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Sample records for annihilation lifetime spectroscopy

  1. Positron annihilation lifetime spectroscopy of macromolecules

    International Nuclear Information System (INIS)

    Simon, G.

    1996-01-01

    Positron annihilation lifetime spectroscopy (PALS) is a technique which makes use of the anti- particle of the electron, the positron (e + ), first predicted by Dirac in 1931. This talk will concentrate on the use of PALS as a technique in characterising macromolecules. PALS has been used by various groups to evaluate many properties that one associates with free volume such as physical ageing, gas permeability, the glass transition, uptake of a solvent, crystallinity, crosslinking, molecular mobility. One area of much interest has been the use of this technique in looking at miscibility of polymer blends. In miscible blends, the interactions of the different polymers may be expected to lead to a negative free volume of mixing because of the strong attraction between the different chains. This may influence the free volume properties. Conversely, if a material is partially miscible or totally immiscible, this should influence both the size and total content of free volume. This should be related to other properties such as mechanical properties and molecular mobility, such as measured by dielectric relaxation spectroscopy. Variations on this involve copolymerization of crosslinked materials or linear thermoplastics (the ultimate 'molecular' miscibility) and this will also be discussed. Multiphase systems such as water uptake in polymers can vary polymer properties by filling molecular voids, as well as disturbing chain conformations and, in the case of polar polymers, associating with the polymer chains. The effect of polymer molecular structure on free volume - particularly in rigid polymer chains such as substituted poly(phenylenes) and liquid crystalline polymers will also be presented. Indeed, the unusual packing which arises from such anisotropic molecules leads to unusual behaviours both of the homolpolymers and subsequent liquid crystal polymer - liquid crystal polymer blends

  2. Positron annihilation lifetime spectroscopy of ZnO bulk samples

    International Nuclear Information System (INIS)

    Zubiaga, A.; Plazaola, F.; Garcia, J. A.; Tuomisto, F.; Munoz-Sanjose, V.; Tena-Zaera, R.

    2007-01-01

    In order to gain a further insight into the knowledge of point defects of ZnO, positron annihilation lifetime spectroscopy was performed on bulk samples annealed under different atmospheres. The samples were characterized at temperatures ranging from 10 to 500 K. Due to difficulties in the conventional fitting of the lifetime spectra caused by the low intensity of the defect signals, we have used an alternative method as a solution to overcome these difficulties and resolve all the lifetime components present in the spectra. Two different vacancy-type defects are identified in the samples: Zn vacancy complexes (V Zn -X) and vacancy clusters consisting of up to five missing Zn-O pairs. In addition to the vacancies, we observe negative-ion-type defects, which are tentatively attributed to intrinsic defects in the Zn sublattice. The effect of the annealing on the observed defects is discussed. The concentrations of the V Zn -X complexes and negative-ion-type defects are in the 0.2-2 ppm range, while the cluster concentrations are 1-2 orders of magnitude lower

  3. Positron annihilation lifetime spectroscopy study of roller burnished magnesium alloy

    Directory of Open Access Journals (Sweden)

    Zaleski Radosław

    2015-12-01

    Full Text Available The effect of roller burnishing on Vickers’ hardness and positron lifetimes in the AZ91HP magnesium alloy was studied. The microhardness increases with an increase in the burnishing force and with a decrease in the feed. The comparison of various methods of analysis of positron annihilation lifetime (PAL spectra allowed identification of two components, which are related to solute-vacancy complexes and vacancy clusters, respectively. It was found that the increase in microhardness was related to the increase in the concentration of vacancy clusters.

  4. 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 pos......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...

  5. The study of synthetic food dyes by positron annihilation lifetime spectroscopy.

    Science.gov (United States)

    Pivtsaev, A. A.; Razov, V. I.

    2015-06-01

    By method of positron annihilation lifetime spectroscopy (PALS), substances are food dyes were studied: E-102 (Tartrazine), E-124 (Ponso 4R), E 132 (Indigo carmine), E-133 (Brilliant Blue), E-151 (Black Shiny). They are examined for the presence of carcinogenic properties. The difference between dyes having explicit carcinogenic properties and mutagenic properties (non-explicit carcinogens) is established.

  6. The study of synthetic food dyes by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Pivtsaev, A A; Razov, V I

    2015-01-01

    By method of positron annihilation lifetime spectroscopy (PALS), substances are food dyes were studied: E-102 (Tartrazine), E-124 (Ponso 4R), E 132 (Indigo carmine), E-133 (Brilliant Blue), E-151 (Black Shiny). They are examined for the presence of carcinogenic properties. The difference between dyes having explicit carcinogenic properties and mutagenic properties (non-explicit carcinogens) is established. (paper)

  7. Evolution of porosity in a Portland cement paste studied through positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Consolati, G.; Quasso, F.

    2003-01-01

    Positron annihilation lifetime spectroscopy experiments were carried out in an ordinary Portland cement paste characterized by a water-to-cement ratio w/c=0.8, in order to monitor the porosity of the paste. It was found that ortho-positronium intensity is a suitable quantity to this purpose, being sensitive to the amount of water contained in the pores. The experimental data show good agreement with the porosity calculated according to the Powers' thin filmsodel

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

    Science.gov (United States)

    Kinomura, A; Suzuki, R; Oshima, N; O'Rourke, B E; Nishijima, T; Ogawa, H

    2014-12-01

    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.

  9. Investigation of cation vacancies in Zinc substituted maghemite by positron annihilation lifetime and Doppler broadening spectroscopy.

    Science.gov (United States)

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

    2017-07-01

    In this work we investigated vacancies in maghemite and Zn substituted maghemite (γ-Fe 2-y Zn 3y/2 O 3 , y=0.0, 0.11, 0.24, 0.36, 0.50 and 0.66) nanoparticles using coincidence Doppler broadening and positron annihilation lifetime spectroscopy. Coincidence Doppler broadening spectroscopy (CDBS) measurements showed that the positrons annihilated in cation vacancies that surrounded by oxygen anions. Also, the CDBS showed that in pure maghemite and in the y=0.11 samples the vacancies are in octahedral and tetrahedral sites, respectively. For other samples they are distributed in both octahedral and tetrahedral sites. The positron annihilation lifetime spectroscopy (PALS) measurements confirmed the results of the CDBS measurements and also exhibited that the number of vacancies in y=0.36 sample is less than the other samples. This is attributed to Zn substituted magnetite phase in this sample as well as Zn substituted maghemite phase. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. Ageing phenomenon in acrylic polymer dental materials detected by means of positron annihilation lifetime spectroscopy.

    Science.gov (United States)

    Filipecki, Jacek; Chamerski, Kordian; Boyko, Olha; Kotynia, Katarzyna

    2014-01-01

    Polymer materials based on acrylic monomers are commonly used in dentistry. It is important to research the structure of dental filling materials towards the material ageing. The study has been conducted in order to determine the presence of free volume gaps in the structure of polymer materials. Brand new, acrylic polymer based samples of dental Dipol materials were used as a research material. The study was conducted by means of the positron annihilation lifetime spectroscopy (PALS). As a result of the conducted measurements, curves describing numbers of counts of the acts of annihilation in the time function were obtained. The conducted studies revealed the existence of four components τ1, τ2, τ3 and τ4. The τ3 and τ4 components are attributed to the pick-off annihilation of o-Ps orthopositronium trapping by free volume gaps and provide information about geometrical parameters of the volumes. LT 9 computer program was used to calculate components. Free volume holes were determined from empirical relationship between the radius of free volume and the long lifetime components. Conducted studies indicate the presence of free volume holes in the research materials. It has been noted that a new long lifetime component is assigned to a new kind of free volumes that exist in the structure of material related to the material ageing.

  11. 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

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

    International Nuclear Information System (INIS)

    Sayed Ahmed, Essmat Mahmoud Hassan

    2008-01-01

    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

  13. Positron annihilation lifetime spectroscopy of mechanically milled protein fibre powders and their free volume aspects

    Science.gov (United States)

    Patil, K.; Sellaiyan, S.; Rajkhowa, R.; Tsuzuki, T.; Lin, T.; Smith, S. V.; Wang, X.; Uedono, A.

    2013-06-01

    The present study reports the fabrication of ultra-fine powders from animal protein fibres such as cashmere guard hair, merino wool and eri silk along with their free volume aspects. The respectively mechanically cleaned, scoured and degummed cashmere guard hair, wool and silk fibres were converted into dry powders by a process sequence: Chopping, Attritor Milling, and Spray Drying. The fabricated protein fibre powders were characterised by scanning electron microscope, particle size distribution and positron annihilation lifetime spectroscopy (PALS). The PALS results indicated that the average free volume size in protein fibres increased on their wet mechanical milling with a decrease in the corresponding intensities leading to a resultant decrease in their fractional free volumes.

  14. Chemical environment in halogenated styrene polymers studied by using positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Zhang, R.; Wu, Y.C.; Chen, H.; Zhang, J.; Li, Y.; Sandreczki, T.C.; Jean, Y.C.

    2003-01-01

    Polystyrene samples, incorporated with halogen elements (F, Cl, Br, I) on the para-position of the benzene ring, were studied using positron annihilation lifetime spectroscopy. It was found that the free-volume hole size is significantly affected by the internal Coulombic interaction of the halogen group, and is mainly related to the electronegativity of halogen-carbon bonds. In addition, it is found that the free-volume is secondarily modified by the steric effect of the side groups. The intensity of o-Ps has a linear relationship with the strength of the C-X bond and is strongly affected by the chemical environment in a halogenated styrene polymer system

  15. Ion implantation induced defects in Fe-Cr alloys studied by conventional positron annihilation lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Krsjak, V [Joint Research Centre, Institute for Energy, European Commission, PO Box 2, 1755 ZG Petten (Netherlands); Sojak, S; Slugen, V; Petriska, M, E-mail: vladimir.krsjak@ec.europa.eu [Department of Nuclear Physics and Technology, FEI, Slovak University of Technology, Ilkovicova 3, 812 19 Bratislava (Slovakia)

    2011-01-10

    The influence of chromium on the radiation damage resistance of the iron based alloys has been studied using conventional positron annihilation lifetime spectroscopy (PALS). Experimental data evaluation has been supported by the former theoretical calculation of positron lifetimes in the studied materials and well-defined types of defects. For this purpose, density functional theory (DFT) computation method has been applied. The spectrum of used {sup 22}Na positron source was decomposed into discrete fractions to better calculate efficiency of near surface layers study. For the experimental simulation of a-radiation and obtaining of defined cascade collisions in the materials, helium implantation was used. Different level of the implanted dose (6.24x10{sup 17} - 3.12x10{sup 18} cm{sup -2}) corresponds to local damage up to 90 DPA acquired in thin <1 {mu}m region. Experimental measurement has been performed using the PALS technique on the four different Fe-Cr binary alloys (2.36; 4.62; 8.39; 11.62 wt% of Cr). The results showed that chromium has a significant effect on the size and density of the implanted defects and specific Cr content should prevent the vacancy clusters formation.

  16. Free-volume characterization of nanostructurized substances by positron annihilation lifetime spectroscopy

    Science.gov (United States)

    Shpotyuk, O.; Ingram, A.; Shpotyuk, Ya.

    2018-02-01

    Methodological possibilities of positron annihilation lifetime (PAL) spectroscopy are examined to parameterize free-volume structural evolution processes in some nanostructurized substances obeying conversion from positronium (Ps) decaying to positron trapping. Unlike conventional x3-term fitting analysis based on admixed positron trapping and Ps decaying, the effect of nanostructurization is considered as occurring due to conversion from preferential Ps decaying in initial host matrix to positron trapping in modified (nanostructurized) host-guest matrix. The developed approach referred to as x3-x2-CDA (coupling decomposition algorithm) allows estimation defect-free bulk and defect-specific positron lifetimes of free-volume elements responsible for nanostructurization. The applicability of this approach is proved for some nanostructurized materials allowing free-volume changes through Ps-to-positron trapping conversion, such as (i) metallic Ag nanoparticles embedded in polymer matrix, (ii) structure-modification processes caused by swift heavy ions irradiation in polystyrene, and (iii) host-guest chemistry problems like water immersion in alumomagnesium spinel ceramics. This approach is considered to be used as test-indicator, separating processes of host-matrix nanostructurization due to embedded nanoparticles from uncorrelated changes in positron-trapping and Ps-decaying channels.

  17. 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...

  18. 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.

  19. Structural study of polymer hydrogel contact lenses by means of positron annihilation lifetime spectroscopy and UV-vis-NIR methods.

    Science.gov (United States)

    Filipecki, J; Kocela, A; Korzekwa, P; Miedzinski, R; Filipecka, K; Golis, E; Korzekwa, W

    2013-08-01

    A study has been conducted in order to determine presence of free volume gaps in the structure of structure of polymer hydrogel contact lenses made in phosphoryl choline technology and of the degree of defect of its structure. The study was made by means of positron annihilation lifetime spectroscopy. As a result of the conducted measurements, curves were obtained, which described numbers of counts of the acts of annihilation in the time function. The conducted studies revealed existence of three components τ(1), τ(2) and τ(3). The τ(3) component is attributed to the pick-off annihilation of o-Ps orthopositronium trapping by free volume gaps and provides information about geometrical parameters of the volumes. At the same time, the UV-vis-NIR spectrometry examination was conducted on the same samples in the spectral range 200-1,000 nm.

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

    International Nuclear Information System (INIS)

    Buriova, M.

    2001-12-01

    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)

  1. Positron annihilation in polypropylene studied by lifetime and coincidence Doppler-broadening spectroscopy

    Science.gov (United States)

    Djourelov, N.; He, C.; Suzuki, T.; Shantarovich, V. P.; Ito, Y.; Kondo, K.; Ito, Y.

    2003-12-01

    The momentum density distributions (MDDs) of electrons taking part in the annihilation processes in polypropylene (PP) have been measured by coincidence Doppler-broadening spectroscopy. MDDs at the beginning of measurements to those at the saturation level of Ps formation have been compared in order to follow the possible changes in concentration of carbonyl groups (CG). A high initial CG concentration in PP has been observed, while for antioxidant-containing PP no significant presence of CG has been detected, and no changes have been observed during positron irradiation.

  2. Investigation of the Degree of Disorder of the Structure of Polymer Soft Contact Lenses Using Positron Annihilation Lifetime Spectroscopy PALS.

    Science.gov (United States)

    Filipecki, Jacek; Kotynia, Katarzyna; Filipecka, Katarzyna

    2016-01-01

    Hydrogel and silicone-hydrogel polymeric materials are widely used in ophthalmology for the manufacture of contact lenses. An important aspect is the investigation of the structure of these materials. This study has been conducted in order to compare the degree of disorder and presence of free volumes in the internal structure of the polymeric soft contact lenses Omafilcon A (hydrogel) and Comfilcon A (silicone-hydrogel). Differences in the occurrence of trapping centers for positrons and free volumes between the types of investigated contact lenses have been demonstrated. Two types of polymeric contact lenses were used as materials: Omafilcon A (hydrogel) and Comfilcon A (silicone-hydrogel). The study was performed using positron annihilation lifetime spectroscopy (PALS). When the results of the measurements has been obtained, a graphical curve has created to describe the relationship of the number of annihilation acts in time. Significant changes were observed between the contact lenses investigated in positron trapping in macropores (based on a two-state model) and the presence of free volumes (based on the Tao-Eldrup model). The use of the positron annihilation two-state model made it possible to demonstrate that a higher positron trapping rate in macropores occurs in the silicone-hydrogel contact lens. Additionally, calculations using the Tao-Eldrup model show the existence of free volumes in both types of materials. The size and fraction of free volumes is much larger in the silicone-hydrogel contact lens.

  3. Free-volume structure of fluoropolymer-based radiation-grafted electrolyte membranes investigated by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Sawada, S; Maekawa, Y; Kawasuso, A; Maekawa, M; Yabuuchi, A

    2010-01-01

    In the field of polymer-electrolyte-membrane (PEM) fuel cell technology, the structures of free-volume holes in the PEMs are very important because they are correlated to the supplied-gas crossover phenomenon, which sometimes deteriorates the cell performance. In this study, we investigated the size and location of free-volume holes in the crosslinked-polytetrafluoroethylene (cPTFE) based radiation-grafted PEMs by positron annihilation lifetime (PAL) spectroscopy. For comparison, the base cPTFE and polystyrene grafted films were also measured. From the analysis of PAL spectra, it was found that there were free-volume holes with different radius of 0.28-0.30 nm and 0.44-0.45 nm. The smaller holes should be located in both PTFE crystallites and poly(styrene sulfonic acid) grafts, while the larger holes are considered to exist in amorphous PTFE phases.

  4. Structural analysis of poly(vinyl alcohol hydrogels) produced by freezing and thawing process Positron annihilation lifetime spectroscopy (PALS)

    International Nuclear Information System (INIS)

    Paranhos, Caio M.; Oliveira, Renata N.; Soares, Bluma G.

    2005-01-01

    In this work, poly(vinyl alcohol) hydrogels with a entrapped polyelectrolyte were characterized through Positron Annihilation Lifetime Spectroscopy (PALS). PALS was used to determine the average pore radii (R), average free volume (V f ) and the intensity of ortho-positronium (I 3 ). The free volume estimated for the hydrogels increases with increasing polyelectrolyte content, while the intensity of o-Ps decreases with the increasing polyelectrolyte content. Degree of crystallinity of the samples decreases with the presence of polyelectrolyte. The structural changes observed can be discussed in terms of the changes in hydrogels structure due to a hindrance capacity of the polyelectrolyte on the crystalline behavior and the different polymer-polymer interactions. (author)

  5. Free volume of mixed cation borosilicate glass sealants elucidated by positron annihilation lifetime spectroscopy and its correlation with glass properties

    Science.gov (United States)

    Ojha, Prasanta K.; Rath, Sangram K.; Sharma, Sandeep K.; Sudarshan, Kathi; Pujari, Pradeep K.; Chongdar, Tapas K.; Gokhale, Nitin M.

    2015-01-01

    The role of La+3/Sr+2 ratios, which is varied from 0.08 to 5.09, on density, molar volume, packing fraction, free volume, thermal and electrical properties in strontium lanthanum aluminoborosilicate based glass sealants intended for solid oxide fuel cell (SOFC) applications is evaluated. The studies reveal expansion of the glass network evident from increasing molar volume and decreasing packing fraction of glasses with progressive La+3 substitutions. The molecular origin of these macroscopic structural features can be accounted for by the free volume parameters measured from positron annihilation lifetime spectroscopy (PALS). The La+3 induced expanded glass networks show increased number of subnanoscopic voids with larger sizes, as revealed from the ortho-positronium (o-Ps) lifetime and its intensity. A remarkably direct correspondence between the molar volume and fractional free volume trend is established with progressive La2O3 substitution in the glasses. The effect of these structural changes on the glass transition temperature, softening temperature, coefficient of thermal expansion, thermal stability as well as electrical conductivity has been studied.

  6. Free volume evolution in 50 MeV Li3+ ion-irradiated polymers studied by positron annihilation lifetime spectroscopy

    Science.gov (United States)

    Singh, Paramjit; Kumar, Rajesh; Prasad, Rajendra

    2013-02-01

    This article is aimed at studying the effect of ion irradiation on free volume of polyethersulphone (PES) and polyamide nylon-6 (PN-6) polymers by positron annihilation lifetime spectroscopy (PALS). Free volume properties of polymeric materials change with swift heavy ion irradiation. Free volume is found to have a strong correlation with the macroscopic properties of the polymer. PALS has recently emerged as a unique non-destructive and non-interfering nano-probe, capable of measuring the free volume hole size in polymers with high detection efficiency. PES and PN-6 polymer films of thickness of 250 μm were irradiated with Li3+ ions of energy 50 MeV from the 15 UD Pelletron accelerator at the Inter University Accelerator Centre, New Delhi, India. PES films were irradiated to the fluences of 1011, 1012, 1013 and 1014 ions/cm2, whereas PN-6 films were irradiated to the fluences of 1011, 1012 and 1013 ions/cm2. The average free volume and fractional free volume obtained from the long-lived component, attributed to ortho-positronium lifetime, are found to vary with the variation of fluence in both the cases.

  7. Effect of water on glass transition in starch/sucrose matrices investigated through positron annihilation lifetime spectroscopy: a new approach.

    Science.gov (United States)

    Sharma, Sandeep Kumar; Zaydouri, Abdelhadi; Roudaut, Gaëlle; Duplâtre, Gilles

    2011-11-21

    Glass transition is studied through positron annihilation lifetime spectroscopy (PALS) in maize starch matrices containing 10 (batch STS10) and 20 (STS20) w/w% sucrose, as a function of temperature (T) and water content (c(w)). To circumvent important losses of water upon heating while recording the PALS spectra, a new method is developed: instead of a series of measurements of τ(3), the triplet positronium lifetime, at different T, the latter is kept constant and the series relates to c(w), which is left to decrease at a constant rate. Similarly to the changes in τ(3) with T, the τ(3)vs. c(w) plots obtained show a smooth linear increase until a break, denoting the occurrence of glass transition, followed by a sharper increase. The gradients appear to be independent of T. The variation of the glass transition temperature, T(g), with c(w) shows a broad sigmoid with a large linear central part; as expected from the plasticising effect of sucrose, the plot for STS20 lies some 10 K below that for STS10. Results from differential scanning calorimetry for STS20 yield T(g) values some 15 K higher than from PALS. On the basis of the general shape of the τ(3)vs. T variations, a general equation is set for τ(3)(T, c(w)), leading one to expect a similar shape for τ(3)vs. c(w), as experimentally observed. This journal is © the Owner Societies 2011

  8. The effect of electron irradiation on high-density polyethylene: Positron annihilation lifetime spectroscopy, differential scanning calorimetry and X-ray scattering studies

    Energy Technology Data Exchange (ETDEWEB)

    Zaydouri, A. [Laboratoire de Chimie-Physique et Rayonnement-Alain Chambaudet, UMR CEA E4, Universite de Franche Comte, 16 route de Gray, 25030 Besancon Cedex (France)], E-mail: zaydouri@hotmail.com; Grivet, M. [Laboratoire de Chimie-Physique et Rayonnement-Alain Chambaudet, UMR CEA E4, Universite de Franche Comte, 16 route de Gray, 25030 Besancon Cedex (France)], E-mail: manuel.grivet@univ-fcomte.fr

    2009-09-15

    Electron irradiation effects in HDPE have been studied using positron annihilation lifetime spectroscopy. In the four-component analysis of a spectrum, two long-lived states are ascribed to ortho-positronium (o-Ps) annihilation in the crystalline phase and in the amorphous phase. The study of the o-Ps parameters highlights the different behaviour of the two phases. From the o-Ps lifetime in the crystalline phase, it is shown that the effect of irradiation is larger at 250 kGy. Thermal analysis (DSC) reveals two different melting temperatures and also an increase in the fusion enthalpy, at 250 kGy. This phenomenon induced by an electron beam is erased by thermal treatment: fusion and re-crystallisation. However, before and after thermal treatment no changes are observed in the crystallite size and in the crystalline rate using wide-angle X-ray scattering.

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

    International Nuclear Information System (INIS)

    Hsu, Chia-Wen; Ma, Chen-Chi M.; Tan, Chung-Sung; Li, Hsun-Tien

    2015-01-01

    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 1 ) and 753.6 h (ζ 2 ) at 55 °C. The ζ 1 of the IPNs hybrid can be attributed to the network relaxation of PMSE, and the ζ 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

  10. 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.

  11. First positron annihilation lifetime measurement of Pu

    International Nuclear Information System (INIS)

    Colmenares, C.; Howell, R.H.; Ancheta, D.; Cowan, T.; Hanafee, J.; Sterne, P.

    1996-01-01

    We have made the first measurement of defects in an aged sample of δ phase, Ga stabilized Pu, using positron annihilation lifetime spectroscopy. This measurement validates the procedure necessary to perform measurements on this highly toxic material and obtain data representative of sample conditions. Comparison of the positron annihilation lifetime analysis of the data with calculated values suggests that He filled vacancies or vacancy clusters dominate the defect population. Such defects are the necessary precursor to void growth and swelling. The evolution of defects resulting from the radioactive decay of Pu during its life in the stockpile is one of the unknown quantities affecting our confidence in predictions of the limit on stockpile components. Radiation damage leads to changes in the size and strength of metals studied for reactor and accelerator use and similar effects may be expected in Pu. The evolution of radiation produced vacancies into larger void structures and accompanying macroscopic swelling may occur in Pu at some age. A detailed understanding of the defects in self irradiated Pu is required to predict the time scale of void swelling and related radiation effects. 1 fig

  12. Detection of atomic scale changes in the free volume void size of three-dimensional colorectal cancer cell culture using positron annihilation lifetime spectroscopy.

    Science.gov (United States)

    Axpe, Eneko; Lopez-Euba, Tamara; Castellanos-Rubio, Ainara; Merida, David; Garcia, Jose Angel; Plaza-Izurieta, Leticia; Fernandez-Jimenez, Nora; Plazaola, Fernando; Bilbao, Jose Ramon

    2014-01-01

    Positron annihilation lifetime spectroscopy (PALS) provides a direct measurement of the free volume void sizes in polymers and biological systems. This free volume is critical in explaining and understanding physical and mechanical properties of polymers. Moreover, PALS has been recently proposed as a potential tool in detecting cancer at early stages, probing the differences in the subnanometer scale free volume voids between cancerous/healthy skin samples of the same patient. Despite several investigations on free volume in complex cancerous tissues, no positron annihilation studies of living cancer cell cultures have been reported. We demonstrate that PALS can be applied to the study in human living 3D cell cultures. The technique is also capable to detect atomic scale changes in the size of the free volume voids due to the biological responses to TGF-β. PALS may be developed to characterize the effect of different culture conditions in the free volume voids of cells grown in vitro.

  13. Detection of Atomic Scale Changes in the Free Volume Void Size of Three-Dimensional Colorectal Cancer Cell Culture Using Positron Annihilation Lifetime Spectroscopy

    Science.gov (United States)

    Castellanos-Rubio, Ainara; Merida, David; Garcia, Jose Angel; Plaza-Izurieta, Leticia; Fernandez-Jimenez, Nora; Plazaola, Fernando; Bilbao, Jose Ramon

    2014-01-01

    Positron annihilation lifetime spectroscopy (PALS) provides a direct measurement of the free volume void sizes in polymers and biological systems. This free volume is critical in explaining and understanding physical and mechanical properties of polymers. Moreover, PALS has been recently proposed as a potential tool in detecting cancer at early stages, probing the differences in the subnanometer scale free volume voids between cancerous/healthy skin samples of the same patient. Despite several investigations on free volume in complex cancerous tissues, no positron annihilation studies of living cancer cell cultures have been reported. We demonstrate that PALS can be applied to the study in human living 3D cell cultures. The technique is also capable to detect atomic scale changes in the size of the free volume voids due to the biological responses to TGF-β. PALS may be developed to characterize the effect of different culture conditions in the free volume voids of cells grown in vitro. PMID:24392097

  14. Mathematical modeling of elementary trapping-reduction processes in positron annihilation lifetime spectroscopy: methodology of Ps-to-positron trapping conversion

    Science.gov (United States)

    Shpotyuk, Ya; Cebulski, J.; Ingram, A.; Shpotyuk, O.

    2017-12-01

    Methodological possibilities of positron annihilation lifetime (PAL) spectroscopy in application to nanostructurized substances treated within three-term fitting procedure are reconsidered to parameterize their atomic-deficient structural arrangement. In contrast to conventional three-term fitting analysis of the detected PAL spectra based on admixed positron trapping and positronium (Ps) decaying, the nanostructurization due to guest nanoparticles embedded in host matrix is considered as producing modified trapping, which involves conversion between these channels. The developed approach referred to as x3-x2-coupling decomposition algorithm allows estimation free volumes of interfacial voids responsible for positron trapping and bulk lifetimes in nanoparticle-embedded substances. This methodology is validated using experimental data of Chakraverty et al. [Phys. Rev. B71 (2005) 024115] on PAL study of composites formed by guest NiFe2O4 nanocrystals grown in host SiO2 matrix.

  15. Drug release profiles and microstructural characterization of cast and freeze dried vitamin B12 buccal films by positron annihilation lifetime spectroscopy.

    Science.gov (United States)

    Szabó, Barnabás; Kállai, Nikolett; Tóth, Gergő; Hetényi, Gergely; Zelkó, Romána

    2014-02-01

    Solvent cast and freeze dried films, containing the water-soluble vitamin B12 as model drug were prepared from two polymers, sodium alginate (SA), and Carbopol 71G (CP). The proportion of the CP was changed in the films. The microstructural characterization of various samples was carried out by positron annihilation lifetime spectroscopy (PALS). The drug release kinetics of untreated and stored samples was evaluated by the conventionally applied semi-empirical power law. Correlation was found between the changes of the characteristic parameters of the drug release and the ortho-positronium (o-Ps) lifetime values of polymer samples. The results indicated that the increase of CP concentration, the freeze-drying process and the storage at 75% R.H. decreased the rate of drug release. The PALS method enabled the distinction between the micro- and macrostructural factors influencing the drug release profile of polymer films. Copyright © 2013 Elsevier B.V. All rights reserved.

  16. Study of free volumes of polymer hydrogel and -silicone-hydrogel contact lenses by means of the positron annihilation lifetime spectroscopy method.

    Science.gov (United States)

    Filipecki, Jacek; Kocela, Agnieszka; Korzekwa, Witold

    2014-01-01

    Polymer materials based on hydrogel and silicone-hydrogel materials are commonly used in ophthalmology. It is important to research the structure of these materials, mainly the prevalence of free volumes. The study has been conducted in order to determine the presence of free volume gaps in the structure of polymer hydrogel and silicone-hydrogel contact lenses. In addition, to demonstrate differences in the occurrence of free volumes between types of represented contact lenses. Three different hydrogel and three different silicone-hydrogel polymer contact lenses were used as research material. The study was done by means of positron annihilation lifetime spectroscopy (PALS). As a result of the performed measurements, a graphical curve resulted which describes the relationship between the number of the annihilation acts in the time function. The study revealed the existence of three τ1, τ2 and τ3 components. Significant changes were observed in the ortho-positronium long life component τ3 and their intensities between the examined polymer contact lenses. The conducted study using the Tao-Eldrup model indicates the presence of free volume holes in all research materials. The results lead to the following connection: contact lenses of higher oxygen permeability coefficient (silicone-hydrogel contact lenses) have more and larger free volumes than contact lenses of less oxygen permeability coefficient (hydrogel contact lenses).

  17. Effects of plasticizer and strain on the percolation threshold in polyisoprene-carbon nanocomposites: Positron annihilation lifetime spectroscopy and electrical resistance measurements

    International Nuclear Information System (INIS)

    Knite, M.; Hill, A.J.; Pas, S.J.; Teteris, V.; Zavickis, J.

    2006-01-01

    A study of the effects of plasticizer and stretching strain on the percolation transition in polyisoprene-carbon nanocomposites (PCNC) is reported. The ortho-positronium (oPs) accessible free volume sites are measured by positron annihilation lifetime spectroscopy (PALS) in relaxed and stretched PCNC samples containing different amounts of plasticizer. The lifetime of oPs, τ 3 , is related to the size of the free volume, and the intensity, I 3 , to the concentration of free volume sites. The number of free volume cavities is found to decrease during stretching regardless of the content of either carbon nanoparticles (CNP) or plasticizer. The free volume cavity size reaches its maximum value in the region of percolation transition. The percolation threshold is determined by measurements of electrical resistance (ERM). Both PALS and ERM show that the percolation threshold shifts to higher concentration of CNP under stretching strain. A shift of the percolation threshold to lower concentration of CNP was observed for addition of plasticizer. It is interesting that addition of CNP increases the mean size of free volume cavities below the percolation threshold and decreases it at CNP concentrations exceeding the percolation threshold. The relative number of free volume cavities represented by I 3 also decreases at CNP concentrations exceeding the percolation threshold. The results are interpreted as filling of cavities above the percolation threshold. ERM during application of cyclic tensile stress revealed fatigue of the tensoresistance effect in samples containing 10 m.p. of CNP with and without added plasticizer

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

    International Nuclear Information System (INIS)

    Pujari, P.K.; Datta, T.; Tomar, B.S.; Das, S.K.

    1992-01-01

    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

  19. Positron annihilation spectroscopy in condensed matter

    International Nuclear Information System (INIS)

    Brauer, G.

    1982-09-01

    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 V 3 Si. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, J. [Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, The Australian National University, Canberra (Australia); Gaugliardo, P. [Centre for Antimatter-Matter Studies, School of Physics, University of Western Australia (Australia); Farnan, I.; Zhang, M. [Department of Earth Sciences, University of Cambridge (United Kingdom); Vance, E.R.; Davis, J.; Karatchevtseva, I.; Knott, R.B. [Australian Nuclear Science and Technology Organisation (Australia); Mudie, S. [The Australian Synchrotron, Victoria (Australia); Buckman, S.J. [Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, The Australian National University, Canberra (Australia); Institute for Mathematical Sciences, University of Malaya, Kuala Lumpur (Malaysia); Sullivan, J.P., E-mail: james.sullivan@anu.edu.au [Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, The Australian National University, Canberra (Australia)

    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 ∼10{sup 19} 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. - Highlights: • Study of a range of naturally occurring zircons damaged by alpha radiation. • Characterised using a range of techniques, including PALS spectroscopy. • Effects on hydrous material appear important, rather than direct radiation damage. • Annealing is shown to remove the observed voids.

  1. Positron Annihilation Spectroscopy study of minerals commonly found in shale

    Science.gov (United States)

    Alsleben, Helge; Ameena, Fnu; Bufkin, James; Chun, Joah; Quarles, C. A.

    2018-01-01

    Positron Annihilation Lifetime and Doppler Broadening spectroscopies are used to investigate twenty-three different rock-forming minerals that are commonly found in shale. Doppler Broadening provides information about the positron and positronium (Ps) trapping sites for comparison among the various minerals. Correlations of positron lifetime and Doppler Broadening are observed for different groups of minerals. Finally, Ps formation, or lack thereof, in the various minerals has been determined.

  2. Investigation of highly activated materials by conventional positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Sabelova, V.; Petriska, M.; Slugen, V.; Krsjak, V.

    2013-01-01

    Positron annihilation process is helpful tool for material microstructure study. Many useful methods for detecting vacancies and their clusters in various alloys use its principle. Experimental procedure of positron source preparation (radioactive 22 Na) for these methods is difficult task. The unusual small sample dimensions of studied irradiated Eurofer 97 alloy form difficult conditions for its manufacturing. The unique sodium positron source proper preparation is confirmed by positron annihilation lifetime spectroscopy (PALS) and coincidence Doppler broadening spectroscopy (CDBS) in Paul Scherrer Institute in Switzerland. (authors)

  3. Positron annihilation in polypropylene studied by lifetime and coincidence Doppler-broadening spectroscopy[Positron annihilation; Doppler broadening; Coincidence Doppler system; PP; Antioxidant; Carbonyl group; Irradiation effect; Core electrons

    Energy Technology Data Exchange (ETDEWEB)

    Djourelov, N. E-mail: nikdjour@post.kek.jp; He, C.; Suzuki, T.; Shantarovich, V.P.; Ito, Y.; Kondo, K.; Ito, Y

    2003-12-01

    The momentum density distributions (MDDs) of electrons taking part in the annihilation processes in polypropylene (PP) have been measured by coincidence Doppler-broadening spectroscopy. MDDs at the beginning of measurements to those at the saturation level of Ps formation have been compared in order to follow the possible changes in concentration of carbonyl groups (CG). A high initial CG concentration in PP has been observed, while for antioxidant-containing PP no significant presence of CG has been detected, and no changes have been observed during positron irradiation.

  4. Correlation of Gas Permeability in a Metal-Organic Framework MIL-101(Cr)-Polysulfone Mixed-Matrix Membrane with Free Volume Measurements by Positron Annihilation Lifetime Spectroscopy (PALS).

    Science.gov (United States)

    Jeazet, Harold B Tanh; Koschine, Tönjes; Staudt, Claudia; Raetzke, Klaus; Janiak, Christoph

    2013-10-25

    Hydrothermally stable particles of the metal-organic framework MIL-101(Cr) were incorporated into a polysulfone (PSF) matrix to produce mixed-matrix or composite membranes with excellent dispersion of MIL-101 particles and good adhesion within the polymer matrix. Pure gas (O2, N2, CO2 and CH4) permeation tests showed a significant increase of gas permeabilities of the mixed-matrix membranes without any loss in selectivity. Positron annihilation lifetime spectroscopy (PALS) indicated that the increased gas permeability is due to the free volume in the PSF polymer and the added large free volume inside the MIL-101 particles. The trend of the gas transport properties of the composite membranes could be reproduced by a Maxwell model.

  5. Correlation of Gas Permeability in a Metal-Organic Framework MIL-101(Cr)–Polysulfone Mixed-Matrix Membrane with Free Volume Measurements by Positron Annihilation Lifetime Spectroscopy (PALS)

    Science.gov (United States)

    Jeazet, Harold B. Tanh; Koschine, Tönjes; Staudt, Claudia; Raetzke, Klaus; Janiak, Christoph

    2013-01-01

    Hydrothermally stable particles of the metal-organic framework MIL-101(Cr) were incorporated into a polysulfone (PSF) matrix to produce mixed-matrix or composite membranes with excellent dispersion of MIL-101 particles and good adhesion within the polymer matrix. Pure gas (O2, N2, CO2 and CH4) permeation tests showed a significant increase of gas permeabilities of the mixed-matrix membranes without any loss in selectivity. Positron annihilation lifetime spectroscopy (PALS) indicated that the increased gas permeability is due to the free volume in the PSF polymer and the added large free volume inside the MIL-101 particles. The trend of the gas transport properties of the composite membranes could be reproduced by a Maxwell model. PMID:24957061

  6. New insights into the nanostructure of innovative thin film solar cells gained by positron annihilation spectroscopy

    NARCIS (Netherlands)

    Eijt, S.W.H.; Shi, W.; Mannheim, A.; Butterling, M.; Schut, H.; Egger, W; Dickmann, M.; Hugenschmidt, C; Shakeri, B.; Meulenberg, R; Callewaert, V.; Saniz, R; Partoens, B; Barbiellini, B; Bansil, A; Melskens, J.; Zeman, M.; Smets, A.H.M.; Kulbak, M.; Hodes, G.; Cahen, D.; Brück, E.H.

    2017-01-01

    Recent studies showed that positron annihilation methods can provide key insights into the nanostructure and electronic structure of thin film solar cells. In this study, positron annihilation lifetime spectroscopy (PALS) is applied to investigate CdSe quantum dot (QD) light absorbing layers,

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

    Science.gov (United States)

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

    2016-01-05

    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. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. Measurements of Defect Structures by Positron Annihilation Lifetime Spectroscopy of the Tellurite Glass 70TeO2-5XO-10P2O5-10ZnO-5PbF2(X = Mg, Bi2, Ti) Doped with Ions of the Rare Earth Element Er3.

    Science.gov (United States)

    Pach, K; Filipecki, J; Golis, E; Yousef, El S; Boyko, V

    2017-12-01

    The objective of the study was the structural analysis of the 70TeO 2 -5XO-10P 2 O 5 -10ZnO-5PbF 2 (X = Mg, Bi 2 , Ti) tellurite glasses doped with ions of the rare-earth elements Er 3+ , based on the PALS (positron annihilation lifetime spectroscopy) method of measuring positron lifetimes. Values of positron lifetimes and the corresponding intensities may be connected with the sizes and number of structural defects, the sizes of which range from a few angstroms to a few dozen nanometers. Experimental positron lifetime spectrum revealed existence of two positron lifetime components τ 1 andτ 2 . Their interpretation was based on two-state positron trapping model where the physical parameters are the positron annihilation rate and positron trapping rate.

  9. Positron annihilation induced Auger electron spectroscopy

    Science.gov (United States)

    Weiss, Alex; Koymen, A. R.; Mehl, David; Jensen, K. O.; Lei, Chun; Lee, K. H.

    1990-01-01

    Recently, Weiss et al. have demonstrated that it is possible to excite Auger transitions by annihilating core electrons using a low energy (less than 30eV) beam of positrons. This mechanism makes possible a new electron spectroscopy, Positron annihilation induced Auger Electron Spectroscopy (PAES). The probability of exciting an Auger transition is proportional to the overlap of the positron wavefunction with atomic core levels. Since the Auger electron energy provides a signature of the atomic species making the transition, PAES makes it possible to determine the overlap of the positron wavefunction with a particular element. PAES may therefore provide a means of detecting positron-atom complexes. Measurements of PAES intensities from clean and adsorbate covered Cu surfaces are presented which indicate that approx. 5 percent of positrons injected into CU at 25eV produce core annihilations that result in Auger transitions.

  10. Studying the recovery of as-received industrial Al alloys by positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Hady, E.E. [Physics Department, Faculty of Science, El-Minia University, BO 61519, El-Minia (Egypt)]. E-mail: esamhady@link.net; Ashry, A. [Faculty of Education, Ain Shams University, Cairo (Egypt); Ismail, H. [Faculty of Education, Ain Shams University, Cairo (Egypt); El-Gamal, S. [Faculty of Education, Ain Shams University, Cairo (Egypt)

    2006-02-28

    Positron annihilation lifetime (PAL) spectroscopy, Doppler broadening of annihilation radiation (DBAR) spectroscopy and Vickers microhardness (Hv) measurements were performed to study the micro- and macro-structure variations during isochronal annealing from room temperature (RT) to 500 deg. Cof commercial pure Al (1 1 0 0), Al-Mn-Mg (3 0 0 4) and Al-Mg-Si (6 2 0 1) alloys. Three annealing stages of microstructures have been identified as recovery, partial recrystallization and complete recrystallization followed by grain growth. A positive correlation between the macroscopic mechanical properties (Hv) and positron annihilation parameters has been achieved for the three samples under investigation.

  11. A multi-parameter, acquisition system positron annihilation lifetime spectrometer

    International Nuclear Information System (INIS)

    Sharshar, T.

    2004-01-01

    A positron annihilation lifetime spectrometer employing a multi-parameter acquisition system has been prepared for various purposes such as the investigation and characterization of solid-state materials. The fast-fast coincidence technique was used in the present spectrometer with a pair of plastic scintillation detectors. The acquisition system is based on the Kmax software and on CAMAC modules. The data are acquired in event-by-event list mode. The time spectrum for the desired energy windows can be obtained by off-line data sorting and analysis. The spectrometer for event-by-event data acquisition is an important step to construct a positron age-momentum correlation (AMOC) spectrometer. The AMOC technique is especially suited for the observation of positron transitions between different states during their lifetime. The system performance was tested and the results were presented and discussed

  12. Temperature dependence of o-Ps annihilation lifetime in non-uniform cylindrical pores in comparison with ETE model

    Energy Technology Data Exchange (ETDEWEB)

    Khaghani, Morteza, E-mail: m.khaghani@pgs.usb.ac.ir; Mehmandoost-Khajeh-Dad, Ali Akbar, E-mail: mehmandoost@phys.usb.ac.ir

    2017-04-01

    Highlights: • Using the well known multi-physics program COMSOL calculating o-Ps annihilation lifetime in complex geometries. • Investigation of shape non-uniformity of cylindrical pores on o-Ps annihilation lifetime. • Verifying temperature dependency of o-Ps lifetime in non-uniform cylindrical pores. • Suggesting PALS at low temperature as a method to verify pore uniformity in porous material. - Abstract: Ortho-positronium (o-Ps) annihilation lifetime was calculated in non-uniform cylinder-shaped pores by solving Schrodinger equation using a well-known multi-physics program called COMSOL. The o-Ps annihilation lifetime variation in terms of temperature was calculated on the basis of ETE model via a numerical method. The COMSOL simulations indicate that as long as the pore is uniform cylinder-shaped, the results agree with those of two-dimensional ETE model, whereas deformations in the cylinder shape (indentation or protrusion) change the temperature behavior of ETE model and, thereby, higher values are predicted for o-Ps lifetime in the pore at lower temperatures. The geometry of the non-uniform cylinder-shaped pores, which is accompanied by empirical evidence, can be used for the analysis of empirical results obtained from positron lifetime spectroscopy in different temperatures.

  13. A study of some properties for substituted Li-ferrite using positron annihilation lifetime technique

    Directory of Open Access Journals (Sweden)

    E. Hassan Aly

    2015-01-01

    Full Text Available Positron annihilation lifetime spectroscopy (PALS is used to investigate polycrystalline substituted Li-ferrite samples. The dray ceramic technique was used to prepare all investigated samples. The variation of positron annihilation parameters I1%, I2%, τ1, and τ2 has been demonstrated with porosity and the initial permeability against the ionic radii of substituted ions for Li ferrite. The grain size (G.S. increased with increasing the ionic radii of the substituted ions for Li-ferrite. The correlation between I2 and τ2 has opposite behavior with the ionic radii of the substituted ions. Whereas the correlation between I1 and τ1; has nearly the same behavior with the ionic radii of the substituted ions except for V and Gd samples. There is mostly a direct correlation between the electrical resistivity and I2 values except for Sm sample with increasing the ionic radii of substituted ions.

  14. Fe-Cr alloys studied by positron annihilation lifetime technique after helium implantation

    Energy Technology Data Exchange (ETDEWEB)

    Slugen, Vladimir; Krsjak, Vladimir; Petriska, Martin; Sojak, Stanislav [Slovak Univ. of Technology, Bratislava (Slovakia). Dept. of Nuclear Physics and Technology; Egger, Werner [Univ. der Bundeswehr Muenchen, Neubiberg (Germany). Inst. fuer Angewandte Physik und Messtechnik

    2009-07-01

    The present work demonstrates that conventional positron annihilation lifetime spectroscopy can provide valuable information about the microstructure of helium implanted Fe-Cr alloys. At the same time the connection between results from this technique and the PLEPS lifetime measurements has been studied. Positron lifetime experiments show that chromium plays an important role in the formation of the microstructure under radiation treatment. In particular, higher chromium content in FeCr alloys leads to a higher density of uniformly distributed small defects. Depth profiles of defects, obtained with PLEPS, in the helium implanted region reflect the helium implantation profiles and show the creation of small vacancy clusters and large voids. These defects cannot be observed by any other technique in a non-destructive way. (orig.)

  15. 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.)

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

    International Nuclear Information System (INIS)

    Boyko, Olha; Shpotyuk, Yaroslav; Filipecki, Jacek

    2013-01-01

    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. Characterization of the melting process of PTFE using positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Honda, Y; Nishijima, S

    2015-01-01

    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. (paper)

  18. Positron annihilation lifetime studies of changes in free volume on some biorelevant nitrogen heterocyclic compounds and their S-glycosylation.

    Science.gov (United States)

    Mahmoud, K R; Khodair, A I; Shaban, S Y

    2015-11-01

    A series of N-heterocyclic compounds was investigated by positron annihilation lifetime spectroscopy as well as Doppler broadening of annihilation radiation (DBAR) at room temperature. The results showed that the formation probability and life time of ortho-positronium in this series are structure and electron-donation character dependent, and can give more information about the structure. The DBAR provides direct information about the change of core and valance electrons as well as the number of defect types present in these compounds. Copyright © 2015 Elsevier Ltd. All rights reserved.

  19. Studies of defects and defect agglomerates by positron annihilation spectroscopy

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Singh, B.N.

    1997-01-01

    A brief introduction to positron annihilation spectroscopy (PAS), and in particular lo its use for defect studies in metals is given. Positrons injected into a metal may become trapped in defects such as vacancies, vacancy clusters, voids, bubbles and dislocations and subsequently annihilate from...

  20. Pore Topology Effects in Positron Annihilation Spectroscopy of Zeolites.

    Science.gov (United States)

    Zubiaga, Asier; Warringham, Robbie; Mitchell, Sharon; Gerchow, Lars; Cooke, David; Crivelli, Paolo; Pérez-Ramírez, Javier

    2017-03-03

    Positron annihilation spectroscopy (PAS) is a powerful method to study the size and connectivity of pores in zeolites. The lifetime of positronium within the host material is commonly described by the Tao-Eldrup model. However, one of its largest limitations arises from the simple geometries considered for the shape of the pores, which cannot describe accurately the complex topologies in zeolites. Here, an atomic model that combines the Tao potential with the crystallographic structure is introduced to calculate the distribution and lifetime of Ps intrinsic to a given framework. A parametrization of the model is undertaken for a set of widely applied zeolite framework types (*BEA, FAU, FER, MFI, MOR, UTL), before extending the model to all known structures. The results are compared to structural and topological descriptors, and to the Tao-Eldrup model adapted for zeolites, demonstrating the intricate dependence of the lifetime on the pore architecture. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. 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. Copyright © 2013 Elsevier B.V. All rights reserved.

  2. Development of positron annihilation spectroscopy to test accelerated weathering of protective polymer coatings

    CERN Document Server

    Zhang, R; Chen, H M; Mallon, P; Sandreczki, T C; Richardson, J R; Jean, Y C; Nielsen, B; Suzuki, R; Ohdaira, T

    2000-01-01

    A variable mono-energetic positron beam with a computer-controlled system has recently been constructed at the University of Missouri-Kansas City for weathering studies of polymeric coatings. The beam is designed to measure the S-parameter from Doppler-broadening energy spectra and the sub-nanometer defect properties from positron annihilation lifetimes (PAL). Significant variations of S-parameter and ortho-positronium intensity in coatings, as obtained from the newly built beam and from the Electrotechnical Laboratory's beam, respectively, are observed as a function of depth and exposure time due to the Xe-light irradiation. A high sensitivity of positron annihilation signal response to the early stage of degradation is observed. Development of positron annihilation spectroscopy to test accelerated weathering of polymeric coatings is discussed.

  3. Positron annihilation lifetime studies of changes in free volume on some biorelevant nitrogen heterocyclic compounds and their S-glycosylation

    International Nuclear Information System (INIS)

    Mahmoud, K.R.; Khodair, A.I.; Shaban, S.Y.

    2015-01-01

    A series of N-heterocyclic compounds was investigated by positron annihilation lifetime spectroscopy as well as Doppler broadening of annihilation radiation (DBAR) at room temperature. The results showed that the formation probability and life time of ortho-positronium in this series are structure and electron-donation character dependent, and can give more information about the structure. The DBAR provides direct information about the change of core and valance electrons as well as the number of defect types present in these compounds. - Highlights: • N-heterocyclic compounds were studied by PALS and DBAR at room temperature. • These compounds contain thiohydantoins which have wide applications as anticarcinogenic, antiviral, human immunodeficiency virus (HIV) and antimicrobial activity. • The DBAR provides direct information about the change of core and valance electrons as well as the number of defect types present in these compounds.

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

    Energy Technology Data Exchange (ETDEWEB)

    Chai, L.; Schut, H.; Schaarenburg, L. C. van; Eijt, S. W. H., E-mail: S.W.H.Eijt@tudelft.nl [Department of Radiation, Radionuclides and Reactors, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, NL-2629 JB Delft (Netherlands); Al-Sawai, W.; Barbiellini, B.; Bansil, A. [Physics Department, Northeastern University, Boston, Massachusetts 02115 (United States); Gao, Y. [Department of Chemical Engineering, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, NL-2628 BL Delft (Netherlands); Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, NL-2628 CJ Delft (Netherlands); Houtepen, A. J. [Department of Chemical Engineering, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, NL-2628 BL Delft (Netherlands); Mijnarends, P. E. [Department of Radiation, Radionuclides and Reactors, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, NL-2629 JB Delft (Netherlands); Physics Department, Northeastern University, Boston, Massachusetts 02115 (United States); Huis, M. A. van [Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, NL-2628 CJ Delft (Netherlands); Ravelli, L.; Egger, W. [Institut für Angewandte Physik und Messtechnik, Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, D-85579 Neubiberg (Germany); Kaprzyk, S. [Physics Department, Northeastern University, Boston, Massachusetts 02115 (United States); Academy of Mining and Metallurgy AGH, PL-30059 Kraków (Poland)

    2013-08-01

    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.

  5. 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.

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

    International Nuclear Information System (INIS)

    Romero, R.; Salgueiro, W.; Somoza, A.

    1990-01-01

    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) [es

  7. Phase behaviour in confined geometry via positronium annihilation spectroscopy

    International Nuclear Information System (INIS)

    Fretwell, H.M.; Duffy, J.A.; Clarke, A.P.; Dugdale, S.B.; Alam, M.A.; Evans, R.

    1997-01-01

    Positronium annihilation spectroscopy has recently been successfully applied to the study of phase behaviour of fluids confined in nano-pores. In this paper we provide a brief survey of the new technique in mapping out the phase diagram in confinement and in elucidating some intricate phase behaviour. (author). 12 refs, 3 figs

  8. Positron annihilation lifetime in float-zone n-type silicon irradiated by fast electrons: a thermally stable vacancy defect

    Energy Technology Data Exchange (ETDEWEB)

    Arutyunov, Nikolay [Martin Luther University Halle, Department of Physics, von-Danckelmann-Platz 3, 06120 Halle (Germany); Ioffe Physico-Technical Institute, 194021 St. Petersburg (Russian Federation); Institute of Ion-Plasma and Laser Technologies (Institute of Electronics), 700170 Tashkent (Uzbekistan); Emtsev, Vadim; Oganesyan, Gagik [Ioffe Physico-Technical Institute, 194021 St. Petersburg (Russian Federation); Krause-Rehberg, Reinhard [Martin Luther University Halle, Department of Physics, von-Danckelmann-Platz 3, 06120 Halle (Germany); Elsayed, Mohamed [Martin Luther University Halle, Department of Physics, von-Danckelmann-Platz 3, 06120 Halle (Germany); Minia University, Faculty of Science, Physics Department, 61519 Minia (Egypt); Kozlovskii, Vitalii [St. Petersburg State Polytechnical University, 195251 St. Petersburg (Russian Federation)

    2016-12-15

    Temperature dependency of the average positron lifetime has been investigated for n-type float-zone silicon, n-FZ-Si(P), subjected to irradiation with 0.9 MeV electrons at RT. In the course of the isochronal annealing a new defect-related temperature-dependent pattern of the positron lifetime spectra has been revealed. Beyond the well known intervals of isochronal annealing of acceptor-like defects such as E-centers, divacancies and A-centers, the positron annihilation at the vacancy defects has been observed in the course of the isochronal annealing from ∝ 320 C up to the limit of reliable detecting of the defect-related positron annihilation lifetime at ≥ 500 C. These data correlate with the ones of recovery of the concentration of the charge carriers and their mobility which is found to continue in the course of annealing to ∝ 570 C; the annealing is accomplished at ∝650 C. A thermally stable complex consisting of the open vacancy volume and the phosphorus impurity atom, V{sub op}-P, is suggested as a possible candidate for interpreting the data obtained by the positron annihilation lifetime spectroscopy. An extended couple of semi-vacancies, 2V{sub s-ext}, as well as a relaxed inwards a couple of vacancies, 2V{sub inw}, are suggested as the open vacancy volume V{sub op} to be probed with the positron. It is argued that a high thermal stability of the V{sub s-ext} PV{sub s-ext} (or V{sub inw}PV{sub inw.}) configuration is contributed by the efficiency of PSi{sub 5} bonding. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. 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.

  10. Characterizing free volumes and layer structures in polymeric membranes using slow positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Jean, Y C; Chen Hongmin; Awad, Somia; Zhang Sui; Chen Hangzheng; Lau, Cher Hon; Wang Huan; Li Fuyun; Chung, Tai-Shung; Lee, L James; Huang, James

    2011-01-01

    Positron annihilation spectroscopy coupled with a newly built slow positron beam at National University of Singapore has been used to study the free volume, pore, and depth profile (0 - 10 μm) in cellulose acetate polymeric membrane at the bottom and top sides of membranes for ionic separation in water purification applications. The S and R parameters from Doppler broadening energy of annihilation radiation representing free volumes (0.1-1 nm size) and pores (>1 nm-μm) as a function of depth have been analyzed into multilayers, i.e. skin dense, transition, and porous layers, respectively. The top side of membrane has large free volumes and pores and the bottom side has a skin dense layer, which plays a key role in membrane performance. Positron annihilation lifetime results provide additional information about free-volume size and distribution at the atomic and molecular scale in polymeric membrane systems. Doppler broadening energy and lifetime spectroscopies coupled with a variable mono-energy slow positron beam are sensitive and novel techniques for characterization of polymeric membrane in separation applications.

  11. Positron annihilation lifetime studies of SrTiO.sub.3./sub. crystal and ceramic materials

    Czech Academy of Sciences Publication Activity Database

    Keeble, D.J.; McGuire, R.; Singh, S.; Su, B.; Button, T.W.; Petzelt, Jan

    2005-01-01

    Roč. 128, - (2005), s. 111-114 ISSN 1155-4339 Institutional research plan: CEZ:AV0Z10100520 Keywords : positron annihilation * SrTiO 3 crystal * spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.389, year: 2005

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

    Science.gov (United States)

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

    2018-02-01

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

  13. Defect evolution during annealing of deformed FeSi alloys studied by positron annihilation spectroscopy

    Science.gov (United States)

    Mostafa, K. M.; Cámara, F. González; Petrov, Roumen; Calvillo, P. Rodríguez; De Grave, E.; Segers, D.; Houbaert, Y.

    2011-04-01

    High silicon steel is widely used in electrical appliances. Alloying iron with silicon improves its magnetic performance. A silicon content up to 6.5 wt. % gives excellent magnetic properties such as high saturation magnetization, near zero magnetostriction and low iron loss in high frequencies. Their workability is greatly reduced by the appearance of ordered structures, namely B2 and D03, as soon as the Si content becomes higher than 3.5 wt. %. This limits the mass production by conventional rolling to this maximum percentage of Si. In this work a series of FeSi (7.5 wt. % Si) samples with different degrees of deformation are investigated with positron annihilation spectroscopy and optical microscopy (OM). The influence of annealing on the concentration of defects of different deformed FeSi alloys has been investigated by positron annihilation lifetime spectroscopy and Doppler broadening of the annihilation radiation. OM is used to investigate the microstructure of deformed samples before and after annealing. The values of the S parameter present a decrease for all studied FeSi alloys with the increase of the annealing temperature, being attributed to a decrease of the concentration of defects. A sudden increase of the S-parameter value at 600 °C was observed for all samples, which could be related to the change of the ordering of the FeSi alloys at that temperature. At 700 °C, the values of the S parameter decreased drastically and starting from 900 °C, they became constant. The microstructures of the alloys, investigated by OM, show that recrystallization is completed at 900 °C and the samples are mainly free of defects, which is in agreement with the positron annihilation lifetime data.

  14. Determination of the tau lifetime in high energy e+e- annihilations

    International Nuclear Information System (INIS)

    Althof, M.; Braunschweig, W.; Kirschfink, F.J.; Luebelsmeyer, K.; Martyn, H.U.; Rimkus, J.; Rosskamp, P.; Sander, H.G.; Schmitz, D.; Siebke, H.; Wallraff, W.; Fohrmann, R.; Hilger, E.; Kracht, T.; Krasemann, H.L.; Leu, P.; Lohrmann, E.; Pandoulas, D.; Poelz, G.; Poesnecker, K.U.; Wiik, B.H.; Duchovni, E.; Karshon, U.; Mikenberg, G.; Mir, R.; Revel, D.; Ronat, E.; Shapira, A.; Yekutieli, G.; Baranko, G.; Barklow, T.; Caldwell, A.; Cherney, M.; Izen, J.M.; Memikides, M.; Rudolph, G.; Strom, D.; Takashima, M.; Venkataramania, H.; Wicklund, E.; Sau Lan Wu; Zobernig, G.

    1984-01-01

    We have determined the tau lifetime in e + e - annihilation at an average centre of mass energy of 42.5 GeV, using a pressurized drift chamber close to the interaction point. We find the lifetime to be (3.18(+0.59-0.75)+-0.56)x10 -13 s. The charged weak tau coupling constant relative to that of the μ is found to be Gsub(tau)/Gsub(μ)=0.94(+0.12-0.09+-0.09, in good agreement with lepton universality. (orig.)

  15. Probing sub-nano level molecular packing and correlated positron annihilation characteristics of ionic cross-linked chitosan membranes using positron annihilation spectroscopy.

    Science.gov (United States)

    Xia, Rui; Cao, Xingzhong; Gao, Meizhen; Zhang, Peng; Zeng, Minfeng; Wang, Baoyi; Wei, Long

    2017-02-01

    Chitosan, CS, cross-linked with bivalent palladium has shown enhanced mechanical and thermal properties depending on the transformation of the structure at a microscopic scale. In the present study, CS directly cross-linked by palladium cation membranes (CS-cr-PM) was prepared through a solution-casting method. Mobility of chitosan chains were greatly reduced after crosslinking, making a great reduction in the swelling ratio studied by a water-swelling degree measurement, which led to an improvement in molecular chain rigidity. In order to investigate the chain packing at the molecular level in the ionic cross-linked CS system, the structure of chemically-crosslinked CS is investigated by means of the combined use of wide angle X-ray diffraction (WAXD) and infrared measurements, and a combination of positron annihilation lifetime spectroscopy (PALS) and simultaneous coincidence Doppler broadening (CDB) spectroscopy offers coherent information on both the free-volume related sub-nano level molecular packing and the chemical surrounding of free volume nanoholes in CS-cr-PM as a function of palladium salt loading. The variations in the free volume size and size distribution have been determined through the ortho-positronium (o-Ps) lifetime and its lifetime distribution. The studies showed that a strong interaction between CS molecules and palladium cations results in the change in crystallinity in formed CS-cr-PM leading to variational chain packing density. Meanwhile, significant inhibition effects on positronium formation due to doping are observed, which could be interpreted in terms of the existence of chloride ions. Applications of positron annihilation spectroscopy to study the microstructure and correlated positron annihilation characteristics of an ionic cross-linked CS system are systematically discussed.

  16. Solid-state amorphization in the Ni-Zr system investigated by positron lifetime spectroscopy

    International Nuclear Information System (INIS)

    Bernal, M.J.; De La Cruz, R.M.; Leguey, T.; Pareja, R.; Riveiro, J.M.

    1995-01-01

    The process of mechanical alloying and amorphization of Ni-Zr powders is investigated by positron lifetime spectroscopy, X-ray diffraction and differential scanning calorimetry. The short-lived component of the lifetime spectra is composition and milling-time dependent. The second lifetime component, found during the initial stages of the milling process, appears to be due to annihilation from states trapped at crystalline interface joints. The results indicate that the solid-state reactions induced by ball milling involve the transformation and disappearance of the crystalline interface joints in the powder particles. (orig.)

  17. Morphology of Thermoset Polyimides by Positron Annihilation Spectroscopy

    Science.gov (United States)

    Ranganathaiah, C.; Pater, R. H.; Sprinkle, D. R.; Baugher, A. H.; Eftekhari, A.; Singh, J. J.

    1994-01-01

    Thermoset polyimides have great potential for successfully meeting tough stress and temperature challenges in the advanced aircraft development program. However, studies of structure/property relationships in these materials have not been very successful so far. Positron annihilation spectroscopy has been used to investigate free volumes and associated parameters. It has been noted that the free volume correlates well with the molecular weight, cross-link density and thermal coefficient of expansion of these materials. Currently no other techniques are available for direct measurement of these parameters. Experimental results and their interpretations will be discussed.

  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. Positron annihilation lifetime and Doppler broadening study in 50 MeV Li{sup 3+} ion irradiated polystyrene films

    Energy Technology Data Exchange (ETDEWEB)

    Asad Ali, S., E-mail: asadapd@yahoo.co [Department of Applied Physics, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh 202002 (India); Kumar, Rajesh [Department of Physics, University School of Basic and Applied Sciences, G.G.S.I.P University, New Delhi 110403 (India); Nambissan, P.M.G. [Saha Institute of Nuclear Physics, 1/AF, Bidhan Nagar, Kolkata 700064 (India); Singh, F. [Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India); Prasad, Rajendra [Department of Applied Physics, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh 202002 (India); Vivekananda College of Technology and Management, Aligarh 202002 (India)

    2010-06-15

    Swift heavy ion (SHI) irradiation of polymeric materials results in the change of their free volume properties which have strong correlation with their macroscopic properties. The modification depends on the polymer and ion beam parameters, namely ion energy, fluence and ion species. Polystyrene films were irradiated with Li{sup 3+} ions of energy 50 MeV from 15 UD Pelletron accelerators at Inter University Accelerator Centre (IUAC), New Delhi, India to the fluences of 10{sup 11}, 10{sup 12} and 10{sup 13} ions/cm{sup 2}. Nanosized free volume parameters in the polymer have been studied by positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS). From o-Ps lifetime {tau}{sub 3,} free volume hole radius, mean free volume of microvoids and fractional free volume are computed and modification in free volume with the fluence is studied. Free volume parameters change slowly with ion fluence with a decrease at the highest fluence of 10{sup 13} ions/cm{sup 2}. The decrease in {tau}{sub 3} and I{sub 3} (reflecting the number of free volume holes) may be interpreted on the process of cross-linking. S parameter obtained from DBS measurements showed a minor decrease with increasing fluence.

  20. Detailed positron annihilation lifetime spectroscopic investigation of atrazine imprinted polymers grafted onto PE/PP non-woven fabrics.

    Science.gov (United States)

    Söylemez, Meshude Akbulut; Güven, Olgun

    2018-01-01

    This study presents the preparation of molecularly imprinted matrices by using radiation-induced grafting technique onto polyethylene/polypropylene (PE/PP) non-woven fabrics. Atrazine imprinted polymers were grafted onto PE/PP non-woven fabrics through the use of methacrylic acid (MAA) and ethylene glycol dimethylacrylate (EGDMA) as the functional monomer and crosslinking agent, respectively. Grafted MIPs were characterized by attenuated total reflectance Fourier transform infra-red spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), elemental analysis, scanning electron microscopy (SEM), and positron annihilation lifetime spectroscopy (PALS). The average diameter of free volume holes was determined as 0.612 nm which correlates very well with the size of template molecule atrazine, 0.512 nm. Binding behaviors were investigated against various factors, such as concentration of template molecule, pH, and contact time. Furthermore, the specific selectivity of grafted MIP on non-woven fabric was studied by using other common triazine compounds, such as simazine and metribuzine which show structural similarities to atrazine. The specific binding values for atrazine, simazine, and metribuzine were determined as 40%, 2.5%, and 1.5%, respectively. Copyright © 2017 John Wiley & Sons, Ltd.

  1. Development of positron annihilation spectroscopy for characterizing neutron irradiated tungsten

    Energy Technology Data Exchange (ETDEWEB)

    C.N. Taylor; M. Shimada; D.W. Akers; M.W. Drigert; B.J. Merrill; Y. Hatano

    2013-05-01

    Tungsten samples (6 mm diameter, 0.2 mm thick) were irradiated to 0.025 and 0.3 dpa with neutrons in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Samples were then exposed to deuterium plasma in the tritium plasma experiment (TPE) at 100, 200 and 500ºC to a total fluence of 1 x 1026 m-2. Nuclear reaction analysis (NRA) and Doppler broadening positron annihilation spectroscopy (DB-PAS) were performed at various stages to characterize damage and retention. We present the first known results of neutron damaged tungsten characterized by DB-PAS in order to study defect concentration. Two positron sources, 22Na and 68Ge, probe ~58 µm and through the entire 200 µm thick samples, respectively. DB-PAS results reveal clear differences between the various irradiated samples. These results, and the calibration of DB-PAS to NRA data are presented.

  2. The precipitation process in Mg-Ca-(Zn) alloys investigated by positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ortega, Yanicet [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, 28040 Madrid (Spain)], E-mail: yanicet@fis.ucm.es; Monge, Miguel Angel; Pareja, Ramiro [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain)

    2008-09-08

    Coincidence doppler broadening (CDB) spectroscopy has been applied to study the precipitation process induced by aging in Mg-1.0 wt.% Ca and Mg-1.0 wt.% Ca-1.0 wt.% Zn alloys. In addition positron lifetime experiments and microhardness measurements have been performed. A peak centered at {approx}11.5 x 10{sup -3}m{sub 0}c is found in the CDB ratio spectra of the alloys aged at 473 K. It is attributed to annihilations with the core electrons of Ca. The results indicate the formation of a particle dispersion that hardens the alloys. This dispersion is correlated with the appearance of the peak attributed to Ca atoms. Zn atoms in the Mg matrix inhibit the formation of quenched-in vacancies bound to Ca atoms in the aged ternary alloy producing the dispersion refinement.

  3. The precipitation process in Mg-Ca-(Zn) alloys investigated by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Ortega, Yanicet; Monge, Miguel Angel; Pareja, Ramiro

    2008-01-01

    Coincidence doppler broadening (CDB) spectroscopy has been applied to study the precipitation process induced by aging in Mg-1.0 wt.% Ca and Mg-1.0 wt.% Ca-1.0 wt.% Zn alloys. In addition positron lifetime experiments and microhardness measurements have been performed. A peak centered at ∼11.5 x 10 -3 m 0 c is found in the CDB ratio spectra of the alloys aged at 473 K. It is attributed to annihilations with the core electrons of Ca. The results indicate the formation of a particle dispersion that hardens the alloys. This dispersion is correlated with the appearance of the peak attributed to Ca atoms. Zn atoms in the Mg matrix inhibit the formation of quenched-in vacancies bound to Ca atoms in the aged ternary alloy producing the dispersion refinement

  4. Vacancy profile in reverse osmosis membranes studied by positron annihilation lifetime measurements and molecular dynamics simulations

    International Nuclear Information System (INIS)

    Shimazu, A; Shintani, T; Hirose, M; Goto, H; Suzuki, R; Kobayashi, Y

    2013-01-01

    The positron annihilation technique using a slow positron beam can be used for the study of the vacancy profiles in typical reverse osmosis (RO) membranes. In this study, the vacancy profile in the polyamide membrane that exhibits a high permselectivity between ions and water was studied using the positron annihilation technique and molecular dynamics simulations. Ortho-positronium (o-Ps) lifetimes in the surface region of the membranes were evaluated by using a slow positron beam. The diffusion behavior of Na + and water in the polyamides was simulated by molecular dynamics (MD) methods using the TSUBAME2 supercomputer at the Tokyo Institute of Technology and discussed with the vacancy profile probed by the o-Ps. The results suggested that the large hydration size of Na + compared to the vacancy size in the polyamides contributes to the increased diffusivity selectivity of water/Na + that is related to the NaCl desalination performance of the membrane. Both the hydration size of the ions and the vacancy size appeared to be significant parameters to discuss the diffusivity selectivity of water/ions in typical polyamide membranes.

  5. Positron Annihilation Spectroscopy and Small Angle Neutron Scattering Characterization of Nanostructural Features in Irradiated Fe-Cu-Mn Alloys

    International Nuclear Information System (INIS)

    Wirth, B D; Asoka-Kumar, P; Howell, R H; Odette, G R; Sterne, P A

    2001-01-01

    Radiation embrittlement of nuclear reactor pressure vessel steels results from a high number density of nanometer sized Cu-Mn-Ni rich precipitates (CRPs) and sub-nanometer matrix features, thought to be vacancy-solute cluster complexes (VSC). However, questions exist regarding both the composition of the precipitates and the defect character and composition of the matrix features. We present results of positron annihilation spectroscopy (PAS) and small angle neutron scattering (SANS) characterization of irradiated and thermally aged Fe-Cu and Fe-Cu-Mn alloys. These complementary techniques provide insight into the composition and character of both types of nanoscale features. The SANS measurements indicate populations of CRPs and VSCs in both alloys. The CRPs are coarser in the Fe-Cu alloy and the number densities of CRP and VSC increase with the addition of Mn. The PAS involved measuring both the positron lifetimes and the Doppler broadened annihilation spectra in the high momentum region to provide elemental sensitivity at the annihilation site. The spectra in Fe-Cu-Mn specimens thermally aged to peak hardness at 450 C and irradiated at 288 C are nearly identical to elemental Cu. Positron lifetime and spectrum measurements in Fe-Cu specimens irradiated at 288 C clearly show the existence of long lifetime (∼500 ps) open volume defects, which also contain Cu. Thus the SANS and PAS provide a self-consistent picture of nanostructures composed of CRPs and VSCs and tend to discount high Fe concentrations in the CRPs

  6. Synthesis and characterization of highly conductive charge-transfer complexes using positron annihilation spectroscopy

    Science.gov (United States)

    Adam, Abdel Majid A.; Refat, Moamen S.; Sharshar, T.; Heiba, Z. K.

    Molecular charge-transfer complexes of the tetramethylethylenediamine (TMEDA) with picric acid (Pi-OH), benzene-1,4-diol (QL), tin(IV) tetrachloride (SnCl4), iodine, bromine, and zinc chloride (ZnCl2) have been synthesized and investigated by elemental and thermal analysis, electronic, infrared, Raman and proton-NMR, energy-dispersive X-ray spectroscopy, X-ray powder diffraction and positron annihilation lifetime spectroscopy, and scanning electron microscopy. In this work, three types of acceptors π-acceptors (Pi-OH and QL), σ-acceptors (iodine and bromine), and vacant orbital acceptors (SnCl4 and ZnCl2) were covered. The results of elemental analysis indicated that the CT complexes were formed with ratios 1:1 and 1:2 for QL, SnCl4, and ZnCl2 acceptors and iodine, Pi-OH, and Br2 acceptors, respectively. The type of chelating between the TMEDA donor and the mentioned acceptors depends upon the behavior of both items. The positron annihilation lifetime parameters were found to be dependent on the structure, electronic configuration, and the power of acceptors. The correlation between these parameters and the molecular weight and biological activities of studied complexes was also observed. Regarding the electrical properties, the AC conductivity and the dielectric coefficients were measured as a function of frequency at room temperature. The TMEDA charge-transfer complexes were screened against antibacterial (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa) and antifungal (Aspergillus flavus and Candida albicans) activities.

  7. Study of microstructure of modified polyethylene films with acrylic and methacrylic acids, by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Lopez C, R.

    1995-09-01

    Low density polyethylene (LDPE) was preirradiated with γ -rays and after some contact time with the monomers AA and MAA, suitable graft copolymers were obtained at different grafting grades. After their physical-chemistry characterization, the copolymers were studied using the Positron Annihilation Lifetime Spectroscopy (PALS). Owing to its sensitive and non-destructive nature PALS has proven to be very useful in studying free-volume properties -at the molecular level- during phase transitions in molecular solids, such as the graft copolymers of LDPE/AA and LDPE/MAA. Using PALS it was possible to detect the changes in the melting point of the LDPE as a function of the grafting degree, obtaining thus, valuable information about the microstructure of this kind of copolymers. The increase in the values of the o-Ps lifetime, was interpreted as suggesting that the melting transition is followed by a free-volume cavity expansion as the temperature increased. The o-Ps intensity of formation behavior is in accord with the distortions occurring in the electronic density surrounding the o-Ps as well as the changes in the number of cavities available to the formation of o-Ps. (Author)

  8. To the application of the emission Mössbauer and positron annihilation spectroscopies for detection of carcinogens

    Science.gov (United States)

    Bokov, A. V.; Byakov, V. M.; Kulikov, L. A.; Perfiliev, Yu. D.; Stepanov, S. V.

    2017-11-01

    Being the main cause of cancer, almost all chemical carcinogens are strong electrophiles, that is, they have a high affinity for the electron. We have shown that positron annihilation lifetime spectroscopy (PALS) is able to detect chemical carcinogens by their inhibition of positronium (Ps) formation in liquid media. Electrophilic carcinogens intercept thermalized track electrons, which are precursors of Ps, and as a result, when they are present Ps atom does not practically form. Available biophysical data seemingly indicate that frozen solutions model better an intracellular medium than the liquid ones. So it is reasonable to use emission Mössbauer spectroscopy (EMS) to detect chemical carcinogens, measuring the yield of 57Fe2+ions formed in reactions of Auger electrons and other secondary electrons they produced with 57Fe3+. These reactions are similar to the Ps formation process in the terminal part the positron track: e++ e- =>Ps. So EMS and PALS are complementary methods for detection of carcinogenic compounds.

  9. Future directions of positron annihilation spectroscopy in low-k dielectric films

    International Nuclear Information System (INIS)

    Gidley, D.W.; Vallery, R.S.; Liu, M.; Peng, H.G.

    2007-01-01

    Positronium Annihilation Lifetime Spectroscopy (PALS) has become recognized in the microelectronics industry as one of only several methods capable of quantitatively characterizing engineered nanopores in next-generation (k < 2.2) interlayer dielectric (ILD) thin films. Successes and shortcomings of PALS to date will be assessed and compared with other methods of porosimetry such as ellipsometric and X-ray porosimetries (EP and XRP). A major theme in future low-k research focuses on the ability to integrate porous ILD's into chip fabrication; the vulnerability of porous dielectrics to etching, ashing, and chemical-mechanical polishing in process integration is delaying the introduction of ultra-low-k films. As device size approaches 45 nm the need to probe very small (sub-nanometer), semi-isolated pores beneath thin diffusion barriers is even more challenging. Depth-profiled PALS with its ability to determine a quantitative pore interconnection length and easily resolve 0.3 nm pores beneath diffusion barriers or in trench-patterned dielectrics should have a bright future in porous ILD research. The ability of PALS (and PAS in general) to deduce evolution and growth of pores with porosity should find broad applicability in the emerging field of high performance materials with strategically engineered nanopores. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Effect of Hydrogen on Vacancy Formation in Sputtered Cu Films Studied by Positron Annihilation Spectroscopy

    Science.gov (United States)

    Yabuuchi, Atsushi; Kihara, Teruo; Kubo, Daichi; Mizuno, Masataka; Araki, Hideki; Onishi, Takashi; Shirai, Yasuharu

    2013-04-01

    As a part of the LSI interconnect fabrication process, a post-deposition high-pressure annealing process is proposed for embedding copper into trench structures. The embedding property of sputtered Cu films has been recognized to be improved by adding hydrogen to the sputtering argon gas. In this study, to elucidate the effect of hydrogen on vacancy formation in sputtered Cu films, normal argon-sputtered and argon-hydrogen-sputtered Cu films were evaluated by positron annihilation spectroscopy. As a result, monovacancies with a concentration of more than 10-4 were observed in the argon-hydrogen-sputtered Cu films, whereas only one positron lifetime component corresponding to the grain boundary was detected in the normal argon-sputtered Cu films. This result means monovacancies are stabilized by adding hydrogen to sputtering gas. In the annealing process, the stabilized monovacancies began clustering at around 300 °C, which indicates the dissociation of monovacancy-hydrogen bonds. The introduced monovacancies may promote creep deformation during high-pressure annealing.

  11. Characterization of defect accumulation in neutron-irradiated Mo by positron annihilation spectroscopy

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Li, Meimei; Snead, L.L.

    2008-01-01

    Positron annihilation lifetime spectroscopy measurements were performed on neutron-irradiated low carbon arc cast Mo. Irradiation took place in the high flux isotope reactor, Oak Ridge National Laboratory, at a temperature of 80 +/- 10 degrees C. Neutron fluences ranged from 2 x 10(21) to 8 x 10......(24) n/m(2) (E > 0.1 MeV), corresponding to displacement damage levels in the range from 7.2 x 10(-5) to 2.8 x 10(-1) displacements per atom (dpa). A high density of submicroscopic cavities was observed in the neutron-irradiated Mo and their size distributions were estimated. Cavities were detected even...... at a very low-dose of similar to 10(-4) dpa. The average size of the cavities did not change significantly with dose, in contrast to neutron-irradiated bcc Fe where cavity sizes increased with increasing dose. It is suggested that the in-cascade vacancy clustering may be significant in neutron-irradiated Mo...

  12. Characterization of vacancy type defects in Electronic Materials by Positron Lifetime and Age-Momentum Correlation Spectroscopy

    Science.gov (United States)

    Suzuki, Ryoichi; Ohdaira, Toshiyuki

    2002-03-01

    Positron annihilation spectroscopy is known to be sensitive to vacancy type defects. At the National Institute of Advanced Industrial Science and Technology (AIST) Japan, the authors have developed a measurement system which enables us to perform depth-selective positron annihilation lifetime spectroscopy (PALS) and positron age-momentum correlation (AMOC) spectroscopy with an intense slow positron beam. PALS gives us information on the size of vacancies whereas AMOC gives us information on not only vacancy sizes but also impurities or chemical environments. Using this system, we have carried out defect characterization experiments on various electronic materials, e.g. ion implanted Si, SiO2/Si, MOS, CVD or SOD (spin-on-dielectric) grown low dielectric insulator films, etc.

  13. 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.)

  14. Positron Annihilation in Carbon Nanotubes Studied by Coincidence Doppler Broadening Spectroscopy

    Science.gov (United States)

    Murakami, H.; Sato, K.; Kanazawa, I.; Sano, M.

    2008-05-01

    In order to assign the sites of positron annihilation, coincidence Doppler broadening spectra were measured for a highly oriented pyrolytic graphite crystal, graphite powder, multi-walled carbon nanotubes (MNTs) and cup-stacked carbon nanotubes (CNTs). The spectrum for graphite powder normalized to that for highly oriented pyrolytic graphite (HOPG) is almost flat in the momentum region from 7×10-3 to 13×10-3 mec, having a ratio close to unity. The flat spectrum demonstrates that positrons injected into graphite powder annihilate in the interlayer spaces of piled graphite sheets, in the same manner as positrons in highly oriented pyrolytic graphite annihilate in the bulk. The coincidence Doppler broadening spectra for MNTs and CNTs are quite different from that for highly oriented pyrolytic graphite, which indicates that positrons injected into MNTs and CYTs annihilate not in the bulk, but on surface. The positron lifetime spectrum for multi-walled carbon nanotubes is analyzed in terms of a single component due to surface-trapped positrons, while that for CNTs is decomposed into three components attributable to para-positronium surface-trapped positrons and ortho-positronium. The difference between the coincidence Doppler broadening spectrum for CNTs and that for MNTs is explained in terms of positron annihilation on zigzag surfaces of CNTs which are composed of both graphite-sheet and graphite-edge planes.

  15. A study on lead myristate (LM) soap film crystal by positron annihilation life spectroscopy

    International Nuclear Information System (INIS)

    Shi Zikang; Yu xianchun

    1992-01-01

    The quality of the LM soap film crystal is determined by means of the positron annihilation life spectroscopy. It is found that the technology to be used to make soap film will influence the film quality and the film quality can be improved by a reasonable heat treatment

  16. Measurement of positron annihilation lifetimes for positron burst by multi-detector array

    Science.gov (United States)

    Wang, B. Y.; Kuang, P.; Liu, F. Y.; Han, Z. J.; Cao, X. Z.; Zhang, P.

    2018-03-01

    It is currently impossible to exploit the timing information in a gamma-ray pulse generated within nanoseconds when a high-intensity positron burst annihilation event occurs in a target using conventional single-detector methods. A state-of-the-art solution to the problem is proposed in this paper. In this approach, a multi-detector array composed of many independent detection cells mounted spherically around the target is designed to detect the time distribution of the annihilated gamma rays generated following, in particular, a positron burst emitting huge amounts of positrons in a short pulse duration, even less than a few nano- or picoseconds.

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

    International Nuclear Information System (INIS)

    Abdel-Latif, R.M.; Mohamed, H.F.M.; Abdel-Hady, E.E.; Mohamed, S.S.

    2005-01-01

    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, T g (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, T g 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

  18. New approaches for a time- and position-resolved detector for positron annihilation spectroscopy at PLEPS

    Energy Technology Data Exchange (ETDEWEB)

    Ackermann, Ulrich; Egger, Werner; Sperr, Peter; Loewe, Benjamin; Ravelli, Luca; Koegel, Gottfried; Dollinger, Guenther [Universitaet der Bundeswehr Muenchen, LRT2 (Germany); Jagutzki, Ottmar [Universitaet Frankfurt, RoentDek GmbH (Germany)

    2013-07-01

    The pulsed low energy positron system PLEPS at NEPOMUC at the FRM II is a tool for depth resolved positron lifetime measurements. Besides positron lifetime measurements 2D-AMOC (two dimensional age momentum correlation) experiments are also possible. 2D-AMOC provides in coincidence the lifetime of the positron and the longitudinal momentum distribution of the annihilating electron. It would be of great scientific concern to measure simultaneously the entire 3D-momentum distribution of the annihilating electron and the corresponding lifetime of the positron (4D-AMOC). To perform 4D-AMOC measurements, a time and spatially resolving detector with a time resolution of about 100 ps (FWHM) and a spatial resolution of circa 2 mm over an area of about 12 cm{sup 2} is required in coincidence with a pixelated Ge-detector and currently under development at our institute. It is intended to use a MCP-based UV-light detector with two MCP-stages coupled to a BaF{sub 2} scintillator. To achieve the spatial resolution the centroid information of the photoelectron-cloud is detected with a position sensitive anode installed outside the housing of the MCP detector. As an alternative to a MCP-based detector, silicon photomultipliers are also envisaged.

  19. Determinations of phase transitions in nylon 6-12, nylon-6, polyvinyl chloride and polyethylene terephthalate by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Camacho Reyes, M.J.

    1993-01-01

    Positron annihilation lifetime spectroscopy (PALS) was used to investigate the phase transitions, mainly the glass transition, of poly(vinyl chloride) (PVC), Nylon-6,12, Nylon-6, poly(ethylene terephthalate) during the thermal treatment of these polymers. The longest lived component lifetime and intensity, indicative of ortho-Positronium pick-off exhibit thermal dependencies that can be attributed to the anticipated free volume changes associated with structural transitions. Positron lifetime measurements were performed using an E G and G Ortec standard fast-fast coincidence system. Three spectra were collected at each temperature, each consisting of a peak height of approximately 25000 counts. The resulting spectra were consistently modeled with a three component fit using the computer program PATFIT. For nylon-6,12, nylon-6, PVC systems three transitions were obtained in both tau-3 and I-3 as a function of temperature. Changes in the slope of the curves appear for both parameters, these could be attributed to T g1 , T g2 and T c , respectively. In the case of PET analysis two transitions were obtained as is shown by the variations of tau-3 as a function of the heating temperature. These transitions can be attributed to T g1 and T g2 . Similar changes can be observed for I-3 in relation with temperature. Glass transition behavior was evident in the lifetime behavior of polymers. Increases in slope of the lifetime temperature plots were interpreted free-volume cavity expansion as temperature is increased. The intensity responses in the vicinity of the upper glass transition were consistent with the association of this transition with the reduction of crystalline constraint of segmental mobility in the amorphous phase. (Author)

  20. Positron annihilation spectroscopy of vacancy aggregates in neutron-irradiated MgO crystals

    International Nuclear Information System (INIS)

    Pareja, R.; De La Cruz, R.M.; Gonzalez, R.; Chen, Y.; Department of Energy, Washington, DC

    1992-01-01

    Positron annihilation measurements in neutron-irradiated MgO crystals show that the positron lifetime is shorter than in as-grown crystals, suggesting that most of the defects produced by neutron irradiations are positively charged. The concentration of the neutral anion vacancy (possibly also the neutral anion divacancy) is estimated to be no more than ∼ 10 16 cm -3 for samples irradiated to a dose of 10 17 to 10 19 n cm -2 . Annealing experiments on the neutron-irradiated crystals show a significant increase in the positron lifetime after anneals at 900 K. The increase is attributed to positron trapping by anion-vacancy aggregates. A lifetime of (284±15)ps is tentatively assigned to positrons trapped in these aggregates. (Author)

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

    International Nuclear Information System (INIS)

    Sato, K.; Inoue, K.; Yoshiie, T.; Xu, Q.; Wakai, E.; Kutsukake, C.; Ochiai, K.

    2009-01-01

    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.

  2. Characterization of interfaces in Binary and Ternary Polymer Blends by Positron Lifetime Spectroscopy

    Science.gov (United States)

    Ranganathaiah, C.

    2015-06-01

    A miscible blend is a single-phase system with compact packing of the polymeric chains/segments due configuration/conformational changes upon blending. Differential Scanning Calorimetry (DSC) is the most employed method to ascertain whether the blend is miscible or immiscible. Positron Lifetime Spectroscopy (PLS) has been employed in recent times to study miscibility properties of polymer blends by monitoring the ortho-Positronium annihilation lifetimes as function of composition. However, just free volume monitoring and the DSC methods fail to provide the composition dependent miscibility of blends. To overcome this limitation, an alternative approach based on hydrodynamic interactions has been developed to derive this information using the same o-Ps lifetime measurements. This has led to the development of a new method of measuring composition dependent miscibility level in binary and ternary polymer blends. Further, the new method also provides interface characteristics for immiscible blends. The interactions between the blend components has a direct bearing on the strength of adhesion at the interface and hence the hydrodynamic interaction. Understanding the characteristic of interfaces which decides the miscibility level of the blend and their end applications is made easy by the present method. The efficacy of the present method is demonstrated for few binary and ternary blends.

  3. 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.

  4. Application of the Positron Annihilation Spectroscopy for Chromium Effect Investigation in Binary Fe-Cr Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Sojak, S.; Krsjak, V.; Slugen, V.; Stancek, S.; Petriska, M.; Vitazek, K.; Stacho, M. [Department of Nuclear Physics and Technology, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, Ilkovicova 3, 812 19 Bratislava (Slovakia)

    2008-07-01

    Positron annihilation spectroscopy (PAS) is one of the non-destructive techniques applied with advantage for evaluation of the radiation treated materials microstructure. In this work, the PAS was used for study of different Fe-Cr alloys implanted by ions of helium. Investigation was focused on the chromium effect and the radiation defects resistance. In particular, the vacancy type defects (mono-vacancies, vacancy clusters) have been studied. The results show that the specific content of chromium has important influence on the size and distribution of induced defects. (authors)

  5. 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.)

  6. Positron annihilation characterization of nanostructured ferritic alloys

    International Nuclear Information System (INIS)

    Alinger, M.J.; Glade, S.C.; Wirth, B.D.; Odette, G.R.; Toyama, T.; Nagai, Y.; Hasegawa, M.

    2009-01-01

    Nanostructured ferritic alloys (NFAs) were produced by mechanically alloying Fe-14Cr-3W-0.4Ti and 0.25Y 2 O 3 (wt%) powders followed by hot isostatic pressing consolidation at 850, 1000 and 1150 deg. C. Positron annihilation lifetime and orbital momentum spectroscopy measurements are in qualitative agreement with small angle neutron scattering, transmission electron microscopy and atom probe tomography observations, indicating that up to 50% of the annihilations occur at high densities of Y-Ti-O enriched nm-scale features (NFs). Some annihilations may also occur in small cavities. In Y-free control alloys, that do not contain NFs, positrons primarily annihilate in the Fe-Cr matrix and at features such as dislocations, while a small fraction annihilate in large cavities or Ar bubbles.

  7. Polymerization of epoxy resins studied by positron annihilation

    International Nuclear Information System (INIS)

    Suzuki, T.; Hayashi, T.; Ito, Y.

    1999-01-01

    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 o C) 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)

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

    International Nuclear Information System (INIS)

    Abdel-Hady, E.E.; Hammam, A.M.

    2010-01-01

    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 I 3 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.

  9. Spatially resolved positron annihilation spectroscopy on friction stir weld induced defects.

    Science.gov (United States)

    Hain, Karin; Hugenschmidt, Christoph; Pikart, Philip; Böni, Peter

    2010-04-01

    A friction stir welded (FSW) Al alloy sample was investigated by Doppler broadening spectroscopy (DBS) of the positron annihilation line. The spatially resolved defect distribution showed that the material in the joint zone becomes completely annealed during the welding process at the shoulder of the FSW tool, whereas at the tip, annealing is prevailed by the deterioration of the material due to the tool movement. This might be responsible for the increased probability of cracking in the heat affected zone of friction stir welds. Examination of a material pairing of steel S235 and the Al alloy Silafont36 by coincident Doppler broadening spectroscopy (CDBS) indicates the formation of annealed steel clusters in the Al alloy component of the sample. The clear visibility of Fe in the CDB spectra is explained by the very efficient trapping at the interface between steel cluster and bulk.

  10. 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.

  11. Diffusion of permanent liquid dye molecules in human hair investigated by positron lifetime spectroscopy.

    Science.gov (United States)

    Chandrashekara, M N; Ranganathaiah, C

    2009-02-15

    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 positron technique makes it possible to non-invasively characterize the angstrom sized free volume holes in hair, which are supposed to be express pathways for diffusion of small molecules. The o-Ps lifetime parameters tau3 and I3 decrease rapidly during the first 60 min of sorption time. The overall decrease in o-Ps lifetime (tau3) was well over 200 ps and o-Ps intensity (I3) drops by 3.5%. These positron results are explained in terms of dye molecules filling the free volume holes and hair morphology. The dye penetrates the cuticle rapidly, but slowly in cortex. The first hour of dyeing appears to be the most effective period of deposition of dye molecules within hair. These results are well corroborated by the sorption results which suggest that the dye diffusion is essentially a diffusion controlled (i.e. Fickian) process, with no observable relaxation effects. 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 sorption curve also yielded an average value of apparent diffusivity of the dye in hair. From this study, we conclude 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.

  12. Exploiting the benefit of S0→ T1excitation in triplet-triplet annihilation upconversion to attain large anti-stokes shifts: tuning the triplet state lifetime of a tris(2,2'-bipyridine) osmium(ii) complex.

    Science.gov (United States)

    Liu, Dongyi; Zhao, Yingjie; Wang, Zhijia; Xu, Kejing; Zhao, Jianzhang

    2018-03-07

    Os(ii) complexes are particularly interesting for triplet-triplet annihilation (TTA) upconversion, due to the strong direct S 0 → T 1 photoexcitation, as in this way, energy loss is minimized and large anti-Stokes shift can be achieved for TTA upconversion. However, Os(bpy) 3 has an intrinsic short T 1 state lifetime (56 ns), which is detrimental for the intermolecular triplet-triplet energy transfer (TTET), one of the crucial steps in TTA upconversion. In order to prolong the triplet state lifetime, we prepared an Os(ii) tris(bpy) complex with a Bodipy moiety attached, so that an extended T 1 state lifetime is achieved by excited state electronic configuration mixing or triplet state equilibrium between the coordination center-localized state ( 3 MLCT state) and Bodipy ligand-localized state ( 3 IL state). With steady-state and time-resolved transient absorption/emission spectroscopy, we proved that the 3 MLCT is slightly above the 3 IL state (by 0.05 eV), and the triplet state lifetime was prolonged by 31-fold (from 56 ns to 1.73 μs). The TTA upconversion quantum yield was increased by 4-fold as compared to that of the unsubstituted Os(ii) complex.

  13. Positron annihilation spectroscopy studies of bronze exposed to sandblasting at different pressure

    Science.gov (United States)

    Kurdyumov, S.; Siemek, K.; Horodek, P.

    2017-11-01

    An application of Doppler broadening of annihilation line spectroscopy to samples of beryllium bronze DIN-CuBe2 exposed to sandblasting is presented in performed studies. It is familiar that sandblasting introduces open-volume defects. Samples were sandblasted under different pressure for 1 minute using 110 μm particles of Al2O3. For a non-defected sample the constant value of S-parameter was detected. In the cases of sandblasted samples, S-parameter decreased when the depth enhanced. In our studies the thicknesses of defected zones were determined (it was c.a. 30 μm for a sample blasted under pressure of 1 bar and 110 μm – for 5 bar), and it was also observed that if sandblasting pressure is higher the defected zone is larger.

  14. Bounds on Cross-sections and Lifetimes for Dark Matter Annihilation and Decay into Charged Leptons from Gamma-ray Observations of Dwarf Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Essig, Rouven; /SLAC; Sehgal, Neelima; Strigari, Louis E.; /KIPAC, Menlo Park

    2009-06-19

    We provide conservative bounds on the dark matter cross-section and lifetime from final state radiation produced by annihilation or decay into charged leptons, either directly or via an intermediate particle {phi}. Our analysis utilizes the experimental gamma-ray flux upper limits from four Milky Way dwarf satellites: HESS observations of Sagittarius and VERITAS observations of Draco, Ursa Minor, and Willman 1. Using 90% confidence level lower limits on the integrals over the dark matter distributions, we find that these constraints are largely unable to rule out dark matter annihilations or decays as an explanation of the PAMELA and ATIC/PPB-BETS excesses. However, if there is an additional Sommerfeld enhancement in dwarfs, which have a velocity dispersion {approx} 10 to 20 times lower than that of the local Galactic halo, then the cross-sections for dark matter annihilating through {phi}'s required to explain the excesses are very close to the cross-section upper bounds from Willman 1. Dark matter annihilation directly into {tau}'s is also marginally ruled out by Willman 1 as an explanation of the excesses, and the required cross-section is only a factor of a few below the upper bound from Draco. Finally, we make predictions for the gamma-ray flux expected from the dwarf galaxy Segue 1 for the Fermi Gamma-ray Space Telescope. We find that for a sizeable fraction of the parameter space in which dark matter annihilation into charged leptons explains the PAMELA excess, Fermi has good prospects for detecting a gamma-ray signal from Segue 1 after one year of observation.

  15. Positron annihilation characteristics in multi-wall carbon nanotubes with different average diameters

    International Nuclear Information System (INIS)

    Tuyen, L A; Khiem, D D; Phuc, P T; Kajcsos, Zs; Lázár, K; Tap, T D

    2013-01-01

    Positron lifetime spectroscopy was used to study multi-wall carbon nanotubes. The measurements were performed in vacuum on the samples having different average diameters. The positron lifetime values depend on the nanotube diameter. The results also show an influence of the nanotube diameter on the positron annihilation intensity on the nanotube surface. The change in the annihilation probability is described and interpreted by the modified diffusion model introducing the positron escape rate from the nanotubes to their external surface.

  16. Microstructural characterization of alumina-zirconia layered ceramics using positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Parente, P., E-mail: pparente@fis.uc3m.es [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Ortega, Y. [Departamento de Fisica de Materiales, Facultad de Ciencias Fisicas, Univ. Complutense de Madrid, 28040 Madrid (Spain); Savoini, B.; Monge, M.A. [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Tucci, A.; Esposito, L. [Centro Ceramico Bologna, 40128 Bologna (Italy); Sanchez-Herencia, A.J. [Instituto de Ceramica y Vidrio, Consejo Superior de Investigaciones Cientificas, 28049 Madrid (Spain)

    2010-05-15

    Positron annihilation spectroscopy (PAS), indentation, nanoindentation experiments and scanning electron microscopy (SEM) observations were performed on Al{sub 2}O{sub 3}-ZrO{sub 2} laminates samples to assess the effect of residual stresses on their mechanical and microstructural properties. Layered samples were implemented by slip-casting, constituted by two thin Al{sub 2}O{sub 3} external layers and an intermediate thick one, consisting of a mixture of Al{sub 2}O{sub 3} and monoclinic ZrO{sub 2} in the range 0-30 vol.%. In these systems residual tensile stresses fields were generated inside the external layers during cooling from the sintering temperature, by the expansion of the adjacent ZrO{sub 2}-containing layer. SEM observations showed the microstructural effects due to the level of tension related to the zirconia content. A correlation between the PAS parameters and the microstructural changes caused by the presence of residual stresses was found. Nanoindentation measurements were used to trace the sign and magnitude of the residual stress gradient across the interface between the layers.

  17. Development of positron annihilation spectroscopy for investigating deuterium decorated voids in neutron-irradiated tungsten

    Science.gov (United States)

    Taylor, C. N.; Shimada, M.; Merrill, B. J.; Akers, D. W.; Hatano, Y.

    2015-08-01

    The present work is a continuation of a recent research to develop and optimize positron annihilation spectroscopy (PAS) for characterizing neutron-irradiated tungsten. Tungsten samples were exposed to neutrons in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory and damaged to 0.025 and 0.3 dpa. Subsequently, they were exposed to deuterium plasmas in the Tritium Plasma Experiment (TPE) at Idaho National Laboratory. The implanted deuterium was desorbed through sample heating to 900 °C, and Doppler broadening (DB)-PAS was performed both before and after heating. Results show that deuterium impregnated tungsten is identified as having a smaller S-parameter. The S-parameter increases after deuterium desorption. Microstructural changes also occur during sample heating. These effects can be isolated from deuterium desorption by comparing the S-parameters from the deuterium-free back face with the deuterium-implanted front face. The application of using DB-PAS to examine deuterium retention in tungsten is examined.

  18. Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations

    Science.gov (United States)

    Šedivý, L.; Čížek, J.; Belas, E.; Grill, R.; Melikhova, O.

    2016-01-01

    Positron annihilation spectroscopy (PAS) was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The as-grown crystals contain open-volume defects connected with Cd vacancies . It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. While annealing in Cd pressure reduces of the density, subsequent annealing in Te pressure restores . The CdTe:Cl contains negatively-charged shallow traps interpreted as Rydberg states of A-centres and representing the major positron trapping sites at low temperature. Positrons confined in the shallow traps exhibit lifetime, which is shorter than the CdTe bulk lifetime. Interpretation of the PAS data was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis, and allowed us to determine the principal point defect densities. PMID:26860684

  19. Application of positron annihilation technique to reverse osmosis membrane materials

    International Nuclear Information System (INIS)

    Shimazu, A.; Ikeda, K.; Miyazaki, T.; Ito, Y.

    2000-01-01

    Positron annihilation lifetime spectroscopy has been adopted as a new approach for studying vacancies of reverse osmosis membrane materials composed of cellulose acetate films and aromatic polyamide resins. The intensity of the ortho-positronium (o-Ps) lifetime increased with the amount of vacancies determined using N 2 isotherm at -195 deg. C. Changes of vacancy profiles induced by heat treatment in the cellulose acetate films were detected using o-Ps. It was found that the positron annihilation technique is applicable to the study of vacancy profiles associated with salt selectivity in typical reverse osmosis membranes.

  20. Evaluation of epoxy resin for cryogenic use by positron annihilation method. Change of characteristics of epoxy resin with cross-linking density and positron lifetime

    International Nuclear Information System (INIS)

    Nishijima, Shigehiro; Honda, Yoshihide; Okada, Toichi; Kobayashi, Yoshinori; Namba, Shingo.

    1994-01-01

    The positron annihilation method has been applied to evaluate unoccupied space in epoxy aiming at the design of the molecular structure for cryogenic use. To confirm the model in which molecular free space is needed in the epoxy for cryogenic use, the molecular weight between cross-linkings in epoxy was changed. The increase of molecular weight between cross-linkings brought an increase of fracture toughness even at liquid helium temperature and the model was found to be confirmed. The increase of molecular weight between cross-linkings was also found to decrease the 3rd lifetime of positrons. It suggested that the epoxy main chains were folded and this was confirmed by the molecular mechanical calculation. (author)

  1. Lifetime spectroscopy a method of defect characterization in silicon for photovoltaic applications

    CERN Document Server

    Rein, Stefan

    2005-01-01

    Lifetime spectroscopy is one of the most sensitive diagnostic tools for the identification and analysis of impurities in semiconductors. Since it is based on the recombination process, it provides insight into precisely those defects that are relevant to semiconductor devices such as solar cells. This book introduces a transparent modeling procedure that allows a detailed theoretical evaluation of the spectroscopic potential of the different lifetime spectroscopic techniques. The various theoretical predictions are verified experimentally with the context of a comprehensive study on different metal impurities. The quality and consistency of the spectroscopic results, as explained here, confirms the excellent performance of lifetime spectroscopy.

  2. Photoexcited Muon Spin Spectroscopy: A New Method for Measuring Excess Carrier Lifetime in Bulk Silicon.

    Science.gov (United States)

    Yokoyama, K; Lord, J S; Miao, J; Murahari, P; Drew, A J

    2017-12-01

    We have measured excess carrier lifetime in silicon using photoexcited muon spin spectroscopy. Positive muons implanted deep in a wafer can interact with the optically injected excess carriers and directly probe the bulk carrier lifetime while minimizing the effect from surface recombination. The method is based on the relaxation rate of muon spin asymmetry, which depends on the excess carrier density. The underlying microscopic mechanism has been understood by simulating the four-state muonium model in Si under illumination. We apply the technique to different injection levels and temperatures, and demonstrate its ability for injection- and temperature-dependent lifetime spectroscopy.

  3. 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.

  4. Fluorescence Lifetime Correlation Spectroscopy (FLCS): Concepts, Applications and Outlook

    Czech Academy of Sciences Publication Activity Database

    Kapusta, Peter; Macháň, Radek; Benda, A.; Hof, Martin

    2012-01-01

    Roč. 13, č. 10 (2012), s. 12890-12910 E-ISSN 1422-0067 R&D Projects: GA ČR GBP208/12/G016 Institutional support: RVO:61388955 Keywords : fluorescence correlation spectroscopy (FCS) * time correlated single photon counting (TCSPC) * fluorescence cross-correlation spectroscopy (FCCS) Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.464, year: 2012

  5. Positron annihilation spectroscopy (PALS) the effect of crosslinking on free volume size in poly-methyl-methacrylate

    CERN Document Server

    Atevikj, A

    2000-01-01

    Positron annihilation Spectroscopy (PALS) is used for analyzing the samples of polymethyl-methacrylate (PMMA) with different contents of crosslinks. The measurements are performed at room temperature. The times of life (tau sub 1 , tau sub 2 , tau sub 3) and the intensities (I sub I , I sub 2 , 1 sub 3) of para-positronium, the free positrons and the orto-positrons are calculated for each type of polymer, but only (tau sub 3) and (I sub 3) are of interest because we can calculate the size of free volume. It is shown that the radius of free volume is proportional to the crosslinking density. Defects of sizes in the range of 0.1 to 1 nm are detected with Positron Spectroscopy, while other techniques do not give results. (Original)

  6. Mn-Doping in NiO Nanoparticles: Defects-Modifications and Associated Effects Investigated Through Positron Annihilation Spectroscopy.

    Science.gov (United States)

    Das, Anjan; Mandal, Atis Chandra; Roy, Soma; Nambissan, P M G

    2016-04-01

    Manganese-doped nickel oxide (Ni1-xMnxO) nanoparticulate samples with x in the range 0 (undoped sample) to 0.35 were synthesized by sol-gel method involving chemical reactions between the solutions of nickel nitrate hexahydrate and manganese acetate tetrahydrate. The nanocrystallites obtained after annealing of the precipitates for different durations were characterized by X-ray diffraction and high resolution transmission electron microscopy. The samples showed high degree of purity with no secondary phase up to 35 at.% (x = 0.35) of Mn-doping. At the initial doping concentrations, the crystallite sizes increased due to vacancy type defects being recombined with some of the doped Mn2+ ions. However, substitution-induced strain soon overtook the crystallite dynamics and the sizes rapidly started reducing again as an indirect consequence of the necessity to accommodate majority of the doped cations on the surfaces of the nanocrystallites. There was conspicuous changes in the lattice parameter too which could again be attributed to the strain and charge effects. The average sizes of the crystallites were obtained in the range 5.5 nm to 13.1 nm for the different samples. UV-Vis absorption studies indicated the formation of excitonic states in NiO on Mn-doping. The band gap energy (Eg) derived from the optical absorption spectra showed a continuous increase with increase of Mn-doping of the samples. Positron lifetime and Doppler broadening spectroscopic studies were carried out on those samples to characterize the vacancy type defects and defect clusters/complexes. There were also indications to suggest positron annihilation at the crystallite surfaces owing to their sizes of nanometer order. Positron lifetimes decreased upon increase of Mn-doping. The coincidence Doppler broadened ratio curves indicated definite shifts of the prominent oxygen-electron-annihilation peak and the variation of the lineshape parameter S also indicated clearly the effects of Mn-doping.

  7. Fluorescence lifetime correlation spectroscopy combined with lifetime tuning: New perspectives in supported phospholipid bilayer research

    Czech Academy of Sciences Publication Activity Database

    Benda, Aleš; Fagulová, Veronika; Deyneka, Alexander; Enderlain, J.; Hof, Martin

    2006-01-01

    Roč. 22, č. 23 (2006), s. 9580-9585 ISSN 0743-7463 R&D Projects: GA ČR GA203/05/2308; GA MŠk LC06063 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z10100522 Keywords : spectroscopy * fluorescence * FLCS Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.902, year: 2006

  8. Structural analysis of IPC zeolites and related materials using positron annihilation spectroscopy and high-resolution argon adsorption

    Czech Academy of Sciences Publication Activity Database

    Jagiello, J.; Sterling, N.C.; Eliášová, Pavla; Opanasenko, Maksym; Zukal, Arnošt; Morris, R. E.; Navaro, M.; Mayoral, A.; Crivelli, P.; Warringham, R.; Mitchell, S.; Pérez-Ramirez, J.; Čejka, Jiří

    2016-01-01

    Roč. 18, MAY 2016 (2016), s. 15269-15277 ISSN 1463-9076 R&D Projects: GA ČR(CZ) GAP106/12/0189 EU Projects: European Commission(XE) 604307 - CASCATBEL Institutional support: RVO:61388955 Keywords : PORE-SIZE * POROUS MATERIALS * LIFETIME SPECTROSCOPY Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.123, year: 2016

  9. Distribution of diffusion times determined by fluorescence (lifetime) correlation spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Pánek, Jiří; Loukotová, Lenka; Hrubý, Martin; Štěpánek, Petr

    2018-01-01

    Roč. 51, č. 8 (2018), s. 2796-2804 ISSN 0024-9297 R&D Projects: GA MŠk(CZ) LO1507 Institutional support: RVO:61389013 Keywords : polymer solution * fluorescence correlation spectroscopy * diffusion time distribution Subject RIV: CD - Macromolecular Chemistry OBOR OECD: Polymer science Impact factor: 5.835, year: 2016

  10. Positron beam lifetime spectroscopy of atomic scale defect distributions in bulk and microscopic volumes

    International Nuclear Information System (INIS)

    Howell, R.H.; Cowan, T.E.; Hartley, J.; Sterne, P.; Brown, B.

    1996-05-01

    We are developing a defect analysis capability based on two positron beam lifetime spectrometers: the first is based on a 3 MeV electrostatic accelerator and the second on our high current linac beam. The high energy beam lifetime spectrometer is operational and positron lifetime analysis is performed with a 3 MeV positron beam on thick samples. It is being used for bulk sample analysis and analysis of samples encapsulated in controlled environments for insitu measurements. A second, low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopies is under development at the LLNL high current positron source. This beam will enable defect specific, 3-D maps of defect concentration with sub-micron location resolution and when coupled with first principles calculations of defect specific positron lifetimes it will enable new levels of defect concentration mapping and defect identification

  11. Exciton dynamics and annihilation in WS2 2D semiconductors.

    Science.gov (United States)

    Yuan, Long; Huang, Libai

    2015-04-28

    We systematically investigate the exciton dynamics in monolayered, bilayered, and trilayered WS2 two-dimensional (2D) crystals by time-resolved photoluminescence (TRPL) spectroscopy. The exciton lifetime when free of exciton annihilation was determined to be 806 ± 37 ps, 401 ± 25 ps, and 332 ± 19 ps for WS2 monolayer, bilayer, and trilayer, respectively. By measuring the fluorescence quantum yields, we also establish the radiative and nonradiative lifetimes of the direct and indirect excitons. The exciton decay in monolayered WS2 exhibits a strong excitation density-dependence, which can be described using an exciton-exciton annihilation (two-particle Auger recombination) model. The exciton-exciton annihilation rate for monolayered, bilayered, and trilayered WS2 was determined to be 0.41 ± 0.02, (6.00 ± 1.09) × 10(-3) and (1.88 ± 0.47) × 10(-3) cm(2) s(-1), respectively. Notably, the exciton-exciton annihilation rate is two orders of magnitude faster in the monolayer than in the bilayer and trilayer. We attribute the much slower exciton-exciton annihilation rate in the bilayer and trilayer to reduced many-body interaction and phonon-assisted exciton-exciton annihilation of indirect excitons.

  12. Compensation models in chlorine doped CdTe based on positron annihilation and photoluminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Stadler, W.; Hofman, D.M.; Meyer, B.K. [Technische Universitaet Muenchen, Garching (Germany); Krause-Rehberg, R.; Polity, A.; Abgarjan, Th. [Martin-Luther Universitaet Halle-Wittenberg, FB Physik, Halle (Germany); Salk, M.; Benz, K.W. [Kristallographisches Institut, Universitaet Freiburg, Freiburg (Germany); Azoulay, M. [Soreq, Nuclear Research Centre, Yavne (Israel)

    1995-12-31

    In this investigation positron annihilation, photoluminescence and electron paramagnetic resonance techniques are employed to gain insight in the compensation of CdTe doped with the halogen Cl. We will demonstrate that the high resistivity of CdTe:Cl cannot be explain by the interaction between the shallow effective mass type donor Cl on Te site and the doping induced shallow acceptor complex, a Cd vacancy paired off with a nearest-neighbour Cl atom (A centre). From electron paramagnetic resonance investigations we conclude that the mid gap trap, often detected by electrical methods in CdTe, is not the isolated Cd vacancy. (author). 9 refs, 2 figs, 1 tab.

  13. Ohmic contact formation mechanism of nonalloyed Pd contacts to p-type GaN observed by positron annihilation spectroscopy

    Science.gov (United States)

    Lee, Jong-Lam; Weber, Marc; Kim, Jong Kyu; Lee, Jae Won; Park, Yong Jo; Kim, Taeil; Lynn, Kelvin

    1999-04-01

    The change of the Fermi energy level at the interface of Pd/p-type GaN by surface treatment was investigated using positron annihilation spectroscopy, and the results were used to provide interpretation of the electrical properties of the contact. Changes in the positron parameters at the interface in the aqua regia-treated GaN are more pronounced than that in the HCl-treated one. This provides evidence that the surface treatment with aqua regia prior to Pd metal deposition removes surface oxides, resulting in the shift of the Fermi level position from a middle of the bandgap to near the valence band. Thus, the barrier for hole injection from metal to p-type GaN is lowered, subsequent to the decrease of contact resistivity by two orders of magnitude.

  14. Advances in Contactless Silicon Defect and Impurity Diagnostics Based on Lifetime Spectroscopy and Infrared Imaging

    Directory of Open Access Journals (Sweden)

    Jan Schmidt

    2007-01-01

    Full Text Available This paper gives a review of some recent developments in the field of contactless silicon wafer characterization techniques based on lifetime spectroscopy and infrared imaging. In the first part of the contribution, we outline the status of different lifetime spectroscopy approaches suitable for the identification of impurities in silicon and discuss—in more detail—the technique of temperature- and injection-dependent lifetime spectroscopy. The second part of the paper focuses on the application of infrared cameras to analyze spatial inhomogeneities in silicon wafers. By measuring the infrared signal absorbed or emitted from light-generated free excess carriers, high-resolution recombination lifetime mappings can be generated within seconds to minutes. In addition, mappings of non-recombination-active trapping centers can be deduced from injection-dependent infrared lifetime images. The trap density has been demonstrated to be an important additional parameter in the characterization and assessment of solar-grade multicrystalline silicon wafers, as areas of increased trap density tend to deteriorate during solar cell processing.

  15. Structure of dislocations in Al and Fe as studied by positron-annihilation spectroscopy

    DEFF Research Database (Denmark)

    Hidalgo, C.; González-Doncel, G.; Linderoth, Søren

    1992-01-01

    Positron-lifetime-spectra measurements have been performed on single crystals of Al and polycrystals of Fe deformed under the tensile mode at room temperature and 77 K, respectively. It is shown that the positron-trapping component in Al depends on the number of slip systems activated: The positr...

  16. Some aspects of free volume studies in molecular substances using positron annihilation experiments

    International Nuclear Information System (INIS)

    Shantarovich, V.P.; Gustov, V.W.; Kevdina, I.B.; Suzuki, T.; Djourelov, N.; Shimazu, A.

    2005-01-01

    Positron annihilation lifetime spectroscopy is accepted now as a method for the studies of elementary free volumes (free volume holes) in solids, in polymers in particular. The aim of this paper is to discuss some problems, the difficulties on the way of this application and to illustrate them by several examples obtained by the authors. (author)

  17. Deep level transient spectroscopy and minority carrier lifetime study on Ga-doped continuous Czochralski silicon

    Science.gov (United States)

    Yoon, Yohan; Yan, Yixin; Ostrom, Nels P.; Kim, Jinwoo; Rozgonyi, George

    2012-11-01

    Continuous-Czochralski (c-Cz) crystal growth has been suggested as a viable technique for the fabrication of photovoltaic Si wafers due to its low resistivity variation of any dopant, independent of segregation, compared to conventional Cz. In order to eliminate light induced degradation due to boron-oxygen traps in conventional p-type silicon wafers, gallium doped wafers have been grown by c-Cz method and investigated using four point probe, deep level transient spectroscopy (DLTS), and microwave-photoconductance decay. Iron-gallium related electrically active defects were identified using DLTS as the main lifetime killers responsible for reduced non-uniform lifetimes in radial and axial positions of the c-Cz silicon ingot. A direct correlation between minority carrier lifetime and the concentration of electrically active Fe-Ga pairs was established.

  18. Fluorescence lifetime spectroscopy in multiple-scattering environments: an application to biotechnology

    Science.gov (United States)

    Cerussi, Albert E.; Gratton, Enrico; Fantini, Sergio

    1999-07-01

    Over the past few years, there has been significant research activity devoted to the application of fluorescence spectroscopy to strongly scattering media, where photons propagate diffusely. Much of this activity focused on fluorescence as a source of contrast enhancement in optical tomography. Our efforts have emphasized the quantitative recovery of fluorescence parameters for spectroscopy. Using a frequency-domain diffusion-based model, we have successfully recovered the lifetime, the absolute quantum yield, the fluorophore concentration, and the emission spectrum of the fluorophore, as well as the absorption and the reduced scattering coefficients at the emission wavelength of the medium in different measurements. In this contribution, we present a sensitive monitor of the binding between ethidium bromide and bovine cells in fresh milk. The spectroscopic contrast was the approximately tenfold increase in the ethidium bromide lifetime upon binding to DNA. The measurement clearly demonstrated that we could quantitatively measure the density of cells in the milk, which is an application vital to the tremendous economic burden of bovine subclinical mastitis detection. Furthermore, we may in principle use the spirit of this technique as a quantitative monitor of the binding of fluorescent drugs inside tissues. This is a first step towards lifetime spectroscopy in tissues.

  19. Characterization of zeolite Y pastilles for the ortho-positronium annihilation studies

    International Nuclear Information System (INIS)

    Alvarado D, E.; Garcia S, I.; Cabral P, A.

    2008-01-01

    This paper presents the characterization of zeolite Y pastilles prior to their study by the Positronium Annihilation Lifetimes Spectroscopy. The characterization is the estimation of porosity, the determination of its purity and crystal size for X-ray diffraction, the determination of its morphology and particle size by scanning electron microscopy and its specific area by the Brunauer-Emmett-Teller method. Presenting the first lifetimes measurements of positronium in zeolites LTA and Y. (Author)

  20. Positron annihilation in transparent ceramics

    International Nuclear Information System (INIS)

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

    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. (paper)

  1. The influence of antioxidant on positron annihilation in polypropylene

    International Nuclear Information System (INIS)

    Djourelov, N.; He, C.; Suzuki, T.; Ito, Y; Kondo, K.; Ito, Y.; Shantarovich, V.P.

    2003-01-01

    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)

  2. Microstructure characterization of rapidly solidified Al-Fe-Cr-Ce alloy by positron annihilation spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Michalcová, A.; Vojtěch, D.; Čízek, J.; Procházka, I.; Drahokoupil, Jan; Novák, P.

    2011-01-01

    Roč. 509, č. 7 (2011), s. 3211-3218 ISSN 0925-8388 Institutional research plan: CEZ:AV0Z10100520 Keywords : metals and alloy s * nanostructured materials * rapid solidification * positron spectroscopies * transmission electron microscopy * x-ray diffraction Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.289, year: 2011

  3. Study of bicontinuous phase in (TTAB+pentanol)/water/n-octane reverse micellar system using positron lifetime spectroscopy

    International Nuclear Information System (INIS)

    Singh, K Chandramani; Yadav, R; Khani, P H

    2013-01-01

    A phase diagram of (TTAB+pentanol)/water/n-octane has been mapped by using optical method. It exhibits a reverse micellar (L 2 ) phase extending over a wide range of concentrations of the constituents. To investigate the fine structure of the L 2 phase, a series of (TTAB+pentanol)/n-octane ternary mixtures having initial concentrations of (TTAB+pentanol) (1:1) in n-octane as 35%, 50% and 65% by weight were prepared. In each of these mixtures, positron lifetime measurements were performed as a function of the concentration of water, using a standard lifetime spectrometer. At water concentrations of 11.8%, 8.5% and 8.4% by weight respectively for the above systems, the o-Ps pick-off lifetime τ 3 shows an oscillatory behaviour while I 3 representing the Ps formation exhibits an abrupt change. These changes in the positron annihilation parameters have been explained on the basis of onset of bicontinuity in the microemulsion phase. The positron annihilation technique thus suggests the existence of droplet-like and bicontinuous structures in the L 2 phase which is otherwise considered optically to be a single phase as the system remains clear and isotropic throughout this phase. Supporting evidence has been provided by the electrical conductivity measurements performed in these systems. These results are presented in this paper.

  4. Mapping of exciton-exciton annihilation in MEH-PPV by time-resolved spectroscopy: experiment and microscopic theory.

    Science.gov (United States)

    Hader, Kilian; Consani, Cristina; Brixner, Tobias; Engel, Volker

    2017-12-06

    Transient absorption traces taken on samples of the polymer MEH-PPV are measured as a function of the laser intensity. In increasing the laser power, different decay dynamics of the signal are obtained. This suggests that effective exciton-exciton annihilation takes place. The signals are interpreted using a microscopic quantum mechanical model. The analysis points at an ultrafast excitonic decay via interchain and intrachain annihilation, where the latter process is roughly thirty times slower. Afterwards, diffusion-induced annihilation and relaxation become effective and thus determine the long-time behavior of the excited-state decay.

  5. Investigation of Oxygen-Induced Quenching of Phosphorescence in Photoexcited Aromatic Molecules by Positron Annihilation Spectroscopy

    Science.gov (United States)

    Singh, Jag J.; Eftekhari, Abe

    1996-01-01

    Platinum OctaEthyl Porphyrin (Pt.OEP) is an efficient phosphor under ultraviolet excitation. The phosphorescent triplet state P(T(Sup 1)) is readily quenched by the oxygen O2 molecules. This phenomenon is being utilized as the basis for global air pressure measurements in aerodynamic facilities at various laboratories. The exact mechanism by which O2 molecules quench the P(T(Sup 1) approaches P(S(Sub O)) transitions is still unknown. The diamagnetic singlet states P(S(Sub n)), which feed P(T(Sub 1)) states via intersystem crossings, would presumably not be affected by O2. It must be only the magnetic P(T(Sub 1)) states, which can interact with the paramagnetic O2 molecules, that are affected. However, our positron lifetime and Doppler broadening studies suggest the formation of O2P(S(Sub n)), complexes which can also eventually reduce the population of the P(T(Sub 1)) states (i.e., quench phosphorescence). This reduction is possible because higher triplet states in (Pt.OEP) are admixed with the P(S(Sub 1)), states via spin orbit interactions. The experimental procedures and the results of various measurements are presented in this paper.

  6. Mechanism of phosphorescence quenching in photomagnetic molecules determined by positron annihilation spectroscopy

    Science.gov (United States)

    Singh, Jag J.; Eftekhari, A.; Naidu, S. V. N.

    1994-01-01

    Platinum Octaethyl Porphyrin (Pt.OEP) is an efficient phosphor under ultraviolet excitation. The phosphorescent triplet state (T(sub 1)) is readily quenched by the oxygen (O2) molecules. This phenomenon is being utilized as the basis for global air pressure measurements in aerodynamic facilities at various laboratories. The exact mechanism by which O2 molecules quench the (T(sub 1) - S(sub 0)) transitions is still unknown. The diamagnetic S(sub n) singlet states, which feed T(sub 1) states via intersystem crossings, would presumably not be affected by O2. It must be the magnetic T(sub 1) states, which can interact with the paramagnetic O2 molecules, that are affected. However, our positron lifetime and Doppler broadening studies suggest the formation of (S(sub n) central dot O2) complexes which can also eventually reduce the population of the T(sub 1) states (i.e. quench phosphorescence). This is possible since higher triplet states in (Pt.OEP) are admixed with the S(sub n) states via spin orbit interactions. The experimental procedures and the results of various measurements are discussed in this paper.

  7. Lifetime-resolved photoacoustic (LPA) spectroscopy for monitoring oxygen change and photodynamic therapy (PDT)

    Science.gov (United States)

    Jo, Janggun; Lee, Chang Heon; Kopelman, Raoul; Wang, Xueding

    2016-03-01

    The Methylene Blue loaded Polyacrylamide Nanoparticles (MB-PAA NPs) are used for oxygen sensing and Photodynamic therapy (PDT), a promising therapeutic modality employed for various tumors, with distinct advantages of delivery of biomedical agents and protection from other bio-molecules overcoming inherent limitations of molecular dyes. Lifetime-resolved photoacoustic spectroscopy using quenched-phosphorescence method is applied with MB-PAA NPs so as to sense oxygen, while the same light source is used for PDT. The dye is excited by absorbing 650 nm wavelength light from a pump laser to reach triplet state. The probe laser at 810 nm wavelength is used to excite the first triplet state at certain delayed time to measure the dye lifetime which indicates oxygen concentration. The 9L cells (106 cells/ml) incubated with MB-PAA NP solution are used for monitoring oxygen level change during PDT in situ test. The oxygen level and PDT efficacy are confirmed with a commercial oximeter, and fluorescence microscope imaging and flow cytometry results. This technique with the MB-PAA NPs allowed us to demonstrate a potential non-invasive theragnostic operation, by monitoring oxygen depletion during PDT in situ, without the addition of secondary probes. Here, we demonstrate this theragnostic operation, in vitro, performing PDT while monitoring oxygen depletion. We also show the correlation between O2 depletion and cell death.

  8. Use of interfacial layers to prolong hole lifetimes in hematite probed by ultrafast transient absorption spectroscopy

    Science.gov (United States)

    Paradzah, Alexander T.; Diale, Mmantsae; Maabong, Kelebogile; Krüger, Tjaart P. J.

    2018-04-01

    Hematite is a widely investigated material for applications in solar water oxidation due primarily to its small bandgap. However, full realization of the material continues to be hampered by fast electron-hole recombination rates among other weaknesses such as low hole mobility, short hole diffusion length and low conductivity. To address the problem of fast electron-hole recombination, researchers have resorted to growth of nano-structured hematite, doping and use of under-layers. Under-layer materials enhance the photo-current by minimising electron-hole recombination through suppressing of back electron flow from the substrate, such as fluorine-doped tin oxide (FTO), to hematite. We have carried out ultrafast transient absorption spectroscopy on hematite in which Nb2O5 and SnO2 materials were used as interfacial layers to enhance hole lifetimes. The transient absorption data was fit with four different lifetimes ranging from a few hundred femtoseconds to a few nanoseconds. We show that the electron-hole recombination is slower in samples where interfacial layers are used than in pristine hematite. We also develop a model through target analysis to illustrate the effect of under-layers on electron-hole recombination rates in hematite thin films.

  9. Development and Optimization of a Positron Annihilation Lifetime Spectrometer to Measure Nanoscale Defects in Solids and Borane Cage Molecules in Aqueous Nitrate Solutions

    National Research Council Canada - National Science Library

    Ross, Matthew A

    2008-01-01

    .... The timing resolution of the optimized system is 197 +or- 14 ps as measured with a known (60)Co source. A single-crystal tungsten sample was used to confirm the system calibration resulting in a lifetime of 101...

  10. On mechanism of intermediate-sized circular DNA compaction mediated by spermine: Contribution of fluorescence lifetime correlation spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Humpolíčková, Jana; Štěpánek, M.; Kral, Teresa; Benda, Aleš; Procházka, K.; Hof, Martin

    2008-01-01

    Roč. 18, 3-4 (2008), s. 679-684 ISSN 1053-0509 R&D Projects: GA AV ČR IAA400400621; GA MŠk(CZ) LC06063 Institutional research plan: CEZ:AV0Z40400503 Keywords : DNA compaction * fluorescence correlation spectroscopy * fluorescence lifetime correlation spectroscopy * dynamic light scattering Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.880, year: 2008

  11. Stability of a positron lifetime measurement system, and investigation the types and concentrations of defects induced by10 MeV electron irradiation on n- and p-types Si

    Directory of Open Access Journals (Sweden)

    E Tayebfard

    2015-07-01

    Full Text Available Positron annihilation lifetime spectroscopy method with valuation of non-destructive investigation of material, provides information about electron density, defect concentration, type of defects and atoms around the defects. The stability of the system was tested with a source. The time resolution of the whole system has been derived about 365 ps at FWHM. Then n- and p-type silicon samples were irradiated with a 10 MeV electron beam with dosage of 3, 12, and 30 kGy. Three components were fitted to the lifetime spectra using the PAScual program. The first component is related to the positron annihilation in the positron source which was obtained 186 ps. The second component is related to the positron annihilation lifetime in the sample bulk which was obtained 218 ps. The last lifetime component which is related to the positron annihilation in defect was small and sample dependent

  12. Evaluation of epoxy resin for cryogenic use by positron annihilation method. Change of characteristics of epoxy resin with plasticizer and positron lifetime

    International Nuclear Information System (INIS)

    Nishijima, Shigehiro; Honda, Yoshihide; Okada, Toichi; Kobayashi, Yoshinori; Namba, Shingo.

    1994-01-01

    The evaluation of unoccupied space in epoxies has been evaluated in terms of positron annihilation method. Based on the evaluated unoccupied space the cohesive condition of the epoxy molecular was modeled. The model suggested that the epoxies were classified into two types that is the epoxy could be explain by the free volume and that by free space. Two former was understood as the epoxy of which molecular network was destroyed by the plasticizer and the latter as that of which molecular weight between crosslinks was changed. In this work the former mechanism was confirmed experimentally. The addition of plasticizer was confirmed not to be effective to improve the cryogenic mechanical properties as expected by the model. (author)

  13. Characterization of lacunar defects by positrons annihilation

    CERN Document Server

    Barthe, M F; Blondiaux, G

    2003-01-01

    Among the nondestructive methods for the study of matter, the positrons annihilation method allows to sound the electronic structure of materials by measuring the annihilation characteristics. These characteristics depend on the electronic density as seen by the positon, and on the electron momentums distribution which annihilate with the positon. The positon is sensible to the coulombian potential variations inside a material and sounds preferentially the regions away from nuclei which represent potential wells. The lacunar-type defects (lack of nuclei) represent deep potential wells which can trap the positon up to temperatures close to the melting. This article describes the principles of this method and its application to the characterization of lacunar defects: 1 - positrons: matter probes (annihilation of electron-positon pairs, annihilation characteristics, positrons sources); 2 - positrons interactions in solids (implantation profiles, annihilation states, diffusion and trapping, positon lifetime spec...

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

    International Nuclear Information System (INIS)

    Oshtrakh, M.I.; Kopelyan, E.A.; Semionkin, V.A.

    1995-01-01

    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

  15. PALSfit3: A software package for analysing positron lifetime spectra

    DEFF Research Database (Denmark)

    Kirkegaard, Peter; Olsen, Jens V.; Eldrup, Morten Mostgaard

    The present report describes a Windows based computer program called PALSfit3. The purpose of the program is to carry out analyses of spectra that have been measured by positron annihilation lifetime spectroscopy (PALS). PALSfit3 is based on the well tested PATFIT and PALS fit programs, which hav...... in a text window. PALSfit3 is verified on Windows XP and Windows 7, 8 and 10. The PALSfit3 software can be acquired from the Technical University of Denmark (http://PALSfit.dk)......The present report describes a Windows based computer program called PALSfit3. The purpose of the program is to carry out analyses of spectra that have been measured by positron annihilation lifetime spectroscopy (PALS). PALSfit3 is based on the well tested PATFIT and PALS fit programs, which have...

  16. Time-resolved laser fluorescence spectroscopy of organic ligands by europium: Fluorescence quenching and lifetime properties

    Science.gov (United States)

    Nouhi, A.; Hajjoul, H.; Redon, R.; Gagné, J. P.; Mounier, S.

    2018-03-01

    Time-resolved Laser Fluorescence Spectroscopy (TRLFS) has proved its usefulness in the fields of biophysics, life science and geochemistry to characterize the fluorescence probe molecule with its chemical environment. The purpose of this study is to demonstrate the applicability of this powerful technique combined with Steady-State (S-S) measurements. A multi-mode factor analysis, in particular CP/PARAFAC, was used to analyze the interaction between Europium (Eu) and Humic substances (HSs) extracted from Saint Lawrence Estuary in Canada. The Saint Lawrence system is a semi-enclosed water stream with connections to the Atlantic Ocean and is an excellent natural laboratory. CP/PARAFAC applied to fluorescence S-S data allows introspecting ligands-metal interactions and the one-site 1:1 modeling gives information about the stability constants. From the spectral signatures and decay lifetimes data given by TRLFS, one can deduce the fluorescence quenching which modifies the fluorescence and discuss its mechanisms. Results indicated a relatively strong binding ability between europium and humic substances samples (Log K value varies from 3.38 to 5.08 at pH 7.00). Using the Stern-Volmer plot, it has been concluded that static and dynamic quenching takes places in the case of salicylic acid and europium interaction while for HSs interaction only a static quenching is observed.

  17. Impact of oxygen diffusion on superconductivity in YBa2Cu3O7 -δ thin films studied by positron annihilation spectroscopy

    Science.gov (United States)

    Reiner, M.; Gigl, T.; Jany, R.; Hammerl, G.; Hugenschmidt, C.

    2018-04-01

    The oxygen deficiency δ in YBa2Cu3O7 -δ (YBCO) plays a crucial role for affecting high-temperature superconductivity. We apply (coincident) Doppler broadening spectroscopy of the electron-positron annihilation line to study in situ the temperature dependence of the oxygen concentration and its depth profile in single crystalline YBCO film grown on SrTiO3 (STO) substrates. The oxygen diffusion during tempering is found to lead to a distinct depth dependence of δ , which is not accessible using x-ray diffraction. A steady state reached within a few minutes is defined by both, the oxygen exchange at the surface and at the interface to the STO substrate. Moreover, we reveal the depth-dependent critical temperature Tc in the as prepared and tempered YBCO film.

  18. Multiple gamma lines from semi-annihilation

    International Nuclear Information System (INIS)

    D'Eramo, Francesco; McCullough, Matthew; Thaler, Jesse

    2013-01-01

    Hints in the Fermi data for a 130 GeV gamma line from the galactic center have ignited interest in potential gamma line signatures of dark matter. Explanations of this line based on dark matter annihilation face a parametric tension since they often rely on large enhancements of loop-suppressed cross sections. In this paper, we pursue an alternative possibility that dark matter gamma lines could arise from ''semi-annihilation'' among multiple dark sector states. The semi-annihilation reaction ψ i ψ j → ψ k γ with a single final state photon is typically enhanced relative to ordinary annihilation ψ i ψ-bar i → γγ into photon pairs. Semi-annihilation allows for a wide range of dark matter masses compared to the fixed mass value required by annihilation, opening the possibility to explain potential dark matter signatures at higher energies. The most striking prediction of semi-annihilation is the presence of multiple gamma lines, with as many as order N 3 lines possible for N dark sector states, allowing for dark sector spectroscopy. A smoking gun signature arises in the simplest case of degenerate dark matter, where a strong semi-annihilation line at 130 GeV would be accompanied by a weaker annihilation line at 173 GeV. As a proof of principle, we construct two explicit models of dark matter semi-annihilation, one based on non-Abelian vector dark matter and the other based on retrofitting Rayleigh dark matter

  19. Generation of a new spectral format, the lifetime synchronous spectrum (LiSS), using phase-resolved fluorescence spectroscopy

    International Nuclear Information System (INIS)

    Shaver, J.M.; McGown, L.B.

    1994-01-01

    A new fluorescence spectral format is introduced in which fluorescence lifetime is shown as a function of synchronously scanned wavelength to generate a Lifetime Synchronous Spectrum (LiSS). Lifetimes are determined in the frequency domain with the use of Phase-Resolved Fluorescence Spectroscopy (PRFS) to obtain the phase of the fluorescence signal. Theory and construction of the LiSS are presented and experimental results are shown for solutions of single components and simple binary and ternary mixtures. These results show how the lifetime information in the LiSS augments the steady-state intensity information of a standard synchronous spectrum, providing unique information for identification of components and resolution of overlapping spectral peaks. The LiSS technique takes advantage of noise reduction inherent in the extraction of lifetime from PRFS in addition to standard spectral smoothing techniques. The precision of phase determination through PRFS is found to be comparable to that of direct phase measurements at normal fluorescence intensities and superior for low-intensity signals

  20. Deconvolution of Positrons' Lifetime spectra

    International Nuclear Information System (INIS)

    Calderin Hidalgo, L.; Ortega Villafuerte, Y.

    1996-01-01

    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

  1. Thermal treatment of the Fe78 Si9 B13 alloy and the analysis of it magnetic properties through Moessbauer spectroscopy and Positronium annihilation

    International Nuclear Information System (INIS)

    Lopez M, A.

    2005-01-01

    The present work is divided in five chapters. In the first one a general vision of the amorphous alloys is given from antecedents, structure, obtaining methods, properties and problems that at the moment, focusing us in a certain moment to the iron base alloys and the anomalous problem of hardness that it presents the alloy Fe 78 Si 9 B 13 like previously mention us. The second chapter tries on the basic theory of the techniques of Moessbauer spectroscopy and Positron Annihilation spectroscopy, used for the characterization of our alloy as well as the complementary technique of X-ray diffraction (XRD) to observe that the amorphous phase was even studying. The third chapter describes the experimental conditions that were used to study the alloy Fe 78 Si 9 B 13 in each one of their thermal treatments. In the fourth chapter the obtained results and their discussion are presented. In the fifth chapter the conclusions to which were arrived after analyzing the results are presented. (Author)

  2. Photoluminescence and positron annihilation spectroscopic investigation on a H(+) irradiated ZnO single crystal.

    Science.gov (United States)

    Sarkar, A; Chakrabarti, Mahuya; Sanyal, D; Bhowmick, D; Dechoudhury, S; Chakrabarti, A; Rakshit, Tamita; Ray, S K

    2012-08-15

    Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6 MeV H(+) ions in a hydrothermally grown ZnO single crystal. Prior to irradiation, the emission from donor bound excitons is at 3.378 eV (10 K). The irradiation creates an intense and narrow emission at 3.368 eV (10 K). The intensity of this peak is nearly four times that of the dominant near band edge peak of the pristine crystal. The characteristic features of the 3.368 eV emission indicate its origin as a 'hydrogen at oxygen vacancy' type defect. The positron annihilation lifetime measurement reveals a single component lifetime spectrum for both the unirradiated (164 ± 1 ps) and irradiated crystal (175 ± 1 ps). It reflects the fact that the positron lifetime and intensity of the new irradiation driven defect species are a little higher compared to those in the unirradiated crystal. However, the estimated defect concentration, even considering the high dynamic defect annihilation rate in ZnO, comes out to be ∼4 × 10(17) cm(-3) (using SRIM software). This is a very high defect concentration compared to the defect sensitivity of positron annihilation spectroscopy. A probable reason is the partial filling of the incorporated vacancies (positron traps), which in ZnO are zinc vacancies. The positron lifetime of ∼175 ps (in irradiated ZnO) is consistent with recent theoretical calculations for partially hydrogen-filled zinc vacancies in ZnO. Passivation of oxygen vacancies by hydrogen is also reflected in the photoluminescence results. A possible reason for such vacancy filling (at both Zn and O sites) due to irradiation has also been discussed.

  3. Positron annihilation studies on reactor irradiated and thermal annealed ferrocene

    International Nuclear Information System (INIS)

    Marques Netto, A.; Carvalho, R.S.; Magalhaes, W.F.; Sinisterra, R.D.

    1996-01-01

    Retention and thermal annealing following (n, γ) reaction in solid ferrocene, Fe(C 5 H 5 ) 2 , were studied by positron annihilation lifetime spectroscopy (PAL). Positronium (Ps) formation was observed in the non-irradiated compound with a probability or intensity (I 3 ) of 30%. Upon irradiation of the compound with thermal neutrons in a nuclear reactor, I 3 decreases with increasing irradiation time. Thermal treatment again increases I 3 values from 16% to 25%, revealing an important proportion of molecular reformation without variation of the ortho-positronium lifetime (τ 3 ). These results point out the major influence of the electronic structure as determining the Ps yields in the pure complex. In the irradiated and non irradiated complexes the results are satisfactorily explained on the basis of the spur model. (orig.)

  4. Fluorescence Lifetime and UV-Vis Spectroscopy to Evaluate the Interactions Between Quercetin and Its Yeast Microcapsule.

    Science.gov (United States)

    Pham-Hoang, Bao-Ngoc; Winckler, Pascale; Waché, Yves

    2018-01-01

    Quercetin is a fragile bioactive compound. Several works have tried to preserve it by encapsulation but the form of encapsulation (mono- or supra-molecular structure, tautomeric form), though important for stability and bioavailability, remains unknown. The present work aims at developing a fluorescence lifetime technique to evaluate the structure of quercetin during encapsulation in a vector capsule that has already proven efficiency, yeast cells. Molecular stabilization was observed during a 4-month storage period. The time-correlated single-photon counting (TCSPC) technique was used to evaluate the interaction between quercetin molecules and the yeast capsule. The various tautomeric forms, as identified by UV-Vis spectroscopy, result in various lifetimes in TCSPC, although they varied also with the buffer environment. Quercetin in buffer exhibited a three-to-four longer long-time after 24 h (changing from 6-7 to 18-23 ns), suggesting an aggregation of molecules. In yeast microcapsules, the long-time population exhibited a longer lifetime (around 27 ns) from the beginning and concerned about 20% of molecules compared to dispersed quercetin. This shows that lifetime analysis can show the monomolecular instability of quercetin in buffer and the presence of interactions between quercetin molecules and their microcapsules. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. 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.

  6. Time-Resolved Fluorescence Spectroscopy and Fluorescence Lifetime Imaging Microscopy for Characterization of Dendritic Polymer Nanoparticles and Applications in Nanomedicine

    Directory of Open Access Journals (Sweden)

    Alexander Boreham

    2016-12-01

    Full Text Available The emerging field of nanomedicine provides new approaches for the diagnosis and treatment of diseases, for symptom relief and for monitoring of disease progression. One route of realizing this approach is through carefully constructed nanoparticles. Due to the small size inherent to the nanoparticles a proper characterization is not trivial. This review highlights the application of time-resolved fluorescence spectroscopy and fluorescence lifetime imaging microscopy (FLIM for the analysis of nanoparticles, covering aspects ranging from molecular properties to particle detection in tissue samples. The latter technique is particularly important as FLIM allows for distinguishing of target molecules from the autofluorescent background and, due to the environmental sensitivity of the fluorescence lifetime, also offers insights into the local environment of the nanoparticle or its interactions with other biomolecules. Thus, these techniques offer highly suitable tools in the fields of particle development, such as organic chemistry, and in the fields of particle application, such as in experimental dermatology or pharmaceutical research.

  7. Time-Resolved Fluorescence Spectroscopy and Fluorescence Lifetime Imaging Microscopy for Characterization of Dendritic Polymer Nanoparticles and Applications in Nanomedicine.

    Science.gov (United States)

    Boreham, Alexander; Brodwolf, Robert; Walker, Karolina; Haag, Rainer; Alexiev, Ulrike

    2016-12-24

    The emerging field of nanomedicine provides new approaches for the diagnosis and treatment of diseases, for symptom relief and for monitoring of disease progression. One route of realizing this approach is through carefully constructed nanoparticles. Due to the small size inherent to the nanoparticles a proper characterization is not trivial. This review highlights the application of time-resolved fluorescence spectroscopy and fluorescence lifetime imaging microscopy (FLIM) for the analysis of nanoparticles, covering aspects ranging from molecular properties to particle detection in tissue samples. The latter technique is particularly important as FLIM allows for distinguishing of target molecules from the autofluorescent background and, due to the environmental sensitivity of the fluorescence lifetime, also offers insights into the local environment of the nanoparticle or its interactions with other biomolecules. Thus, these techniques offer highly suitable tools in the fields of particle development, such as organic chemistry, and in the fields of particle application, such as in experimental dermatology or pharmaceutical research.

  8. Evidence for confinement induced phase separation in ethanol-water mixture: a positron annihilation study.

    Science.gov (United States)

    Muthulakshmi, T; Dutta, D; Maheshwari, Priya; Pujari, P K

    2018-01-17

    We report an experimental evidence for the phase separation of ethanol-water mixture confined in mesoporous silica with different pore size using positron annihilation lifetime spectroscopy (PALS). A bulk-like liquid in the core of the pore and a distinct interfacial region near the pore surface have been identified based on ortho-positronium lifetime components. The lifetime corresponding to the core liquid shows similar behavior to the bulk liquid mixture while the interfacial lifetime shows an abrupt rise within a particular range of ethanol concentration depending on the pore size. This abrupt increase is attributed to the appearance of excess free-volume near the interfacial region. The excess free-volume is originated due to microphase separation of confined ethanol-water primarily at the vicinity of the pore wall. We envisage that probing free-volume changes at the interface using PALS is a sensitive way to investigate microphase separation under nanoconfinement.

  9. Porous silicon investigated by positron annihilation

    International Nuclear Information System (INIS)

    Cruz, R.M. de la; Pareja, R.

    1989-01-01

    The effect of the anodic conversion in silicon single crystals is investigated by positron lifetime measurements. Anodization at constant current induces changes in the positron lifetime spectrum of monocrystalline silicon samples. It is found that theses changes are primarily dependent on the silicon resistivity. The annihilation parameter behaviour of anodized samples, treated at high temperature under reducing conditions, is also investigated. The results reveal that positron annihilation can be a useful technique to characterize porous silicon formed by anodizing as well as to investigate its thermal behaviour. (author)

  10. Time gated fluorescence lifetime imaging and micro-volume spectroscopy using two-photon excitation

    NARCIS (Netherlands)

    Sytsma, J.; Vroom, J.M.; de Grauw, C.J.; Gerritsen, H.C.

    A scanning microscope utilizing two-photon excitation in combination with fluorescence lifetime contrast is presented. The microscope makes use of a tunable femtosecond titanium:sapphire laser enabling the two-photon excitation of a broad range of fluorescent molecules, including UV probes.

  11. Positron annihilation studies of neutron irradiated reactor pressure vessel steels

    International Nuclear Information System (INIS)

    Brauer, G.; Liszkay, L.; Molnar, B.

    1988-01-01

    Several annealing studies by positron annihilation (Doppler broadening, lifetime) on neutron irradiated Cr-Mo-V reactor pressure vessel steels (Soviet type 15Kh2MFA) regarding the influences of irradiation temperature, fluence of fast neutrons as well as different impurity contents are presented and discussed. A possibility of explaining the positron annihilation data by irradiation induced carbide formation is proposed. (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...

  13. Membrane lipid domains and rafts: current applications of fluorescence lifetime spectroscopy and imaging.

    Science.gov (United States)

    de Almeida, Rodrigo F M; Loura, Luís M S; Prieto, Manuel

    2009-02-01

    Membrane microdomains and their involvement in cellular processes are part of the current paradigm of biomembranes. However, a better characterization of domains, namely lipid rafts, is needed. In this review, it is shown how the use of time-resolved fluorescence, with the adequate parameters and probes, helps elucidating the type, number, fraction, composition and size of lipid phases and domains in multicomponent model systems. The determination of phase diagrams for lipid mixtures containing sphingolipids and/or cholesterol is exemplified. The use of fluorescence quenching and Förster resonance energy transfer (FRET) are also illustrated. Strategies for studying protein-induced domains are presented. The advantages of using single point microscopic decays and fluorescence lifetime imaging microscopy (FLIM) in systems with three-phase coexistence are explained. Finally, the introduction of FLIM allows studies in live cell membranes, and the nature of the microdomains observed is readily elucidated due to the information retrieved from fluorescence lifetimes.

  14. Positron annihilation spectroscopy and small angle neutron scattering characterization of nanostructural features in high-nickel model reactor pressure vessel steels

    International Nuclear Information System (INIS)

    Glade, Stephen C.; Wirth, Brian D.; Odette, G. Robert; Asoka-Kumar, P.

    2006-01-01

    Irradiation embrittlement in nuclear reactor pressure vessel steels results from the hardening by a high number density of nanometer scale features. In steels with more than ∼0.10% Cu, the dominant features are often Cu-rich precipitates typically alloyed with Mn, Ni and Si. At low-Cu and low-to-intermediate Ni levels, so-called matrix hardening features are believed to be vacancy-solute cluster complexes, or their remnants. However, Mn-Ni-Si rich precipitates, with Mn plus Ni contents greater than Cu, can form at high alloy Ni contents and are promoted at irradiation temperatures lower than the nominal 290 deg. C. Even at very low-Cu levels, late blooming Mn-Ni-Si rich precipitates are a significant concern due to their potential to form large volume fractions of hardening features. Positron annihilation spectroscopy (PAS) and small angle neutron scattering neutron (SANS) measurements were used to characterize the fine-scale microstructure in split-melt A533B steels with varying Ni and Cu contents, irradiated at selected conditions from 270 to 310 deg. C between ∼0.04 and 1.6 x 10 23 n m -2 . The objective was to assess the character, composition and magnetic properties of Cu-rich precipitates, as well as to gain insight on the matrix features. The results suggest that the irradiated very low-Cu and intermediate Ni steel contains small vacancy-Mn-Ni-Si cluster complexes, but not large, well-formed and highly enriched Mn-Ni-Si phases. The hardening features in steels containing 0.2% and 0.4% Cu, and 0.8% and 1.6% Ni are consistent with well-formed, non-magnetic Cu-Ni-Mn precipitates. The precipitate number densities and volume fractions increase, while their sizes decrease, with increasing Ni and decreasing irradiation temperature. The precipitates evolve with fluence in stages of nucleation, growth and limited coarsening

  15. The kinetics of formation and growth of TiC precipitates in Ti-modified stainless steel studied by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Gopalan, P.; Rajaraman, R.; Viswanathan, B.; Venkadesan, S.

    1998-01-01

    The formation and growth of TiC precipitates in Ti-modified austenitic stainless steel (D-9 alloy) is monitored by positron lifetime spectroscopy. From isochronal annealing studies various recovery stages are identified. TiC precipitates are found to be more stable in 20% cold worked alloy than in a 17.5% cold worked sample. From the isothermal annealing studies, it is found that TiC precipitation is controlled by dislocations. The limited temperature dependence of dislocation controlled TiC precipitation is governed by an apparent activation energy of 1.6 eV. In 20% cold worked alloy, TiC precipitates are found to be stable against growth even after 1000 h of annealing at 923 K. For higher annealing temperatures, TiC precipitate coarsening occurs due to recrystallisation. (orig.)

  16. 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 ...

  17. 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...

  18. Thermal equilibrium defects in anthracene probed by positron annihilation

    International Nuclear Information System (INIS)

    Uedono, Akira; Tanigawa, Shoichiro; Tachibana, Masaru; Shimizu, Mikio; Satoh, Masaaki; Kojima, Kenichi; Ishibashi, Shoji; Kawano, Takao.

    1996-01-01

    Defects in anthracene were investigated by the positron annihilation technique. Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured in the temperature range between 305 K and 516 K. The lifetime of positrons annihilated from the delocalized state was determined to be 0.306 ns around room temperature. Below the melting point, the observed temperature dependence of the line shape parameter S was explained assuming the formation energy of thermal equilibrium defects was 1 eV. Above the melting point, the pick-off annihilation of ortho-positronium in open spaces was observed, where the size of these spaces was estimated to be 0.2 nm 3 . The annihilation of positrons from the self-trapped state was also discussed. (author)

  19. Thermal equilibrium defects in anthracene probed by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Uedono, Akira; Tanigawa, Shoichiro [Tsukuba Univ., Ibaraki (Japan). Inst. of Materials Science; Tachibana, Masaru; Shimizu, Mikio; Satoh, Masaaki; Kojima, Kenichi; Ishibashi, Shoji; Kawano, Takao

    1996-06-01

    Defects in anthracene were investigated by the positron annihilation technique. Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured in the temperature range between 305 K and 516 K. The lifetime of positrons annihilated from the delocalized state was determined to be 0.306 ns around room temperature. Below the melting point, the observed temperature dependence of the line shape parameter S was explained assuming the formation energy of thermal equilibrium defects was 1 eV. Above the melting point, the pick-off annihilation of ortho-positronium in open spaces was observed, where the size of these spaces was estimated to be 0.2 nm{sup 3}. The annihilation of positrons from the self-trapped state was also discussed. (author)

  20. ANTICOOL: Simulating positron cooling and annihilation in atomic gases

    Science.gov (United States)

    Green, D. G.

    2018-03-01

    The Fortran program ANTICOOL, developed to simulate positron cooling and annihilation in atomic gases for positron energies below the positronium-formation threshold, is presented. Given positron-atom elastic scattering phase shifts, normalised annihilation rates Zeff, and γ spectra as a function of momentum k, ANTICOOL enables the calculation of the positron momentum distribution f(k , t) as a function of time t, the time-varying normalised annihilation rate Z¯eff(t) , the lifetime spectrum and time-varying annihilation γ spectra. The capability and functionality of the program is demonstrated via a tutorial-style example for positron cooling and annihilation in room temperature helium gas, using accurate scattering and annihilation cross sections and γ spectra calculated using many-body theory as input.

  1. Positron Annihilation and Complementary Studies of Copper Sandblasted with Alumina Particles at Different Pressures

    Directory of Open Access Journals (Sweden)

    Paweł Horodek

    2017-11-01

    Full Text Available Positron annihilation spectroscopy and complementary methods were used to detect changes induced by sandblasting of alumina particles at different pressures varying from 1 to 6 bar in pure well-annealed copper. The positron lifetime measurements revealed existence of dislocations and vacancy clusters in the adjoined surface layer. The presence of retained alumina particles in the copper at the depth below 50 µm was found in the SEM pictures and also in the annihilation line shape parameter profiles measured in the etching experiment. The profiles show us that the total depth of damaged zones induced by sandblasting of alumina particles ranges from 140 µm up to ca. 800 µm and it depends on the applied pressure. The work-hardening of the adjoined surface layer was found in the microhardness measurements at the cross-section of the sandblasted samples.

  2. Positron Annihilation and Complementary Studies of Copper Sandblasted with Alumina Particles at Different Pressures.

    Science.gov (United States)

    Horodek, Paweł; Siemek, Krzysztof; Dryzek, Jerzy; Wróbel, Mirosław

    2017-11-23

    Positron annihilation spectroscopy and complementary methods were used to detect changes induced by sandblasting of alumina particles at different pressures varying from 1 to 6 bar in pure well-annealed copper. The positron lifetime measurements revealed existence of dislocations and vacancy clusters in the adjoined surface layer. The presence of retained alumina particles in the copper at the depth below 50 µm was found in the SEM pictures and also in the annihilation line shape parameter profiles measured in the etching experiment. The profiles show us that the total depth of damaged zones induced by sandblasting of alumina particles ranges from 140 µm up to ca. 800 µm and it depends on the applied pressure. The work-hardening of the adjoined surface layer was found in the microhardness measurements at the cross-section of the sandblasted samples.

  3. Spectroscopy and lifetime measurements of states in $^{76}$Kr populated in $^{76}$Rb decay

    CERN Document Server

    Giannatiempo, A; Perego, A; Sona, P; Mach, H; Fogelberg, B; García-Borge, M J; Tengblad, O; Fraile-Prieto, L M; Aas, A J; Gulda, K; CERN. Geneva

    2005-01-01

    The properties of the excited states of $^{76}$Kr, populated in the decay of $^{76}$Rb produced at ISOLDE isotopic separator, have been investigated by using K-conversion electron, $\\gamma$-ray, and $\\gamma\\gamma$ coincidence measurements. The lifetimes of several levels have been measured by means of the Advanced Time-Delayed $\\beta\\gamma\\gamma (t)$ method. The identification of 19 new levels and 55 transitions and the information deduced on spin and/or parity of the observed states from K-conversion coefficients, log ft values and decay properties have led to an improved knowledge of the level scheme. In particular, six 1$^-$ states have been definitely identified and $J^{\\pi} =2^{-}$ has been assigned to the 2227 keV level, on which a band proposed to have negative-parity and even-spin had been previously observed. The strengths of the $E$0 and $E$2 transitions de-exciting the 0$^{+}_{2}$ and 0$^{+}_{3}$ states (the latter is here identified with the state at 1598 keV) have been measured. The experimental ...

  4. Positron annihilation measurements in high-energy alpha-irradiated n-type gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Sandip; Mandal, Arunava; SenGupta, Asmita [Visva-Bharati, Department of Physics, Santiniketan, West Bengal (India); Roychowdhury, Anirban [UGC-DAE Consortium for Scientific Research, Kolkata Centre, Kolkata, West Bengal (India)

    2015-07-15

    Positron annihilation lifetime spectroscopy and Doppler broadening annihilation line-shape measurements have been carried out in 40-MeV alpha-irradiated n-type GaAs. After irradiation, the sample has been subjected to an isochronal annealing over temperature region of 25-800 C with an annealing time of 30 min at each set temperature. After each annealing, the positron measurements are taken at room temperature. Formation of radiation-induced defects and their recovery with annealing temperature are investigated. The lifetime spectra of the irradiated sample have been fitted with two lifetimes. The average positron lifetime τ{sub avg} = 244 ps at room temperature after irradiation indicates the presence of defects, and the value of τ{sub 2} (262 ps) at room temperature suggests that the probable defects are mono-vacancies. Two distinct annealing stages in τ{sub avg} at 400-600 C and at 650-800 C are observed. The variations in line-shape parameter (S) and defect-specific parameter (R) during annealing in the temperature region 25-800 C resemble the behaviour of τ{sub avg} indicating the migration of vacancies, formation of vacancy clusters and the disappearance of defects between 400 and 800 C. (orig.)

  5. Probing the photoluminescence properties of gold nanoclusters by fluorescence lifetime correlation spectroscopy

    International Nuclear Information System (INIS)

    Yuan, C. T.; Lin, T. N.; Shen, J. L.; Lin, C. A.; Chang, W. H.; Cheng, H. W.; Tang, J.

    2013-01-01

    Gold nanoclusters (Au NCs) have attracted much attention for promising applications in biological imaging owing to their tiny sizes and biocompatibility. So far, most efforts have been focused on the strategies for fabricating high-quality Au NCs and then characterized by conventional ensemble measurement. Here, a fusion single-molecule technique combining fluorescence correlation spectroscopy and time-correlated single-photon counting can be successfully applied to probe the photoluminescence (PL) properties for sparse Au NCs. In this case, the triplet-state dynamics and diffusion process can be observed simultaneously and the relevant time constants can be derived. This work provides a complementary insight into the PL mechanism at the molecular levels for Au NCs in solution

  6. Probing Positron Cooling in Noble Gases via Annihilation γ Spectra.

    Science.gov (United States)

    Green, D G

    2017-11-17

    γ spectra for positron annihilation in noble-gas atoms are calculated using many-body theory for positron momenta up to the positronium-formation threshold. These data are used, together with time-evolving positron-momentum distributions determined in the preceding Letter [Phys. Rev. Lett. 119, 203403 (2017)PRLTAO0031-9007], to calculate the time-varying γ spectra produced during positron cooling in noble gases. The γ spectra and their S[over ¯] and W[over ¯] shape parameters are shown to be sensitive probes of the time evolution of the positron momentum distribution and thus provide a means of studying positron cooling that is complementary to positron lifetime spectroscopy.

  7. Positron annihilation studies of 4-n-butyl-4'-isothiocyanato-1,1'-biphenyl.

    Science.gov (United States)

    Dryzek, E; Juszyńska, E; Zaleski, R; Jasińska, B; Gorgol, M; Massalska-Arodź, M

    2013-08-01

    Positron annihilation lifetime spectroscopy (PALS) measurements were performed between 93 and 293 K in order to study the supercooled smectic-E (Sm-E) phase of 4-n-butyl-4'-isothiocyanato-1,1'-biphenyl (4TCB), the ordered molecular crystal of 4TCB, and the phase transition between the Sm-E phase and the ordered molecular crystal of 4TCB. The phase transition was well reflected in the abrupt increase of the ortho-positronium (o-Ps) lifetime and intensity. The value of the o-Ps lifetime in the Sm-E liquid crystalline phase of 4TCB, i.e., 2.21 ns at room temperature, was explained by the formation of bubbles induced by Ps atoms, which are created due to a liquidlike state of the butyl chains of 4TCB molecules in the Sm-E phase. The temperature dependence of the o-Ps intensity for the supercooled Sm-E phase can be explained by thermal generation of sites where bubbles are formed; an activation energy equal to 0.30±0.02 eV was estimated. This value was compared with the activation energies of molecular motions. The o-Ps lifetime in the ordered molecular crystal was interpreted as originating from the annihilation of o-Ps confined in molecular vacancy-type imperfections in the crystal lattice. The value of the o-Ps pickoff annihilation between 1.8 and 1.9 ns is in accordance with the size of the molecular vacancy for the 4TCB crystal lattice. Its intensity is lower than 5%. The isothermal crystallization of the 4TCB Sm-E phase was observed by PALS. The low-dimensional crystal growth was concluded from the Avrami equation fitted to the time dependence of the o-Ps intensity, which resulted in an Avrami exponent equal to 1.73.

  8. Positron annihilation in polymers and permeability of gases

    International Nuclear Information System (INIS)

    Buriova, E.

    2001-05-01

    An analysis of positron annihilation spectroscopy (PAS) results for different substituted polyacetylenes samples under vacuum and in air is presented with the aim to investigate the influence of the external atmosphere on the experimental PAS measurements and to determine correctly the size and the number of the free volume holes. The existence of special structure elements in polymers is responsible for the appearance of the fourth component of the time spectrum. The latter is formed at the expense of free volume elements in disordered regions of the polymer. A study of a number of glassy polymers with widely varying free volume and gas permeability showed that a bimodal size distribution of free volume elements is not an exception in some polymers but is a typical feature of the microstructure of amorphous glassy polymers. Oxygen-induced quenching of positronium lifetimes is demonstrated for all polymer samples. Good correlation of permeability of polymers with the size of free volume elements is demonstrated. This correlation can be used for a fast assessment of gas permeation properties of novel polymers using positron annihilation data (author)

  9. PAES: Positron annihilation induced Auger electron spectrometer

    Directory of Open Access Journals (Sweden)

    Christoph Hugenschmidt

    2015-08-01

    Full Text Available Positron annihilation induced Auger electron spectroscopy (PAES is a newly developed application for surface studies with high elemental selectivity and exceptional surface sensitivity. The instrument is operated by the Technische Universität München and is located at NEPOMUC.

  10. Flavoured co-annihilation

    Indian Academy of Sciences (India)

    2012-10-06

    annihilating part- ners of the neutralino is the lightest stau, ˜τ1. In the presence of flavour violation in the right-handed sector, the co-annihilating partner would be a flavour mixed state. The flavour effect is two-fold: (a) It changes the ...

  11. Study of radiation damage in metals by positron annihilation

    International Nuclear Information System (INIS)

    Gauster, W.B.

    1977-01-01

    Positron annihilation is a sensitive technique for probing defects in metals and it has recently been shown to be a valuable tool for the study of radiation damage. After an introduction to the three basic experimental methods (angular correlation, Doppler broadening, and lifetime measurements), the interaction of positrons with lattice defects is reviewed. Results for the annealing of damage after low temperature irradiation are used to show that positron annihilation has provided new information on annealing kinetics. The role of positron techniques in characterizing complex defect structures resulting from high-temperature neutron irradiation is reviewed and the possible utility of positron annihilation as a nondestructive monitor of property changes is pointed out

  12. Identification of equilibrium and irradiation-induced defects in nuclear ceramics: electronic structure calculations of defect properties and positron annihilation characteristics

    International Nuclear Information System (INIS)

    Wiktor, Julia

    2015-01-01

    During in-pile irradiation the fission of actinide nuclei causes the creation of large amounts of defects, which affect the physical and chemical properties of materials inside the reactor, in particular the fuel and structural materials. Positron annihilation spectroscopy (PAS) can be used to characterize irradiation induced defects, empty or containing fission products. This non-destructive experimental technique involves detecting the radiation generated during electron-positron annihilation in a sample and deducing the properties of the material studied. As positrons get trapped in open volume defects in solids, by measuring their lifetime and momentum distributions of the annihilation radiation, one can obtain information on the open and the chemical environments of the defects. In this work electronic structure calculations of positron annihilation characteristics were performed using two-component density functional theory (TCDFT). To calculate the momentum distributions of the annihilation radiation, we implemented the necessary methods in the open-source ABINIT program. The theoretical results have been used to contribute to the identification of the vacancy defects in two nuclear ceramics, silicon carbide (SiC) and uranium dioxide (UO 2 ). (author) [fr

  13. Ortho-positronium annihilation parameters in polyvinyl alcohol films with various degrees of polymerization, saponification and crystallinity

    International Nuclear Information System (INIS)

    Muramatsu, Hisakazu; Matsumoto, Kuniyuki; Minekawa, Sachiko; Yagi, Yukiko; Sasai, Shigenori

    2001-01-01

    Positron annihilation lifetime (PAL) spectroscopy has been applied to polyvinyl alcohol (PVA) films prepared with commercially available PVA or from polyvinyl acetate (PVac). The variation of lifetimes of ortho-positronium (o-Ps) formed in the films was investigated as a function of the degrees of polymerization, saponification, or crystallinity. For the fully saponificated samples, no dependence was found to exist on the degrees of polymerization or of crystallinity. For the partially saponificated samples, however, the dependence of the o-Ps lifetime on the degree of saponification was clearly observed, and this is explained by both the formation of hydrogen bonds among the polymer chains and the existence of acetyl group strongly inhibiting the hydrogen-bond formation due to steric hindrance. (orig.)

  14. Direct Vpr-Vpr Interaction in Cells monitored by two Photon Fluorescence Correlation Spectroscopy and Fluorescence Lifetime Imaging

    Directory of Open Access Journals (Sweden)

    Mély Yves

    2008-09-01

    Full Text Available Abstract Background The human immunodeficiency virus type 1 (HIV-1 encodes several regulatory proteins, notably Vpr which influences the survival of the infected cells by causing a G2/M arrest and apoptosis. Such an important role of Vpr in HIV-1 disease progression has fuelled a large number of studies, from its 3D structure to the characterization of specific cellular partners. However, no direct imaging and quantification of Vpr-Vpr interaction in living cells has yet been reported. To address this issue, eGFP- and mCherry proteins were tagged by Vpr, expressed in HeLa cells and their interaction was studied by two photon fluorescence lifetime imaging microscopy and fluorescence correlation spectroscopy. Results Results show that Vpr forms homo-oligomers at or close to the nuclear envelope. Moreover, Vpr dimers and trimers were found in the cytoplasm and in the nucleus. Point mutations in the three α helices of Vpr drastically impaired Vpr oligomerization and localization at the nuclear envelope while point mutations outside the helical regions had no effect. Theoretical structures of Vpr mutants reveal that mutations within the α-helices could perturb the leucine zipper like motifs. The ΔQ44 mutation has the most drastic effect since it likely disrupts the second helix. Finally, all Vpr point mutants caused cell apoptosis suggesting that Vpr-mediated apoptosis functions independently from Vpr oligomerization. Conclusion We report that Vpr oligomerization in HeLa cells relies on the hydrophobic core formed by the three α helices. This oligomerization is required for Vpr localization at the nuclear envelope but not for Vpr-mediated apoptosis.

  15. Lifetime of kaonium

    International Nuclear Information System (INIS)

    Krewald, S.; Lemmer, R.H.; Sassen, F.P.

    2004-01-01

    The kaon-antikaon system is studied in both the atomic and the strongly interacting sector. We discuss the influence of the structures of the f 0 (980) and the a 0 (980) mesons on the lifetime of kaonium. The strong interactions are generated by vector meson exchange within the framework of the standard SU(3) V xSU(3) A invariant effective Lagrangian. In the atomic sector, the energy levels and decay widths of kaonium are determined by an eigenvalue equation of the Kudryavtsev-Popov type, with the strong interaction effects entering through the complex scattering length for KK-bar scattering and annihilation. The presence of two scalar mesons f 0 (980) and a 0 (980) leads to a ground state energy for the kaonium atom that is shifted above the point Coulomb value by a few hundred eV. The effect on the lifetime for the kaonium decay into two pions is much more dramatic. This lifetime is reduced by two orders of magnitude from 1.2x10 -16 sec for annihilation in a pure Coulomb field down to 3.2x10 -18 sec when the strong interactions are included. The analysis of the two photon decay width of the f 0 (980) suggests a generalization of the molecular picture which reduces the lifetime of kaonium still further to 1.1x10 -18 sec

  16. A measurement of the D0 lifetime

    International Nuclear Information System (INIS)

    Althoff, M.; Braunschweig, W.; Gerhards, R.; Kirschfink, F.J.; Martyn, H.U.; Rosskamp, R.; Wallraff, W.; Hilger, E.; Kracht, T.; Krasemann, H.L.; Krueger, J.; Lohrmann, E.; Poelz, G.; Poesnecker, K.U.; Bowler, M.G.; Bull, P.; Cashmore, R.J.; Dauncey, P.; Devenish, R.; Heath, G.; Mellor, D.J.; Ratoff, P.; Yelton, J.M.; Baranko, G.; Caldwell, A.; Cherney, M.; DeMille, D.; Izen, J.M.; Messersmith, J.; Ritz, S.; Strom, D.; Takashima, M.; Wicklund, E.; Wu Saulan; Zobernig, G.

    1986-01-01

    We have determined the D 0 lifetime from reconstructed vertices of D 0 mesons produced in e + e - annihilations at an average center of mass energy of 42.2 GeV. From fifteen events the D 0 lifetime was determined to be (4.3+-1.7+-0.8)x10 -13 s. (orig.)

  17. Subnanopore filling during water vapor adsorption on microporous silica thin films as seen by low-energy positron annihilation

    Science.gov (United States)

    Ito, Kenji; Yoshimoto, Shigeru; O'Rourke, Brian E.; Oshima, Nagayasu; Kumagai, Kazuhiro

    2018-02-01

    Positron annihilation lifetime spectroscopy (PALS) using a low-energy positron microbeam extracted into air was applied to elucidating molecular-level pore structures formed in silicon-oxide-backboned microporous thin films under controlled humidity conditions; as a result, a direct observation of the interstitial spaces in the micropores filled with water molecules was achieved. It was demonstrated that PALS using a microbeam extracted into air in combination with water vapor adsorption is a powerful tool for the in-situ elucidation of both open and closed subnanoscaled pores of functional thin materials under practical conditions.

  18. 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...

  19. Fluorescence lifetime imaging spectroscopy in living cells with particular regards to pH dependence and electric field effect

    Science.gov (United States)

    Ohta, Nobuhiro; Nakabayashi, Takakazu; Oshita, Shugo; Kinjo, Masataka

    2010-02-01

    Intracellular pH of a single cell can be imaged using FLIM of enhanced green fluorescent protein (EGFP). The correlation between the intracellular pH and the fluorescence lifetime of EGFP in HeLa cells is explained by considering the pH-dependent acid-base equilibrium of the p-hydroxybenzylidene-imidazolidinone structure of the chromophore of EGFP. The equilibrium between different forms of chromophore depends on pH of the medium. The equilibrium constant between the neutral and anionic EGFP chromophores in HeLa cells is obtained by analyzing the fluorescence lifetimes observed with different values of intracellular pH. The intracellular pH dependence has been also observed in HeLa cells where enhanced yellow fluorescent protein (EYFP) is expressed. The pH dependence of the fluorescence lifetime of EYFP may result from the pH dependence of the molecular structure of the protein bound ionic form of EYFP or the conformational change of the EYFP chromophore induced by lowering pH. The fluorescence lifetimes both of EGFP and of EYFP are not uniform in the cell. At each pH, for example, the fluorescence lifetime of EGFP located near the outer cell membrane is shorter than those located inside cell, whereas the lifetime of EYFP located near the outer cell membrane is longer than those located inside the cell. These differences are ascribed to the different distribution of the electric field surrounding the fluorescent chromophore in the cells, implying that the chromophores of EGFP and EYFP show the opposite electric field effects of the fluorescence lifetime to each other. The fact that the fluorescence lifetime of BCECF in solution is different from the one observed at the same pH in intact cells of Halobacterium salinarum has been also ascribed to the local field produced by membranes in vivo.

  20. A Position Annihilation Study of Defect Recovery in Electron-Irradiated alpha-Zr

    DEFF Research Database (Denmark)

    Hood, G. M.; Eldrup, Morten Mostgaard; Mogensen, O. E.

    1977-01-01

    The presence of vacancy defects in α-Zr, irradiated at 320 > T > 290 K with 1.5 MeV electrons, has been indicated by positron annihilation measurements. It was found that positron lifetimes associated with annihilation in well-annealed α-Zr, fell in the range 173 to 181 psec, with no obvious...

  1. Controlling Positronium Annihilation with Electric Fields.

    Science.gov (United States)

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

    2015-10-30

    We show that the annihilation dynamics of excited positronium (Ps) atoms can be controlled using parallel electric and magnetic fields. To achieve this, Ps atoms were optically excited to n=2 sublevels in fields that were adjusted to control the amount of short-lived and long-lived character of the resulting mixed states. Inclusion of the former offers a practical approach to detection via annihilation radiation, whereas the increased lifetimes due to the latter can be exploited to optimize resonance-enhanced two-photon excitation processes (e.g., 1^{3}S→2^{3}P→nS/nD), either by minimizing losses through intermediate state decay, or by making it possible to separate the excitation laser pulses in time. In addition, photoexcitation of mixed states with a 2^{3}S_{1} component represents an efficient route to producing long-lived pure 2^{3}S_{1} atoms via single-photon excitation.

  2. Time-resolved nanosecond fluorescence lifetime imaging and picosecond infrared spectroscopy of combretastatin A-4 in solution and in cellular systems

    Science.gov (United States)

    Bisby, Roger H.; Botchway, Stanley W.; Greetham, Greg M.; Hadfield, John A.; McGown, Alan T.; Parker, Anthony W.; Scherer, Kathrin M.; Towrie, Mike

    2012-08-01

    Fluorescence lifetime images of intrinsic fluorescence obtained with two-photon excitation at 630 nm are shown following uptake of a series of E-combretastatins into live cells, including human umbilical vein endothelial cells (HUVECs) that are the target for the anticancer activity of combretastatins. Images show distribution of the compounds within the cell cytoplasm and in structures identified as lipid droplets by comparison with images obtained following Nile red staining of the same cells. The intracellular fluorescent lifetimes are generally longer than in fluid solution as a consequence of the high viscosity of the cellular environment. Following incubation, the intracellular concentrations of a fluorinated derivative of E-combretastatin A-4 in HUVECs are between two and three orders of magnitude higher than the concentration in the surrounding medium. Evidence is presented to indicate that at moderate laser powers (up to 6 mW), it is possible to isomerize up to 25% of the combretastatin within the femtolitre focal volume of the femtosecond laser beam. This suggests that it may be possible to activate the E-combretastatin (with low cellular toxicity) to the Z-isomer with high anticancer drug activity using two-photon irradiation. The isomerization of Z- and E-combretastatins by 266 nm irradiation has been probed by ultrafast time-resolved infrared spectroscopy. Results for the E-isomer show a rapid loss of excess vibrational energy in the excited state with a lifetime of 7 ps, followed by a slower process with a lifetime of 500 ps corresponding to the return to the ground state as also determined from the fluorescence lifetime. In contrast, the Z-isomer, whilst also appearing to undergo a rapid cooling of the initial excited state, has a much shorter overall excited state lifetime of 14 ps. DedicationThis paper is dedicated to the memory of Professor Christopher G Morgan (1949-2011). He was a valued colleague and friend at the University of Salford and made

  3. 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...

  4. Diabolo creation and annihilation.

    Science.gov (United States)

    Freund, Isaac; Soskin, Marat S; Egorov, Roman I; Denisenko, Vladimir

    2006-08-15

    A point of circular polarization embedded in a paraxial field of elliptical polarization is a polarization singularity called a C point. At such a point the major axis a and minor axis b of the ellipse become degenerate. Away from the C point this degeneracy is lifted such that surfaces a and b form nonanalytic cones that are joined at their apex (the C point) to produce a double cone called a diabolo. Typically, during propagation diabolo pairs are created or annihilated. We present rules based on geometry and topology that govern these events, provide initial experimental confirmation, and enumerate the allowed configurations in which diabolos can be created or annihilated.

  5. Excited-level lifetimes and hyperfine-structure measurements on ions using collinear laser--ion-beam spectroscopy

    International Nuclear Information System (INIS)

    Jin, J.; Church, D.A.

    1994-01-01

    The mean lifetimes τ of the Ca II 4p 2 P 1/2 and 4p 2 P 3/2 levels, and the 35 Cl II 4p' 1 F 3 level, have been measured by a variant of the collinear laser--ion-beam lifetime technique applied previously to the Ar II 4p' 2 F 7/2 o level [Jian Jin and D. A. Church, Phys. Rev. A 47, 132 (1993)]. The present results are τ(Ca II, 4p 2 P 1/2 )=7.098(0.020) ns, τ(Ca II, 4p 2 P 3/2 )=6.924(0.019) ns, and τ(Cl II, 4p' 1 F 3 ) =11.17(0.06) ns. The experimental lifetimes of these, plus the Ar II 4p' 2 F 7/2 level, are compared with available recent many-electron calculations. Typically 1%--3% differences between measurement and ab initio theory are found, while certain semiempirical calculations are in better agreement with experiment. Data for other precise lifetime measurements on alkali-metal systems are compared with recent ab initio and semiempirical calculations to provide perspective on the Ca II results. The hyperfine structure of the 35 Cl II 3d' 1 G 4 --4p' 1 F 3 transition was also measured and analyzed in the course of the measurements, with the resulting hyperfine-structure constants: A( 1 F 3 )=301.9(0.5) MHz, B( 1 F 3 )=-6.7(0.8) MHz, A( 1 G 4 )=205.1(0.5) MHz, and B( 1 G 4 )=-3.9(2.4) MHz

  6. 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)

  7. Positron annihilation processes update

    Science.gov (United States)

    Guessoum, Nidhal; Skibo, Jeffrey G.; Ramaty, Reuven

    1997-01-01

    The present knowledge concerning the positron annihilation processes is reviewed, with emphasis on the data of the cross sections of the various processes of interest in astrophysical applications. Recent results are presented including results on reaction rates and line widths, the validity of which is verified.

  8. Influence of substituents on positron annihilation in styrene copolymers

    International Nuclear Information System (INIS)

    Baranowski, A.; Debowska, M.; Jerie, K.; Rudzinska-Girulska, J.

    1995-01-01

    Results of angular correlation of annihilation radiation (ACAR) and positron annihilation lifetime (PAL) measurements are presented for five styrene copolymers: poly(co-styrene-phenylmaleimide) and its three derivatives with chlorine as well as for one with the OH group substituted at the benzene ring. It occurs that the chlorine substituted at three different positions at the benzene ring poly(co-styrene-o (or -m,-p)-chlorophenylmaleimide) inhibits the formation of the positronium to different extent. The greatest effect is observed in case of the chlorine atom substituted at the benzene ring at the ortho-position towards the nitrogen atom. The two long lifetime (τ 3 and τ 4 ) observed in the lifetime spectra are connected with the bimodal distributions of the free volume radius in the samples. (author) 13 refs.; 3 figs.; 3 tabs

  9. Positron annihilation characterization of Fe-Y2O3 composite powder after mechanical alloying and heat treatment.

    Science.gov (United States)

    Lee, Jae Hoon

    2012-02-01

    Fe-1 wt% Y2O3 composite powders were mechanically alloyed for 12 hr and then heat-treated at 1050 degrees C for 1 hr. Positron annihilation lifetime and coincidence Doppler broadening measurements are in qualitative agreement with X-ray diffraction studies, indicating that in the as-mixed Fe-1Y2O3 composite, up to approximately equal to 70% of the annihilations occur at vacancy clusters; a small fraction annihilates in its matrix. In the case of mechanically alloyed composite, up to approximately equal to 60% of the positrons annihilate at vacancy clusters. Some annihilations also occur in dislocations. In the heat-treated Fe-1Y2O3, positrons primarily annihilate at yttria precipitates, while a small fraction annihilates in the matrix.

  10. Fluorescence Lifetime Correlation Spectroscopy Reveals Compaction Mechanism of 10 and 49 kbp DNA and Differences between Polycation and Cationic Surfactant

    Czech Academy of Sciences Publication Activity Database

    Humpolíčková, Jana; Beranová, Lenka; Štěpánek, M.; Benda, Aleš; Procházka, K.; Hof, Martin

    2008-01-01

    Roč. 112, č. 51 (2008), s. 16823-16829 ISSN 1520-6106 R&D Projects: GA MŠk(CZ) LC06063; GA AV ČR IAA400400621 Institutional research plan: CEZ:AV0Z40400503 Keywords : fluorescence-correlation spectroscopy * DNA * AFM Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.189, year: 2008

  11. Positron Annihilation in the Undergraduate Laboratory

    Science.gov (United States)

    Engbrecht, Jason

    2017-04-01

    While there are a variety of undergraduate laboratory experiments in the literature, they tend to focus on specific positron experiments and use specialized equipment that limit their flexibility. Here we present a positron spectroscopy experimental apparatus designed for the undergraduate lab. Rather than specialized pulse processing the apparatus utilizes a PC oscilloscope as its primary data acquisition utility with pulse processing happening in software instead of hardware. This allows the apparatus to explore a variety of physical phenomena with the positron annihilation including material science, 2 and 3 gamma annihilation properties, polarimetry via Compton scattering, QED tests, and local hidden variable theories. The supporting software is flexible and allows students to pursue these experiments through exploration rather than simply supporting data acquisition. St. Olaf College.

  12. Positron Annihilation Study of Ion-irradiated Si

    International Nuclear Information System (INIS)

    Shin, Jung Ki; Kwon, Jun Hyun; Lee, Jong Yong

    2009-01-01

    Structural parts like a spaceship, satellite and solar cell are composed of metal alloy or semiconductor materials. Especially, Si is used as a primary candidate alloy. But, manned and robotic missions to the Earth's moon and Mars are exposed to a continuous flux of Galactic Cosmic Rays (GCR) and occasional, but intense, fluxes of Solar Energetic Particles. These natural radiations impose hazards to manned exploration. Irradiation of cosmic particle induces various changes in the mechanical and physical properties of device steels. It is, therefore, important to investigate radiation damage to the component materials in semiconductor. The evolution of radiation-induced defects leads to degradation of the mechanical properties. One of them includes irradiation embrittlement, which can cause a loss of ductility and further increase the probability of a brittle fracture. It can be more dangerous in the space. Positron annihilation lifetime spectroscopy(PALS) have been applied to investigate the production of vacancy-type defects for Ion-irradiated Si wafer penetrated by H, He, O and Fe ions. Then, we carried out a comparison with an un-irradiated Si wafer

  13. Bubble chamber: antiproton annihilation

    CERN Multimedia

    1971-01-01

    These images show real particle tracks from the annihilation of an antiproton in the 80 cm Saclay liquid hydrogen bubble chamber. A negative kaon and a neutral kaon are produced in this process, as well as a positive pion. The invention of bubble chambers in 1952 revolutionized the field of particle physics, allowing real tracks left by particles to be seen and photographed by expanding liquid that had been heated to boiling point.

  14. Lifetime, Mobility, and Diffusion of Photoexcited Carriers in Ligand-Exchanged PbSe Nanocrystal Films Measured by Time-Resolved Terahertz Spectroscopy

    Science.gov (United States)

    Li, Siming; Guglietta, Glenn; Wu, Yaoting; Gogotsi, Natalie; Murray, Christopher; Baxter, Jason

    Colloidal semiconductor nanocrystals have been used as building blocks for electronic and optoelectronic devices ranging from field effect transistors to solar cells. Properties of the nanocrystal films depend sensitively on the choice of capping ligand to replace the insulating synthesis ligands. Thus far, ligands leading to the best performance in transistors result in poor solar cell performance, and vice versa. To understand this dichotomy, we used time-resolved terahertz spectroscopy to study the mobility and lifetime of PbSe nanocrystal films with five common ligand-exchange reagents. The films treated with different displacing ligands show more than an order of magnitude difference in the peak conductivities and a bifurcation of time-dynamics. Inorganic chalcogenide ligand-exchanges with Na2S or NH4SCN show high mobilities but nearly complete decay of transient photocurrent in 1.4 ns. In contrast, ligand exchanges with EDA, EDT, and TBAI show lower mobilities but longer lifetimes, resulting in longer diffusion lengths. This bifurcated behavior may explain the divergent performance of field-effect transistors and photovoltaics constructed from nanocrystal building blocks with different ligand exchanges. Ref: Guglietta et al., ACS Nano, 2015. NSF

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

    International Nuclear Information System (INIS)

    He Chunqing; Muramatsu, Makoto; Ohdaira, Toshiyuki; Kinomura, Atsushi; Suzuki, Ryoichi; Ito, Kenji; Kabayashi, Yoshinori

    2006-01-01

    Positron annihilation lifetime spectra were measured for mesoporous silica films, which were synthesized using triblock copolymer (EO 106 PO 70 EO 106 ) 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

  16. Nuclear lifetimes

    International Nuclear Information System (INIS)

    Caraca, J.M.G.

    1976-01-01

    The importance of the results obtained in experiments of measurement of lifetimes for a detailed knowledge of nuclear structure is referred. Direct methods of measurement of nuclear lifetimes are described, namely, electronic methods, recoil-distance method, doppler shift atenuation method and blocking-method. A brief reference is made to indirect methods for measurement of life-times

  17. Positron annihilation studies on chalcone chromophore doped PVA

    Energy Technology Data Exchange (ETDEWEB)

    Bhajantri, R.F.; Ravindrachary, V.; Harisha, A.; Ismayil [Department of Physics, Mangalore University, Mangalagangotri (India); Ranganathaiah, C. [Department of Studies in Physics, University of Mysore, Manasagangotri (India)

    2009-11-15

    A novel organic non-linear optical material 1-(4-methylphenyl)-3-(4- N, N dimethyl amino phenyl)-2-propen-1-one (MPDMAPP) chalcone chromophore has been synthesized by standard method. Pure and MPDMAPP doped Poly(vinyl alcohol) films are prepared using solution casting method and characterized using UV-Visible absorption and Positron Annihilation Lifetime Spectroscopy. The optical spectroscopic study shows three absorption bands, 196-202 nm assigned to localized n {yields}{pi}* transitions, 205-320 nm to n {yields}{pi} inter-band and 385-428 nm assigned to {pi} {yields}{pi}* transition and arises due to the charge transfer complex. Using observed UV-Vis spectra, three optical energy gaps, E{sub g1} (4.96-4.25 eV), E{sub g2} (3.47-3.32 eV) and E{sub g3} (2.33-2.24 eV) have been estimated. The observed change in E{sub g} upon doping is understood based on the formation of charge transfer complex arising from the -HC=CH- structure present in the composite and due to the interactions of dopant and OH group of PVA. The PALS results shows that the o-Ps lifetime decreases continuously as doping concentration increases and I{sub 3} initially increases (from 18.82% to 20.95%) from 0 wt% to 0.05 wt% and then decreases gradually up to 16.76% for higher dopant concentrations with decrease in optical band gaps. The variation of positron data with E{sub g} is understood by correlating the probability of Ps formation with the complex. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Biological Effectiveness of Antiproton Annihilation

    DEFF Research Database (Denmark)

    Maggiore, C.; Agazaryan, N.; Bassler, N.

    2004-01-01

    from the annihilation of antiprotons produce an increase in ‘‘biological dose’’ in the vicinity of the narrow Bragg peak for antiprotons compared to protons. This experiment is the first direct measurement of the biological effects of antiproton annihilation. The background, description, and status...

  19. Lifetime measurements

    International Nuclear Information System (INIS)

    Fossan, D.B.; Warburton, E.K.

    1974-01-01

    Lifetime measurements are discussed, concentrating on the electronic technique, the recoil distance method (RDM), and the Doppler shift attenuation method (DSAM). A brief review of several indirect timing techniques is given, and their specific advantages and applicability are considered. The relationship between lifetimes of nuclear states and the nuclear structure information obtained from them is examined. A short discussion of channeling and microwave methods of lifetime measurement is presented. (23 figures, 171 references) (U.S.)

  20. Digital positron annihilation spectrometer

    International Nuclear Information System (INIS)

    Cheng Bin; Weng Huimin; Han Rongdian; Ye Bangjiao

    2010-01-01

    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)

  1. Brane annihilations during inflation

    International Nuclear Information System (INIS)

    Battefeld, Diana; Battefeld, Thorsten; Firouzjahi, Hassan; Khosravi, Nima

    2010-01-01

    We investigate brane inflation driven by two stacks of mobile branes in a throat. The stack closest to the bottom of the throat annihilates first with antibranes, resulting in particle production and a change of the equation of state parameter w. We calculate analytically some observable signatures of the collision; related decays are common in multi-field inflation, providing the motivation for this case study. The discontinuity in w enters the matching conditions relating perturbations in the remaining degree of freedom before and after the collision, affecting the power-spectrum of curvature perturbations. We find an oscillatory modulation of the power-spectrum for scales within the horizon at the time of the collision, and a slightly redder spectrum on super-horizon scales. We comment on implications for staggered inflation

  2. Diffuse galactic annihilation radiation

    Science.gov (United States)

    Ramaty, R.; Lingenfelter, R. E.

    1993-01-01

    The study reports observations of positron annihilation radiation from the inner region of the Galaxy which show that there are two components of the radiation: a steady, diffuse Galactic component and a variable component from discrete, presumably compact sources. The existence of the variable component is supported by the ensemble of all narrow FOV 511 keV line observations, including recent detections with OSSE. The fit of this ensemble to a time-independent source distribution can be excluded at the approximately 3-sigma level. The same ensemble, combined with the broad FOV SMM observations of Galactic 511 keV line emission, sets constraints on the Galactic distribution of the diffuse component.

  3. Positron annihilation in modified zeolites LTA and 13X

    Energy Technology Data Exchange (ETDEWEB)

    Cabral-Prieto, A.; Garcia-Sosa, I.; Jimenez-Becerril, J. [Departamento de Quimica, Instituto Nacional de Investigaciones Nucleares, Apartado Postal 18-1027, Col. Escandon, Del. M. Hidalgo, Mexico D. F., c. p. 11801 (Mexico); Lopez-Castanares, R.; Olea-Cardoso, O. [Facultad de Quimica, Universidad Autonoma del Estado de Mexico, Paseo Tollocan esquina paseo Tollocan, esquina paseo Colon, Toluca, c. p. 50120, Estado de Mexico (Mexico)

    2007-07-01

    The pick-off annihilation lifetimes of o -Ps, {tau}{sub po}, in dehydrated Co{sup 2+} and Mn{sup 2+} exchanged zeolites LTA, in dehydrated Co{sup 2+} exchanged zeolite 13X, and in dehydrated Na{sup +} zeolites LTA and 13X, are estimated. Although {tau}{sub po} can be estimated from the lifetime spectra of the cation exchanged zeolites LTA and 13X, this lifetime can not be estimated from those spectra of Na{sup +} zeolite LTA unambiguously. The estimated pick-off lifetimes due to the annihilation of o-Ps in the internal walls of the zeolites are systematically lower than the average lifetime of p-Ps and o-Ps in vacuum {tau}{sub a}=0.5 ns. Since the pick-off process of o-Ps occurs particularly on the internal cavity walls of dehydrated zeolites, the replacement of {tau}{sub a} by {tau}{sub po} within the classical model of Tao-Eldrup to calculate cavity radius should provide more realistic cavity radii of these porous materials than when using {l_brace}{tau}{sub a}{r_brace}. This suggestion is supported by previous and present results. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Positron Annihilation Lifetime Studies of Deformed and Shock Loaded Tantalum

    National Research Council Canada - National Science Library

    Stepp, David

    1999-01-01

    .... The authors conclude that these results support the theory that deformation in tantalum is controlled by dislocation drag above the Peierls stress and that strain rate effects, which are dearly...

  5. Free volume study on the miscibility of PEEK/PEI blend using positron annihilation and dynamic mechanical thermal analysis

    International Nuclear Information System (INIS)

    Ramani, R; Alam, S

    2015-01-01

    High performance polymer blend of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) was examined for their free volume behaviour using positron annihilation lifetime spectroscopy and dynamic mechanical thermal analysis methods. The fractional free volume obtained from PALS shows a negative deviation from linear additivity rule implying good miscibility between PEEK and PEI. The dynamic modulus and loss tangent were obtained for the blends at three different frequencies 1, 10 and 100 Hz at temperatures close to and above their glass transition temperature. Applying Time-Temperature-Superposition (TTS) principle to the DMTA results, master curves were obtained at a reference temperature T o and the WLF coefficients c 0 1 and c 0 2 were evaluated. Both the methods give similar results for the dependence of fractional free volume on PEI content in this blend. The results reveal that free volume plays an important role in determining the visco-elastic properties in miscible polymer blends. (paper)

  6. Singlet-triplet annihilation in single LHCII complexes.

    Science.gov (United States)

    Gruber, J Michael; Chmeliov, Jevgenij; Krüger, Tjaart P J; Valkunas, Leonas; van Grondelle, Rienk

    2015-08-14

    In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states and therefore avoid the production of harmful singlet oxygen. The resulting Car triplet states lead to a non-linear self-quenching mechanism called singlet-triplet (S-T) annihilation that strongly depends on the excitation density. In this work we investigated the fluorescence decay kinetics of single immobilized LHCIIs at room temperature and found a two-exponential decay with a slow (3.5 ns) and a fast (35 ps) component. The relative amplitude fraction of the fast component increases with increasing excitation intensity, and the resulting decrease in the fluorescence quantum yield suggests annihilation effects. Modulation of the excitation pattern by means of an acousto-optic modulator (AOM) furthermore allowed us to resolve the time-dependent accumulation and decay rate (∼7 μs) of the quenching species. Inspired by singlet-singlet (S-S) annihilation studies, we developed a stochastic model and then successfully applied it to describe and explain all the experimentally observed steady-state and time-dependent kinetics. That allowed us to distinctively identify the quenching mechanism as S-T annihilation. Quantitative fitting resulted in a conclusive set of parameters validating our interpretation of the experimental results. The obtained stochastic model can be generalized to describe S-T annihilation in small molecular aggregates where the equilibration time of excitations is much faster than the annihilation-free singlet excited state lifetime.

  7. Studies of Phase Transformation in Molecular Crystals Using the Positron Annihilation Technique

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Lightbody, David; Sherwood, John N.

    1980-01-01

    An examination has been made of the brittle/plastic phase transformation in the molecular crystals cyclohexane, DL-camphene and succinonitrile using the positron annihilation technique. In each material, the transition is characterized by a distinct increase in ortho-positronium lifetime. The inf......An examination has been made of the brittle/plastic phase transformation in the molecular crystals cyclohexane, DL-camphene and succinonitrile using the positron annihilation technique. In each material, the transition is characterized by a distinct increase in ortho-positronium lifetime...

  8. Charge recombination and exciton annihilation reactions in conjugated polymer blends.

    Science.gov (United States)

    Howard, Ian A; Hodgkiss, Justin M; Zhang, Xinping; Kirov, Kiril R; Bronstein, Hugo A; Williams, Charlotte K; Friend, Richard H; Westenhoff, Sebastian; Greenham, Neil C

    2010-01-13

    Bimolecular interactions between excitations in conjugated polymer thin films are important because they influence the efficiency of many optoelectronic devices that require high excitation densities. Using time-resolved optical spectroscopy, we measure the bimolecular interactions of charges, singlet excitons, and triplet excitons in intimately mixed polyfluorene blends with band-edge offsets optimized for photoinduced electron transfer. Bimolecular charge recombination and triplet-triplet annihilation are negligible, but exciton-charge interactions are efficient. The annihilation of singlet excitons by charges occurs on picosecond time-scales and reaches a rate equivalent to that of charge transfer. Triplet exciton annihilation by charges occurs on nanosecond time-scales. The surprising absence of nongeminate charge recombination is shown to be due to the limited mobility of charge carriers at the heterojunction. Therefore, extremely high densities of charge pairs can be maintained in the blend. The absence of triplet-triplet annihilation is a consequence of restricted triplet diffusion in the blend morphology. We suggest that the rate and nature of bimolecular interactions are determined by the stochastic excitation distribution in the polymer blend and the limited connectivity between the polymer domains. A model based on these assumptions quantitatively explains the effects. Our findings provide a comprehensive framework for understanding bimolecular recombination and annihilation processes in nanostructured materials.

  9. Positron annihilation in superconductive metals

    Energy Technology Data Exchange (ETDEWEB)

    Dekhtjar, I.J.

    1969-03-10

    A correlation is shown between the parameters of superconductive metals and those of positron annihilation. Particular attention is paid to the density states obtained from the electron specific heat.

  10. Annihilation in Gases and Galaxies

    Science.gov (United States)

    Drachman, Richard J. (Editor)

    1990-01-01

    This publication contains most of the papers, both invited and contributed, that were presented at the Workshop of Annihilation in Gases and Galaxies. This was the fifth in a biennial series associated with the International Conference on the Physics of Electronic and Atomic Collisions. Subjects covered included the scattering and annihilation of positrons and positronium atoms in various media, including those of astrophysical interest. In addition, the topics of antimatter and dark matter were covered.

  11. ATHENA: an actual antihydrogen annihilation

    CERN Document Server

    2002-01-01

    This is an image of an actual matter-antimatter annihilation due to an atom of antihydrogen in the ATHENA experiment, located on the Antiproton Decelerator (AD) at CERN since 2001. The antiproton produces four charged pions (yellow) whose positions are given by silicon microstrips (pink) before depositing energy in CsI crystals (yellow cubes). The positron also annihilates to produce back-to-back gamma rays (red).

  12. Positron annihilation characteristics, water uptake and proton conductivity of composite Nafion membranes.

    Science.gov (United States)

    Yin, Chongshan; Wang, Lingtao; Li, Jingjing; Zhou, Yawei; Zhang, Haining; Fang, Pengfei; He, Chunqing

    2017-06-21

    The free volumes and proton conductivities of Nafion membranes were investigated at different humidities by positron annihilation lifetime spectroscopy (PALS) and using an electrochemical workstation, respectively. The results showed that the variation in o-Ps lifetime τ o-Ps was closely associated with the microstructure evolution and the development of hydrophilic ion clusters in Nafion membranes as a function of water uptake, regardless of metal oxide additives. In particular, with increasing relative humidity, the maximum value of τ o-Ps in the Nafion membranes corresponded to the formation of numerous water channels for proton transportation. Numerous well-connected water channels in Nafion-TiO 2 hybrid membranes could be formed at a much lower relative humidity (∼40% RH) than in the pristine one (∼75% RH), due to the better water retention ability of the Nafion-TiO 2 membranes. Further, a percolation behavior of proton conductivity at high water uptake in Nafion membranes was observed, which showed that the percolation of ionic-water clusters occurred at the water uptake of ∼4.5 wt%, and ∼6 wt% was basically enough for the formation of a well-connected water channel network.

  13. Evaluation of the reactor pressure vessel steels by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Slugeň, V., E-mail: Vladimir.Slugen@elf.stuba.sk [Institute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovičova 3, 81219 Bratislava (Slovakia); Hein, H. [AREVA NP GmbH, Paul Gossen Strasse 100, 91 001 Erlangen (Germany); Sojak, S.; Simeg Veterníková, J.; Petriska, M.; Sabelová, V.; Pavúk, M.; Hinca, R.; Stacho, M. [Institute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovičova 3, 81219 Bratislava (Slovakia)

    2013-11-15

    This paper presents a comparison of commercially used German and Russian reactor pressure vessel steels from the positron annihilation spectroscopy (PAS) point of view, having in mind knowledge obtained also from other techniques from the last decades. The second generation of Russian RPV steels seems to be fully comparable with German steels and their quality allows prolongation of NPP operating lifetime over projected 40 years. The embrittlement of CrMoV steels is relatively low due to effect of higher temperature which implies partial in situ annealing of primary microstructural point defects and therefore delays the degradation processes caused by neutron irradiation. PAS techniques can be effectively applied for evaluation of microstructural changes caused by extreme external loads (characterized by high dpa values) by proton implantation, with aim to simulate irradiation and for the evaluation of the effectiveness of post-irradiation thermal treatments. We used our actual and previous results, collected during last 20 years from measurements of different RPV-steels in “as received”, irradiated and post-irradiation annealed state and compare them with the aim to contribute to general knowledge based on experimental PAS data. Actual results from irradiated German and Russian steels confirmed that no large voids or vacancy clusters were formed at defined irradiation conditions stated according to the real operational conditions at nuclear power plants. This indicate the fact that vacancy type defects bear hardly any responsibility for radiation-induced hardening and embrittlement of reactor pressure vessel steels and does not affect significantly the long-term operation of nuclear power plants from safety point of view.

  14. Glass transition and relaxation processes of polymers studied by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Uedono, Akira; Tanigawa, Shoichiro [Tsukuba Univ., Ibaraki (Japan). Inst. of Materials Science

    1996-10-01

    The glass transition and relaxation processes of polymers were studied by the positron annihilation technique. A positron implanted into polymers might annihilate from positronium (Ps) states in open spaces. Ps is a bound state between a positron and an electron, and its nonrelativistic quantum mechanics is practically identical to that of a hydrogen atom. The lifetime of Ps can be associated with the size of the open spaces, and the formation probability of Ps provides information of motions of molecules. Since the glass transition or relaxation processes affect behavior of open spaces, one can study these phenomena through the detection of the open spaces using the positron annihilation technique. In the present paper, we report studies of the glass transition and relaxation processes in polyethylene, polypropylene, and polystyrene by measurements of lifetime spectra of positrons and those of Doppler broadening profiles of the annihilation radiation. For these specimens, by measurements of the lifetime of Ps, {tau}{sub 3}, as a function of temperature, the glass transition temperature, T{sub g}, was determined as an onset temperature of the increase in the temperature coefficient of {tau}{sub 3}. Below T{sub g}, local motions of molecules were detected by measurements of the formation probability of Ps. The positron annihilation as a tool for the characterization of polymers was discussed. (author). 51 refs.

  15. Annihilation vs. Decay: Constraining dark matter properties from a gamma-ray detection

    CERN Document Server

    Palomares-Ruiz, Sergio

    2010-01-01

    Most proposed dark matter candidates are stable and are produced thermally in the early Universe. However, there is also the possibility of unstable (but long-lived) dark matter, produced thermally or otherwise. We propose a strategy to distinguish between dark matter annihilation and/or decay in the case that a clear signal is detected in gamma-ray observations of Milky Way dwarf spheroidal galaxies with current or future gamma-ray experiments. The sole measurement of the energy spectrum of an indirect signal would render the discrimination between these cases impossible. We show that by examining the dependence of the intensity and energy spectrum on the angular distribution of the emission, the origin could be identified as decay, annihilation, or both. In addition, once the type of signal is established, we show how these measurements could help to extract information about the dark matter properties, including mass, annihilation cross section, lifetime, dominant annihilation and decay channels, and the p...

  16. Positron annihilation in pivalic acid. Temperature dependence of angular correlation curves

    DEFF Research Database (Denmark)

    Jain, P. C.; Eldrup, Morten Mostgaard; Pedersen, Niels Jørgen

    1986-01-01

    Positron annihilation angular correlation curves have been measured as a function of temperature for trimethylacetic (pivalic) acid in both the brittle and plastic phases. A simple fitting of the data to a sum of three gaussians shows the presence of a narrow component due to para-positronium (p......-Ps) annihilation. In the brittle phase the intensity of the narrow component is inconsistent with previous positron lifetime data. A more detailed analysis, requiring consistency with the lifetime data, results in the determination of the shapes of the angular correlation components for free positron-, pick......-off-, and p-Ps intrinsic annihilation. The p-Ps component has a width (fwhm) of 3.75 mrad in the brittle phase, probably due to Ps self-trapping or trapping in defects smaller than molecular vacancies. In the plastic phase the width (fwhm) is 3.25 mrad which is ascribed to Ps localization in vacancies...

  17. Study on the effect of atmospheric gases adsorbed in MnFe2O4/MCM-41 nanocomposite on ortho-positronium annihilation

    Directory of Open Access Journals (Sweden)

    Wiertel Marek

    2015-12-01

    Full Text Available In this paper, results of positron annihilation lifetime spectroscopy (PALS studies of MnFe2O4/MCM-41 nanocomposites in N2 and O2 atmosphere have been presented. In particular, the influence of manganese ferrite loading and gas filling on pick-off ortho-positronium (o-Ps annihilation processes in the investigated samples was a point of interest. Disappearance of the longest-lived o-Ps component with τ5 present in the PAL spectrum of initial MCM-41 mesoporous material in the PAL spectra of MnFe2O4-impregnated MCM-41 measured in vacuum is a result of either a strong chemical o-Ps quenching or the Ps inhibition effects. The intensity I4 of the medium-lived component initially increases, reaching a maximum value for the sample with minimum manganese ferrite content, and then decreases monotonically. Analogous dependence for the intensity I3 of the shortest-lived component shows a maximum at higher MnFe2O4 content. Filling of open pores present in the studied nanocomposites by N2 or O2 at ambient pressure causes partial reappearance of the τ4 and τ5 components, except a sample with maximum ferrite content. The lifetimes of these components measured in O2 are shortened in comparison to that observed in N2 because of paramagnetic quenching. Anti-inhibition and anti-quenching effects of atmospheric gases observed in the MnFe2O4/MCM-41 samples are a result of neutralization of some surface active centers acting as inhibitors and weakening of pick-off annihilation mechanism, respectively.

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

    International Nuclear Information System (INIS)

    Balogh, A.G.; Liszkay, L.; Molnar, B.; Puff, W.

    1987-08-01

    First positron annihilation measurements are reported on high T c superconductor YBa 2 Cu 3 O 7-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)

  19. A Positron Annihilation Study of Copper Containing a High Concentration of Krypton

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Evans, John H.

    1982-01-01

    Bulk Cu samples containing up to 4 at.% Kr have been produced by the Harwell combined ion implantation and sputtering method at temperatures near ambient, and then examined by the positron annihilation technique. Both angular correlation and lifetime measurements were made and, in addition...

  20. Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, Hal

    1968-01-01

    This booklet discusses spectroscopy, the study of absorption of radiation by matter, including X-ray, gamma-ray, microwave, mass spectroscopy, as well as others. Spectroscopy has produced more fundamental information to the study of the detailed structure of matter than any other tools.

  1. Biological effectiveness of antiproton annihilation

    CERN Document Server

    Holzscheiter, Michael H.; Bassler, Niels; Beyer, Gerd; De Marco, John J.; Doser, Michael; Ichioka, Toshiyasu; Iwamoto, Keisuke S.; Knudsen, Helge V.; Landua, Rolf; Maggiore, Carl; McBride, William H.; Møller, Søren Pape; Petersen, Jorgen; Smathers, James B.; Skarsgard, Lloyd D.; Solberg, Timothy D.; Uggerhøj, Ulrik I.; Withers, H.Rodney; Vranjes, Sanja; Wong, Michelle; Wouters, Bradly G.

    2004-01-01

    We describe an experiment designed to determine whether or not the densely ionizing particles emanating from the annihilation of antiprotons produce an increase in “biological dose” in the vicinity of the narrow Bragg peak for antiprotons compared to protons. This experiment is the first direct measurement of the biological effects of antiproton annihilation. The experiment has been approved by the CERN Research Board for running at the CERN Antiproton Decelerator (AD) as AD-4/ACE (Antiproton Cell Experiment) and has begun data taking in June of 2003. The background, description and the current status of the experiment are given.

  2. Biological effectiveness of antiproton annihilation

    DEFF Research Database (Denmark)

    Holzscheiter, M.H.; Agazaryan, N.; Bassler, Niels

    2004-01-01

    We describe an experiment designed to determine whether or not the densely ionizing particles emanating from the annihilation of antiprotons produce an increase in ‘‘biological dose’’ in the vicinity of the narrow Bragg peak for antiprotons compared to protons. This experiment is the first direct...... measurement of the biological effects of antiproton annihilation. The experiment has been approved by the CERN Research Board for running at the CERN Antiproton Decelerator (AD) as AD-4/ACE (Antiproton Cell Experiment) and has begun data taking in June of 2003. The background, description and the current...

  3. Spectroscopy

    CERN Document Server

    Walker, S

    1976-01-01

    The three volumes of Spectroscopy constitute the one comprehensive text available on the principles, practice and applications of spectroscopy. By giving full accounts of those spectroscopic techniques only recently introduced into student courses - such as Mössbauer spectroscopy and photoelectron spectroscopy - in addition to those techniques long recognised as being essential in chemistry teaching - sucha as e.s.r. and infrared spectroscopy - the book caters for the complete requirements of undergraduate students and at the same time provides a sound introduction to special topics for graduate students.

  4. Determination of the average lifetime of bottom hadrons

    International Nuclear Information System (INIS)

    Althoff, M.; Braunschweig, W.; Kirschfink, F.J.; Martyn, H.U.; Rosskamp, P.; Schmitz, D.; Siebke, H.; Wallraff, W.; Hilger, E.; Kracht, T.; Krasemann, H.L.; Leu, P.; Lohrmann, E.; Pandoulas, D.; Poelz, G.; Poesnecker, K.U.; Duchovni, E.; Eisenberg, Y.; Karshon, U.; Mikenberg, G.; Mir, R.; Revel, D.; Shapira, A.; Baranko, G.; Caldwell, A.; Cherney, M.; Izen, J.M.; Mermikides, M.; Ritz, S.; Rudolph, G.; Strom, D.; Takashima, M.; Venkataramania, H.; Wicklund, E.; Wu, S.L.; Zobernig, G.

    1984-01-01

    We have determined the average lifetime of hadrons containing b quarks produced in e + e - annihilation to be tausub(B)=1.83x10 -12 s. Our method uses charged decay products from both non-leptonic and semileptonic decay modes. (orig./HSI)

  5. 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

    A comparison of the results of a series of positron annihilation lifetime measurements performed in 12 laboratories is presented. The measurements were conducted on three different polymer samples, all prepared in one laboratory under standard conditions. The objective of the work was to gain...

  6. Positron annihilation near fractal surfaces

    International Nuclear Information System (INIS)

    Lung, C.W.; Deng, K.M.; Xiong, L.Y.

    1991-07-01

    A model for positron annihilation in the sub-surface region near a fractal surface is proposed. It is found that the power law relationship between the mean positron implantation depth and incident positron energy can be used to measure the fractal dimension of the fractal surface in materials. (author). 10 refs, 2 figs

  7. Selection Rule for Enhanced Dark Matter Annihilation.

    Science.gov (United States)

    Das, Anirban; Dasgupta, Basudeb

    2017-06-23

    We point out a selection rule for enhancement (suppression) of odd (even) partial waves of dark matter coannihilation or annihilation using the Sommerfeld effect. Using this, the usually velocity-suppressed p-wave annihilation can dominate the annihilation signals in the present Universe. The selection mechanism is a manifestation of the exchange symmetry of identical incoming particles, and generic for multistate DM with off-diagonal long-range interactions. As a consequence, the relic and late-time annihilation rates are parametrically different and a distinctive phenomenology, with large but strongly velocity-dependent annihilation rates, is predicted.

  8. Characterization of dynamics in complex lyophilized formulations: II. Analysis of density variations in terms of glass dynamics and comparisons with global mobility, fast dynamics, and Positron Annihilation Lifetime Spectroscopy (PALS)

    Science.gov (United States)

    Chieng, Norman; Cicerone, Marcus T.; Zhong, Qin; Liu, Ming; Pikal, Michael J.

    2013-01-01

    Amorphous HES/disaccharide (trehalose or sucrose) formulations, with and without added polyols (glycerol and sorbitol) and disaccharide formulations of human growth hormone (hGH), were prepared by freeze drying and characterized with particular interest in methodology for using high precision density measurements to evaluate free volume changes and a focus on comparisons between “free volume” changes obtained from analysis of density data, fast dynamics (local mobility), and PALS characterization of “free volume” hole size. Density measurements were performed using a helium gas pycnometer, and fast dynamics was characterized using incoherent neutron scattering spectrometer. Addition of sucrose and trehalose to hGH decreases free volume in the system with sucrose marginally more effective than trehalose, consistent with superior pharmaceutical stability of sucrose hGH formulations well below Tg relative to trehalose. We find that density data may be analyzed in terms of free volume changes by evaluation of volume changes on mixing and calculation of apparent specific volumes from the densities. Addition of sucrose to HES decreases free volume, but the effect of trehalose is not detectable above experimental error. Addition of sorbitol or glycerol to HES/trehalose base formulations appears to significantly decrease free volume, consistent with the positive impact of such additions on pharmaceutical stability (i.e., degradation) in the glassy state. Free volume changes, evaluated from density data, fast dynamics amplitude of local motion, and PALS hole size data generally are in qualitative agreement for the HES/disaccharide systems studied. All predict decreasing molecular mobility as disaccharides are added to HES. Global mobility as measured by enthalpy relaxation times, increases as disaccharides, particularly sucrose, are added to HES. PMID:23623797

  9. Characterization of dynamics in complex lyophilized formulations: II. Analysis of density variations in terms of glass dynamics and comparisons with global mobility, fast dynamics, and Positron Annihilation Lifetime Spectroscopy (PALS).

    Science.gov (United States)

    Chieng, Norman; Cicerone, Marcus T; Zhong, Qin; Liu, Ming; Pikal, Michael J

    2013-10-01

    Amorphous HES/disaccharide (trehalose or sucrose) formulations, with and without added polyols (glycerol and sorbitol) and disaccharide formulations of human growth hormone (hGH), were prepared by freeze drying and characterized with particular interest in methodology for using high precision density measurements to evaluate free volume changes and a focus on comparisons between "free volume" changes obtained from analysis of density data, fast dynamics (local mobility), and PALS characterization of "free volume" hole size. Density measurements were performed using a helium gas pycnometer, and fast dynamics was characterized using incoherent neutron scattering spectrometer. Addition of sucrose and trehalose to hGH decreases free volume in the system with sucrose marginally more effective than trehalose, consistent with superior pharmaceutical stability of sucrose hGH formulations well below Tg relative to trehalose. We find that density data may be analyzed in terms of free volume changes by evaluation of volume changes on mixing and calculation of apparent specific volumes from the densities. Addition of sucrose to HES decreases free volume, but the effect of trehalose is not detectable above experimental error. Addition of sorbitol or glycerol to HES/trehalose base formulations appears to significantly decrease free volume, consistent with the positive impact of such additions on pharmaceutical stability (i.e., degradation) in the glassy state. Free volume changes, evaluated from density data, fast dynamics amplitude of local motion, and PALS hole size data generally are in qualitative agreement for the HES/disaccharide systems studied. All predict decreasing molecular mobility as disaccharides are added to HES. Global mobility as measured by enthalpy relaxation times, increases as disaccharides, particularly sucrose, are added to HES. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. Characterization of dynamics in complex lyophilized formulations: II. Analysis of density variations in terms of glass dynamics and comparisons with global mobility, fast dynamics, and Positron Annihilation Lifetime Spectroscopy (PALS)

    OpenAIRE

    Chieng, Norman; Cicerone, Marcus T.; Zhong, Qin; Liu, Ming; Pikal, Michael J.

    2013-01-01

    Amorphous HES/disaccharide (trehalose or sucrose) formulations, with and without added polyols (glycerol and sorbitol) and disaccharide formulations of human growth hormone (hGH), were prepared by freeze drying and characterized with particular interest in methodology for using high precision density measurements to evaluate free volume changes and a focus on comparisons between “free volume” changes obtained from analysis of density data, fast dynamics (local mobility), and PALS characteriza...

  11. Absorbed dose in polymers during a positron annihilation experiment

    International Nuclear Information System (INIS)

    Suzuki, T.; Namito, Y.; Oki, Y.; Numajiri, M.; Miura, T.; Hirayama, H.; Kondo, K.; Ito, Y.

    1994-01-01

    A positron annihilation lifetime (PAL) technique has been recognized as being a useful method to study the characteristics of polymers. However, radiation effects due to positrons used as a probe have been raised as being a problem, since positrons emitted from 22 Na have sufficient energy to induce radiation damage in polymers. In this study, the radiation dose induced by positrons emitted from 22 Na was estimated for such polymers like polyethylenes and polypropylenes using the EGS4 code. The radiation damage during PAL measurements is also discussed. It has been shown that the calculated dose is consistent with that estimated from an empirical equation of the mass-attenuation coefficient. (author)

  12. Study of the ortho-positron annihilation process in zeolite Y

    International Nuclear Information System (INIS)

    Alvarado D, M. E.

    2010-01-01

    For several years a great interest has existed for the study of the natural and synthetic zeolites due to its properties. The porosity, one of their main characteristics allows that these materials are used as molecular sieves, catalysts, gases drying, etc. In order to investigating the porosity and other zeolite properties one carries out the study of the process of positron annihilation lifetime spectroscopy (Pals). This is a technique that provides information about the size and the pores form since is highly sensitive to the free volume and the superficial area of those porous materials as the zeolites. The study began with the elaboration of zeolite Y tablets in a hydraulic press where different pressures (from 0 to 1.26 GPa) and masses (70, 80 and 100 mg) were proven to obtain the estimate porosity of each tablet. A graph was elaborated and the effect of the mass and pressure with regard to the zeolite porosity was analyzed. Later on, the powder and tablets of 70 mg were characterized by means of X-ray diffraction (the glass size, interplanar distance, length and the volume of the unitary cell); scanning electron microscopy (the particles size and morphology); thermo gravimetric analysis (dehydration temperature and the stability up to 700 C) and the Brunauer Emmett Teller method (specific area). After the zeolite Y tablets characterization was carried out the positron annihilation process by means of Pals where its free volume of zeolite Y was analyzed, which includes to the structural cavities and the interparticle volume. The powdered zeolite was analyzed to different experimental conditions (preparation of the sample and the Pals equipment) to obtain the optimal conditions (a window with a time of 400 ns and a enlarged energy window) of analysis. On the other hand, the tablets were analyzed under optimal conditions to obtain the four components of time and intensity (τ, Ι), result of the different ways of positrons annihilation in the zeolite. These

  13. Positron annihilation in solids: positronium diffusion; Annihilation du positon dans les solides diffusion du positonium

    Energy Technology Data Exchange (ETDEWEB)

    Paulin, R. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1969-04-01

    The existence of two slow components in life-time spectrum of positron annihilation in silicium, aluminium and alkaline-earth oxides powders is established. These two long mean-lives {approx_equal} 10{sup -9} s and {approx_equal} 10{sup -7} s result from annihilation, inside and outside the grains respectively, of ortho-positronium formed in defects present in ionic crystals investigated. Dynamic behaviour of Ps, so revealed, is analyzed in terms of diffusion in excellent agreement with experiment. Diffusion constants of the order of 10{sup -4} cm{sup 2} sec{sup -1} and mean path before annihilation from 50 to 300 Angstrom are measured. From 100 to 500 K the temperature influence upon diffusion process is effective only in SiO{sub 2} where activation energy is found about 10{sup -2} eV. The p-Ps zero point energy evaluated by angular correlation gives the order of magnitude for defects dimensions and diffusion mean-time. Finally, o-Ps behaviour in space between grains, where its interaction with atmospheric gases can be only detected, is analysed. (author) [French] Nous mettons en evidence l'existence de deux composantes lentes dans le spectre de temps de vie du positon avant annihilation dans des poudres d'oxydes alcalinoterreux d'alumine et de silice. Ces deux longues vies moyennes {approx_equal} 10{sup -9} s et {approx_equal} 10{sup -7} s resultent respectivement de l'annihilation a l'interieur et a l'exterieur des grains de l'ortho-positonium forme dans certains defauts presents dans les cristaux ioniques etudies. L'analyse des proprietes dynamiques du Ps ainsi revelees, est effectuee en termes de diffusion en excellent accord avec l'experience. Des constantes de diffusion de l'ordre de 10{sup -4} cm{sup 2} sec{sup -1} et des parcours moyens avant annihilation variant de 50 a 300 Angstrom sont ainsi mesures. Entre 100 et 500 K l'influence de la temperature sur le processus de diffusion n'est sensible

  14. High sensitivity of positron annihilation to thermal oxidation of polyethylene

    Science.gov (United States)

    Ito, Kenji; Kobayashi, Yoshinori; Nanasawa, Atsushi

    2003-01-01

    We demonstrate the high sensitivity of positron annihilation to compositional changes related to the thermal degradation of polyethylene (PE). Positron annihilation γ-ray and lifetime measurements were conducted for PE films with and without antioxidant (1000-ppm Ciba® IRGANOX® 1076), subjected to heat treatment at 100 °C for different periods, to a maximum of 30 days. For the film without antioxidant, the positron Doppler parameter (S) and ortho-positronium formation probability (Io-Ps) appreciably decreased with increased heat treatment times, whereas they barely changed for the film with antioxidant. This, together with the Fourier transform infrared measurements, demonstrated that the variations of S and Io-Ps are caused by the thermal oxidation of PE. The S parameter was found to be sensitive to the early stage of degradation, where the carbonyl concentration is inferred to be lower than 100 ppm. The high sensitivity results from the large positron mobility in PE and from the high positron affinity of oxygen-containing polar groups. This work provides the basis for an application of positron annihilation to sensitive detection of the initial degradation of PE and other nonpolar polymers.

  15. Determination of the solubility of neodymium in iron by positron annihilation

    International Nuclear Information System (INIS)

    Yu, W.Y.; Qing, L.N.; Zhuo, T.Z.; Rong, C.X.

    1985-01-01

    The authors have measured the lineshape parameters and lifetimes of positron annihilation in eleven samples of iron containing various concentration of Nd between 0 and 0.87 wt. %, which have been heat-treated at two different temperatures successively. According to the abrupt increase, for the two conditions of heat-treatment the solubility of Nd in iron is interpreted to be 0.082 wt. % and 0.088 wt. % respectively. Using positron annihilation technique for determining the solubility of Nd in iron appears to be more sensitive and accurate than metallography method and X-ray diffraction analysis

  16. Lifetime learning and lifetime education

    Directory of Open Access Journals (Sweden)

    Aljana Lepšina

    2008-12-01

    Full Text Available Effective education and lifetime learning are becoming a key to competitive, knowledge-based economy. Our country is at present, such as other European countries facing new approaches and developments in the area of education along with changes and difficulties. Third-level is known for an increased number of students, weak financial backing of universities, initial difficulties with Bologna Agreement and increased competitiveness in Europe. It is necessary to improve the education quality, encourage life-long learning and increase investments into research and development.

  17. Positron Lifetime as a Nano probe for Free Volume in Microbial Poly(3- Hydroxybutyrate/ Polymethylmethacrylate) Blends

    International Nuclear Information System (INIS)

    Abdel-Hady, E.E.; Abdel-El-Latif, R.M.; Mohamed, S.S.

    2009-01-01

    Poly(β-hydroxybutyrate) PHB is a bio technologically produced polyesters, highly crystalline, totally biodegradable with low versatility in mechanical properties. To overcome this problem it is performed a reactive blending producer with a glassy acrylic polymer, Poly(methylmethacrylate) (PMMA) with different concentrations. positron annihilation lifetime (PAL) spectroscopy has been used to study the effect of PMMA concentrations on the free volume hole properties of PHB. PAL spectra were analyzed using PALSF it program into three components which reflected three different morphologies of the polymer structure. The ortho positronium (ο-Ps) parameters revealed an inflection at (75/25 wt/wt) PHB/PMMA blend. Pure PHB and (75/25 wt/wt) PHB/PMMA blend have been measured as a function of temperature from -30 degree C to 90 degree C. The data clearly revealed the glass transition temperature (T g ) at zero degree C. An attempt is done to find a correlation between the electrical properties of PHB with different concentrations of PMMA and the positron annihilation parameters.

  18. Positron annihilation method for α self radiation effect studies in doped actinide UO2 samples

    International Nuclear Information System (INIS)

    Roudil, D.; Vella, F.; Bonnal, M.; Broudic, V.; Barthe, M.F.; Gentils, A.; Moineau, V.; Jolly, L.

    2008-01-01

    Towards disposal problematic, fine understanding of the α aging of UO 2 and (U, Pu)O 2 remains a fundamental challenge for the prediction of the potential increase of the radionuclide source terms with presence of water. The intrinsic evolution of the matrix is closely related to the behavior of radiogenic helium produced by actinide decay. Interactions between helium atoms and vacancy defects are involved in these mechanisms. Positron Annihilation Spectroscopy is also an appropriated method owing to its sensitivity to the vacancy type defects in solid materials. It is a non destructive technique with a remote acquiring data possibility. Because positron implanted in the material is sensitive to the electronic density, the positron lifetime method allows the characterization of the vacancy defects, namely size and concentration. Such equipment has been implemented in the L30 laboratory of the DHA facility in Atalante and will be applied on doped actinides samples, simulating α aging. This article presents, the analytical protocols and validation results on depleted UO 2 samples and highlights the perspectives on (U, Pu)O 2 for the investigation of different stages of self irradiation matrices and helium behavior. (authors)

  19. Antinucleon-nucleon annihilation dynamics

    International Nuclear Information System (INIS)

    Myhrer, F.; Massachusetts Inst. of Tech., Cambridge

    1989-01-01

    The antinucleon-nucleon annihilation is predominantly described by a hot-fireball process where the many final quantum numbers are distributed in a statistical fashion. It is argued that caution must be used in employing the long-range meson-exchange forces to describe the protonium atomic states. The simplest processes of two final mesons do show puzzling behavior which might be a reflection of quark dynamics, but no guiding principles for these quark calculations have been established yet. (orig.)

  20. Spectroscopy

    DEFF Research Database (Denmark)

    Berg, Rolf W.

    This introductory booklet covers the basics of molecular spectroscopy, infrared and Raman methods, instrumental considerations, symmetry analysis of molecules, group theory and selection rules, as well as assignments of fundamental vibrational modes in molecules.......This introductory booklet covers the basics of molecular spectroscopy, infrared and Raman methods, instrumental considerations, symmetry analysis of molecules, group theory and selection rules, as well as assignments of fundamental vibrational modes in molecules....

  1. Positron annihilation in the interstellar medium

    Science.gov (United States)

    Guessoum, Nidhal; Ramaty, Reuven; Lingenfelter, Richard E.

    1991-01-01

    Positronium formation and annihilation are studied in a model for the interstellar medium consisting of cold cloud cores, warm partially ionized cloud envelopes, and hot intercloud gas. The gamma-ray spectra resulting from positron annihilation in these components of the interstellar medium are calculated. The spectra from the individual components are then combined, using two limiting assumptions for the propagation of the positrons, namely, that the positrons propagate freely throughout the interstellar medium, and that the positrons are excluded from the cold cloud cores. In the first case, the bulk of the positrons annihilate in the cloud cores and the annihilation line exhibits broad wings resulting from the annihilation of positronium formed by charge exchange in flight. In the second case, the positrons annihilate mainly in the warm envelopes, and the line wings are suppressed.

  2. Radiative lifetimes of neutral samarium

    International Nuclear Information System (INIS)

    Den Hartog, E A; Lawler, J E

    2013-01-01

    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)

  3. Production bias and cluster annihilation: Why necessary?

    DEFF Research Database (Denmark)

    Singh, B.N.; Trinkaus, H.; Woo, C.H.

    1994-01-01

    the primary cluster density is high. Therefore, a sustained high swelling rate driven by production bias must involve the annihilation of primary clusters at sinks. A number of experimental observations which are unexplainable in terms of the conventional dislocation bias for monointerstitials is considered....... It is found that the production bias and cluster annihilation are necessary to explain these observations, with, in many cases, the explicit consideration of the annihilation of the primary interstitial clusters....

  4. Multimode vibrational couplings in resonant positron annihilation.

    Science.gov (United States)

    d'A Sanchez, Sergio; Lima, Marco A P; Varella, Márcio T do N

    2011-09-02

    The mechanisms for multimode vibrational couplings in resonant positron annihilation are not well understood. We show that these resonances can arise from positron-induced distortions of the potential energy surface (target response to the positron field). Though these distortions can transfer energy into single- and multiquantum vibrations, they have so far been disregarded as a pathway to resonant annihilation. We also compare the existing annihilation theories and show that the currently accepted model can be cast as a special case of the Feshbach annihilation theory.

  5. Thermal treatment of the Fe{sub 78} Si{sub 9} B{sub 13} alloy and the analysis of it magnetic properties through Moessbauer spectroscopy and Positronium annihilation; Tratamiento termico de la aleacion Fe{sub 78} Si{sub 9} B{sub 13} y el analisis de sus propiedades magneticas mediante Espectroscopia de Moessbauer y Aniquilacion de positronio

    Energy Technology Data Exchange (ETDEWEB)

    Lopez M, A

    2005-07-01

    The present work is divided in five chapters. In the first one a general vision of the amorphous alloys is given from antecedents, structure, obtaining methods, properties and problems that at the moment, focusing us in a certain moment to the iron base alloys and the anomalous problem of hardness that it presents the alloy Fe{sub 78}Si{sub 9}B{sub 13} like previously mention us. The second chapter tries on the basic theory of the techniques of Moessbauer spectroscopy and Positron Annihilation spectroscopy, used for the characterization of our alloy as well as the complementary technique of X-ray diffraction (XRD) to observe that the amorphous phase was even studying. The third chapter describes the experimental conditions that were used to study the alloy Fe{sub 78}Si{sub 9}B{sub 13} in each one of their thermal treatments. In the fourth chapter the obtained results and their discussion are presented. In the fifth chapter the conclusions to which were arrived after analyzing the results are presented. (Author)

  6. Measurements of heavy quark and lepton lifetimes

    International Nuclear Information System (INIS)

    Jaros, J.A.

    1985-02-01

    The PEP/PETRA energy range has proved to be well-suited for the study of the lifetimes of hadrons containing the b and c quarks and the tau lepton for several reasons. First, these states comprise a large fraction of the total interaction rate in e + e - annihilation and can be cleanly identified. Second, the storage rings have operated at high luminosity and so produced these exotic states copiously. And finally, thanks to the interplay of the Fermi coupling strength, the quark and lepton masses, and the beam energy, the expected decay lengths are in the 1/2 mm range and so are comparatively easy to measure. This pleasant coincidence of cleanly identified and abundant signal with potentially large effects has made possible the first measurements of two fundamental weak couplings, tau → nu/sub tau/W and b → cW. These measurements have provided a sharp test of the standard model and allowed, for the first time, the full determination of the magnitudes of the quark mixing matrix. This paper reviews the lifetime studies made at PEP during the past year. It begins with a brief review of the three detectors, DELCO, MAC and MARK II, which have reported lifetime measurements. Next it discusses two new measurements of the tau lifetime, and briefly reviews a measurement of the D 0 lifetime. Finally, it turns to measurements of the B lifetime, which are discussed in some detail. 18 references, 14 figures, 1 table

  7. spectroscopy

    African Journals Online (AJOL)

    Aghomotsegin

    2015-10-14

    Oct 14, 2015 ... Full Length Research Paper. Determination of lactic acid bacteria in Kaşar cheese and identification by Fourier transform infrared (FTIR) spectroscopy. İlkay Turhan1* and Zübeyde Öner2. 1Department of Nutrition and Dietetic, School of Health Sciences, T.C.Istanbul Arel University, 34537 Buyukcekmece /.

  8. Radiative lifetime and Lande-factor measurements of the Se I 4p35S 5S2 level using pulsed laser spectroscopy

    International Nuclear Information System (INIS)

    Zerne, R.

    1992-01-01

    This diploma project consists of spectroscopic examinations of atomic selenium. Natural selenium was thermally dissociated in a quarts resonance cell keeping the background pressure of selenium molecules low by differential heating. The 4p 3 5S 5 S 2 level was excited by frequency-tripled pulsed dye-laser radiation at 207 nm. From time-resolved recording of the fluorescence decay at 216 nm the natural radiative lifetime of the 5 S 2 level was determined to be 493(15) ns. Quantum-beat and optical double resonance measurements in an external magnetic field yielded g j = 2.0004(10) for the Lande factor

  9. Simple picture of the annihilation process

    International Nuclear Information System (INIS)

    Gotsman, E.; Nussinov, S.

    1980-01-01

    We propose a simple geometrical picture for B-barB annihilations, which is motivated by the electric-flux-tube model and is consistent with the quark-rearrangement model, as well as the nonplanar multiperipheral quark-exchange model. Within its framework we are able to explain all the salient features of the experimental annihilation data

  10. Positron annihilation in gamma-ray bursts

    Science.gov (United States)

    Harding, Alice K.

    1990-01-01

    Emission features appear at energies of 350 to 450 keV in the spectra of a number of gamma ray burst sources. These features were interpreted as electron-positron annihilation lines, redshifted by the gravitational field near the surface of a neutron star. Evidence that gamma ray bursts originate at neutron stars with magnetic field strengths of approx. 10(exp 12) Gauss came from recent observations of cyclotron scattering harmonics in the spectra of two bursts. Positrons could be produced in gamma ray burst sources either by photon-photon pair production or by one-photon pair production in a strong magnetic field. The annihilation of positrons is affected by the presence of a strong neutron star magnetic field in several ways. The relaxation of transverse momentum conservation causes an intrinsic broadening of the two-photon annihilation line and there is a decrease in the annihilation cross section below the free-space value. An additional channel for one-photon annihilation also becomes possible in high magnetic fields. The physics of pair production and annihilation near strongly magnetized neutron stars will be reviewed. Results from a self-consistent model for non-thermal synchrotron radiation and pair annihilation are beginning to identify the conditions required to produce observable annihilation features from strongly magnetized plasmas.

  11. WIMP Annihilation and Cooling of Neutron Stars

    DEFF Research Database (Denmark)

    Kouvaris, Christoforos

    2007-01-01

    We study the effect of WIMP annihilation on the temperature of a neutron star. We shall argue that the released energy due to WIMP annihilation inside the neutron stars, might affect the temperature of stars older than 10 million years, flattening out the temperature at $\\sim 10^4$ K for a typical...

  12. Geant4 simulation of annihilation and excitation of positronium

    CERN Document Server

    AUTHOR|(CDS)2156323

    2016-01-01

    The purpose of this report is to document the work done during the summer of 2016 (18/6- 26/8) as a part of the CERN Summer Student Programme. The work has been done at the AEgIS (Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy) collaboration under the supervision of Lillian Smestad and Michael Doser. The goal of the project was to create a Monte Carlo simulation in Geant4, of Positronium annihilation and excitation in the positron test chamber of the AEgIs experiment.

  13. Study of the effect of ionizing radiation on the structure of natural rubber latex by positron annihilation technique

    International Nuclear Information System (INIS)

    Lopez Saldana, I.R.

    1993-01-01

    At the present research, were studied the changes in natural rubber latex structure, due to electron beam by a 3 MeV, 25 m A Dynamitron electron accelerator. The natural rubber latex was irradiated at 30, 40 and 50 kGy/s dose rate, over a total dose range from 150 to 250 kGy, for each dose rate used. From natural rubber latex irradiated films were prepared by casting with 0.7 mm. thickness. In the main part, the study was made by positron annihilation lifetime (PAL), this technique is unique in the determination of free-volume properties due to the fact that positronium atom (Ps) is found to be preferentially localized in the free-volume region of polymeric materials. The positron lifetime measurements were performing using a gamma-gamma coincidence system. These results were analyzed by PATFIT-88 program computer into three components, the long-lived component for orthopositronium (o-Ps) with parameters lifetime (τ 3 ) and formation intensity (I 3 ), were plotted and analyzed for each dose rate and total dose used. Besides with τ 3 were calculated the mean free-volume size based on the spherical model for the free-volume bubble, found that the free-volume decrease slightly with the total dose due to the crosslinking of natural rubber latex. Besides was studied the effect of dose rate on tensile strength, the tensile strength is increased with the total dose although there was not a clear effect due to the dose rate. Also the films were subjected to aging in order to determined the thermal stability of natural rubber latex irradiated, the results show that the films have good stability. Besides was used the infrared spectroscopy to determine the changes due to the crosslinking by variations in the characteristically absorption bands for cis 1,4-polyisoprene. (Author)

  14. Antimatter annihilation detection with AEgIS

    CERN Document Server

    Gligorova, Angela

    2015-01-01

    AE ̄ gIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is an antimatter exper- iment based at CERN, whose primary goal is to carry out the first direct measurement of the Earth’s gravitational acceleration on antimatter. A precise measurement of antimatter gravity would be the first precision test of the Weak Equivalence Principle for antimatter. The principle of the experiment is based on the formation of antihydrogen through a charge exchange reaction between laser excited (Rydberg) positronium and ultra-cold antiprotons. The antihydrogen atoms will be accelerated by an inhomogeneous electric field (Stark acceleration) to form a pulsed cold beam. The free fall of the antihydrogen due to Earth’s gravity will be measured using a moiré de- flectometer and a hybrid position detector. This detector is foreseen to consist of an active silicon part, where the annihilation of antihydrogen takes place, followed by an emulsion part coupled to a fiber time-of-flight detector. This overview prese...

  15. Laser Spectroscopy of Antiprotonic Helium Atoms

    CERN Multimedia

    2002-01-01

    %PS205 %title\\\\ \\\\Following the discovery of metastable antiprotonic helium atoms ($\\overline{p}He^{+} $) at KEK in 1991, systematic studies of their properties were made at LEAR from 1991 to 1996. In the first two years the lifetime of $\\overline{p}He^{+}$ in liquid and gaseous helium at various temperatures and pressures was measured and the effect of foreign gases on the lifetime of these atoms was investigated. Effects were also discovered which gave the antiproton a 14\\% longer lifetime in $^4$He than in $^3$He, and resulted in important differences in the shape of the annihilation time spectra in the two isotopes.\\\\ \\\\Since 1993 laser spectroscopy of the metastable $\\overline{p}He^{+}$ atoms became the main focus of PS205. Transitions were stimulated between metastable and non-metastable states of the $\\overline{p}He^{+}$ atom by firing a pulsed dye laser beam into the helium target every time an identified metastable atom was present (Figure 1). If the laser frequency matched the transition energy, the...

  16. 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)

  17. Defects in Czochralski-grown silicon crystals investigated by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Ikari, Atsushi; Kawakami, Kazuto; Haga, Hiroyo [Nippon Steel Corp., Sagamihara, Kanagawa (Japan). Electronics Research Labs.; Uedono, Akira; Wei, Long; Kawano, Takao; Tanigawa, Shoichiro

    1994-10-01

    Positron lifetime and Doppler broadening experiments were performed on Czochralski-grown silicon crystals. A monoenergetic positron beam was also used to measure the diffusion length of positrons in the wafer. From the measurements, it was observed that the value of diffusion length of positrons decreased at the region where microdefects were formed during the crystal growth process. It was also found that the line shape parameter S decreased and the lifetime of positrons increased at the region. These results can be attributed to the annihilation of positrons trapped by vacancy oxygen complexes which are formed in association with the microdefects. (author).

  18. 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.

  19. Different emissive states in the bulk and at the surface of methylammonium lead bromide perovskite revealed by two-photon micro-spectroscopy and lifetime measurements

    Directory of Open Access Journals (Sweden)

    Khadga Jung Karki

    2016-07-01

    Full Text Available Two photon photoluminescence (2PPL from single crystals of methyl ammonium lead bromide (CH3NH3PbBr3, MAPbBr3 is studied. We observe two components in the 2PPL spectra, which we assign to the photoluminescence (PL from the carrier recombination at the band edge and the recombination due to self-trapping of excitons. The PL Stokes shift of self-trapped excitons is about 100 meV from the band-gap energy. Our measurements show that about 15% of the total PL from regions about 40 μm deep inside the crystal is due to the emission from self-trapped exciton. This contribution increases to about 20% in the PL from the regions close to the surface. Time resolved measurements of 2PPL show that the PL due to band-edge recombination has a life time of about 8 ns while the PL lifetime of self-trapped excitons is in the order of 100 ns. Quantification of self-trapped excitons in the materials used in photovoltaics is important as such excitons hinder charge separation. As our results also show that an appreciable fraction of photo-generated carriers get trapped, the results are important in rational design of photovoltaics. On the other hand, our results also show that the self-trapped excitons broaden the emission spectrum, which may be useful in designing broadband light emitting devices.

  20. Free volume from positron lifetime and pressure-volume-temperature experiments in relation to structural relaxation of van der Waals molecular glass-forming liquids.

    Science.gov (United States)

    Dlubek, G; Shaikh, M Q; Rätzke, K; Paluch, M; Faupel, F

    2010-06-16

    Positron annihilation lifetime spectroscopy (PALS) is employed to characterize the temperature dependence of the free volume in two van der Waals liquids: 1, 1'-bis(p-methoxyphenyl)cyclohexane (BMPC) and 1, 1'-di(4-methoxy-5-methylphenyl)cyclohexane (BMMPC). From the PALS spectra analysed with the routine LifeTime9.0, the size (volume) distribution of local free volumes (subnanometer size holes), its mean, [v(h)], and mean dispersion, σ(h), were calculated. A comparison with the macroscopic volume from pressure-volume-temperature (PV T) experiments delivered the hole density and the specific hole free volume and a complete characterization of the free volume microstructure in that sense. These data are used in correlation with structural (α) relaxation data from broad-band dielectric spectroscopy (BDS) in terms of the Cohen-Grest and Cohen-Turnbull free volume models. An extension of the latter model allows us to quantify deviations between experiments and theory and an attempt to systematize these in terms of T(g) or of the fragility. The experimental data for several fragile and less fragile glass formers are involved in the final discussion. It was concluded that, for large differences in the fragility of different glass formers, the positron lifetime mirrors clearly the different character of these materials. For small differences in the fragility, additional properties like the character of bonds and chemical structure of the material may affect size, distribution and thermal behaviour of the free volume.

  1. Moisture dependence of positron annihilation spectra in nylon-6

    Science.gov (United States)

    Singh, J. J.; St. Clair, T. L.; Holt, W. H.; Mock, W., Jr.

    1984-01-01

    Positron annihilation time spectra have been measured in nylon-6 samples as a function of their moisture content. The measured average long life component lifetime values are: 1722 + or - 47 ps (dry), 1676 + or - 40 ps (14.6 percent saturation value), 1719 + or - 26 ps (29.3 percent saturation value), 1720 + or - 35 ps (50 percent of saturation value), 1857 + or - 35 ps (78.1 percent saturation value), and 1936 + or - 57 ps (saturated). It appears that nylon-6 has a special affinity for water at low concentration levels where H2O molecules enter between the (C = O - H-N) chemical bonds between nylon molecular chains. As the water concentration increases beyond a critical level, nylon-6 specimens start trapping H2O molecules in other bond sites or potential wells. The trapped water increases the free volume in the test specimens and reduces Ps atom formation as well as its subsequent decay rate.

  2. Charmonium spectroscopy - A review

    Indian Academy of Sciences (India)

    to a renewed interest in the precision spectroscopy of charmonium. These are the successful exploitation of proton-antiproton annihilation in the /× = 2 9-4.0. GeV range at Fermilab (FNAL experiments E760, E835), and the BEs spectrometer program at BEPC, the electron positron collider at Beijing. Both these experiments.

  3. Electrical properties of MOS structures on nitrogen-doped Czochralski-grown silicon: A positron annihilation study

    International Nuclear Information System (INIS)

    Slugen, V.; Harmatha, L.; Tapajna, M.; Ballo, P.; Pisecny, P.; Sik, J.; Koegel, G.; Krsjak, V.

    2006-01-01

    Measurements of interface trap density, effective generation lifetime (GL) and effective surface generation velocity have been performed using different methods on selected MOS structures prepared on nitrogen-doped Czochralski-grown (NCz) silicon. The application of the positron annihilation technique using a pulsed low energy positron system (PLEPS) focused on the detection of nitrogen-related defects in NCz silicon in the near surface region. In the case of p-type Cz silicon, all the results could be used for the testing of homogeneity. In n-type Cz silicon, positron annihilation was found insensitive to nitrogen doping

  4. Positron annihilation at grain boundaries in metals

    Czech Academy of Sciences Publication Activity Database

    Kuriplach, J.; Melikhova, O.; Hou, M.; Van Petegem, S.; Zhurkin, E.; Šob, Mojmír

    2007-01-01

    Roč. 4, č. 10 (2007), s. 3461-3464 ISSN 1862-6351. [International Conference on Positron Annihilation /14./. Hamilton, Ontario, 23.07.2006-28.07.2006] R&D Projects: GA AV ČR IAA1041302; GA MŠk OC 147 Institutional research plan: CEZ:AV0Z20410507 Keywords : positron annihilation * grain boundaries * electronic structure Subject RIV: BM - Solid Matter Physics ; Magnetism

  5. Probing dark matter decay and annihilation with Fermi LAT observations of nearby galaxy clusters

    International Nuclear Information System (INIS)

    Huang, Xiaoyuan; Vertongen, Gilles; Weniger, Christoph

    2011-09-01

    Galaxy clusters are promising targets for indirect dark matter searches. Gamma-ray signatures from the decay or annihilation of dark matter particles inside these clusters could be observable with the Fermi Large Area Telescope (LAT). Based on three years of Fermi LAT gamma-ray data, we analyze the flux coming from eight nearby clusters individually as well as in a combined likelihood analysis. Concentrating mostly on signals from dark matter decay, we take into account uncertainties of the cluster masses as determined by X-ray observations and model the cluster emission with extended sources. We do not find significant emission from any of the considered clusters and present limits on the dark matter lifetime and annihilation cross-section. We compare our lifetime limits derived from cluster observations with the limits that can be obtained from the extragalactic gamma-ray background, and find that in case of hadronic decay the cluster limits become competitive at dark matter masses below a few hundred GeV. Finally, we show that in presence of dark matter substructures down to 10 -6 solar masses the limits on the dark matter annihilation cross-section could improve by a factor of a few hundred, possibly going down to the thermal cross-section of 3 x 10 -26 cm 3 s -1 for dark matter masses < or similar 150 GeV and annihilation into b anti b. As a direct application of our results, we derive limits on the lifetime of gravitino dark matter in scenarios with R-parity violation. Implications of these limits for the possible observation of long-lived superparticles at the LHC are discussed. (orig.)

  6. Probing dark matter decay and annihilation with Fermi LAT observations of nearby galaxy clusters

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Xiaoyuan [Chinese Academy of Sciences, Beijing (China). National Astronomical Observatories; Max-Planck-Institut fuer Physik, Muenchen (Germany); Vertongen, Gilles [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Institut d' Astrophysique de Paris, 75 - Paris (France); Weniger, Christoph [Max-Planck-Institut fuer Physik, Muenchen (Germany)

    2011-09-15

    Galaxy clusters are promising targets for indirect dark matter searches. Gamma-ray signatures from the decay or annihilation of dark matter particles inside these clusters could be observable with the Fermi Large Area Telescope (LAT). Based on three years of Fermi LAT gamma-ray data, we analyze the flux coming from eight nearby clusters individually as well as in a combined likelihood analysis. Concentrating mostly on signals from dark matter decay, we take into account uncertainties of the cluster masses as determined by X-ray observations and model the cluster emission with extended sources. We do not find significant emission from any of the considered clusters and present limits on the dark matter lifetime and annihilation cross-section. We compare our lifetime limits derived from cluster observations with the limits that can be obtained from the extragalactic gamma-ray background, and find that in case of hadronic decay the cluster limits become competitive at dark matter masses below a few hundred GeV. Finally, we show that in presence of dark matter substructures down to 10{sup -6} solar masses the limits on the dark matter annihilation cross-section could improve by a factor of a few hundred, possibly going down to the thermal cross-section of 3 x 10{sup -26} cm{sup 3}s{sup -1} for dark matter masses annihilation into b anti b. As a direct application of our results, we derive limits on the lifetime of gravitino dark matter in scenarios with R-parity violation. Implications of these limits for the possible observation of long-lived superparticles at the LHC are discussed. (orig.)

  7. Theory of the temperature dependence of positron bulk lifetimes-implications for vacancy formation enthalpy measurements via positron experiments

    International Nuclear Information System (INIS)

    Tam, S.W.; Sinha, S.K.; Siegel, R.W.

    1977-02-01

    Temperature dependent effects, which may have a bearing on determinations of vacancy formation enthalpies in metals by positron annihilation, have been observed in certain metals. These effects have been observed to occur both at temperatures below those at which positron annihilation is most sensitive to equilibrium vacancies and at temperatures well within the vacancy-sensitive region. The effect of thermal lattice displacements on positron lifetimes in metals was investigated to help understand these phenomena

  8. A positron annihilation study on the microstructure of the interpenetration polymer networks of cyanate ester resin/epoxy resin

    International Nuclear Information System (INIS)

    Qi Chenze; Li Chunqing; Zeng Minfeng; Zhang Jian; Wang Baoyi

    2010-01-01

    Cyanate ester (CE) resin was blended with epoxy resin (EP) at different mass ratios (CE/EP: 100/0, 90/10, 70/30, 50/50, 30/70, 10/90, 0/100). The free volume size of CE/EP IPNs has been determined by positron annihilation lifetime spectroscopy (PALS). The size decreased as the epoxy resin content increased. The PALS results are consistent with the chemical structure changes for the copolymerizing between CE and EP. The crosslinking units of curing products (oxazoline, oxazolidinone, and polyether network) of the blends are all smaller in size than those of triazine ring structure from neat CE. Therefore, the free volume size of the blends decreases with increase of EP content. Examination of the mechanical properties, thermal stability, and morphology of the blend systems showed that addition of epoxy resin resulted in improved toughness but a little sacrifice in thermal stability when compared with pure CE. The correlations between the free volume properties and physical properties (thermal stability and mechanical properties) have been discussed.

  9. Annihilation vs. decay: constraining dark matter properties from a gamma-ray detection

    International Nuclear Information System (INIS)

    Palomares-Ruiz, Sergio; Siegal-Gaskins, Jennifer M.

    2010-01-01

    Most proposed dark matter candidates are stable and are produced thermally in the early Universe. However, there is also the possibility of unstable (but long-lived) dark matter, produced thermally or otherwise. We propose a strategy to distinguish between dark matter annihilation and/or decay in the case that a clear signal is detected in gamma-ray observations of Milky Way dwarf spheroidal galaxies with gamma-ray experiments. The sole measurement of the energy spectrum of an indirect signal would render the discrimination between these cases impossible. We show that by examining the dependence of the intensity and energy spectrum on the angular distribution of the emission, the origin could be identified as decay, annihilation, or both. In addition, once the type of signal is established, we show how these measurements could help to extract information about the dark matter properties, including mass, annihilation cross section, lifetime, dominant annihilation and decay channels, and the presence of substructure. Although an application of the approach presented here would likely be feasible with current experiments only for very optimistic dark matter scenarios, the improved sensitivity of upcoming experiments could enable this technique to be used to study a wider range of dark matter models

  10. Annihilation vs. decay: constraining dark matter properties from a gamma-ray detection

    Energy Technology Data Exchange (ETDEWEB)

    Palomares-Ruiz, Sergio [Centro de Física Teórica de Partículas, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Siegal-Gaskins, Jennifer M., E-mail: sergio.palomares.ruiz@ist.utl.pt, E-mail: jsg@mps.ohio-state.edu [Center for Cosmology and AstroParticle Physics, The Ohio State University, 191 W. Woodruff Ave., Columbus OH 43210 (United States)

    2010-07-01

    Most proposed dark matter candidates are stable and are produced thermally in the early Universe. However, there is also the possibility of unstable (but long-lived) dark matter, produced thermally or otherwise. We propose a strategy to distinguish between dark matter annihilation and/or decay in the case that a clear signal is detected in gamma-ray observations of Milky Way dwarf spheroidal galaxies with gamma-ray experiments. The sole measurement of the energy spectrum of an indirect signal would render the discrimination between these cases impossible. We show that by examining the dependence of the intensity and energy spectrum on the angular distribution of the emission, the origin could be identified as decay, annihilation, or both. In addition, once the type of signal is established, we show how these measurements could help to extract information about the dark matter properties, including mass, annihilation cross section, lifetime, dominant annihilation and decay channels, and the presence of substructure. Although an application of the approach presented here would likely be feasible with current experiments only for very optimistic dark matter scenarios, the improved sensitivity of upcoming experiments could enable this technique to be used to study a wider range of dark matter models.

  11. Heating of galactic gas by dark matter annihilation in ultracompact minihalos

    Energy Technology Data Exchange (ETDEWEB)

    Clark, Hamish A.; Iwanus, Nikolas; Lewis, Geraint F. [Sydney Institute for Astronomy, School of Physics A28, The University of Sydney, NSW 2006 (Australia); Elahi, Pascal J. [International Centre for Radio Astronomy Research, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Scott, Pat, E-mail: hamish.clark@sydney.edu.au, E-mail: nikolas.iwanus@sydney.edu.au, E-mail: pascal.elahi@uwa.edu.au, E-mail: geraint.lewis@sydney.edu.au, E-mail: p.scott@imperial.ac.uk [Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (United Kingdom)

    2017-05-01

    The existence of substructure in halos of annihilating dark matter would be expected to substantially boost the rate at which annihilation occurs. Ultracompact minihalos of dark matter (UCMHs) are one of the more extreme examples of this. The boosted annihilation can inject significant amounts of energy into the gas of a galaxy over its lifetime. Here we determine the impact of the boost factor from UCMH substructure on the heating of galactic gas in a Milky Way-type galaxy, by means of N-body simulation. If 1% of the dark matter exists as UCMHs, the corresponding boost factor can be of order 10{sup 5}. For reasonable values of the relevant parameters (annihilation cross section 3×10{sup −26} cm{sup 3} s{sup −1}, dark matter mass 100 GeV, 10% heating efficiency), we show that the presence of UCMHs at the 0.1% level would inject enough energy to eject significant amounts of gas from the halo, potentially preventing star formation within ∼1 kpc of the halo centre.

  12. Positron lifetime studies of the dose dependence of nanohole free volumes in ion-irradiated conducting poly-(ethylene-oxide)-salt polymers

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Rajesh [Department of Applied Physics, Z.H. College of Engineering and Technology, Aligarh Muslim University, Aligarh 202 002 (India); De, Udayan [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata 700 064 (India); Nambissan, P.M.G. [Saha Institute of Nuclear Physics, 1/AF, Bidhan Nagar, Kolkata 700 064 (India); Maitra, M. [CMPR Centre, Department of Physics, Jadavpur University, Kolkata 700 032 (India); Ali, S. Asad [Department of Applied Physics, Z.H. College of Engineering and Technology, Aligarh Muslim University, Aligarh 202 002 (India); Middya, T.R.; Tarafdar, S. [CMPR Centre, Department of Physics, Jadavpur University, Kolkata 700 032 (India); Singh, F.; Avasthi, D.K. [Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067 (India); Prasad, Rajendra [Department of Applied Physics, Z.H. College of Engineering and Technology, Aligarh Muslim University, Aligarh 202 002 (India)], E-mail: rajendraprasad1@rediffmail.com

    2008-04-15

    Polymer based ion conducting materials have potential applications as an electrolyte and separator in the field of lithium batteries. Solid polymer electrolytes for lithium batteries are one of the best applications. The irradiation of polymeric materials with swift heavy ions results into the change of their free volume properties which have strong correlation with their macroscopic properties. Poly-ethylene-oxide (PEO)-salt polymers were prepared using solution-cast method. Irradiation of the films with 95 MeV oxygen (O{sup 6+}) ions from the pelletron accelerator at IUAC, New Delhi, India, to different fluences up to 10{sup 13} ions/cm{sup 2} was carried out under high vacuum of the order of 4 x 10{sup -6} Torr. Nanosized free volume parameters in PEO-salt polymer complex have been studied by positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS). From orthopositronium (o-Ps) lifetime, free volume hole radius, free volume of micro voids and fractional free volume are computed. Free volume changes with the fluence are studied. The variation of o-Ps lifetime, mean free volume and fractional free volume with the ion fluence is studied. o-Ps lifetime, free volume radius, mean free volume and fractional free volume decrease for the fluence 10{sup 10} and 10{sup 11} ions/cm{sup 2} and then increase with fluences of 10{sup 12} and 10{sup 13} ions/cm{sup 2}. The S parameter showed a continuous decrease with increasing fluence of irradiation. The intermediate lifetime {tau}{sub 2} also showed a similar decrease. These results indicate the occurrence of scission in the polymer chains and the fragmentation of larger free volumes into smaller ones.

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

    International Nuclear Information System (INIS)

    Hasegawa, Masayuki; Kajino, Masahiro; Yamaguchi, Sadae; Iwata, Tadao; Kuramoto, Eiichi; Takenaka, Minoru.

    1992-01-01

    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 C 60 /C 70 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 C 60 /C 70 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 C 60 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)

  14. Study by the positron annihilation technique of Graft copolimerization of methyl methacrylate in polyethylene induced by gamma radiation

    International Nuclear Information System (INIS)

    Zaldivar Gonzalez, M.E.

    1992-01-01

    Radiation initiated grafting is a very broad field which has attracted considerable interest over the last two decades. Graft copolymers may combine suitable properties of two polymeric components. Radiation methods are particulary appropiate for the production of a large variety of graft copolymers having interesting properties. Ionizing radiation has provided a convenient and clean method to activate a sustrate polymer and undoubtedly, it has added impetus to this field of research. In the present work, graft polymerization of methyl methacrylate (MMA) onto low density polyethylene (LDPE) was carried out. The effect of gamma ray irradiation dose on the grafting degree was investigated for two different methods: direct and preirradiation. The best method to prepare the copolymer for the LDPE film thickness studied: 0.05 and 0.2 mm., was direct method. In both polyethylene thickness, the grafting degree increased as a function of the reaction time. However, grafting for LDPE 0.2 mm. it is better, because the copolymer with that thickness conserve the main physical-chemistry properties of the LDPE along the different grafting degrees obtained, which it is important for practical purposes. Infrared spectroscopy was used to probe the changes ocurred in the LDPE structure with the graft of MMA, first spectrum showed typical bands for LDPE structure, while in the second spectrum new bands appeared which corresponded to PMMA structure grafted onto LDPE. Positron annihilation lifetime technique was applied to study the copolymer microstructure according to increase of grafting degree. O-PS lifetime and intensity tend to decrease. This behavior could be due to the diminution of free volume in the original LDPE matrix as grafting proceeds. Copolymer morphology was observed using optical microscopy (Author)

  15. Estimates of Uncertainties in Analysis of Positron Lifetime Spectra for Metals

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Huang, Y. M.; McKee, B. T. A.

    1978-01-01

    The effects of uncertainties and errors in various constraints used in the analysis of multi-component life-time spectra of positrons annihilating in metals containing defects have been investigated in detail using computer simulated decay spectra and subsequent analysis. It is found that the err...

  16. Positron Cooling and Annihilation in Noble Gases.

    Science.gov (United States)

    Green, D G

    2017-11-17

    Positron cooling and annihilation in room temperature noble gases is simulated using accurate scattering and annihilation cross sections calculated with many-body theory, enabling the first simultaneous probing of the energy dependence of the scattering and annihilation cross sections. A strikingly small fraction of positrons is shown to survive to thermalization: ∼0.1 in He, ∼0 in Ne, ∼0.15 in Ar, ∼0.05 in Kr, and ∼0.01 in Xe. For Xe, the time-varying annihilation rate Z[over ¯]_{eff}(τ) is shown to be highly sensitive to the depletion of the momentum distribution due to annihilation, conclusively explaining the long-standing discrepancy between gas-cell and trap-based measurements. Overall, the use of the accurate atomic data gives Z[over ¯]_{eff}(τ) in close agreement with experiment for all noble gases except Ne, the experiment for which is proffered to have suffered from incomplete knowledge of the fraction of positrons surviving to thermalization and/or the presence of impurities.

  17. Determination of phase transitions in a lyotropic liquid crystal by Positron Annihilation technique

    International Nuclear Information System (INIS)

    Castillo V, V.M.

    1994-01-01

    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 (τ 3 ) and intensity of formation (I 3 ). 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)

  18. Element specificity of ortho-positronium annihilation for alkali-metal loaded SiO2 glasses.

    Science.gov (United States)

    Sato, K; Hatta, T

    2015-03-07

    Momentum distributions associated with ortho-positronium (o-Ps) pick-off annihilation photon are often influenced by light elements, as, e.g., carbon, oxygen, and fluorine. This phenomenon, so-called element specificity of o-Ps pick-off annihilation, has been utilized for studying the elemental environment around the open spaces. To gain an insight into the element specificity of o-Ps pick-off annihilation, the chemical shift of oxygen 1s binding energy and the momentum distributions associated with o-Ps pick-off annihilation were systematically investigated for alkali-metal loaded SiO2 glasses by means of X-ray photoelectron spectroscopy and positron-age-momentum correlation spectroscopy, respectively. Alkali metals introduced into the open spaces surrounded by oxygen atoms cause charge transfer from alkali metals to oxygen atoms, leading to the lower chemical shift for the oxygen 1s binding energy. The momentum distribution of o-Ps localized into the open spaces is found to be closely correlated with the oxygen 1s chemical shift. This correlation with the deepest 1s energy level evidences that the element specificity of o-Ps originates from pick-off annihilation with orbital electrons, i.e., dominantly with oxygen 2p valence electrons and s electrons with lower probability.

  19. Positron annihilation in low-temperature rare gases. II. Argon and neon

    International Nuclear Information System (INIS)

    Canter, K.F.; Roellig, L.O.

    1975-01-01

    Lifetime measurements of slow-positron and ortho-positronium (o-Ps) annihilation were made in argon and neon gases at room temperature and below. The argon experiments cover the temperature range 115 to 300 0 K and the density range 0.0356 to 0.0726 g/cm 3 (approximately equal to 20 to 40 amagat). The slow-positron spectra in argon exhibit a departure from free-positron annihilation below 200 0 K. The departure becomes more marked as the temperature is lowered. No deviation from free o-Ps pickoff annihilation is observed in argon at low temperatures. The neon measurements cover the temperature range 30 to 300 0 K and the density range 0.032 to 0.89 g/cm 3 (approximately equal to 35 to 980 amagat). No effect of temperature on the slow-positron spectra throughout the temperature and density ranges investigated in neon is observed. The spectra are very exponential with a corresponding decay rate which is temperature as well as time independent and is directly proportional to density over the ranges investigated. The o-Ps data are more eventful in that the o-Ps lifetime at near-liquid densities is approximately 20 nsec, a factor of nearly 4 greater than the value obtained using the pickoff-annihilation coefficient obtained at lower densities. This is evidence for positronium-induced cavities in low-temperature neon. A brief discussion of the argon and neon results is given in the context of the explanations offered for the low-temperature effects observed in helium gas

  20. Electronic structure and vacancy formation in photochromic yttrium oxy-hydride thin films studied by positron annihilation

    NARCIS (Netherlands)

    Plokker, M.P.; Eijt, S.W.H.; Naziris, F.; Schut, H.; Nafezarefi, F.; Schreuders, H.; Cornelius, S.; Dam, B.

    2018-01-01

    In order to investigate the mechanism of the photochromic effect in yttrium oxy-hydride (YOxHy) thin films, Doppler broadening positron annihilation spectroscopy (PAS) was applied to probe the electronic structure and the presence of vacancies in YOxHy

  1. 3D-AP and positron annihilation study of precipitation behavior in Cu-Cr-Zr alloy

    DEFF Research Database (Denmark)

    Hatakeyama, M.; Toyama, T.; Yang, J.

    2009-01-01

    Precipitation behavior in a Cu-0.78%Cr-0.13%Zr alloy during aging and reaging has been studied by laser-assisted local electrode three-dimensional atom probe (Laser-LEAP) and positron annihilation spectroscopy (PAS). After the prime aging at 460 degrees C, Cr clusters enriched with Zr were observed...

  2. Radiative corrections to neutralino annihilation. Recent developments

    International Nuclear Information System (INIS)

    Herrmann, Bjoern

    2010-11-01

    Evaluating the relic density of dark matter is an interesting possibility to constrain the parameter space of new physics models. However, this calculation is affected by several sources of uncertainty. On the particle physics side, considerable progress has been made in the recent years concerning the calculation of the annihilation cross-section of dark matter, which is needed in this context. In particular, within the Minimal Supersymmetric Standard Model, the theoretical uncertainty has been reduced through the calculation of loop corrections. The present contribution gives an overview over the achievements that have been made in QCD corrections to neutralino pair annihilation. The numerical impact is illustrated for a few examples. (orig.)

  3. Energy-resolved positron annihilation for molecules

    International Nuclear Information System (INIS)

    Barnes, L.D.; Gilbert, S.J.; Surko, C.M.

    2003-01-01

    This paper presents an experimental study designed to address the long-standing question regarding the origin of very large positron annihilation rates observed for many molecules. We report a study of the annihilation, resolved as a function of positron energy (ΔE∼25 meV, full width at half maximum) for positron energies from 50 meV to several eV. Annihilation measurements are presented for a range of hydrocarbon molecules, including a detailed study of alkanes, C n H 2n+2 , for n=1-9 and 12. Data for other molecules are also presented: C 2 H 2 , C 2 H 4 ; CD 4 ; isopentane; partially fluorinated and fluorinated methane (CH x F 4-x ); 1-fluorohexane (C 6 H 13 F) and 1-fluorononane (C 9 H 19 F). A key feature of the results is very large enhancements in the annihilation rates at positron energies corresponding to the excitation of molecular vibrations in larger alkane molecules. These enhancements are believed to be responsible for the large annihilation rates observed for Maxwellian distributions of positrons in molecular gases. In alkane molecules larger than ethane (C 2 H 6 ), the position of these peaks is shifted downward by an amount ∼20 meV per carbon. The results presented here are generally consistent with a physical picture recently considered in detail by Gribakin [Phys. Rev. A 61, 022720 (2000)]. In this model, the incoming positron excites a vibrational Feshbach resonance and is temporarily trapped on the molecule, greatly enhancing the probability of annihilation. The applicability of this model and the resulting enhancement in annihilation rate relies on the existence of positron-molecule bound states. In accord with this reasoning, the experimental results presented here provide the most direct evidence to date that positrons bind to neutral molecules. The shift in the position of the resonances is interpreted as a measure of the binding energy of the positron to the molecule. Other features of the results are also discussed, including large

  4. Work station for low temperature positron annihilation studies

    International Nuclear Information System (INIS)

    Chaturvedi, T.P.; Venkiteswaran, S.; Pujari, P.K.

    1999-05-01

    This report describes the automation implemented in the low temperature Positron Annihilation Spectroscopy studies system. Temperature programmer and controller (Lakeshore 330) is interfaced to PC-AT through an IEEE-488 add-on card. Through this data can be read and written to the temperature controller and it can be handled remotely. The PC- AT also houses the PCA-II card. Software (TEMP330.EXE) was developed to communicate with the temperature controller. A master software is also developed under which TEMP330.EXE and PCAII.EXE should run. Another program DATASEG.EXE creates a user file to store the temperature points given by user over which data acquisition is required. This has not only widened the scope of the positron research, but also helps achieve result with better precision. (author)

  5. Inverse Compton Gamma Rays from Dark Matter Annihilation in the ...

    Indian Academy of Sciences (India)

    Electron spectrum as a function of electron energy for three different values of Mχ annihilating into b¯b final state. the annihilation cross sections are obtained from Ackermann et al. (2014). The DM annihilation takes place predominantly through some combination of the final states b¯b, tt, W. +. W. − or ZZ. The gamma ray ...

  6. Positron lifetime measurements on electron irradiated amorphous alloys

    International Nuclear Information System (INIS)

    Moser, P.; Hautojaervi, P.; Chamberod, A.; Yli-Kauppila, J.; Van Zurk, R.

    1981-08-01

    Great advance in understanding the nature of point defects in crystalline metals has been achieved by employing positron annihilation technique. Positrons detect vacancy-type defects and the lifetime value of trapped positrons gives information on the size of submicroscopic vacancy aglomerates and microvoids. In this paper it is shown that low-temperature electron irradiations can result in a considerable increase in the positron lifetimes in various amorphous alloys because of the formation of vacancy-like defects which, in addition of the pre-existing holes, are able to trap positrons. Studied amorphous alloys were Fe 80 B 20 , Pd 80 Si 20 , Cu 50 Ti 50 , and Fe 40 Ni 40 P 14 B 6 . Electron irradiations were performed with 3 MeV electrons at 20 K to doses around 10 19 e - /cm 2 . After annealing positron lifetime spectra were measured at 77 K

  7. Effects of electrical conductivity on the formation and annihilation of positronium in porous materials.

    Science.gov (United States)

    Li, Chongyang; Zhao, Bin; Zhou, Bo; Qi, Ning; Chen, Zhiquan; Zhou, Wei

    2017-03-15

    In this paper we show the preliminary evidence that the formation of positronium depends on the electrical conductivity of porous materials. Porous nano γ-Al 2 O 3 was chosen as the base material, and it was filled with carbon of different allotropes (commercial graphite, carbon black, carbon nanotubes and home-made ordered mesoporous carbon) by a mechanical mixing method. The positron lifetime and Doppler broadening of the annihilation radiation were measured for these composites. In the pure γ-Al 2 O 3 sample, there are two long positron lifetime components τ 3 (3.5 ns) and τ 4 (101.3 ns) with intensities of 1.0% and 24.6%, which indicates the formation and annihilation of positronium in small and large pores, respectively. In the carbon filled γ-Al 2 O 3 samples, the longest lifetime τ 4 and its intensity I 4 both show a continuous decrease with increasing carbon content. The Doppler broadening S parameter shows a similar tendency to τ 4 and I 4 . This suggests that carbon has a quenching effect on positronium and also inhibits the formation of positronium. Among these four carbon allotropes, carbon nanotubes have the strongest quenching and inhibition effect, while graphite has the weakest effect. A detailed study further reveals that the decreasing rate of τ 4 and I 4 as well as the S parameter depend on the electrical conductivity of the carbon filled γ-Al 2 O 3 and also the specific surface area of the filled carbon. Our results suggest that the formation and annihilation of positronium are strongly affected by the electrical conductivity of the materials.

  8. Nondestructive examination using neutron activated positron annihilation

    Science.gov (United States)

    Akers, Douglas W.; Denison, Arthur B.

    2001-01-01

    A method is provided for performing nondestructive examination of a metal specimen using neutron activated positron annihilation wherein the positron emitter source is formed within the metal specimen. The method permits in situ nondestructive examination and has the advantage of being capable of performing bulk analysis to determine embrittlement, fatigue and dislocation within a metal specimen.

  9. Positron annihilation and electron microscopy study in the early stage of fatigue of polycrystalline copper

    International Nuclear Information System (INIS)

    Diaz, L.; Pareja, R.; Pedrosa, M.A.; Gonzalez, R.

    1985-01-01

    Positron annihilation and transmission electron microscopy are used to study the early stage of fatigue in polycrystalline copper cyclically deformed at various temperatures. The concentration of positron traps is correlated to the cumulative plastic strain and to the work done during deformation. The average lifetimes of the trapped positrons are (177 +- 4) and (186 +- 3) ps for samples fatigued at T 15 s -1 for the samples deformed at T <= 293 K. Vacancy clusters like small dislocation loops, are proposed as the main defects responsible for the positron trapping. (author)

  10. Study of the ortho-positron annihilation process in zeolite Y; Estudio del proceso de aniquilacion de ortopositronio en zeolita Y

    Energy Technology Data Exchange (ETDEWEB)

    Alvarado D, M. E.

    2010-07-01

    For several years a great interest has existed for the study of the natural and synthetic zeolites due to its properties. The porosity, one of their main characteristics allows that these materials are used as molecular sieves, catalysts, gases drying, etc. In order to investigating the porosity and other zeolite properties one carries out the study of the process of positron annihilation lifetime spectroscopy (Pals). This is a technique that provides information about the size and the pores form since is highly sensitive to the free volume and the superficial area of those porous materials as the zeolites. The study began with the elaboration of zeolite Y tablets in a hydraulic press where different pressures (from 0 to 1.26 GPa) and masses (70, 80 and 100 mg) were proven to obtain the estimate porosity of each tablet. A graph was elaborated and the effect of the mass and pressure with regard to the zeolite porosity was analyzed. Later on, the powder and tablets of 70 mg were characterized by means of X-ray diffraction (the glass size, interplanar distance, length and the volume of the unitary cell); scanning electron microscopy (the particles size and morphology); thermo gravimetric analysis (dehydration temperature and the stability up to 700 C) and the Brunauer Emmett Teller method (specific area). After the zeolite Y tablets characterization was carried out the positron annihilation process by means of Pals where its free volume of zeolite Y was analyzed, which includes to the structural cavities and the interparticle volume. The powdered zeolite was analyzed to different experimental conditions (preparation of the sample and the Pals equipment) to obtain the optimal conditions (a window with a time of 400 ns and a enlarged energy window) of analysis. On the other hand, the tablets were analyzed under optimal conditions to obtain the four components of time and intensity ({tau}, {Iota}), result of the different ways of positrons annihilation in the zeolite

  11. Positron annihilation radiation from the Galactic center region

    Science.gov (United States)

    Ramaty, R.; Lingenfelter, R. E.

    1991-01-01

    Observations show that there are two components of positron annihilation radiation from the region of the Galactic center: a variable component resulting from one or just a few compact sources at or near the Galactic center and a steady, diffuse component resulting from positron annihilation in the Galactic disk. The diffuse component is modeled using the observed longitude distributions of 70-150 MeV gamma rays, CO, and hot plasma revealed by Fe line emission. Recent results on positron annihilation in the interstellar medium are reviewed and the implications of the annihilation processes on the fraction of positrons annihilating via positronium and on the shape of the 511 keV annihilation line are discussed. The sources of diffuse Galactic positrons are also reviewed and the nature of the compact source of annihilation radiation near the Galactic center is discussed.

  12. Symposium on atomic spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    1979-01-01

    Topics covered by the conference include: fast beam spectroscopy; astrophysical and other spectra; highly ionized spectroscopy; complex spectra; rydberg levels; fine structure, hyperfine structure and isotope shift; lineshapes; lifetimes, oscillator strengths and Einstein coefficients; and spectroscopy with lasers. Abstracts of the conference papers are presented. (GHT)

  13. Symposium on atomic spectroscopy

    International Nuclear Information System (INIS)

    1979-01-01

    Topics covered by the conference include: fast beam spectroscopy; astrophysical and other spectra; highly ionized spectroscopy; complex spectra; rydberg levels; fine structure, hyperfine structure and isotope shift; lineshapes; lifetimes, oscillator strengths and Einstein coefficients; and spectroscopy with lasers. Abstracts of the conference papers are presented

  14. Computing Battery Lifetime Distributions

    NARCIS (Netherlands)

    Cloth, L.; Haverkort, Boudewijn R.H.M.; Jongerden, M.R.

    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

  15. Three Dimensional Positron Annihilation Momentum Spectroscopy of Lithium Tetraborate Crystals

    Science.gov (United States)

    2013-03-21

    L ::II · - - ... .... .. 1.1 ::. 1! 11" • l’l’ H.PJI II:II . r l:ll -:19-1 _ . ..... 1!11 .. .. ..... ::. ... .. .. · ; 11: :r a 1:1 ,. f" lol !5...l:lli::I.EIB PI 1 . .. P. lol L" :II Ill • I I i!l -. . .. .. . " 1!: 41 • .. , ••• . ·. . ·. Horizontal Axis (mm] 69 angular deviation, and

  16. Positron annihilation characteristics of ODS and non-ODS EUROFER isochronally annealed

    International Nuclear Information System (INIS)

    Ortega, Y.; Castro, V. de; Monge, M.A.; Munoz, A.; Leguey, T.; Pareja, R.

    2008-01-01

    Yttrium oxide dispersion strengthened (ODS) and non-ODS EUROFER produced by mechanical alloying and hot isostatic pressing have been subjected to isochronal annealing up to 1523 K, and the evolution of the open-volume defects and their thermal stability have been investigated using positron lifetime and coincidence Doppler broadening (CDB) techniques. Transmission electron microscopy (TEM) observations have also been performed on the studied samples to verify the characteristics of the surviving defects after annealing at 1523 K. The CDB spectra of ODS EUROFER exhibit a characteristic signature that is attributed to positron annihilation in Ar-decorated cavities at the oxide particle/matrix interfaces. The variation of the positron annihilation parameters with the annealing temperature shows three stages: up to 623 K, between 823 and 1323 K, and above 1323 K. Three-dimensional vacancy clusters, or voids, are detected in either materials in as-HIPed condition and after annealing at T ≤ 623 K. In the temperature range 823-1323 K, these voids' growth and nucleation and the growth of other new species of voids take place. Above 1323 K, some unstable cavities start to anneal out, and cavities associated to oxide particles and other small precipitates survive to annealing at 1523 K. The TEM observations and the positron annihilation results indicate that these cavities should be decorated with Ar atoms absorbed during the mechanical alloying process

  17. Positron annihilation characteristics of ODS and non-ODS EUROFER isochronally annealed

    Energy Technology Data Exchange (ETDEWEB)

    Ortega, Y. [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain)], E-mail: yanicet@fis.ucm.es; Castro, V. de; Monge, M.A.; Munoz, A.; Leguey, T.; Pareja, R. [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain)

    2008-05-31

    Yttrium oxide dispersion strengthened (ODS) and non-ODS EUROFER produced by mechanical alloying and hot isostatic pressing have been subjected to isochronal annealing up to 1523 K, and the evolution of the open-volume defects and their thermal stability have been investigated using positron lifetime and coincidence Doppler broadening (CDB) techniques. Transmission electron microscopy (TEM) observations have also been performed on the studied samples to verify the characteristics of the surviving defects after annealing at 1523 K. The CDB spectra of ODS EUROFER exhibit a characteristic signature that is attributed to positron annihilation in Ar-decorated cavities at the oxide particle/matrix interfaces. The variation of the positron annihilation parameters with the annealing temperature shows three stages: up to 623 K, between 823 and 1323 K, and above 1323 K. Three-dimensional vacancy clusters, or voids, are detected in either materials in as-HIPed condition and after annealing at T {<=} 623 K. In the temperature range 823-1323 K, these voids' growth and nucleation and the growth of other new species of voids take place. Above 1323 K, some unstable cavities start to anneal out, and cavities associated to oxide particles and other small precipitates survive to annealing at 1523 K. The TEM observations and the positron annihilation results indicate that these cavities should be decorated with Ar atoms absorbed during the mechanical alloying process.

  18. Deciphering the Role of Charge Compensator in Optical Properties of SrWO4:Eu3+:A (A = Li+, Na+, K+): Spectroscopic Insight Using Photoluminescence, Positron Annihilation, and X-ray Absorption.

    Science.gov (United States)

    Gupta, Santosh Kumar; Sudarshan, Kathi; Yadav, Ashok Kumar; Gupta, Ruma; Bhattacharyya, Dibyendu; Jha, Shambhu Nath; Kadam, Ramakant Mahadeo

    2018-01-16

    Studies have been carried out to understand the specific role of the alkali charge compensator on the luminescence properties of an alkali ion (Li + , Na + , and K + ) codoped SrWO 4 :Eu phosphor. The oxidation state of the europium ion was found to be +3 on the basis of X-ray absorption near edge structure (XANES) measurements. This is the first report of its kind where opposite effects of Li + ion and Na + /K + ions on photoluminescence intensity have been observed. Li + ion codoping enhanced the photoluminescence intensity from SrWO 4 :Eu 3+ phosphor while Na + /K + ion codoping did not. On the other hand, the luminescence lifetime is maximum for the Na + ion codoped sample and minimum for the Li + ion codoped sample. The results could be explained successfully using time-resolved luminescence, positron annihilation lifetime spectroscopy (PALS), and extended X-ray absorption fine structure (EXAFS) spectroscopy measurements. Changes in the Eu-O bond length and Debye-Waller Factor (σ 2 ) upon Li + /Na + /K + codoping were monitored through EXAFS measurements. PALS also highlighted the fact that Li + codoping is not contributing to reduction in the cation vacancies and might be occupying interstitial sites rather than lattice positions due to its very small size. On europium doping there is lowering in symmetry of SrO 8 polyhedra from S 4 to C 6 , which is reflected in an intense electric dipole transition in comparison to the magnetic dipole transition. This is also corroborated using trends in Judd-Ofelt parameters. The results have shown that the luminescence lifetime is better when the vacancy concentration is lower as induced by Na + and K + codoping, while the emission intensity is higher in the samples when distortion around Eu 3+ is reduced as induced by Li + codoping.

  19. Identification of effective exciton-exciton annihilation in squaraine-squaraine copolymers.

    Science.gov (United States)

    Hader, Kilian; May, Volkhard; Lambert, Christoph; Engel, Volker

    2016-05-11

    Ultrafast time-resolved transient absorption spectroscopy is able to monitor the fate of the excited state population in molecular aggregates or polymers. Due to many competing decay processes, the identification of exciton-exciton annihilation (EEA) is difficult. Here, we use a microscopic model to describe exciton annihilation processes in squaraine-squaraine copolymers. Transient absorption time traces measured at different laser powers exhibit an unusual time-dependence. The analysis points towards dynamics taking place on three time-scales. Immediately after laser-excitation a localization of excitons takes place within the femtosecond time-regime. This is followed by exciton-exciton annihilation which is responsible for a fast decay of the exciton population. At later times, excitations being localized on units which are not directly connected remain so that diffusion dominates the dynamics and leads to a slower decay. We thus provide evidence for EEA tracked by time-resolved spectroscopy which has not been reported that clearly before.

  20. 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...

  1. Point defects and precipitation phenomena in Cu-Zn-Al alloys. A study by positrons annihilation

    International Nuclear Information System (INIS)

    Romero, R.; Salgueiro, W.; Somoza, A.; Ahlers, M.H.

    1990-01-01

    Monocrystalline phase Cu-Zn-Al samples in phase β (derived from a bcc structure) were treated with different homogenization thermal treatments, isothermal annealing, and tempering at different time intervals. In this way, point defects are fixed and gamma phase precipitation is induced. The evolution of this technique's characteristic parameters was followed with positron annihilation temporal spectroscopy at room temperature. Owing to the extreme sensitivity of positrons to defects like vacancies, it is possible to study the migration of these defects in detail. It can be seen that the presence of precipitates within the matrix phase modifies the annihilation parameters. Results are discussed as a function of the standard model for positron trapping by defects. (Author). 9 refs., 4 figs

  2. Beam Diagnostics for Measurements of Antiproton Annihilation Cross Sections at Ultra-low Energy

    Directory of Open Access Journals (Sweden)

    Todoroki K.

    2014-03-01

    Full Text Available The ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons collaboration of CERN is currently attempting to measure the antiproton-nucleus in-flight annihilation cross sections on thin target foils of C, Pd, and Pt at 130 keV of kinetic energy. The low-energy antiprotons were supplied by the Antiproton Decelerator (AD and a radio-frequency quadrupole decelerator. For this measurement, a beam profile monitor based on secondary electron emission was developed. Data from this monitor was used to ensure that antiprotons were precisely tuned to the position of an 80-mm-diameter experimental target, by measuring the spatial profile of 200-ns-long beam pulses containing 105 − 106 antiprotons with an active area of 40 mm × 40 mm and a spatial resolution of 4 mm. By using this monitor, we succeeded in finely tuning antiproton beams on the target, and observed some annihilation events originating from the target.

  3. Positron scattering and annihilation from hydrogenlike ions

    International Nuclear Information System (INIS)

    Novikov, S.A.; Bromley, M.W.J.; Mitroy, J.

    2004-01-01

    The Kohn variational method is used with a configuration-interaction-type wave function to determine the J=0 and J=1 phase shifts and annihilation parameter Z eff for positron-hydrogenic ion scattering. The phase shifts are within 1-2% of the best previous calculations. The values of Z eff are small and do not exceed unity for any of the momenta considered. At thermal energies Z eff is minute with a value of order 10 -50 occurring for He + at k=0.05a 0 -1 . In addition to the variational calculations, analytic expressions for the phase shift and annihilation parameters within the Coulomb wave Born approximation are derived and used to help elucidate the dynamics of positron collisions with positive ions

  4. Two photon annihilation operators and squeezed vacuum

    Science.gov (United States)

    Roy, Anil K.; Mehta, C. L.; Saxena, G. M.

    1993-01-01

    Inverses of the harmonic oscillator creation and annihilation operators by their actions on the number states are introduced. Three of the two photon annihilation operators, viz., a(sup +/-1)a, aa(sup +/-1), and a(sup 2), have normalizable right eigenstates with nonvanishing eigenvalues. The eigenvalue equation of these operators are discussed and their normalized eigenstates are obtained. The Fock state representation in each case separates into two sets of states, one involving only the even number states while the other involving only the odd number states. It is shown that the even set of eigenstates of the operator a(sup +/-1)a is the customary squeezed vacuum S(sigma) O greater than.

  5. Method for photon activation positron annihilation analysis

    Science.gov (United States)

    Akers, Douglas W.

    2006-06-06

    A non-destructive testing method comprises providing a specimen having at least one positron emitter therein; determining a threshold energy for activating the positron emitter; and determining whether a half-life of the positron emitter is less than a selected half-life. If the half-life of the positron emitter is greater than or equal to the selected half-life, then activating the positron emitter by bombarding the specimen with photons having energies greater than the threshold energy and detecting gamma rays produced by annihilation of positrons in the specimen. If the half-life of the positron emitter is less then the selected half-life, then alternately activating the positron emitter by bombarding the specimen with photons having energies greater then the threshold energy and detecting gamma rays produced by positron annihilation within the specimen.

  6. A possible signature of annihilating dark matter

    Science.gov (United States)

    Chan, Man Ho

    2018-02-01

    In this article, we report a new signature of dark matter annihilation based on the radio continuum data of NGC 1569 galaxy detected in the past few decades. After eliminating the thermal contribution of the radio signal, an abrupt change in the spectral index is shown in the radio spectrum. Previously, this signature was interpreted as an evidence of convective outflow of cosmic ray. However, we show that the cosmic ray contribution is not enough to account for the observed radio flux. We then discover that if dark matter annihilates via the 4-e channel with the thermal relic cross-section, the electrons and positrons produced would emit a strong radio flux which can provide an excellent agreement with the observed signature. The best-fitting dark matter mass is 25 GeV.

  7. Study of vacancy-type defects by positron annihilation in ultrafine-grained aluminum severely deformed at room and cryogenic temperatures

    International Nuclear Information System (INIS)

    Su, L.H.; Lu, C.; He, L.Z.; Zhang, L.C.; Guagliardo, P.; Tieu, A.K.; Samarin, S.N.; Williams, J.F.; Li, H.J.

    2012-01-01

    Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes. It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP passes, while the CT-ECAPed samples displayed slightly elongated microstructure and slightly smaller grain size. Moreover, the CT-ECAPed samples had higher hardness values than the RT-ECAPed samples subjected to the same amount of deformation. Positron annihilation lifetime spectroscopy (PALS) was used to investigate the evolution of vacancy-type defects during the ECAP deformation process. The results showed that three types of defects existed in the ECAPed samples: vacancies associated with dislocations, bulk monovacancies and bulk divacancies. The CT-ECAPed samples had a higher fraction of monovacancies and divacancies. These two types of defects are the major vacancy-type defects that can work as dislocation pinning centers and induce hardening, resulting in higher hardness values in the CT-ECAPed samples. A quantitative relationship between material hardness and the defect concentration and defect diffusion coefficient has been established.

  8. The role of positronium decoherence in positron annihilation in matter

    Energy Technology Data Exchange (ETDEWEB)

    Pietrow, M., E-mail: mrk@kft.umcs.lublin.pl [Institute of Physics, M. Curie-Sklodowska University, ul. Pl. M. Curie-Sklodowskiej 1, 20-031 Lublin (Poland); Slomski, P. [Geographic Information Systems Development Company Martinex, ul. Melgiewska 95, 21-040 Swidnik (Poland)

    2011-10-24

    A small difference between the energies of the para-positronium (p-Ps) and ortho-positronium (o-Ps) states suggests the possibility of the superposition of p-Ps and o-Ps during the formation of positronium (Ps) from pre-Ps, terminating its migration in the matter in a void. It is shown that such a superposition decoheres in the basis of p-Ps and o-Ps. The decoherence time scale estimated here motivates a correction in the precise analysis of the positron annihilation lifetime spectra. More generally, the superposited Ps state should contribute to the theory of the evolution of positronium in matter. -- Highlights: → Decoherence time decrease exponentially with the number of e{sup -} interacting with Ps. → Time scale of the decoherence motivates correction in decomposition of PALS spectra. → We showed the way of modification for formulas used for PALS spectra decomposition. → The superposited Ps should contribute to the positronium in matter evolution theory. → We examined the magnetisation influence to be expected on the process of decoherence.

  9. Effect of structural relaxation of metallic glasses on positron annihilation parameters

    International Nuclear Information System (INIS)

    Tian Decheng; Xiong Liangyue; Tang Zhongxun; Xu Yinhua

    1987-07-01

    The results of a comparative study of positron lifetime and a Doppler broadening line-shape parameter for two metallic glasses are presented. The change of lifetime τ-bar and the S-parameter for these two metallic glasses are shown to have a common feature, i.e. at the initial stage of structural relaxation, τ-bar presents a peak-form as a function of annealing time or temperature while the S-parameter decreases monotonically. A possible mechanism is proposed for explaining the peak-form of τ-bar which has been observed in many metallic glasses; the initial rise and the following decrease of τ-bar are attributed to the homogenization of defects taking place during the structural relaxation. The monotonic behaviour of the S-parameter seems to indicate that the annihilation of positrons in free state with the high momentum core electrons is negligible. (author). 8 refs, 2 figs

  10. Overlapping resonances in e+e- annihilation

    International Nuclear Information System (INIS)

    Dothan, Y.; Horn, D.

    1976-06-01

    The application of the general formalism of two overlapping resonances to the inclusive process of hadron production in e + e - annihilation is discussed. The strong dip observed near 4 GeV can be fitted by three different classes of solutions, all of which have to use an overlap close to its maximal value. This suggests that both resonances have one common main decay channel. The implications of this conclusion are briefly discussed

  11. Systems of branching, annihilating, and coalescing particles

    Czech Academy of Sciences Publication Activity Database

    Athreya, S. R.; Swart, Jan M.

    2012-01-01

    Roč. 17, č. 80 (2012), s. 1-32 ISSN 1083-6489 R&D Projects: GA ČR GAP201/10/0752 Institutional support: RVO:67985556 Keywords : reaction-diffusion process * branching * coalescence * annihilation * thinning * Poissonization Subject RIV: BA - General Mathematics Impact factor: 0.785, year: 2012 http://library.utia.cas.cz/separaty/2012/SI/swart-0381108.pdf

  12. Excited-state annihilation reduces power dependence of single-molecule FRET experiments.

    Science.gov (United States)

    Nettels, Daniel; Haenni, Dominik; Maillot, Sacha; Gueye, Moussa; Barth, Anders; Hirschfeld, Verena; Hübner, Christian G; Léonard, Jérémie; Schuler, Benjamin

    2015-12-28

    Single-molecule Förster resonance energy transfer (FRET) experiments are an important method for probing biomolecular structure and dynamics. The results from such experiments appear to be surprisingly independent of the excitation power used, in contradiction to the simple photophysical mechanism usually invoked for FRET. Here we show that excited-state annihilation processes are an essential cause of this behavior. Singlet-singlet annihilation (SSA) is a mechanism of fluorescence quenching induced by Förster-type energy transfer between two fluorophores while they are both in their first excited singlet states (S1S1), which is usually neglected in the interpretation of FRET experiments. However, this approximation is only justified in the limit of low excitation rates. We demonstrate that SSA is evident in fluorescence correlation measurements for the commonly used FRET pair Alexa 488/Alexa 594, with a rate comparable to the rate of energy transfer between the donor excited state and the acceptor ground state (S1S0) that is exploited in FRET experiments. Transient absorption spectroscopy shows that SSA occurs exclusively via energy transfer from Alexa 488 to Alexa 594. Excitation-power dependent microsecond correlation experiments support the conclusion based on previously reported absorption spectra of triplet states that singlet-triplet annihilation (STA) analogously mediates energy transfer if the acceptor is in the triplet state. The results indicate that both SSA and STA have a pronounced effect on the overall FRET process and reduce the power dependence of the observed FRET efficiencies. The existence of annihilation processes thus seems to be essential for using FRET as a reliable spectroscopic ruler at the high excitation rates commonly employed in single-molecule spectroscopy.

  13. Triplet Excited State of BODIPY Accessed by Charge Recombination and Its Application in Triplet-Triplet Annihilation Upconversion.

    Science.gov (United States)

    Chen, Kepeng; Yang, Wenbo; Wang, Zhijia; Iagatti, Alessandro; Bussotti, Laura; Foggi, Paolo; Ji, Wei; Zhao, Jianzhang; Di Donato, Mariangela

    2017-10-12

    The triplet excited state properties of two BODIPY phenothiazine dyads (BDP-1 and BDP-2) with different lengths of linker and orientations of the components were studied. The triplet state formation of BODIPY chromophore was achieved via photoinduced electron transfer (PET) and charge recombination (CR). BDP-1 has a longer linker between the phenothiazine and the BODIPY chromophore than BDP-2. Moreover, the two chromophores in BDP-2 assume a more orthogonal geometry both at the ground and in the first excited state (87°) than that of BDP-1 (34-40°). The fluorescence of the BODIPY moiety was significantly quenched in the dyads. The charge separation (CS) and CR dynamics of the dyads were studied with femtosecond transient absorption spectroscopy (k CS = 2.2 × 10 11 s -1 and 2 × 10 12 s -1 for BDP-1 and BDP-2, respectively; k CR = 4.5 × 10 10 and 1.5 × 10 11 s -1 for BDP-1 and BDP-2, respectively; in acetonitrile). Formation of the triplet excited state of the BODIPY moiety was observed for both dyads upon photoexcitation, and the triplet state quantum yield depends on both the linker length and the orientation of the chromophores. Triplet state quantum yields are 13.4 and 97.5% and lifetimes are 13 and 116 μs for BDP-1 and BDP-2, respectively. The spin-orbit charge transfer (SO-CT) mechanism is proposed to be responsible for the efficient triplet state formation. The dyads were used for triplet-triplet annihilation (TTA) upconversion, showing an upconversion quantum yield up to 3.2%.

  14. Temperature dependence of positron lifetime in ordered porous silica (SBA-3)

    International Nuclear Information System (INIS)

    Kunishige, S.; Koshimizu, M.; Asai, K.

    2009-01-01

    The temperature dependence of positron lifetime in uniform mesopores was analyzed. We used SBA-3 as the sample material, which possesses an ordered porous structure with uniform cylindrical mesopores. The positron lifetime corresponding to the annihilation in the mesopores increased gradually with a decrease in temperature down to 100 K, and its relative intensity also increased concomitantly. This result was attributed to the lower probability of the escape of the ortho-positronium (o-Ps) from the mesopores into the intergrain space at lower temperatures. An anomalous and sudden increase in the lifetime was observed at around 100 K; this result was in agreement with an increase in the positron lifetime reported in a previous study. It was revealed that the increase in the lifetime is very steep in cases of uniform mesopores, suggesting that the temperature dependence is influenced by the pore size.

  15. Initial angular momentum state in pp annihilation at rest

    CERN Document Server

    Bizzarri, R

    1972-01-01

    The author shows that no quantitative statement on the relative importance of initial P-states in pp annihilation can be made. Annihilations in flight indicate that P-wave annihilation into K/sub 1 //sup 0/K/sub 1//sup 0/ is inhibited while annihilation into pi pi is enhanced and might suggest a P-wave contamination approximately 10%. The observatory of the final state K/sub 1//sup 0/K/sub 1//sup 0/n from annihilations at rest indicates that the depression of the K/sub 1//sup 0/K/sub 1//sup 0/ final state is not so important and suggests a P-wave contamination smaller than 4%. Furthermore the successes obtained in the analysis of various final states on the assumption of S-wave annihilation are hard to reconcile with a P-wave contribution bigger than approximately 5%. (20 refs).

  16. Detection of defects in electron-irradiated synthetic silica quartz probed by positron annihilation

    International Nuclear Information System (INIS)

    Watauchi, Satoshi; Uedono, Akira; Ujihira, Yusuke; Yoda, Osamu.

    1994-01-01

    Defects in amorphous SiO 2 films, formed on MOS(metal/oxide/semiconductor) devices as gates, perturb its operation. The positron annihilation techniques, were applied to the study of the annealing behavior of the defects, introduced in the high purity synthetic quartz glass by the irradiation of 3-MeV electrons up to the 1x10 18 e - /cm 2 dosage. It was proved that the positron annihilation techniques were sufficiently sensitive to detect the defects in the electron-irradiated silica glasses. Three types of open-space defects were detected by the positron lifetime measurements. These can be attributed to monovacancy or divacancy type defects, vacancy clusters, and open-volume defects. A high formation probability (∼90%) of positroniums(Ps) was found in unirradiated specimens. These Ps were considered to be formed in open-volume defects. The formation probability of Ps was drastically decreased by the electron irradiation. But the size of open-volume defects was kept unchanged by the irradiation. These facts suggest that vacancy-type defects were introduced by the electron irradiation and that positrons were trapped in these defects. By the isochronal annealing in nitrogen atmosphere, the lifetime component (τ 2 ) and its relative intensity (I 2 ), attributed to positrons trapped in monovacancy or divacancy type defects and annihilated there, changed remarkably. τ 2 was constant in the temperature range up to 300degC, getting slightly shorter between 300degC and 700degC, and constant above 700degC. I 2 decreased gradually up to 300degC, constant between 300degC and 550degC, decreased above 550degC, and constant above 700degC. This revealed that the behavior of the defects, in which positrons were trapped, change by the elevation of the annealing temperature. (author)

  17. Role of vibrational dynamics in resonant positron annihilation on molecules.

    Science.gov (United States)

    Jones, A C L; Danielson, J R; Natisin, M R; Surko, C M

    2013-05-31

    Vibrational Feshbach resonances are dominant features of positron annihilation for incident positron energies in the range of the molecular vibrations. Studies in relatively small molecules are described that elucidate the role of intramolecular vibrational energy redistribution into near-resonant multimode states, and the subsequent coupling of these modes to the positron continuum, in suppressing or enhancing these resonances. The implications for annihilation in other molecular species, and the necessary ingredients of a more complete theory of resonant positron annihilation, are discussed.

  18. Application of the Positron Annihilation Technique to the study of vapors absorption process in polyethylene (LDPE) and in imide polymer (6FDA-TMPD PI)

    International Nuclear Information System (INIS)

    Sanchez Mendieta, V.

    1992-01-01

    It is well recognized that positron annihilation lifetime (PAL) spectra in polymers have a long-lived component that can be ascribed to ortho-positronium (o-Ps). The lifetime, τ 3 , is considered to be a measure of the size of the micro-vacancies in which o-Ps is trapped and is annihilated through pick-off annihilation with the rate which depends on the size of the vacancy. Positron lifetime measurements were performed for two different kinds of polymers (low density polyethylene and a polyimide (6FDA-TMPD) during sorption of various vapors (hexane, cyclohexane, benzene, acrylic acid, methyl acrylate, water and oxygen). The vapor sorption affected the long-lived component (ortho-positronium component) in a systematic way regardless of the kind of the vapor molecules, i.e. for the polyethylene both the lifetime and the intensity of the long-lived component were enhanced, while for the polyimide they were decreased significantly. These different effects are interpreted in terms of different states of sorbed molecules in rubbery (the polyethylene) and in glassy (the polyimide) polymers. (Author)

  19. 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)

    Kristiak, J.

    1995-11-01

    The positron lifetime results obtained on amorphous thermally treated Ni 25 Zr 55 Al 20 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 C 60 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 C 60 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 -10 m. Refs, figs, tabs

  20. Positron Annihilation Study of Defects in Succinonitrile

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Pedersen, Niels Jørgen; Sherwood, J. N.

    1979-01-01

    Positron lifetime and angular correlation measurements have been made on the plastic crystal succinonitrile. They confirm the phase transition at 234 ± 1 K. In the plastic phase the average orthopositronium lifetime increases with temperature and saturates at the highest temperatures. This is int...

  1. 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...... tests. Acceleration factors were determined using the ISOS-protocols, which enabled reproducible data acquisition between different laboratories and operators within the OPV community. A semi-automatic filtering method was employed for processing data acquired in outdoor tests. It was found...... results reveal that while the accelerated ageing studies reveal days and weeks of lifetime for the studied samples, in outdoor real operational conditions the samples demonstrate stability up to months and seasons....

  2. Local vacancies in optical modulation polymers studied by positron annihilation lifetime measurements

    International Nuclear Information System (INIS)

    Shimazu, Akira

    2009-01-01

    The ability of a slow positron beam to prove vacancies at the surface and in bulk regions of optical modulation polymers was demonstrated. A slow positron beam system was found to be a powerful tool to study the change in the microstructure driven by photopolymerization of novel optical modulation polymers. (author)

  3. Dark Matter Annihilation at the Galactic Center

    Energy Technology Data Exchange (ETDEWEB)

    Linden, Timothy Ryan [Univ. of California, Santa Cruz, CA (United States)

    2013-06-01

    Observations by the WMAP and PLANCK satellites have provided extraordinarily accurate observations on the densities of baryonic matter, dark matter, and dark energy in the universe. These observations indicate that our universe is composed of approximately ve times as much dark matter as baryonic matter. However, e orts to detect a particle responsible for the energy density of dark matter have been unsuccessful. Theoretical models have indicated that a leading candidate for the dark matter is the lightest supersymmetric particle, which may be stable due to a conserved R-parity. This dark matter particle would still be capable of interacting with baryons via weak-force interactions in the early universe, a process which was found to naturally explain the observed relic abundance of dark matter today. These residual annihilations can persist, albeit at a much lower rate, in the present universe, providing a detectable signal from dark matter annihilation events which occur throughout the universe. Simulations calculating the distribution of dark matter in our galaxy almost universally predict the galactic center of the Milky Way Galaxy (GC) to provide the brightest signal from dark matter annihilation due to its relative proximity and large simulated dark matter density. Recent advances in telescope technology have allowed for the rst multiwavelength analysis of the GC, with suitable e ective exposure, angular resolution, and energy resolution in order to detect dark matter particles with properties similar to those predicted by the WIMP miracle. In this work, I describe ongoing e orts which have successfully detected an excess in -ray emission from the region immediately surrounding the GC, which is di cult to describe in terms of standard di use emission predicted in the GC region. While the jury is still out on any dark matter interpretation of this excess, I describe several related observations which may indicate a dark matter origin. Finally, I discuss the

  4. Separating annihilation and excitation energy transfer dynamics in light harvesting systems.

    Science.gov (United States)

    Vengris, Mikas; Larsen, Delmar S; Valkunas, Leonas; Kodis, Gerdenis; Herrero, Christian; Gust, Devens; Moore, Thomas; Moore, Ana; van Grondelle, Rienk

    2013-09-26

    The dependence of excitation energy transfer kinetics on the electronic state of the acceptor (ground vs excited) has been resolved with a novel multipulse prePump-Pump-Probe spectroscopy. The primary energy transfer and annihilation dynamics in two model light-harvesting systems were explored: an artificially synthesized carotenoid-zinc-phthalocyanine dyad and a naturally occurring light-harvesting peridinin-chlorophyll protein complex from Amphidinium carterae. Both systems use carotenoid as the primary excitation energy donor with porphyrin chromophores as the acceptor molecules. The prePump-Pump-Probe transient signals were analyzed with Monte Carlo modeling to explicitly address the underlying step-by-step kinetics involved in both excitation migration and annihilation processes. Both energy transfer and annihilation dynamics were demonstrated to occur with approximately the same rate in both systems, regardless of the excitation status of the acceptor pigments. The possible reasons for these observations are discussed in the framework of the Förster energy transfer model.

  5. Detection of helium in irradiated Fe9Cr alloys by coincidence Doppler broadening of slow positron annihilation

    Science.gov (United States)

    Cao, Xingzhong; Zhu, Te; Jin, Shuoxue; Kuang, Peng; Zhang, Peng; Lu, Eryang; Gong, Yihao; Guo, Liping; Wang, Baoyi

    2017-03-01

    An element analysis method, coincidence Doppler broadening spectroscopy of slow positron annihilation, was employed to detect helium in ion-irradiated Fe9Cr alloys. Spectra with higher peak to background ratio were recorded using a two-HPGe detector coincidence measuring system. It means that information in the high-momentum area of the spectra can be used to identify helium in metals. This identification is not entirely dependent on the helium concentration in the specimens, but is related to the structure and microscopic arrangement of atoms surrounding the positron annihilation site. The results of Doppler broadening spectroscopy and transmission electron microscopy show that vacancies and dislocations were formed in ion-irradiated specimens. Thermal helium desorption spectrometry was performed to obtain the types of He traps.

  6. Annihilation model of the Tormac sheath

    International Nuclear Information System (INIS)

    Hammer, J.H.

    1979-02-01

    A one-dimensional, steady state fluid model is developed to describe the boundary layer between plasma and magnetic field that occurs in the Tormac sheath. Similar systems which may be treatable by the same model are tokamaks with divertors and reversed field mirrors. The model includes transport across the magnetic field as well as mirror losses along the field, the latter being represented as annihilation terms in the one-dimensional equations. The model equations are derived from the two-dimensional, time dependent hierarchy of equations generated by taking velocity moments of the kinetic equation including collisions

  7. On baryogenesis from dark matter annihilation

    International Nuclear Information System (INIS)

    Bernal, Nicolás; Colucci, Stefano; Ubaldi, Lorenzo; Josse-Michaux, François-Xavier; Racker, J.

    2013-01-01

    We study in detail the conditions to generate the baryon asymmetry of the universe from the annihilation of dark matter. This scenario requires a low energy mechanism for thermal baryogenesis, hence we first discuss some of these mechanisms together with the specific constraints due to the connection with the dark matter sector. Then we show that, contrary to what stated in previous studies, it is possible to generate the cosmological asymmetry without adding a light sterile dark sector, both in models with violation and with conservation of B−L. In addition, one of the models we propose yields some connection to neutrino masses

  8. From creation and annihilation operators to statistics

    Science.gov (United States)

    Hoyuelos, M.

    2018-01-01

    A procedure to derive the partition function of non-interacting particles with exotic or intermediate statistics is presented. The partition function is directly related to the associated creation and annihilation operators that obey some specific commutation or anti-commutation relations. The cases of Gentile statistics, quons, Polychronakos statistics, and ewkons are considered. Ewkons statistics was recently derived from the assumption of free diffusion in energy space (Hoyuelos and Sisterna, 2016); an ideal gas of ewkons has negative pressure, a feature that makes them suitable for the description of dark energy.

  9. Jets in e+e- annihilation

    International Nuclear Information System (INIS)

    Hanson, G.G.

    1978-05-01

    The latest results on R, the ratio of the total cross section for production of multihadronic events to the muon pair production cross section, and inclusive distributions of hadrons from e + e - annihilation in the center-of-mass energy range from 2.6 to 7.8 GeV are presented. The evidence for jet structure is reviewed. Inclusive distributions of hadrons in Feynman x, rapidity, and transverse momentum relative to the jet direction are studied. Particular emphasis is placed on the method used to measure these inclusive distributions and the biases which might result from this method

  10. Particle-antiparticle asymmetries from annihilations.

    Science.gov (United States)

    Baldes, Iason; Bell, Nicole F; Petraki, Kalliopi; Volkas, Raymond R

    2014-10-31

    An extensively studied mechanism to create particle-antiparticle asymmetries is the out-of-equilibrium and CP violating decay of a heavy particle. We, instead, examine how asymmetries can arise purely from 2→2 annihilations rather than from the usual 1→2 decays and inverse decays. We review the general conditions on the reaction rates that arise from S-matrix unitarity and CPT invariance, and show how these are implemented in the context of a simple toy model. We formulate the Boltzmann equations for this model, and present an example solution.

  11. Apparatus for photon activation positron annihilation analysis

    Science.gov (United States)

    Akers, Douglas W [Idaho Falls, ID

    2007-06-12

    Non-destructive testing apparatus according to one embodiment of the invention comprises a photon source. The photon source produces photons having predetermined energies and directs the photons toward a specimen being tested. The photons from the photon source result in the creation of positrons within the specimen being tested. A detector positioned adjacent the specimen being tested detects gamma rays produced by annihilation of positrons with electrons. A data processing system operatively associated with the detector produces output data indicative of a lattice characteristic of the specimen being tested.

  12. Studies of the subsurface zone created in aluminium and its alloys by means of positron annihilation and complementary methods

    International Nuclear Information System (INIS)

    Dryzek, E.

    2008-01-01

    There are presented the results of the studies of the subsurface zone created in aluminium and its alloys during sliding or other surface modification treatments. The application of the positron annihilation techniques due to their high sensitivity to crystal lattice defects enabled to determine defects profiles in the subsurface zone. The positron annihilation studies were correlated with other conventional measurements applied in tribology, i.e. microhardness measurements, scanning electron microscopy, X-ray diffraction and in a special case stress distribution calculated theoretically. It was shown that the positron annihilation spectroscopy is a useful tool for profiling of the subsurface zone created during sliding even for light metals their alloys and composites. The total range of the subsurface zone detected by the positron annihilation extends from 50 μm to 450 μm depending on the material studied and surface modification treatment. Additionally, the type of the main defects can be determined. The studies of the pure aluminium samples after dry sliding enabled to find the defect concentration of vacancy type in the depth less then 1 μm and to correlate its value with the size of crystallites. It supports the conclusion on recovery processes taking place in this layer. There was made the attempt to apply the Doppler broadening coincidence spectroscopy to the studies of aluminium alloy and composite. In view of the interdisciplinary character the present thesis enclose also the review of the basic issues of tribology, measurement methods applied to the subsurface zone studies and positron annihilation experimental techniques. (author)

  13. New particles produced in electron--positron annihilation

    International Nuclear Information System (INIS)

    Perl, M.L.

    1975-01-01

    The main properties of the new particles produced in e + e - annihilation are reviewed. Included are properties of the continuum region, the 4.1-GeV enhancement, the psi and psi', radiative decays of the psi and psi', singly charmed particle searches in e + - e - annihilation, and the e/sub μ/ events

  14. Study of double scattering effect in antiproton--deuteron annihilation

    International Nuclear Information System (INIS)

    Zemany, P.D.

    1975-01-01

    The double scattering process in the deuteron is investigated for the reaction anti pd → p/sub s/ + mesons. About 30 percent of the apparent anti pn annihilations are involved in double scattering. A model which describes the properties of protons emerging from apparent anti pn annihilations is presented

  15. Soliton annihilation in the perturbed sine-Gordon system

    DEFF Research Database (Denmark)

    Pedersen, Niels Falsig; Samuelsen, Mogens Rugholm; Welner, D.

    1984-01-01

    Fluxon-antifluxon annihilation in the perturbed sine-Gordon equation with loss and driving terms is investigated. For the infinite line we find a simple analytic expression for the threshold driving term corresponding to annihilation. With the application of the results to a Josephson junction of...

  16. Impact of dark matter decays and annihilations on structure formation

    NARCIS (Netherlands)

    Mapelli, M.; Ripamonti, E.

    2007-01-01

    Abstract: We derived the evolution of the energy deposition in the intergalactic medium (IGM) by different decaying (or annihilating) dark matter (DM) candidates. Heavy annihilating DM particles (with mass larger than a few GeV) have no influence on reionization and heating, even if we assume that

  17. CMB constraint on dark matter annihilation after Planck 2015

    Energy Technology Data Exchange (ETDEWEB)

    Kawasaki, Masahiro [Institute for Cosmic Ray Research, The University of Tokyo, Kashiwa, Chiba 277-8568 (Japan); Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Nakayama, Kazunori, E-mail: kazunori@hep-th.phys.s.u-tokyo.ac.jp [Department of Physics, Faculty of Science, The University of Tokyo, Bunkyo-ku, Tokyo 133-0033 (Japan); Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Sekiguchi, Toyokazu [Institute for Basic Science, Center for Theoretical Physics of the Universe, Daejeon 34051 (Korea, Republic of)

    2016-05-10

    We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.

  18. Nucleon-antinucleon annihilation in chiral soliton model

    International Nuclear Information System (INIS)

    Musakhanov, M.M.; Tashkentskij Gosudarstvennyj Univ., Tashkent; Musatov, I.V.

    1991-01-01

    We investigate annihilation process of nucleons in the chiral soliton model by the path integral method. A soliton-antisoliton pair is shown to decay into mesons at range of about 1fm, defined by the S bar S potential. Contribution of the annihilation channel to the elastic scattering is discussed

  19. CMB constraint on dark matter annihilation after Planck 2015

    Directory of Open Access Journals (Sweden)

    Masahiro Kawasaki

    2016-05-01

    Full Text Available We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.

  20. The Antiproton-Nucleon Annihilation Process (Antiproton Collaboration Experiment)

    Science.gov (United States)

    Barkas, W. H.; Birge, R. W.; Chupp, W. W.; Ekspong, A. G.; Goldhaber, G.; Goldhaber, S.; Heckman, H. H.; Perkins, D. H.; Sandweiss, J.; Segre, E.; Smith, F. M.; Stork, D. H.; Rossum, L. Van; Amaldi, E.; Baroni, G.; Castagnoli, C.; Franzinetti, C.; Manfredini, A.

    1956-09-10

    In the exposure to a 700-MeV/c negative particle beam, 35 antiproton stars have been found. Of these antiprotons, 21 annihilate in flight and three give large-angle scatters ({Theta} > 15 , T{sub P-} > 50 Mev), while 14 annihilate at rest. From the interactions in flight we obtain the total cross section for antiproton interaction.

  1. Component lifetime modelling

    NARCIS (Netherlands)

    Verweij, J.F.; Verweij, J.F.; Brombacher, A.C.; Brombacher, A.C.; Lunenborg, M.M.; Lunenborg, M.M.

    1994-01-01

    There are two approaches to component lifetime modelling. The first one uses a reliability prediction method as described in the (military) handbooks with the appropriate models and parameters. The advantages are: (a) It takes into account all possible failure mechanisms. (b) It is easy to use. The

  2. Constraining annihilating dark matter by radio data of M33

    Science.gov (United States)

    Chan, Man Ho

    2017-08-01

    Recent studies of radio data put strong constraints on annihilation cross sections for dark matter. In this article, we provide the first analysis of using M33 radio data in constraining annihilating dark matter. The resulting constraints of annihilation cross sections for some channels are more stringent than that obtained from six years of Fermi Large Area Telescope (Fermi-LAT) gamma-ray observations of the Milky Way dwarf spheroidal satellite galaxies. In particular, the conservative lower limits of dark matter mass annihilating via e+e-, μ+μ- and τ+τ- channels are 190, 120 and 70 GeV, respectively, with the thermal relic annihilation cross section. These results are in significant tension with some of the recent quantitative analyses of the AMS-02 and Fermi-LAT data of the Milky Way center.

  3. Positron annihilation in the nuclear outflows of the Milky Way

    Science.gov (United States)

    Panther, Fiona H.; Crocker, Roland M.; Birnboim, Yuval; Seitenzahl, Ivo R.; Ruiter, Ashley J.

    2018-02-01

    Observations of soft gamma rays emanating from the Milky Way from SPI/INTEGRAL reveal the annihilation of ˜2 × 1043 positrons every second in the Galactic bulge. The origin of these positrons, which annihilate to produce a prominent emission line centred at 511 keV, has remained mysterious since their discovery almost 50 yr ago. A plausible origin for the positrons is in association with the intense star formation ongoing in the Galactic centre. Moreover, there is strong evidence for a nuclear outflow in the Milky Way. We find that advective transport and subsequent annihilation of positrons in such an outflow cannot simultaneously replicate the observed morphology of positron annihilation in the Galactic bulge and satisfy the requirement that 90 per cent of positrons annihilate once the outflow has cooled to 104 K.

  4. Positron annihilation studies in high-Tc superconductors RBa2Cu3Oy, R: La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er

    International Nuclear Information System (INIS)

    Lagouri, T.; Dedoussis, S.; Chardalas, M.; Liolios, A.

    1997-01-01

    Positron lifetime and Doppler broadening of the annihilation line measurements have been performed at room temperature in high-T c superconductors RBa 2 Cu 3 O y , where R: La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er and 6.9 c superconducting samples RBa 2 Cu 3 O y , where R: Nd, Sm, Eu, Ho, Y, Er as a function of temperature between 14 K and 293 K. It was observed that the positron lifetime and the S parameter values at room temperature have no obvious trend in their variation from the yttrium substitution by a rare-earth element. It was also observed that the temperature dependence of the positron annihilation parameters is similar in the high-T c superconducting samples. (orig.)

  5. Studying functional properties of hydrogel and silicone-hydrogel contact lenses with PALS, MIR and Raman spectroscopy

    Science.gov (United States)

    Filipecki, J.; Sitarz, M.; Kocela, A.; Kotynia, K.; Jelen, P.; Filipecka, K.; Gaweda, M.

    2014-10-01

    Determination of free volume holes of the hydrogel and silicone-hydrogel polymer contact lenses were investigated. Two types of polymer contact lenses were used as materials: the first is a hydrogel contact lenses Proclear family (Omafilcon A), while the second is a silicone-hydrogel contact lens of the family Biofinity (Comfilcon A). Positron annihilation lifetime spectroscopy PALS was used to characterize geometrical sizes and fraction of the free volume holes in the investigated samples. There is a clear difference in the free volume sizes and their fractions between silicone-hydrogel and polymer hydrogel contact lenses which in turn are connected with oxygen permeability in these lenses. Apart from that, spectroscopic (middle infrared) MIR and Raman examinations were carried out in order to demonstrate the differences of the water content in the test contact lenses.

  6. Lifetime of heavy hypernuclei and its implications on the weak LAMBDA N interaction

    CERN Document Server

    Cassing, W; Kamys, B; Kulessa, P; Niewodniczanski, H; Ohm, H; Pysz, K; Rudy, Z; Schult, O W B; Ströher, H

    2003-01-01

    The lifetime of the LAMBDA-hyperon in heavy hypernuclei measured in proton-Au, -Bi and -U collisions by the COSY-13 Collaboration at COSY-Juelich has been analyzed to yield tau subLAMBDA=(145+-11) ps. This value for tau subLAMBDA is compatible with the lifetime extracted from antiproton annihilation on Bi and U targets, albeit much more accurate. Theoretical models based on the meson exchange picture and assuming the validity of the phenomenological DELTA I=1/2 rule predict the lifetime of heavy hypernuclei to be significantly larger (2-3 standard deviations). Such large differences indicate that at least one of the assumptions in these models is not fulfilled. A much better reproduction of the lifetimes of heavy hypernuclei is achieved in the phase space model, if the DELTA I=1/2 rule is discarded in the nonmesonic LAMBDA decay. (orig.)

  7. Measurement of pO2 by luminescence lifetime spectroscopy: A comparative study of the phototoxicity and sensitivity of [Ru(Phen)3 ]2+ and PdTCPP in vivo.

    Science.gov (United States)

    Huntosova, Veronika; Gerelli, Emmanuel; Horvath, Denis; Wagnieres, Georges

    2017-05-01

    Dysfunctions in tissue metabolism can be detected at early stages by oxygen partial pressure (pO 2 ) measurement. The measurement of emission lifetimes offers very promising and non-invasive approach to estimate pO 2 in vivo. This study compares two extensively used oxygen sensors and assesses their in vivo oxygen sensitivity and phototoxic effect. Luminescence lifetime of Ru-polypyridyl complex and of Pd-porphyrin is measured in the Chick's Chorioallantoic Membrane (CAM) model with a dedicated optical fiber-based, time-resolved spectrometer. The Pd-porphyrin luminescence lifetimes measured in the CAM model exposed to different pO 2 levels are longer and have a broader dynamic range (10-100 μs) than those of Ru-polypyridyl complex (0.6-1 μs). The combined statistical analysis based on an estimate of the kurtosis and skewness, bootstrapping method and routine normality tests is performed. The indicators of the averages and signal to noise ratio stability are also calculated. The combination of several data processing allows selection of the better sensor for a given application. In particular, it is found that the advantage of Ru-polypyridyl complex over Pd-porphyrin is two-fold: i) Ru-polypyridyl complex datasets have consistently better statistical characteristics, ii) Ru-polypyridyl exhibits lower cytotoxicity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Filter replacement lifetime prediction

    Science.gov (United States)

    Hamann, Hendrik F.; Klein, Levente I.; Manzer, Dennis G.; Marianno, Fernando J.

    2017-10-25

    Methods and systems for predicting a filter lifetime include building a filter effectiveness history based on contaminant sensor information associated with a filter; determining a rate of filter consumption with a processor based on the filter effectiveness history; and determining a remaining filter lifetime based on the determined rate of filter consumption. Methods and systems for increasing filter economy include measuring contaminants in an internal and an external environment; determining a cost of a corrosion rate increase if unfiltered external air intake is increased for cooling; determining a cost of increased air pressure to filter external air; and if the cost of filtering external air exceeds the cost of the corrosion rate increase, increasing an intake of unfiltered external air.

  9. Decreasing luminescence lifetime of evaporating phosphorescent droplets

    Science.gov (United States)

    van der Voort, D. D.; Dam, N. J.; Sweep, A. M.; Kunnen, R. P. J.; van Heijst, G. J. F.; Clercx, H. J. H.; van de Water, W.

    2016-12-01

    Laser-induced phosphorescence has been used extensively to study spray dynamics. It is important to understand the influence of droplet evaporation in the interpretation of such measurements, as it increases luminescence quenching. By suspending a single evaporating n-heptane droplet in an acoustic levitator, the properties of lanthanide-complex europium-thenoyltrifluoroacetone-trioctylphosphine oxide (Eu-TTA-TOPO) phosphorescence are determined through high-speed imaging. A decrease was found in the measured phosphorescence decay coefficient (780 → 200 μs) with decreasing droplet volumes (10-9 → 10-11 m3) corresponding to increasing concentrations (10-4 → 10-2 M). This decrease continues up to the point of shell-formation at supersaturated concentrations. The diminished luminescence is shown not to be attributable to triplet-triplet annihilation, quenching between excited triplet-state molecules. Instead, the pure exponential decays found in the measurements show that a non-phosphorescent quencher, such as free TTA/TOPO, can be attributable to this decay. The concentration dependence of the phosphorescence lifetime can therefore be used as a diagnostic of evaporation in sprays.

  10. Simulation of the annihilation emission of galactic positrons

    International Nuclear Information System (INIS)

    Gillard, W.

    2008-01-01

    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. D-brane scattering and annihilation

    International Nuclear Information System (INIS)

    D’Amico, Guido; Gobbetti, Roberto; Kleban, Matthew; Schillo, Marjorie

    2015-01-01

    We study the dynamics of parallel brane-brane and brane-antibrane scattering in string theory in flat spacetime, focusing on the pair production of open strings that stretch between the branes. We are particularly interested in the case of scattering at small impact parameter bannihilating, so long as g s is small and the relative velocity v is neither too small nor too close to 1. Our analysis is relevant also to the case of charged open string production in world-volume electric fields, and we make use of this T-dual scenario in our analysis. We briefly discuss the application of our results to a stringy model of inflation involving moving branes.

  12. The spectroscopy of the new particles

    International Nuclear Information System (INIS)

    Gottfried, K.

    1977-01-01

    Theories and models of heavy quark-antiquark systems are reviewed. The principal topics are: i) the spectroscopy of the psi-family both above and below charm threshold; ii) production of charmed mesons in e + e - annihilation; and iii) the consequences of interpreting UPSILON and UPSILON' as bound states of a new quark-antiquark system. (orig.) [de

  13. Gamma Irradiation Effect on Biodegradable Poly (Hydroxybutyrate) Studied by Positron Annihilation Technique

    International Nuclear Information System (INIS)

    Abdel-Hady, E.E.; Mohamed, S.S.

    2010-01-01

    -Bacterial polyesters have attracted much attention as biodegradable polymers. An ecofriendly alternative to this biodegradable material is poly-3-hydroxybutyrate (PHB) which has attracted industrial attention as an environmentally degradable plastic for a wide range of medical applications. Free volume holes in polymers play a crucial role in determining its physical properties. The Positron Annihilation Lifetime (PAL) technique has been established as a powerful probe for microstructures of polymers, in particular, angstrom-sized free volume holes. The PHB samples were irradiated using 60 Co source at room temperature with doss ranging from 5 to 300 kGy. The PAL spectra for all the samples have been measured at room temperature as a function of gamma-irradiation dose. The free volume hole size decreases with increasing the irradiation dose up to 25 kGy followed by slowly increases up to 200 kGy, then decreases at higher doses. On the other hand, the free volume content decreases with increasing the gamma-irradiation dose which is due to the increase of the degree of crystallinity. The variations in the free volume with the irradiation dose will be discussed in the frame of free volume model. A correlation between the macroscopic mechanical properties Hv and positron annihilation parameters has been done

  14. Linear and non-linear approaches to solve the inverse problem: applications to positron annihilation experiments

    International Nuclear Information System (INIS)

    Hoffmann, L.; Shukla, A.; Peter, M.; Barbiellini, B.; Manuel, A.A.

    1993-01-01

    We present linear and non-linear filters to solve the ill-posed inverse problem and we use them to extract relevant information from positron lifetime and 2D-angular correlation of the annihilation radiation of positrons in solids. A general optimal linear filter is first derived. Then a second linear approach, based on Bayes' theorem, is described. We show that these two linear approaches are indeed equivalent. Two non-linear methods are then discussed. The first is a Bayesian approach which makes use of the maximum entropy principle. The second is an iterative method derived from the general optimal linear filter. Applications of these filtering techniques to positron lifetime decay curves illustrate how lifetimes shorter than the instrumental resolution can be extracted. Finally, we apply the iterative non-linear filter to the problem of the ridge-like Fermi surface on the high temperature superconducting compound YBa 2 Cu 3 O 7-δ . For the first time a direct measurement of the ridge width through a Brillouin zone is obtained. It is compared with results of band structure calculations. (orig.)

  15. Positron Spectroscopy of Nanodiamonds after Hydrogen Sorption

    Directory of Open Access Journals (Sweden)

    Lyudmila Nikitina

    2018-01-01

    Full Text Available The structure and defects of nanodiamonds influence the hydrogen sorption capacity. Positronium can be used as a sensor for detecting places with the most efficient capture of hydrogen atoms. Hydrogenation of carbon materials was performed from gas atmosphere. The concentration of hydrogen absorbed by the sample depends on the temperature and pressure. The concentration 1.2 wt % is achieved at the temperature of 243 K and the pressure of 0.6 MPa. The hydrogen saturation of nanodiamonds changes the positron lifetime. Increase of sorption cycle numbers effects the positron lifetime, as well as the parameters of the Doppler broadening of annihilation line. The electron-positron annihilation being a sensitive method, it allows detecting the electron density fluctuation of the carbon material after hydrogen saturation.

  16. Annihilation of vortex dipoles in an Oblate Bose-Einstein Condensate

    OpenAIRE

    Prabhakar, Shashi; Singh, R. P.; Gautam, S.; Angom, D.

    2011-01-01

    We theoretically explore the annihilation of vortex dipoles, generated when an obstacle moves through an oblate Bose-Einstein condensate, and examine the energetics of the annihilation event. We show that the gray soliton, which results from the vortex dipole annihilation, is lower in energy than the vortex dipole. We also investigate the annihilation events numerically and observe that the annihilation occurs only when the vortex dipole overtakes the obstacle and comes closer than the cohere...

  17. Dynamics of vortex-antivortex creation and annihilation in current-driven mesoscopic superconducting squares

    Science.gov (United States)

    Liang, Xiao-Meng; Zha, Guo-Qiao

    2015-12-01

    In this paper, based on the time-dependent Ginzburg-Landau theory, we study the dynamics of vortex-antivortex (V-Av) pairs in a mesoscopic superconducting square with a small hole under applied bias currents. For the sample with a centered hole, a V-Av pair can nucleate at the hole edges and moves in opposite directions perpendicular to applied constant DC drive. The influence of the external magnetic field on the (anti)vortex velocity and the lifetime of V-Av pairs is mainly investigated. Different modes in the dynamical process of the V-Av collision and annihilation are identified. Moreover, in the case when the hole is displaced from the center of the square, the V-Av dynamics behaves quite differently from the symmetric case due to the shift of the V-Av creation point.

  18. Subliminal psychodynamic activation method and annihilation anxiety: preliminary findings.

    Science.gov (United States)

    Greenberg, A C

    1992-02-01

    Research with the subliminal psychodynamic activation (SPA) method has led to improvements in subjects' functioning in a variety of areas, including but not limited to weight control, school grades, and feelings of general anxiety. In 1987, Hurvich proposed that the SPA method could be used to further the understanding of annihilation anxiety. 100 nonclinical subjects completed questionnaires pertaining to annihilation anxiety, psychological differentiation, and state anxiety and were tachistoscopically exposed to the subliminal message of symbiotic-like oneness, MOMMY AND I ARE ONE, and to control messages. Analysis showed that women with low annihilation anxiety had significantly lower state anxiety than women with high annihilation anxiety, regardless of the content of the subliminal message; results did not reach significance for men. Correlations among scores on the questionnaires also were noted.

  19. Entanglement-annihilating and entanglement-breaking channels

    International Nuclear Information System (INIS)

    Moravcikova, Lenka; Ziman, Mario

    2010-01-01

    We introduce and investigate a family of entanglement-annihilating channels. These channels are capable of destroying any quantum entanglement within the system they act on. We show that they are not necessarily entanglement breaking. In order to achieve this result we analyze the subset of locally entanglement-annihilating channels. In this case, the same local noise applied on each subsystem individually is less entanglement annihilating (with respect to multi-partite entanglement) as the number of subsystems is increasing. Therefore, the bipartite case provides restrictions on the set of local entanglement-annihilating channels for the multipartite case. The introduced concepts are illustrated on the family of single-qubit depolarizing channels.

  20. φ production in anti pp annihilation at rest

    International Nuclear Information System (INIS)

    Reifenroether, J.; Beuchert, K.; Duch, K.D.; Kalinowsky, H.; Klempt, E.; May, B.; Weidenauer, P.; Gastaldi, U.; Landua, R.; Dahme, W.; Bizot, J.C.; Delcourt, B.; White, B.L.; Amsler, C.; Doser, M.; Riedlberger, J.; Straumann, U.; Truoel, P.

    1991-01-01

    We report on measurements of the branching ratios for φ production in anti pp annihilation at rest in H 2 gas. Branching ratios for φπ 0 , φη, φρ 0 , φω and φπ + π - are determined for two data sets with different contributions of annihilations from S and P states of the anti pp system. The branching ratios are compared to corresponding annihilation modes where the φ is replaced by an ω meson. We conclude that φ production is in most reactions enhanced with respect to the expectation based on the OZI rule. In annihilations from the spin triplet ground state of antiprotonic hydrogen into φπ the OZI rule is violated dramatically. (orig.)

  1. Black Hole Window into p-Wave Dark Matter Annihilation.

    Science.gov (United States)

    Shelton, Jessie; Shapiro, Stuart L; Fields, Brian D

    2015-12-04

    We present a new method to measure or constrain p-wave-suppressed cross sections for dark matter (DM) annihilations inside the steep density spikes induced by supermassive black holes. We demonstrate that the high DM densities, together with the increased velocity dispersion, within such spikes combine to make thermal p-wave annihilation cross sections potentially visible in γ-ray observations of the Galactic center (GC). The resulting DM signal is a bright central point source with emission originating from DM annihilations in the absence of a detectable spatially extended signal from the halo. We define two simple reference theories of DM with a thermal p-wave annihilation cross section and establish new limits on the combined particle and astrophysical parameter space of these models, demonstrating that Fermi Large Area Telescope is currently sensitive to thermal p-wave DM over a wide range of possible scenarios for the DM distribution in the GC.

  2. Fluorescence lifetime based bioassays

    Science.gov (United States)

    Meyer-Almes, Franz-Josef

    2017-12-01

    Fluorescence lifetime (FLT) is a robust intrinsic property and material constant of fluorescent matter. Measuring this important physical indicator has evolved from a laboratory curiosity to a powerful and established technique for a variety of applications in drug discovery, medical diagnostics and basic biological research. This distinct trend was mainly driven by improved and meanwhile affordable laser and detection instrumentation on the one hand, and the development of suitable FLT probes and biological assays on the other. In this process two essential working approaches emerged. The first one is primarily focused on high throughput applications employing biochemical in vitro assays with no requirement for high spatial resolution. The second even more dynamic trend is the significant expansion of assay methods combining highly time and spatially resolved fluorescence data by fluorescence lifetime imaging. The latter approach is currently pursued to enable not only the investigation of immortal tumor cell lines, but also specific tissues or even organs in living animals. This review tries to give an actual overview about the current status of FLT based bioassays and the wide range of application opportunities in biomedical and life science areas. In addition, future trends of FLT technologies will be discussed.

  3. Significant gamma-ray lines from dark matter annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Duerr, Michael [DESY, Notkestrasse 85, 22607 Hamburg (Germany); Fileviez Perez, Pavel; Smirnov, Juri [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg (Germany)

    2016-07-01

    Gamma-ray lines from dark matter annihilation are commonly seen as a ''smoking gun'' for the particle nature of dark matter. However, in many dark matter models the continuum background from tree-level annihilations makes such a line invisible. I present two simple extensions of the Standard Model where the continuum contributions are suppressed and the gamma-ray lines are easily visible over the continuum background.

  4. Breit-Wigner Enhancement of Dark Matter Annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Ibe, Masahiro; /SLAC; Murayama, Hitoshi; /Tokyo U., IPMU /UC, Berkeley /LBL, Berkeley; Yanagida, T.T.; /Tokyo U. /Tokyo U., IPMU

    2009-06-19

    We point out that annihilation of dark matter in the galactic halo can be enhanced relative to that in the early universe due to a Breit-Wigner tail, if the dark matter annihilates through a pole just below the threshold. This provides a new explanation to the 'boost factor' which is suggested by the recent data of the PAMELA, ATIC and PPB-BETS cosmic-ray experiments.

  5. Fusion Reactions and Matter-Antimatter Annihilation for Space Propulsion

    Science.gov (United States)

    2005-07-13

    FUSION REACTIONS AND MATTER- ANTIMATTER ANNIHILATION FOR SPACE PROPULSION Claude DEUTSCH LPGP (UMR-CNRS 8578), Bât. 210, UPS, 91405 Orsay...REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE šFusion Reactions And Matter- Antimatter Annihilation For Space Propulsion 5a...which is possible with successful MCF or ICF. Appropriate vessel designs will be presented for fusion as well as for antimatter propulsion. In

  6. Structure formation constraints on Sommerfeld-enhanced dark matter annihilation

    International Nuclear Information System (INIS)

    Armendariz-Picon, Cristian; Neelakanta, Jayanth T.

    2012-01-01

    We study the growth of cosmic structure in a ΛCDM universe under the assumption that dark matter self-annihilates with an averaged cross section times relative velocity that grows with the scale factor, an increase known as Sommerfeld-enhancement. Such an evolution is expected in models in which a light force carrier in the dark sector enhances the annihilation cross section of dark matter particles, and has been invoked, for instance, to explain anomalies in cosmic ray spectra reported in the past. In order to make our results as general as possible, we assume that dark matter annihilates into a relativistic species that only interacts gravitationally with the standard model. This assumption also allows us to test whether the additional relativistic species mildly favored by cosmic-microwave background data could originate from dark matter annihilation. We do not find evidence for Sommerfeld-enhanced dark matter annihilation and derive the corresponding upper limits on the annihilation cross-section

  7. Positron Transport and Annihilation in the Galactic Bulge

    Directory of Open Access Journals (Sweden)

    Fiona Helen Panther

    2018-03-01

    Full Text Available The annihilation of positrons in the Milky Way Galaxy has been observed for ∼50 years; however, the production sites of these positrons remains hard to identify. The observed morphology of positron annihilation gamma-rays provides information on the annihilation sites of these Galactic positrons. It is understood that the positrons responsible for the annihilation signal originate at MeV energies. The majority of sources of MeV positrons occupy the star-forming thin disk of the Milky Way. If positrons propagate far from their sources, we must develop accurate models of positron propagation through all interstellar medium (ISM phases in order to reveal the currently uncertain origin of these Galactic positrons. On the other hand, if positrons annihilate close to their sources, an alternative source of MeV positrons with a distribution that matches the annihilation morphology must be identified. In this work, I discuss the various models that have been developed to understand the origin of the 511 keV line from the direction of the Galactic bulge, and the propagation of positrons in the ISM.

  8. Cosmic gamma-ray background from dark matter annihilation

    International Nuclear Information System (INIS)

    Ando, Shin'ichiro

    2007-01-01

    High-energy photons from pair annihilation of dark matter particles contribute to the cosmic gamma-ray background (CGB) observed in a wide energy range. The precise shape of the energy spectrum of CGB depends on the nature of dark matter particles. In order to discriminate between the signals from dark matter annihilation and other astrophysical sources, however, the information from the energy spectrum of CGB may not be sufficient. We show that dark matter annihilation not only contributes to the mean CGB intensity, but also produces a characteristic anisotropy, which provides a powerful tool for testing the origins of the observed CGB. We show that the expected sensitivity of future gamma-ray detectors such as GLAST should allow us to measure the angular power spectrum of CGB anisotropy, if dark matter particles are supersymmetric neutralinos and they account for most of the observed mean intensity. As the intensity of photons from annihilation is proportional to the density squared, we show that the predicted shape of the angular power spectrum of gamma rays from dark matter annihilation is different from that due to other astrophysical sources such as blazars, whose intensity is linearly proportional to density. Therefore, the angular power spectrum of the CGB provides a 'smoking-gun' signature of gamma rays from dark matter annihilation

  9. SIMP spectroscopy

    International Nuclear Information System (INIS)

    Hochberg, Yonit; Kuflik, Eric; Murayama, Hitoshi

    2016-01-01

    We study the interactions between strongly interacting massive particle dark matter and the Standard Model via a massive vector boson that is kinetically mixed with the hypercharge gauge boson. The relic abundance is set by 3→2 self-interactions of the dark matter, while the interactions with the vector mediator enable kinetic equilibrium between the dark and visible sectors. We show that a wide range of parameters is phenomenologically viable and can be probed in various ways. Astrophysical and cosmological constraints are evaded due to the p-wave nature of dark matter annihilation into visible particles, while direct detection methods using electron recoils can be sensitive to parts of the parameter space. In addition, we propose performing spectroscopy of the strongly coupled dark sector at e + e − colliders, where the energy of a mono-photon can track the resonance structure of the dark sector. Alternatively, some resonances may decay back into Standard Model leptons or jets, realizing ‘hidden valley’ phenomenology at the LHC and ILC in a concrete fashion.

  10. SIMP spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hochberg, Yonit [Ernest Orlando Lawrence Berkeley National Laboratory, University of California,Berkeley, CA 94720 (United States); Department of Physics, University of California,Berkeley, CA 94720 (United States); Kuflik, Eric [Department of Physics, LEPP, Cornell University,Ithaca NY 14853 (United States); Murayama, Hitoshi [Ernest Orlando Lawrence Berkeley National Laboratory, University of California,Berkeley, CA 94720 (United States); Department of Physics, University of California,Berkeley, CA 94720 (United States); Kavli Institute for the Physics and Mathematics of the Universe (WPI),University of Tokyo Institutes for Advanced Study, University of Tokyo,Kashiwa 277-8583 (Japan); Center for Japanese Studies, University of California,Berkeley, CA 94720 (United States)

    2016-05-16

    We study the interactions between strongly interacting massive particle dark matter and the Standard Model via a massive vector boson that is kinetically mixed with the hypercharge gauge boson. The relic abundance is set by 3→2 self-interactions of the dark matter, while the interactions with the vector mediator enable kinetic equilibrium between the dark and visible sectors. We show that a wide range of parameters is phenomenologically viable and can be probed in various ways. Astrophysical and cosmological constraints are evaded due to the p-wave nature of dark matter annihilation into visible particles, while direct detection methods using electron recoils can be sensitive to parts of the parameter space. In addition, we propose performing spectroscopy of the strongly coupled dark sector at e{sup +}e{sup −} colliders, where the energy of a mono-photon can track the resonance structure of the dark sector. Alternatively, some resonances may decay back into Standard Model leptons or jets, realizing ‘hidden valley’ phenomenology at the LHC and ILC in a concrete fashion.

  11. Positron lifetime calculations of defects in vanadium containing hydrogen

    International Nuclear Information System (INIS)

    Troev, T.; Markovski, A.; Petrova, M.; Peneva, S.; Yoshiie, T.

    2006-01-01

    Positron lifetime quantum-mechanical calculations were carried out for the investigation of defects in vanadium containing hydrogen atoms. The convergence of electronic structure calculations for supercell size is studied for vacancies, vacancy-clusters (nano-voids) and vacancy-clusters containing hydrogen. The electron wave functions have been obtained in the local density approximation (LDA) to the density functional theory (DFT). On the basis of the calculated results, the behaviours of empty nano-voids and nano-voids with hydrogen are discussed. It is found that hydrogen in larger three-dimensional vacancy-clusters change the annihilation characteristics drastically. The hydrogen atoms are trapped by lattice vacancies. These results provide physical insight for positron interactions with defects in vanadium and can be used for the prediction of hydrogen generation useful for the design of a fusion reactor

  12. Experimental positions and lifetimes of Be-like 1s{sup 2}3lnl'(n=3 to 5) states of O{sup 4+} and Ne{sup 6+} ions investigated by high resolution electron spectroscopy: test of calculations

    Energy Technology Data Exchange (ETDEWEB)

    Bordenave-Montesquieu, A.; Moretto-Capelle, P.; Bordenave-Montesquieu, D. [Univ. Paul Sabatier, Toulouse (France). Lab. Collisions - Agregats - Reactivite

    1999-07-01

    Using high resolution electron spectroscopy, positions and lifetimes of many Be-like singlet states of the 1s{sup 2}3lnl' Rydberg series (n = 3 to 5) of oxygen and neon have been measured for the first time. This was achieved by a fitting procedure which takes into account an accurate definition of the post-collisional electron lineshapes. These states are produced after a double electron capture by multicharged ions has occurred in O{sup 6+}(1s{sup 2})+He, H{sub 2} and Ne{sup 8+}(1s{sup 2})+He collisions at about 4 keV/amu collision energy. (orig.)

  13. B meson lifetime measurement

    International Nuclear Information System (INIS)

    Piccolo, M.

    1989-01-01

    The lifetime of hadrons containing b-quark has been the subject of extensive experimental work and theoretical speculation; its importance is due to implications on some of the fundamental parameters of the Standard Model, such as the top quark mass and the mixing angles. Since the pioneer measurements of the MAC and MARK II collaborations at PEP in 1983 the progress has been impressive; but many issues still remain open and await further study. In this paper the field's present status is discussed. An overview of the theoretical motivations for this measurements in the Standard Model framework is done. Then the experimental techniques used are reviewed, emphasizing the most recent measurements. A comparison of the results obtained is done and systematic errors are discussed. In conclusion there are some remarks on the further developments foreseen in the near future

  14. Frequency domain kinetic of positron-electron annihilation in the MgO-Al2O3 spinel-type ceramics

    Science.gov (United States)

    Fl'unt, Orest; Klym, Halyna; Ingram, Adam

    2018-03-01

    In this work, the kinetic of positron-electron annihilation in the MgO-Al2O3 spinel-type ceramics sintered at different temperatures (1100, 1200 and 1400 °C) has been calculated and analyzed in a frequency domain. The spectra of real (in-phase) and imaginary (quadrature) components of positron-electron annihilation kinetic have been obtained numerically from usual temporal characteristics using integral Fourier transform. The numerical calculations were carried out using cubic spline interpolation of the pulse characteristics of MgO-Al2O3 ceramics in time domain with following analytical calculations of integrals. The obtained spectra as real so imaginary part of MgO-Al2O3 ceramics in frequency domain almost good obey a Debye law denying correlation between elementary positron annihilation processes. Complex diagrams of frequency domain responses of as-prepared samples have a shape of semicircles with close characteristic frequencies. Some deviation on low-frequency side of the semicircles is observed confirming an availability of longer time kinetic processes. Sintering temperature dependencies of the relaxation times and characteristic frequencies of positron-electron annihilation processes have been obtained. It is shown that position of large maxima on the frequency dependencies of imaginary part corresponds to fast average relaxation lifetime representing the most intensive interaction process of positrons with small cavity traps in solids.

  15. Astrophysical constraints from gamma-ray spectroscopy

    International Nuclear Information System (INIS)

    Diehl, Roland; Prantzos, Nikos; Ballmoos, Peter von

    2006-01-01

    Gamma-ray lines from cosmic sources provide unique isotopic information, since they originate from energy level transitions in the atomic nucleus. Gamma-ray telescopes explored this astronomical window in the past three decades, detecting radioactive isotopes that have been ejected in interstellar space by cosmic nucleosynthesis events and nuclei that have been excited through collisions with energetic particles. Astronomical gamma-ray telescopes feature standard detectors of nuclear physics, but have to be surrounded by effective shields against local instrumental background, and need special detector and/or mask arrangements to collect imaging information. Due to exceptionally-low signal/noise ratios, progress in the field has been slow compared with other wavelengths. Despite the difficulties, this young field of astronomy is well established now, in particular due to advances made by the Compton Gamma-Ray Observatory in the 90ies. The most important achievements so far concern: short-lived radioactivities that have been detected in a couple of supernovae ( 56 Co and 57 Co in SN1987A, 44 Ti in Cas A), the diffuse glow of long-lived 26 Al that has been mapped along the entire plane of the Galaxy, several excited nuclei that have been detected in solar flares, and, last but not least, positron annihilation that has been observed in the inner Galaxy since the 70ies. High-resolution spectroscopy is now being performed: since 2002, ESAs INTEGRAL and NASAs RHESSI, two space-based gamma-ray telescopes with Ge detectors, are in operation. Recent results include: imaging and line shape measurements of e - -e + annihilation emission from the Galactic bulge, which can hardly be accounted for by conventional sources of positrons; 26 Al emission and line width measurement from the inner Galaxy and from the Cygnus region, which can constrain the properties of the interstellar medium; and a diffuse 60 Fe gamma-ray line emission which appears rather weak, in view of current

  16. Measurement of the lifetimes of the neutral and charged D mesons

    International Nuclear Information System (INIS)

    Gladney, L.D.

    1985-03-01

    Results are presented on the use of a high-resolution drift chamber in the Mark II Detector at PEP to measure the lifetimes of D 0 and D +- mesons produced in e + e - annihilations at 29 GeV. Based on a sample of 74 events for the D 0 mesons and 23 events for the D +- mesons, the lifetimes are found to be tau/sub D 0 = 4.7/sub -0.8//sup +0.9/ +- 0.5 x 10 -13 s; tau/sub D +- / = 8.9/sub -2.7//sup +3.8/ +- 1.3 x 10 -13 s. The ratio of these lifetimes, tau/sub D 0 //tau/sub D +- / = 1.9/sub -0.7//sup +0.9/ +- 0.3, indicates that the decays of these mesons cannot be explained by the simple spectator model of charmed particle decay

  17. Charmed Mesons Produced in e+e- Annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Goldhaber, G.; Wiss, J. E.

    1980-12-01

    We shall begin our review by summarizing the first experimental indications for the existence of charm as obtained from experiments in e{sup +}e{sup -} annihilation. This will include a brief discussion of the role of charm in the understanding of the {psi} mesons, as well as the unraveling of the intricate structure present in the e{sup +} e{sup -} total hadronic cross section. Next we shall discuss the discovery of the D{sup 0}, and D{sup +}, and detail those properties crucial to their identification as charmed particles. Following will be a review of the properties of the D{sup 0} and D{sup +} learned through studies at the {psi}(3770) resonance, Compelling evidence will be summarized indicating that this state decays nearly exclusively into D{bar D}, thus making it particularly useful in establishing inclusive and exclusive D branching fractions. Our discussion of branching fractions will include two particularly important D decay modes, D{sup 0}{yields}{pi}{sup +}{pi}{sup -} and D{sup 0}{yields}K{sup +}{sup -}. These processes are suppressed relative to D{sup 0}{yields}K{sup -}{pi}{sup +} in the standard charm model, and thus serve as a critical test of that theory. This will be followed by a discussion of the D semileptonic decay modes which provide useful information on the D{sup 0} and D{sup +} lifetimes. Turning our attention to the data collected beyond the {psi}(3770) we will discuss the properties and production mechanisms of the excited charm mesons, the D*{sup 0} and the D*{sup +}. D production just above the {psi}(3770) appears to be dominated by the three quasi-two-body processes e{sup +} e{sup -} {yields} D{bar D}, D*{bar D} + {bar D}*D, and D*{bar D}*, in accordance with early theoretical predictions. The relative amounts of each process, on the other hand, is somewhat surprising, and has led to considerable theoretical speculation. Finally, we will summarize evidence for the existence of the F meson which is as yet not on as solid a footing as

  18. 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.

  19. Positron lifetimes in deformed copper

    International Nuclear Information System (INIS)

    Hinode, Kenji; Tanigawa, Shoichiro; Doyama, Masao

    1976-01-01

    Positron lifetime measurements were performed for Cu samples with different densities of lattice defects. The lifetime spectra were successfully resolved into two components with the help of the well established analysis program. Obtained results were quite consistent with those expected from the trapping model. The positron trapping mechanism from free to trapped states and the initial condition of the model were especially checked. Deduced values obtained for tau sub(c) (lifetime of free positrons) and tau sub(t) (lifetime of trapped positrons) were 122+-5 psec and 176+-5 psec, respectively. (auth.)

  20. Parity lifetime of bound states in a proximitized semiconductor nanowire

    DEFF Research Database (Denmark)

    Higginbotham, Andrew Patrick; Albrecht, Sven Marian; Kirsanskas, Gediminas

    2015-01-01

    superconductor layer, yielding an isolated, proximitized nanowire segment. We identify Andreev-like bound states in the semiconductor via bias spectroscopy, determine the characteristic temperatures and magnetic fields for quasiparticle excitations, and extract a parity lifetime (poisoning time) of the bound...

  1. Precision lifetime measurements of Ar II 4p doublet levels

    International Nuclear Information System (INIS)

    Marger, D.; Schmoranzer, H.

    1990-01-01

    The lifetimes of the Ar II 4p doublet fine-structure levels 4p 2 D 0 5/2 , 4p' 2 F 0 5/2 and 4p' 2 F 0 7/2 were measured by beam-dye laser spectroscopy. The experimental uncertainty was reduced to below 1%. (orig.)

  2. Ultrahigh-resolution (1+1) photoionization spectroscopy of Kr I: Hyperfine structures, isotope shifts, and lifetimes for the n = 5,6,7 4p5ns Rydberg levels

    International Nuclear Information System (INIS)

    Trickl, T.; Vrakking, M.J.J.; Cromwell, E.; Lee, Y.T.; Kung, A.H.

    1989-01-01

    High-resolution measurements of the hyperfine structures and isotope shifts are reported for Kr I n = 5,6,7 4p 5 ns Rydberg levels, obtained using an extreme-ultraviolet laser with a bandwidth of 210 MHz in a resonant two-photon-ionization scheme. Use of known I 2 frequencies yields an improved absolute calibration of the Kr energy levels by more than one order of magnitude. The nuclear quadrupole hyperfine structure indicates that the 4p 5 6s and 4p 5 7s states are described by a pure jj-coupling scheme, whereas the 4p 5 5s states depart from a pure jj-coupling scheme by 0.37(6)%. The magnetic hyperfine structure shows that the 4p 5 ns states are mixed with 4p 5 n'd states. The isotope shifts can be described as pure mass effects within the precision of our experiment. For the 4p 5 6s and 4p 5 7s states, lifetimes were determined that differ markedly from theoretical literature values

  3. Lifetime-broadening-suppressed X-ray absorption spectrum of β-YbAlB4 deduced from Yb 3d → 2p resonant X-ray emission spectroscopy

    International Nuclear Information System (INIS)

    Kawamura, Naomi; Mizumaki, Masaichiro; Kanai, Noriko; Hayashi, Hisashi; Matsuda, Yasuhiro H.; Kuga, Kentaro; Nakatsuji, Satoru; Watanabe, Shinji

    2017-01-01

    In this work, the Yb 3d → 2p (Yb Lα 1,2 ) resonant X-ray emission spectrum of β-YbAlB 4 was acquired using excitation energies around the Yb L 3 -edge, at 2 K. Subsequently, the lifetime-broadening-suppressed (LBS) X-ray absorption structure (XAS) spectrum was obtained using the SIM-RIXS program. This spectrum was found to exhibit clearly resolved pre-edge and shoulder structures. Resonant Lα 1 emission spectra were well reproduced from LBS-XAS profiles over wide ranges of excitation and emission energies. In contrast, noticeable discrepancies appeared between the experimental and simulated Lα 2 emission spectra, suggesting an effect resulting from M 4 M 5 O 1 Coster-Kronig transitions. LBS-XAS, in conjunction with partial fluorescence yield (PFY) XAS and transmission XAS, determined a value for the Yb valence (v) in β-YbAlB 4 of 2.76 ± 0.08 at 2 K. Despite this relatively large uncertainty in v, each method provided a consistent variation in valence (δv) as the temperature was raised from 2 to 280 K: 0.060 ± 0.004 (LBS-XAS), 0.061 ± 0.005 (PFY-XAS) and 0.058 ± 0.007 (transmission XAS). The smaller δv associated with LBS-XAS demonstrates the greater precision of this method. (author)

  4. An accurate test of calculated positions and lifetimes for Ne{sup 6+}(1s{sup 2}3lnl{sup '}) {sup 1}L states (n=3 and 4) using a high-resolution electron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Bordenave-Montesquieu, A. E-mail: abm@irsamc.ups-tlse.fr; Moretto-Capelle, P.; Bordenave-Montesquieu, D

    2003-05-01

    An accurate test of available calculations for the autoionizing doubly excited states belonging to the Be-like 1s{sup 2}3lnl{sup '} Rydberg series of neon (positions and lifetimes) is presented in this short communication. These theoretical data are used to calculate electron line shapes which are compared, through a fitting procedure, with a high-resolution electron spectrum measured in Ne{sup 8+}(1s{sup 2}) + He collisional system, at 80 keV collision energy and 13.1 deg. observation angle. Present tests concern the n=3 and n=4 singlet states. It is found that some of these calculations suffer from large discrepancies with experiment and do not allow a description of the electron spectrum. A quantitative comparison of measured and calculated post-collisional Coulomb interaction-shifted line positions is also given and briefly discussed; for one theoretical data set, the agreement with experiment is found to be generally within {+-}50 meV; in contrast agreement with other data often considerably scatters within {+-}500 meV and sometimes more.

  5. Low-temperature positron lifetime and Doppler-broadening measurements for single-crystal nickel oxide containing cation vacancies

    International Nuclear Information System (INIS)

    Waber, J.T.; Snead, C.L. Jr.; Lynn, K.G.

    1985-01-01

    Lifetime and Doppler-broadening measurements for positron annihilation in substoichiometric nickelous oxide have been made concomitantly from liquid-helium to room temperature. The concentration of cation vacancies is readily controlled by altering the ambient oxygen pressure while annealing the crystals at 1673 0 K. It was found that neither of the three lifetimes observed or their relative intensities varied significantly with the oxygen pressure, and the bulk rate only increased slightly when the specimen was cooled from room to liquid-helium temperatures. These results are interpreted as indicating that some of the positrons are trapped by the existing cation vacancies and a smaller fraction by vacancy clusters

  6. Synthesis and characterization of titania nanorods from ilmenite for photocatalytic annihilation of E. coli.

    Science.gov (United States)

    Sethi, Diptipriya; Jada, Naresh; Kumar, Rohit; Ramasamy, Sakthivel; Pandey, Sony; Das, Trupti; Kalidoss, Jayasankar; Mukherjee, Partha Sarathi; Tiwari, Ashish

    2014-11-01

    Titania nanorod structures have been obtained by thermal plasma reduction of ilmenite (FeTiO₃) followed by chemical treatments. Inherently present iron in the titania nanorods acts as a dopant which results in shifting the absorption edge of titania from ultraviolet to visible region. X-ray diffraction (XRD) study confirms the existence of rutile phase of titania. X-ray Photoelectron Spectroscopy (XPS) reveals the presence of Ti(4+), O(2-), Fe(3+) and surface hydroxyl group. Transmission Electron Microscopy (TEM) confirms the formation of nanorod structure having width of 6 nm and length of 32 nm. Photocatalytic annihilation property of titania nanorods derived from ilmenite (titania-I), rutile titania obtained from titanium(IV) butoxide (titania-A) and Degussa P25 titania was studied under UV and UV-Visible irradiation conditions separately and compared. The time required for complete photocatalytic annihilation of Escherichiacoli cells are 10, 15 and 45 min under UV irradiation whereas it has taken 15, 10-15, 30 min under UV-Visible irradiation for titania-A, Degussa P25 titania and titania-I respectively. It is observed that titania-I shows significantly stronger antibacterial property under UV-Visible irradiation compared to UV alone. Copyright © 2014 Elsevier B.V. All rights reserved.

  7. On fascination and fear of annihilation.

    Science.gov (United States)

    Thys, Michel

    2017-06-01

    In this paper fascination phenomenologically is described as a state of radically being captured by an imposing object. What is left of the impoverished and paralysed subject clings to the exclusive fascinating object. Fascination is the eye of the storm of extreme ambivalence towards an exclusive object: being the only remaining object it is necessary for living in an object world, but at the same time it is threatening to life by absorbing the subject totally. So the subject is sucked in by a yet frightening object. From a metapsychological point of view fascination is understood as the congealed result of excessive projective identification and a strong confusional state connected with it: the subject empties itself so much in the object that it comes to stand for the subject. The fascinating object embodies in a condensed way - as a special form of a bizarre object - split off unconscious threatening material. So fascination is linked to the Kleinian theory of anxiety. Two clinical vignettes illustrate how states of fascination can be understood as an ultimate defence against unconscious menacing material welling up. The hypothesis is developed that fascination points to a revelation of fundamental psychic truth that promptly cramps the subject because the reintegration of it is felt as annihilating. In the vignettes this takes the form of a 'transformation in hallucinosis'. Fascination is at the same time 'the moment of truth' and possibly a serious obstruction of the analytic process. This unconscious truth seems to concern primitive 'superego violence'. The challenge consists in thawing the frozen fascinating object by linking it to other material. Copyright © 2016 Institute of Psychoanalysis.

  8. Substructure boosts to dark matter annihilation from Sommerfeld enhancement

    International Nuclear Information System (INIS)

    Bovy, Jo

    2009-01-01

    The recently introduced Sommerfeld enhancement of the dark matter annihilation cross section has important implications for the detection of dark matter annihilation in subhalos in the Galactic halo. In addition to the boost to the dark matter annihilation cross section from the high densities of these subhalos with respect to the main halo, an additional boost caused by the Sommerfeld enhancement results from the fact that they are kinematically colder than the Galactic halo. If we further believe the generic prediction of the cold dark matter paradigm that in each subhalo there is an abundance of substructure which is approximately self-similar to that of the Galactic halo, then I show that additional boosts coming from the density enhancements of these small substructures and their small velocity dispersions enhance the dark matter annihilation cross section even further. I find that very large boost factors (10 5 to 10 9 ) are obtained in a large class of models. The implications of these boost factors for the detection of dark matter annihilation from dwarf spheroidal galaxies in the Galactic halo are such that, generically, they outshine the background gamma-ray flux and are detectable by the Fermi Gamma-ray Space Telescope.

  9. The Isotropic Radio Background and Annihilating Dark Matter

    Energy Technology Data Exchange (ETDEWEB)

    Hooper, Dan [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Belikov, Alexander V. [Institut d' Astrophysique (France); Jeltema, Tesla E. [Univ. of California, Santa Cruz, CA (United States); Linden, Tim [Univ. of California, Santa Cruz, CA (United States); Profumo, Stefano [Univ. of California, Santa Cruz, CA (United States); Slatyer, Tracy R. [Princeton Univ., Princeton, NJ (United States)

    2012-11-01

    Observations by ARCADE-2 and other telescopes sensitive to low frequency radiation have revealed the presence of an isotropic radio background with a hard spectral index. The intensity of this observed background is found to exceed the flux predicted from astrophysical sources by a factor of approximately 5-6. In this article, we consider the possibility that annihilating dark matter particles provide the primary contribution to the observed isotropic radio background through the emission of synchrotron radiation from electron and positron annihilation products. For reasonable estimates of the magnetic fields present in clusters and galaxies, we find that dark matter could potentially account for the observed radio excess, but only if it annihilates mostly to electrons and/or muons, and only if it possesses a mass in the range of approximately 5-50 GeV. For such models, the annihilation cross section required to normalize the synchrotron signal to the observed excess is sigma v ~ (0.4-30) x 10^-26 cm^3/s, similar to the value predicted for a simple thermal relic (sigma v ~ 3 x 10^-26 cm^3/s). We find that in any scenario in which dark matter annihilations are responsible for the observed excess radio emission, a significant fraction of the isotropic gamma ray background observed by Fermi must result from dark matter as well.

  10. THE EFFECTS OF DARK MATTER ANNIHILATION ON COSMIC REIONIZATION

    Energy Technology Data Exchange (ETDEWEB)

    Kaurov, Alexander A.; Hooper, Dan; Gnedin, Nickolay Y., E-mail: kaurov@uchicago.edu [Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637 (United States)

    2016-12-20

    We revisit the possibility of constraining the properties of dark matter (DM) by studying the epoch of cosmic reionization. Previous studies have shown that DM annihilation was unlikely to have provided a large fraction of the photons which ionized the universe, but instead played a subdominant role relative to stars and quasars. The DM might, however, have begun to efficiently annihilate with the formation of primordial microhalos at z  ∼ 100–200, much earlier than the formation of the first stars. Therefore, if DM annihilation ionized the universe at even the percent level over the interval z  ∼ 20–100, it could leave a significant imprint on the global optical depth, τ . Moreover, we show that cosmic microwave background polarization data and future 21 cm measurements will enable us to more directly probe the DM contribution to the optical depth. In order to compute the annihilation rate throughout the epoch of reionization, we adopt the latest results from structure formation studies and explore the impact of various free parameters on our results. We show that future measurements could make it possible to place constraints on the DM’s annihilation cross-sections, which are at a level comparable to those obtained from the observations of dwarf galaxies, cosmic-ray measurements, and studies of recombination.

  11. Dark matter annihilation in the circumgalactic medium at high redshifts

    Science.gov (United States)

    Schön, S.; Mack, K. J.; Wyithe, J. S. B.

    2018-03-01

    Annihilating dark matter (DM) models offer promising avenues for future DM detection, in particular via modification of astrophysical signals. However, when modelling such potential signals at high redshift, the emergence of both DM and baryonic structure, as well as the complexities of the energy transfer process, needs to be taken into account. In the following paper, we present a detailed energy deposition code and use this to examine the energy transfer efficiency of annihilating DM at high redshift, including the effects on baryonic structure. We employ the PYTHIA code to model neutralino-like DM candidates and their subsequent annihilation products for a range of masses and annihilation channels. We also compare different density profiles and mass-concentration relations for 105-107 M⊙ haloes at redshifts 20 and 40. For these DM halo and particle models, we show radially dependent ionization and heating curves and compare the deposited energy to the haloes' gravitational binding energy. We use the `filtered' annihilation spectra escaping the halo to calculate the heating of the circumgalactic medium and show that the mass of the minimal star-forming object is increased by a factor of 2-3 at redshift 20 and 4-5 at redshift 40 for some DM models.

  12. Lifetime Improvement by Battery Scheduling

    NARCIS (Netherlands)

    Jongerden, M.R.; Schmitt, Jens B.; Haverkort, Boudewijn R.H.M.

    The use of mobile devices is often limited by the lifetime of their batteries. For devices that have multiple batteries or that have the option to connect an extra battery, battery scheduling, thereby exploiting the recovery properties of the batteries, can help to extend the system lifetime. Due to

  13. Lifetime improvement by battery scheduling

    NARCIS (Netherlands)

    Jongerden, M.R.; Haverkort, Boudewijn R.H.M.

    The use of mobile devices is often limited by the lifetime of its battery. For devices that have multiple batteries or that have the option to connect an extra battery, battery scheduling, thereby exploiting the recovery properties of the batteries, can help to extend the system lifetime. Due to the

  14. Positron annihilation and polymerization of epoxy

    International Nuclear Information System (INIS)

    Suzuki, T.; Ito, Y.; Endo, K.; Fujita, S.

    1989-01-01

    Positron lifetime measurement has been applied to the investigation of solidification from the liquid state to the solid state in epoxy with different mixing ratios of resin and hardener. It has been shown that the mixing ratios and the physical states of liquid, gel, and solid affect positronium formation. In samples with an excess of hardener, long-lived components were observed in the liquid and gel states, while they disappeared after solidification. Positronium formation in epoxy is strongly affected by the heating process of epoxy samples. (author)

  15. The positron annihilation technique applied to the study of inhomogeneous solids: aluminium alloys, layered compound 1T-TaS2

    International Nuclear Information System (INIS)

    Boileau, F.

    1983-01-01

    This thesis is an experimental investigation of inhomogeneous solids using the standard positron annihilation techniques (angular correlation of annihilation γ-rays, Doppler broadening, lifetime). The investigations are concerned with different types of more or less extended defects. The effect of impurities on the migration properties of the vacancy-type defects is first studied in electron irradiated and quenched aluminium alloys. The affinity of the positron for precipitates formed in supersatured aluminium alloys is shown experimentally and explained. The effects of low dimensionality on the behaviour of the positron are then studied in the layered dichalcogenide 1T-TaS 2 where the presence of charge density waves modifies the electronic properties. An experimental and theoretical insight on the Fermi surface of this compound has been successfully undertaken [fr

  16. 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...... in 2000. The prevalence of CP in eastern Denmark was approximately 1.7 per 1000. Information on productivity and the use of health care was retrieved from registers. The lifetime cost of CP was about euro860 000 for men and about euro800 000 for women. The largest component was social care costs......, particularly during childhood. A sensitivity analysis found that alterations in social care costs had a small effect, whereas lowering the discount rate from 5 to 3 per cent markedly increased total lifetime costs. Discounting decreases the value of costs in the future compared with the present. The high...

  17. Positron annihilation studies of the AlOx/SiO2/Si interface in solar cell structures

    Science.gov (United States)

    Edwardson, C. J.; Coleman, P. G.; Li, T.-T. A.; Cuevas, A.; Ruffell, S.

    2012-03-01

    Film and film/substrate interface characteristics of 30 and 60 nm-thick AlOx films grown on Si substrates by thermal atomic layer deposition (ALD), and 30 nm-thick AlOx films by sputtering, have been probed using variable-energy positron annihilation spectroscopy (VEPAS) and Doppler-broadened spectra ratio curves. All samples were found to have an interface which traps positrons, with annealing increasing this trapping response, regardless of growth method. Thermal ALD creates an AlOx/SiOx/Si interface with positron trapping and annihilation occurring in the Si side of the SiOx/Si boundary. An induced positive charge in the Si next to the interface reduces diffusion into the oxides and increases annihilation in the Si. In this region there is a divacancy-type response (20 ± 2%) before annealing which is increased to 47 ± 2% after annealing. Sputtering seems to not produce samples with this same electrostatic shielding; instead, positron trapping occurs directly in the SiOx interface in the as-deposited sample, and the positron response to it increases after annealing as an SiO2 layer is formed. Annealing the film has the effect of lowering the film oxygen response in all film types. Compared to other structural characterization techniques, VEPAS shows larger sensitivity to differences in film preparation method and between as-deposited and annealed samples.

  18. The dating game at dimension zero: creation and annihilation of phase singularities in optical random waves

    NARCIS (Netherlands)

    De Angelis, L.; Alpeggiani, F.; Di Falco, Andrea; Kuipers, L.

    2017-01-01

    Phase singularities can be created and annihilated, but always in pairs. With optical near-field measurements, we track singularities in random waves as a function of wavelength, and discover correlations between creation and annihilation events.

  19. Models of pair annihilation in 1E 1740.7-2942 and the HEAO 1 A-4 annihilation source

    Science.gov (United States)

    Maciolek-Niedzwiecki, Andrzej; Zdziarski, Andrzej

    1994-01-01

    We study possible models of two Galactic sources of transient pair annihilation radiation, 1E 1740.7-2942 and a source observed by High Energy Astronomy Observatory (HEAO) 1 A-4. We fit the observed spectral features by thermal annihilation spectra and find that the redshifts obtained by us are much larger than those obtained from fitting Caussian lines centered on 511 keV. This effect, which is due to the net blueshift (with respect to 511 keV) of the annihilation spectrum due to the thermal energies of pairs, puts strong constraints on models of sources. We consider those constraints first without considering the mechanism of positron production. From the shape of the observed spectra, we are able to rule out both spherical clouds and layers above cold matter as possible source geometries. The observed spectra are compatible with two source geometries: (1) a nearly face-on disk in the Kerr metric and (2) a jet close to a black hole. We consider, then, the origin of the pairs. Theories of both thermal and nonthermal pair equilibria predict that photon-pair production is unable to produce annihilation features that contain as much as half of the bolometric luminosity, which is observed. A possible solution to this problem is obscuration of a nonthermal source (in which pairs are produced by photon-photon collisions) and an outflow of pairs to an unobscured region. This makes annihilation in a jet the most likely model of the considered sources.

  20. The Distribution and Annihilation of Dark Matter Around Black Holes

    Science.gov (United States)

    Schnittman, Jeremy D.

    2015-01-01

    We use a Monte Carlo code to calculate the geodesic orbits of test particles around Kerr black holes, generating a distribution function of both bound and unbound populations of dark matter (DM) particles. From this distribution function, we calculate annihilation rates and observable gamma-ray spectra for a few simple DM models. The features of these spectra are sensitive to the black hole spin, observer inclination, and detailed properties of the DM annihilation cross-section and density profile. Confirming earlier analytic work, we find that for rapidly spinning black holes, the collisional Penrose process can reach efficiencies exceeding 600%, leading to a high-energy tail in the annihilation spectrum. The high particle density and large proper volume of the region immediately surrounding the horizon ensures that the observed flux from these extreme events is non-negligible.

  1. Internal-fusion diagrams for p-barp annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Genz, H.; Tatur, S.

    1984-07-01

    We investigate p-barp annihilation into B-barB' (where B and B' represent baryons) via q-barq annihilation into Q-barQ (where q and Q represent quarks). Specifying the q-barq (or q-barQ) annihilation spin structure determines the ratios of all polarized amplitudes with B,B' from the 56 under SU(6). We propose to parametrize q-barq..-->..Q-barQ by intermediate gluon and meson states. The model with q-barq..-->..one gluon..-->..Q-barQ with Q = s is worked out in detail. With the exception of p-barp..-->..Sigma-bar/sup -/..sigma../sup asterisk+/+charge conjugate, it compares favorably with experiment.

  2. Notes on symmetric and exterior depth and annihilator numbers

    Directory of Open Access Journals (Sweden)

    Gesa Kampf

    2008-11-01

    Full Text Available We survey and compare invariants of modules over the polynomial ring and the exterior algebra. In our considerations, we focus on the depth. The exterior analogue of depth was first introduced by Aramova, Avramov and Herzog. We state similarities between the two notion of depth and exhibit their relation in the case of squarefree modules. Work of Conca, Herzog and Hibi and Trung, respectively, shows that annihilator numbers are a meaningful generalization of depth over the polynomial ring. We introduce and study annihilator numbers over the exterior algebra. Despite some minor differences in the definition, those invariants show common behavior. In both situations a positive linear combination of the annihilator numbers can be used to bound the symmetric and exterior graded Betti numbers, respectively, from above.

  3. Molecular model for annihilation rates in positron complexes

    International Nuclear Information System (INIS)

    Assafrao, Denise; Walters, H.R. James; Mohallem, Jose R.

    2008-01-01

    The molecular approach for positron interaction with atoms is developed further. Potential energy curves for positron motion are obtained. Two procedures accounting for the nonadiabatic effective positron mass are introduced for calculating annihilation rate constants. The first one takes the bound-state energy eigenvalue as an input parameter. The second is a self-contained and self-consistent procedure. The methods are tested with quite different states of the small complexes HPs, e + He (electronic triplet) and e + Be (electronic singlet and triplet). For states yielding the positronium cluster, the annihilation rates are quite stable, irrespective of the accuracy in binding energies. For the e + Be states, annihilation rates are larger and more consistent with qualitative predictions than previously reported ones

  4. Positron annihilation in germanium in thermal equilibrium at high temperature

    Energy Technology Data Exchange (ETDEWEB)

    Uedono, Akira; Moriya, Tsuyoshi; Komuro, Naoyuki; Tanigawa, Shoichiro [Tsukuba Univ., Ibaraki (Japan). Inst. of Materials Science; Kawano, Takao; Ikari, Atsushi

    1996-09-01

    Annihilation characteristics of positrons in Ge in thermal equilibrium at high temperature were studied using a monoenergetic positron beam. Precise measurements of Doppler broadening profiles of annihilation radiation were performed in the temperature range between 300 K and 1211 K. The line shape parameters of Doppler broadening profiles were found to be almost constant at 300-600 K. The changes in these parameters were observed to start above 600 K. This was attributed to both the decrease in the fraction of positrons annihilating with core electrons and the lowering of the crystal symmetry around the region detected by positron-electron pairs. This suggests that behaviors of positrons are dominated by some form of positron-lattice coupling in Ge at high temperatures. The temperature dependence of the diffusion length of positrons was also discussed. (author)

  5. Molecular model for annihilation rates in positron complexes

    Energy Technology Data Exchange (ETDEWEB)

    Assafrao, Denise [Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, P.O. Box 702, 30123-970 Belo Horizonte, MG (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom); Walters, H.R. James [Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom); Mohallem, Jose R. [Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, P.O. Box 702, 30123-970 Belo Horizonte, MG (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom)], E-mail: rachid@fisica.ufmg.br

    2008-02-15

    The molecular approach for positron interaction with atoms is developed further. Potential energy curves for positron motion are obtained. Two procedures accounting for the nonadiabatic effective positron mass are introduced for calculating annihilation rate constants. The first one takes the bound-state energy eigenvalue as an input parameter. The second is a self-contained and self-consistent procedure. The methods are tested with quite different states of the small complexes HPs, e{sup +}He (electronic triplet) and e{sup +}Be (electronic singlet and triplet). For states yielding the positronium cluster, the annihilation rates are quite stable, irrespective of the accuracy in binding energies. For the e{sup +}Be states, annihilation rates are larger and more consistent with qualitative predictions than previously reported ones.

  6. Simulation of structure and annihilation of screw dislocation dipoles

    DEFF Research Database (Denmark)

    Rasmussen, Torben; Vegge, Tejs; Leffers, Torben

    2000-01-01

    Large scale atomistic simulations are used to investigate the properties of screw dislocation dipoles in copper. Spontaneous annihilation is observed for dipole heights less than 1 nm. Equilibrated dipoles of heights larger than 1 nm adopt a skew configuration due to the elastic anisotropy of Cu....... The equilibrium splitting width of the screw dislocations decreases with decreasing dipole height, as expected from elasticity theory. The energy barriers, and corresponding transition states for annihilation of stable dipoles are determined for straight and for flexible dislocations for dipole heights up to 5.......2 nm. In both cases the annihilation is initiated by cross-slip of one of the dislocations. For straight dislocations the activation energy shows a linear dependence on the inverse dipole height, and for flexible dislocations the dependence is roughly linear for the dipoles investigated....

  7. Relativistic hydrodynamics, heavy ion reactions and antiproton annihilation

    International Nuclear Information System (INIS)

    Strottman, D.

    1985-01-01

    The application of relativistic hydrodynamics to relativistic heavy ions and antiproton annihilation is summarized. Conditions for validity of hydrodynamics are presented. Theoretical results for inclusive particle spectra, pion production and flow analysis are given for medium energy heavy ions. The two-fluid model is introduced and results presented for reactions from 800 MeV per nucleon to 15 GeV on 15 GeV per nucleon. Temperatures and densities attained in antiproton annihilation are given. Finally, signals which might indicate the presence of a quark-gluon plasma are briefly surveyed

  8. Annihilation physics of exotic galactic dark matter particles

    Science.gov (United States)

    Stecker, F. W.

    1990-01-01

    Various theoretical arguments make exotic heavy neutral weakly interacting fermions, particularly those predicted by supersymmetry theory, attractive candidates for making up the large amount of unseen gravitating mass in galactic halos. Such particles can annihilate with each other, producing secondary particles of cosmic-ray energies, among which are antiprotons, positrons, neutrinos, and gamma-rays. Spectra and fluxes of these annihilation products can be calculated, partly by making use of positron electron collider data and quantum chromodynamic models of particle production derived therefrom. These spectra may provide detectable signatures of exotic particle remnants of the big bang.

  9. Computer Simulation of Electron Positron Annihilation Processes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, y

    2003-10-02

    With the launching of the Next Linear Collider coming closer and closer, there is a pressing need for physicists to develop a fully-integrated computer simulation of e{sup +}e{sup -} annihilation process at center-of-mass energy of 1TeV. A simulation program acts as the template for future experiments. Either new physics will be discovered, or current theoretical uncertainties will shrink due to more accurate higher-order radiative correction calculations. The existence of an efficient and accurate simulation will help us understand the new data and validate (or veto) some of the theoretical models developed to explain new physics. It should handle well interfaces between different sectors of physics, e.g., interactions happening at parton levels well above the QCD scale which are described by perturbative QCD, and interactions happening at much lower energy scale, which combine partons into hadrons. Also it should achieve competitive speed in real time when the complexity of the simulation increases. This thesis contributes some tools that will be useful for the development of such simulation programs. We begin our study by the development of a new Monte Carlo algorithm intended to perform efficiently in selecting weight-1 events when multiple parameter dimensions are strongly correlated. The algorithm first seeks to model the peaks of the distribution by features, adapting these features to the function using the EM algorithm. The representation of the distribution provided by these features is then improved using the VEGAS algorithm for the Monte Carlo integration. The two strategies mesh neatly into an effective multi-channel adaptive representation. We then present a new algorithm for the simulation of parton shower processes in high energy QCD. We want to find an algorithm which is free of negative weights, produces its output as a set of exclusive events, and whose total rate exactly matches the full Feynman amplitude calculation. Our strategy is to create

  10. Segmented scintillation detectors with silicon photomultiplier readout for measuring antiproton annihilations

    CERN Document Server

    Sótér, A.; Kobayashi, T.; Barna, D.; Horváth, D.; Hori, M.

    2014-01-01

    The Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA) experiment at the Antiproton Decelerator (AD) facility of CERN constructed segmented scintillators to detect and track the charged pions which emerge from antiproton annihilations in a future superconducting radiofrequency Paul trap for antiprotons. A system of 541 cast and extruded scintillator bars were arranged in 11 detector modules which provided a spatial resolution of 17 mm. Green wavelength-shifting fibers were embedded in the scintillators, and read out by silicon photomultipliers which had a sensitive area of 1 x 1 mm^2. The photoelectron yields of various scintillator configurations were measured using a negative pion beam of momentum p ~ 1 GeV/c. Various fibers and silicon photomultipliers, fiber end terminations, and couplings between the fibers and scintillators were compared. The detectors were also tested using the antiproton beam of the AD. Nonlinear effects due to the saturation of the silicon photomultiplier were seen a...

  11. Exciton–exciton annihilation and biexciton stimulated emission in graphene nanoribbons

    Science.gov (United States)

    Soavi, Giancarlo; Dal Conte, Stefano; Manzoni, Cristian; Viola, Daniele; Narita, Akimitsu; Hu, Yunbin; Feng, Xinliang; Hohenester, Ulrich; Molinari, Elisa; Prezzi, Deborah; Müllen, Klaus; Cerullo, Giulio

    2016-01-01

    Graphene nanoribbons display extraordinary optical properties due to one-dimensional quantum-confinement, such as width-dependent bandgap and strong electron–hole interactions, responsible for the formation of excitons with extremely high binding energies. Here we use femtosecond transient absorption spectroscopy to explore the ultrafast optical properties of ultranarrow, structurally well-defined graphene nanoribbons as a function of the excitation fluence, and the impact of enhanced Coulomb interaction on their excited states dynamics. We show that in the high-excitation regime biexcitons are formed by nonlinear exciton–exciton annihilation, and that they radiatively recombine via stimulated emission. We obtain a biexciton binding energy of ≈250 meV, in very good agreement with theoretical results from quantum Monte Carlo simulations. These observations pave the way for the application of graphene nanoribbons in photonics and optoelectronics. PMID:26984281

  12. On the Role of the Annihilation Channel in Front Form Positronium

    OpenAIRE

    Trittmann, Uwe

    1997-01-01

    The annihilation channel is implemented into the front form calculations of the positronium spectrum presented in a previous publication. The effective Hamiltonian is calculated analytically. Its eigensolutions are obtained numerically. A complete separation of the dynamical and instantaneous part of the annihilation interaction is observed. We find the remarkable effect that the annihilation channel stabilizes the cutoff behavior of the spectrum.

  13. Effect of Voids on Angular Correlation of Positron Annihilation Photons in Molybdenum

    DEFF Research Database (Denmark)

    Mogensen, O. E.; Petersen, K.; Cotterill, R. M. J.

    1972-01-01

    POSITRON annihilation investigations of defects in crystals have shown that for sufficiently high defect concentrations (typically above about 10−6) all positrons become trapped in the defects before annihilation, thus changing the characteristics of the annihilation process. For example, trapping...... be disturbed either in a random fashion or arranged in a macro lattice7....

  14. Electricite de France: Lifetime Project

    International Nuclear Information System (INIS)

    Combes, Jean-Pierre

    1991-01-01

    Electricite de France produces almost 80% of its electricity by means of standardized PWR nuclear power stations. Starting in 1986, therefore, a project known as the 'Lifetime Project' was developed, whose aim was initially to ensure that the lifetime defined at design stage (40 years in general) could be attained without major difficulty (follow up of the aging process). It then became apparent that it would be useful to know just how far it would be technically and economically possible to go. As a result, the project is now working towards increasing the lifetime of power stations. (author)

  15. Measurement of b hadron lifetimes and effective lifetimes at LHCb

    CERN Document Server

    Eklund, E

    2013-01-01

    This paper presents two recent measurements of b-hadron lifetimes, using 1 fb$^{-1}$ of data collected by LHCb. The effective lifetime of the $B_{s} \\to J/\\Psi K_{S}$ decay is measured and found to be $\\tau_{B_{s} \\to J/\\Psi K_{S}}^{\\rm{eff}} = 1.75 \\pm 0.12~(\\rm{stat})~0.07~(\\rm{syst})~\\rm{ps}$. The result is compatible with the Standard Model prediction and is the first measurement of this quantity. The $\\Lambda_{b}$ lifetime is measured in the $\\Lambda_{b} \\to J/\\Psi p K$ decay using the same data set. The measured quantity is the difference in reciprocal lifetimes of the $B^0$ and $\\Lambda^0_b$ hadrons and found to be $1/\\tau_{\\Lambda_{b}} - 1/\\tau_{B_{d}}= 16.4 \\pm 8.2 \\pm 4.4~\\rm{ns^{-1}}$. Using the world average of the $B^0$ lifetime, this translates into a lifetime ratio of $\\tau_{\\Lambda_{b}}/\\tau_{B_{d}} = 0.976 \\pm 0.012 \\pm 0.006$, which is the precise measurement of this quantity to date.

  16. Origin and annihilation physics of positrons in the Galaxy

    International Nuclear Information System (INIS)

    Alexis, Anthony

    2014-01-01

    A gamma radiation at 511 keV is observed since the early 1970's toward the Galactic bulge region. This emission is the signature of a large number of electron-positron annihilations, the positron being the electron's antiparticle. Unfortunately, the origin of the positrons responsible for this emission is still a mystery. Many positron-source candidates have been suggested but none of them can account for the galactic annihilation emission. The spatial distribution of this emission is indeed very atypical. Since 2002, the SPI spectrometer onboard the INTEGRAL space laboratory revealed an emission strongly concentrated toward the galactic bulge and a weaker emission from the galactic disk. This morphology is unusual because it does not correspond to any of the known galactic astrophysical-object or interstellar-matter distributions. The assumption that positrons annihilate close to their sources (i.e. the spatial distribution of the annihilation emission reflects the spatial distribution of the sources) has consequently been called into question. Recent studies suggest that positrons could propagate far away from their sources before annihilating. This physical aspect could be the key point to solve the riddle of the galactic positron origin. This thesis is devoted to the modelling of the propagation and annihilation of positrons in the Galaxy, in order to compare simulated spatial models of the annihilation emission with recent measurements provided by SPI/INTEGRAL. This method allows to put constraints on the origin of galactic positrons. We therefore developed a propagation Monte-Carlo code of positrons within the Galaxy in which we implemented all the theoretical and observational knowledge about positron physics (sources, transport modes, energy losses, annihilation modes) and the interstellar medium of our Galaxy (interstellar gas distributions, galactic magnetic fields, structures of the gaseous phases). Due to uncertainties in several physical parameters

  17. Study of $ \\bar{p} $ and $ \\bar{n} $ annihilations at LEAR with OBELIX, a large acceptance and high resolution detector based on the Open Axial Field Spectrometer

    CERN Multimedia

    2002-01-01

    % PS201 Study of $\\bar{p}$ and $\\bar{n}$ annihilations at LEAR with OBELIX, a large acceptance and high resolution detector based on the Open Axial Field Spectrometer \\\\ \\\\OBELIX is designed to study exclusive final states of antiproton and antineutron annihilations at low energies with protons and nuclei. \\\\ \\\\The physics motivations of the experiment are:\\\\ \\\\\\begin{itemize} \\item (gg, ggg), hybrids ($ q \\bar{q} g $), multiquarks ($ q q \\bar{q} \\bar{q} $) and light mesons ($ q \\bar{q} $) produced in $ N \\bar{N} $ annihilations and study of their spectroscopy and decays. Also broad structures will be searched for by comparing identical decay modes in exclusive final states of the same type occuring from initial states with different angular momentum or isospin. \\item Study of the dynamics of $ N \\bar{N} $ interactions and of the dependence of the final and intermediate resonant states of annihilation upon the quantum numbers of the initial $ N \\bar{N} $ state (angular momentum: S and P-wave in $\\bar{p}p $ at...

  18. Fluorescence lifetime evaluation of whole soils from the Amazon rainforest.

    Science.gov (United States)

    Nicolodelli, Gustavo; Tadini, Amanda Maria; Nogueira, Marcelo Saito; Pratavieira, Sebastião; Mounier, Stephane; Huaman, Jose Luis Clabel; Dos Santos, Cléber Hilário; Montes, Célia Regina; Milori, Débora Marcondes Bastos Pereira

    2017-08-20

    Time-resolved fluorescence spectroscopy (TRFS) is a new tool that can be used to investigate processes of interaction between metal ions and organic matter (OM) in soils, providing a specific analysis of the structure and dynamics of macromolecules. To the best of our knowledge, there are no studies in the literature reporting the use of this technique applied to whole/non-fractionated soil samples, making it a potential method for use in future studies. This work describes the use of TRFS to evaluate the fluorescence lifetimes of OM of whole soils from the Amazon region. Analysis was made of pellets of soils from an oxisol-spodosol system, collected in São Gabriel da Cachoeira (Amazonas, Brazil). The fluorescence lifetimes in the oxisol-spodosol system were attributed to two different fluorophores. One was related to complexation of an OM fraction with metals, resulting in a shorter fluorophore lifetime. A short fluorescence lifetime (2-12 ns) could be associated with simpler structures of the OM, while a long lifetime (19-66 ns) was associated with more complex OM structures. This new TRFS technique for analysis of the fluorescence lifetime in whole soil samples complies with the principles of green chemistry.

  19. Radiative lifetimes of neutral gadolinium

    International Nuclear Information System (INIS)

    Den Hartog, E A; Bilty, K A; Lawler, J E

    2011-01-01

    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.

  20. Inverse Compton Gamma Rays from Dark Matter Annihilation in the ...

    Indian Academy of Sciences (India)

    didates for dark matter search due to their high mass-to-light (M/L) ratio. One of the most favored dark matter candidates is the lightest neutralino. (neutral χ particle) as predicted in the Minimal Supersymmetric Standard. Model (MSSM). In this study, we model the gamma ray emission from dark matter annihilation coming ...

  1. Precise tests of QCD in e+e- annihilation

    International Nuclear Information System (INIS)

    Burrows, P.N.

    1997-03-01

    A pedagogical review is given of precise tests of QCD in electron-positron annihilation. Emphasis is placed on measurements that have served to establish QCD as the correct theory of strong interactions, as well as measurements of the coupling parameter α s . An outlook is given for future important tests at a high-energy e + e - collider

  2. Study of wino pair production in e+e- annihilation

    International Nuclear Information System (INIS)

    Fukai, Tomoki; Kizukuri, Yoshiki; Oshimo, Noriyuki; Otake, Yoshie; Sugiyama, Naoshi

    1987-01-01

    We discuss wino pair production in e + e - annihilation and subsequent leptonic wino decay for various types of supersymmetric or supergravity models. Phenomenological predictions on this process depend considerably on a specific model. We analyze the energy distribution, forward-backward asymmetry and angular distribution of a charged lepton in the final state. (Author shortened by G.Q.)

  3. Monoenergetic neutrinos from dark matter annihilation: Issues of exposure

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Jason, E-mail: jkumar@hawaii.edu [Department of Physics and Astronomy, University of Hawai’i, Honolulu, HI 96822 (United States)

    2016-06-21

    We consider searches for dark matter annihilation in the Sun resulting in monoenergetic neutrinos, produced either directly or through the decay of stopped pions and kaons. We find that this strategy is very successful at increasing the signal-to-background ratio, but that current experiments may be signal limited. We discuss the exposures need to fully exploit this search strategy.

  4. Annihilation of the triplet excitons in the nanoporous glass matrices

    International Nuclear Information System (INIS)

    Afanasyev, D.A.; Ibrayev, N.Kh.; Saletsky, A.M.; Starokurov, Y.V.; Gun'ko, V.M.; Mikhalovsky, S.V.

    2013-01-01

    The spectra and kinetics of fluorescence decay of 1,2-benzanthracene (1,2-BA) molecular clusters adsorbed in nanoporous borosilicate glasses were investigated. It has been shown that the type of the decay kinetics of delayed fluorescence is determined by the annihilation of triplet excitons in crystalline and percolation clusters. The influence of an external magnetic field on the annihilation rate constant of triplet excitons in the adsorbed 1,2-BA molecules has been studied. The response of the molecular clusters to the magnetic field strongly depends on temperature, pore size and time scale of the observation. Clusters with the crystal structure dominate in the decay kinetics of triplet–triplet annihilation (TTA) and delayed fluorescence in the initial microsecond period of time after excitation. Amorphous clusters determine the form of decay kinetics of delayed fluorescence in the millisecond range. The increase in the pore size and concentration of the adsorbate lead to the dominance of crystalline components. The results presented here can be used to develop techniques for probing the structure of the adsorbed layer in nanoporous systems examining the effect of an external magnetic field on the annihilation delayed fluorescence (ADF) kinetics. Highlights: ► Molecular clusters of 1,2-benzanthracene adsorbed in nanoporous borosilicate glasses. ► Form of decay kinetics of delayed fluorescence. ► Magnetic field effects depend on temperature, pore size and observation time range. ► Clusters with crystal structure and amorphous clusters form in porous glasses

  5. Annihilation of Domain Walls in a Ferromagnetic Wire

    Science.gov (United States)

    Ghosh, Anirban; Huang, Kevin; Tchernyshyov, Oleg

    We study the annihilation of topological solitons in one of the simplest systems that support them: a one-dimensional ferromagnetic wire with an easy axis along its length. In the presence of energy dissipation due to viscous losses, two solitons (domain walls) on the wire, when released from afar, approach each other and eventually annihilate to create a uniformly magnetized state. Starting from a class of exact solutions for stationary two-domain-wall configurations in the absence of dissipation, we develop an effective theory that describes this annihilation in terms of four collective coordinates: a) the two zero modes corresponding to the location of the center and the average azimuthal angle of the full structure and b) their two conjugate momenta which describe the relative twist and the relative separation of the two domain walls respectively. Comparison with micromagnetic simulation on OOOMF confirms that this theory captures well the essential physics of the process. We believe this work will be a good starting point for studying the annihilation of more complicated topological solitons like vortices and skyrmions in ferromagnetic thin films. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-08ER46544.

  6. Significant Enhancement of Neutralino Dark Matter Annihilation from Electroweak Bremsstrahlung

    NARCIS (Netherlands)

    Bringmann, T.; Calore, F.

    2014-01-01

    ndirect searches for the cosmological dark matter have become ever more competitive during the past years. Here, we report the first full calculation of leading electroweak corrections to the annihilation rate of supersymmetric neutralino dark matter. We find that these corrections can be huge,

  7. Production of new particles in electron-positron annihilation

    International Nuclear Information System (INIS)

    Gilman, F.J.

    1977-02-01

    A number of areas are reviewed where there is important progress in the production of new particles in electron--positron annihilation, but of a more detailed quantitative nature. Charmonium states, charmed mesons, and evidence for a charged heavy lepton are covered. 50 references

  8. Chemical application of positron annihilation through triple coincidence measurement

    International Nuclear Information System (INIS)

    Yegnasubramanian, S.; Gangadharan, S.

    1982-01-01

    This report summarises the work on the application of triple coincidence measurement of annihilation radiation for providing chemical state information; the observations have been corroborated by angular correlation and Doppler broadening measurements and supplemented by the magnetic quenching in the angular correlation and peak-to-valley ratio in the Ge(Li) singles spectrum for the 511 keV line. (author)

  9. Peculiarities of the early Universe (Universes) birth and positron annihilation

    International Nuclear Information System (INIS)

    Svetlov-Prokop'ev, E.P.

    2003-01-01

    Works on the problem of quantum birth of the Universe are reviewed. Possible peculiarities of electron-positron annihilation at the early stages of the Universe (s) birth in connection with black holes are considered. Possible concept of Eternity is discussed. (author)

  10. Annihilation of antiprotons stopped in liquid hydrogen and deuterium

    International Nuclear Information System (INIS)

    Dalkarov, O.D.; Kerbikov, B.O.; Markushin, V.E.

    1976-01-01

    Detailed analysis is given of stopping antiproton annihilation in liquid hydrogen and deuterium. Connection between capture schedule and properties of bound states in nucleon-antinucleon system is established. The theoretical predictions are compared with experimental data which appeared in 1971-75

  11. The electroweak interaction in e+e- annihilations

    International Nuclear Information System (INIS)

    Marshall, R.

    1982-04-01

    The role of e + e - annihilation in studying the weak neutral current, at PETRA and PEP, is reviewed. The way in which the vector and axial vector couplings appear in the total cross sections, the angular distributions and the polarisation dependences are discussed. The dependence of external gauge models on the results of PETRA and PEP experiments is examined. (U.K.)

  12. Hidden strangeness production in two body nbarp annihilation in flight

    CERN Document Server

    Filippi, A

    1999-01-01

    The relative production rates of the final states phi pi sup + , omega pi sup + , eta pi sup + , eta'pi sup + in nbarp annihilation in flight are studied in order to check OZI rule violation effects in both the vectorial and pseudoscalar sectors.

  13. Positron annihilation and tribological studies of nano-embedded Al ...

    Indian Academy of Sciences (India)

    Positron annihilation studies of aluminium alloys with nanodispersions of insoluble elements, i.e., In, Sn, Pb and Au were reported. The alloys were obtained using a rapid solidification process. For all alloys, except that with Au, the average diameter of nanoparticles in aluminium matrix was 100 nm, and variance of the size ...

  14. Positron annihilation in vacancies at grain boundaries in metals

    Czech Academy of Sciences Publication Activity Database

    Kuriplach, J.; Melikhova, O.; Hou, M.; Van Petegem, S.; Zhurkin, E.; Šob, Mojmír

    2008-01-01

    Roč. 255, č. 1 (2008), s. 128-132 ISSN 0169-4332 R&D Projects: GA MŠk OC 147; GA AV ČR IAA1041302 Institutional research plan: CEZ:AV0Z20410507 Keywords : Positron annihilation * Grain boundaries * Vacancies Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.576, year: 2008

  15. Is positron annihilation in polyamide 6 affected by morphology?

    Czech Academy of Sciences Publication Activity Database

    Debowska, M.; Piglowski, J.; Slusarczyk, C.; Schmidt, Pavel; Rudzinska-Girulska, J.; Suzuki, T.; Yu, R.; Binias, W.

    2005-01-01

    Roč. 132, SI (2005), s. 64-68 ISSN 1230-3666. [International Conference on X-Ray Investigation of Polymer Structure /6./. Bielsko-Biala, 08.12.2004-11.12.2004] Institutional research plan: CEZ:AV0Z40500505 Keywords : polyamide 6 * crystalline regions * positron annihilation Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.397, year: 2005

  16. World View, the University Establishment, and Cultural Annihilation

    Science.gov (United States)

    Toelken, Barre

    1975-01-01

    Suggests that in the name of liberalism, the social system annihilates other cultures by ensuring that only their sellouts can get on in the world while the subjects and processes which could more fully inform the academic process is ignored. (Author/AM)

  17. Invariant Distributionally Scrambled Manifolds for an Annihilation Operator

    Directory of Open Access Journals (Sweden)

    Xinxing Wu

    2014-01-01

    Full Text Available This note proves that the annihilation operator of a quantum harmonic oscillator admits an invariant distributionally ε-scrambled linear manifold for any 0<ε<2. This is a positive answer to Question 1 by Wu and Chen (2013.

  18. Modelling of Excess Vacancy Annihilation at Different Types of Sinks

    Czech Academy of Sciences Publication Activity Database

    Fischer, F. D.; Svoboda, Jiří; Appel, F.; Kozeschnik, E.

    2011-01-01

    Roč. 59, č. 9 (2011), s. 3463-3472 ISSN 1359-6454 R&D Projects: GA ČR GAP108/10/1781 Institutional research plan: CEZ:AV0Z20410507 Keywords : Vacancies * Annihilation * Substitutional diffusion Subject RIV: BJ - Thermodynamics Impact factor: 3.755, year: 2011

  19. Noncolocated Structural Vibration Suppression Using Zero Annihilation Periodic Control

    Science.gov (United States)

    Bayard, David S.; Boussalis, Dhemetrios

    1993-01-01

    The Zero Annihilation Periodic (ZAP) controller is applied to the problem of vibration control of a noncolocated flexible structure. It is shown that even though the transfer function is nonminimum-phase, a plant inverse controller can be designed which elicits a deadbeat closed-loop response.

  20. Photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Shirley, D.A.

    1976-01-01

    Research activities in photoelectron spectroscopy at Lawrence Radiation Laboratory during 1976 are described. Topics covered include: the orientation of CO on Pt(III) and Ni(III) surfaces from angle-resolved photoemission; photoemission from CO on Pt(III) in the range 40 eV less than or equal to dirac constant ω less than or equal to 150 eV; photoemission studies of electron states at clean surfaces using synchrotron radiation; angle and energy dependent photoemission studies of plasmon loss structure in Al and In; d-orbital directed photoemission from copper; interpretation of angle-resolved x-ray photoemission from valence bands; atomic cross-section effects in soft x-ray photoemission from Ag, Au, and Pt valence bands; x-ray photoelectron spectroscopic studies of the electronic structure of transition metal difluorides; x-ray photoemission investigation of the density of states of B'-NiAl; the electronic structure of SrTiO 3 and some simple related oxides; fluorescence lifetime measurements of np 5 (n+1)S' states in krypton and xenon; Zeeman beats in the resonance fluorescence of the 3P 1 , states in krypton and xenon; lifetime measurements of rare-gas dimers; configuration interaction effects in the atomic photoelectron spectra of Ba, Sm, Eu, and Yb; glow discharge lamps as electron sources for electron impact excitation; electron impact excitation of electron correlation states in Ca, Sr, and Ba; photoelectron spectroscopy of atomic and molecular bismuth; relativistic effects in the uv photoelectron spectra of group VI diatomic molecules; and relative gas-phase acidities and basicities from a proton potential model

  1. A new positron lifetime spectrometer using a fast digital oscilloscope and BaF sub 2 scintillators

    CERN Document Server

    Saito, H; Kurihara, T; Hyodo, T

    2002-01-01

    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 BaF sub 2 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 gamma-ray from sup 2 sup 2 Na and one of the two positron annihilation gamma-rays of 0.511 MeV. The time resolution is further improved with a 'double-stop' setup, where timing information carried by the positron annihilation gamma-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 th...

  2. Finite quasiparticle lifetime in disordered superconductors.

    Energy Technology Data Exchange (ETDEWEB)

    Zemlicka, M.; Neilinger, P.; Trgala, M; Rehak, M; Manca, D.; Grajcar, M.; Szabo, P.; Samuely, P.; Gazi, S.; Hubner, U.; Vinokur, V. M.; Il' ichev, E.

    2015-12-08

    We investigate the complex conductivity of a highly disordered MoC superconducting film with k(F)l approximate to 1, where k(F) is the Fermi wave number and l is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature T-c. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, tau, offers a perfect description of the experimentally observed complex conductivity. We show that iota is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by scanning tunneling spectroscopy and agree with those determined from the complex conductivity.

  3. Positron lifetime calculations of defects in chromium containing hydrogen or helium

    International Nuclear Information System (INIS)

    Troev, T.; Markovski, A.; Peneva, S.; Yoshiie, T.

    2006-01-01

    The characteristics of defects in chromium containing hydrogen or helium atoms have been investigated by positron lifetime quantum calculations. On the basis of calculated results, the behaviors of empty nano-voids and nano-voids with hydrogen or helium were discussed. It was found that hydrogen and helium in larger three-dimensional vacancy clusters change the annihilation characteristics dramatically. The hydrogen and helium atoms are trapped by lattice vacancies. Helium bound with vacancies can form larger size cluster in chromium. These results provide physical insight for positron interactions with defects in chromium and can be used for prediction of hydrogen or helium generation for the design of fission and fusion reactors. The positron lifetime calculations were performed by the standard DFT density functional theory method. The electron wave functions have been obtained in the local density approximation LDA to the DFT

  4. Intrinsic spin lifetimes in GaAs (110) quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, Georg; Roemer, Michael; Huebner, Jens; Oestreich, Michael [Institut fuer Festkoerperphysik, Gottfried Wilhelm Leibniz Universitaet Hannover, Hannover (Germany); Schuh, Dieter; Wegscheider, Werner [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg (Germany)

    2009-07-01

    GaAs(110) quantum wells attract great attention due to the long spin lifetime for electron spins along the growth axis and are, therefore, of interest for future spin based optoelectronic devices. At low temperatures, optical injection of a finite spin polarization yields strongly enhanced spin dephasing due to the Bir Aronov Pikus mechanism that arises from the exchange interaction between electrons and holes. Thus, the intrinsic spin lifetime in GaAs(110) quantum wells has been unknown. In this work, the non-demolition technique of spin noise spectroscopy, which only relies on statistical spin fluctuations, is applied to GaAs(110) quantum wells in order to measure the intrinsic spin lifetimes. Furthermore, the Brownian motion of the electrons modifies the linewidth of the measured spin noise spectra due to time of flight broadening. This effect uniquely allows to study electronic motion at thermal equilibrium.

  5. Occupational risk and lifetime exposure

    International Nuclear Information System (INIS)

    Lapp, R.E.

    1991-01-01

    Any lowering of annual radiation limits for occupational exposure should be based on industry experience with lifetime doses and not on a worst case career exposure of 47 years. Two decades of experience show a lifetime accumulation of less than 1.5 rem for workers with measurable exposure. This is 5% of the normal lifetime exposure of Americans to natural and medical radiation. Any epidemiology of the US nuclear power workforce's two decade long exposure would have to focus on excess leukemia. Application of the Hiroshima and Nagasaki cancer mortality shows that too few leukemias would be expressed to permit a feasible epidemiology. Ionizing radiation appears to be a mild carcinogen as compared to physical and chemical agents presented in the occupational environment. A realistic factor in determining any change in occupational exposure limits for ionizing radiation should take into account the past performance of the licensee and potential health effects applicable to the workplace. Specifically, the lifetime exposure data for workers at nuclear power plants and naval shipyards should be considered. The nuclear industry and the US Navy have detailed data on the annual exposure of workers with a combined collective exposure approaching 1 million worker-rem. The lifetime dose for naval personnel and shipyard workers averages 1.1 rem J 1990. Shipyard workers have an annual dose of 0.28 rem per work-year and a mean exposure time of 4.4 years. The data apply to workers with measurable dose

  6. Positron Annihilation Spectroscopic Investigation on the Origin of Temperature-Dependent Electrical Response in Methylammonium Lead Iodide Perovskite.

    Science.gov (United States)

    Dhar, Joydeep; Sil, Sayantan; Dey, Arka; Ray, Partha Pratim; Sanyal, Dirtha

    2017-04-20

    Organic-inorganic hybrid perovskite has appeared as one of the leading materials for realizing solution-based high-performing optoelectronic devices. The charge transport properties in this class of material are quite intriguing and still need to be carefully investigated. The temperature-dependent electrical property of methylammonium lead iodide (CH 3 NH 3 PbI 3 ) has been investigated by employing positron annihilation spectroscopy (PAS), which unambiguously reveals the gradual formation of open volume defects with the enhancement in temperature. The high-temperature ionic conductivity is due to the generation of both cationic (CH 3 NH 3 + ) and anionic (I - ) vacancies, possibly because of the elimination of methylammonium iodide (CH 3 NH 3 I) as identified from the coincidence Doppler broadening (CDB) of the positron annihilation spectroscopy. Further, the evolution of temperature-dependent defect density and corresponding electrical responses has been correlated with the structural phase transitions of CH 3 NH 3 PbI 3 . This is the first ever report of temperature-dependent PAS measurement on hybrid lead halide perovskites to understand the nature and the origin of its electrical characteristics arising due to the variation in temperature.

  7. Thermally-induced crystallization behaviour of 80GeSe{sub 2}–20Ga{sub 2}Se{sub 3} glass as probed by combined X-ray diffraction and PAL spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, O., E-mail: shpotyuk@novas.lviv.ua [Scientific Research Company “Carat”, 202, Stryjska str., Lviv 79031 (Ukraine); Institute of Physics of Jan Dlugosz University, 13/15, al. Armii Krajowej, Czestochowa 42201 (Poland); Calvez, L.; Petracovschi, E. [Equipe Verres et Céramiques, UMR-CNRS 6226, Institute des Sciences chimiques de Rennes, Université de Rennes 1, 35042 Rennes Cedex (France); Klym, H. [Lviv polytechnic National University, 12 Bandera str., Lviv 79013 (Ukraine); Ingram, A. [Physics Faculty of Opole University of Technology, 75, Ozimska str., Opole 45370 (Poland); Demchenko, P. [Ivan Franko National University of Lviv, 6, Kyryla and Mefodiya Str., Lviv 79005 (Ukraine)

    2014-01-05

    Highlights: • Chalcogenide Ge–Ga–Se glasses were annealed at 380 °C for 10, 25 and 50 h. • Crystallization of glasses during annealing indicates formation of crystals. • Structural changes are described by two-state positron trapping model. • Modification leading to nucleation and fragmentation of free volume of glasses. • The Ge–Ga–Se systems cannot be classified as typical pseudo-binary system. -- Abstract: Crystallization behaviour of 80GeSe{sub 2}–20Ga{sub 2}Se{sub 3} glass caused by thermal annealing at 380 °C for 10, 25 and 50 h are studied using X-ray diffraction and positron annihilation lifetime spectroscopy. It is shown that the structural changes caused by crystallization can be adequately described by positron trapping modes determined within two-state model. The observed changes in defect-related component in the fit of experimental positron lifetime spectra for annealed glasses testifies in a favour of structural fragmentation of larger free volume entities into smaller ones with preceding nucleation in the initial stage of thermal annealing. Because of strong deviation in defect-free bulk positron lifetime from corresponding additive values proper to boundary constituents, the studied glasses cannot be considered as typical representatives of pseudo-binary cut-section.

  8. Radiative lifetimes of neutral neodymium

    International Nuclear Information System (INIS)

    Den Hartog, E A; Fittante, A J; Lawler, J E

    2011-01-01

    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.

  9. Effect of Copper on the Carrier Lifetime in Black Silicon

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Persheyev, Saydulla

    2011-01-01

    Black silicon is produced by laser annealing of a-Si:H films. During annealing, silicon microstructures are formed on the surface. We use time-resolved terahertz spectroscopy to study the photoconductivity dynamics in black silicon. We find that when a copper film is deposited on top of the a......-Si:H layer prior to laser annealing, the carrier lifetime of black silicon is significantly reduced....

  10. Positron lifetime study of electron-irradiated epoxy resins

    International Nuclear Information System (INIS)

    Suevegh, K.; Vertes, A.; Wojnarovits, L.; Foeldiak, G.; Liszkai, L.; Kajcsos, Zs.

    1990-01-01

    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

  11. High energy resolution and first time-dependent positron annihilation induced Auger electron spectroscopty

    International Nuclear Information System (INIS)

    Mayer, Jakob

    2010-01-01

    It was the aim of this thesis to improve the existing positron annihilation induced Auger spectrometer at the highly intense positron source NEPOMUC (NEutron induced POsitron source MUniCh) in several ways: Firstly, the measurement time for a single spectrum should be reduced from typically 12 h to roughly 1 h or even less. Secondly, the energy resolution, which amounted to ΔE/E∼10%, should be increased by at least one order of magnitude in order to make high resolution positron annihilation induced Auger spectroscopy (PAES)-measurements of Auger transitions possible and thus deliver more information about the nature of the Auger process. In order to achieve these objectives, the PAES spectrometer was equipped with a new electron energy analyzer. For its ideal operation all other components of the Auger analysis chamber had to be adapted. Particularly the sample manipulation and the positron beam guidance had to be renewed. Simulations with SIMION registered ensured the optimal positron lens parameters. After the adjustment of the new analyzer and its components, first measurements illustrated the improved performance of the PAES setup: Firstly, the measurement time for short overview measurements was reduced from 3 h to 420 s. The measurement time for more detailed Auger spectra was shortened from 12 h to 80 min. Secondly, even with the reduced measurement time, the signal to noise ratio was also enhanced by one order of magnitude. Finally, the energy resolution was improved to ΔE/E 2,3 VV-transition with PAES. Thus, within this thesis two objectives were achieved: Firstly, the PAES spectrometer was renewed and improved by at least one order of magnitude with respect to the signal to noise ratio, the measurement time and the energy resolution. Secondly, several measurements have been carried out, demonstrating the high performance of the spectrometer. Amongst them are first dynamic PAES measurements and a high resolution measurement of the CuM 2,3 VV

  12. Dark matter distribution and annihilation at the Galactic center

    International Nuclear Information System (INIS)

    Dokuchaev, V I; Eroshenko, Yu N

    2016-01-01

    We describe a promising method for measuring the total dark matter mass near a supermassive black hole at the Galactic center based on observations of nonrelativistic precession of the orbits of fast S0 stars. An analytical expression for the precession angle has been obtained under the assumption of a power-law profile of the dark matter density. The awaited weighing of the dark matter at the Galactic center provides the strong constraints on the annihilation signal from the neuralino dark matter particle candidate. The mass of the dark matter necessary for the explanation of the observed excess of gamma-radiation owing to the annihilation of the dark matter particles has been calculated with allowance for the Sommerfeld effect. (paper)

  13. Appearance of a Minimal Length in $e^+ e^-$ Annihilation

    CERN Document Server

    Dymnikova, Irina; Ulbricht, Jürgen

    2014-01-01

    Experimental data reveal with a 5$\\sigma$ significance the existence of a characteristic minimal length $l_e$= 1.57 × 10$^{−17}$ cm at the scale E = 1.253 TeV in the annihilation reaction $e^+e^- \\to \\gamma\\gamma(\\gamma)$ . Nonlinear electrodynamics coupled to gravity and satisfying the weak energy condition predicts, for an arbitrary gauge invariant Lagrangian, the existence of spinning charged electromagnetic soliton asymptotically Kerr-Newman for a distant observer with the gyromagnetic ratio g=2 . Its internal structure includes a rotating equatorial disk of de Sitter vacuum which has properties of a perfect conductor and ideal diamagnetic, displays superconducting behavior, supplies a particle with the finite positive electromagnetic mass related to breaking of space-time symmetry, and gives some idea about the physical origin of a minimal length in annihilation.

  14. Gamma rays from the annihilation of singlet scalar dark matter

    Science.gov (United States)

    Yaguna, Carlos E.

    2009-03-01

    We consider an extension of the Standard Model by a singlet scalar that accounts for the dark matter of the Universe. Within this model we compute the expected gamma ray flux from the annihilation of dark matter particles in a consistent way. To do so, an updated analysis of the parameter space of the model is first presented. By enforcing the relic density constraint from the very beginning, the viable parameter space gets reduced to just two variables: the singlet mass and the higgs mass. Current direct detection constraints are then found to require a singlet mass larger than 50 GeV. Finally, we compute the gamma ray flux and annihilation cross section and show that a large fraction of the viable parameter space lies within the sensitivity of Fermi-GLAST.

  15. High nuclear temperatures by antimatter-matter annihilation

    International Nuclear Information System (INIS)

    Gibbs, W.R.; Strottman, D.

    1985-01-01

    It is suggested that the quark-gluon phase be created through the use of antiproton or antideuteron beams. The first advantage to this method, using higher energy antiprotons than 1.5 GeV/c, is that the higher momenta antiprotons penetrate more deeply so that mesons produced are more nearly contained within the nucleus. Another advantage is that the annihilation products are very forward-peaked and tend to form a beam of mesons so that the energy density does not disperse very rapidly. Calculations were performed using the intranuclear cascade to try to follow the process of annihilation in some detail. The intranuclear cascade type calculation method is compared to the hydrodynamic approach. 8 refs., 8 figs

  16. Gamma rays from the annihilation of singlet scalar dark matter

    International Nuclear Information System (INIS)

    Yaguna, Carlos E.

    2009-01-01

    We consider an extension of the Standard Model by a singlet scalar that accounts for the dark matter of the Universe. Within this model we compute the expected gamma ray flux from the annihilation of dark matter particles in a consistent way. To do so, an updated analysis of the parameter space of the model is first presented. By enforcing the relic density constraint from the very beginning, the viable parameter space gets reduced to just two variables: the singlet mass and the higgs mass. Current direct detection constraints are then found to require a singlet mass larger than 50 GeV. Finally, we compute the gamma ray flux and annihilation cross section and show that a large fraction of the viable parameter space lies within the sensitivity of Fermi-GLAST

  17. Beyond 'invisibility': queer intelligibility and symbolic annihilation in healthcare.

    Science.gov (United States)

    Müller, Alex

    2018-01-01

    Sexual minority health is increasingly receiving attention by health sciences education and healthcare, with the core argument being that health can be improved by challenging sexual minority invisibility. Invisibility as a concept, however, does not allow for a deeper theoretical engagement with the reasons and consequences of the lack of representation of queerness in healthcare. Drawing on empirical research with queer healthcare users in South Africa, I argue that 'invisibility' actually encompasses two distinct, though related, concepts: queer symbolic annihilation as the reason for the exclusion of queer identities in health professions education and, by consequence, in healthcare; and queer (un)intelligibility as the consequence of this systemic erasure. By simply attributing discriminatory healthcare experiences of queer people to 'invisibility' we are missing opportunities to address underlying issues of queer symbolic annihilation and unintelligibility.

  18. Structure, electric properties and positron annihilation studies of CuZnFe2O4 doped with BaTiO3

    Science.gov (United States)

    Hemeda, O. M.; Mahmoud, K. R.; Sharshar, T.

    2014-08-01

    Composite materials of spinel CuZnFe2O4 ferrite (CZF) and barium titanate BaTiO3 (BT) were prepared by using the high-energy ball milling technique. The X-ray diffraction (XRD) patterns of the composite system confirmed the composite preparation with two piezomagnetic and piezoelectric phases. The results of scanning electron microscope (SEM) measurements show a nearly homogeneous microstructure with good dispersion of BT grains as well as the presence of some pores. The positron annihilation lifetime (PAL) is used to probe the defects and structural changes of the BT-CZF composites. The PAL parameters ( , I1, , I2 and mean lifetime) show that the doped BT content affects the size and concentration of the vacant type defects.

  19. Lifetime of heavy flavour particles

    International Nuclear Information System (INIS)

    Lueth, V.

    1985-10-01

    Recent measurements of the lifetime of the tau leptons and charm and beauty hadrons are reviewed and their significance for the couplings of the charged weak current, flavour mixing, and models relating quarks to hadron decay are discussed. 70 refs., 17 figs., 5 tabs

  20. Lifetime value in business process

    Directory of Open Access Journals (Sweden)

    Martin Souček

    2011-01-01

    Full Text Available The paper focuses on lifetime value assessment and its implementation and application in business processes. The lifetime value is closely connected to customer relationship management. The paper presents results of three consecutive researches devoted to issues of customer relationship management. The first two from 2008 and 2010 were conducted as quantitative ones; the one from 2009 had qualitative nature. The respondents were representatives of particular companies. The means for data collection was provided by ReLa system. We will focus on individual attributes of lifetime value of a customer, and relate them to approaches of authors mentioned in introduction. Based on the qualitative research data, the paper focuses on individual customer lifetime value parameters. These parameters include: the cost to the customer relationship acquisition and maintenance, profit generated from a particular customer, customer awareness value, the level of preparedness to adopt new products, the value of references and customer loyalty level. For each of these parameters, the paper provides specific recommendations. Moreover, it is possible to learn about the nature of these parameter assessments in the Czech environment.

  1. Comments on charm production in electron positron annihilation

    International Nuclear Information System (INIS)

    Close, F.E.

    1976-09-01

    The circumstances are discussed in which the production of D anti D: DD*: D* anti D* in electron positron annihilation is expected to be in the ratio 1:4:7 suggested by counting the available spin states. The physical significance of the requisite assumptions is discussed. The importance of taking into account the finite detector acceptance is stressed and tests for a possible 3 D 1 component in the D* are proposed. (author)

  2. Multiwavelength analysis of dark matter annihilation and RX-DMFIT

    Energy Technology Data Exchange (ETDEWEB)

    McDaniel, A.; Jeltema, T.; Profumo, S. [Department of Physics, University of California, 1156 High St. Santa Cruz, CA, 95064 (United States); Storm, E., E-mail: alexmcdaniel@ucsc.edu, E-mail: tesla@ucsc.edu, E-mail: profumo@ucsc.edu, E-mail: e.m.storm@uva.nl [GRAPPA, Institute of Physics, Universiteit van Amsterdam Science Park 904, 1098XH Amsterdam (Netherlands)

    2017-09-01

    Dark matter (DM) particles are predicted by several well motivated models to yield Standard Model particles through self-annihilation that can potentially be detected by astrophysical observations. In particular, the production of charged particles from DM annihilation in astrophysical systems that contain magnetic fields yields radio emission through synchrotron radiation and X-ray emission through inverse Compton scattering of ambient photons. We introduce RX-DMFIT, a tool used for calculating the expected secondary emission from DM annihilation. RX-DMFIT includes a wide range of customizable astrophysical and particle parameters and incorporates important astrophysics including the diffusion of charged particles, relevant radiative energy losses, and magnetic field modelling. We demonstrate the use and versatility of RX-DMFIT by analyzing the potential radio and X-ray signals for a variety of DM particle models and astrophysical environments including galaxy clusters, dwarf spheroidal galaxies and normal galaxies. We then apply RX-DMFIT to a concrete example using Segue I radio data to place constraints for a range of assumed DM annihilation channels. For WIMP models with M {sub χ} ≤ 100 GeV and assuming weak diffusion, we find that the leptonic μ{sup +}μ{sup −} and τ{sup +}τ{sup −} final states provide the strongest constraints, placing limits on the DM particle cross-section well below the thermal relic cross-section, while even for the b b-bar channel we find limits close to the thermal relic cross-section. Our analysis shows that radio emission provides a highly competitive avenue for dark matter searches.

  3. Annihilators in infinite-dimensional Grassmann-Banach algebras

    International Nuclear Information System (INIS)

    Ivashchuk, V.D.

    1989-01-01

    A family of infinite-dimensional Grassmann-Banach algebras over a complete normed field K is considered. It is shown that every element G of the family is an associative supercommutative Banach superalgebra over K: G double-bond G 0 circle-plus G 1 with zero annihilators G 0 perpendicular double-bond G 1 perpendicular double-bond(G 1 (κ) ) perpendicular double-bond(0), k ≥ 2

  4. Experimental study of jets in electron-positron-annihilation

    International Nuclear Information System (INIS)

    Bartel, W.; Cords, D.; Dittmann, P.; Eichler, R.; Felst, R.; Haidt, D.; Krehbiel, H.; Naroska, B.; O'Neill, L.H.; Steffen, P.

    1981-02-01

    Data on hadron production by e + e - -annihilation at c.m. energies between 30 GeV and 36 GeV are presented and compared with two models both based on first order QCD but using different schemes for the fragmentation of quarks and gluons into hadrons. In one model the fragmentation proceeds along the parton momenta, in the other along the colour-anticolour axes. The data are reproduced better by fragmentation along the colour axes. (orig.)

  5. Inclusive anomalous muon production in e+e- annihilation

    International Nuclear Information System (INIS)

    Feldman, G.J.; Bulos, F.; Lueke, D.; Abrams, G.S.; Alam, M.S.; Boyarski, A.M.; Breidenbach, M.; Dorfan, J.; Friedberg, C.E.; Fryberger, D.; Goldhaber, G.; Hanson, G.; Heile, F.B.; Jaros, J.A.; Kadyk, J.A.; Larsen, R.R.; Litke, A.M.; Lueth, V.; Madaras, R.J.; Morehouse, C.C.; Nguyen, H.K.; Paterson, J.M.; Perl, M.L.; Peruzzi, I.; Piccolo, M.; Pierre, F.M.; Pun, T.P.; Rapidis, P.; Richter, B.; Sadoulet, B.; Schwitters, R.F.; Tanenbaum, W.; Trilling, G.H.; Vannucci, F.; Whitaker, J.S.; Wiss, J.E.

    1977-01-01

    We present measurements of inclusive anomalous muon production in e + e - annihilations in three energy ranges. In all three ranges we observe a large anomalous muon production rate in two-prong events which is compatible with the expected decays of pairs of heavy leptons. In the highest energy range there is also appreciable anomalous muon production in multiprong events which, due to its magnitude and momentum dependence, must come in part from a source other than a heavy lepton

  6. Zero-Annihilation Periodic Control For Damping Vibrations

    Science.gov (United States)

    Bayard, David S.; Boussalis, Dhemetrios

    1995-01-01

    Report presents study on use of recently developed zero-annihilation periodic (ZAP) controller for active suppression of vibrations in flexible structures characterized by non-minimum-phase transfer functions. Non-minimum-phase situation occurs if certain kinds of vibration-sensor/vibration-actuator pairs (e.g., piezoelectric) used, and/or if vibration sensor(s) not colocated with vibration actuator(s).

  7. Investigation of corrosion defects in titanium by positron annihilation

    Directory of Open Access Journals (Sweden)

    Pietrzak Ryszard

    2015-12-01

    Full Text Available The positron annihilation method was used to study the formation of defects in titanium samples during their corrosion in the vapor of a 3% HCl solution. In particular, the distribution of defects depending on the distance from the corroding surface and the impact of an external magnetic field on the concentration of vacancies forming during the corrosion of titanium layers close to the surface were determined.

  8. Search for Dark Matter Annihilation in Galaxy Groups

    Science.gov (United States)

    Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L.; Safdi, Benjamin R.

    2018-03-01

    We use 413 weeks of publicly available Fermi Pass 8 gamma-ray data combined with recently developed galaxy group catalogs to search for evidence of dark matter annihilation in extragalactic halos. In our study, we use luminosity-based mass estimates and mass-to-concentration relations to infer the J factors and associated uncertainties for hundreds of galaxy groups within a redshift range z ≲0.03 . We employ a conservative substructure boost factor model, which only enhances the sensitivity by an O (1 ) factor. No significant evidence for dark matter annihilation is found, and we exclude thermal relic cross sections for dark matter masses below ˜30 GeV to 95% confidence in the b b ¯ annihilation channel. These bounds are comparable to those from Milky Way dwarf spheroidal satellite galaxies. The results of our analysis increase the tension but do not rule out the dark matter interpretation of the Galactic Center excess. We provide a catalog of the galaxy groups used in this study and their inferred properties, which can be broadly applied to searches for extragalactic dark matter.

  9. φ meson production in pp annihilation at rest

    International Nuclear Information System (INIS)

    Srisuphaphon, S.; Yan, Y.; Gutsche, Thomas; Lyubovitskij, Valery E.

    2011-01-01

    Apparent channel-dependent violations of the Okubo-Zwieg-Iizuka (OZI) rule in nucleon-antinucleon annihilation reactions in the presence of an intrinsic strangeness component in the nucleon are discussed. Admixture of ss quark pairs in the nucleon wave function enables the direct coupling to the φ-meson in the annihilation channel without violating the OZI rule. Three forms are considered in this work for the strangeness content of the proton wave function, namely, the uud cluster with a ss sea-quark component, kaon-hyperon clusters based on a simple chiral quark model, and the pentaquark picture uudss. Nonrelativistic quark model calculations reveal that the strangeness magnetic moment μ s and the strangeness contribution to the proton spin σ s from the first two models are consistent with recent experimental data, where μ s and σ s are negative. For the third model, the uuds subsystem with the configurations [31] FS [211] F [22] S and [31] FS [31] F [22] S leads to negative values of μ s and σ s . With effective quark line diagrams incorporating the 3 P 0 model, we give estimates for the branching ratios of the annihilation reactions at rest pp→φX (X=π 0 , η, ρ 0 , ω). Results for the branching ratios of φX production from atomic pp s-wave states are for the first and third model found to be strongly channel dependent, in good agreement with measured rates.

  10. Search for Dark Matter Annihilation in Galaxy Groups.

    Science.gov (United States)

    Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L; Safdi, Benjamin R

    2018-03-09

    We use 413 weeks of publicly available Fermi Pass 8 gamma-ray data combined with recently developed galaxy group catalogs to search for evidence of dark matter annihilation in extragalactic halos. In our study, we use luminosity-based mass estimates and mass-to-concentration relations to infer the J factors and associated uncertainties for hundreds of galaxy groups within a redshift range z≲0.03. We employ a conservative substructure boost factor model, which only enhances the sensitivity by an O(1) factor. No significant evidence for dark matter annihilation is found, and we exclude thermal relic cross sections for dark matter masses below ∼30  GeV to 95% confidence in the bb[over ¯] annihilation channel. These bounds are comparable to those from Milky Way dwarf spheroidal satellite galaxies. The results of our analysis increase the tension but do not rule out the dark matter interpretation of the Galactic Center excess. We provide a catalog of the galaxy groups used in this study and their inferred properties, which can be broadly applied to searches for extragalactic dark matter.

  11. The PAMELA positron excess from annihilations into a light boson

    Energy Technology Data Exchange (ETDEWEB)

    Cholis, Ilias; Goodenough, Lisa; Weiner, Neal [Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10003 (United States); Finkbeiner, Douglas P., E-mail: ijc219@nyu.edu, E-mail: dfinkbeiner@cfa.harvard.edu, E-mail: lcg261@nyu.edu, E-mail: neal.weiner@nyu.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

    2009-12-01

    Recently published results from the PAMELA experiment have shown conclusive evidence for an excess of positrons at high ( ∼ 10–100 GeV) energies, confirming earlier indications from HEAT and AMS-01. Such a signal is generally expected from dark matter annihilations. However, the hard positron spectrum and large amplitude are difficult to achieve in most conventional WIMP models. The absence of any associated excess in anti-protons is highly constraining on models with hadronic annihilation modes. We revisit an earlier proposal, wherein the dark matter annihilates into a new light (∼

  12. Dynamical effects of annihilation in pair-dominated winds

    Science.gov (United States)

    Becker, Peter A.; Begelman, Mitchell C.

    1990-01-01

    The steady, spherically symmetric flow of an ideal fluid dominated by photons and ultrarelativistic electron-positron pairs is analyzed. A new wind equation and a set of critical point conditions are obtained which describe the relativistic flow of an annihilation gas in which the flow velocity exceeds the diffusion velocity of the photons. Numerical results are reported which suggest the possible existence of trapped, pure-pair winds driven by the combined pressure of the pairs and the photons. Most of the annihilation occurs below the critical radius in trapped flows, and a substantial fraction of the total energy of the injected pairs is converted into kinetic energy and radiation. Accurate numerical solutions for the flow velocity and the positron loss rate in optically thin, Newtonian winds are obtained, and a useful approximate analytic relation between the positron loss rate and the flow velocity is derived which suggests that a large number of pairs may survive the annihilation region, ultimately escaping the potential well.

  13. Compton-backscattered annihilation radiation from the Galactic Center region

    Science.gov (United States)

    Smith, D. M.; Lin, R. P.; Feffer, P.; Slassi, S.; Hurley, K.; Matteson, J.; Bowman, H. B.; Pelling, R. M.; Briggs, M.; Gruber, D.

    1993-01-01

    On 1989 May 22, the High Energy X-ray and Gamma-ray Observatory for Nuclear Emissions, a balloon-borne high-resolution germanium spectrometer with an 18-deg FOV, observed the Galactic Center (GC) from 25 to 2500 keV. The GC photon spectrum is obtained from the count spectrum by a model-independent method which accounts for the effects of passive material in the instrument and scattering in the atmosphere. Besides a positron annihilation line with a flux of (10.0 +/- 2.4) x 10 exp -4 photons/sq cm s and a full width at half-maximum (FWHM) of (2.9 + 1.0, -1.1) keV, the spectrum shows a peak centered at (163.7 +/- 3.4) keV with a flux of (1.55 +/- 0.47) x 10 exp -3 photons/sq cm s and a FWHM of (24.4 +/- 9.2) keV. The energy range 450-507 keV shows no positronium continuum associated with the annihilation line, with a 2-sigma upper limit of 0.90 on the positronium fraction. The 164 keV feature is interpreted as Compton backscatter of broadened and redshifted annihilation radiation, possibly from the source 1E 1740.7-2942.

  14. Photodegradation in ballistic laminates: Spectroscopy and lifetime extension

    Energy Technology Data Exchange (ETDEWEB)

    Renschler, C.L.; Stallard, B.R.; White, C.A.; Garcia, M.J.; Morse, H.E. [Sandia National Labs., Albuquerque, NM (United States). Properties of Organic Materials Dept.

    1996-06-01

    Several years ago, the Materials and Process Sciences Center (Org. 1800) was asked by Dept. 9613 to study the materials aging issues which had led to the loss of ballistic protection by Armored Tractor (AT) windshields and windows. The authors speculated that this loss of impact strength was due to photodegradation of the polycarbonate (PC) inboard ply. They developed a spectroscopic method to identify changes in the outboard surface of the PC, and showed that the changes in the surface which occurred upon natural aging in the field could be reproduced by exposing the laminates to a simulated solar flux. Based on these results, they recommended changes in the adhesive interlayers to filter out the ultraviolet (UV) light causing the aging problem. Working with the laminate vendor, PPG, they re-designed the laminates to implement these changes and block essentially all UV light from the inboard ply. The most recent phase of this work involved accelerated solar aging of laminates made with the new design to verify that photoaging effects have been blocked by the new materials. They report here the results of that study, and recommended follow-on work.

  15. Cosmological constraints on dark matter annihilation and decay. Cross-correlation analysis of the extragalactic γ-ray background and cosmic shear

    International Nuclear Information System (INIS)

    Shirasaki, Masato; Macias, Oscar; Horiuchi, Shunsaku; Yoshida, Naoki; Tokyo Univ., Chiba; Japan Science and Technology Agency, Saitama

    2016-07-01

    We derive constraints on dark matter (DM) annihilation cross section and decay lifetime from cross-correlation analyses of the data from Fermi-LAT and weak lensing surveys that cover a wide area of ∝660 squared degrees in total. We improve upon our previous analyses by using an updated extragalactic γ-ray background data reprocessed with the Fermi Pass 8 pipeline, and by using well-calibrated shape measurements of about twelve million galaxies in the Canada-France-Hawaii Lensing Survey (CFHTLenS) and Red-Cluster-Sequence Lensing Survey (RCSLenS). We generate a large set of full-sky mock catalogs from cosmological N-body simulations and use them to estimate statistical errors accurately. The measured cross correlation is consistent with null detection, which is then used to place strong cosmological constraints on annihilating and decaying DM. For leptophilic DM, the constraints are improved by a factor of ∝ 100 in the mass range of O(1) TeV when including contributions from secondary γ rays due to the inverse-Compton upscattering of background photons. Annihilation cross-sections of left angle σν right angle ∝ 10 -23 cm 3 /s are excluded for TeV-scale DM depending on channel. Lifetimes of ∝10 25 sec are also excluded for the decaying TeV-scale DM. Finally, we apply this analysis to wino DM and exclude the wino mass around 200 GeV. These constraints will be further tightened, and all the interesting wino DM parameter region can be tested, by using data from future wide-field cosmology surveys.

  16. One-photon annihilation of thermal positrons with bound atomic electrons

    Science.gov (United States)

    Jung, Young-Dae

    1994-01-01

    Direct one-photon annihilation rate of positrons with a bound atomic electron is evaluated in the nonrelativistic limit. The K- and L-shell contributions are estimated including the screening and effective Coulomb repulsion effects. The annihilation rate of thermal positrons is calculated for various temperatures. The total number of one-photon annihilation events in the interstellar medium is discussed. These results provide the directional and structural information for cosmic gamma-ray sources.

  17. Properties of n-eicosane-filled microcapsules with different morphology. Phase Change Materials studied by positron spectroscopy and complementary methods

    Energy Technology Data Exchange (ETDEWEB)

    Zgardzińska, B., E-mail: bozena.zgardzinska@poczta.umcs.lublin.pl [Department of Nuclear Methods, Institute of Physics, Maria Curie-Sklodowska University, Pl. M. Curie-Sklodowskiej 1, 20-031 Lublin (Poland); Filipek, M. [Department of Nuclear Methods, Institute of Physics, Maria Curie-Sklodowska University, Pl. M. Curie-Sklodowskiej 1, 20-031 Lublin (Poland); Fortuniak, W. [Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź (Poland); Mroczek, P. [Department of Geoecology and Palaeogeography, Faculty of Earth Sciences and Spatial Management, Maria Curie-Sklodowska University, Al. Kraśnicka 2cd, 20-718 Lublin (Poland)

    2016-07-01

    The Positron Annihilation Lifetime Spectroscopy (PALS) was used to investigate properties of selected Phase Change Materials (PCMs) as a function of temperature from 123 K to 333 K. Three different PCM microcapsules investigated in this work were built of n-eicosane filling and a siloxane polymer as a shell material. It has been found that the properties of ortho-positronium (o-Ps) annihilating in n-eicosane filler depend on the microcapsule morphology. In the samples where the whole interior is composed of n-eicosane and the polymer forms the outer shell only, the n-eicosane behaves like a neat macroscopic sample. In the microcapsules containing the network of polymer threads inside the globule, n-eicosane shows no rise of o-Ps intensity with time which is typical for all pure alkanes. For this morphology, the melting point of n-eicosane is preceded by the 4 K wide temperature range, where the structure resembling the rotator phase is observed (rotator phase appears in neat even-numbered alkanes with carbon chain over 20 atoms). Supplementary data were obtained by the DSC method. SEM images confirmed the morphological differentiation of microcapsules. Low temperature (close to liquid nitrogen) destroys the structure of microcapsules, particularly their outer shell. - Highlights: • Polymer-alkane microcapsules were synthesized with different morphology. • Morphological diversity of microcapsules is reflected in the parameters of the PALS. • PALS show the effect of spatial limitations on the formation of lamellar structure. • PALS is a new way to determine the percentage of microcapsules components.

  18. Lifetime of a black hole

    International Nuclear Information System (INIS)

    Carlitz, R.D.; Willey, R.S.

    1987-01-01

    We study the constraints placed by quantum mechanics upon the lifetime of a black hole. In the context of a moving-mirror analog model for the Hawking radiation process, we conclude that the period of Hawking radiation must be followed by a much longer period during which the remnant mass (of order m/sub P/) may be radiated away. We are able to place a lower bound on the time required for this radiation process, which translates into a lower bound for the lifetime of the black hole. Particles which are emitted during the decay of the remnant, like the particles which comprise the Hawking flux, may be uncorrelated with each other. But each particle emitted from the decaying remnant is correlated with one particle emitted as Hawking radiation. The state which results after the remnant has evaporated is one which locally appears to be thermal, but which on a much larger scale is marked by extensive correlations

  19. Luminosity lifetime in the Tevatron

    International Nuclear Information System (INIS)

    Jackson, G.; Finley, D.; Johnson, R.P.; Kerns, Q.; McCarthy, J.; Siemann, R.; Zhang, P.

    1988-01-01

    Since the inauguration of colliding proton-antiproton operations in 1987, the Tevatron has exhibited luminosity lifetimes shorter than expected. During a typical colliding beam storage period, called a store, luminosity is calculated periodically by measuring the charge and emittances of each bunch. The growth of the transverse bunch emittances is the dominant cause of luminosity deterioration. Throughout, this period, the position spectrum of the bunches exhibited betatron signals larger than expected from Schottky noise. A model assuming externally driven betatron oscillations explains both the betatron signals and the emittance growth. A program is underway to improve the Tevatron luminosity lifetime. The abort kickers have been identified as sources of emittance growth, and some quadrupole power supplies are further candidates. Because the horizontal dispersion through the RF cavities is nonzero, RF phase noise has been investigated. Noise in the main dipole regulation circuit has also been studied. 13 refs., 4 figs

  20. 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)