2003-01-01

    textabstractBACKGROUND: This article presents cost-effectiveness analyses of the major diabetes interventions as formulated in the revised Dutch guidelines for diabetes type 2 patients in primary and secondary care. The analyses consider two types of care: diabetes control and the treatment of complications, each at current care level and according to the guidelines. METHODS: A validated probabilistic diabetes model describes diabetes and its complications over a lifetime in the Dutch populat...

  6. Electron-Positron Accumulator (EPA)

    CERN Multimedia

    Photographic Service

    1986-01-01

    After acceleration in the low-current linac LIL-W, the electrons and positrons are accumulated in EPA to obtain a sufficient intensity and a suitable time-structure, before being passed on to the PS for further acceleration to 3.5 GeV. Electrons circulate from right to left, positrons in the other direction. Dipole bending magnets are red, focusing quadrupoles blue, sextupoles for chromaticity-control orange. The vertical tube at the left of the picture belongs to an optical transport system carrying the synchrotron radiation to detectors for beam size measurement. Construction of EPA was completed in spring 1986. LIL-W and EPA were conceived for an energy of 600 MeV, but operation was limited to 500 MeV.

  7. PEBS - Positron Electron Balloon Spectrometer

    CERN Document Server

    Von Doetinchem, P; Kirn, T; Yearwood, G R; Schael, S

    2007-01-01

    The best measurement of the cosmic ray positron flux available today was performed by the HEAT balloon experiment more than 10 years ago. Given the limitations in weight and power consumption for balloon experiments, a novel approach was needed to design a detector which could increase the existing data by more than a factor of 100. Using silicon photomultipliers for the readout of a scintillating fiber tracker and of an imaging electromagnetic calorimeter, the PEBS detector features a large geometrical acceptance of 2500 cm^2 sr for positrons, a total weight of 1500 kg and a power consumption of 600 W. The experiment is intended to measure cosmic ray particle spectra for a period of up to 20 days at an altitude of 40 km circulating the North or South Pole. A full Geant 4 simulation of the detector concept has been developed and key elements have been verified in a testbeam in October 2006 at CERN.

  8. The Work of a Lifetime

    Science.gov (United States)

    Olson, Cathy Applefeld

    2012-01-01

    If there's one message that Joan Hillsman wants to get across to music directors, it's this: Teaching is a lifetime commitment. Hillsman is a longtime music educator, African-American music historian, author, consultant, music producer, clinician, radio show host, and current member of the Academic Board of the James Cleveland Gospel Music…

  9. Structural transition of partially Ba-filled thermoelectric CoSb{sub 3} investigated by positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, T.; Li, X. F.; Chen, Z. Q., E-mail: chenzq@whu.edu.cn [Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 (China); Zhou, K. [School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing 210044 (China); Su, X. L.; Tang, X. F., E-mail: tangxf@whut.edu.cn [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China)

    2015-02-07

    Microstructure of unfilled and Ba-filled CoSb{sub 3} has been studied by positron lifetime measurements together with theoretical calculation. Positron trapping in intrinsic voids is observed in the CoSb{sub 3}, which contributes a positron lifetime of 263 ± 2 ps. After filling Ba atoms with content up to x = 0.4, the positron lifetime shows continuous increase. By comparing the experimental results with calculation following the phase diagram of Ba{sub x}Co{sub 4}Sb{sub 12} with x in the range of 0–0.5, it is found that when the Ba content is lower than 0.16, the filling of Ba atoms is in a phase of solid solution. At x = 0.2, γ phase is formed, which is mixed with solid solution. At x > 0.25, transition from γ phase to a mixture of γ and α phases is confirmed.

  10. Positron decay of 153Dy

    International Nuclear Information System (INIS)

    Positron spectrum of the 153Dy → 153Tb decay was investigated by means of the iron-free β-spectrometer with a toroidal magnetic field. Maximum spectrometer transmission constituted approximately 20% and resolving power was 1.1%. The 153Dy sources are preparaed by introduction of the 153Dy ions into the aluminium substrate 0.68 mgxcm-2 thick (four sources) and 1.85 mgxcm-2 thick (three sources). The positron decay spectrum was determined to be complicated; it consisted of three components with the boundary energies of 1069+-10, 886+-2 and 427+-22 keV and with relative intensities of 0.17+-0.03, 1.0 and 0.06+-0.02, respectively. The 153Dy → 153Tb mass difference is determined to be equal to 2171+-2 keV. Analysis of the data obtained and their comparison with the available data does not permit to make a conclusion about the positron 153Dy decay intensity and about epsilon/β+ value

  11. Nonplanar positron-acoustic Gardner solitary waves in electron-positron-ion plasmas with superthermal electrons and positrons

    Energy Technology Data Exchange (ETDEWEB)

    Uddin, M. J., E-mail: josim.phys2007@gmail.com; Alam, M. S.; Mamun, A. A. [Department of Physics, Jahangirnagar University, Savar, Dhaka-1342 (Bangladesh)

    2015-02-15

    Nonplanar (cylindrical and spherical) positron-acoustic (PA) Gardner solitary waves (SWs) in an unmagnetized plasma system consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated. The modified Gardner equation is derived by using the reductive perturbation technique. The effects of cylindrical and spherical geometries, superthermal parameter of hot positrons and electrons, relative temperature ratios, and relative number density ratios on the PA Gardner SWs are studied by using the numerical simulations. The implications of our results in various space and laboratory plasma environments are briefly discussed.

  12. Positron annihilation and XRD studies on deformed Al-alloys with low concentrations of Mg

    Energy Technology Data Exchange (ETDEWEB)

    Badawi, E.; Abdel-Rahman, M.A.; Mahmoud, S.A. [Physics Dept., El-Minia Univ. (Egypt); Ramadan, A.A. [Physics Dept., Helwan Univ. (Egypt)

    2001-07-01

    The behaviour of positron in grain boundaries, is characterized by their bulk diffusibility D, their bulk (free) lifetime {tau}{sub f}, and their trapped lifetime {tau}{sub t} ({tau}{sub t} > {tau}{sub f}). Al-Mg{sub x} samples(x=0-1.4 at%) have been homogenized at 573 K for 12 hours. The obtained mean lifetime results showed a good fitting with Sigmodel giving {tau}{sub t} = 180.664 ps and {tau}{sub f} = 163.9 ps. The mean lifetime was found to vary exponentially with degree of deformation. XRD study showed that preferred orientation occurred at degree of deformation > 32%, whereas the peak intensity then increases with sample deformation. Recrystallization is also followed by XRD. Peak intensities decrease with increasing annealing time which is attributed to recrystallization, but it does not completely reverse to the origin condition. For all cases, no peaks of Mg were revealed indicating the positron annihilation as a sensitive technique for detecting low concentrations in alloys. (orig.)

  13. A positron accumulator for antihydrogen synthesis

    CERN Document Server

    Jørgensen, L V; Fine, K S; Watson, T L; Van der Werf, D P; Charlton, M

    2001-01-01

    A positron accumulator based on the modified Penning-Malmberg design of Surko and co-workers at UCSD has been constructed and undergone testing in preparation for the ATHENA experiment now under way at CERN. This experiment aims to produce and characterize atomic anti- hydrogen. The positron accumulator utilises nitrogen buffer gas to cool and trap a continuous beam of positrons emanating from a /sup 22 /Na radioactive source. A solid neon moderator slows the positrons from the source down to epithermal energies of a few eV before being injected into the trap. It is estimated that around 10/sup 7/ positrons can be trapped and cooled to ambient temperature within a couple of minutes in this scheme using a 6 mCi source. Preliminary tests have so far demonstrated trapping of approximately 3*10/sup 6/ positrons and an efficiency of the Ne moderator of nearly 1%. (8 refs).

  14. Intense positron beams: linacs - preworkshop copy

    International Nuclear Information System (INIS)

    Beams of monoenergetic positrons with energies of a few eV to many keV have been used in experiments in atomic physics, solid-state physics and materials science. The production of positron beams from a new source, an electron linac, is described. Intense, pulsed beams of low-energy positrons have been produced by a high-energy beam from an electron linac. The production efficiency, moderator geometry, beam spot size and other positron beam parameters have been determined for electrons with energies from 60 to 120 MeV. Low-energy positron beams produced with a high-energy electron linac can be of much higher intensity than those beams currently derived from radioactive sources. These higher-intensity beams will make possible positron experiments previously infeasible

  15. Intense positron beams: linacs. Preworkshop copy

    International Nuclear Information System (INIS)

    Beams of monoenergetic positrons with energies of a few eV to many keV have been used in experiments in atomic physics, solid state physics and materials science. The production of positron beams from a new source, an electron linac, is described. Intense, pulsed beams of low-energy positrons have been produced by a high-energy beam from an electron linac. The production efficiency, moderator geometry, beam spot size and other positron beam parameters have been determined for electrons with energies from 60 to 120 MeV. Low-energy positron beams produced with a high-energy electron linac can be of much higher intensity than those beams currently derived from radioactive sources. These higher intensity beams will make possible positron experiments previously infeasible

  16. Development of a transmission positron microscope

    International Nuclear Information System (INIS)

    A practical transmission positron microscope (TPM) JEM-1011B has been developed to survey differences in the interaction of positron and electron beams with materials, and is installed in the Slow Positron Facility of High Energy Accelerator Research Organization (KEK). The TPM can share positron and electron beams, and can also be used as a transmission electron microscope (TEM). Positron transmission images up to magnification 10,000x (resolution: 50 nm) and positron diffraction patterns up to 044 family were successfully obtained by the TPM comparing them with those of electrons. The differences in material transmittances for both beams have been measured, and can be explained by the calculated results of the Monte Carlo simulation code PENELOPE-2008.

  17. Design of a transmission electron positron microscope

    International Nuclear Information System (INIS)

    This paper reports the plans and design of positron-electron microscopes being built at KEK (High Energy Accelerator Research Organization), Tsukuba, Japan. A used electron microscope is altered. The kinetic energies of positrons produced by accelerators or by nuclear decays are not a unique value but show a spread over in a wide range. Positron beam is guided to a transmission electron microscope (JEM100SX). Positrons are moderated by a tungsten foil, are accelerated and are focused on a nickel sheet. The monochromatic focused beam is injected into an electron microscope. The focusing and aberration of positrons are the same as electrons in a magnetic system which are used in commercial electron microscopes. Imaging plates are used to record positron images for the transmission electron microscope. (author)

  18. Development of a transmission positron microscope

    Energy Technology Data Exchange (ETDEWEB)

    Matsuya, M., E-mail: matsuya@jeol.co.jp [JEOL Ltd., 1-2 Musashino, 3-Chome, Akishima, Tokyo 196-8558 (Japan); Jinno, S. [Department of Applied Chemistry, Chiba University, Yayoi, Inage, Chiba, Chiba 263-8552 (Japan); Ootsuka, T.; Inoue, M. [JEOL Ltd., 1-2 Musashino, 3-Chome, Akishima, Tokyo 196-8558 (Japan); Kurihara, T. [High Energy Accelerator Research Organization, Oho, Tsukuba, Ibaraki 305-0801 (Japan); Doyama, M.; Inoue, M. [Teikyo University of Science and Technology, Uenohara, Yamanashi 409-0913 (Japan); Fujinami, M. [Department of Applied Chemistry, Chiba University, Yayoi, Inage, Chiba, Chiba 263-8552 (Japan)

    2011-07-21

    A practical transmission positron microscope (TPM) JEM-1011B has been developed to survey differences in the interaction of positron and electron beams with materials, and is installed in the Slow Positron Facility of High Energy Accelerator Research Organization (KEK). The TPM can share positron and electron beams, and can also be used as a transmission electron microscope (TEM). Positron transmission images up to magnification 10,000x (resolution: 50 nm) and positron diffraction patterns up to 044 family were successfully obtained by the TPM comparing them with those of electrons. The differences in material transmittances for both beams have been measured, and can be explained by the calculated results of the Monte Carlo simulation code PENELOPE-2008.

  19. Lifetime modelling of lead acid batteries

    Energy Technology Data Exchange (ETDEWEB)

    Bindner, H.; Cronin, T.; Lundsager, P.

    2005-04-01

    The performance and lifetime of energy storage in batteries are an important part of many renewable based energy systems. Not only do batteries impact on the system performance but they are also a significant expenditure when considering the whole life cycle costs. Poor prediction of lifetime can, therefore, lead to uncertainty in the viability of the system in the long term. This report details the work undertaken to investigate and develop two different battery life prediction methodologies with specific reference to their use in hybrid renewable energy systems. Alongside this, results from battery tests designed to exercise batteries in similar modes to those that they experience in hybrid systems have also been analysed. These have yielded battery specific parameters for use in the prediction software and the first results in the validation process of the software are also given. This work has been part of the European Union Benchmarking research project (ENK6-CT-2001-80576), funded by the European Union, the United States and Australian governments together with other European states and other public and private financing bodies. The project has concentrated on lead acid batteries as this technology is the most commonly used. Through this work the project partner institutions have intended to provide useful tools to improve the design capabilities of organizations, private and public, in remote power systems. (au)

  20. Pressure dependence of positron annihilation in Si

    International Nuclear Information System (INIS)

    The pressure dependence of the electron-positron and the electron-electron momentum densities in silicon are studied. The observations that the electron-positron momentum density increases more rapidly with pressure than the electron-electron momentum density alone is explained in terms of increased positron penetration into the ion cores. The computational technique used here is based on the independent-particle model (IPM) coupled with the use of the electron pseudo-wave functions. (orig.)

  1. Characterization of silicon dioxide deposited by low-temperature CVD using TEOS and ozone by monoenergetic positron beams

    International Nuclear Information System (INIS)

    Monoenergetic positrons were used as a nondestructive probe for SiO2 films deposited on Si substrates by atmospheric-pressure chemical vapor deposition using tetraethylorthosilicate (TEOS, Si(OC2H5)4) and O3. The formation of positronium (Ps) in the SiO2 films was found from measurements of Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons. A clear correlation between the formation probability of Ps and the concentration of H2O in the SiO2 films was established. (orig.)

  2. Solvated Positron Chemistry. The Reaction of Hydrated Positrons with Chloride Ions

    DEFF Research Database (Denmark)

    Mogensen, O. E.; Shantarovich, V. P.

    1974-01-01

    The reaction of hydrated positrons (caq+ with cloride ions in aqueous solutions has been studied by means of positron annihilation angular correlation measurements. A rate constant of k = (2.5 ± 0.5) × 1010 M−1 s−1 was found. Probably the reacting positrons annihilated from an e+ Cl− bound state ...... resulting in an angular correlation curve 8% narrower than for the hydrated positron. Carbontetrachloride in benzene seems to give similar, but smaller effect....

  3. Low-energy contributions to positron implantation

    International Nuclear Information System (INIS)

    A detailed knowledge of low-energy positron implantation is of considerable importance for depth profiling and data analysis in slow positron experiments. Existing Monte Carlo models are capable of simulating the behavior of positrons incident at keV energies, then following the energy-loss process to final kinetic energies of from 20 to 100 eV. A Monte Carlo calculation of the final stages of positron thermalization in Al, Cu, and Au, from 25 eV to thermal energies, is described via the mechanisms of conduction-electron and longitudinal acoustic-phonon scattering. This calculation produces a wide variety of data, including implantation profiles, fraction and energy distribution of reemitted positrons, and the mean thermalization time. A way to obtain information about positron energy loss by considering the time evolution of a point concentration (delta-function distribution) of positrons is described. Diffusion coefficients are obtained that are in good agreement with experiment. The effects of a positive positron work function are examined in the context of a positron Monte Carlo calculation. It is shown that the latter stages of thermalization can have important effects on the stopping profiles and mean depth. In particular, calculated stopping profiles and mean implantation depth are not adequately described by the Makhovian distribution, in agreement with recent experimental findings. A parameterization of these profiles is provided which will be of use in the analysis of experimental data

  4. KEK-IMSS Slow Positron Facility

    Energy Technology Data Exchange (ETDEWEB)

    Hyodo, T; Wada, K; Yagishita, A; Kosuge, T; Saito, Y; Kurihara, T; Kikuchi, T; Shirakawa, A; Sanami, T; Ikeda, M; Ohsawa, S; Kakihara, K; Shidara, T, E-mail: toshio.hyodo@kek.jp [High Energy Accelerator Research Organization (KEK) 1-1 Oho, Tsukuba, Ibaraki, 305-0801 (Japan)

    2011-12-01

    The Slow Positron Facility at the Institute of Material Structure Science (IMSS) of High Energy Accelerator Research Organization (KEK) is a user dedicated facility with an energy tunable (0.1 - 35 keV) slow positron beam produced by a dedicated 55MeV linac. The present beam line branches have been used for the positronium time-of-flight (Ps-TOF) measurements, the transmission positron microscope (TPM) and the photo-detachment of Ps negative ions (Ps{sup -}). During the year 2010, a reflection high-energy positron diffraction (RHEPD) measurement station is going to be installed. The slow positron generator (converter/ moderator) system will be modified to get a higher slow positron intensity, and a new user-friendly beam line power-supply control and vacuum monitoring system is being developed. Another plan for this year is the transfer of a {sup 22}Na-based slow positron beam from RIKEN. This machine will be used for the continuous slow positron beam applications and for the orientation training of those who are interested in beginning researches with a slow positron beam.

  5. KEK-IMSS Slow Positron Facility

    International Nuclear Information System (INIS)

    The Slow Positron Facility at the Institute of Material Structure Science (IMSS) of High Energy Accelerator Research Organization (KEK) is a user dedicated facility with an energy tunable (0.1 - 35 keV) slow positron beam produced by a dedicated 55MeV linac. The present beam line branches have been used for the positronium time-of-flight (Ps-TOF) measurements, the transmission positron microscope (TPM) and the photo-detachment of Ps negative ions (Ps-). During the year 2010, a reflection high-energy positron diffraction (RHEPD) measurement station is going to be installed. The slow positron generator (converter/ moderator) system will be modified to get a higher slow positron intensity, and a new user-friendly beam line power-supply control and vacuum monitoring system is being developed. Another plan for this year is the transfer of a 22Na-based slow positron beam from RIKEN. This machine will be used for the continuous slow positron beam applications and for the orientation training of those who are interested in beginning researches with a slow positron beam.

  6. Development of a positron probe micro analyzer with a high intensity positron beam

    International Nuclear Information System (INIS)

    A positron probe micro analyzer (PPMA) has been developed in AIST. When a positron microbeam is injected into a specimen, radiations including secondary electrons, back scattered positrons, and annihilation gamma-rays are emitted from the beam injected point. In the PPMA, these radiations are detected to characterize small area of specimens. We report on details of designs and specifications of the PPMA. (author)

  7. Lifetimes of 167Yb excited states

    International Nuclear Information System (INIS)

    Lifetimes of 167Yb excited states arising at the decay of 167Lu → 167Yb monoisotope have been determined using eγ and γγ delayed coincidence methods. The time spectrometers mounted on the base of a magnetic lens β-spectrometer and a scintillation detector, a scintillation and a Ge(Li) detectors, a scintillation and Si(Li)-detectors are used. 167Yb level fifetimes are measured with energies of 29 keV (Tsub(1/2)=13.5(7) ns), 78 keV (Tsub(1/2=0.84(4) ns), 178 keV (Tsub(1/2)167Yb investigated levels are analysed. On the basis of intrarotational transitions internal quadrupole momenta of 5/2-/523/, 3/2-/512/ and 1/2-/521/ bands have been determined

  8. Radiative lifetimes of neutral cerium

    International Nuclear Information System (INIS)

    Radiative lifetimes, accurate to ±5%, have been measured for 153 levels of neutral cerium using time-resolved laser-induced fluorescence (TRLIF) on a slow beam of cerium atoms. Of the 153 levels studied, 150 are even parity and 3 are odd parity. The levels range in energy from 16 869 to 28 557 cm-1. This set of Ce I lifetimes is much more extensive than others published to date, and will provide the absolute calibration for a very large set of measured Ce I transition probabilities. Accurate transition probabilities for lines in the visible and ultraviolet are needed both in astrophysics, for the determination of elemental abundances, and by the lighting community, for research and development of metal halide high-intensity discharge lamps.

  9. Radiative lifetimes of neutral cerium

    Energy Technology Data Exchange (ETDEWEB)

    Den Hartog, E A; Buettner, K P; Lawler, J E [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States)], E-mail: eadenhar@wisc.edu, E-mail: Kevin.Buettner@usma.edu, E-mail: jelawler@wisc.edu

    2009-04-28

    Radiative lifetimes, accurate to {+-}5%, have been measured for 153 levels of neutral cerium using time-resolved laser-induced fluorescence (TRLIF) on a slow beam of cerium atoms. Of the 153 levels studied, 150 are even parity and 3 are odd parity. The levels range in energy from 16 869 to 28 557 cm{sup -1}. This set of Ce I lifetimes is much more extensive than others published to date, and will provide the absolute calibration for a very large set of measured Ce I transition probabilities. Accurate transition probabilities for lines in the visible and ultraviolet are needed both in astrophysics, for the determination of elemental abundances, and by the lighting community, for research and development of metal halide high-intensity discharge lamps.

  10. Lifetime of Doubly Charmed Baryons

    Institute of Scientific and Technical Information of China (English)

    XU Xue-Fen; CHANG Chao-Hsi; LI Tong; LI Xue-Qian; WANG Yu-Ming

    2008-01-01

    In this work, we evaluate the lifetimes of the doubly charmed baryons cc+, cc++, and Ωcc+. We carefully calculate the non-spectator contributions at the quark level, where the Cabibbo-suppressed diagrams are also included. The hadronic matrix elements are evaluated in the simple non-relativistic harmonic oscillator model. Our numerical results are generally consistent with that obtained by other authors who used the diquark model. However, all the theoretical predictions on the lifetimes are one order larger than the upper limit set by the recent SELEX measurement. This discrepancy would be clarified by the future experiment. If more accurate experiment still confirms the value of the SELEX collaboration, there must be some unknown mechanism to be explored.

  11. Spectrally resolved fluorescent lifetime imaging

    OpenAIRE

    Hanley, Quentin S.

    2008-01-01

    Placing an imaging spectrograph or related components capable of generating a spectrum between a microscope and the image intensifier of a conventional fluorescence lifetime imaging (FLIM) system creates a spectrally resolved FLIM (SFLIM). This arrangement provides a number of opportunities not readily available to conventional systems using bandpass filters. The examples include: simultaneous viewing of multiple fluorophores; tracking of both the donor and acceptor; and observation of a rang...

  12. Personality, IQ, and Lifetime Earnings

    OpenAIRE

    Gensowski, Miriam

    2014-01-01

    Talented individuals are seen as drivers of long-term growth, but how do they realize their full potential? In this paper, I show that even in a group of high-IQ men and women, lifetime earnings are substantially influenced by their education and personality traits. I identify a previously undocumented interaction between education and traits in earnings generation, which results in important heterogeneity of the net present value of education. Personality traits directly affect men's earning...

  13. Lifetime reproductive effort in humans

    OpenAIRE

    Burger, Oskar; Walker, Robert; Hamilton, Marcus J.

    2009-01-01

    Lifetime reproductive effort (LRE) measures the total amount of metabolized energy diverted to reproduction during the lifespan. LRE captures key components of the life history and is particularly useful for describing and comparing the life histories of different organisms. Given a simple energetic production constraint, LRE is predicted to be similar in value for very different life histories. However, humans have some unique ecological characteristics that may alter LRE, such as the long p...

  14. Lifetime of MCP-PMTs

    Science.gov (United States)

    Lehmann, A.; Britting, A.; Eyrich, W.; Pfaffinger, M.; Uhlig, F.; Belias, A.; Dzhygadlo, R.; Gerhardt, A.; Götzen, K.; Kalicy, G.; Krebs, M.; Lehmann, D.; Nerling, F.; Patsyuk, M.; Peters, K.; Schepers, G.; Schmitt, L.; Schwarz, C.; Schwiening, J.; Traxler, M.; Zühlsdorf, M.; Düren, M.; Etzelmüller, E.; Föhl, K.; Hayrapetyan, A.; Kröck, B.; Merle, O.; Rieke, J.; Schmidt, M.; Cowie, E.; Keri, T.; Achenbach, P.; Cardinali, M.; Hoek, M.; Lauth, W.; Schlimme, S.; Sfienti, C.; Thiel, M.

    2016-05-01

    The hadron identification in the PANDA experiment at FAIR will be done with DIRC detectors. Because of design and space reasons the sensors of the DIRCs have to be placed inside the strong magnetic field of the solenoid. As the favored photon sensors microchannel-plate photomultipliers (MCP-PMTs) were identified. However, these devices showed serious aging problems until very recently, which manifest themselves by a fast degrading quantum efficiency (QE) of the photo cathode (PC). This is mainly due to feedback ions from the residual gas. In this paper we discuss the recently accomplished huge improvements in the lifetime of MCP-PMTs. With innovative countermeasures applied to the MCP-PMTs in the attempt to reduce the aging effects the manufacturers were able to increase the lifetime of MCP-PMT prototypes by almost two orders of magnitude compared to the former commercially available devices. Our group has studied the aging of MCP-PMTs for more than four years by simultaneously illuminating different types of lifetime-enhanced MCP-PMTs at the same photon rate. Gain, dark count rate, and QE as a function of the wavelength and the PC surface were measured in regular time intervals and studied in dependence of the integrated anode charge. We observe that MCP-PMTs treated with an atomic layer deposition (ALD) technique are by far the best devices available now. A lifetime of up to 10 C/cm2 integrated anode charge was reached with these sensors. This is sufficient for both PANDA DIRCs.

  15. New mathematical approach to the treatment of positron annihilhumidity lifetime data for humidity-sensitive ceramics

    OpenAIRE

    Klym, Halyna; Ingram, Adam; Shpotyuk, Oleh

    2009-01-01

    A mathematical model is considered as a problem of Steafan for equation of heat conductivity. The decision of problem is found in spase of gridding functions of the Rote method and by a report to nonlinear intgral equation of Gammershteyn type with a basis of Grina's functions. Basic parameter of control of the temperature distributing are conducted.

  16. On positron annihilation in zinc

    International Nuclear Information System (INIS)

    The purpose of this work is to understand Mogensen's and Petersen's positron annihilation curves for zinc. Mijnarends approach is used as an auxiliary method of localizing inhomogeneities of the electronic density in momentum space, as defined in the paper. Evidence is found for a new effect consisting of a strong enhancement of the annihilation probability in the lenses obtained by the intersection of the Fermi surface with HMC surfaces. This effect, not the anisotropy of the Fermi surface, is the main reason for the anisotropy of the annihilation curves. (orig.)

  17. Facility for positron computed tomography

    International Nuclear Information System (INIS)

    For positron computed tomography two or more rings of scintillation detectors are used by which three or more sections of the object may be determined at a time. The rings are placed in parallel planes having got some distance from each other, axially movable collimator rings being provided for. Each collimator can be moved towards the opposite collimator and towards a central collimator which also is ring-shaped and is placed between the rows of detectors. The external and internal collimator are used for data selection and image-forming. (DG)

  18. The Galactic Positron Annihilation Radiation and the Propagation of Positrons in the Interstellar Medium

    OpenAIRE

    Higdon, J. C.; Lingenfelter, R. E.; Rothschild, R.E.

    2009-01-01

    The ratio of the luminosity of diffuse 511 keV positron annihilation radiation, measured by INTEGRAL in its four years, from a Galactic "positron bulge" (3.5 kpc), the cascade of the magnetic turbulence, which scatters the positrons, is damped by ion-neutral friction, allowing positrons to stream along magnetic flux tubes. We find that nearly 1/2 of the positrons produced in the disk escape from it into the halo. On the other hand, we show that within the extended, or interstellar, bulge (

  19. Lifetimes of charm and beauty hadrons

    International Nuclear Information System (INIS)

    Recent results on the lifetimes of charm and beauty hadrons at the LEP collider experiment and at the fixed target experiments E653 are reviewed and discussed. The world average of b lifetime is now =1.29±0.05 ps. The exclusive lifetime measurements for b+, b-, b0 are presented. The lifetime difference among the different species of charm and of beauty hadrons are discussed. (author) 25 refs., 13 figs., 12 tabs

  20. The positron camera in nuclear medicine

    International Nuclear Information System (INIS)

    Positron emission tomography is making headway in health care delivery. With improvements in instrumentation and physiologic tracers and with the development of hospital-based compact cyclotrons, 'physiopathologic tomography' is around the corner in nuclear medicine. This paper is a brief review of positron emission tomography: instrumentation and applications

  1. Positron spectroscopy after heavy ion collisions

    International Nuclear Information System (INIS)

    The author reviews the theoretical and experimental results on positron production in heavy ion collisions. After a discussion of the quasi-atomic picture, the possible observation of the axion, and the inverse Bhabha scattering, the positron spectrometer EPOS of the GSI Darmstadt is described. Thereafter the experimental results are presented. (HSI)

  2. Positron prevacancy effects in pure annealed metals

    International Nuclear Information System (INIS)

    The low-temperature prevacancy effects sometimes observed with positrons in well-annealed high-purity metals are discussed. It is shown that these effects are not experimental artifacts, but are due to trapping of the positrons. It is suggested that dislocations are responsible for these trapping effects. 46 references, 5 figures

  3. Electron and Positron Stopping Powers of Materials

    Science.gov (United States)

    SRD 7 NIST Electron and Positron Stopping Powers of Materials (PC database for purchase)   The EPSTAR database provides rapid calculations of stopping powers (collisional, radiative, and total), CSDA ranges, radiation yields and density effect corrections for incident electrons or positrons with kinetic energies from 1 keV to 10 GeV, and for any chemically defined target material.

  4. Descriptions of positron defect analysis capabilities

    International Nuclear Information System (INIS)

    A series of descriptive papers and graphics appropriate for distribution to potential collaborators has been assembled. These describe the capabilities for defect analysis using positron annihilation spectroscopy. The application of positrons to problems in the polymer and semiconductor industries is addressed

  5. Slow positron beam at the JINR, Dubna

    Directory of Open Access Journals (Sweden)

    Horodek Paweł

    2015-12-01

    Full Text Available The Low Energy Positron Toroidal Accumulator (LEPTA at the Joint Institute for Nuclear Research (JINR proposed for generation of positronium in flight has been adopted for positron annihilation spectroscopy (PAS. The positron injector generates continuous slow positron beam with positron energy range between 50 eV and 35 keV. The radioactive 22Na isotope is used. In distinction to popular tungsten foil, here the solid neon is used as moderator. It allows to obtain the beam intensity of about 105 e+/s width energy spectrum characterized by full width at half maximum (FWHM of 3.4 eV and a tail to lower energies of about 30 eV. The paper covers the characteristic of variable energy positron beam at the LEPTA facility: parameters, the rule of moderation, scheme of injector, and transportation of positrons into the sample chamber. Recent status of the project and its development in the field of PAS is discussed. As an example, the measurement of the positron diffusion length in pure iron is demonstrated.

  6. Positron acoustic shock waves in four-component plasmas with nonthermal electrons and positrons

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, M. M.; Mamun, A. A. [Jahangirnagar University, Savar, Dhaka (Bangladesh); Alam, M. S. [Mawlana Bhashani Science and Technology University, Santosh, Tangail (Bangladesh)

    2014-06-15

    Positron acoustic shock waves (PASWs) in an unmagnetized four-component plasma system consisting of a cold mobile viscous positron fluid, hot positrons and electrons following the nonthermal distributions of Cairns et al. [Geophys. Res. Lett. 22, 2709 (1995)], and immobile positive ions are studied both analytically and numerically. The well-known reductive perturbation method is used to derive the Burgers equation. The basic features of the PASWs are significantly modified by the effects of the kinematic viscosity, the nonthermal electrons and hot positrons, the ratio of the electron temperature to the hot positron temperature σ, and the ratio of the hot positron (electron) number density to the cold positron number density μ{sub 1} (μ{sub 2}). The importance of our results to various astrophysical and laboratory plasmas are concisely discussed.

  7. Positron annihilation spectroscopy as a tool to develop self healing in aluminium alloys

    International Nuclear Information System (INIS)

    Positron lifetime and Doppler broadening spectroscopy have been applied to probe the free volume generation (vacancies, dislocations and nano-cracks) during plastic deformation of a commercial aluminium AA2024 (T3) alloy. Aim of the total program is to study how solute atoms can be driven to the areas where initial cracking may occur in order to prevent the failure of the specimen. The phenomenon of closing the nano-crack is called Self Healing, and can provide extra strength and ductility to the alloy under some loading conditions. Plastic deformation of over-aged aluminum alloy at room temperature increases the average positron lifetime from initial value of 190 ps to 203 ps. The low momentum parameter S increases in agreement with the increase of open volume defects. The elastic deformation of the sample does not have a recordable effect on the positron annihilation data. It is also shown that the induced damage does not recover after loading the sample, i.e. the AA2024 in the T3 state is non self healing material, as expected, providing important first state result in the research of self healing Al alloys. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Limits on dark matter from AMS-02 antiproton and positron fraction data

    Science.gov (United States)

    Lu, Bo-Qiang; Zong, Hong-Shi

    2016-05-01

    Herein we derive limits on dark matter annihilation cross section and lifetime using measurements of the AMS-02 antiproton ratio and positron fraction data. In deriving the limits, we consider the scenario of secondary particles accelerated in supernova remnants (SNRs), which has been argued to be able to reasonably account for the AMS-02 high-energy positron/antiproton fraction/ratio data. We parametrize the contribution of secondary particles accelerated in SNRs and then fit the observational data within the conventional cosmic ray propagation model by adopting the galprop code. We use the likelihood ratio test to determine the 95% confidence level upper limits of possible dark matter (DM) contribution to the antiproton/positron fractions measured by AMS-02. Under the assumption taken in this work, we find that our limits are stronger than that set by the Fermi-LAT gamma ray Pass 8 data observation on the dwarf spheroidal satellite galaxies. We show that the solar modulation (cosmic ray propagation) parameters can play a non-negligible role in modifying the constraints on dark matter annihilation cross section and lifetime for mχ100 GeV ), where mχ is the rest mass of dark matter particles. We also find that constrains on DM parameters from AMS-02 data would become more stringent when the solar modulation is weak. Using these results, we also put limits on the effective field theory of dark matter.

  9. Positronic complexes with unnatural parity

    International Nuclear Information System (INIS)

    The structure of the unnatural parity states of PsH, LiPs, NaPs, and KPs are investigated with the configuration interaction and stochastic variational methods. The binding energies (in hartree) are found to be 8.17x10-4, 4.42x10-4, 15.14x10-4, and 21.80x10-4, respectively. These states are constructed by first coupling the two electrons into a configuration which is predominantly 3Pe, and then adding a p-wave positron. All the active particles are in states in which the relative angular momentum between any pair of particles is at least L=1. The LiPs state is Borromean since there are no three-body bound subsystems (of the correct symmetry) of the (Li+, e-, e-, e+) particles that make up the system. The dominant decay mode of these states will be radiative decay into a configuration that autoionizes or undergoes positron annihilation

  10. The scaling of electron and positron generation in intense laser-solid interactions

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Hui; Link, A.; Fiuza, F.; Hazi, A.; Heeter, R. F.; Kemp, A. J.; Kemp, G. E.; Nagel, S. R.; Park, J.; Tommasini, R.; Williams, G. J. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Sentoku, Y. [University of Nevada, Reno, Nevada 89557 (United States); Audebert, P. [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau Cedex (France); Hill, M.; Hobbs, L. [Directorate of Science and Technology, AWE plc, Reading RG7 4PR (United Kingdom); Kerr, S. [University of Alberta, Edmonton, Alberta T6G 2R3 (Canada); Meyerhofer, D. D.; Myatt, J. [LLE, University of Rochester, Rochester, New York 14623 (United States)

    2015-05-15

    This paper presents experimental scalings of the electrons and positrons produced by intense laser-target interactions at relativistic laser intensities (10{sup 18}–10{sup 20} W cm{sup −2}). The data were acquired from three short-pulse laser facilities with laser energies ranging from 80 to 1500 J. We found a non-linear (≈E{sub L}{sup 2}) scaling of positron yield [Chen et al., Phys. Rev. Lett. 114, 215001 (2015)] and a linear scaling of electron yield with the laser energy. These scalings are explained by theoretical and numerical analyses. Positron acceleration by the target sheath field is confirmed by the positron energy spectrum, which has a pronounced peak at energies near the sheath potential, as determined by the observed maximum energies of accelerated protons. The parameters of laser-produced electron-positron jets are summarized together with the theoretical energy scaling. The measured energy-squared scaling of relativistic electron-positron jets indicates the possibility to create an astrophysically relevant experimental platform with such jets using multi-kilojoule high intensity lasers currently under construction.

  11. Variable Energy Positron Annihilation Spectroscopy of GaN Grown on Sapphire Substrates with MOCVD

    Institute of Scientific and Technical Information of China (English)

    HU Yi-Fan; C.D. Beling; S. Fung

    2005-01-01

    @@ Depth profiled Doppler broadening of positron annihilation spectroscopy (DBPAS), which is also called the variable energy positron annihilation spectroscopy (VEPAS), is used in characterization of GaN grown on sapphire substrates with metal-organic chemical vapour deposition (MOCVD). The GaN film and the film/substrate interface are investigated. The VEPFIT (variable energy positron fit) software was used for analysing the data,and the positron diffusion length of the sapphire is obtained. The results suggest that there is a highly defected region near the GaN/sapphire interface. This thin dislocated region is generated at the film/substrate interface to relieve the strain. Effects of implantation dose on defect formation, for the GaN/Sapphire samples, which implanted by Al+ ions, are also investigated. Studies on Al+ implanted GaN films (not including the interface and sapphire) have revealed that there are two different regions of implantation damage. For the low Al+ implantation dose samples, in the region close to the surface, defects are mainly composed of vacancy pairs with small amount of vacancy clusters, and in the interior region of the film the positron traps are vacancy clusters without micro-voids. For the highest dose sample, however, some positron trap centres are in the form of micro-voids in the second region.

  12. Estimation of luminescence lifetime in frequency domain

    Institute of Scientific and Technical Information of China (English)

    Zhang Fu-Jun; Xu Zheng; Zhao Su-Ling; Lou Zhi-Dong; Yang Sheng-Yi; Xu Xu-Rong

    2006-01-01

    Absorption is the origin of luminescence. But it must be noticed that the lifetime of luminescence might reversely influence the rate of absorption. In this paper, it is reported that the luminescence intensity of copper and manganese changes with the driving frequency at constant voltage. The variation of luminescent intensity depends only on the lifetime of luminescence but not on the type of quenching or other factors. Generally the rate of absorption is dominantly determined by the material property and the lifetime of luminescence centres, the absorption of shorter lifetime centre will be larger than that of the longer lifetime centre at the same excited condition.

  13. Positron studies of the temperature-dependence of free volumes in Polydimethylsiloxane/poly(propylene oxide) urethane/urea membranes

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira Marques, M.F. [Departamento de Engenharia Quimica, Instituto Superior de Engenharia, 3030-199 Coimbra (Portugal) and ICEMS, Departamento de Fisica, Universidade de Coimbra, 3004-516 Coimbra (Portugal)]. E-mail: fatima@lipc.fis.uc.pt; Gordo, P.M. [ICEMS, Departamento de Fisica, Universidade de Coimbra, 3004-516 Coimbra (Portugal); Kajcsos, Zs. [KFKI Research Institute for Particle and Nuclear Physics, H-1525 Budapest P.O.B.49 (Hungary); Lopes Gil, C. [ICEMS, Departamento de Fisica, Universidade de Coimbra, 3004-516 Coimbra (Portugal); Lima, A.P. de [ICEMS, Departamento de Fisica, Universidade de Coimbra, 3004-516 Coimbra (Portugal); Queiroz, D.P. [Departamento de Engenharia Quimica, Instituto Superior Tecnico, 1049-001 Lisbon (Portugal); Pinho, M.N. de [Departamento de Engenharia Quimica, Instituto Superior Tecnico, 1049-001 Lisbon (Portugal)

    2007-02-15

    Free-volume parameters in polyurethane/urea membranes have been studied by positron annihilation lifetime and Doppler broadening measurements. The bi-soft segment membranes were obtained by varying the ratio of the structural constituents, polypropylene oxide and polydimethylsiloxane (PU/PDMS), with PDMS content from 25 to 75 wt%. The free-volume holes determined by PALS are correlated with gas permeation features. The phase separation of the various soft and hard segments in the membranes is mirrored in both lifetime and Doppler results.

  14. Positron studies of the temperature-dependence of free volumes in Polydimethylsiloxane/poly(propylene oxide) urethane/urea membranes

    International Nuclear Information System (INIS)

    Free-volume parameters in polyurethane/urea membranes have been studied by positron annihilation lifetime and Doppler broadening measurements. The bi-soft segment membranes were obtained by varying the ratio of the structural constituents, polypropylene oxide and polydimethylsiloxane (PU/PDMS), with PDMS content from 25 to 75 wt%. The free-volume holes determined by PALS are correlated with gas permeation features. The phase separation of the various soft and hard segments in the membranes is mirrored in both lifetime and Doppler results

  15. Investigation Of Helium Implanted Fe-Cr Alloys By Means Of X-Ray Diffraction And Positron Annihilation Spectroscopy

    Science.gov (United States)

    Novák, Patrik; Gokhman, Aleksandr; Dobročka, Edmund; Bokor, Jozef; Pecko, Stanislav

    2015-11-01

    X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS) have been used for the characterization of the two binary alloys Fe-Cr with Cr content 2.36 and 8.39 wt%. The influence of ion implantation on these alloys was studied. Different implantation doses of helium, up to 0.5 C/cm2, were used to simulate neutron-induced damage in a sub-surface region. To characterize the damage, a lattice parameter, coherent domain size, residual stress and a crystallographic texture have been studied by grazing incidence X-ray diffraction (GIXRD). It was found out that these parameters showed a similar dependence on the implantation dose as the positron lifetime determined by positron annihilation spectroscopy.

  16. Influence of high pressure torsion on precipitation in Al-Cu-Mg alloys studied by positron annihilation spectroscopy.

    Energy Technology Data Exchange (ETDEWEB)

    Lechner, Wolfgang; Puff, Werner; Wuerschum, Roland [Institut fuer Materialphysik, Technische Universitaet Graz, Petersgasse 16, 8010 Graz (Austria); Zehetbauer, Michael; Schafler, Erhard [Fakultaet fuer Physik, Forschungsgruppe Physik Nanostrukturierter Materialien, Universitaet Wien, Boltzmanngasse 5, Universitaet Wien, 1090 Wien (Austria)

    2008-07-01

    High pressure torsion (HPT) may open up an efficient way to refine precipations of supersaturated solutions. In the present work, the influence of HPT on the precipitation in Al-Cu-Mg alloys and on the evolution of the precipitates with subsequent annealing is studied by positron annihilation spectroscopy. HPT is observed to give rise to a fragmentation of metastable nanoscaled precipitates which have formed upon pre-annealing at 200 C (3 hours). Positron lifetime spectroscopy in combination with coincident Doppler broadening of the positron-electron annihilation enables a specific and chemical sensitive distinction between interfacial vacancy-type defects associated with precipitates and the vacancy-type lattice defects formed upon high pressure torsion. Different aging behaviour is observed for undeformed and HPT-deformed samples.

  17. Study of local structure in hyper-eutectic Zr-Cu-Al bulk glassy alloys by positron annihilation techniques

    Science.gov (United States)

    Ishiyama, T.; Ishii, K.; Yokoyama, Y.; Konno, T. J.; Iwase, A.; Hori, F.

    2016-01-01

    The Zr-Cu-Al bulk glassy (BG) alloy, which has amorphous structure, possesses various properties such as high strength and toughness with compositional dependence. In the present study, density, positron annihilation lifetime and coincidence Doppler Broadening measurement have been performed for various compositional hyper-eutectic Zr-Cu-Al BG alloys. The density of hyper-eutectic Zr-Cu-Al BG alloys increases with decreasing of Zr fraction. In contrast, positron lifetime for all compositional alloys is almost constant about 165 psec. In addition, the CDB ratio profile is almost the same for hyper-eutectic alloys. This unchanging trend of CDB ratio profile is quite different from that of hypo-eutectic BG alloys. These results reveal that different internal structure exists in hyper and hypo-eutectic BG alloys.

  18. Positron annihilation spectroscopy study on annealing effect of CuO nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Jianjian; Wang, Jiaheng; Yang, Wei; Zhu, Zhejie; Wu, Yichu, E-mail: ycwu@whu.edu.cn [School of Physics and Technology, Hubei Key Laboratory of Nuclear Solid State Physics, Wuhan University (WHU), Wuhan (China)

    2016-03-15

    The microstructure and defects of CuO nanoparticles under isochronal annealing were investigated by positron annihilation spectroscopy (PAS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD and SEM results indicated that the average grain sizes of CuO nanoparticles grew slowly below 800 °C, and then increased rapidly with the annealing temperature from 800 to 1000 °C. Positron lifetime analysis exhibited that positrons were mainly annihilated in mono-vacancies (V{sub Cu}, V{sub O}) and vacancy clusters when annealing from 200 to 800 °C. Furthermore, W-S plot of Doppler broadening spectra at different annealing temperatures found that the (W, S) points distributed on two different defect species, which suggested that V{sup −}{sub Cu} - V{sup +}{sub O} complexes were produced when the grains grew to bigger size after annealing above 800 °C, and positrons might annihilate at these complexes. (author)

  19. Carrier lifetimes in thin-film photovoltaics

    Science.gov (United States)

    Baek, Dohyun

    2015-09-01

    The carrier lifetimes in thin-film solar cells are reviewed and discussed. Shockley-Read-Hall recombination is dominant at low carrier density, Auger recombination is dominant under a high injection condition and high carrier density, and surface recombination is dominant under any conditions. Because the surface photovoltage technique is insensitive to the surface condition, it is useful for bulk lifetime measurements. The photoconductance decay technique measures the effective recombination lifetime. The time-resolved photoluminescence technique is very useful for measuring thin-film semiconductor or solar-cell materials lifetime, because the sample is thin, other techniques are not suitable for measuring the lifetime. Many papers have provided time-resolved photoluminescence (TRPL) lifetimes for copper-indium-gallium-selenide (CIGS) and CdTe thin-film solar cell. The TRPL lifetime strongly depends on open-circuit voltage and conversion efficiency; however, the TRPL life time is insensitive to the short-circuit current.

  20. Imaging optimizations with non-pure and high-energy positron emitters in small animal positron computed tomography; Optimierung der Bildgebung mit nichtreinen und hochenergetischen Positronenstrahlern in der Kleintier-Positronen-Emissions-Tomographie

    Energy Technology Data Exchange (ETDEWEB)

    Harzmann, Sophie

    2014-03-21

    The contribution on imaging optimizations with non-pure and high-energy positron emitters in small animal positron emission tomography (PET) covers the following topics: physical fundamentals of PET, mathematical image reconstruction and data analyses, Monte-Carlo simulations and implemented correction scheme, quantification of cascade gamma coincidences based on simulations and measurements, sinogram based corrections, restoration of the spatial resolution, implementation of full corrections.

  1. The Westinghouse equipment lifetime monitor

    International Nuclear Information System (INIS)

    The Westinghouse Equipment LIFETIME Monitor addresses a long-standing need in the nuclear industry-A way to continuously and passively monitor the temperature and radiation environment of components located throughout the plant. This compact device (approximately 2.5 x 2.3 x 1.3 inches) is capable of performing up to six different functions. Each function is designed to measure a different type or range of environmental parameter. Monitoring options include peak temperature, integrated temperature, low and high range gamma ray dose, beta particle dose, and neutron radiation. These various functions allow flexibility in selecting the precise environmental parameters to be monitored to meet plant specific requirements and budget constraints. The data acquired from the Equipment LIFETIME Monitor can be used in a variety of ways, including: - Extending the qualified life of safety-related equipment by improving on initial assumptions regarding service environment, - Conducting long term temperature and radiation surveys to ensure operation within qualified limits, - Assessing potential age-related degradation of major high cost components for purposes of plant life extension, and - Justifying continued use of equipment following an accidental excursion in environmental radiation or temperature. (author)

  2. Corrosion Preventive Compounds Lifetime Testing

    Science.gov (United States)

    Hale, Stephanie M.; Kammerer, Catherine C.; Copp, Tracy L.

    2007-01-01

    Lifetime Testing of Corrosion Preventive Compounds (CPCs) was performed to quantify performance in the various environments to which the Space Shuttle Orbiter is exposed during a flight cycle. Three CPCs are approved for use on the Orbiter: RD Calcium Grease, Dinitrol AV-30, and Braycote 601 EF. These CPCs have been rigorously tested to prove that they mitigate corrosion in typical environments, but little information is available on how they perform in the unique combination of the coastal environment at the launch pad, the vacuum of low-earth orbit, and the extreme heat of reentry. Currently, there is no lifetime or reapplication schedule established for these compounds that is based on this combination of environmental conditions. Aluminum 2024 coupons were coated with the three CPCs and exposed to conditions that simulate the environments to which the Orbiter is exposed. Uncoated Aluminum 2024 coupons were exposed to the environmental conditions as a control. Visual inspection and Electro- Impedance Spectroscopy (EIS) were performed on the samples in order to determine the effectiveness of the CPCs. The samples were processed through five mission life cycles or until the visual inspection revealed the initiation of corrosion and EIS indicated severe degradation of the coating.

  3. Positron emission tomography and migraine

    International Nuclear Information System (INIS)

    Positron emission tomography (PET) is a brain imaging technique that allows in vivo studies of numerous physiological parameters. There have been few PET studies in migraine patients. Cerebral blood flow changes with no variations in brain oxygen consumption have been reported in patients with prolonged neurologic manifestations during migraine attacks. Parenteral administration of reserpine during migraine headache has been followed by a fall in the overall cerebral uptake of glucose. The small sample sizes and a number of methodologic problems complicate the interpretation of these results. Recent technical advances and the development of new PET tracers can be expected to provide further insight into the pathophysiology of migraine. Today cerebral cortex 5 HT2 serotonin receptors can be studied in migraine patients with PET

  4. Positron emission tomography wrist detector

    Science.gov (United States)

    Schlyer, David J.; O'Connor, Paul; Woody, Craig; Junnarkar, Sachin Shrirang; Radeka, Veljko; Vaska, Paul; Pratte, Jean-Francois

    2006-08-15

    A method of serially transferring annihilation information in a compact positron emission tomography (PET) scanner includes generating a time signal representing a time-of-occurrence of an annihilation event, generating an address signal representing a channel detecting the annihilation event, and generating a channel signal including the time and address signals. The method also includes generating a composite signal including the channel signal and another similarly generated channel signal concerning another annihilation event. An apparatus that serially transfers annihilation information includes a time signal generator, address signal generator, channel signal generator, and composite signal generator. The time signal is asynchronous and the address signal is synchronous to a clock signal. A PET scanner includes a scintillation array, detection array, front-end array, and a serial encoder. The serial encoders include the time signal generator, address signal generator, channel signal generator, and composite signal generator.

  5. Positron and positronium in insulators

    International Nuclear Information System (INIS)

    Positron annihilation spectroscopy has been widely applied to study the microstructure in various insulators: polymers, oxides, ceramics, molecular substances, zeolites and so on. The most important experimental observation is that the positronium (Ps) can be formed in those materials and then localized in the regions with lower electron density. The Ps annihilation parameter is used to characterize the microstructure in nanometer scale, and related to physical and chemical properties of insulators. In this paper the Ps formation and localization, the Ps interaction with dopants and gases, the recent results in studying the free volume in polymers and micro-voids in porous materials will be briefly reviewed. The unique information explored by Ps probe and its fundamental importance and potential industrial application will be presented. (orig.)

  6. Positron emission tomography basic sciences

    CERN Document Server

    Townsend, D W; Valk, P E; Maisey, M N

    2003-01-01

    Essential for students, science and medical graduates who want to understand the basic science of Positron Emission Tomography (PET), this book describes the physics, chemistry, technology and overview of the clinical uses behind the science of PET and the imaging techniques it uses. In recent years, PET has moved from high-end research imaging tool used by the highly specialized to an essential component of clinical evaluation in the clinic, especially in cancer management. Previously being the realm of scientists, this book explains PET instrumentation, radiochemistry, PET data acquisition and image formation, integration of structural and functional images, radiation dosimetry and protection, and applications in dedicated areas such as drug development, oncology, and gene expression imaging. The technologist, the science, engineering or chemistry graduate seeking further detailed information about PET, or the medical advanced trainee wishing to gain insight into the basic science of PET will find this book...

  7. Identifying electrons and positrons with AMS-02

    International Nuclear Information System (INIS)

    The AMS-02 experiment is a multi-purpose detector for cosmic ray particles mounted on the International Space Station. It recorded over 40 billion events since its installation in 2011. The bulk of these events are protons, which are most abundant in cosmic rays. Electrons are 100 times and positrons 1000 times less abundant. Measuring the positrons as function of energy is especially interesting, as an excess over the expected astrophysical background may hint at an additional source of positrons in the galaxy or a new phenomena responsible for the excess, e.g. dark-matter annihilation. In order to measure positrons accurately with a small uncertainty, a large proton rejection of 106 is needed. AMS-02 offers a transition radiation detector to separate positrons from protons and an electromagnetic calorimeter allowing a precise measurement of the kinetic energy of an incoming lepton. This talk covers the general strategy of identifying electrons/positrons with AMS-02 and presents the so-obtained electron/positron fluxes that were recently published.

  8. Investigation of nanopores in nanofiltration membranes using slow positron beam techniques

    International Nuclear Information System (INIS)

    The pore distribution of the commercial nanofiltration membranes Desal 5DL, Desal 51HL, N30F, NTR 7450 and NF-PES-10 were analyzed by positron annihilation spectroscopy using slow positron beam analysis. From the depth selective 3γ/2γ analysis a dense nanoporous filtration layer could be determined. From the depth selective lifetime analysis the size and distribution of the nanopores could be extracted. The measurements indicate the presence of 2 pore sizes in the samples with a radius of 1.25-1.55 Aa and 3.2-3.95 Aa. These experimental values are compared with the molecular weight cut-off values of these membranes. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Determination of phase transitions in a lyotropic liquid crystal by Positron Annihilation technique

    International Nuclear Information System (INIS)

    Positron annihilation technique was used to determine the phase transitions in a lyotropic liquid crystal, as a function of temperature. Seven different concentrations of the surfactant cetyldimethylethylammonium bromide, were studied. The liquid crystal studied consisted of a binary system, formed by the surfactant and water. Positron annihilation technique has a very high sensitivity toward changes in the microestructure, in condensed matter, this is useful in order to detect the temperatures at which phase transitions occur and the number of these, in a liquid crystalline system. Thus, phase transitions are related with changes occurred in the ortho-positronium parameters: lifetime (τ3) and intensity of formation (I3). Six different kinds of phases were detected in the system studied in a temperature range of 35 to 140 Centigrade degrees, those phases were: hexagonal, hexagonal-lamellae, lamellae, lamellae-cubic, nematic and anisotropic. Using optical microscopic the textures of these phases were assigned. (Author)

  10. Characterization of the melting process of PTFE using positron annihilation spectroscopy

    Science.gov (United States)

    Honda, Y.; Nishijima, S.

    2015-06-01

    Poly(tetrafluoroethylene) (PTFE) is a semi-crystalline polymer and the lifetime of ortho-positronium(o-Ps) is known to be able to be separated into two components due to annihilation in the crystal region and in the amorphous region. The melting process of PTFE was investigated using positron annihilation spectroscopy and X-ray diffraction. The results indicated that volume expansion with an increase of temperature is dominantly due to the expansion of the amorphous region and a Ps bubble is formed at melting in both regions. The o-Ps relating to the crystal region definitely remains on the surface of crystal at the time of annihilation. The production of lower energy electrons at melting was deduced by the analysis of the Doppler broadened annihilation photopeak, and the increase in the number of such electrons was found to have great influence on the formation of the o-Ps and annihilation processes of positron and o-Ps.

  11. Scintillators for positron emission tomography

    International Nuclear Information System (INIS)

    Like most applications that utilize scintillators for gamma detection, Positron Emission Tomography (PET) desires materials with high light output, short decay time, and excellent stopping power that are also inexpensive, mechanically rugged, and chemically inert. Realizing that this ''ultimate'' scintillator may not exist, this paper evaluates the relative importance of these qualities and describes their impact on the imaging performance of PET. The most important PET scintillator quality is the ability to absorb 511 keV photons in a small volume, which affects the spatial resolution of the camera. The dominant factor is a short attenuation length (≤ 1.5 cm is required), although a high photoelectric fraction is also important (> 30% is desired). The next most important quality is a short decay time, which affects both the dead time and the coincidence timing resolution. Detection rates for single 511 keV photons can be extremely high, so decay times ≤ 500 ns are essential to avoid dead time losses. In addition, positron annihilations are identified by time coincidence so ≤5 ns fwhm coincidence pair timing resolution is required to identify events with narrow coincidence windows, reducing contamination due to accidental coincidences. Current trends in PET cameras are toward septaless, ''fully-3D'' cameras, which have significantly higher count rates than conventional 2-D cameras and so place higher demands on scintillator decay time. Light output affects energy resolution, and thus the ability of the camera to identify and reject events where the initial 511 keV photon has undergone Compton scatter in the patient. The scatter to true event fraction is much higher in fully-3D cameras than in 2-D cameras, so future PET cameras would benefit from scintillators with a 511 keV energy resolution < 10--12% fwhm

  12. Comparison of the Free Volume of LiCl-Added SPPO Membrane and SPPO-PES Blend Membrane by Positron Annihilation Method

    Institute of Scientific and Technical Information of China (English)

    Htwe Htwe YIN; HUANG Huan; MA Qingli; TANG Shibiao

    2007-01-01

    Positron annihilation lifetime spectroscopy (PALS) is a powerful technique for the study of free volume in polymers. The lifetime of ortho-positronium (o-Ps), a bound state of an electron and a positron, can be used to assess the pore size, while the intensity can be used to characterize the number of pores. Based on the values of the long-lived o-Ps components in the lifetime spectra, the radii and fractional free volumes of sulfonated poly (2,6-dimethyl-l,4-phenyleneoxide) (SPPO) membranes with added LiCl and SPPO-PES (Polyethersulfone) blend were compared. Free volume radii in both kinds of membranes are discussed.

  13. Rapid global fitting of large fluorescence lifetime imaging microscopy datasets.

    Directory of Open Access Journals (Sweden)

    Sean C Warren

    Full Text Available Fluorescence lifetime imaging (FLIM is widely applied to obtain quantitative information from fluorescence signals, particularly using Förster Resonant Energy Transfer (FRET measurements to map, for example, protein-protein interactions. Extracting FRET efficiencies or population fractions typically entails fitting data to complex fluorescence decay models but such experiments are frequently photon constrained, particularly for live cell or in vivo imaging, and this leads to unacceptable errors when analysing data on a pixel-wise basis. Lifetimes and population fractions may, however, be more robustly extracted using global analysis to simultaneously fit the fluorescence decay data of all pixels in an image or dataset to a multi-exponential model under the assumption that the lifetime components are invariant across the image (dataset. This approach is often considered to be prohibitively slow and/or computationally expensive but we present here a computationally efficient global analysis algorithm for the analysis of time-correlated single photon counting (TCSPC or time-gated FLIM data based on variable projection. It makes efficient use of both computer processor and memory resources, requiring less than a minute to analyse time series and multiwell plate datasets with hundreds of FLIM images on standard personal computers. This lifetime analysis takes account of repetitive excitation, including fluorescence photons excited by earlier pulses contributing to the fit, and is able to accommodate time-varying backgrounds and instrument response functions. We demonstrate that this global approach allows us to readily fit time-resolved fluorescence data to complex models including a four-exponential model of a FRET system, for which the FRET efficiencies of the two species of a bi-exponential donor are linked, and polarisation-resolved lifetime data, where a fluorescence intensity and bi-exponential anisotropy decay model is applied to the analysis

  14. Electron beam and gamma irradiation effects on conducting polystyrene studied by positron annihilation technique

    International Nuclear Information System (INIS)

    The effects of electron beam and gamma irradiation on microscopic structure of a conducting polystyrene (polystyrene + 15% carbon black) have been studied using positron annihilation lifetime spectroscopy. X-ray diffraction profiles for non-irradiated and irradiated conducting polystyrene are performed to investigate the structural nature of the samples. The samples were irradiated at room temperature with doses ranging from 30 up to 1500 kGy. The observed lifetime spectra were resolved into three components and the ortho-positronium (o-Ps) lifetime component was associated with the pick-off annihilation of positronium trapped by the free volume. After gamma irradiation no detectable changes are observed in the o-Ps lifetime. In contrast, the intensity of the o-Ps component, I3, decreases with the dose, up to about 540 kGy, followed by a much smooth decrease up to 1200 kGy then it levels off up to 1500 kGy. Meanwhile, after electron irradiation, the intensity of the o-Ps lifetime component as the dose increases exhibits two different regions may be identified as a rapid drop, followed by a smooth increase, then, it levels off and remains constant. The back increase in the electron curve seems to be absent in the case of gamma irradiation. These results are discussed on the basis of the free volume model

  15. Influence of structure of a crosslinked epoxy resin on its properties studied by positron annihilation and other methods

    International Nuclear Information System (INIS)

    Positron annihilation has been applied to study samples of two crosslinked epoxy resins: diglycidyl ether of bisphenol A (Epikote 828) and polyglycidyl-ether of phenol-formaldehyde novolac (Epikote 155) cured with 4,4'-diamino-diphenylo-methane (MDA), phenol-formaldehyde novolac resin (Novolac Z) and bisphenol A (formaldehyde resin). Results of measurements of positron lifetime spectra were compared with the ones coming from DMTA, flexural strength testing and density measurements. The most important features of samples (glass transition temperature, storage modulus, flexural strength, crosslinking density and tan δ) proved to be correlated with the product Ι3 x v-bar, proportional to the fractional free volume in samples. Values of v-bar have been estimated from the values of τ3, the longest lifetime in positron lifetime spectra. Ι3 corresponds to the intensity of the longest-lived component in them. Distributions of free volume radii reconstructed in the basis of PAL measurements are given for all samples. The influences of structure of both cured resin and the curing agent on the properties of the crosslinked products is clearly seen from the presented results. (author)

  16. Prototyping of the ILC Baseline Positron Target

    Energy Technology Data Exchange (ETDEWEB)

    Gronberg, J; Brooksby, C; Piggott, T; Abbott, R; Javedani, J; Cook, E

    2012-02-29

    The ILC positron system uses novel helical undulators to create a powerful photon beam from the main electron beam. This beam is passed through a titanium target to convert it into electron-positron pairs. The target is constructed as a 1 m diameter wheel spinning at 2000 RPM to smear the 1 ms ILC pulse train over 10 cm. A pulsed flux concentrating magnet is used to increase the positron capture efficiency. It is cooled to liquid nitrogen temperatures to maximize the flatness of the magnetic field over the 1 ms ILC pulse train. We report on prototyping effort on this system.

  17. Hypernovae as possible sources of Galactic positrons

    OpenAIRE

    Schanne, Stephane; Casse, Michel; Cordier, Bertrand; Paul, Jacques

    2004-01-01

    INTEGRAL/SPI has recently observed a strong and extended emission resulting from electron-positron annihilation located in the Galactic center region, consistent with the Galactic bulge geometry, without any counterpart at high gamma-ray energies, nor in the 1809 keV $^{26}$Al decay line. In order to explain the rate of positron injection in the Galactic bulge, estimated to more than 10$^{43}$ s$^{-1}$, the most commonly considered positron injection sources are type Ia supernovae. However, S...

  18. Positron beam production with a deuteron accelerator

    International Nuclear Information System (INIS)

    A graphite target was bombarded with 1.5 MeV deuterons, producing the isotope 13N, which is a positron emitter. Using the activated material a slow positron beam with an intensity of 0.7 (0.14)x105 s-1 was produced. A (saturated) 13N yield of 63 (11) MBq/μA was observed, with 1.5 MeV deuterons, which is consistent with previous calculations and experiments. Our results show that, with the method we outline, positron beams with an average intensity of up to 1x108 s-1 may be produced

  19. Characteristics of the positron annihilation process in the matter

    International Nuclear Information System (INIS)

    In this report the positrons annihilation spectroscopy, as a method for the matter study is described. The interaction of positrons of high as well as thermal energies are discussed and different models of mentioned interactions are presented. Special attention is paid for positrons interaction with crystal lattice and its defects. The influence of positron beams characteristics on measured values are also discussed

  20. Measurement of the BS lifetime

    International Nuclear Information System (INIS)

    This thesis presents a measurement of the Bs lifetime using 3 million hadronic Z decays collected by the DELPHI detector at LEP from 1991 to 1994. Decays of Bs mesons are tagged by the reconstruction of a Ds-→φπ-or Ds-→K*0K- decay (including the charge conjugated states of these decay modes). The decay time is obtained by reconstructing both the Bs momentum and the Bs flight distance. The combined result for the Ds-lepton and Ds-hadron samples is: τ(Bs)=1.54±0.31±0.15 ps where the first error is statistical and the second is systematic. (orig./HSI)