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Sample records for positronium annihilation tratamiento

  1. Positron annihilation in solids: positronium diffusion

    International Nuclear Information System (INIS)

    Paulin, R.

    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 ≅ 10 -9 s and ≅ 10 -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 -4 cm 2 sec -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 2 where activation energy is found about 10 -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) [fr

  2. Peculiarities of annihilation of polarized positronium in polarized media

    International Nuclear Information System (INIS)

    Silenko, A.Ya.

    2005-01-01

    Features of positronium annihilation (PA) in polarized media are investigated. Strong exchange interaction with nonpaired electrons of paramagnetic atoms essentially accelerates the PA in comparison with annihilation of free positrons. The value of the spin projection on the direction of polarized nonpaired electrons has essential effect on the orthopositronium lifetime and on the width of the gamma spectrum annihilation line. It is shown that these features of PA permit to use it for studying the paramagnetic polarization [ru

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

    International Nuclear Information System (INIS)

    Pietrow, M.; Slomski, P.

    2011-01-01

    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 - 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.

  4. Positron Annihilation Ratio Spectroscopy (PsARS) Applied to Positronium Formation Studies

    Science.gov (United States)

    2010-03-01

    Positron Annihilation Ratio Spectroscopy (PsARS). These experimental techniques have been used for a variety of military and civilian applications ... POSITRON ANNIHILATION RATIO SPECTROSCOPY (PsARS) APPLIED TO POSITRONIUM FORMATION STUDIES THESIS...of Defense, or the United States Government. AFIT/GNE/ENP/10-M07 POSITRON ANNIHILATION RATIO SPECTROSCOPY

  5. 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.

  6. Nanoporosity studies of novel catalysts through positronium annihilation

    Science.gov (United States)

    Félix, M. V.; Rodríguez-Rojas, R. A.; Castañeda-Contreras, J.; Nava, R.; Consolati, G.; Castaño, V. M.

    2006-10-01

    Eight novel hybrid silica gel-succinic acid-zinc acetate samples were analyzed through Positron annihilation lifetime spectroscopy in order to study average free volume quantities and free volume distributions. The aim of this work was to understand the type of porosity within these species and its relationship with surface textural properties (tested by the BET method) and catalytic activity. We found a noticeable dependence of o-Ps lifetimes on the nature of each modifier agent (succinic acid, Zn acetate, succinic acid-Zn acetate) fixed on the surface of SiO 2 and SiO 2-Al 2O 3 particles. We observed the trend of the Zinc acetate to create mesopores among silica particles, while succinic acid acts as a positronium quencher and a nanoporosity performer. Long o-Ps lifetimes were decomposed into two components accounting for the existence of interparticle and intraparticle holes, however discrepancies beyond elementary facts between the BET method measurements and our positronium calculations were found. A discussion of the kind of open spaces analysis necessary to fully understand the porosity in these hybrid materials is also presented.

  7. Positron Annihilation Ratio Spectroscopy Study of Electric Fields Applied to Positronium at Material Interfaces

    Science.gov (United States)

    2011-03-01

    from 142 ns to a few ns [3:3]. Through the application of positron annihilation lifetime spectroscopy (PALS) on a material, the o-Ps lifetime can be...Force Base, Ohio APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. POSITRON ANNIHILATION RATIO SPECTROSCOPY STUDY OF ELECTRIC FIELDS APPLIED TO...protection in the United States. AFIT/GNE/ENP/11-M19 POSITRON ANNIHILATION RATIO SPECTROSCOPY STUDY OF ELECTRIC FIELDS APPLIED TO POSITRONIUM AT

  8. 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)

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

    International Nuclear Information System (INIS)

    Suzuki, R.; Ohdaira, T.; Kobayashi, Y.; Ito, K.; Shioya, Y.; Ishimaru, T.

    2003-01-01

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

  10. Positronium chemistry

    CERN Document Server

    Green, James

    1964-01-01

    Positronium Chemistry focuses on the methodologies, reactions, processes, and transformations involved in positronium chemistry. The publication first offers information on positrons and positronium and experimental methods, including mesonic atoms, angular correlation measurements, annihilation spectra, and statistical errors in delayed coincidence measurements. The text then ponders on positrons in gases and solids. The manuscript takes a look at the theoretical chemistry of positronium and positronium chemistry in gases. Topics include quenching, annihilation spectrum, delayed coincidence

  11. Temperature dependence study of positronium formation in high density polyethylene by positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Nahid, F.; Beling, C.D.; Fung, S.

    2007-01-01

    Positron annihilation lifetime spectroscopy has been used to study the formation of positronium in high density polyethylene as a function of temperature over the range 30 K-350 K. It is observed that the thermal history of the sample, while having no influence on the positronium lifetime, has a strong effect on the formation of positronium. A hysteresis is seen in the positronium formation probability in cooling and heating cycles. This is explained on a two channel formation model, the first channel being through ''blob'' formation and the second through the pick-up of shallow trapped electrons. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Hyperfine splitting in positronium to O(α7me). One-photon annihilation contribution

    International Nuclear Information System (INIS)

    Baker, M.; Penin, A.A.; Karlsruher Institut fuer Technologie; Piclum, J.; RWTH Aachen; Steinhauser, M.

    2014-02-01

    We present the complete result for the O(α 7 m e ) one-photon annihilation contribution to the hyperfine splitting of the ground state energy levels in positronium. Numerically it increases the prediction of quantum electrodynamics by 217±1 kHz.

  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 que dans SiO{sub 2} ou l'energie d'activation est trouvee

  14. Nonlinear narrow Doppler-free resonances for optical transitions and annihilation radiation of a positronium atom

    International Nuclear Information System (INIS)

    Letokhov, V.S.; Minogin, V.G.

    1976-01-01

    The possibilities of obtaining narrow resonances without the Doppler broadening for transition between the fine structure levels of the ground and first excited states of a positronium atom are considered. An analysis is carried out of the conditions required for observation of the narrow resonances of saturation of single quantum absorption in the 1S-2P transitions and observation of narrow two-photon absorption resonances in the 1S-2S transitions. It is shown that narrow 2γ annihilation radiation lines of a positronium atom may be obtained with a width much smaller than the Doppler one

  15. 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

  16. Determination and applications of enhancement factors for positron and ortho-positronium annihilations

    International Nuclear Information System (INIS)

    Mitroy, J.

    2005-01-01

    Electron-positron annihilation rates calculated directly from the electron and positron densities are known to underestimate the true annihilation rate. A correction factor, known as the enhancement factor, allows for the local increase of the electron density around the positron caused by the attractive electron-positron interaction. Enhancement factors are given for positrons annihilating with the 1s electron in H, He + , He, Li 2+ , and Li + . The enhancement factor for a free positron annihilating with He + and He is found to be close to that of ortho-positronium (i.e., Ps in its triplet state) annihilating with these atoms. The enhancement factor for Ps-He scattering is used in conjunction with the known annihilation rate for pickoff annihilation to derive a scattering length of 1.47a 0 for Ps-He scattering. Further, enhancement factors for e + -Ne and e + -Ar annihilation are used in conjunction with the pickoff annihilation rate to estimate scattering lengths of 1.46a 0 for Ps-Ne scattering and 1.75a 0 for Ps-Ar scattering

  17. Positron and positronium annihilation in low-dielectric-constant films studied by a pulsed positron beam

    International Nuclear Information System (INIS)

    Suzuki, R.; Ohdaira, T.; Kobayashi, Y.; Ito, K.; Yu, R.S.; Shioya, Y.; Ichikawa, H.; Hosomi, H.; Ishikiriyama, K.; Shirataki, H.; Matsuno, S.; Xu, J.

    2004-01-01

    Positron and positronium annihilation in porous low-dielectric-constant (low-k) films deposited by plasma-enhanced chemical vapor deposition (PECVD) and spin-on dielectric (SOD) have been investigated by means of positron annihilation lifetime spectroscopy (PALS) and age-momentum correlation (AMOC) spectroscopy with a pulsed slow positron beam. The ortho-positronium (o-Ps) lifetime strongly depends on the deposition condition. In general, PECVD low-k films have shorter o-Ps lifetimes than SOD low-k films, indicating PECVD low-k films have smaller pores. Since o-Ps diffusion and escaping from the surface occurs in most of porous SOD films, three-gamma annihilation measurement is important. To investigate o-Ps behavior in SOD films, we have carried out two-dimensional (2D) PALS measurement, which measures annihilation time and pulse-height of the scintillation detector simultaneously. Monte-Carlo simulation of the o-Ps diffusion and escaping in porous films has been carried out to simulate the 2D-PALS results. (orig.)

  18. Bound-state perturbation theory and annihilation effects in positronium

    International Nuclear Information System (INIS)

    Abbasabadi, A.; Repko, W.W.

    1987-01-01

    Working in Coulomb gauge and using the lowest-order equation proposed by Barbieri and Remiddi it is calculated, in the one-loop order of perturbation theory, the decay rate and the energy shift of the ground states of parapositronium and orthopositronium, respectively. Our result for the decay rate agrees with that of Harris and Brown. For contribution of one-photon-annihilation channel to the energy shift, it is confirmed the result of Karplus and Klein. These results are derived completely within the bound-state formalism and avoid the necessity of performing on-mass-shell wave function and vertex renormalization subtractions

  19. Positronium annihilation in liquids in the framework of non-local interaction

    International Nuclear Information System (INIS)

    Mukherjee, Tapas; Dutta, Dhanadeep

    2012-01-01

    In the bubble model of ortho positronium (o-Ps) annihilation in liquid the origin of the trapping of o-Ps is the electron-exchange repulsive interaction between the electron of o-Ps and the electron of the medium. The corresponding effective interaction is non-local in nature. However, in the prevalent bubble model, this effective interaction is usually treated as local (model) potential (sharp or smooth). In the present study, we have taken an approach to consider this trapping interaction as non-local in nature, which is included through a model separable non-local function to tackle the problem in analytically solvable manner. The analytical calculations show that this non-local interaction effectively acts as a gauge potential in the energy of the Ps atom in parameter (bubble radius) space. The computed bubble variables obtained using experimental Ps annihilation data are shown. A comparison between the present data with the calculated results using prevalent bubble model has been presented. Discussions have been made on the input parameter dependencies of the computed data. - Highlights: ► Bubble model has been modified by considering positronium-atom non-local interaction. ► No straight forward correlation between bubble size and effective potential is observed. ► Non-local potential acts as a guage potential.

  20. Quantum beats in positroniumannihilation decay observed in an age dependent, magnetically perturbed angular distribution (ADPAD), experiment

    International Nuclear Information System (INIS)

    Ivanov, E.; Vata, I.; Dudu, D.; Rusen, I.; Stefan, N.; Catavencu, V.

    2005-01-01

    We have been able to observe experimentally quantum beat oscillations of Positroniumannihilation decay at Positronium ages from 5 ns to 300 ns. We describe in some detail our equipment aiming at a consolidation of a new method of Positron Annihilation Spectroscopy. The equipment is dedicated to the study of hyperfine interactions of Positronium atoms in weak magnetic fields; four identical time spectrometers which have been used to measure simultaneously oscillations of positron life time spectra at privileged angles for the 3γ detectors. To overcome typical uncertainties in revealing small oscillation amplitudes the four life time spectra have been registered using a unique chronometer (TAC-ADC line) associated to a mixing - routing unit interfacing a PC memory. The present stage of performance is illustrated and further developments are suggested. (authors)

  1. Annihilation of positronium atoms confined in mesoporous and macroporous SiO2 films

    Science.gov (United States)

    Cooper, B. S.; Boilot, J.-P.; Corbel, C.; Guillemot, F.; Gurung, L.; Liszkay, L.; Cassidy, D. B.

    2018-05-01

    We report experiments in which positronium (Ps) atoms were created in thin, porous silica films containing isolated voids with diameters ranging from 5 to 75 nm. Ps lifetimes in the pore structures were measured directly via time-delayed laser excitation of 13S1→23PJ transitions. In a film containing 5-nm pores Ps was predominantly emitted into vacuum, with a small component of confined Ps with a lifetime of 75 ns also observed. In films with larger pores Ps atoms were not emitted into vacuum except from the film surface, and confined Ps lifetimes of ≈90 ns were measured with no dependence on the pore size. However, for such large pores, extended Tao-Eldrup (ETE)-type models predict Ps lifetimes close to the 142-ns vacuum value. Moreover, 13S1→23PJ excitation of Ps atoms inside the pores was found to result in annihilation and exhibited an extremely broad (≈10 THz) linewidth. We attribute these observations to a process in which nonthermal Ps atoms in the isolated voids become temporarily trapped in a series of surface states that dissociate following excitation. The occurrence of this mechanism is not necessarily apparent from ground-state Ps decay rates without some prior knowledge of the sample structure, and it precludes the application of ETE-type models as they do not take into account surface interactions other than pickoff annihilation.

  2. 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.

  3. 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.)

  4. Magnetic interaction of positronium atoms measured by perturbed angular distribution in 3 gamma annihilation decay

    International Nuclear Information System (INIS)

    Ivanov, E.; Vata, I.; Plostinaru, D.; Catana, D.; Dudu, D.; Constantinescu, O.

    2003-01-01

    The Time Differential Perturbed Angular Distribution (TDPAD) method in connection with long-lived Positron Life-Time Spectroscopy (PLTS) have been used to observe 'quantum beat' spin oscillations of positronium atom in an external magnetic field. Our results offer an encouraging hint toward a new method of condensed matter investigation by PLTS. Similarities with Muonium Spin Rotation (μSR) method are suggested. (authors)

  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. Three-gamma annihilation of ortho-positronium in NiO/γ-Al2O3 catalysts detected by positron lifetime and coincidence Doppler broadening measurements

    International Nuclear Information System (INIS)

    Huang, S.H.; Chen, Z.Q.; Zhang, H.J.

    2012-01-01

    The pore structure of NiO/γ-Al 2 O 3 catalysts is characterized by positron lifetime and Doppler broadening measurements. A very long lifetime τ 4 of 92 ns is resolved from the positron lifetime spectrum measured for pure Al 2 O 3 , which could be attributed to the ortho-positronium (o-Ps) lifetime in large pores. It was also found that the fitted lifetime τ 4 and its corresponding intensity I 4 obtained from the lifetime spectra both decrease with narrowing energy window of the stop channel in the fast–fast coincidence lifetime measurement system. This suggests that the ultra long lifetime is primarily due to the self annihilation of o-Ps which emits three gamma-rays. Such 3γ annihilation is further evidenced by measuring the Doppler broadening of annihilation gamma rays in coincidence with the prompt gamma rays (1.28 MeV) emitted from the 22 Na positron source. In NiO/γ-Al 2 O 3 catalysts both the lifetime τ 4 and its intensity I 4 decreases with increasing NiO content (from 3 wt% to 40 wt%), which indicates decreasing of the number of 3γ events. The 3γ annihilation parameter analyzed from the coincidence Doppler broadening spectrum shows consistent decrease with increasing NiO content. - Highlights: ► Above paper reported study of the 3-gamma annihilation of o-Ps. ► 3γ annihilation was verified by varying the energy window of the lifetime system. ► A new coincidence Doppler broadening technique is also used to record 3γ events. ► 3γ parameter decreases with NiO content in NiO/γ-Al 2 O 3 catalysts.

  7. Density dependence of a positron annihilation and positronium formation in H2 gas at temperatures between 77 and 297 K

    International Nuclear Information System (INIS)

    Laricchia, G.; Charlton, M.; Beling, C.D.; Griffith, T.C.

    1987-01-01

    Positron lifetime experiments have been performed on H 2 gas at temperatures between 77 and 297 K and in the density range from 12-160 Amagat. The extracted parameters are discussed in terms of current models. In the case of the positronium fraction it has been found that the observed density dependence can, in part, be interpreted using a combined Ore and spur model. (author)

  8. Positrons and positronium

    International Nuclear Information System (INIS)

    Jean, Y.C.; Lambrecht, R.M.

    1988-01-01

    This bibliography includes articles, proceedings, abstracts, reports and patents published between 1930 and 1984 on the subject of positrons, positron annihilation and positronium. The subject covers experimental and theoretical results in the areas of physics and chemistry of low and intermediate energy (< 0.6 MeV) positrons and positronium. The topics of interest are: fundamental properties, interactions with matter, nuclear technology, the history and philosophy of antimatter, the theory of the universe, and the applications of positrons in the chemical, physical, and biomedical sciences

  9. Relativistic corrections to fine structure of positronium

    International Nuclear Information System (INIS)

    Martynenko, A.P.; Faustov, R.N.

    1997-01-01

    On the basis of the quasipotential method, we have calculated the relativistic corrections in the positronium fine structure intervals 2 3 S 1 -2 3 P J . The contributions of order of mα 6 for the positronium S-levels were obtained from the one-photon, two-photon interactions and the second-order perturbation theory. We have obtained also the contribution of the two-photon annihilation diagrams to the interaction operator of the P-wave positronium. The corrections of order of α 5 R ∞ and α 5 1nαR ∞ to the P-wave energy levels of positronium were calculated

  10. Positronium physicochemistry and radiation chemistry

    International Nuclear Information System (INIS)

    Duplatre, G.

    1991-01-01

    A brief survey is given of the most salient experiments showing the links which exist between positronium formation in liquids as studied by positron annihilation techniques and data from pulse radiolysis. Some current trends in the field are also sketched [fr

  11. Positronium Annihilation Gamma Ray Laser

    Science.gov (United States)

    2009-07-01

    90 deg F using a 75-ohm resistor and the program maintained the temperature at 90 deg F with an inaccuracy of ±1.0 deg. The thermocouple was...pulse train, and propagating the multiple beams from the laser table and enclosure into the positron beam vacuum chamber using piezo - controlled

  12. Positronium formation in nanostructured metals

    Czech Academy of Sciences Publication Activity Database

    Čížek, J.; Melikhova, O.; Hruška, P.; Vlček, M.; Anwand, W.; Liedke, M.O.; Novotný, Michal; Bulíř, Jiří

    2017-01-01

    Roč. 132, č. 5 (2017), s. 1579-1584 ISSN 0587-4246 R&D Projects: GA ČR GBP108/12/G043 Institutional support: RVO:68378271 Keywords : positronium * positron annihilation spectroscopy * black gold Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 0.469, year: 2016

  13. Free volume dilatation in polymers by ortho-positronium

    DEFF Research Database (Denmark)

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

    2012-01-01

    The possibility of positronium induced free volume cavity expansion in some polymers above the glass transition temperature was investigated using experimental positron annihilation lifetime data from the literature for polydimethylsiloxane, polyisobutylene, and polybutadiene as function of tempe......The possibility of positronium induced free volume cavity expansion in some polymers above the glass transition temperature was investigated using experimental positron annihilation lifetime data from the literature for polydimethylsiloxane, polyisobutylene, and polybutadiene as function...

  14. Relativistic corrections to the fine structure of positronium

    International Nuclear Information System (INIS)

    Faustov, R. N.; Martynenko, A. P.

    1997-01-01

    The quasipotential method is used to calculate relativistic corrections in the positronium-fine-structure intervals 2 3 S 1 -2 3 P J . From analysis of one- and two-photon interactions, corrections of order mα 6 are found for positronium S states in the second order of perturbation theory. The contribution of the two-photon annihilation diagrams to the interaction operator for P-wave positronium is determined, and corrections of orders α 5 R ∞ and α 5 ln αR ∞ to the P-wave levels of positronium are calculated

  15. Positronium-photon and photon-positronium quantum transitions in strong magnetic fields

    International Nuclear Information System (INIS)

    Leinson, L.B.; Oraevskii, V.N.; Radio-Wave Propagation, Academy of Sciences of the USSR)

    1985-01-01

    The wave functions and energy levels of bound electron-positron pairs in a strong magnetic field H>>α 2 H 0 , where H 0 = m 2 0 c 3 /eh = 4.4 x 10 13 G and α = e 2 /hc, are found in the nonrelativistic approximation. The probabilities of one-photon annihilation of positronium and of the inverse transition from a resonance photon to a positronium atom are calculated. It is shown that in a sufficiently strong magnetic field H∼H 0 , when the probability of one-photon annihilation is considerably greater than the probability of two-photon annihilation of positronium, the lifetime of the decay photon with respect to the inverse transformation to a positronium atom is so small that the decay photon cannot propagate freely in the magnetic field. Therefore, the lifetime of the positronium atom in the case H∼H 0 is determined by the two-photon decay. The possibility of the decay γ→γ 1 +γ 2 via intermediate positronium states in a magnetic field with curved field lines is discussed

  16. Coherent decay of positronium bose condensate

    International Nuclear Information System (INIS)

    Vanyashin, V.S.

    1992-07-01

    The rate of self-stimulated emission of photon pairs by pseudoscalar particles from Bose condensate is calculated. Growing with density this rate exceeds the density independent rate of spontaneous two photon decay at plausible density values of positronium gas, thus opening in principle, the way to the annihilation gamma ray laser realization. (author). 2 refs

  17. Positronium chemistry in porous materials

    International Nuclear Information System (INIS)

    Kobayashi, Y.; Ito, K.; Oka, T.; Hirata, K.

    2007-01-01

    Porous materials have fascinated positron and positronium chemists for over decades. In the early 1970s it was already known that ortho-positronium (o-Ps) exhibits characteristic long lifetimes in silica gels, porous glass and zeolites. Since then, our understanding of Ps formation, diffusion and annihilation has been drastically deepened. Ps is now well recognized as a powerful porosimetric and chemical probe to study the average pore size, pore size distribution, pore connectivity and surface properties of various porous materials including thin films. In this paper, developments of Ps chemistry in porous materials undertaken in the past some 40 yr are surveyed and problems to be addressed in future are briefly discussed

  18. Positronium reflection and positronium beams

    International Nuclear Information System (INIS)

    Weber, M.; Tang, S.; Khatri, R.; Roellig, L.O.; Viescas, A.J.; Berko, S.; Canter, K.F.; Lynn, K.G.; Mills, A.P. Jr.

    1989-01-01

    We have observed specular reflection of positronium, Ps, and established that there is adequate intensity at higher energies to make further study worthwhile. The scattering appears to be restricted to the outermost surface with a mean free path of (0.75 ± 0.15)Angstrom for Ps in LiF(100). With a greater intensity Ps beam one should see higher order diffraction beams as the result of the periodicity of the surface. Ps diffraction thus offers the possibility of being a novel and valuable probe to study the outermost surface and to study adsorbents on it. Two methods for producing Ps beams are described. 29 refs., 11 figs

  19. 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)

  20. Positrons and positronium in grainy and porous solids

    International Nuclear Information System (INIS)

    Kajcsos, Zs.; Liszkay, L.; Varga, L.; Lohonyai, L.; Duplatre, G.; Lazar, K.; Pal-Borbely, G.; Beyer, H.K.; Caullet, P.; Patarin, J.

    2001-01-01

    Systematic investigations have been performed using positron annihilation techniques on micrograins of crystalline powders (e.g., MgO; Al 2 O 3 , SiO 2 ) and on various zeolites (e.g., silicalite 1, Na-X, Na-Y, ZSM-5, mordenite) aiming at a better understanding of the formation and decay of the long-lived ortho-positronium states. The techniques were lifetime spectroscopy, Doppler-effect measurements and the recording of the full energy distribution of the annihilation radiation. The influences of heat treatment, sample evacuation and presence of gases were investigated. Lifetimes over 130 ns and o-Ps fractions of about 30% were found. A strong correlation of positron annihilation technique data with a water content of the samples was evidenced. Possible pictures of the formation and decay of ortho-positronium in porous media are discussed. (author)

  1. Micellar effects on positronium lifetime in aqueous SDS solutions

    International Nuclear Information System (INIS)

    Vass, Sz.; Kajcsos, Zs.; Molnar, B.; Stergiopoulos, Ch.

    1981-09-01

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

  2. Polarization of positronium in amorphous polar polymers: A case study

    Energy Technology Data Exchange (ETDEWEB)

    Consolati, G., E-mail: giovanni.consolati@polimi.it; Quasso, F. [Department of Aerospace Science and Technology, Politecnico di Milano, via La Masa, 34, Milano 20156 (Italy)

    2013-11-28

    The features of positronium in an amorphous copolymer (polyvinyl acetate-crotonic acid) in a range of temperatures including the glass transition were investigated by means of positron annihilation lifetime spectroscopy. In particular, para-positronium lifetime was found to be longer than in a vacuum and to decrease with the temperature. This was attributed to the electron density at the positron (contact density), which is lower than in vacuo due to the presence of polar groups in the copolymer. A three quantum yield experiment confirmed the lifetime results.

  3. Evaluation of nonuniformity of polymeric membrane materials by positron annihilation technique

    International Nuclear Information System (INIS)

    Shantarovich, V.P.; Kevdina, I.B.; Yampol'skij, Yu.P.

    2000-01-01

    Time distribution of annihilation radiation of positrons in some glass-like polymers including polymer membrane materials in the air and in nitrogen atmosphere was studied experimentally. Main attention is paid to long-lived component of distribution, i.e. ortho-positronium annihilation (positron-electron bound system). Influence of atmospheric oxygen on positronium annihilation characteristics was detected. The conceived notions on the mechanisms of positronium formation, localization and annihilation in the polymers suggest irregularity of distribution of free volumes of different size in the polymer matrix. The concentration and size of the elementary free volumes, as well as sizes of micro heterogeneities containing the volumes are evaluated [ru

  4. The annihilation of ortho-positronium in the α and β cavities of the 4A zeolite and those CoZ4A and MnZ4A

    International Nuclear Information System (INIS)

    Cabral P, A.; Garcia S, I.; Jimenez B, J.; Solache R, M.; Bonifacio M, J.; Rodriguez F, C.; Bulbulian, S.

    2002-01-01

    The lifetime of the ortho-positronium in the zeolite 4A, partially dehydrated, changes to three characteristic modes. The first mode could be associated with the water elimination of the small β cavity of this zeolite. At the end of this first dehydration process it is estimated a cavity radius, R = 33.8 nm. The other two types of variation of lifetime of ortho-positronium would be associated with the water elimination of the α great cavity and of the rest of the zeolite. From the zeolite 4A totally dehydrated and of the zeolite 4A exchanged with Co (II) and MN (II), also dehydrated radius are respectively determined for the α great cavity of R = 48.1, 54.5 and 56.5 nm. (Author)

  5. Competitive and successive reactions in the position cluster and energy state of positronium in the liquids

    International Nuclear Information System (INIS)

    Didierjean, F.

    1991-10-01

    By combining two independent positron annihilation techniques, it is shown that, in polar solvents, the halogenated compounds inhibit positronium formation by quasi-free electron scavenging followed by positron capture. This sequence occurs before halide detachment intervenes. Studying mixtures of solutes allows both to confirm the existence of these successive reactions and to stress the influence, towards positronium formation, of the trap depth for the electron captured by nitrates, whether ion associated or not, in methanol. Finally, experiments in the presence of a magnetic field allow to conclude that the formed positronium is very rapidly thermalized, then localised in a potential well in the liquids, the so-called bubble [fr

  6. Positron annihilation spectroscopy study of porous silicon

    International Nuclear Information System (INIS)

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

    2007-01-01

    Experimental studies of porous silicon by means of a standard positron annihilation technique based on measuring the angular distribution of annihilation photons, are reported. It was shown that the spectra of angular correlation of annihilation radiation in porous silicon are approximated well by a parabola (I p ) and two Gaussians (I g1 , I g2 ). The narrow Gaussian component I g1 is most likely due to the annihilation of localized para-positronium in pores. The full width at half maximum is on the order of 0.8 mrad, a value that corresponds to the kinetic energy of an annihilating positron-electron pair (0.079 ± 0.012 eV), and its intensity is about 1.5%. The total positronium yield in porous silicon reaches 6% in this case. The particle radius determined in the study is about 10-20 A [ru

  7. Positronium emission spectroscopy

    International Nuclear Information System (INIS)

    Howell, R.H.; Tuomisaari, M.

    1988-08-01

    Measurements of the intensity, velocity, and angular distribution of positronium emitted from solid samples of metals and insulators have been performed using the intense, pulsed positron beam from the 100 MeV electron linac. From these data it is possible to determine properties of both the surface interactions and volume potentials of the materials studied. Examples of these effects will be given using measurements of positronium time of flight performed with the Livermore intense positron beam. The time of flight data have been augmented by positron lifetime and angular correlation measurements performed with the beam. Measurements resulting in workfunctions, deformation potentials and surface interaction effects will be reported for both metals and insulators. 18 refs., 2 figs

  8. Positron two-photon annihilation coincidence technique: difference mode

    Energy Technology Data Exchange (ETDEWEB)

    Karol, P J; Klobuchar, R L [Carnegie-Mellon Univ., Pittsburgh, Pa. (USA). Dept. of Chemistry

    1978-05-01

    A difference (or comparative) mode in the measurement of two-photon coincidences from positron or positronium annihilation has been developed. The method can be used to advantage, particularly in gases, in determining annihilation parameters such as quenching cross sections for low concentration strongly quenching chemical species in a reference medium which is relatively non-quenching.

  9. Positronium formation at surfaces and studies towards the production of low energy antihydrogen

    Science.gov (United States)

    Cassidy, David Barry

    A magnetically guided slow positron beam has been used to measure positronium formation fractions via spectroscopy of annihilation radiation. Positrons with energies in the range 0-3 keV were implanted into tungsten, copper, magnesium oxide powder and silica aerogel targets at room temperature and at cryogenic temperatures ( 30 K). This was done with and without nitrogen gas condensed on the surface of these materials. The resulting gamma rays were detected by a CsI detector and an associated PC-based spectroscopy system. In most cases studied the measured energy dependence of the positronium fractions was consistent with previous similar work, however, anomalous behaviour was found in some of the data when gas was condensed on metal surfaces. Using the same positron beam initial measurements of positronium energy distributions have been made. This was accomplished using a HPGe detector to measure the Doppler shift of the energy' of the positronium annihilation radiation. This novel technique has not yet been refined and estimates of its potential are reported. A Monte Carlo simulation of the reaction to form antihydrogen by positronium impact upon antiprotons has been undertaken. Total and differential cross sections have been utilised as input to the simulation which models the conditions foreseen in planned antihydrogen formation experiments using antiprotons and positrons held in Penning traps. Thus, predictions of antihydrogen production rates, angular distributions and the variation of the mean antihydrogen temperature as a function of the incident positronium energy have been made.

  10. Laser excitation of the n=3 level of positronium for antihydrogen production

    CERN Document Server

    Aghion, S; Ariga, A; Ariga, T; Bonomi, G; Braunig, P; Bremer, J; Brusa, R S; Cabaret, L; Caccia, M; Caravita, R; Castelli, F; Cerchiari, G; Chlouba, K; Cialdi, S; Comparat, D; Consolati, G; Demetrio, A; Di Noto, L; Doser, M; Dudarev, A; Ereditato, A; Evans, C; Ferragut, R; Fesel, J; Fontana, A; Forslund, O K; Gerber, S; Giammarchi, M; Gligorova, A; Gninenko, S N; Guatieri, F; Haider, S; Holmestad, H; Huse, T; Jernelv, I L; Jordan, E; Kellerbauer, A; Kimura, M; Koetting, T; Krasnicky, D; Lagomarsino, V; Lansonneur, P; Lebrun, P; Lehner, S; Liberadzka, J; Malbrunot, C; Mariazzi, S; Marx, L; Matveev, V A; Mazzotta, Z; Nebbia, G; Nedelec, P; Oberthaler, M K; Pacifico, N; Pagano, D; Penasa, L; Petracek, V; Pistillo, C; Prelz, F; Prevedelli, M; Ravelli, L; Resch, L; Rienacker, B; Røhne, O M; Rotondi, A; Sacerdoti, M; Sandaker, H; Santoro, R; Scampoli, P; Smestad, L; Sorrentino, F; Spacek, M; Storey, J; Strojek, I M; Testera, G; Tietje, I; Vamosi, S; Widmann, E; Yzombard, P; Zmeskal, J; Zurlo, N.

    2016-01-01

    We demonstrate laser excitation of the n=3 state of positronium (Ps) in vacuum. A specially designed high-efficiency pulsed slow positron beam and single shot positronium annihilation lifetime spectroscopy were used to produce and detect Ps. Pulsed laser excitation of n=3 level at 205 nm was monitored via Ps photoionization induced by a second intense laser pulse at 1064 nm. About 15% of the overall positronium emitted in vacuum was excited to n=3 and photoionized. Saturation of both the n=3 excitation and the following photoionization was observed and is explained by a simple rate equation model. Scanning the laser frequency allowed us to extract the positronium transverse temperature related to the width of the Doppler-broadened line. Moreover, preliminary observation of excitation to Rydberg states (n = 15...17) using n=3 as intermediate level was observed, giving an independent confirmation of efficient excitation to the 33P state.

  11. Contribution for study on positron annihilation in tris (dipivaloilmethanates) lanthanides (III)

    International Nuclear Information System (INIS)

    Ribeiro e Silva, M.E.S.

    1988-01-01

    Some data on life time of positron and annihilation by Doppler effect in tris (dipivaloilmethanates) lanthanides (III), Ln (dpm) 3 , and Ln = Eu, Gd, Dy, Ho, Er, Tm and Yb are shown. Some results from positronium (Ps) in complexes except Eu (dpm) 3 , chemical aspects and properties of positron and positronium are evaluated. (M.J.C.) [pt

  12. Nanometer cavities studied by positron annihilation

    International Nuclear Information System (INIS)

    Mogensen, O.E.

    1992-01-01

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

  13. 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...

  14. Positron annihilation study of structural subnanovoids and irradiation damages in silica-based glasses

    International Nuclear Information System (INIS)

    Inoue, K.

    2004-01-01

    Structural subnanovoids in glass solidified with radioactive waste disposal were studied by positron annihilation 2-dimensional angular correlation and positron life time measurements. Positroniums in crystalline SiO 2 were in a delocalized state, but in glass SiO 2 were in a localized state. Pick-off annihilation (pair annihilation between an ortho-positroniums and a spin antiparallel electron) rate was shortened with decreasing molarity of glass network formers and consequently radii of structural subnanovoids were reduced. The sizes of structural subnanovoids determined from the pick-off annihilation were good agreement with those measured by momentum distribution of para-positroniums. In waste disposal model glass, no presence of positronims indicated that radioactive substances occupied almost all subnanovoids, and therefore voids with large size enough to localize positroniums (above 0.1 nm radius) could not be present. (Y. Kazumata)

  15. Applications of positron annihilation to dermatology and skin cancer

    International Nuclear Information System (INIS)

    Liu, Guang; Chen, Hongmin; Chakka, Lakshmi; Gadzia, Joseph E.; Jean, Y.C.

    2007-01-01

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

  16. Applications of positron annihilation to dermatology and skin cancer

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-07-01

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

  17. Three instruments for positron annihilation spectroscopy (PAS)

    International Nuclear Information System (INIS)

    Ivanov, E.A.; Plostinaru, D.; Catana, D.; Racolta, P.M.; Vata, I.

    2003-01-01

    The instruments presented here and dedicated to positron annihilation spectroscopy, PAS, are: 1. High Resolution Life Time Spectrometer (LTS) with time resolution τ = 260 ps, based on large BaF 2 scintillators; 2. Doppler Broadening Spectrometer (DBS) having a 1.6 keV resolution at 514 keV; 3. Positronium Life Time - Perturbed Angular Distribution Spectrometer ( PLT-PAD); positronium life time, in samples under high vacuum in magnetic field, is measured for time intervals up to 500 ns. Results of measurements are shown to illustrate performances of the instruments. (authors)

  18. 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...... insight into the variation in derived positron and positronium lifetimes and intensities measured in the different laboratories on identical specimens. Lifetime data were collected at room temperature by each laboratory following their own standard measurement and data evaluation procedures. The polymers...

  19. Many-Body Theory for Positronium-Atom Interactions

    Science.gov (United States)

    Green, D. G.; Swann, A. R.; Gribakin, G. F.

    2018-05-01

    A many-body-theory approach has been developed to study positronium-atom interactions. As first applications, we calculate the elastic scattering and momentum-transfer cross sections and the pickoff annihilation rate 1Zeff for Ps collisions with He and Ne. For He the cross section is in agreement with previous coupled-state calculations, while comparison with experiment for both atoms highlights discrepancies between various sets of measured data. In contrast, the calculated 1Zeff (0.13 and 0.26 for He and Ne, respectively) are in excellent agreement with the measured values.

  20. Positronium bloch function, and trapping of positronium in vacancies, in ice

    International Nuclear Information System (INIS)

    Mogensen, O.E.; Eldrup, M.

    1977-08-01

    Positron annihilation techniques were used to study the behaviour of positronium (Ps) in pure light and heavy ice in the temperature interval -185 2 was extracted by very detailed computer analyses. A nearly-free-Ps theory, including phonon influence, could not explain the temperature dependence of /Asub(g vector)/ 2 . The Ps trapping in vacancies could not be explained in detail in terms of several models, including the simple 'trapping model'. A main difficulty was the fact that para-Ps and ortho-Ps are trapped at roughly the same amount at a certain vacancy concentration. Our results imply a high (several ppm) vacancy concentration at the melting point in ice in agreement with other independent estimates. This fact might introduce pronounced changes in currently accepted theories of the electrical properties of ice. (author)

  1. Positron Annihilation in Insulating Materials

    International Nuclear Information System (INIS)

    Asoka-Kumar, P; Sterne, PA

    2002-01-01

    We describe positron results from a wide range of insulating materials. We have completed positron experiments on a range of zeolite-y samples, KDP crystals, alkali halides and laser damaged SiO 2 . Present theoretical understanding of positron behavior in insulators is incomplete and our combined theoretical and experimental approach is aimed at developing a predictive understanding of positrons and positronium annihilation characteristics in insulators. Results from alkali halides and alkaline-earth halides show that positrons annihilate with only the halide ions, with no apparent contribution from the alkali or alkaline-earth cations. This contradicts the results of our existing theory for metals, which predicts roughly equal annihilation contributions from cation and anion. We also present result obtained using Munich positron microprobe on laser damaged SiO 2 samples

  2. Bremsstrahlung in electron-positronium scattering

    International Nuclear Information System (INIS)

    Amusia, M.Ya.; Korol, A.V.; Solovyov, A.V.

    1986-01-01

    The spectrum of radiation formed in the fast nonrelativistic electron scattering on positronium is calculated. It is shown that all the radiation proceeds via virtual positronium deformations during the collision. An essential difference of bremsstrahlung spectra in electron on positronium and electron on hydrogen scattering is demonstrated. (orig.)

  3. Positron annihilation in vitreous silica glasses

    International Nuclear Information System (INIS)

    Uedono, Akira; Tanigawa, Shoichiro

    1993-01-01

    The annihilation characteristics of positrons in vitreous silica glasses (v-SiO 2 ) were studied by measurements of two-dimensional angular correlation of positron annihilation radiations and positron lifetime spectra. From the measurements, it was found that positrons and positronium (Ps) atoms mainly annihilate from trapped states by vacancy-type defects in v-SiO 2 . For v-SiO 2 specimens with cylindrical porous structures, annihilations of Ps with anisotropic momentum distributions were observed. This fact was attributed to the momentum uncertainty due to localization of Ps in a finite dimension of pores. This investigation showed possibilities for the detection of microstructures in v-SiO 2 by the positron annihilation technique. (author)

  4. Chemical Quenching of Positronium in CuO/Al2O3 Catalysts

    International Nuclear Information System (INIS)

    Zhang Hong-Jun; Liu Zhe-Wen; Chen Zhi-Quan; Wang Shao-Jie

    2011-01-01

    CuO/Al 2 O 3 catalysts were prepared by mixing CuO and γ-Al 2 O 3 nanopowders. Microstructure and chemical environment of the catalysts are characterized by positron annihilation spectroscopy. The positron annihilation lifetime measurements reveal two long lifetime components τ 3 and τ 4 , which correspond to ortho-positronium (o-Ps) annihilating in microvoids and large pores, respectively. With increasing CuO content from 0 to 40 wt%, both τ 4 and its intensity I 4 show significant decrease, which indicates quenching effect of o-Ps. The para-positronium (p-Ps) intensities derived from multi-Gaussian fitting of the coincidence Doppler broadening spectra also decreases gradually with increasing CuO content. This excludes the possibility of spin-conversion of positronium. Therefore, the chemical quenching by CuO is probably responsible for the decrease of o-Ps lifetime. Variation in the o-Ps annihilation rate λ 4 (1/τ 4 ) as a function of CuO content can be well fitted by a straight line, and the slope of the fitting line is (1.83 ± 0.05) × 10 −7 s −1 . (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  5. Searches for discrete symmetries violation in ortho-positronium decay using the J-PET detector

    Directory of Open Access Journals (Sweden)

    Kamińska Daria

    2015-12-01

    Full Text Available In this paper, we present prospects for using the Jagiellonian positron emission tomograph (J-PET detector to search for discrete symmetries violations in a purely leptonic system of the positronium atom. We discuss tests of CP and CPT symmetries by means of ortho-positronium decays into three photons. No zero expectation values for chosen correlations between ortho-positronium spin and momentum vectors of photons would imply the existence of physics phenomena beyond the standard model. Previous measurements resulted in violation amplitude parameters for CP and CPT symmetries consistent with zero, with an uncertainty of about 10−3. The J-PET detector allows to determine those values with better precision, thanks to the unique time and angular resolution combined with a high geometrical acceptance. Achieving the aforementioned is possible because of the application of polymer scintillators instead of crystals as detectors of annihilation quanta.

  6. Temperature dependence of positronium reactivities with charge transfer molecules in bilayer membranes

    International Nuclear Information System (INIS)

    Jean, Y.C.; Yu, C.; Wang, Y.Y.; Yeh, Y.Y.

    1984-01-01

    Rate constants for positronium atoms reacting chemically with charge-transfer molecules such as p-benzoquinone, nitrobenzene, and coenzyme Q-10 in a model bilayer membrane, dipalmitoylphosphatidylcholine (DPPC), have been measured at temperatures between 23 and 65 0 C. A strong variation of the positronium chemical reactivities, k/sub Ps/ was observed in these systems: k/sub Ps/ increases with increasing temperature until the pretransition temperature of the membrane reaches a maximum value near the main transition temperature and decreases at temperatures higher than the main transition temperature. This variation is interpreted in terms of fluidity and permeability changes associated with the phase transitions of membranes and in terms of charge-transfer-complex formation between the solubilized molecules and the polar head of the membrane. These results demonstrate that positronium and its annihilation characteristics can be employed to investigate charge transport phenomena and microstructural changes of real biological membranes

  7. A trap-based pulsed positron beam optimised for positronium laser spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cooper, B. S., E-mail: ben.cooper.13@ucl.ac.uk; Alonso, A. M.; Deller, A.; Wall, T. E.; Cassidy, D. B. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)

    2015-10-15

    We describe a pulsed positron beam that is optimised for positronium (Ps) laser-spectroscopy experiments. The system is based on a two-stage Surko-type buffer gas trap that produces 4 ns wide pulses containing up to 5 × 10{sup 5} positrons at a rate of 0.5-10 Hz. By implanting positrons from the trap into a suitable target material, a dilute positronium gas with an initial density of the order of 10{sup 7} cm{sup −3} is created in vacuum. This is then probed with pulsed (ns) laser systems, where various Ps-laser interactions have been observed via changes in Ps annihilation rates using a fast gamma ray detector. We demonstrate the capabilities of the apparatus and detection methodology via the observation of Rydberg positronium atoms with principal quantum numbers ranging from 11 to 22 and the Stark broadening of the n = 2 → 11 transition in electric fields.

  8. Doppler-broadening of positron annihilation in a biological environment

    International Nuclear Information System (INIS)

    Torrisi, L.; La Mela, C.; Catania, Univ.

    1997-01-01

    The aim of this study was to investigate the Doppler effect of the 511 keV γ peak from positron annihilation in biological matter: The broadening of the annihilation peak is due to positron annihilation with electrons that have high momentum. In aqueous solutions annihilation depends on the temperature and it is linked positronium formation. Measurements in vivo, on human brain, were taken during the diagnosis of positron emission tomography (PET) on healthy patients by injecting them with the beta emitter of short lifetime 18F . The Doppler-broadening in biological tissues rich in water content decreased significantly compared to biological solutions and water

  9. Present status of the low energy linac-based slow positron beam and positronium spectrometer in Saclay

    Science.gov (United States)

    Liszkay, L.; Comini, P.; Corbel, C.; Debu, P.; Grandemange, P.; Pérez, P.; Rey, J.-M.; Reymond, J.-M.; Ruiz, N.; Sacquin, Y.; Vallage, B.

    2014-04-01

    A new slow positron beamline featuring a large acceptance positronium lifetime spectrometer has been constructed and tested at the linac-based slow positron source at IRFU CEA Saclay, France. The new instrument will be used in the development of a dense positronium target cloud for the GBAR experiment. The GBAR project aims at precise measurement of the gravitational acceleration of antihydrogen in the gravitational field of the Earth. Beyond application in fundamental science, the positron spectrometer will be used in materials research, for testing thin porous films and layers by means of positronium annihilation. The slow positron beamline is being used as a test bench to develop further instrumentation for positron annihilation spectroscopy (Ps time-of-flight, pulsed positron beam). The positron source is built on a low energy linear electron accelerator (linac). The 4.3 MeV electron energy used is well below the photoneutron threshold, making the source a genuine on-off device, without remaining radioactivity. The spectrometer features large BGO (Bismuth Germanate) scintillator detectors, with sufficiently large acceptance to detect all ortho-positronium annihilation lifetime components (annihilation in vacuum and in nanopores).

  10. Monolayer dispersion of CoO on Al2O3 probed by positronium atom

    International Nuclear Information System (INIS)

    Liu, Z.W.; Zhang, H.J.; Chen, Z.Q.

    2014-01-01

    CoO/Al 2 O 3 catalysts were prepared by wet impregnation method with CoO contents ranging from 0 wt% to 24 wt%. X-ray diffraction and X-ray photoelectron spectroscopy measurements suggest formation of CoO after calcined in N 2 . Quantitative X-ray diffraction analysis indicates monolayer dispersion capacity of CoO in CoO/Al 2 O 3 catalysts to be about 3 wt%. Positron annihilation lifetime and coincidence Doppler broadening measurements were performed to study the dispersion state of CoO on Al 2 O 3 . The positron lifetime measurements reveal two long lifetime components τ 3 and τ 4 , which correspond to ortho-positronium annihilation lifetime in microvoids and large pores, respectively. It was found that the positronium atom is very sensitive to the dispersion state of CoO on Al 2 O 3 . The presence of CoO significantly decreases both the lifetime and the intensity of τ 4 . Detailed analysis of the coincidence Doppler broadening measurements suggests that with the CoO content lower than the monolayer dispersion, spin conversion reaction of positronium is induced by CoO. When the cobalt content is higher than the monolayer dispersion capacity, inhibition of positronium formation becomes the dominate effect.

  11. Coincidence Doppler broadening study on hydrocarbons with pi and sigma valence electrons: positronium correction

    International Nuclear Information System (INIS)

    Djourelov, N.; Suzuki, T.; Yu, R.S.; Ito, Y.

    2005-01-01

    The coincidence Doppler broadening (CDB) technique was applied to study the electron momentum distribution in anthracene, diphenyl, naphthalene, and polystyrene. A method for separation of the positron and positronium (Ps) components from the Doppler-broadened annihilation line (DBAL) was developed further to be applicable to hydrocarbons with different π and σ valence electron distributions. This method allows extraction of the electron momentum distribution (EMD) from DBAL for samples when Ps formation occurs. The annihilation on π valence electrons was detected as broadening of the EMD compared to that obtained for a polymer sample only with σ valence electrons. The broadening appeared as a significant change in the shape of the CDB ratio of the corresponding positronium-corrected curves: a slight enhancement above the unity line in the low-momentum region and a drop in the momentum region, 10-20x10 -3 m o c

  12. To the measurement of 3γ/2γ ratio for positron annihilation in matter using annihilation energy spectrum

    International Nuclear Information System (INIS)

    Andrukhovich, S.K.; Berestov, A.V.; Antovich, N.M.; Metelitsa, O.N.

    2001-01-01

    Processes of the summation of cascade γ-quanta usually neglected, when registering the annihilation energy spectrum for the determination of the three-photon annihilation probability P 3γ of positronium in samples, are studied. The deviations of the actual P 3γ value from that determined without allowance made for the summation processes are 56% and 25% for Na(Tl) and Ge detectors placed at the distance of 3 cm from a positron source respectively. (author)

  13. Calculation of the life time of ortho positronium in different geometrical free spaces

    International Nuclear Information System (INIS)

    Cabral P, A.; Jimenez D, H.; Bulbulian, S.

    2001-01-01

    In this work two simple models of free volume to determine the geometrical effect over the positronium atom annihilation were developed. For this study also was used the spherical model already existing. In the analysis it was found an inverse relation of the phenomenological type between the positron life time and the area/volume ratio among such geometries. The new models are used to study the local free volume of zeolites such as the 4A and the ZSM-5. (Author)

  14. Positron and positronium reactivities with hemin compounds in alkaline water/ethyleneglycol mixture (50%)

    International Nuclear Information System (INIS)

    Mbungu, T.; Lohalo, O.R.; Kanyinda, M.; Gushimana, Y.

    1993-09-01

    Positron lifetime experiments have been performed in 50% water/ethyleneglycol with various hemin concentrations at pH 9. Due to the time resolution of the spectrometer, the short lifetimes were not significant separately. We only discussed the long live component ascribed to the orthopositronium annihilation. A critical hemin concentration was observed. We described the annihilation characteristics in relation with the formation of hemin aggregates. An analytical model for positron and positronium chemistry is proposed in terms of interaction with various compounds in the solution, with the reaction rates forming a continuous set within boundaries. (author). 22 refs, 3 figs

  15. Connections between radiation and positronium chemistry

    International Nuclear Information System (INIS)

    Hirade, Tetsuya

    2007-01-01

    Some of the important connections between radiation chemistry and positronium chemistry started from the establishment of the spur reaction model proposed by Mogensen. Now, the modified model, the blob model proposed by Stepanov and Byakov, is making it possible to have the quantitative or semi-quantitative view of the positronium formation by using the distributions of positrons and excess electrons. Some of the interesting topics will be picked up here to understand the connections between radiation chemistry and positronium chemistry

  16. 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.

  17. Spur Reaction Model of Positronium Formation

    DEFF Research Database (Denmark)

    Mogensen, O. E.

    1974-01-01

    A new model of positronium (Ps) formation is proposed. Positronium is assumed to be formed by a reaction between a positron and an electron in the positron spur. Ps formation must compete with electron‐ion recombination and electron or positron reactions with solvent molecules and scavenger...

  18. Positronium formation studies in crystalline molecular complexes: Triphenylphosphine oxide - Acetanilide

    Science.gov (United States)

    Oliveira, F. C.; Denadai, A. M. L.; Guerra, L. D. L.; Fulgêncio, F. H.; Windmöller, D.; Santos, G. C.; Fernandes, N. G.; Yoshida, M. I.; Donnici, C. L.; Magalhães, W. F.; Machado, J. C.

    2013-04-01

    Hydrogen bond formation in the triphenylphosphine oxide (TPPO), acetanilide (ACN) supramolecular heterosynton system, named [TPPO0.5·ACN0.5], has been studied by Positron Annihilation Lifetime Spectroscopy (PALS) and supported by several analytical techniques. In toluene solution, Isothermal Titration Calorimetry (ITC) presented a 1:1 stoichiometry and indicated that the complexation process is driven by entropy, with low enthalpy contribution. X-ray structure determination showed the existence of a three-dimensional network of hydrogen bonds, allowing also the confirmation of the existence of a 1:1 crystalline molecular complex in solid state. The results of thermal analysis (TGA, DTA and DSC) and FTIR spectroscopy showed that the interactions in the complex are relatively weaker than those found in pure precursors, leading to a higher positronium formation probability at [TPPO0.5·ACN0.5]. These weak interactions in the complex enhance the possibility of the n- and π-electrons to interact with positrons and consequently, the probability of positronium formation is higher. Through the present work is shown that PALS is a sensible powerful tool to investigate intermolecular interactions in solid heterosynton supramolecular systems.

  19. Partial-wave analysis for positronium-xenon collisions in the ultralow-energy region

    Science.gov (United States)

    Shibuya, Kengo; Saito, Haruo

    2018-05-01

    We propose a method to convert measured positronium annihilation rates in gaseous xenon into total and differential cross sections of positronium-xenon collisions in an ultralow-energy region of less than 80 meV where their experimental determinations as functions of the positronium kinetic energy are extremely difficult. This method makes it possible to determine not only the s -wave collisional parameters but also the p -wave and d -wave parameters. We have found a small positive value of the scattering length, A0=2.06 ±0.10 a0 , which indicates that the positronium-xenon interaction in this energy region is repulsive and suggests that it is dominated by the scattering amplitude of the positron rather than that of the electron. An extrapolation of the analytical result into the experimentally inaccessible energy regions from 80 meV to 1.0 eV indicates that there should not be a Ramsauer-Townsend minimum but rather a peak in the total cross section at an energy of approximately 0.4 eV.

  20. Chemical quenching of positronium in Fe2O3/Al2O3 catalysts

    International Nuclear Information System (INIS)

    Li, C.; Zhang, H.J.; Chen, Z.Q.

    2010-01-01

    Fe 2 O 3 /Al 2 O 3 catalysts were prepared by solid state reaction method using α-Fe 2 O 3 and γ-Al 2 O 3 nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ 3 and τ 4 are attributed to positronium annihilation in two types of pores distributed inside Al 2 O 3 grain and between the grains, respectively. With increasing Fe 2 O 3 content from 3 wt% to 40 wt%, the lifetime τ 3 keeps nearly unchanged, while the longest lifetime τ 4 shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe 2 O 3 content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ 4 is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.

  1. Chemical quenching of positronium in Fe 2O 3/Al 2O 3 catalysts

    Science.gov (United States)

    Li, C.; Zhang, H. J.; Chen, Z. Q.

    2010-09-01

    Fe 2O 3/Al 2O 3 catalysts were prepared by solid state reaction method using α-Fe 2O 3 and γ-Al 2O 3 nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ3 and τ4 are attributed to positronium annihilation in two types of pores distributed inside Al 2O 3 grain and between the grains, respectively. With increasing Fe 2O 3 content from 3 wt% to 40 wt%, the lifetime τ3 keeps nearly unchanged, while the longest lifetime τ4 shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe 2O 3 content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ4 is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.

  2. Long-living positron and positronium states in zeolites and microcrystalline oxides

    International Nuclear Information System (INIS)

    Kajcsos, Zs.; Liszkay, L.; Varga, L.; Lohonyai, L.; Lazar, K.

    1995-01-01

    Positron annihilation (PA) investigation were performed on zeolites (X, Y and ZSM-5) and on microcrystalline MgO, Al 2 O 3 and SiO 2 , providing long lifetime components attributed to o-Ps atoms. In addition to the positron lifetime (LT) measurements, the energy distribution (ED) of the annihilation gamma radiation spectrum was recorded in the 30 keV - 1.5 MeV range for different samples and was compared to reference distributions for Si and GaAs samples, where no long-living Ps states are formed. Apart from the strong correlation with the water content in the samples, the positron data collected testify much more pronounced positronium hosting features for powders of the mentioned oxides than for zeolites. Positron LT spectroscopy combined with recording of the ED of the annihilation radiation provides reliable information on the forming of long living 3γ states. (author) 15 refs.; 4 figs

  3. 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)

  4. 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)

  5. The annihilation of ortho-positronium in the {alpha} and {beta} cavities of the 4A zeolite and those CoZ4A and MnZ4A; La aniquilacion del orto-positronio en las cavidades {alpha} y {beta} de la zeolita 4A y en las de CoZ4A y MnZ4A

    Energy Technology Data Exchange (ETDEWEB)

    Cabral P, A.; Garcia S, I.; Jimenez B, J.; Solache R, M.; Bonifacio M, J.; Rodriguez F, C.; Bulbulian, S. [Instituto Nacional de Investigaciones Nucleares, A.P. 18-1027, 11801 Mexico D.F. (Mexico)

    2002-07-01

    The lifetime of the ortho-positronium in the zeolite 4A, partially dehydrated, changes to three characteristic modes. The first mode could be associated with the water elimination of the small {beta} cavity of this zeolite. At the end of this first dehydration process it is estimated a cavity radius, R = 33.8 nm. The other two types of variation of lifetime of ortho-positronium would be associated with the water elimination of the {alpha} great cavity and of the rest of the zeolite. From the zeolite 4A totally dehydrated and of the zeolite 4A exchanged with Co (II) and MN (II), also dehydrated radius are respectively determined for the {alpha} great cavity of R = 48.1, 54.5 and 56.5 nm. (Author)

  6. Inhibition and quenching effect on positronium formation in metal salt doped polymer blend

    Science.gov (United States)

    Praveena, S. D.; Ravindrachary, V.; Ismayil, Bhajantri, R. F.; Harisha, A.; Guruswamy, B.; Hegde, Shreedatta; Sagar, Rohan N.

    2018-04-01

    Sodium Bromide (NaBr) doped PVA/PVP (50:50) polymer blend composites were prepared using solution casting technique. Pure PVA/PVP blend and PVA/PVP:NaBr composites were studied using XRD and Positron Annihilation Lifetime Spectroscopy (PALS). XRD study shows increase in amorphous nature of the blend due to the NaBr dopant and PALS studies reveal that the o-Ps lifetime (τ3) and intensity (I3) decreases with increase in NaBr doping level. This shows chemical quenching and inhibition process of positronium (Ps) formation in the composite. Here the electron acceptor (Br-) acts as a strong chemical quencher for positronium formation and same is understood based on the spur model.

  7. On the existence of hot positronium reactions

    International Nuclear Information System (INIS)

    Lazzarini, E.

    1984-01-01

    The existence of hot Ps reactions is nowadays questioned; the controversy arises from the two models (the Ore gap and the spur theories) advanced in order to explain the mechanism of the positronium formation and of its inhibition in liquids by dissolution of certain compounds. The hypothesis of the hot Ps reactions was initially advanced as an additional statement for explaining the inhibition phenomenon within the framework of the Ore gap theory, but it is not considered necessary for the spur theory. The present paper is chiefly intended as a presentation of this particular aspect of Ps chemistry to hot atom chemists unspecialized in the field. The reader is assumed to be familiar with the basic physics and experimental methods used in positronium chemistry. Contents: positrons and positronium formation; inhibition and enhancement of Ps formation in solutions; positronium reactions in gases. (Auth.)

  8. Application of positron annihilation to the characterization of polymer structure

    International Nuclear Information System (INIS)

    Suzuki, T.; Yu, R.S.; Ito, Y.; Kondo, K.; Shantarovich, V.

    2005-01-01

    Positron annihilation has been applied to study characteristics of polymers last many years. Positron behaves as a nano-meter probe and brings out information of chemical structures, geometric structures, and momentum of electrons through the annihilation gamma-rays. Positrons injected in polymers tends to form positronium, which is similar structure to hydrogen atom and consists of electron and positron. Positronium diffuses through polymer structures and preferentially trapped by intermolecular spaces, if there is not any strong polar group in the chemical structure. Inside the spaces positronium annihilates through pick-off annihilation with electrons constituting walls of the spaces. Thus the pick-off annihilation brings out information about the interaction with electrons on the walls forming the spaces. These information can be measured by the positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy: from the former lifetimes and intensities of positronium can be measured and from the latter energy spectrum of the positron annihilation gamma-rays. The lifetimes are connected with the nano-meter size of the spaces and, using an empirical formula, the pore size can be estimated quantitatively. However the intensities bring out many kinds of information. Knowing the sample chemical structures, the values can be simply connected with the amount of spaces and often reflect the polar effect and temperature effect. In the positron annihilation technique, the energy distribution of-positron annihilation gamma-rays plays important role in the investigation of positron interaction with atoms constituting polymer chemical structures. The energy distribution can be measured using a high pure Ge detector. Although the spectrum obtained by one Ge detector has a large peak to back-ground ratio, using a coincidence technique of two Ge detectors, the coincidence Doppler broadening spectrum (CDBS) can improve the ratio from the order of 10-2 to 10

  9. Positronium collisions with molecular nitrogen

    Science.gov (United States)

    Wilde, R. S.; Fabrikant, I. I.

    2018-05-01

    For many atomic and molecular targets positronium (Ps) scattering looks very similar to electron scattering if total scattering cross sections are plotted as functions of the projectile velocity. Recently this similarity was observed for the resonant scattering by the N2 molecule. For correct treatment of Ps-molecule scattering incorporation of the exchange interaction and short-range correlations is of paramount importance. In the present work we have used a free-electron-gas model to describe these interactions in collisions of Ps with the N2 molecule. The results agree reasonably well with the experiment, but the position of the resonance is somewhat shifted towards lower energies, probably due to the fixed-nuclei approximation employed in the calculations. The partial-wave analysis of the resonant peak shows that its composition is more complex than in the case of e -N2 scattering.

  10. Positron deposition in plasmas by positronium beam ionization and transport of positrons in tokamak plasmas

    International Nuclear Information System (INIS)

    Murphy, T.J.

    1986-11-01

    In a recently proposed positron transport experiment, positrons would be deposited in a fusion plasma by forming a positronium (Ps) beam and passing it through the plasma. Positrons would be deposited as the beam is ionized by plasma ions and electrons. Radial transport of the positrons to the limiter could then be measured by detecting the gamma radiation produced by annihilation of positrons with electrons in the limiter. This would allow measurements of the transport of electron-mass particles and might shed some light on the mechanisms of electron transport in fusion plasmas. In this paper, the deposition and transport of positrons in a tokamak are simulated and the annihilation signal determined for several transport models. Calculations of the expected signals are necessary for the optimal design of a positron transport experiment. There are several mechanisms for the loss of positrons besides transport to the limiter. Annihilation with plasma electrons and reformation of positronium in positron-hydrogen collisions are two such processes. These processes can alter the signal and place restrictions ons on the plasma conditions in which positron transport experiments can be effectively performed

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

    International Nuclear Information System (INIS)

    Consolati, G.; Quasso, F.

    2007-01-01

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

  12. 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...

  13. 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.

  14. Depth-dependent positron annihilation in different polymers

    Energy Technology Data Exchange (ETDEWEB)

    Yang, J.; Zhang, P.; Cheng, G.D.; Li, D.X.; Wu, H.B.; Li, Z.X.; Cao, X.Z. [Key Laboratory of Nuclear Analysis Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, No. 19 Yuquan Lu, Beijing 100049 (China); Jia, Q.J. [Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, No. 19 Yuquan Lu, Beijing 100049 (China); Yu, R.S. [Key Laboratory of Nuclear Analysis Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, No. 19 Yuquan Lu, Beijing 100049 (China); Wang, B.Y., E-mail: wangboy@ihep.ac.cn [Key Laboratory of Nuclear Analysis Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, No. 19 Yuquan Lu, Beijing 100049 (China)

    2013-09-01

    Depth-dependent positron annihilation Doppler broadening measurements were conducted for polymers with different chemical compositions. Variations of the S parameter with respect to incident positron energy were observed. For pure hydrocarbons PP, HDPE and oxygen-containing polymer PC, S parameter rises with increasing positron implantation depth. While for PI and fluoropolymers like PTFE, ETFE and PVF, S parameter decreases with higher positron energy. For chlorine-containing polymer PVDC, S parameter remains nearly constant at all incident positron energies. It is suggested that these three variation trends are resulted from a competitive effect between the depth-dependent positronium formation and the influence of highly electronegative atoms on positron annihilation characteristics.

  15. The chemistry of positronium. Part VI: inhibition and enhancement of positronium formation in aqueous solutions of halides, sulfide and thiocyanate

    International Nuclear Information System (INIS)

    Duplatre, G.; Abbe, J.C.; Maddock, A.G.; Haessler, A.

    1977-01-01

    The formation of positronium in aqueous solutions of halides, sulfide and thiocyanate has been investigated. Inhibiting and enhancing reactions of positronium formation are found. The results are discussed in terms of the spur model

  16. Sensitivity of orthopositronium annihilation to density fluctuations in ethane gas

    International Nuclear Information System (INIS)

    Eftekhari, A.

    1982-01-01

    The annihilation rates of orthopositronium (o-Ps) and free positrons and positronium formation fractions have been measured in gaseous ethane at seven temperatures between 295 and 377 K for densities in the range 1.2-286 amagat. The pick off quenching rate of o-Ps is observed to vary with temperature at low densities of ethane. The observed behavior of the o-Ps annihilation rates with density and temperature is interpreted in terms of density fluctuations in ethane gas. A simple theoretical model is developed which explains the observed annihilation behavior reasonably well at those temperatures and densities where density fluctuations are small. The annihilation rates of flow-energy positrons indicate the formation of positron-ethane collision complexes and self-trapping of positrons in clusters of ethane molecules. The o-Ps yields appear to be independent of temperature and show a strong dependence on the density of the gas

  17. A time-pulsed positronium beam and a study of oxides on silicon using positrons

    International Nuclear Information System (INIS)

    Khatri, R.K.

    1993-01-01

    The studies on rare gas solid moderators were carried out with a 350 μCi 22 Na radioactive source. The corrected efficiency for neon moderator in conical geometrical configuration was as high as (1.4 ± 0.2)%. The conical configuration moderator performed better by a factor of (2.2 ± 0.2) than the cylindrical configuration. A time pulsed positron beam was built to carry out investigations on the positronium formation processes and positronium beam. This beam has the capability to store low energy e + in a magnetic bottle, with a magnetic bottle at one end and an electrostatic mirror at the other. These stored e + are then bunched to form a pulse with a buncher. The bunched beam had a FWHM of 17 nsec and contained 1 to 2 e + /pulse. A thin carbon foil of 50 angstrom thickness was used for positronium formation by process of charge exchange. Positronium Annihilation Spectroscopy (PAS) was utilized to carry out studies on the activation energy of hydrogen at the interface of oxide and silicon substrate and the effect of irradiation on the oxides in SiO 2 /Si(100) sample. The activation energy of hydrogen at the interface of SiO 2 /Si(100) samples with n- and p-type substrate was measured to be 2.60(6) eV and 2.47(6) eV respectively. The investigations of the samples irradiated with x-ray and γ-ray led to the first time identification of creation of E' centers with PAS

  18. Diffusion length of positrons and positronium investigated using a positronbeam with longitudinal geometry

    Science.gov (United States)

    van Petegem, S.; Dauwe, C.; van Hoecke, T.; de Baerdemaeker, J.; Segers, D.

    2004-09-01

    Positronium emission from single crystalline Al2O3 , MgO and vitreous a-SiO2 surfaces was studied as a function of the positron implantation energy E by means of Doppler broadening spectroscopy and Compton-to-peak ratio analysis. When the Ge-detector is in-line with the positron beam, the emission of para-positronium yields a red-shifted fly-away peak with intensity IpPse . An analysis of IpPse versus E for Al2O3 and MgO where no Ps is formed in the bulk (fPs=0) results in positron diffusion lengths L+(Al2O3)=(18±1)nm and L+(MgO)=(14±1)nm , and efficiencies for the emission of Ps by picking up of a surface electron of fpu(Al2O3)=(0.28±0.2) and fpu(MgO)=(0.24±0.2) . For a-SiO2 the bulk Ps fraction is fPs(a-SiO2)=(0.72±0.01) , fpu(a-SiO2)=(0.12±0.01) and the diffusion lengths of positrons, para-positronium and ortho-positronium are L+(SiO2)=(8±2)nm , LpPs(SiO2)=(14.5±2)nm and LoPs(SiO2)=(11±2)=nm . Depending on the specimen-detector geometry the emission of Ps at low implantation energy may cause either an increase or a decrease of the width of the annihilation line shape at low implantation energies.

  19. New techniques of positron annihilation

    International Nuclear Information System (INIS)

    1983-02-01

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

  20. Positronium chemistry in porous adsorbents

    International Nuclear Information System (INIS)

    Foti, G.; Nagy, L.G.; Moravcsik, G.; Schay, G.

    1981-01-01

    Kinetic studies on the annihilation of orthopositronium in porous adsorbents have been performed using lifetime spectroscopy. The positron source applied was 22 Na with 0.2 MBq activity. The adsorbents investigated were silica gels of different particle size and pore structure. The appearance of the long-lived component in the lifetime spectra can be explained by the diffusion of the orthopositronium into the pores affected by the particle size and the pore size of the adsorbent, the coverage on it and the chemical nature of the adsorbate. The long-term aim of the work is to determine and to explain these effects. (author)

  1. Applications of positron annihilation spectroscopy to study microstructural properties of polymers

    International Nuclear Information System (INIS)

    Jean, Y.C.

    1992-01-01

    Positron annihilation spectroscopy (PAS) has been applied to characterize the free-volume properties of polymers. Positron annihilation lifetime measurements give direct information about the dimension, content, and hole-size distributions of free-volume in amorphous materials. The angular correlation of positron annihilation radiation measurements give additional information about the shape of the free-volume holes in oriented polymeric materials. The unique capability of PAS to probe free-volume properties is from the fact that positronium atom is preferentially trapped in the atomic-scale holes which have a size ranging from 1 to 10 A. (author)

  2. Studying the gelation process of titanium isopropoxide by method of positron annihilation spectroscopy; Studium procesu gelacie izopropoxidu titaniciteho metodou pozitronovej anihilacnej spektroskopie

    Energy Technology Data Exchange (ETDEWEB)

    Nyblova, D.; Jesenak, K. [Univerzita Komenskeho, Prirodovedecka fakulta, Katedra anorganickej chemie, 84215 Bratislava (Slovakia); Sausa, O. [Slovenska akademia vied, Fyzikalny ustav, 84511 Bratislava (Slovakia)

    2013-04-16

    Thank to its harmlessness titanium dioxide is widely utilized material. One of the new areas to use titanium dioxide is photocatalysis, which could be the way to e.g. remove organic pollutants from water or air. Titanium dioxide based gels are perspective form of TiO{sub 2} for photocatalysis because of their high porosity thus high surface area. Positron annihilation spectroscopy is a physical method to study microporous structure and electron energy distribution in materials. We studied gelation process of titanium isopropoxide in ethanol with various amount of water catalyzed by hydrochloric acid by positron annihilation lifetime spectroscopy and doppler broadening of annihilation line in this work. Positronium is weakly formed in TiO{sub 2} in general wherefore it cannot be monitored by positron annihilation spectroscopy very well. Gelation process can be monitored through pick-off annihilation of ortho-positronium. (authors)

  3. 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.

  4. Positron annihilation probing for the hydratation rate of cement paste

    International Nuclear Information System (INIS)

    Myllylae, R.; Karras, M.

    1975-01-01

    Positron annihilation has been found to be a possible probe for the exponential hydratation of cement paste. Both lifetime and Doppler line broadening measurements revealed the hydratation rate. With the aid of increased stability in the lifetime spectrometer it has been possible to extend the measuring sensitivity over a period of several weeks. Two main lifetimes, tau 1 = 480 +- 20 psec and tau 2 = 2.1 +- 0.1 nsec, were observed to be constant during the hydratation. The intensity of the 2.1 nsec component changed from 4 to 8% after 47 days, and simultaneously the annihilation line narrowed from 2.6 to 2.4 keV. This behaviour has been interpreted as an increase in positronium formation. The possible practical applications of positron annihilation radiation as a hydratation probe has been evaluated for use in a concrete laboratory and even for regular construction work. (orig.) [de

  5. 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

  6. 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.)

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

    International Nuclear Information System (INIS)

    Jean, Y.C.; Li Ying; Liu Gaung; Chen, Hongmin; Zhang Junjie; Gadzia, Joseph E.

    2006-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-02-28

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

  9. 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)

  10. Physics of positronium acceptor complex formation reactions

    International Nuclear Information System (INIS)

    Gangopadhyay, Debarshi; Ganguly, Bichitra Nandi; Mukherjee, Tapas; Dutta-Roy, Binayak

    2002-01-01

    Positronium (P s ) reaction rates (κ) with weak Acceptors (Ac) leading to the formation of Ps-Ac complexes show several interesting features: non-monotonic temperature dependence of κ(departing from the usual Arrhenius behaviour), considerable variability of κ with respect to different solvents, and anomalies in response to external pressure at ambient temperature. The object of this work is to explain all these phenomena using a remarkably simple bubble model (the widely used model for the pick-off component of ortho-positronium decay in liquids), which has been revisited several times in the context and as a result smooth diffuse boundary of the bubble was suggested that yields reasonable agreement of the experimental data. The contractile force on the bubble relies much on the surface tension of the liquid, through our calculation the notion of critical surface tension emerges and enables us to explain the experimental observations satisfactorily. (author)

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

    International Nuclear Information System (INIS)

    Derlet, P.M.; Choy, T.C.

    1996-01-01

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

  12. Positron annihilation study on free volume of amino acid modified, starch-grafted acrylamide copolymer

    International Nuclear Information System (INIS)

    Mahmoud, K.R.; Al-Sigeny, S.; Sharshar, T.; El-Hamshary, H.

    2006-01-01

    Free volume measurements using positron annihilation lifetime spectroscopy was performed for uncrosslinked and crosslinked starch-grafted polyacrylamide, and their modified amino acid samples including some of their iron(III) complexes. The measurements were performed at room temperature. The analysis of lifetime spectra yielded mostly three lifetime components. It was observed that the values of the short lifetime component τ 1 are slightly higher than the lifetime associated with the self-decay of para-positronium atoms in polymers. The free volume was probed using ortho-positronium pick-off annihilation lifetime parameters. The mean free volume has also been calculated from the lifetime data. The avrage value of this parameter of the crosslinked polymer were found to be higher than those of the uncrosslinked polymer

  13. Ionization in positron- and positronium- collisions with atoms and molecules

    Energy Technology Data Exchange (ETDEWEB)

    Laricchia, G; Brawley, S; Cooke, D A; Murtagh, D J; Williams, A I [UCL Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Koever, A [permanent address: ATOMKI, Institute for Nuclear Research, Debrecen (Hungary)

    2009-11-15

    Recent progress in the experimental study of positron- and positronium-induced ionization of atoms and molecules is outlined. Investigations include integral and differential cross-sections, as well as formation of positronium in the first excited state. Future prospects are discussed.

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

    International Nuclear Information System (INIS)

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

    2008-01-01

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

  15. Investigation of density inhomogeneities in liquids by positron annihilation

    International Nuclear Information System (INIS)

    Vass, Sz.

    1990-11-01

    The case of positronium diffusion and annihilation in micellar solutions as well as in liquid normal alkanes is discussed. The traps are assumed to be the structural sparse density regions in these liquids. The traps in micellar solutions are the micelles, in alkanes they are found around the terminal -CH 3 groups. The surface tension inside the micellar core (one of the basic parameters of micellization) is determined around the site of o-Ps solubilization. The o-Ps diffusivity parameters are determined in both systems. (K.A.) 48 refs.; 4 figs

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

    International Nuclear Information System (INIS)

    Dolveck, J.Y.; Moser, P.; Guo-Huan Dai

    1992-01-01

    The lifetime measurement of positrons injected in a metal allows to investigate defects of atomic dimension. Many crucial problems in metallurgy have found their solutions by the positron annihilation (PA) techniques for about three decades. Application to semiconductors research has been developed in recent years. Specific theory and analysing method can be used in the studies of the free-volume hole in polymers, the size of the empty spaces being between 0.3 and 1.5 nanometers. In many insulating materials, the diffusing positron can trap an electron and form a metastable positronium (Ps). Like a gas bubble, the Ps atom may diffuse and get trapped by the free-volume hole. When this mechanism is governing, lifetimes over the range of 1-10 ns are well observable and a correspondence exists between the positronium lifetime and minimum diameter of the trapping open space. Example of application is given in a study of polyimide membranes used for gas separation. A good correlation is revealed between the Ps lifetime and H 2 and/or CH 4 permeabilities. Recent progress in polymers research is also reviewed

  17. Characterization of a transmission positron/positronium converter for antihydrogen production

    Science.gov (United States)

    Aghion, S.; Amsler, C.; Ariga, T.; Bonomi, G.; Brusa, R. S.; Caccia, M.; Caravita, R.; Castelli, F.; Cerchiari, G.; Comparat, D.; Consolati, G.; Demetrio, A.; Di Noto, L.; Doser, M.; Ereditato, A.; Evans, C.; Ferragut, R.; Fesel, J.; Fontana, A.; Gerber, S.; Giammarchi, M.; Gligorova, A.; Guatieri, F.; Haider, S.; Hinterberger, A.; Holmestad, H.; Kellerbauer, A.; Krasnický, D.; Lagomarsino, V.; Lansonneur, P.; Lebrun, P.; Malbrunot, C.; Mariazzi, S.; Matveev, V.; Mazzotta, Z.; Müller, S. R.; Nebbia, G.; Nedelec, P.; Oberthaler, M.; Pacifico, N.; Pagano, D.; Penasa, L.; Petracek, V.; Povolo, L.; Prelz, F.; Prevedelli, M.; Ravelli, L.; Resch, L.; Rienäcker, B.; Robert, J.; Røhne, O. M.; Rotondi, A.; Sacerdoti, M.; Sandaker, H.; Santoro, R.; Scampoli, P.; Simon, M.; Smestad, L.; Sorrentino, F.; Testera, G.; Tietje, I. C.; Widmann, E.; Yzombard, P.; Zimmer, C.; Zmeskal, J.; Zurlo, N.; Andersen, S. L.; Chevallier, J.; Uggerhøj, U. I.; Lyckegaard, F.

    2017-09-01

    In this work a characterization study of forward emission from a thin, meso-structured silica positron/positronium (Ps) converter following implantation of positrons in light of possible antihydrogen production is presented. The target consisted of a ∼1 μm thick ultraporous silica film e-gun evaporated onto a 20 nm carbon foil. The Ps formation and emission was studied via Single Shot Positron Annihilation Lifetime Spectroscopy measurements after implantation of pulses with 3 - 4 ·107 positrons and 10 ns temporal width. The forward emission of implanted positrons and secondary electrons was investigated with a micro-channel plate - phosphor screen assembly, connected either to a CCD camera for imaging of the impinging particles, or to a fast photomultiplier tube to extract information about their time of flight. The maximum Ps formation fraction was estimated to be ∼10%. At least 10% of the positrons implanted with an energy of 3.3 keV are forward-emitted with a scattering angle smaller than 50° and maximum kinetic energy of 1.2 keV. At least 0.1-0.2 secondary electrons per implanted positron were also found to be forward-emitted with a kinetic energy of a few eV. The possible application of this kind of positron/positronium converter for antihydrogen production is discussed.

  18. Positronium hydride in hydrogen-laden thermochemically reduced MgO single crystals

    International Nuclear Information System (INIS)

    Pareja, R.; la Cruz, R.M. de; Pedrosa, M.A.; Gonzalez, R.; Chen, Y.

    1990-01-01

    Thermochemical reduction of hydrogen-laden MgO single crystals at T∼2400 K results in a large concentration of both hydride (H - ) ions and anion vacancies (>10 24 m -3 ). Positron-lifetime experiments of these crystals provide evidence for bound positronium hydride states also referred to as [e + -H - ] or PsH states. The presence of the anion vacancies was found to inhibit the formation of these states. After thermally annealing out these vacancies, such that H - concentration remains intact, two long-lived components appear in the lifetime spectrum. Furthermore, these two components correlate with the presence of the H - ions. These results suggest the existence of bound [e + -H - ] states when positrons are trapped by the H - ions, and the subsequent formation of positronium (Ps) states by the dissociation of the [e + -H - ] states. From the values of the intermediate lifetime component, a value of (570±50) ps is obtained for the lifetime of the PsH state located in an anion vacancy in MgO. The longest lifetime component ∼(1--3) ns is attributed to pick-off annihilation of ortho-Ps states

  19. Positronium hydride in hydrogen-laden thermochemically reduced MgO single crystals

    Science.gov (United States)

    Pareja, R.; de La Cruz, R. M.; Pedrosa, M. A.; González, R.; Chen, Y.

    1990-04-01

    Thermochemical reduction of hydrogen-laden MgO single crystals at T~2400 K results in a large concentration of both hydride (H-) ions and anion vacancies (>1024 m-3). Positron-lifetime experiments of these crystals provide evidence for bound positronium hydride states also referred to as [e+-H-] or PsH states. The presence of the anion vacancies was found to inhibit the formation of these states. After thermally annealing out these vacancies, such that H- concentration remains intact, two long-lived components appear in the lifetime spectrum. Furthermore, these two components correlate with the presence of the H-ions. These results suggest the existence of bound [e+-H-] states when positrons are trapped by the H- ions, and the subsequent formation of positronium (Ps) states by the dissociation of the [e+-H-] states. From the values of the intermediate lifetime component, a value of (570+/-50) ps is obtained for the lifetime of the PsH state located in an anion vacancy in MgO. The longest lifetime component ~(1-3) ns is attributed to pick-off annihilation of ortho-Ps states.

  20. 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

  1. Application of positron annihilation techniques to the study of micels and microemulsions

    International Nuclear Information System (INIS)

    Olea C, O.

    1981-01-01

    The molecular auto-association mechanisms in sodium-oleate-alcohol-alkane-water systems were studied, applying positron and positronium annihilation techniques. The effects of the different component structures of these systems and of their concentrations on the swelled micel formation process which eventually produce microemulsions, were also investigated. The influences studied were: a) co-surfactant (alcohol) hydrocarbon chain lengths, b) alkane (oil) hydrocarbon chain lengths, c) surfactant concentrations, and d) surfactant double link alkylic chains. (author)

  2. Spin conversion induced by spin-orbit interaction in positronium collisions

    International Nuclear Information System (INIS)

    Saito, H; Nakayama, T; Hyodo, T

    2009-01-01

    The positronium spin conversion reaction induced by spin-orbit interaction is investigated. We obtain the reaction rates during positronium-Xe and positronium-Kr collisions by using the Zeeman mixing of positronium states. At thermal energies corresponding to room temperature, the reaction rate for spin conversion due to spin-orbit interaction is found to be almost twice that for the positronium pick-off reaction. We also study the energy dependence of the reaction rate. The mean energy of positronium is controlled by changing the gas temperature and using positronium in thermal equilibrium. We found that the reaction rate increases with the collision energy.

  3. Positronium interactions in liquids and porous substances

    International Nuclear Information System (INIS)

    Ganguly, Bichitra; Gangopadhyay, Debarshi; Dutta, Dhanadeep; Chatterjee, Sujib; Mukherjee, Tapas; Dutta Roy, Binayak

    2007-01-01

    Positronium (Ps) is an important chemical probe for any given medium since it can interact with a variety of molecular electronic system to yield information, relevant to the understanding of underlying mechanistic processes, when subjected to the changes in physical parameters. In this article, its interaction is focused on two media that are important from the perspective of bio-chemical and technological studies, namely Ps-electron acceptor bound state formation in liquids (specially hydrogen bonding solvents) and also on a variety of porous material which are applicable in chemical/biochemical separations and other applications in technology. The underlying physical phenomenology in each case is separately dealt with giving suitable examples

  4. Positrons annihilation and the Galactic center

    International Nuclear Information System (INIS)

    Wallyn, Pierre

    1992-01-01

    The Galactic center has been observed in gamma rays, many times since more than two decades and we do not still have a full comprehensive picture of this region. It is fairly well established that the 511 keV annihilation line has two origins: a steady diffuse emission, which follows more or less the type I supernovae distribution along the Galactic plane and a variable emission coming from the positrons emitted by (at least) one compact object and annihilating in a nearby cold molecular cloud. We present here an analysis of the profiles and intensifies of the 511 keV annihilation line observed in the direction of the Galactic center. We find that a warm medium (temperature of 8000 K) can describe the annihilation of positrons from the diffuse component of the line. The high state observations of the 511 keV line can be explained if the time-variable component is coming from the annihilation of the positrons in a cold medium (temperature around 80 K). This constraint on the annihilation medium temperature supports the association with the molecular cloud G-0.86-0.08 in the direction of 1E1740.7-2942. On may 22, 1989, HEXAGONE detected a narrow 511 keV line and also a broad emission around 170 keV in the direction of the Galactic center. Two weeks before, EXITE observed in the same direction a new transient source EXS 1737.9-2952 which showed a bump around 102 keV. We propose a simple semi-quantitative model which can mimic the bumps as well as its time variations and emphasize the strong similarities between EXS1737.9-2952 and Nova Muscae. We study the behaviour of positron annihilation by charge exchange in the cold phase of the interstellar medium. We calculate formula for the slowing-down time before thermalization of positrons of a given initial energy, for different medium densities. Our scenario explains the lack of detection of the recombination lines from positronium and gives new constraints on their possible observation. (author) [fr

  5. 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)

  6. Experimental progress in positronium laser physics

    Science.gov (United States)

    Cassidy, David B.

    2018-03-01

    The field of experimental positronium physics has advanced significantly in the last few decades, with new areas of research driven by the development of techniques for trapping and manipulating positrons using Surko-type buffer gas traps. Large numbers of positrons (typically ≥106) accumulated in such a device may be ejected all at once, so as to generate an intense pulse. Standard bunching techniques can produce pulses with ns (mm) temporal (spatial) beam profiles. These pulses can be converted into a dilute Ps gas in vacuum with densities on the order of 107 cm-3 which can be probed by standard ns pulsed laser systems. This allows for the efficient production of excited Ps states, including long-lived Rydberg states, which in turn facilitates numerous experimental programs, such as precision optical and microwave spectroscopy of Ps, the application of Stark deceleration methods to guide, decelerate and focus Rydberg Ps beams, and studies of the interactions of such beams with other atomic and molecular species. These methods are also applicable to antihydrogen production and spectroscopic studies of energy levels and resonances in positronium ions and molecules. A summary of recent progress in this area will be given, with the objective of providing an overview of the field as it currently exists, and a brief discussion of some future directions.

  7. Correlation between the Inhibition of Positronium Formation by Scavenger Molecules, and Chemical Reaction Rate of Electrons with these Molecules in Nonpolar Liquids

    DEFF Research Database (Denmark)

    Levay, B.; Mogensen, O. E.

    1977-01-01

    a correlation between the inhibition coefficient and the chemical rate constant of electrons with scavenger molecules. We found that the dependence of the inhibition coefficient on the work function (VOo)f electrons in different liquids shows a very unusual behavior, similar to that recently found...... for the chemical rate constants of quasifree electrons with the same scavenger molecules. The inhibition coefficient as a function of Vo had a maximum for C2HsBr, while it increased monotonously with decreasing V, for CC14. The inhibition coefficient for C2H5Br in a 1:l molar tetramethylsilane......-n-tetradecane mixture was found to be greater than in both of the pure components. The clear correlation found between electron scavenging rate constants and positronium inhibition constitutes the severest test to date of the spur reaction model of positronium formation. The importance of the positron annihilation...

  8. Positron annihilation and Wheeler complexes in semiconductors

    International Nuclear Information System (INIS)

    Prokob'ev, E.P.

    1995-01-01

    The Wheeler complexes Ps-Ex (positronium-exciton) were studied. These complexes are formed during irradiation of semiconductors and ionic crystals with positrons at low temperatures under optical excitation by excitons. The binding energy of these and more complex entities preventing dissociation into Ps and Ex and/or Ex ± is at least 0.1 eV, and the lifetime for the two-photon self-annihilation is τ 2γ ∼ 5.02 x 10 -10 x c 3 s (x c is the phenomenological parameter of the effective-mass method). The estimation of lifetimes τ 2γ and τ 2γ t (the total lifetime of Ps-Ex complexes with account for positron annihilation on valence electrons) led to the conclusion that Ps-Ex complexes can be observed in a number of oxide semiconductors, in zinc sulfide, and in alkali halide crystals; however, it was difficult to observe such complexes in silicon, gallium arsenide, and other A 3 B 5 and A 2 B 6 semiconductors

  9. AMOC studies of positronium in fine MgO powder

    International Nuclear Information System (INIS)

    Waeyenberge, B. van; Dauwe, C.

    2001-01-01

    A first set of AMOC spectra on fine powdered MgO were measured at the Stuttgart relativistic positron beam facility. A special AMOC spectrometer was set up in order to determine the long lifetimes of ortho-positronium in the powder cavities. The spectra were taken on pellets of pressed powder in air and in an oxygen atmosphere to ensure ortho- to para-positronium conversion. An analysis of the data is made in the light of previous lifetime measurements on MgO. Here the lifetime spectrum was fitted with an age dependent lifetime describing the slow thermalisation of epithermal ortho-positronium between the powder grains. Based on the lifetime spectrum of the integrated AMOC spectra the data could not discriminate between a 5-component model and a model including slow positronium thermalisation. On the other hand, analysis of the age dependent line shape parameter shows better variances for a thermalisation model. (orig.)

  10. AMOC studies of positronium in fine MgO powder

    Energy Technology Data Exchange (ETDEWEB)

    Waeyenberge, B. van; Dauwe, C. [Ghent Univ. (Belgium). Dept. of Subatomic and Radiation Physics; Stoll, H. [Max-Planck-Institut fuer Metallforschung, Stuttgart (Germany)

    2001-07-01

    A first set of AMOC spectra on fine powdered MgO were measured at the Stuttgart relativistic positron beam facility. A special AMOC spectrometer was set up in order to determine the long lifetimes of ortho-positronium in the powder cavities. The spectra were taken on pellets of pressed powder in air and in an oxygen atmosphere to ensure ortho- to para-positronium conversion. An analysis of the data is made in the light of previous lifetime measurements on MgO. Here the lifetime spectrum was fitted with an age dependent lifetime describing the slow thermalisation of epithermal ortho-positronium between the powder grains. Based on the lifetime spectrum of the integrated AMOC spectra the data could not discriminate between a 5-component model and a model including slow positronium thermalisation. On the other hand, analysis of the age dependent line shape parameter shows better variances for a thermalisation model. (orig.)

  11. Positron scattering by atomic hydrogen including positronium formation

    International Nuclear Information System (INIS)

    Higgins, K.; Burke, P.G.

    1993-01-01

    Positron scattering by atomic hydrogen including positronium formation has been formulated using the R-matrix method and a general computer code written. Partial wave elastic and ground state positronium formation cross sections have been calculated for L ≤ 6 using a six-state approximation which includes the ground state and the 2s and 2p pseudostates of both hydrogen and positronium. The elastic scattering results obtained are in good agreement with those derived from a highly accurate calculation based upon the intermediate energy R-matrix approach. As in a previous coupled-channel static calculation, resonance effects are observed at intermediate energies in the S-wave positronium formation cross section. However, in the present results, the dominant resonance arises in the P-wave cross sections at an energy of 2.73 Ryd and with a width of 0.19 Ryd. (author)

  12. Can We Observe the Gravitational Quantum States of Positronium?

    Directory of Open Access Journals (Sweden)

    P. Crivelli

    2015-01-01

    Full Text Available We consider the feasibility of observing the gravitational quantum states of positronium. The proposed scheme employs the flow-throw technique used for the first observation of this effect with neutrons. Collimation and Stark deceleration of Rydberg positronium atoms allow selecting the required velocity class. If this experiment could be realized with positronium, it would lead to a determination of g for this matter-antimatter system at the few % level. As discussed in this contribution, most of the required techniques are currently available but important milestones have to be demonstrated experimentally before such an experiment could become reality. Those are the efficient focusing of a bunched positron beam, Stark deceleration of Rydberg positronium, and its subsequent excitation into states with large angular momentum. We provide an estimate of the efficiencies we expect for these steps and assuming those could be confirmed we calculate the signal rate.

  13. Positronium spin conversion during collisions with Xe and its application for measuring the kinetic energy

    International Nuclear Information System (INIS)

    Shibuya, Kengo; Kawamura, Yoshihiro; Saito, Haruo

    2015-01-01

    Positronium(Ps) can undergo ortho-para spin conversion reaction during Ps-Xecollisions due to spin-orbit interaction. We have investigated energy dependence of this reaction rate and found it is nearly proportional to T 2.1 , where T is the temperature (300-623 K), while the pick-off annihilation rate is proportional to T. The strong temperature dependence of the former annihilation rate is attributed to a nature of p-wave scattering because this reaction is forbidden in s-wave scattering. In addition, a new method for measuring Ps kinetic energy has been developed with a high resolution and a high sensitivity by utilizing the strong temperature dependence as a 'thermometer.' Analyzingthe obtained time evolution of Ps kinetic energy, we have determined the momentum transfer cross section during Ps-Xecollisions at a very low energy (40-60 meV) to be 12(2)×10 −16 cm 2 . (paper)

  14. Positronium collisions with atoms and molecules

    Science.gov (United States)

    Fabrikant, I. I.; Gribakin, G. F.; Wilde, R. S.

    2017-11-01

    We review recent theoretical efforts to explain observed similarities between electron-atom and positronium(Ps)-atom scattering which also extends to molecular targets. In the range of the projectile velocities above the threshold for Ps ionization (break-up) this similarity can be explained in terms of quasi-free electron scattering and impulse approximation. However, for lower Ps velocities more sophisticated methods should be developed. Our calculations of Ps scattering by heavy noble-gas atoms agree well with experiments at Ps velocities above the Ps ionization threshold. However, in contrast to electron scattering cross sections, at lower velocities they exhibit maxima whereas the experimental cross sections tend to decrease toward lower velocities indicating the same similarity with electron scattering cross section observed above the threshold. Our preliminary results for Ps-N2 scattering confirm experimental observation of a resonance similar to the ∏ g resonance in electron-N2 scattering.

  15. Positron annihilation in SiO 2-Si studied by a pulsed slow positron beam

    Science.gov (United States)

    Suzuki, R.; Ohdaira, T.; Uedono, A.; Kobayashi, Y.

    2002-06-01

    Positron and positronium (Ps) behavior in SiO 2-Si have been studied by means of positron annihilation lifetime spectroscopy (PALS) and age-momentum correlation (AMOC) spectroscopy with a pulsed slow positron beam. The PALS study of SiO 2-Si samples, which were prepared by a dry-oxygen thermal process, revealed that the positrons implanted in the Si substrate and diffused back to the interface do not contribute to the ortho-Ps long-lived component, and the lifetime spectrum of the interface has at least two components. From the AMOC study, the momentum distribution of the ortho-Ps pick-off annihilation in SiO 2, which shows broader momentum distribution than that of crystalline Si, was found to be almost the same as that of free positron annihilation in SiO 2. A varied interface model was proposed to interpret the results of the metal-oxide-semiconductor (MOS) experiments. The narrow momentum distribution found in the n-type MOS with a negative gate bias voltage could be attributed to Ps formation and rapid spin exchange in the SiO 2-Si interface. We have developed a two-dimensional positron lifetime technique, which measures annihilation time and pulse height of the scintillation gamma-ray detector for each event. Using this technique, the positronium behavior in a porous SiO 2 film, grown by a sputtering method, has been studied.

  16. Positron annihilation studies of bio-related N2S2-tetradentate ligands and their zinc complexes

    International Nuclear Information System (INIS)

    Shaban, S.Y.; Mahmoud, K.R.; Sharshar, T.

    2013-01-01

    In this study, a series of three N 2 S 2 -tetradentate ligands and their zinc complexes were investigated by positron annihilation lifetime spectroscopy. The measurements were performed at room temperature. The analysis of lifetime spectra of all samples yielded four lifetime components, except in one sample that yielded three components. The results showed that the formation probability and lifetime of ortho-positronium in this series are dependent on the structure.

  17. 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.

  18. A positronium beam and positronium reflection from LiF(100)

    International Nuclear Information System (INIS)

    Weber, M.; Tang, S.; Berko, S.; Brown, B.L.; Canter, K.F.; Lynn, K.G.; Mills, A.P. Jr.; Roellig, L.O.; Viescas, A.J.

    1988-01-01

    We report results obtained from a variable energy monoenergetic beam of positronium (Ps). Ps was formed by a charge transfer reaction of positrons colliding with Ar gas atoms in a ''gas cell'' with an efficiency of about 3 /times/ 10/sup /minus/4/. The beam was used to measure the fraction, R, of specularly reflected ortho-Ps from LiF(100). We found R to peak at about 30% for 7 eV Ps at a specular scattering angle of 50/degree/ to 60/degree/. At higher energies R drops sharply to values around 0.5% near 60 eV Ps

  19. 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.

  20. Annihilation characteristics of positrons in oxide powders in relation to catalytic activities

    International Nuclear Information System (INIS)

    Ito, K.; Ohtsu, Y.; Tanigawa, S.; Enomura, A.; Tsuda, N.

    1982-01-01

    The annihilation chaaracteristics in magnesium oxide powders were studied by the measurements of Doppler broadening of annihilation radiations. MgO powders are well known as a solid base and are utilized as a catalyst for the reactions which start by extracting protons from molecules such as decomposition of alcohol. The isochronal annealing behavior of annihilation characteristics in the process Mg(OH) 2 → MgO was found to correspond just to the change in the number of basic points, specific surface area and catalytic activities in some reactions. From the results of the thermal equilibrium measurements of MgO powders after dehydration, the temperature dependence of S parameter can be considered as the thermal activation process of the escape of positrons from trapped states at surface to form positroniums. The derived value of this activation energy was 0.187 eV. (Auth.)

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

    International Nuclear Information System (INIS)

    Consolati, G.; Mariani, M.; Millini, R.; Quasso, F.

    2009-01-01

    Seven well characterized zeolites were investigated by positron annihilation lifetime spectroscopy. The lifetime spectra were analysed in four discrete components. The third one was associated with ortho-positronium annihilation in the channels, framed in terms of infinite cylinders. Differences between the radii determined from the positron annihilation technique and X-ray diffraction data were found and explained in terms of the physical structure of the channel. An analogous study on a high-silica NU-88 zeolite gave a value of 0.33 nm for the corresponding radius, in agreement with Ar and N 2 adsorption data as well as with the catalytic behaviour of this zeolite in several acid catalyzed reactions. The longest lifetime component in NU-88 reveals the existence of mesopores, with average radius of about 1.8 nm, which could explain the importance of hydrogen transfer reactions in this zeolite.

  2. Positron annihilation studies of zirconia doped with metal cations of different valence

    Science.gov (United States)

    Prochazka, I.; Cizek, J.; Melikhova, O.; Konstantinova, T. E.; Danilenko, I. A.; Yashchishyn, I. A.; Anwand, W.; Brauer, G.

    2013-06-01

    New results obtained by applying positron annihilation spectroscopy to the investigation of zirconia-based nanomaterials doped with metal cations of different valence are reported. The slow-positron implantation spectroscopy combined with Doppler broadening measurements was employed to study the sintering of pressure-compacted nanopowders of tetragonal yttria-stabilised zirconia (t-YSZ) and t-YSZ with chromia additive. Positronium (Ps) formation in t-YSZ was proven by detecting 3γ-annihilations of ortho-Ps and was found to gradually decrease with increasing sintering temperature. A subsurface layer with enhanced 3γ-annihilations, compared to the deeper regions, could be identified. Addition of chromia was found to inhibit Ps formation. In addition, first results of positron lifetime measurements on nanopowders of zirconia phase-stabilised with MgO and CeO2 are presented.

  3. CERN: Antiprotons resist annihilation

    International Nuclear Information System (INIS)

    Anon.

    1992-01-01

    Ask any particle physicist what is the eventual fate of an antiproton in matter and he will likely tell you that It annihilates'. True as this answer is, it hides a number of fascinating questions about the actual 'route' followed by the antiproton into the nucleus where it finally stops before annihilating with a nuclear particle

  4. Electron-positronium scattering in Debye plasma environment

    International Nuclear Information System (INIS)

    Basu, Arindam; Ghosh, A.S.

    2008-01-01

    Electron-positronium scattering has been investigated in the Debye plasma environment employing the close-coupling approximation. Three models, viz. 3-state CCA, 6-state CCA and 9-state CCA, have been employed. The 2s 21 S e autodetaching resonant state of the positronium negative ion has been successfully predicted for various plasma environments. The position of the resonance for different Debye lengths are in close agreement with those of Kar and Ho [S. Kar, Y.K. Ho, Phys. Rev. A 71 (2005) 052503

  5. Elastic scattering of positronium: Application of the confined variational method

    KAUST Repository

    Zhang, Junyi

    2012-08-01

    We demonstrate for the first time that the phase shift in elastic positronium-atom scattering can be precisely determined by the confined variational method, in spite of the fact that the Hamiltonian includes an unphysical confining potential acting on the center of mass of the positron and one of the atomic electrons. As an example, we study the S-wave elastic scattering for the positronium-hydrogen scattering system, where the existing 4% discrepancy between the Kohn variational calculation and the R-matrix calculation is resolved. © Copyright EPLA, 2012.

  6. Elastic scattering of positronium: Application of the confined variational method

    KAUST Repository

    Zhang, Junyi; Yan, Zong-Chao; Schwingenschlö gl, Udo

    2012-01-01

    We demonstrate for the first time that the phase shift in elastic positronium-atom scattering can be precisely determined by the confined variational method, in spite of the fact that the Hamiltonian includes an unphysical confining potential acting on the center of mass of the positron and one of the atomic electrons. As an example, we study the S-wave elastic scattering for the positronium-hydrogen scattering system, where the existing 4% discrepancy between the Kohn variational calculation and the R-matrix calculation is resolved. © Copyright EPLA, 2012.

  7. 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.)

  8. 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.)

  9. Positron annihilation in PI189 and PI304 polyimides

    Energy Technology Data Exchange (ETDEWEB)

    Shantarovich, V.P. [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul Kosygina 4 st., 119334 Moscow (Russian Federation)]. E-mail: shant@center.chph.ras.ru; Suzuki, T. [High Energy Accelerator Research Organization KEK, Tsukuba 305-0801 (Japan); He, C. [High Energy Accelerator Research Organization KEK, Tsukuba 305-0801 (Japan); Ito, Y. [Reasearch Center for Nuclear Science and Technology, The University of Tokyo, Tokai, Ibaraki 319-1106 (Japan); Yampolskii, Y.P. [A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 29 Leninskii Pr., 117912 Moscow (Russian Federation); Alentiev, A.Yu. [A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 29 Leninskii Pr., 117912 Moscow (Russian Federation)

    2005-05-01

    Temperature dependence of the lifetime {tau}3 and intensity I{sub 3} of the long-lived ortho-positronium (o-Ps) component was measured for two polyimides PI189 and PI304 both below and above glass-transition temperatures Tg of these polymers. First heating runs of the experiments revealed anomalous, irregular behavior of the lifetime {tau}3 in both PI in the vicinity (below) of the glass transition temperature. The effect was similar to that discussed recently for a number of PI. However, on the cooling stage of the first cycle and on the heating run of the second cycle, such irregularities disappeared. These results show that anomalous behavior of annihilation characteristics of o-Ps in our PI samples were due not to anomalous behavior of PI structure itself close to Tg point (not to a specific phase transition), but to removal of residual solvent in vicinity of Tg during the first heating cycle. Different approaches to estimations of the specific hole volume and of the holes number density N on the basis of positron annihilation data are discussed. Final estimation for PI189 gives the fractional free volume h=3.35% and N=0.44x1027m-3. The effects of positron trapping by polar-CO groups on annihilation characteristics of PI and on the obtained value of N are also considered.

  10. Possible improvements in the bubble model description of positronium pick-off annihilation in liquids

    International Nuclear Information System (INIS)

    Beling, C.D.; Smith, F.A.

    1980-01-01

    The universal applicability of the bubble model is examined and attention is drawn to a number of situations in which it is inadequate. Some possible areas of improvements are considered. The effects of van der Waals forces on the bubble radius are estimated to be insignificant, but the problem of the potential well depth and shape is more intractable. We find that when a linear combination of finite potential components is used, the Ps pressure can become independent of well depth when the infinite component becomes large, as may be the case in certain liquids. We have developed the idea of Tao on the description of the wavefunction overlap occurring in a thin skin in the inside of the bubble surface. By considering the contribution from the protrusion of hydrogen atoms from a hard core bubble surface, we calculate that the pick-off rate can be significantly altered. (orig.)

  11. 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...

  12. Positron annihilation lifetime spectroscopy study of Kapton thin foils

    Science.gov (United States)

    Kanda, G. S.; Ravelli, L.; Löwe, B.; Egger, W.; Keeble, D. J.

    2016-01-01

    Variable energy positron annihilation lifetime spectroscopy (VE-PALS) experiments on polyimide material Kapton are reported. Thin Kapton foils are widely used in a variety of mechanical, electronic applications. PALS provides a sensitive probe of vacancy-related defects in a wide range of materials, including open volume in polymers. Varying the positron implantation energy enables direct measurement of thin foils. Thin Kapton foils are also commonly used to enclose the positron source material in conventional PALS measurements performed with unmoderated radionuclide sources. The results of depth-profiled positron lifetime measurements on 7.6 μm and 25 μm Kapton foils are reported and determine a dominant 385(1) ps lifetime component. The absence of significant nanosecond lifetime component due to positronium formation is confirmed.

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

    Science.gov (United States)

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

    2016-08-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Alonso, A.M., E-mail: a.alonso@ucl.ac.uk; Cooper, B.S.; Deller, A.; Cassidy, D.B.

    2016-08-21

    We have evaluated the application of a lutetium yttrium oxyorthosilicate (LYSO) based detector to single-shot positron annihilation lifetime spectroscopy. We compare this detector directly with a similarly configured PbWO{sub 4} scintillator, which is the usual choice for such measurements. We find that the signal to noise ratio obtained using LYSO is around three times higher than that obtained using PbWO{sub 4} for measurements of Ps excited to longer-lived (Rydberg) levels, or when they are ionized soon after production. This is due to the much higher light output for LYSO (75% and 1% of NaI for LYSO and PbWO{sub 4} respectively). We conclude that LYSO is an ideal scintillator for single-shot measurements of positronium production and excitation performed using a low-intensity pulsed positron beam.

  15. Angular correlation of annihilation photons in ice single crystals

    DEFF Research Database (Denmark)

    Mogensen, O. E.; Kvajic, G.; Eldrup, Morten Mostgaard

    1971-01-01

    -lattice vectors g⃗ on the direction perpendicular to the slits and the sample surface. The relative area of the central plus the side peaks was (15.2 ± 0.4)% for all curves. All the peaks are interpreted as due to parapositronium annihilation. The side peaks are explained as evidence for the positronium center......Linear-slit angular-correlation curves were obtained at - 148 °C for the [0001], [10¯10], and [11¯20] directions in single crystals of ice. Besides the narrow central peak, pronounced narrow side peaks were also observed. They occurred at angles θ=2πℏgz/mc, where gz is the projection of reciprocal...

  16. Positronium formation at low temperatures: The role of trapped electrons

    DEFF Research Database (Denmark)

    Hirade, T.; Maurer, F.H.J.; Eldrup, Morten Mostgaard

    2000-01-01

    Measurements have been carried out of electron spin densities (by electron spin resonance technique) and positronium (Ps) formation probability as functions of Co-60 gamma-irradiation dose in poly(methyl methacrylate) and linear poly(ethylene) at 77 K. We observe a linear relationship between...

  17. Rydberg-Stark states of Positronium for atom optics

    International Nuclear Information System (INIS)

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

    2015-01-01

    Positronium atoms were produced in Rydberg states by means of a two-step optical excitation process (1s→2p→nd/ns). The n = 11 Rydberg-Stark manifold has been studied using different laser polarizations providing greater control over the electric dipole moment. (paper)

  18. Positron and positronium physics in atomic and molecular gases: challenges for the 21. century

    Energy Technology Data Exchange (ETDEWEB)

    Gianturco, F.A. [Rome Univ., Dipt. of Chemistry, INFM (Italy)

    2002-12-01

    The increase in the interest of the scientific community in positrons as a research tool follows the development of low-energy positron beams. Preliminary studies have shown that correlation forces between the impinging positron and the bound electrons, either atomic or molecular, are much more important than the same effects in electron collisions. New experimental techniques which exploit positron accumulators have markedly increased our capabilities for investigating positron and positronium (Ps) interactions with matter at very low energies: they work already in the meV range and expectations to reach the {mu}eV are real. The elastic channels and the annihilation channels are always open as the kinetic energy of the probe approaches zero. Ps formation could also be energetically allowed whenever the target ionization energy is below 6,8 eV, the binding energy of the ground state Ps. One of the puzzling questions is to find experimental evidence on the existence of bound states or of metastable resonant states associated to cold positrons and Ps that are made to interact with fairly cold atomic and molecular gases. Experiments on anti-hydrogen are being performed in order to test the CPT invariance of quantum field theory as well as Einstein's equivalence principle (ATHENA experiment). Antiparticles are also considered as possible candidates for the production of Bose Einstein condensation of bosonic Ps by studying the possibility of creating a dense gas of Ps particles within some solid state material. Other experiments involving slow positrons interacting with polyatomic gases have shown that the measured annihilation rate is a linear function of the test gas pressure and the slope linearity yields the value of the rate. (A.C.)

  19. Positron and positronium studies of irradiation-induced defects and microvoids in vitreous metamict silica

    International Nuclear Information System (INIS)

    Hasegawa, M.; Saneyasu, M.; Tabata, M.; Tang, Z.; Nagai, Y.; Chiba, T.; Ito, Y.

    2000-01-01

    To study irradiation-induced defects and structural microvoids in vitreous silica (v-SiO 2 ), positron lifetime, angular correlation of positron annihilation radiation (ACAR), and electron spin resonance (ESR) were measured on v-SiO 2 and quartz (c-SiO 2 ) samples irradiated with fast neutrons up to a dose of 4.1x10 20 n/cm 2 . Two kinds of positron-trapping defects have been found to form in v-SiO 2 by fast neutron irradiation: type-I and type-II defects. Similar defects also appear in the irradiated c-SiO 2 , indicating that both the defects are common in v-SiO 2 and c-SiO 2 . The detailed annealing and photo-illumination studies of positron annihilation and ESR for these two defects suggest that the type-I defects are non-bridging oxygen hole centers (NBOHC), while the type-II defects are oxygen molecules which cannot be detected by ESR. Higher dose irradiation than 1.0x10 20 n/cm 2 causes c-SiO 2 to change to metamict (amorphous) phase (m-SiO 2 ). Positronium (Ps) atoms are found to form in microvoids with an average radius of about 0.3 nm in the v-SiO 2 and m-SiO 2 . This suggests that microvoids proved by Ps are structurally intrinsic open spaces and reflect the topologically disordered structure of these phases in the subnanometer scale

  20. Quantitative application of positron annihilation lifetime spectroscopy to chemical systems in liquid solutions: typical examples

    International Nuclear Information System (INIS)

    Duplatre, G.

    2007-01-01

    The published works refer only to a few, although large, classes of applications. Nevertheless, the potential applications of Positron Annihilation Lifetime Spectroscopy technique (PALS) are essentially limited by imagination. In the present contribution, the bases of physical particle, positronium (Ps) applications will be illustrated in two cases: first, it will be explained how equilibrium constants can be derived through PALS experiments; next, some more elaborate approaches will be shown to characterize various properties of direct micellar systems as have been developed in recent years in Strasbourg

  1. J-PET detector system for studies of the electron-positron annihilations

    Directory of Open Access Journals (Sweden)

    Pawlik-Niedźwiecka M.

    2016-01-01

    Full Text Available Jagiellonian Positron Emission Tomograph (J-PET has been recently constructed at the Jagiellonian University as a prototype of a cost-effective scanner for the metabolic imaging of the whole human body. J-PET detector is optimized for the measurement of momentum and polarization of photons from the electron-positron annihilations. It is built out of strips of plastic scintillators, forming three cylindrical layers. As detector of gamma quanta it will be used for studies of discrete symmetries and multiparticle entanglement of photons originating from the decays of ortho-positronium atoms.

  2. 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)

  3. Variable-energy positron annihilation study of subnanopores in SiOCH-based PECVD films

    International Nuclear Information System (INIS)

    Ito, Kenji; Oka, Toshitaka; Kobayashi, Yoshinori; Suzuki, Ryoichi; Ohdaira, Toshiyuki

    2007-01-01

    Subnanoporosity was introduced into SiOCH-based thin films by mixing tetraethyl orthosilicate with hexamethyldisiloxane (HMDSO) in the plasma enhanced chemical vapor deposition process, and was evaluated by the variable-energy positron annihilation lifetime technique. It was found that with increasing the HMDSO fraction both porosity and pore size were enhanced, as evidenced by the decreased refractive index and increased ortho-positronium lifetime. The lifetimes from 2.0 to 6.8 ns suggested the tunable pore volumes within a range of 0.1-0.7 nm 3

  4. Effect of surface physical and chemical properties on interaction and annihilation mechanisms of positrons

    International Nuclear Information System (INIS)

    Gol'danskij, V.I.; Levin, B.M.; Shantarovich, V.P.

    1982-01-01

    The possibility of positron use is illustrated, to investigate physical and chemical properties of the surface, by a number of effects found by the authors while studying the interaction and annihilation of β + -decay positrons in highly-dispersed heterogeneous systems positronium formation and ortho-para conversion close to the surface of metal particles in a dielectric matrix, postronium oxidation by proton centers on the surface of an aluminosilicate catalyst). The ways, new in the main, are revealed to study the properties of the surface by the technique of monochromatic positron beams of low energy

  5. Ageing-induced enhancement of open porosity of mesoporous silica films studied by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    He Chunqing; Muramatsu, Makoto; Oshima, Nagayasu; Ohdaira, Toshiyuki; Kinomura, Atsushi; Suzuki, Ryoichi

    2006-01-01

    We show that ageing of the silica sol in a closed vessel enhanced the open porosity of calcined mesoporous silica film studied by positron. Positron annihilation lifetime spectroscopy (PALS) based on a pulsed slow positron beam was used to estimate the mesopore size. 2-dimensional PALS (2D-PALS) and ortho-positronium time-of-flight (Ps-TOF) were used to evaluate the open porosity, interconnectivity and tortuosity of mesopores in the silica films. Results revealed that little change in pore size but significant enhancement of open porosity and/or pore interconnectivity occurred in the silica film deposited after the precursor solution aged for a relative longer time

  6. Antideuteron annihilation on nuclei

    International Nuclear Information System (INIS)

    Cugnon, J.

    1992-01-01

    An investigation of antideuteron annihilation on nuclei within an intranuclear cascade (INC) model is presented. Two models are set up to describe the annihilation itself, which either implies the antideuteron as a whole and occurs at a single point, or which may be considered as two independent nucleon-antinucleon annihilation occurring at different points and different times. Particular attention is paid to the energy transferred from the pions issued from the annihilation to the nuclear system and to the possibility of having a multifragmentation of the target. The latter feature is investigated within a percolation model. The pion distribution and the energy distribution are also discussed. Predictions of proton multiplicity distributions are compared with experiment. (orig.)

  7. Positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Sundar, C.S.; Viswanathan, B.

    1996-01-01

    An overview of positron annihilation spectroscopy, the experimental techniques and its application to studies on defects and electronic structure of materials is presented. The scope of this paper is to present the requisite introductory material, that will enable a better appreciation of the subsequent specialized articles on the applications of positron annihilation spectroscopy to investigate various problems in materials science. (author). 31 refs., 3 figs

  8. Quasinuclear baryonium and annihilation

    International Nuclear Information System (INIS)

    Kerbikov, B.O.; Shapiro, I.S.

    1978-01-01

    The properties of the quasinuclear baryonium are considered in the framework of the dynamical coupled channel model. The main principles of the model are reviewed. The energy spectrum of the N anti N system and the problem of the baryonium radius are discussed. A detailed investigation of the problem of baryonium annihilation width and the low energy N anti N annihilation cross section is presented

  9. Study of micelle formation in solutions of alkylammonium carboxylates in apolar solvents by positron annihilation techniques

    International Nuclear Information System (INIS)

    Fucugauchi, L.A.; Djermouni, B.; Handel, E.D.; Ache, H.J.

    1979-01-01

    The positron annihilation technique was applied to the study of the self-association process in solutions of alkylammonium carboxylates in apolar solvents, such as cyclohexane and benzene. The results indicate that the positronium formation probability responds very sensitively to changes in the microenvironment in these solutions. A distinct cooperative effect of the solution resulting in abrupt changes in the number of thermal ortho-positronium atoms formed was observed and studied as a function of the length and structure of the hydrocarbon chain in the cationic and anionic parts of the surfactant molecules. While the chain length in the cationic portion of the surfactant seems to have little effect on the positronium formation probability, distinct differences can be observed when the structure of the carboxylate is changed. Furthermore, a profound effect in the physical property of the solutions was recognized when cyclohexane was replaced by benzene as a solvent. The results are discussed in terms of the existing models for self-association. 4 figures

  10. 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.

  11. A simple shape-free model for pore-size estimation with positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Wada, Ken; Hyodo, Toshio

    2013-01-01

    Positron annihilation lifetime spectroscopy is one of the methods for estimating pore size in insulating materials. We present a shape-free model to be used conveniently for such analysis. A basic model in classical picture is modified by introducing a parameter corresponding to an effective size of the positronium (Ps). This parameter is adjusted so that its Ps-lifetime to pore-size relation merges smoothly with that of the well-established Tao-Eldrup model (with modification involving the intrinsic Ps annihilation rate) applicable to very small pores. The combined model, i.e., modified Tao-Eldrup model for smaller pores and the modified classical model for larger pores, agrees surprisingly well with the quantum-mechanics based extended Tao-Eldrup model, which deals with Ps trapped in and thermally equilibrium with a rectangular pore.

  12. A simple shape-free model for pore-size estimation with positron annihilation lifetime spectroscopy

    Science.gov (United States)

    Wada, Ken; Hyodo, Toshio

    2013-06-01

    Positron annihilation lifetime spectroscopy is one of the methods for estimating pore size in insulating materials. We present a shape-free model to be used conveniently for such analysis. A basic model in classical picture is modified by introducing a parameter corresponding to an effective size of the positronium (Ps). This parameter is adjusted so that its Ps-lifetime to pore-size relation merges smoothly with that of the well-established Tao-Eldrup model (with modification involving the intrinsic Ps annihilation rate) applicable to very small pores. The combined model, i.e., modified Tao-Eldrup model for smaller pores and the modified classical model for larger pores, agrees surprisingly well with the quantum-mechanics based extended Tao-Eldrup model, which deals with Ps trapped in and thermally equilibrium with a rectangular pore.

  13. Positron annihilation in a metal-oxide semiconductor studied by using a pulsed monoenergetic positron beam

    Science.gov (United States)

    Uedono, A.; Wei, L.; Tanigawa, S.; Suzuki, R.; Ohgaki, H.; Mikado, T.; Ohji, Y.

    1993-12-01

    The positron annihilation in a metal-oxide semiconductor was studied by using a pulsed monoenergetic positron beam. Lifetime spectra of positrons were measured as a function of incident positron energy for a polycrystalline Si(100 nm)/SiO2(400 nm)/Si specimen. Applying a gate voltage between the polycrystalline Si film and the Si substrate, positrons implanted into the specimen were accumulated at the SiO2/Si interface. From the measurements, it was found that the annihilation probability of ortho-positronium (ortho-Ps) drastically decreased at the SiO2/Si interface. The observed inhibition of the Ps formation was attributed to an interaction between positrons and defects at the SiO2/Si interface.

  14. Investigation of transitions and relaxation processes in polystyrene by using positron annihilation

    International Nuclear Information System (INIS)

    Ban, M.; Kyoto, M.

    1996-01-01

    The glass transition and relaxation processes in polystyrene resins with the number average molecular weight ranging from 7.0 x 10 2 to 9.8 x 10 4 were studied with the positron annihilation technique. The pick-off annihilation lifetime of ortho-positronium (τ 3 ) and its intensity (Ι 3 ) were measured in the temperature range from 20 to 430 K. The glass transition temperature (Τ g ) was determined as an onset temperature coefficient of τ 3 x Τ g shows the molecular weight dependence in these samples. Below Τ g , local motions were detected by measurements of Ι 3 . The local motions could be observed above 100 K in this experiment. Ι 3 show the minimum at around 250 K and it does not show molecular weight dependence. (author)

  15. Positron annihilation and 129Xe NMR studies of free volume in polymers

    International Nuclear Information System (INIS)

    Nagasaka, Bunsow; Eguchi, Taro; Nakayama, Hirokazu; Nakamura, Nobuo; Ito, Yasuo

    2000-01-01

    The existence and the average size of free volume in bisphenol-A polycarbonate (PC), low-density polyethylene (LDPE), poly (2,6-dimethyl-phenylene oxide)(PPO), and polytetrafluoroethylene (PTFE) were studied by positron annihilation and 129 Xe NMR measurements. The 129 Xe NMR chemical shifts for xenon adsorbed in the polymers indicated that the average pore size of the free volume increased in the following order: PC, LDPE, PPO, and PTFE. This order of the pore size of the free volume agrees well with that estimated from the longest lifetime (τ 3 ) of ortho-positronium formed in the polymers. The unique correlation that δ -1 ∝ r is established between the 129 Xe NMR chemical shift (δ) and the pore size (r), which is deduced from the positron annihilation measurements.

  16. 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)

  17. Positronium in metal-oxide powders studied with age. The age-momentum correlation technique

    International Nuclear Information System (INIS)

    Waeyenberge, B. van; Dauve, Ch.

    2001-01-01

    For the first time positronium is investigated in the fine powders of MgO and Al 2 O 3 using age-momentum correlation technique based on a relativistic positron beam. The application of this technique for investigating the interaction of positronium with the grain surfaces is discussed and compared with other techniques. The previously reported interaction of the positronium with paramagnetic centers is further studied. A qualitative interpretation of the spectra is given. In the Al 2 O 3 samples we found some unexpected behaviour of the conversion quenching of ortho-positronium at irradiation induced paramagnetic surface defect. (author)

  18. SETI at the spin-flip line frequency of positronium.

    Science.gov (United States)

    Mauersberger, R.; Wilson, T. L.; Rood, R. T.; Bania, T. M.; Hein, H.; Linhart, A.

    1996-02-01

    A directed search for extraterrestrial intelligence (SETI) has been carried out using the IRAM 30m telescope. Following a suggestion by Kardashev (1979), the search was conducted at the spin-flip line of the lightest atom, namely positronium, at 203GHz. Most of the 17 targets are mature stars with excess infrared radiation, which might be the waste heat of a power-rich technological civilisation. The rest frame of the cosmic background radiation was chosen as the velocity frame. The spectral resolution used was 9.7kHz. From the noise level, which was determined by the limited telescope time and weather conditions, the upper limit for the power of artificial omnidirectional transmitters at the positronium line frequency is of order 10^15^W. The relevance of this non-detection is discussed.

  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. Relevance of slow positron beam research to astrophysical studies of positron interactions and annihilation in the interstellar medium

    International Nuclear Information System (INIS)

    Guessoum, N.; Jean, P.; Gillard, W.

    2006-01-01

    The processes undergone by positrons in the interstellar medium (ISM) from the moments of their birth to their annihilation are examined. Both the physics of the positron interactions with gases and solids (dust grains), and the physical conditions and characteristics of the environments where the processes of energy loss, positronium formation, and annihilation taking place, are reviewed. An explanation is given as to how all the relevant physical information are taken into account in order to calculate annihilation rates and spectra of the 511 keV emission for the various phases of the ISM; special attention is paid to positron interactions with dust and with polycyclic aromatic hydrocarbons. An attempt is made to show to what extent the interactions between positrons and interstellar dust grains are similar to laboratory experiments in which beams of slow positrons impinge upon solids and surfaces. Sample results are shown for the effect of dust grains on positron annihilation spectra in some phases of the ISM which, together with high resolution spectra measured by satellites, can be used to infer useful knowledge about the environment where the annihilation is predominantly taking place and ultimately about the birth place and history of positrons in the Galaxy. The important complementarity between work done by the astrophysical and the solid-state positron communities is strongly emphasized and specific experimental work is suggested which could assist the modeling of the interaction and annihilation of positrons in the ISM

  1. Relevance of slow positron beam research to astrophysical studies of positron interactions and annihilation in the interstellar medium

    Energy Technology Data Exchange (ETDEWEB)

    Guessoum, N. [American University of Sharjah, Physics Department, P.O. Box 26666, Sharjah (United Arab Emirates)]. E-mail: nguessoum@aus.ac.ae; Jean, P. [Centre d' Etude Spatiale des Rayonnements, Toulouse (France); Gillard, W. [Centre d' Etude Spatiale des Rayonnements, Toulouse (France)

    2006-02-28

    The processes undergone by positrons in the interstellar medium (ISM) from the moments of their birth to their annihilation are examined. Both the physics of the positron interactions with gases and solids (dust grains), and the physical conditions and characteristics of the environments where the processes of energy loss, positronium formation, and annihilation taking place, are reviewed. An explanation is given as to how all the relevant physical information are taken into account in order to calculate annihilation rates and spectra of the 511 keV emission for the various phases of the ISM; special attention is paid to positron interactions with dust and with polycyclic aromatic hydrocarbons. An attempt is made to show to what extent the interactions between positrons and interstellar dust grains are similar to laboratory experiments in which beams of slow positrons impinge upon solids and surfaces. Sample results are shown for the effect of dust grains on positron annihilation spectra in some phases of the ISM which, together with high resolution spectra measured by satellites, can be used to infer useful knowledge about the environment where the annihilation is predominantly taking place and ultimately about the birth place and history of positrons in the Galaxy. The important complementarity between work done by the astrophysical and the solid-state positron communities is strongly emphasized and specific experimental work is suggested which could assist the modeling of the interaction and annihilation of positrons in the ISM.

  2. 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)

  3. Positron annihilation characterization of free volume in micro- and macro-modified Cu0.4Co0.4Ni0.4Mn1.8O4 ceramics

    International Nuclear Information System (INIS)

    Klym, H.; Ingram, A.; Shpotyuk, O.; Hadzaman, I.; Solntsev, V.; Hotra, O.; Popov, A.

    2016-01-01

    Free volume and pore size distribution size in functional micro and macro-micro-modified Cu 0.4 Co 0.4 Ni 0.4 Mn 1.8 O 4 ceramics are characterized by positron annihilation lifetime spectroscopy in comparison with Hg-porosimetry and scanning electron microscopy technique. Positron annihilation results are interpreted in terms of model implication positron trapping and ortho-positronium decaying. It is shown that free volume of positron traps are the same type for macro and micro modified Cu 0.4 Co 0.4 Ni 0.4 Mn 1.8 O 4 ceramics. Classic Tao-Eldrup model in spherical approximation is used to calculation of the size of nanopores smaller than 2 nm using the ortho-positronium lifetime.

  4. The Positronium Radiative Combination Spectrum: Calculation in the Limit of Thermal Positrons and Low Densities

    Science.gov (United States)

    Wallyn, P.; Mahoney, W. A.; Durouchoux, Ph.; Chapuis, C.

    1996-01-01

    We calculate the intensities of the positronium de-excitation lines for two processes: (1) the radiative combination of free thermal electrons and positrons for transitions with principal quantum number n less than 20, and (2) charge exchange between free positrons and hydrogen and helium atoms, restricting our evaluation to the Lyman-alpha line. We consider a low-density medium modeled by the case A assumption of Baker & Menzel and use the "nL method" of Pengelly to calculate the absolute intensities. We also evaluate the positronium fine and hyperfine intensities and show that these transitions are in all cases much weaker than positronium de-excitation lines in the same wavelength range. We also extrapolate our positronium de-excitation intensities to the submillimeter, millimeter, and centimeter wavelengths. Our results favor the search of infrared transitions of positronium lines for point sources when the visual extinction A, is greater than approx. 5.

  5. Spin polarization of graphene and h -BN on Co(0001) and Ni(111) observed by spin-polarized surface positronium spectroscopy

    Science.gov (United States)

    Miyashita, A.; Maekawa, M.; Wada, K.; Kawasuso, A.; Watanabe, T.; Entani, S.; Sakai, S.

    2018-05-01

    In spin-polarized surface positronium annihilation measurements, the spin polarizations of graphene and h -BN on Co(0001) were higher than those on Ni(111), while no significant differences were seen between graphene and h -BN on the same metal. The obtained spin polarizations agreed with those expected from first-principles calculations considering the positron wave function and the electron density of states from the first surface layer to the vacuum region. The higher spin polarizations of graphene and h -BN on Co(0001) as compared to Ni(111) simply reflect the spin polarizations of these metals. The comparable spin polarizations of graphene and h -BN on the same metal are attributed to the creation of similar electronic states due to the strong influence of the metals: the Dirac cone of graphene and the band gap of h -BN disappear as a consequence of d -π hybridization.

  6. Flavoured co-annihilation

    Indian Academy of Sciences (India)

    2012-10-06

    Oct 6, 2012 ... (2) one can see that increasing δRR will decrease the stau mass or in other words the co-annihilation will occur at a lower neutralino mass for the fixed universal scalar mass parameter (m0). But having large flavour violating entry in the ˜μR–˜τR sectors of the sleptonic mass matrix will also give rise to rare ...

  7. 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.

  8. Annihilation decays of bottomonium

    International Nuclear Information System (INIS)

    Monteiro, Antony Prakash; Bhat, Manjunath; D'Souza, Praveen P.; Vijaya Kumar, K.B.

    2016-01-01

    The bound state of a bottom quark b and its anti quark b-bar known as bottomonium was first seen in the spectrum of μμ"- pairs produced in 400 GeV proton-nucleus collisions at Fermilab. It was discovered as spin triplet states ϒ(1S), ϒ(2S) and ϒ(3S) by E288 collaboration at Fermilab. We have calculated annihilation decay widths of bottomonium states. The calculated decay widths are presented

  9. Low-energy Scattering of Positronium by Atoms

    Science.gov (United States)

    Ray, Hasi

    2007-01-01

    The survey reports theoretical studies involving positronium (Ps) - atom scattering. Investigations carried out in last few decades have been briefly reviewed in this article. A brief description of close-coupling approximation (CCA), the first-Born approximation (FBA) and the Born-Oppenheimer approximation (BOA) for Ps-Atom systems are made. The CCA codes of Ray et a1 [1-6] are reinvestigated using very fine mesh-points to search for resonances. The article advocates the need for an extended basis set & a systematic study using CCAs.

  10. Total cross section for relativistic positronium interaction with atom

    International Nuclear Information System (INIS)

    Pak, A.S.; Tarasov, A.V.

    1985-01-01

    Total cross sections of interaction of positronium relativistic atoms with atoms are calculated. Calculations are conducted within the framework of potential theory in Born approximaton. Contributions in total cross section of coherent (σsub(coh)) and incoherent (σsub(inc)) parts are analyzed. It is shown that for light elements σsub(inc) value is comparable with σsub(coh), and for heavy ones the ratio σsub(inc)/σsub(coh) sufficiently exceeds Zsup(-1) (Z-charge of the atomic nucleus. Numerical calculation results are presented. A conclusion is made on importance of the coherent part account during the calculation of total cross sections

  11. Large-angle positronium emission for Al(110)

    International Nuclear Information System (INIS)

    Schultz, P.J.; Lynn, K.G.; Frieze, W.E.

    1984-10-01

    Mono-energetic positrons have been used to study the time-of-flight distribution of ortho-positronium (o-Ps) formed just outside the surface of an Al(110) single crystal. The data are interpreted in terms of two predominant angular distributions for the directly formed o-Ps: one that is peaked towards the surface normal and another that is directed towards large angles. These processes are shown to be very sensitive to both oxygen exposure and Ar + ion sputtering. Ps emitted at large-angles may be evidence of formation with electrons propagating in a two-dimensional surface state

  12. Annihilation probability density and other applications of the Schwinger multichannel method to the positron and electron scattering

    International Nuclear Information System (INIS)

    Varella, Marcio Teixeira do Nascimento

    2001-12-01

    We have calculated annihilation probability densities (APD) for positron collisions against He atom and H 2 molecule. It was found that direct annihilation prevails at low energies, while annihilation following virtual positronium (Ps) formation is the dominant mechanism at higher energies. In room-temperature collisions (10 -2 eV) the APD spread over a considerable extension, being quite similar to the electronic densities of the targets. The capture of the positron in an electronic Feshbach resonance strongly enhanced the annihilation rate in e + -H 2 collisions. We also discuss strategies to improve the calculation of the annihilation parameter (Z eff ), after debugging the computational codes of the Schwinger Multichannel Method (SMC). Finally, we consider the inclusion of the Ps formation channel in the SMC and show that effective configurations (pseudo eigenstates of the Hamiltonian of the collision ) are able to significantly reduce the computational effort in positron scattering calculations. Cross sections for electron scattering by polyatomic molecules were obtained in three different approximations: static-exchange (SE); tatic-exchange-plus-polarization (SEP); and multichannel coupling. The calculations for polar targets were improved through the rotational resolution of scattering amplitudes in which the SMC was combined with the first Born approximation (FBA). In general, elastic cross sections (SE and SEP approximations) showed good agreement with available experimental data for several targets. Multichannel calculations for e - -H 2 O scattering, on the other hand, presented spurious structures at the electronic excitation thresholds (author)

  13. 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.

  14. Design and setup of an experiment to investigate the properties of the positronium negative ion

    International Nuclear Information System (INIS)

    Plenge, F.

    2000-01-01

    This diploma thesis describes the design and setup of an experiment to investigate the properties of the positronium negative ion Ps - . The positronium negative ion consists of two electrons in singlet spin state and a positron. It represents the simplest three-boby-system with a bound state. It allows tests of quantum electrodynamics practically free from complications due to strong interactions and is of particular interest as its investigation might contribute to a solution of the o-Ps-lifetime-puzzle. The present work particularly focuses on the preparation of the experimental tools necessary to study the Ps - -formation mechanisms and to measure the lifetime of the positronium ion. (orig.) [de

  15. Development of pore interconnectivity/morphology in porous silica films investigated by cyclic voltammetry and slow positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Tang, Xiuqin; Xiong, Bangyun; Li, Qichao; Mao, Wenfeng; Xiao, Wei; Fang, Pengfei; He, Chunqing

    2015-01-01

    Highlights: •Porous silica films were studied by cyclic voltammetry and positron annihilation. •Highly interconnected pores were formed in the film fabricated with more CTAB. •Aligned nanochannels were observed in the porous flim prepared with 25 wt.% CTAB. •I − and Ps diffusion in the films was governed by pore interconnectivity/morphology. •Cyclic voltammetry is feasible to explore pore interconnectivity/morphology. -- Abstract: Cyclic voltammetry and positronium (Ps) 3γ-annihilation spectroscopy were applied to investigate pore interconnectivity/morphology of porous silica films fabricated with various loading of cetyltrimethyl ammonium bromide (CTAB). With increasing the ratio of CTAB up to 15 wt.%, the total charge Q, resulted from I − diffusion across the silica films, increased remarkably, indicative of formation of highly interconnected pores in the films prepared with more porogen. However, it decreased dramatically with further loading CTAB of 25 wt.%. Interestingly, 3γ-annihilation fraction I 3γ due to a triplet-state Ps (ortho-positronium, o-Ps) emission from the silica films showed a similar behavior as a function of CTAB loading. The abnormal decrement in Q and I 3γ in the film fabricated with 25 wt.% CTAB was well explained by formation of long nanochannels aligning parallel to the film surface. The results indicated that the total charge Q and Ps 3γ-annihilation fraction were closely associated with I − and Ps diffusion governed by the pore interconnectivity/morphology of the silica films, which made cyclic voltammetry possible to be a feasible tool to characterize pore interconnectivity/morphology of porous thin films

  16. 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...

  17. Slow-positron annihilation analysis on optical degradation of ZnO white paint irradiated by protons

    International Nuclear Information System (INIS)

    Xiao Haiying; Li Chundong; Yang Dezhuang; He Shiyu; Jia Jin; Ye Bangjiao

    2009-01-01

    The optical degradation in ZnO white paint under low energy proton exposure was investigated in terms of slow-positron annihilation spectroscopy. Experimental results show that with increasing proton fluence, the S-parameter of the Doppler broadening spectrum gradually decreases, and the W-parameter increases.The slope plot of the fitting S-W changes under the proton exposure. The decrease of S-parameter can be attributed to a decrease of zinc vacancy content and the formation of quasi-positronium. The quasi-positronium is viewed as a bounded state of a singly ionized oxygen vacancy (trapping an electron) with a positron, the formation of which could reduce the positron annihilation rate and thus the S-parameter. The decrease of S-parameter demonstrates the amount increase of singly ionized oxygen vacancy of ZnO white paint caused by proton irradiation. The change of the S-Wplot slope is related to the transformation of doubly ionized oxygen vacancies into singly ionized oxygen vacancies under proton irradiation. (authors)

  18. Stimulated cold fusion by positronium atoms, cross sections, and wall interactions in plasmas, used to diagnostics

    International Nuclear Information System (INIS)

    Emami, Z.

    2005-01-01

    Because of the technical complexities, involved in the controlled thermonuclear, reactions, a simple vicegerent agent cold plasma, stimulated by positronium atoms (achieved through a ring storage) as stimulus, introduced by this author in ITC 12 conference. In the present paper, the interaction between γ rays emitted through positronium atoms annihilation (in the forms of doublet and triplet electromagnetic photonic radiation) with plasma particles (including electrons, ions and neutral particles) investigated. Proper lifetime of singlet γ rays τs are about 100 ns and from that of triplet γ rays, i.e τt about 100 fems, reside in the following transition times in Ne and Argon elements in He-Ne and Ar lasers respectively: Ne*(3S2) [transition time τ = 105 ns] -> Ne*(2P4); Ar+*(3P4 4S) [transition time τ = 105 fems] -> Ar+(3P5). Then the interactions of γ rays with mater in plasma could follow up as treated from that of the laser and mater in one extreme while the comparison of this situation with normal plasmas in other extreme could serve as diagnostics key role in magnetically confined plasmas reactors. Collisions between charge and neutral species in plasma with electromagnetic radiation (γ photonic radiation) including the energy loss and scattering lead to different consequences. Light electrons can take up appreciably amounts of energy from the incident rays, lead to heating cold plasma, whereas massive ions absorb very little energy. Thus loss of incident energy in radiation occurs almost entirely in collisions with electrons , which, referred to the γ rays energy this would led to plasma heating about thermonuclear reaction ( Eγ = hν = 0.5 MeV). The heavy ions and neutral species in interaction with electromagnetic γ radiation, result on the other hand in scattering, in turn may increase the ionization level of the cold plasma, toward fully ionized plasma. Although all the essential features of these different interaction cross sections deduced

  19. Radiation chemistry connection with the positronium formation in aqueous solution of triton X-100

    International Nuclear Information System (INIS)

    Das, S.K.; Ganguly, B.N.

    1996-01-01

    Positronium formation bears its connection to radiation chemical phenomenon. This has been demonstrated here to probe the micelle formation and further structural changes in Triton X-100 surfactant solution. (author). 6 refs., 3 figs

  20. 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)

  1. Inelastic processes and interference effects during the interaction of positronium with ultrashort electromagnetic pulses

    Energy Technology Data Exchange (ETDEWEB)

    Eseev, M. K., E-mail: m_eseev@mail.ru; Matveev, V. I., E-mail: matveev.victor@pomorsu.ru [Lomonosov Northern (Arctic) Federal University (Russian Federation)

    2013-11-15

    The excitation, breakup, and reradiation during the interaction of a positronium atom with ultrashort electromagnetic pulses are considered. The probabilities of inelastic processes and reradiation spectra have been obtained. The interference between the amplitudes of the photon emission by the electron and positron is shown to contribute noticeably to the reradiation spectra. The developed approach is applicable for describing the interaction of positronium with ultrashort pulses of attosecond or shorter duration.

  2. Spin conversion induced by the spin-orbit interaction in positronium collisions

    International Nuclear Information System (INIS)

    Saito, Haruo; Nakayama, Takashi; Hyodo, Toshio

    2009-01-01

    We show the existence of a new reaction mechanism of positronium - ortho-Ps - para-Ps conversion reaction induced by the spin-orbit interaction. This interaction was previously believed to be negligibly small. Recently, however, Mitroy has suggested that this interaction could be observed in Ps-Xe collision. In the present work, we have succeeded in observing this effect and obtaining the reaction rate by using the Zeeman mixing of positronium.

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

    International Nuclear Information System (INIS)

    Cheung, C K; Nahid, F; Cheng, C C; Beling, C D; Fung, S; Ling, C C; Djurisic, A B; Pramanik, C; Saha, H; Sarkar, C K

    2007-01-01

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

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

    International Nuclear Information System (INIS)

    Abdel-Hady, E.E.; Hamdy, F. M. M.; Alaa, H.B.

    2005-01-01

    Positron annihilation lifetime of pure and doped polyvinyl chloride (PVC) with Al 2 O 3 reflect the effect of concentration as well as temperature on free volume. Therefore, variations of the ortho-positronium (o-Ps) lifetime and its intensity have been correlated with changes in the dielectric properties of the pure and doped PVC. The o-Ps lifetime and its intensity show a linear dependence with a discontinuity at 20 % concentration of Al 2 O 3 . The size and the fractional of the o-Ps hole volume were estimated from the positron annihilation parameters. Therefore, the temperature dependence of the electrical conductivity and the positron annihilation parameters on pure and doped PVC with 20 % Al 2 O 3 were studied in the range from 20 to 140 degree C. The shift of the glass transition temperature to lower temperature for the 20 % Al 2 O 3 doped PVC might explain the increase in the electrical conductivity with the concentration of the additive

  5. Regularities in positronium formation for atoms and molecules

    International Nuclear Information System (INIS)

    Machacek, J R; Buckman, S J; Sullivan, J P; Blanco, F; Garcia, G

    2016-01-01

    In an effort to aid the modelling of positron and positronium (Ps) transport in biological media we have compiled recent experimental results for the total Ps formation in positron scattering from atoms and molecules. A simple function was found to adequately describe the total Ps formation cross section for both atoms and molecules. The parameters of this function describe the magnitude and shape of the Ps formation cross section and are compared to physical characteristics of the target atoms and molecules. A general trend in the magnitude of the total Ps formation cross section is observed as a function of the target atom/molecule dipole polarisability. The functional form may enable quick estimation of the Ps cross section for molecules for which experimental measurements or theoretical estimates do not exist. (paper)

  6. Positronium hydride defects in thermochemically reduced alkaline-Earth oxides

    International Nuclear Information System (INIS)

    Monge, M.A.; Pareja, R.; Gonzalez, R.; Chen, Y.

    1997-01-01

    Thermochemical reduction of both hydrogen-doped MgO and CaO single crystals results in large concentrations of hydride (H - ) ions. In MgO crystals, positron lifetime and Doppler broadening experiments show that positrons are trapped at H - centers forming positronium hydride molecules [e + - H - ]. A value of 640 ps is obtained for the lifetime of the PsH states located in an anion vacancy In MgO positrons are also trapped at H 2- sites at low temperatures. The H 2- ions were induced in the crystals by blue light illumination. The formation of PsH states in CaO could not be conclusively established. (orig.)

  7. Studies of hypothetical and fundamental decay properties of positronium

    International Nuclear Information System (INIS)

    Wahl, W.

    1985-05-01

    For the solution of the CP problem in the standard theory of the strong interaction the existence of a neutral pseudoscalar boson was postulated which couples to quarks and leptons. If the mass of this so-called axion is smaller than two electron masses for orthopositronium 'o-Ps' the decay into one photon and axion is expected in concurrence to the standard decay into three photons. The detection of a monoenergetic photon would be an indication for this decay channel because the axion would only very weakly interact with matter. In the spectrum no lineshape of a monoenergetic photon is observed. From this results in dependence on the mass of a hypothetical particle and with a confidence limit of 90% for the branching ratio of o-Ps an upper limit which is in the range between 320 keV and 950 keV less than 10 -7 . Applied to the axion model an upper limit for the mass of the standard axion of 250 keV results. For the study of the fundamental decay properties of positronium the lifetime of o-Ps and the 3γ energy distribution of the decay quanta were measured. Furthermore the rare 4γ decay of para-positronium 'p-Ps' was searched for. The measured lifetime of o-Ps τ=141.2±1.2ns agrees well with the theoretical value. Calculations on the 3γ energy distribution are confirmed. For the 4γ decay of p-Ps predicted by QED with a branching ratio of ≅ 1.5x10 -6 an upper limit of 2x10 -5 results. (orig./HSI) [de

  8. Supramolecular interactions between triphenylphosphine oxide and benzamide evaluated by positron annihilation lifetime spectroscopy

    Science.gov (United States)

    Oliveira, F. C.; Denadai, A. M. L.; Fulgêncio, F.; Oliveira, A. M.; Andrade, A. C. A.; Melo, A. C. A.; Yoshida, M. I.; Windmöller, D.; Magalhães, W. F.

    2017-04-01

    In the present work, intermolecular interactions between triphenylphosphine oxide (TPPO) and benzamide (BZM) has been studied in solid state by Positron Annihilation Lifetime Spectroscopy (PALS) and supported by several analytical techniques (in solid state and in solution) and by computational modeling (in gaseous phase). Isothermal Titration Calorimetry (ITC) in ethyl acetate solvent showed that complexation is a stepwise process, with 2:1 and 1:1 TPPO/BZM stoichiometries, both driven by entropy. HPLC analysis of isolated single crystal confirmed the existence of a 2:1 TPPO/BZM crystalline complex in solid state. The results of thermal analysis (TGA, DTA and DSC) and FTIR spectroscopy showed that the interactions in the complexes are relatively weaker than those found in pure precursors. Finally, PALS showed higher positronium formation probability (I3) at [TPPO0.62·BZM0.38] and [TPPO0.25·BZM0.75] molar fractions, corroborating the existence of two stoichiometries for the TPPO/BZM system and suggesting greater electronic availability of n- and π-electrons in heterosynton complexes, as resulting of interactions, bring forward new evidences of the participation of electronic excited states on the positronium formation mechanism.

  9. Localization in fluids: A comparison of competing theories and their application to positron annihilation

    International Nuclear Information System (INIS)

    Miller, B.N.; Fan, Y.

    1990-01-01

    This paper addresses two central issues in our understanding of self-trapping, or localization, of a light particle (e.g., electron, positron, or positronium atom) in a fluid. The first concerns the relationship between the mean-field calculations of localized states carried out from the mid-1950s until the present, and the direct calculation of light-particle (LP) properties from the adiabatic model. The second concerns the universality of the ring polymer representation of the LP, which has proved to be extremely useful for computing the properties of localized electrons. We first demonstrate that the mean-field theories of localization, which are derived from density functionals, can be obtained from the adiabatic model by employing a Gutzwiller type of approximation. We then study the application of the adiabatic model, via the polymer representation, to the annihilation of positrons and positronium atoms in a fluid. Expressions for the decay rate and its variance are derived in terms of the two- and three-point distribution functions for the polymer sites and positions of the atomic nuclei. The momentum distribution of the localized LP is shown to be proportional to the Fourier transform of the distribution function for the displacement between the ends of a broken polymer

  10. 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.

  11. Polymerization of epoxy resins studied by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, T. [Radiation Science Center, High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); Hayashi, T. [Fine Chemical Research Lab., Sumitomo Chemical, Tsukuba (Japan); Ito, Y. [Research Center for Nuclear Science and Technology, Univ. of Tokyo (Japan)

    2001-04-01

    Positron annihilation lifetime spectroscopy (PALS) has been applied to study polymerization of epoxy resins of cresole novolac with a hardener of phenol novolac. PALS uses positrons to probe the microstructure of a nanometer (nm) size. Using PALS polymerization can be followed through three states: powder (monomer), liquid and solid. PALS is a unique method for the detection of intermolecular spaces, hence polymerization was followed from the point of view of free spaces (inter-molecular spaces) between polymer networks. The glass transition temperature (T{sub g}) was determined from the temperature dependence of the positronium (Ps) lifetime. Although Tg determined by PALS is usually lower than that determined by a mechanical analysis (TMA), it was observed that T{sub g} approached the value determined by TMA after long curing. Ps can form bubbles in a liquid, and the surface tension of a mixture of the resin and the hardener was calculated from a simple empirical formula using the Ps lifetime; the resulting value is similar to that of the bisphenol-A epoxy resin. Gelation was observed as an increase in the intensity of Ps and a sharp decrease in the lifetime. (orig.)

  12. Radiation damage of polymers studied by positron annihilation. Positron and gamma-ray irradiation effects

    International Nuclear Information System (INIS)

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

    1995-01-01

    Positron irradiation effects on polypropylene (PP) have been studied using positron sources ( 22 Na) during positron annihilation (PA) experiments. The irradiation effect was measured by the intensity (I 3 ) of the long-lived component of positronium (Ps). At a low temperature of around 100 K, I 3 for unirradiated PP samples increased due to a termination of the thermal motion of the -CH 3 groups. However, the increase in I 3 for γ-ray irradiated samples was reduced in inverse proportion to the amount of irradiation. Although no increase in I 3 was observed for 1 MGy-irradiated PP with γ-rays, an increase was observed again after a 48 h irradiation by positrons emitted from 22 Na. This may be due to a reconstructing of the polymer chains. (author)

  13. On the Correlation between EPR and Positron Annihilation Measurements on gamma-Irradiated Acetyl Methionine

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Lund-Thomsen, E.; Mogensen, O. E.

    1972-01-01

    The dose dependence of the relative EPR signal intensity and positron lifetime spectrum was measured for γ‐irradiated acetyl methionine in the dose range from 0 to 30 Mrad. Angular correlation measurements were performed for the doses 0 and 30 Mrad. The result of the irradiation was the creation...... of EPR centers and inhibition of positronium formation. For one sample, irradiated with a dose of 30 Mrad, EPR and positron lifetime spectra were followed over a period of 50 days after the irradiation. The inhibiting effect and the EPR signal intensity decreased with time. No simple correlation could...... be established between the number of EPR centers and the positron annihilation data, but other possible explanations are discussed....

  14. Further search for selectivity of positron annihilation in the skin and cancerous systems

    International Nuclear Information System (INIS)

    Liu Guang; Chen Hongmin; Chakka, Lakshmi; Cheng Meiling; Gadzia, Joseph E.; Suzuki, R.; Ohdaira, T.; Oshima, N.; Jean, Y.C.

    2008-01-01

    Positronium annihilation lifetime (PAL) spectroscopy and Doppler broadening energy spectra (DBES) have been used to search for selectivity and sensitivity for cancerous skin samples with and without cancer. This study is to further explore the melanoma cancerous system and other different types of skin samples. We found that the S parameter in melanoma skin samples cut at 0.39 mm depth from the same patient's skin is smaller than near the skin surface. However in 10 melanoma samples from different patients, the S parameters vary significantly. Similarly, among 10 normal skin samples without cancer, the S parameters also vary largely among different patients. To understand the sensitivity of PAS as a tool to detect cancer formation at the early stage, we propose a controlled and systematic study of in vivo experiments using UV-induced cancer skin from living animals

  15. Effect of electron-irradiation on the free volume of PEEK studied by positron annihilation

    International Nuclear Information System (INIS)

    Kobayashi, Y.; Haraya, K.; Hattori, S.; Sasuga, T.

    1994-01-01

    A good linear correlation was found between the size of a cavity where ortho-positronium (o-Ps) annihilates by the pick-off mechanism and the total free volume of molecular liquids and polymers. Based on the correlation, the free volume of poly(aryl ether-ether ketone) (PEEK) was evaluated as a function of electron irradiation dose and the result was compared with that obtained from gas diffusivity measurements. It was found that the effect of irradiation on the free volume of PEEK was rather small; the free volume was decreased only by a few percent (relative value) when the samples were irradiated with a dose of 50 MGy in air. ((orig.))

  16. Study of free volume hole distributions in xTiO2(1-x)SiO2 by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Misheva, M.A.; Djourelov, N.; Margaca, M.A.; Salvado, F.I.; Passage, G.

    1999-01-01

    Positron annihilation spectroscopy has been used to get information about the small pore structure of the system xTiO 2 .(1-x)SiO 2 (x=10,30 mol.%). The pore radius and volume probability distribution functions have been received from the ortho-Positronium lifetime probability distribution function, obtained by the lifetime spectra processing with CONTIN (PALS-2) program. The linearity of the S versus W-parameters has been used to check the similarity (or not) of the defect structure of the samples prepared under different experimental conditions. (author)

  17. 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.

  18. Positron annihilation radiation from the Galactic center - Cheshire cat' Compton scattering and the origin of excess continuum

    International Nuclear Information System (INIS)

    Bildsten, L.; Zurek, W.H.

    1988-01-01

    Two observations of the gamma-ray spectrum from the direction of the Galactic center were made by HEAO 3 in the fall of 1979 and the spring of 1980. The 2-gamma 511 keV annihilation line flux decreased by a factor of about three during the 6 months between these observations, while the excess gamma-ray continuum below the annihilation line, often interpreted as 3-gamma decay of orthopositronium, barely changed. This discrepancy in temporal behavior makes the identification of the bulk of excess continuum as 3-gamma decay of positronium difficult. It is shown that Compton scattering of the line and high-energy radiation provides a natural explanation for the surprisingly small changes seen in the excess continuum. Scattered photons are delayed by a time corresponding to the size of the scattering region. For the annihilation source in the Galactic center, this distance is probably a fraction of a parsec. Thus, even after the high-energy continuum and annihilation line are gone, low-energy Compton-scattered photons can still be detected with an almost unchanged flux. 23 references

  19. 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.

  20. ATHENA: an actual antihydrogen annihilation

    CERN Multimedia

    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).

  1. Positronium formation in porous materials for antihydrogen production

    International Nuclear Information System (INIS)

    Ferragut, R; Calloni, A; Dupasquier, A; Consolati, G; Giammarchi, M G; Quasso, F; Trezzi, D; Egger, W; Ravelli, L; Petkov, M P; Jones, S M; Wang, B; Yaghi, O M; Jasinska, B; Chiodini, N; Paleari, A

    2010-01-01

    Positronium (Ps) formation measurements in several porous materials as: Vycor, germanate Xerogel, Metal-Organic Frameworks MOF-177 and Aerogel with two densities (20 and 150 mg/cm 3 ), were performed by means of a variable energy positron beam provided with a Ge detector and a positron lifetime spectrometer. An efficient formation of cooled Ps atoms is a requisite for the production of antihydrogen, with the aim of a direct measurement of the Earth gravitational acceleration g of antimatter, which is a primary scientific goal of AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy). Porous materials are necessary to form a high yield of Ps atoms as well as to cool Ps through collisions with the inner walls of the pores. The different materials were characterized and produce Ps into the pores. Lifetime measurements give an estimation of the typical pores dimension of the substances. A comparative study of the positron lifetime and the Ps fraction values in the above mentioned materials indicates that silica Aerogel, with the appropriate density, is an excellent candidate for an efficient formation of cold Ps atoms for the AEGIS project.

  2. Thermalization of positronium in helium: A numerical study

    Energy Technology Data Exchange (ETDEWEB)

    Marjanovic, S.; Suvakov, M. [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia); Engbrecht, J.J. [Saint Olaf College, Northfield, MN 55057 (United States); Petrovic, Z.Lj., E-mail: zoran@ipb.ac.rs [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia)

    2012-05-15

    In this paper we present a numerical study of positronium (Ps) thermalization in pure helium (He). Recent measurements of Ps thermalization yielded data that were analyzed to produce the scattering cross-sections in helium by using energy balance equations with an assumption of a Maxwell-Boltzmann distribution (MBD) function for Ps. We have applied a Monte Carlo code to test the cross-sections. As our code was developed without any approximations for the energy distribution function we have effectively also tested the assumptions and the validity of the simple theory based on Maxwellian distributions. We present the simulation results using the simulation technique that is limited only by the accuracy of the available cross-sections. We calculate thermalization profiles for several theoretical and measured cross-sections. Also, the temporal evolution of energy distributions has been shown along with diffusion coefficients and spatial ranges of penetration. Thermalization of the initial distribution is rapid and the data follow relatively closely, those calculated in recent experiment, which supports the choice of MBD and the obtained cross-section. However the distribution function most of the time deviates from the MBD due to strong scattering. Finally, we applied the same procedure to analyze Ps thermalization in water vapor.

  3. Experimental support for physisorbed positronium at the surface of quartz

    International Nuclear Information System (INIS)

    Sferlazzo, P.; Berko, S.; Canter, K.F.

    1985-01-01

    We report temperature-dependent positronium (Ps) emission from a single crystal of SiO 2 using a monoenergetic positron beam. Slow positrons (e + ) from an electrostatic beam system were injected with variable energy (0--1600 eV) into the SiO 2 target and Ps emission from the target surface was studied as a function of incident e + energy (E) as well as target temperature (T). Our data suggest a physisorbed Ps surface state which is temperature activated into a ''slow'' Ps emission with an activation energy of approx.0.15 eV. In addition, a large Ps yield (40% of the incident positrons are emitted as Ps at 400 eV) is observed even for T→0, attributed to ''fast'' Ps produced by the bulk Ps formed within the SiO 2 target and diffusing to the surface. From the Ps yield vs E we find a bulk Ps diffusion constant of 0.047 +- 0.013 cm 2 /sec. We also observe a slow e + reemission yield of (15 +- 2)% at 400-eV incident e + energy

  4. Two-state approximation applied to hydrogen formation by proton impact on positronium

    Directory of Open Access Journals (Sweden)

    E Ghanbari Adivi

    2009-09-01

    Full Text Available Although there is no experimental data available for antihydrogen formation following antiprotons impact on positroium atoms, as a charge transfer reaction, at incident energies which are suitable for antimatter high-precision spectroscopic studies, measurements were carried out for its charge-conjugate reaction i. e. hydrogen formation, by protons impact on positronium. In this study, a two-state approximation method is applied to charge exchange process in proton-positronium collision system. The nonorthogonality of initial and final states and its effects on the angular distribution of the differential cross sections is taken into account by using this method. The state-to-state differential cross sections are reported for transition from ground state of positronium into the ground and a few lowest excited states of the formed hydrogen. Integrated cross sections are presented as well.

  5. Study of the anti-hydrogen atom and ion formation in the collisions antiproton-positronium

    International Nuclear Information System (INIS)

    Comini, Pauline

    2014-01-01

    The future CERN experiment called GBAR intends to measure the gravitational acceleration of antimatter on Earth using cold (neV) anti-hydrogen atoms undergoing a free fall. The experiment scheme first needs to cool anti-hydrogen positive ions, obtained thanks to two consecutive reactions occurring when an antiproton beam collides with a dense positronium cloud.The present thesis studies these two reactions in order to optimise the production of the anti-ions. The total cross sections of both reactions have been computed in the framework of a perturbation theory model (Continuum Distorted Wave - Final State), in the range 0 to 30 keV antiproton kinetic energy; several excited states of positronium have been investigated. These cross sections have then been integrated to a simulation of the interaction zone where antiprotons collide with positronium; the aim is to find the optimal experimental parameters for GBAR. The results suggest that the 2P, 3D or, to a lower extend, 1S states of positronium should be used, respectively with 2, less than 1 or 6 keV antiprotons. The importance of using short pulses of antiprotons has been underlined; the positronium will have to be confined in a tube of 20 mm length and 1 mm diameter. In the prospect of exciting the 1S-3D two-photon transition in positronium at 410 nm, a pulsed laser system had already been designed. It consists in the frequency doubling of an 820 nm pulsed titanium-sapphire laser. The last part of the thesis has been dedicated to the realisation of this laser system, which delivers short pulses (9 ns) of 4 mJ energy at 820 nm. (author) [fr

  6. Electron-positron annihilation physics

    International Nuclear Information System (INIS)

    Foster, B.

    1990-01-01

    Electron-Positron Annihilation Physics is a detailed introduction to the main topics in e + e - annihilation, with particular emphasis on experimental work. Four main areas are covered, each in great detail, beginning with the Standard Model and its application to the production of lepton, quark and boson pairs. Secondly, the general features of fragmentation and different fragmentation models are explained. Chapter 3 is devoted to heavy quark and lepton physics, to which e + e - experiments have made an immense contribution. The final chapter, 'Where do we go from here?', looks for new phenomena beyond the Standard Model. Predictions of theory are compared with experimental results, highlighting shortcomings of some current theories. Details of instrumentation are included whenever possible. This ensures that the book is of maximum practical use to research workers. A comprehensive introduction to the major topics in the field, Electron-Positron Annihilation Physics is aimed at both graduate students studying high-energy physics and mature research workers. (author)

  7. The effect of positronium formation in e+ -Li and e+ -Na scattering

    International Nuclear Information System (INIS)

    Adhikari, S.K.; Ghosh, A.S.; Ray, H.

    1994-02-01

    The e + -Li and e + -Na scattering are studied, using the close coupling approximation in the static and coupled static expansion schemes. The effect of the positronium formation on the elastic channel is found to be strong in both cases. In the case of the lithium atom the effect is dramatic; the inclusion of the positronium formation channels transforms the purely repulsive effective e + -Li S wave (static) potential to a predominantly attractive (coupled static) potential. In this case, in the static model δ(0) - δ(∞) = π. According to Levinson's theorem this suggests the presence of a S wave bound or continuum bound state in the e + -Li system. (author)

  8. On Positronium Formation in Crystalline and Amorphous Ice at Low Positron Energy

    DEFF Research Database (Denmark)

    Mogensen, O. E.

    1986-01-01

    The positronium (Ps) yield for ice, measured by Eldrup et al. using a low-energy positron beam, is discussed in terms of the spur model of Ps formation. The pronounced maxima in the Ps yield for crystalline ice at positron energies below 65 eV are well explained by effects due to energy conservat......The positronium (Ps) yield for ice, measured by Eldrup et al. using a low-energy positron beam, is discussed in terms of the spur model of Ps formation. The pronounced maxima in the Ps yield for crystalline ice at positron energies below 65 eV are well explained by effects due to energy...

  9. Hyperfine splitting in positronium measured through quantum beats in the 3γ decay

    International Nuclear Information System (INIS)

    Fan, S.; Beling, C.D.; Fung, S.

    1996-01-01

    Quantum beat oscillations in the 3γ decay of the positronium atom arising from interference between the different spin states have been observed using a simple β-start and γ-stop detection system. Measurements of the beat frequency at different magnetic fields have yielded a value of the 1 1 S 0 -1 3 S 1 hyperfine interaction of 202.5±3.5 GHz, in good agreement with previous measurements. This novel approach does not require high magnetic fields and the use of microwave radiation to quench the triplet substate of the positronium atom. (orig.)

  10. 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...

  11. Defect characterization with positron annihilation

    International Nuclear Information System (INIS)

    Granatelli, L.; Lynn, K.G.

    1980-01-01

    Positron annihilation in metal crystals is reviewed. A brief introduction to the positron annihilation technique is presented first. Then the ability of the positron technique to perform microstructural characterization of four types of lattice defects (vacancies, voids, dislocations, grain boundaries) is discussed. It is frequently not possible to obtain samples that contain only one type of defect in nonnegligible concentrations. Such situations exist for some alloys and for fatigued metal samples. Finally, the current limitations and some future prospects of the technique are presented. 79 references, 14 figures, 1 table

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. Applications of Positron Annihilation Spectroscopy

    OpenAIRE

    Asoka-Kumar , P.; Lynn , K.

    1995-01-01

    We describe the application of Positron Annihilation Spectroscopy (PAS) to some selected technologically important systems. The method involves a nondestructive probe to detect low levels of open-volume defects. The discussion shows the application of PAS to a wide range of advanced material systems.

  17. 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

  18. Angular correlation in positron annihilation

    International Nuclear Information System (INIS)

    Arponen, J.; Pajanne, E.

    1978-01-01

    The angular correlation of the two gamma quanta emitted when a thermalized positron annihilates with metallic conduction electrons is investigated by applying the newly developed theory of electron gas as a system of interacting collective excitations. The method leads in a natural way to the appearance of high-momentum components (i.e. pair momentum p>psub(F) in the annihilation radiation already in the case of annihilation with conduction electrons only. The amount of these components is significant approximately (10 %) in a dilute electron gas (like alkali metals), but fairly irrelevant for higher densities. The momentum-dependence of the enhancement factor for a dense system (with rsub(s) approximately equal to 2) agrees well both with the earlier theories due to Kahana and others, and also with recent accurate experimental observations. As rsub(s) increases into the alkali-metal region, the enhancement factor for p< psub(F) becomes relatively more and more constant, in contrast with the trend in the Kahana theory. In this density regime the experimental results seem to vary widely, although most of them desagree with the present prediction. We discuss the possible discrepancy and try to account for the effects of the core annihilation by a simple model. (author)

  19. Tratamiento de las ictericias

    Directory of Open Access Journals (Sweden)

    Roberto de Zubiría

    1955-05-01

    Full Text Available En el tratamiento de los síndromes ictéricos no existe sistematización de criterios y en más de una ocasión se cometen serios errores terapéuticos. Tal sucede frecuentemente con las hepatitis a virus, por ejemplo las que tratadas con un régimen alimenticio inadecuado, constituído casi siempre por dietas de hambre, se va a complicar más la situación. Otras veces se utilizan sistemáticamente los antibióticos de amplio espectro, los cuales son inútiles e inclusive desaconsejados por la posibilidad de producir fibrosis hepática. Hemos querido hacer un resumen analizando someramente el pro y el contra de las principales medidas terapéuticas.

  20. Strong suppression of the positronium channel in double ionization of noble gases by positron impact

    DEFF Research Database (Denmark)

    Bluhme, H.; Knudsen, H.; Merrison, J.P.

    1998-01-01

    Positron-induced double ionization of helium and neon has been studied at energies from threshold to 900 eV. A remarkable difference between the near-threshold behavior of the single and double ionization cross sections is found: Single ionization is dominated by positronium (Ps) formation, while...

  1. Effect of an External Electric Field on Positronium Formation in Positron Spur

    DEFF Research Database (Denmark)

    Mogensen, O. E.

    1975-01-01

    The decrease of positronium (Ps) formation in condensed matter caused by the presence of an external electric field is discussed in terms of the spur reaction model of Ps formation. The rather few experimental results available are shown to be in good agreement with the predictions of the model...

  2. On the radiative corrections α2lnα to the positronium decay rate

    International Nuclear Information System (INIS)

    Khriplovich, I.B.; Elkhovskij, A.S.

    1990-01-01

    The radiative corrections ∼α 2 ln α to the positronium decay rate are calculated in the Breit approximation which is shown to be quite adequate for the problem. For orthopositronium the result coincides with the previous one, for parapositronium it differs from the old results. 9 refs

  3. Comparison of positronium, positron and electron collisions with hydrogen at low velocities

    International Nuclear Information System (INIS)

    Reeth, P Van; Humberston, J W; Woods, Denton; Ward, S J

    2016-01-01

    Recent experimental findings indicate that at equal velocity electron and ortho-positronium scattering cross sections are similar over a wide range of velocities and targets where both elastic and inelastic processes can take place. We present a comparative study of positronium, positron and electron elastic scattering from atomic hydrogen in order to investigate if a similar behaviour occurs for this target at low velocities where inelastic channels are closed. We calculate elastic cross sections for the three projectiles using Kohn-type variational methods which allows us to make a detailed study of the differences and similarities. We find a qualitative similarity in the spin-weighted elastic integrated cross sections for positronium and electron scattering and a good agreement between the singlet integrated cross sections. However, this agreement does extend to the low velocity region and where the agreement is found in the integrated cross sections we show that it is not present in the individual partial waves cross sections. Interestingly, given the agreement we find in the singlet integrated cross section for electron and positronium scattering, when comparing the overall shapes of the corresponding singlet differential cross sections we find different angular and velocity dependencies. (paper)

  4. 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.

  5. 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)

  6. Positron annihilation response and broadband dielectric spectroscopy: salol.

    Science.gov (United States)

    Bartoš, J; Iskrová, M; Köhler, M; Wehn, R; Sauša, O; Lunkenheimer, P; Krištiak, J; Loidl, A

    2011-09-01

    A phenomenological analysis of the ortho-positronium (o-Ps) annihilation from positron annihilation lifetime spectroscopy (PALS) and the dynamics from broadband dielectric spectroscopy (BDS) are reported on a small molecular glass former of intermediate H-bonding and fragility: salol. The dielectric spectra extend over a very broad frequency range of about 2 × 10(-2)-3.5 × 10(11) Hz, providing information on the α-relaxation, the secondary relaxation giving rise to the excess wing, and the shallow high-frequency minimum in the micro- to milli-meter wave range. A number of empirical correlations between the o-Ps lifetime, τ(3)(T), and the various spectral and relaxation features have been observed. Thus, the phenomenological evaluation of the τ(3)(T) dependence of the PALS response of the amorphous sample reveals three characteristic PALS temperatures: T(g)(PALS), T(b1)(L) = 1.15T(g)(PALS) and T(b2)(L) = 1.25T(g)(PALS), which are discussed in relation to similar findings for some typical small molecular vdW- and H-bonded glass formers. A slighter change of the slope at T(b1)(L) appears to be related to the transition from excess wing to the primary α-process-dominated behavior, with the secondary process dominating in the deeply supercooled liquid state below T(b1)(L). The high-temperature plateau effect in the τ (3)(T) plot occurs at T(b2)(L) and agrees with the characteristic Stickel temperature, T(B)(ST), marking a qualitative change of the primary α process, but it does not follow the relation T(b2)(L) application of the two-order parameter (TOP) model to the structural relaxation as represented by the primary α relaxation times from BDS leads to the characteristic TOP temperature, T(m)(c), close to T(b1) from PALS. Within this model the phenomenological interpretation is offered based on changes in the probability of occurrence of solid-like and liquid-like domains to explain the dynamic as well as PALS responses. In summary, all the empirical

  7. Tratamiento Actual del Pie Zambo

    OpenAIRE

    Salom Taverner, M.; Mínguez Rey, María Fe

    2015-01-01

    El pie zambo es una deformidad congénita en la que el pie presenta una deformidad en equino, varo de retropié, aductus del antepié y cavo. Su tratamiento ha variado con el tiempo. Clásicamente se trataba mediante distintas técnicas quirúrgicas que permitían corregir todas las deformidades pero que se acompañaban de frecuentes complicaciones a corto y largo plazo. Actualmente el tratamiento más extendido de esta deformidad es el tratamiento conservador mediante la técnica de Ponset...

  8. 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)

  9. Investigation of nanoscopic free volume and interfacial interaction in an epoxy resin/modified clay nanocomposite using positron annihilation spectroscopy.

    Science.gov (United States)

    Patil, Pushkar N; Sudarshan, Kathi; Sharma, Sandeep K; Maheshwari, Priya; Rath, Sangram K; Patri, Manoranjan; Pujari, Pradeep K

    2012-12-07

    Epoxy/clay nanocomposites are synthesized using clay modified with the organic modifier N,N-dimethyl benzyl hydrogenated tallow quaternary ammonium salt (Cloisite 10A). The purpose is to investigate the influence of the clay concentration on the nanostructure, mainly on the free-volume properties and the interfacial interactions, of the epoxy/clay nanocomposite. Nanocomposites having 1, 3, 5 and 7.5 wt. % clay concentrations are prepared using the solvent-casting method. The dispersion of clay silicate layers and the morphologies of the fractured surfaces in the nanocomposites are studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The observed XRD patterns reveal an exfoliated clay structure in the nanocomposite with the lowest clay concentration (≤1 wt. %). The ortho-positronium lifetime (τ(3)), a measure of the free-volume size, as well as the fractional free volume (f(v)) are seen to decrease in the nanocomposites as compared to pristine epoxy. The intensity of free positron annihilation (I(2)), an index of the epoxy-clay interaction, decreases with the addition of clay (1 wt. %) but increases linearly at higher clay concentrations. Positron age-momentum correlation measurements are also carried out to elucidate the positron/positronium states in pristine epoxy and in the nanocomposites. The results suggest that in the case of the nanocomposite with the studied lowest clay concentration (1 wt. %), free positrons are primarily localized in the epoxy-clay interfaces, whereas at higher clay concentrations, annihilation takes place from the intercalated clay layers. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Positronium deuteride and hydride in MgO crystals

    International Nuclear Information System (INIS)

    Monge, M.A.; Pareja, R.; Gonzalez, R.; Chen, Y.

    1996-01-01

    Low-temperature positron lifetime and Doppler broadening measurements were made in MgO crystals containing D - or H - ions in order to investigate the temperature dependence of the positron trapping by D - and H - ions and elucidate the possible formation of PsD (PsH) states. Positrons are trapped at D - and H - ions once the oxygen vacancies, which are more effective positron traps, are eliminated by annealing the crystals at high temperatures in a reducing atmosphere. From the temperature dependence of the annihilation parameters the positron trapping coefficients for D - and H - centers were shown to increase with temperature between 100-300 K. The lifetime of the PsD (PsH) state is (650±30) ps and temperature independent. The dissociation rate of the PsD (PsH) state into D (H) and Ps is also temperature independent. No isotopic effect was observed. (author)

  11. 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

  12. 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.)

  13. Positronium formation and hydrated positron reactions in H2O, D2O, 1.74 M PPS/H2O and 1.74 M PPS/D2O solutions of Cl−, Br− and I−

    DEFF Research Database (Denmark)

    Mogensen, O. E.; Pedersen, Niels Jørgen

    1986-01-01

    Angular correlation of annihilation photons were measured for H2O, D2O, 1.74 M PPS/H2O and 1.74 M PPS/D2O solutions of Cl−, Br− and I−. The three components of the angular correlation spectra for D2O and H2O were nearly identical in shape. The positronium (Ps) yields for the H2O and D2O solutions...... before annihilation (lifetime 400 ps) was determined for the three halides in the four solvents. Simple kinetic equations (“trapping model”) with time dependent rate constant, solved analytically, could explain the [X−, e+] formation in H2O fairly well for concentrations below 0.03 M X−, if a diffusion...... controlled reaction with positron diffusion constant D = 5 × 10−5 cm2/s and reaction radius R = 1 nm were assumed. The three halides gave roughly identical [X−, e+] formation below 0.03 M X−. The difference between the four solutions could be explained partly only in terms of viscosity change for the model...

  14. 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...

  15. The mean energy loss by neutrino with magnetic moment in strong magnetic field with consideration of positronium contribution to photon dispersion

    Science.gov (United States)

    Mosichkin, A. F.

    2017-11-01

    The process of radiative decay of the neutrino with a magnetic moment in a strong magnetic field with consideration of positronium influence on photon dispersion has been studied. Positronium contribution to the photon polarization operator induces significant modifications of the photon dispersion law and neutrino radiative decay amplitude. It has been shown that the mean energy loss of a neutrino with magnetic a moment significantly increases, when the positronium contribution to photon dispersion is taken into account.

  16. Characterization of lacunar defects by positrons annihilation

    International Nuclear Information System (INIS)

    Barthe, M.F.; Corbel, C.; 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 spectrum: evolution with the concentration of defects); 3 - measurement of annihilation characteristics with two gamma photons (lifetime spectroscopy with the β + 22 Na isotope, spectroscopy of Doppler enlargement of the annihilation line); 4 - determination of the free volume of defects inside or at the surface of materials (annihilation signature in lacunar defects, lacuna, lacunar clusters and cavities, acceptors nature in semiconductors: ionic or lacunar, interface defects, precipitates in alloys); 5 - conclusions. (J.S.)

  17. Calculation of von Neumann entropy for hydrogen and positronium negative ions

    International Nuclear Information System (INIS)

    Lin, Chien-Hao; Ho, Yew Kam

    2014-01-01

    In the present work, we carry out calculations of von Neumann entropies and linear entropies for the hydrogen negative ion and the positronium negative ion. We concentrate on the spatial (electron–electron orbital) entanglement in these ions by using highly correlated Hylleraas functions to represent their ground states, and to take care of correlation effects. We apply the Schmidt decomposition method on the partial-wave expanded two-electron wave functions, and from which the one-particle reduced density matrix can be obtained, leading to the quantifications of linear entropy and von Neumann entropy in the H − and Ps − ions. - Highlights: • We calculate von Neumann entropies and linear entropies for hydrogen and positronium negative ions. • We employ highly correlated Hylleraas functions to take into account of correlation effects. • Spatial (electron–electron orbital) entanglement is quantified using the Schmidt decomposition method. • The eigenvalues of the one-particle reduced density matrix are calculated

  18. Positronium reactions in the Triton X-100-p-nitro phenol system

    International Nuclear Information System (INIS)

    Kumar Das, S.; Nandi Ganguly, B.

    1997-01-01

    The positronium reactions have been used as a probe to study the solubilization of p-nitro phenol within the micellar phase of a Triton X-100 solution and the corresponding changes in the molecular association phenomenon. The presence of p-nitro phenol resulted in an enhancement of micellization which has been corroborated by surface tension measurements. This paper also lays emphasis on the secondary aggregation phenomenon of Triton X-100 molecules at the far post-micellar stage (∼ 10-15 mM). The solubilization of p-nitro phenol at various stages of aggregation has been discussed through the interaction with positronium atoms by setting up a kinetic model and reaction equilibria. (author)

  19. A study on the performance of an electrostatic focusing mirror for Rydberg positronium

    Science.gov (United States)

    Jones, Adric C. L.; Cecchini, Gabriel G.; Moxom, Jeremy; Osorno, Kevin; Rutbeck-Goldman, Harris J.; Fuentes-Garcia, Melina; Greaves, Rod G.; Adams, Daniel J.; Tom, Harry W. K.; Mills, Allen P., Jr.

    2018-01-01

    Recently, we demonstrated an electrostatic mirror that focuses a beam of Rydberg positronium atoms over a 6 m path to a 32 ± 1 mm FWHM diameter spot on a position sensitive detector. The mirror is comprised of 360 wires arranged in the shape of a nearly-cylindrical revolved truncated ellipse 96 mm in radius, with potentials of equal and opposite magnitude applied to alternating wires to create a short-ranged electric field that decreases in magnitude exponentially with e-folding length = 0.53 mm. Here, we explore in detail the observed resolution and discuss the factors contributing to its broadening from the ideal point focus of a perfect embodiment of the mirror. Improvements to the design are considered, with the aim to achieve a mirror with a resolution of <0.5 mm, which is necessary for a proposed measurement of the gravitational deflection of positronium.

  20. Positronium Inhibition and Quenching by Organic Electron Acceptors and Charge Transfer Complexes

    DEFF Research Database (Denmark)

    Jansen, P.; Eldrup, Morten Mostgaard; Jensen, Bror Skytte

    1975-01-01

    Positron lifetime measurements were performed on a series of organic electron acceptors and charge-transfer complexes in solution. The acceptors cause both positronium (Ps) inhibition (with maybe one exception) and quenching, but when an acceptor takes part in a charge-transfer complex...... in terms of the spur reaction model of Ps formation. Correlation was also made to gas phase reaction between electron acceptors and free electron, as well as to pulse radiolysis data....

  1. An investigation of antiprotons collisions with positronium atom in Debye plasma environments

    International Nuclear Information System (INIS)

    Pandey, M. K.; Lin, Y.-C.; Ho, Y. K.

    2015-01-01

    The effects of Debye plasmas on antihydrogen formation and ionization processes are investigated in antiprotons (p ¯ ) and positronium (Ps) collisions. The classical trajectory Monte Carlo method with Debye Hückel potentials has been used for cross section calculations. In this process, antihydrogen formation and ionization cross sections have been calculated in unscreened as well as in Debye plasmas conditions in energies ranging from 1 to 500 keV. Partial cross sections for antihydrogen formation are also calculated which show the largest cross sections correspond to production of antihydrogen in the n = 2 (2s, 2p) states. Comparative study has been carried out to determine the differences of cross sections in screening and unscreening cases. The results show that the cross sections for both antihydrogen formation and positronium ionization depend on Debye screening lengths as well as on collision energies. The effects of plasmas conditions on antihydrogen formation and positronium ionization are explained in terms of classical trajectory framework. Our results for the unscreened case are in agreement with previously reported results

  2. An investigation of antiprotons collisions with positronium atom in Debye plasma environments

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, M. K., E-mail: pandey@pub.iams.sinica.edu.tw; Lin, Y.-C.; Ho, Y. K., E-mail: ykho@pub.iams.sinica.edu.tw [Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 106, Taiwan (China)

    2015-05-15

    The effects of Debye plasmas on antihydrogen formation and ionization processes are investigated in antiprotons (p{sup ¯}) and positronium (Ps) collisions. The classical trajectory Monte Carlo method with Debye Hückel potentials has been used for cross section calculations. In this process, antihydrogen formation and ionization cross sections have been calculated in unscreened as well as in Debye plasmas conditions in energies ranging from 1 to 500 keV. Partial cross sections for antihydrogen formation are also calculated which show the largest cross sections correspond to production of antihydrogen in the n = 2 (2s, 2p) states. Comparative study has been carried out to determine the differences of cross sections in screening and unscreening cases. The results show that the cross sections for both antihydrogen formation and positronium ionization depend on Debye screening lengths as well as on collision energies. The effects of plasmas conditions on antihydrogen formation and positronium ionization are explained in terms of classical trajectory framework. Our results for the unscreened case are in agreement with previously reported results.

  3. Hernia discal lumbar: Tratamiento conservador

    OpenAIRE

    López-Sastre Núñez, Antonio; Candau Pérez, Ernesto

    1999-01-01

    Existe una gran demanda de patología lumbar crónica y aguda que debe de tratarse conjuntamente entre el especialista en Rehabilitación y el Cirujano de columna vertebral. En este trabajo se detallan las posibilidades del tratamiento conservador antes de optar por la cirugía. Se realiza una revisión bibliográfica de los resultados conservadores del tratamiento de la lumbociática de origen discal comparando aquellos estudios publicados con validez estadística. Se detallan las modernas pautas de...

  4. 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

  5. Hadron production in e+e- annihilation

    International Nuclear Information System (INIS)

    Lueth, V.

    1977-01-01

    The lectures cover recent results on hadron production by e + e - annihilation. Included are total hadronic cross section and scale invariance as applied to e + e - annihilation, the present status of the psi spectroscopy by study of the decay modes of the narrow psi resonances, and the recent discovery of charmed mesons. 93 references

  6. Positron annihilation spectroscopy in materials structure studies

    International Nuclear Information System (INIS)

    Grafutin, Viktor I; Prokop'ev, Evgenii P

    2002-01-01

    A relatively new method of materials structure analysis - positron annihilation spectroscopy (PAS) - is reviewed. Measurements of positron lifetimes, the determination of positron 3γ- and 2γ-annihilation probabilities, and an investigation of the effects of different external factors on the fundamental characteristics of annihilation constitute the basis for this promising method. The ways in which the positron annihilation process operates in ionic crystals, semiconductors, metals and some condensed matter systems are analyzed. The scope of PAS is described and its prospects for the study of the electronic and defect structures are discussed. The applications of positron annihilation spectroscopy in radiation physics and chemistry of various substances as well as in physics and chemistry of solutions are exemplified. (instruments and methods of investigation)

  7. Skyrmion creation and annihilation by spin waves

    International Nuclear Information System (INIS)

    Liu, Yizhou; Yin, Gen; Lake, Roger K.; Zang, Jiadong; Shi, Jing

    2015-01-01

    Single skyrmion creation and annihilation by spin waves in a crossbar geometry are theoretically analyzed. A critical spin-wave frequency is required both for the creation and the annihilation of a skyrmion. The minimum frequencies for creation and annihilation are similar, but the optimum frequency for creation is below the critical frequency for skyrmion annihilation. If a skyrmion already exists in the cross bar region, a spin wave below the critical frequency causes the skyrmion to circulate within the central region. A heat assisted creation process reduces the spin-wave frequency and amplitude required for creating a skyrmion. The effective field resulting from the Dzyaloshinskii-Moriya interaction and the emergent field of the skyrmion acting on the spin wave drive the creation and annihilation processes

  8. 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.

  9. Synthesis and characterization of magnesium oxide nanocrystallites and probing the vacancy-type defects through positron annihilation studies

    Science.gov (United States)

    Das, Anjan; Mandal, Atis Chandra; Roy, Soma; Prashanth, Pendem; Ahamed, Sk Izaz; Kar, Subhrasmita; Prasad, Mithun S.; Nambissan, P. M. G.

    2016-09-01

    Magnesium oxide nanocrystallites exhibit certain abnormal characteristics when compared to those of other wide band gap oxide semiconductors in the sense they are most prone to water absorption and formation of a hydroxide layer on the surface. The problem can be rectified by heating and pure nanocrystallites can be synthesized with controllable sizes. Inevitably the defect properties are distinctly divided between two stages, the one with the hydroxide layer (region I) and the other after the removal of the layer by annealing (region II). The lattice parameters, the optical band gap and even the positron annihilation characteristics are conspicuous by their distinct behavior in the two stages of the surface configurations of nanoparticles. While region I was specific with the formation of positronium-hydrogen complexes that drastically altered the defect-specific positron lifetimes, pick-off annihilation of orthopositronium atoms marked region II. The vacancy clusters within the nanocrystallites also trapped positrons. They agglomerated due to the effect of the higher temperatures and resulted in the growth of the nanocrystallites. The coincidence Doppler broadening spectroscopic measurements supported these findings and all the more indicated the trapping of positrons additionally into the neutral divacancies and negatively charged trivacancies. This is apart from the Mg2+ monovacancies which acted as the dominant trapping centers for positrons.

  10. Neutron mean annihilation time and inverse of the mean annihilation rate in nuclear reactor

    International Nuclear Information System (INIS)

    Hayashi, Masatoshi

    1999-01-01

    There is a dogma in nuclear reactor theory that in a critical reactor the mean annihilation time of neutron is equal to the mean generation time. The author insists that this is a dogma from the basic reexamination of the mean annihilation time of neutron. There are two kinds of neutrons, one participating in chain reactions and the other not participating in chain reactions. The mean annihilation time of neutron is the mean time of the time to annihilation of all neutrons generated in the reactor. The 'prompt neutron life' as a dynamic characteristic parameter proper to nuclear reactor can not be understood as the mean time of neutron to annihilation. The author explains the logic quantitatively with two kinds of nuclear reactors, a bare reactor and an infinite reactor, for which two different mean neutron annihilation times can be defined. Thus, (1) the inverse of the annihilation rate can not simply be considered as the mean annihilation time, (2) the mean annihilation time of a critical reactor is not necessarily equal to the mean generation time, and (3) the prompt neutron life used as a dynamic characteristic parameter of a nuclear reactor can not be understood as the mean time of neutron to annihilation. (M.M.)

  11. Probing vacancy-type free-volume defects in Li2B4O7 single crystal by positron annihilation lifetime spectroscopy

    Science.gov (United States)

    Shpotyuk, O.; Adamiv, V.; Teslyuk, I.; Ingram, A.; Demchenko, P.

    2018-01-01

    Vacancy-type free-volume defects in lithium tetraborate Li2B4O7 single crystal, grown by the Czochralski technique, are probed with positron annihilation spectroscopy in the lifetime measuring mode. The experimental positron lifetime spectrum is reconstructed within the three-component fitting, involving channels of positron and positronium Ps trapping, as well as within the two-component fitting with a positronium-compensating source input. Structural configurations of the most efficient positron traps are considered using the crystallographic specificity of lithium tetraborate with the main accent on cation-type vacancies. Possible channels of positron trapping are visualized using the electronic structure calculations with density functional theory at the basis of structural parameters proper to Li2B4O7. Spatially-extended positron-trapping complexes involving singly-ionized lithium vacancies, with character lifetime close to 0.32 ns, are responsible for positron trapping in the nominally undoped lithium tetraborate Li2B4O7 crystal.

  12. Positron annihilation lifetime spectroscopy (PALS): a probe for molecular organisation in self-assembled biomimetic systems.

    Science.gov (United States)

    Fong, Celesta; Dong, Aurelia W; Hill, Anita J; Boyd, Ben J; Drummond, Calum J

    2015-07-21

    Positron annihilation lifetime spectroscopy (PALS) has been shown to be highly sensitive to conformational, structural and microenvironmental transformations arising from subtle geometric changes in molecular geometry in self-assembling biomimetic systems. The ortho-positronium (oPs) may be considered an active probe that can provide information on intrinsic packing and mobility within low molecular weight solids, viscous liquids, and soft matter systems. In this perspective we provide a critical overview of the literature in this field, including the evolution of analysis software and experimental protocols with commentary upon the practical utility of PALS. In particular, we discuss how PALS can provide unique insight into the macroscopic transport properties of several porous biomembrane-like nanostructures and suggest how this insight may provide information on the release of drugs from these matrices to aid in developing therapeutic interventions. We discuss the potentially exciting and fruitful application of this technique to membrane dynamics, diffusion and permeability. We propose that PALS can provide novel molecular level information that is complementary to conventional characterisation techniques.

  13. 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...

  14. 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.

  15. Studies of unicellular microorganisms Saccharomyces cerevisiae by means of positron annihilation lifetime spectroscopy

    Directory of Open Access Journals (Sweden)

    Kubicz Ewelina

    2015-12-01

    Full Text Available Results of positron annihilation lifetime spectroscopy (PALS and microscopic studies on simple microorganisms, brewing yeasts, are presented. Lifetime of ortho-positronium (o-Ps were found to change from 2.4 to 2.9 ns (longer-lived component for lyophilized and aqueous yeasts, respectively. Also hygroscopicity of yeasts in time was examined, allowing to check how water – the main component of the cell – affects PALS parameters, thus lifetime of o-Ps were found to change from 1.2 to 1.4 ns (shorter-lived component for the dried yeasts. The time sufficient to hydrate the cells was found below 10 hours. In the presence of liquid water, an indication of reorganization of yeast in the molecular scale was observed. Microscopic images of the lyophilized, dried, and wet yeasts with best possible resolution were obtained using inverted microscopy (IM and environmental scanning electron microscopy (ESEM methods. As a result, visible changes to the surface of the cell me mbrane were observed in ESEM images.

  16. Multi-wall carbon nanotubes investigated by positron annihilation techniques and microscopies for further production handling

    Energy Technology Data Exchange (ETDEWEB)

    Luu, A.T.; Thanh, N.D.; Dung, T.Q.; Son, L.T.; Phuc, P.T. [Center for Nuclear Techniques, Vietnam Atomic Energy Commission, Ho Chi Minh City (Viet Nam); Kajcsos, Zs. [KFKI Research Institute for Particle and Nuclear Physics, Budapest (Hungary); Nhon, M.V.; Tap, T.D. [Department of Nuclear Physics, Faculty of Physics, University of Natural Sciences, Ho Chi Minh City (Viet Nam); Lazar, K. [Institute of Isotopes HAS, Budapest (Hungary); Havancsak, K.; Huhn, G. [Department of Materials Physics, Budapest Univ. (Hungary); Horvath, Z.E. [Research Institute for Technical Physics and Materials Sciences, Budapest (Hungary)

    2009-11-15

    Multi-wall carbon nanotube samples with various tube diameters produced by Thermal Chemical Vapor Deposition technique using various catalysts were studied by various microscopic methods and positron annihilation spectroscopy (PAS) with the aim of assessing the applicability of these methods for structural studies in these novel materials. Specifically, positron lifetime (LT) and Doppler broadening (DB) techniques, transmission electron microscopy (TEM) and atomic force microscopy (AFM) were employed, on iron-containing samples Moessbauer spectroscopy was also utilized. The PAS measurements were carried out on densely packed powder samples and on samples pressed into pills in atmospheric pressure and in vacuum as well. The lifetime values could be interpreted by assuming trapping of positrons, the low contribution from longer-living trapped positronium can be probably related to defects on walls of the tubes. Possibility of correlation of LT and DB data with the nanotube sizes and sample composition was also considered. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Structural study of some divalent aluminoborate glasses using ultrasonic and positron annihilation techniques

    Energy Technology Data Exchange (ETDEWEB)

    Saddeek, Yasser B. [Physics Department, Faculty of Science, Al-Azhar University, Assiut (Egypt); Mohamed, Hamdy F.M. [Physics Department, Faculty of Science, El-Minia University, B.O. 61519 El-Minia (Egypt); Azooz, Moenis A. [Glass Research Department, National Research Center, Dokki, Cairo (Egypt)

    2004-07-01

    Positron annihilation lifetime (PAL), ultrasonic techniques, and differential thermal analysis (DTA) were performed to study the structure of some aluminoborate glasses. The basic compositions of these glasses are 50 B{sub 2}O{sub 3}+ 10 Al {sub 2}O {sub 3}+40RO (wt%), where RO is the divalent oxide (MgO, CaO, SrO, and CdO). The ultrasonic data show that the rigidity increases from MgO to CaO then decrease at SrO and again increases at CdO. The glass transition temperature (determined from DTA) decreases from MgO to SrO then increases at CdO. The trend of the thermal properties was attributed to thermal stability. The experimental data are correlated with the internal glass structure and its connectivity. The PAL data show that an inversely correlation between the relative fractional of the open hole volume and the density of the samples. Also, there is a good correlation between the ortho-positronium (o-Ps) lifetime (open hole volume size) and the bulk modulus of the samples (determined from ultrasonic technique). The open volume hole size distribution for the samples shows that the open volume holes expand in size for CaO, SrO, MgO, and CdO, respectively with their distribution function moving to higher volume size. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Structural study of some divalent aluminoborate glasses using ultrasonic and positron annihilation techniques

    International Nuclear Information System (INIS)

    Saddeek, Yasser B.; Mohamed, Hamdy F.M.; Azooz, Moenis A.

    2004-01-01

    Positron annihilation lifetime (PAL), ultrasonic techniques, and differential thermal analysis (DTA) were performed to study the structure of some aluminoborate glasses. The basic compositions of these glasses are 50 B 2 O 3 + 10 Al 2 O 3 +40RO (wt%), where RO is the divalent oxide (MgO, CaO, SrO, and CdO). The ultrasonic data show that the rigidity increases from MgO to CaO then decrease at SrO and again increases at CdO. The glass transition temperature (determined from DTA) decreases from MgO to SrO then increases at CdO. The trend of the thermal properties was attributed to thermal stability. The experimental data are correlated with the internal glass structure and its connectivity. The PAL data show that an inversely correlation between the relative fractional of the open hole volume and the density of the samples. Also, there is a good correlation between the ortho-positronium (o-Ps) lifetime (open hole volume size) and the bulk modulus of the samples (determined from ultrasonic technique). The open volume hole size distribution for the samples shows that the open volume holes expand in size for CaO, SrO, MgO, and CdO, respectively with their distribution function moving to higher volume size. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Structural study of some divalent aluminoborate glasses using ultrasonic and positron annihilation techniques

    Science.gov (United States)

    Saddeek, Yasser B.; Mohamed, Hamdy F. M.; Azooz, Moenis A.

    2004-07-01

    Positron annihilation lifetime (PAL), ultrasonic techniques, and differential thermal analysis (DTA) were performed to study the structure of some aluminoborate glasses. The basic compositions of these glasses are 50 B2O3 + 10 Al2O3 + 40 RO (wt%), where RO is the divalent oxide (MgO, CaO, SrO, and CdO). The ultrasonic data show that the rigidity increases from MgO to CaO then decrease at SrO and again increases at CdO. The glass transition temperature (determined from DTA) decreases from MgO to SrO then increases at CdO. The trend of the thermal properties was attributed to thermal stability. The experimental data are correlated with the internal glass structure and its connectivity. The PAL data show that an inversely correlation between the relative fractional of the open hole volume and the density of the samples. Also, there is a good correlation between the ortho-positronium (o-Ps) lifetime (open hole volume size) and the bulk modulus of the samples (determined from ultrasonic technique). The open volume hole size distribution for the samples shows that the open volume holes expand in size for CaO, SrO, MgO, and CdO, respectively with their distribution function moving to higher volume size.

  20. 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.)

  1. Positron annihilation in transparent ceramics

    Science.gov (United States)

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

    2016-01-01

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

  2. 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)

  3. 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.

  4. Participation of electronic excited states in the positronium formation mechanism in the Gd(III) pentakis (picrate) complexes with imidazolium countercations

    Energy Technology Data Exchange (ETDEWEB)

    Fulgêncio, F., E-mail: fefulgencio@gmail.com [Departam ento de Química – ICEx Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG (Brazil); Borges, A.S. [Coordenadoria de Química e Biologia – Instituto Federal do Espírito Santos – IFES, Campus Vitória, ES (Brazil); Araújo, M.H. [Departam ento de Química – ICEx Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG (Brazil); Brito, H.F. [Instituto de Química, Departamento de Química Fundamental, Universidade de São Paulo, São Paulo (Brazil); Oliveira, F.C. [Departamento de Metalurgia e Química, Centro Federal de Educação Tecnológica de Minas Gerais – CEFET-MG, Campus Timóteo, MG (Brazil); Ribeiro, T.; Windmöller, D. [Departam ento de Química – ICEx Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG (Brazil); Magalhães, W.F., E-mail: welmag@ufmg.br [Departam ento de Química – ICEx Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG (Brazil)

    2016-02-15

    In this work, positron annihilation lifetime (PALS) and optical spectroscopies measurements were performed on [Gd(pic){sub 2}(H{sub 2}O){sub 6}](pic)·6H{sub 2}O and on complexes of general formula C{sub 2}[Gd(pic){sub 5}], where pic corresponds to picrate ligands and C to the countercations butyl-methyl, hexyl-methyl, butyl-ethyl and butyl-butyl imidazoles. Since all of these complexes have high energy ligand-to-metal charge transfer states (LMCTS) but form low amounts of Positronium (Ps), the LMCTS do not act here as a mechanism that suppress luminescence nor prevents Ps formation. This result suggests that, besides LMCTS, other effects should also contribute to prevent Ps formation. The results indicate that the electron withdrawing –NO{sub 2} groups in the picrate ligand are responsible by the effect that prevents Ps formation. Also, a rough correlation between the ligands' triplet states lifetimes and Ps formation was observed. The insertion of electron donor groups (the imidazolium countercations) increased the ligands' first triplet excited states ({sup 3}π{sup ⁎}) lifetimes and Ps formation, indicating that these two spectroscopic parameters are correlated. Also, it is demonstrated that there is no clear correlation between Ps formation probability and the excitation energy of the ligands' first triplet excited states. The results were discussed in terms of the recently proposed Ps formation mechanism, named cybotactic correlated system kinetic mechanism (CCSKM), showing that the Ps formation process involves molecular excited states and is kinetically controlled. - Highlights: • PALS and optical spectroscopies measurements performed on Gd{sup 3+} complexes. • A correlation was obtained between the ligands' {sup 3}π{sup ⁎} lifetimes and Ps formation. • Electronegative groups increased the ligands' {sup 3}π{sup ⁎} lifetimes and Ps formation. • Results discussed in terms of a new Ps formation mechanism (ccskm).

  5. Development of a buffer gas trap for the confinement of positrons and study of positronium production in the GBAR experiment

    CERN Document Server

    AUTHOR|(CDS)2101248; van der Werf, Dirk

    The GBAR experiment relies on the production of antihydrogen positive ions to achieve its goal of measuring the gravitational acceleration of antimatter at rest. The ANTION project, included in the GBAR enterprise, is responsible for the production of these antimatter ions. Moreover, it also aims to measure the cross section of antihydrogen production throughout the collision of antiprotons and positronium atoms, as well as the matter cross sections of hydrogen and the hydrogen negative ion. These experiments imply the formation of a very dense positronium cloud, thus a large amount of positrons will be implanted on a positron/positronium converter material. This thesis reports the construction of a three stage buffer gas trap with the goal of trapping and accumulating positrons for the ANTION project. The combination of the Penning-type trap with a LINAC source constitutes a unique experimental setup. The trap was commissioned and optimized and is now fully operational. Trapping protocols were studied and...

  6. Inhibition and anti-inhibition effects of positronium formation in cyclohexane and their relation to radiation chemistry

    International Nuclear Information System (INIS)

    Ito, Y.; Miyake, Y.; Tabata, Y.

    1982-01-01

    Positronium formation in cyclohexane has been studied using C 2 H 5 Br or CCl 4 as an inhibitor and C 6 F 6 as an anti-inhibitor. The results are analyzed using an empirical formula which is well established in radiation chemistry for electron scavenging reactions in cyclohexane. The reactivity parameters derived from the radiation chemistry are shown to successfully reproduce the experimental results. Very close correlation between positronium formation and radiation chemistry is evident, and the spur reaction model of positronium formation is corroborated. From a simple model of the positron spur in which only a single ion pair and a positron is assumed, it is estimated that about 75% of the spur electron combines with the positron. (author)

  7. Analysis of positron annihilation lifetime data by numerical Laplace inversion: Corrections for source terms and zero-time shift errors

    International Nuclear Information System (INIS)

    Gregory, R.B.

    1991-01-01

    We have recently described modifications to the program CONTIN for the solution of Fredholm integral equations with convoluted kernels of the type that occur in the analysis of positron annihilation lifetime data. In this article, modifications to the program to correct for source terms in the sample and reference decay curves and for shifts in the position of the zero-time channel of the sample and reference data are described. Unwanted source components, expressed as a discrete sum of exponentials, may be removed from both the sample and reference data by modification of the sample data alone, without the need for direct knowledge of the instrument resolution function. Shifts in the position of the zero-time channel of up to half the channel width of the multichannel analyzer can be corrected. Analyses of computer-simulated test data indicate that the quality of the reconstructed annihilation rate probability density functions is improved by employing a refernce material with a short lifetime and indicate that reference materials which generate free positrons by quenching positronium formation (i.e. strong oxidizing agents) have lifetimes that are too long (400-450 ps) to provide reliable estimates of the lifetime parameters for the shortlived components with the methods described here. Well-annealed single crystals of metals with lifetimes less than 200 ps, such as molybdenum (123 ps) and aluminium (166 ps) do not introduce significant errors in estimates of the lifetime parameters and are to be preferred as reference materials. The performance of our modified version of CONTIN is illustrated by application to positron annihilation in polytetrafluoroethylene. (orig.)

  8. Study of the electron-positron annihilation in the galactic center region with the Integral/SPI spectrometer; Etude de l'annihilation electron-positon dans la region du centre galactique avec le spectrometre INTEGRAL/SPI

    Energy Technology Data Exchange (ETDEWEB)

    Sizun, P

    2007-04-15

    A spectral feature was detected in 1970 in the gamma-ray emission from the central regions of the Milky Way, during balloon flight observations. Located near 511 keV, this feature was soon attributed to the gamma-ray line tracing the annihilation of electrons with their anti-particles, positrons. However, none of the multiple astrophysical scenarios contemplated to explain the production of positrons in the Galactic bulge has been able to reproduce the high injection rate deduced from the flux of the 511 keV line, close to 10{sup 43} positrons per second. Launched in 2002, the European gamma-ray satellite INTEGRAL was provided with a spectrometer, SPI, whose unprecedented imaging and spectral capabilities in this energy range enable us to further study the source of the 511 keV line detected in the Galactic centre region. Indeed, a better determination of the spatial extent of the source, the intrinsic width of the line and the fraction of positrons annihilating in-flight, directly or via the formation of ortho-Positronium atoms would improve our knowledge of both the annihilation medium and the initial source of positrons, and could allow us to discriminate between the various explanatory scenarios. The first part of this thesis deals with a key ingredient in the extraction of the annihilation spectrum: the optimization of the instrumental background model. New data screening and tracer selection procedures are presented. Classical multi-linear models are compared to neural and Bayesian networks. Finally, three years of observation are used to constrain the width of the source and derive its spectrum. The second part of the thesis focuses on one of the possible scenarios explaining the high positron injection rate deduced from the flux of the 511 keV line: the annihilation of light dark matter particles into electron-positron pairs. The various radiation mechanisms involved are modeled and confronted to observations in order to set an upper limit on the injection

  9. QCD in e+e- annihilation

    International Nuclear Information System (INIS)

    Ali, A.

    1981-04-01

    The promise of e + e - annihilation as an ideal laboratory to test Quantum Chromodynamics, QCD, has been the dominating theme in elementary particle physics during the last several years. An attempt is made to partially survey the subject in deep perturbative region in e + e - annihilation where theoretical ambiguities are minimal. Topics discussed include a review of the renormalization group methods relevant for e + e - annihilation, total hadronic cross section, jets and large-psub(T) phenomena, non-perturbative quark and gluon fragmentation effects and analysis of the jet distributions measured at DORIS, SPEAR and PETRA. My hope is to review realistic tests of QCD in e + e - annihilation - as opposed to the ultimate tests, which abound in literature. (orig.)

  10. Dislocation dipole annihilation in diamond and silicon

    Energy Technology Data Exchange (ETDEWEB)

    Rabier, J; Pizzagalli, L, E-mail: jacques.rabier@univ-poitiers.fr [Institut PPRIMME, Departement de Physique et Mecanique des Materiaux - UPR 3346 CNRS, Universite de Poitiers, ENSMA - SP2MI, BP 30179, F-86962 Chasseneuil Futuroscope Cedex (France)

    2011-02-01

    The mechanism of dislocation dipole annihilation has been investigated in C and Si using atomistic calculations with the aim of studying their annihilation by-products. It is shown, in C as well as in Si, that dipole annihilation yields debris that can be depicted as a cluster of vacancies, or alternately by two internal free surfaces. These defects have no strain field and can hardly be seen using usual TEM techniques. This suggests that the brown colouration of diamond could be due to microstructures resulting from deformation mechanisms associated with dipole formation and their annihilation rather than to a climb mechanism and vacancy aggregation. In silicon where a number of dipoles have been evidenced by TEM when dislocation trails are found, such debris could be the missing link responsible for the observation of strong chemical reactivity and electrical activity in the wake of moving dislocations.

  11. Radiation damage analysis by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Siegel, R.W.

    1979-01-01

    The application of positron annihilation spectroscopy (PAS) to the characterization and study of defects in metals produced by radiation damage is discussed. The physical basis for the positron annihilation techniques (lifetime, Doppler broadening, angular correlation) is introduced and the techniques briefly described. Some examples of the application of PAS to radiation damage analysis are presented with a view toward elucidating the particular advantages of PAS over more traditional defect characterization techniques

  12. Desorption of surface positrons: A source of free positronium at thermal velocities

    International Nuclear Information System (INIS)

    Mills, A.P. Jr.; Pfeiffer, L.

    1979-01-01

    A direct measurement is reported of the velocity of positronium (Ps) ejected into a vacuum when 0- to 100-eV positrons (e + ) strike a negatively biased Cu(111) surface. At 30 0 C, about half the e + form Ps with normal energy component E-bar=3.4(3) eV. At 790 0 C, most of the remaining e + form Ps but with E-bar=0.14(1) eV, and a non-Maxwellian thermal distribution. We infer that surface-bound e + are thermally desorbed to form the extra Ps. These low Ps velocities suggest exciting possibilities for experiments on free Ps

  13. Experimental considerations for testing antimatter antigravity using positronium 1S-2S spectroscopy

    Science.gov (United States)

    Crivelli, P.; Cooke, D. A.; Friedreich, S.

    2014-05-01

    In this contribution to the WAG 2013 workshop we report on the status of our measurement of the 1S-2S transition frequency of positronium. The aim of this experiment is to reach a precision of 0.5 ppb in order to cross check the QED calculations. After reviewing the current available sources of Ps, we consider laser cooling as a route to push the precision in the measurement down to 0.1 ppb. If such an uncertainty could be achieved, this would be sensitive to the gravitational redshift and therefore be able to assess the sign of gravity for antimatter.

  14. Quantum Entanglement and Shannon Information Entropy for the Doubly Excited Resonance State in Positronium Negative Ion

    Directory of Open Access Journals (Sweden)

    Chien-Hao Lin

    2015-09-01

    Full Text Available In the present work, we report an investigation on quantum entanglement in the doubly excited 2s2 1Se resonance state of the positronium negative ion by using highly correlated Hylleraas type wave functions, determined by calculation of the density of resonance states with the stabilization method. Once the resonance wave function is obtained, the spatial (electron-electron orbital entanglement entropies (von Neumann and linear can be quantified using the Schmidt decomposition method. Furthermore, Shannon entropy in position space, a measure for localization (or delocalization for such a doubly excited state, is also calculated.

  15. The formation and quenching of positronium in solution: some theoretical and experimental studies

    International Nuclear Information System (INIS)

    Beling, C.D.

    1981-05-01

    Reviews are made of the present theoretical knowledge of the formation and quenching of positronium in solution. Formation is described on both the Ore model and the spur model. Quenching via pickoff and chemical processes is considered. The uncertainties that are presently found in the theoretical modelling are considered. Experimentally the positron lifetime technique is used in which positrons are emitted from a vitrified 22 Na source. The lifetime spectrum is obtained conventionally and is analysed by a modified form of the program POSITRONFIT EXTENDED. (author)

  16. First search for invisible decays of ortho-positronium confined in a vacuum cavity

    OpenAIRE

    Vigo, C.; Gerchow, L.; Liszkay, L.; Rubbia, A.; Crivelli, P.

    2018-01-01

    The experimental setup and results of the first search for invisible decays of ortho-positronium (o-Ps) confined in a vacuum cavity are reported. No evidence of invisible decays at a level $\\text{Br}\\left(\\text{o-Ps}\\to\\text{invisible}\\right) < 5.9\\times 10^{-4}$ (90% C. L.) was found. This decay channel is predicted in Hidden Sector models such as the Mirror Matter (MM), which could be a candidate for Dark Matter. Analyzed within the MM context, this result provides an upper limit on the kin...

  17. Study of the electron-positron annihilation in the galactic center region with the Integral/SPI spectrometer

    International Nuclear Information System (INIS)

    Sizun, P.

    2007-04-01

    A spectral feature was detected in 1970 in the gamma-ray emission from the central regions of the Milky Way, during balloon flight observations. Located near 511 keV, this feature was soon attributed to the gamma-ray line tracing the annihilation of electrons with their anti-particles, positrons. However, none of the multiple astrophysical scenarios contemplated to explain the production of positrons in the Galactic bulge has been able to reproduce the high injection rate deduced from the flux of the 511 keV line, close to 10 43 positrons per second. Launched in 2002, the European gamma-ray satellite INTEGRAL was provided with a spectrometer, SPI, whose unprecedented imaging and spectral capabilities in this energy range enable us to further study the source of the 511 keV line detected in the Galactic centre region. Indeed, a better determination of the spatial extent of the source, the intrinsic width of the line and the fraction of positrons annihilating in-flight, directly or via the formation of ortho-Positronium atoms would improve our knowledge of both the annihilation medium and the initial source of positrons, and could allow us to discriminate between the various explanatory scenarios. The first part of this thesis deals with a key ingredient in the extraction of the annihilation spectrum: the optimization of the instrumental background model. New data screening and tracer selection procedures are presented. Classical multi-linear models are compared to neural and Bayesian networks. Finally, three years of observation are used to constrain the width of the source and derive its spectrum. The second part of the thesis focuses on one of the possible scenarios explaining the high positron injection rate deduced from the flux of the 511 keV line: the annihilation of light dark matter particles into electron-positron pairs. The various radiation mechanisms involved are modeled and confronted to observations in order to set an upper limit on the injection

  18. 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

  19. 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

  20. Acne polimorfo: tratamiento con Implacen

    Directory of Open Access Journals (Sweden)

    Rubén Pérez Armas

    1995-06-01

    Full Text Available Se realiza el estudio de 40 pacientes con acné polimorfo, los que fueron atendidos en la Consulta de Dermatología del Hospital Provincial Clinicoquirúrgico Docente "Celia Sánchez Manduley", en el período comprendido de enero de 1988 a diciembre de 1989. Se revisa la literatura médica sobre los diversos métodos y medicamentos utilizados en la terapéutica de esta dermatosis. Se describe el esquema de tratamiento empleado con implacén en 30 pacientes; los 10 restantes se trataron con placebo; se compara dicho esquema con los tradicionales y se observan mejores resultados con nuestro estudio. Se destaca la ausencia de recaídas, así como el resultado del tratamiento de acuerdo con el sexo.A study was performed in 40 patients presenting with polymorphic acne who were attended in the Dermatology Department of "Celia Sánchez Manduley" Clinicosurgical and Teaching Hospital from January, 1988 to December, 1989. A review of the literature was made seeking for the different methods and drugs used for the treatment of this dermatosis. The treatment schedule with the use of implacen in 30 patients is described. Such therapeutic schedule was compared with traditional ones and better results were observed with the use of implacen. The fact that there were no relapses is highlighted, as well as the result of treatment according to sex.

  1. Tratamiento del paciente con artrosis

    Directory of Open Access Journals (Sweden)

    Francisco Vargas Negrín

    2014-01-01

    Full Text Available El manejo terapéutico del paciente con artrosis tiene como objetivo disminuir la sintomatología dolorosa e inflamatoria, mejorar la capacidad funcional del paciente y la aplicación de intervenciones terapéuticas eficaces y lo más seguras posibles. Un enfoque centrado en el paciente implica su participación activa en el diseño del plan terapéutico y en la toma de decisiones informadas oportunas en todas las etapas de la enfermedad. La educación terapéutica, la actividad física y el ejercicio terapéutico junto con el control de peso, en caso de sobrepeso u obesidad, constituyen el núcleo central del tratamiento. Los autocuidados individuales y por los familiares son fundamentales en el control del día a día del paciente. El uso de terapias físicas, ayudas técnicas (bastón, etc. y de fármacos tipo analgésicos simples, opioides y antiinflamatorios tiene evidencias demostradas en el control del dolor, mejora la funcionalidad y la calidad de vida del paciente y una clara recomendación de uso en el tratamiento de la artrosis. La cirugía conservadora y la de reemplazo articular se indican en los casos en los que no se logran los objetivos terapéuticos en casos concretos.

  2. Light dark matter through assisted annihilation

    International Nuclear Information System (INIS)

    Dey, Ujjal Kumar; Maity, Tarak Nath; Ray, Tirtha Sankar

    2017-01-01

    In this paper we investigate light dark matter scenarios where annihilation to Standard Model particles at tree-level is kinematically forbidden. In such cases annihilation can be aided by massive Standard Model-like species, called assisters , in the initial state that enhances the available phase space opening up novel tree-level processes. We investigate the feasibility of such non-standard assisted annihilation processes to reproduce the observed relic density of dark matter. We present a simple scalar dark matter-scalar assister model where this is realised. We find that if the dark matter and assister are relatively degenerate the required relic density can be achieved for a keV-MeV scale dark matter. We briefly discuss the cosmological constraints on such dark matter scenarios.

  3. Positron Annihilation Characteristics in Polymer Composites

    International Nuclear Information System (INIS)

    Ashry, A.; Hemdan, M.; Ismail, A.; Ismail, H.; Osman, H.

    2000-01-01

    The effect of incorporation of GPF-carbon black on the free volume properties as well as the Doppler broadening parameters has been investigated for Natural rubber/Styrene Butadiene rubber (NR/SBR) blends. It is seen that, the free volume decreases with increasing of the GPF-black. Besides, as the size of the free volume decreases, the W-parameter, which corresponds to high momentum region, decreases and the S-parameter, which corresponds to low momentum one, shows an opposite behaviour. Furthermore, the d.c.electrical conductivity, mechanical and swelling behavior have been also investigated. Positron Annihilation Lifetime (PAL) and Doppler Broadening of the Annihilation Radiation (DBAR) results are compared with the other physical parameters measured. The analysis of positron annihilation parameters introduces a trusted support for the interpretations of the other macroscopic physical properties

  4. 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......-field approach. The production bias approach, on the other hand, is based on the physical features of the cascade damage and is therefore considered to be more appropriate for describing the damage accumulation under cascade damage conditions. However, production bias can not produce high a swelling rate when....... 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....

  5. Surface investigations by means of positrons annihilation

    International Nuclear Information System (INIS)

    Dryzek, J.; Stegemann, T.; Cleff, B.

    1996-01-01

    The aim of the report is a presentation of the positron annihilation studies performed on the Cu samples that surface was exposed to the friction and wear processes. Using the measurement of Doppler broadening of annihilation line, we were able to detect the profile of vacancies in the top layers of the defected metals. It was established that one could describe the profile by a simple exponential function of the depth in all cases. The range of vacancies concentration depth depends on the load, time and the speed of the defects creation processes on the surface of a sample. The outline of the positron annihilation method is also given. (author). 10 refs, 16 figs, 5 tabs

  6. Positron annihilation and perturbed angular correlation studies of radiation damage

    International Nuclear Information System (INIS)

    Zhu Jiazheng; Li Anli; Xu Yongjun; Wang Zhiqiang; Zhou Dongmei; Zheng Yongnan; Zhu Shengyun; Iwata, T.

    2002-01-01

    The positron annihilation and perturbed angular correlation techniques have been employed to study radiation damage in Si and Nb. The results obtained by the positron annihilation are consistent with those given by the perturbed angular correlation

  7. 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.)

  8. 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)

  9. Studies of glasses by positron annihilation

    International Nuclear Information System (INIS)

    Brauer, G.; Boden, G.

    1981-04-01

    Investigations of silica glasses, pyrocerams and metallic glasses by positron annihilation (lifetime, Doppler broadening) are presented. The measurements on silica glasses showed, that silica glass fused from naturally occuring quartz exhibits a higher order than that one produced from SiCl 4 . Furthermore it was found that the order of silica glasses increases after heat treatment above 900 0 C. Thus the X-amorphous state of silica glasses could be characterized by positron annihilation what is impossible at present by diffraction methods. (author)

  10. PREFACE: 11th International Workshop on Positron and Positronium Chemistry (PPC-11)

    Science.gov (United States)

    Pujari, P. K.; Sudarshan, K.; Dutta, D.

    2015-06-01

    The International Workshop on Positron and Positronium Chemistry (PPC) is a prestigious triennial conference series with a rich history. The 11th meeting in the series (PPC-11) was held at Cidade de Goa, Goa, India during 9-14, November, 2014. It was organized by Bhabha Atomic Research Centre (BARC), Mumbai. The co-organizers were Saha Institute of Nuclear Physics (SINP), Kolkata, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam and Indian Association of Nuclear Chemists and Allied Scientists (IANCAS), Mumbai. PPC-11 attracted participants both from academic institutions and industries. About 120 participants from 20 countries representing all continents participated in the conference. The conference continued the tradition of excellence in terms of quality of presentations and discussions. There were 33 plenary and invited talks, 39 oral presentations and 40 posters. The conference stood true to its multidisciplinary tag with papers presented in the fields of fundamentals of positron and positronium chemistry, applications in polymers, porous materials, metals/alloys, studies in liquids, biological applications as well as developments in theory and experimental techniques. The enthusiastic participation of senior researchers and young students made the scientific program a grand success. In order to encourage the student participants (twenty) and promote excellence, a committee of senior members evaluated their presentations and the top three contributions were awarded. The positron and positronium community paid homage to the memory of late Profs. J. Kristiak and A.T. Stewart. A brief sketch of their life and work was presented by Profs. Jan Kuriplach and Toshio Hyodo, respectively. All the papers published in these proceedings have been peer reviewed by the participants of PPC-11. Editors thank all the reviewers for sparing their valuable time and helping us in bringing out the proceedings with 43 contributed articles in the scheduled time. We are

  11. Positron annihilation in metallic glasses - a general survey

    International Nuclear Information System (INIS)

    Brauer, G.; Kajcsos, Zs.; Kemeny, T.

    1981-08-01

    This report presents a review of the literature on positron annihilation studies concerning metallic glasses. After some general information and overview on structural models of metallic glasses as well as a short description of the positron annihilation method itself are added. Conclusions regarding information on the structure of metallic glasses obtainable by positron annihilation are also given. (author)

  12. Annihilation probability density and other applications of the Schwinger multichannel method to the positron and electron scattering; Densidade de probabilidade de aniquilacao e outras aplicacoes do metodo multicanal de Schwinger ao espalhamento de positrons e eletrons

    Energy Technology Data Exchange (ETDEWEB)

    Varella, Marcio Teixeira do Nascimento

    2001-12-15

    We have calculated annihilation probability densities (APD) for positron collisions against He atom and H{sub 2} molecule. It was found that direct annihilation prevails at low energies, while annihilation following virtual positronium (Ps) formation is the dominant mechanism at higher energies. In room-temperature collisions (10{sup -2} eV) the APD spread over a considerable extension, being quite similar to the electronic densities of the targets. The capture of the positron in an electronic Feshbach resonance strongly enhanced the annihilation rate in e{sup +}-H{sub 2} collisions. We also discuss strategies to improve the calculation of the annihilation parameter (Z{sub eff} ), after debugging the computational codes of the Schwinger Multichannel Method (SMC). Finally, we consider the inclusion of the Ps formation channel in the SMC and show that effective configurations (pseudo eigenstates of the Hamiltonian of the collision ) are able to significantly reduce the computational effort in positron scattering calculations. Cross sections for electron scattering by polyatomic molecules were obtained in three different approximations: static-exchange (SE); tatic-exchange-plus-polarization (SEP); and multichannel coupling. The calculations for polar targets were improved through the rotational resolution of scattering amplitudes in which the SMC was combined with the first Born approximation (FBA). In general, elastic cross sections (SE and SEP approximations) showed good agreement with available experimental data for several targets. Multichannel calculations for e{sup -} -H{sub 2}O scattering, on the other hand, presented spurious structures at the electronic excitation thresholds (author)

  13. Evidence of two-channel distortion effects in positronium formation reactions

    International Nuclear Information System (INIS)

    Macri, P A; Miraglia, J E; Hanssen, J; Fojon, O A; Rivarola, R D

    2004-01-01

    The formation of ground-state positronium in collisions of positrons on hydrogen-like atoms is considered. In previous theoretical works, two-centre distorted wavefunctions were employed to approximate either the initial or the final channel. Here we report results obtained by means of the eikonal final state continuum distorted wave approximation for which asymptotically correct distorted wavefunctions are used for both the initial and final states of the scattering system. Comparison of the present theoretical total cross sections with experimental data reveals that distortion effects become important in both channels as the impact energy decreases. This work also shows that distorted-wave theories may be extended from their usual domain of high impact energies to lower ones. (letter to the editor)

  14. The positronium and the dipositronium in a Hartree-Fock approximation of quantum electrodynamics

    Science.gov (United States)

    Sok, Jérémy

    2016-02-01

    The Bogoliubov-Dirac-Fock (BDF) model is a no-photon approximation of quantum electrodynamics. It allows to study relativistic electrons in interaction with the Dirac sea. A state is fully characterized by its one-body density matrix, an infinite rank non-negative projector. We prove the existence of the para-positronium, the bound state of an electron and a positron with antiparallel spins, in the BDF model represented by a critical point of the energy functional in the absence of an external field. We also prove the existence of the dipositronium, a molecule made of two electrons and two positrons that also appears as a critical point. More generally, for any half integer j ∈ 1/2 + Z + , we prove the existence of a critical point of the energy functional made of 2j + 1 electrons and 2j + 1 positrons.

  15. Free-volume study of ethylene - vinyl alcohol copolymer evaluated through positronium lifetime measurement

    International Nuclear Information System (INIS)

    Ito, K.; Hong-ling Li; Ujihira, Y.; Nomura, K.; Saito, Y.; Yamamoto, T.; Nishihara, Y.

    2003-01-01

    The free-volume, of size ranging from 0.2 to 0.4 nm in radius, in an ethylene-vinyl alcohol copolymer was estimated using positronium lifetime measurement to elucidate the dependence of oxygen permeability on the free-volume size and fraction, on the ethylene content and on the crystallinity. The permeability and the free-volume fraction with varying the ethylene content were well related and the relation was interpreted based on the free-volume theory near below and above the glass transition temperature. On the other hand, the crystallinity significantly influenced the fraction of the amorphous region, where the free-volume hole exists, along with a slight change of the free-volume size. The variation of the permeability with the crystalline degree cannot be explained from the averaged free-volume fraction estimated by the whole volume of the polymer, but the permeability correlated with the free-volume size apparently. (author)

  16. Evidence of two-channel distortion effects in positronium formation reactions

    Energy Technology Data Exchange (ETDEWEB)

    Macri, P A [Instituto de AstronomIa y FIsica del Espacio, Consejo Nacional de Investigaciones CientIficas y Tecnicas-Universidad de Buenos Aires, Casilla de Correo 67, Suc. 28, 1428 Buenos Aires (Argentina); Miraglia, J E [Instituto de AstronomIa y FIsica del Espacio, Consejo Nacional de Investigaciones CientIficas y Tecnicas-Universidad de Buenos Aires, Casilla de Correo 67, Suc. 28, 1428 Buenos Aires (Argentina); Hanssen, J [Laboratoire de Physique Moleculaire et des Collisions, Institute de Physique Rue Arago, Tecnopole 2000, Metz (France); Fojon, O A [Instituto de FIsica de Rosario, Consejo Nacional de Investigaciones CientIficas y Tecnicas-Universidad Nacional de Rosario, Av. Pellegrini 250, 2000 Rosario (Argentina); Rivarola, R D [Instituto de FIsica de Rosario, Consejo Nacional de Investigaciones CientIficas y Tecnicas-Universidad Nacional de Rosario, Av. Pellegrini 250, 2000 Rosario (Argentina)

    2004-03-28

    The formation of ground-state positronium in collisions of positrons on hydrogen-like atoms is considered. In previous theoretical works, two-centre distorted wavefunctions were employed to approximate either the initial or the final channel. Here we report results obtained by means of the eikonal final state continuum distorted wave approximation for which asymptotically correct distorted wavefunctions are used for both the initial and final states of the scattering system. Comparison of the present theoretical total cross sections with experimental data reveals that distortion effects become important in both channels as the impact energy decreases. This work also shows that distorted-wave theories may be extended from their usual domain of high impact energies to lower ones. (letter to the editor)

  17. Further Examination of a Simplified Model for Positronium-Helium Scattering

    Science.gov (United States)

    DiRienzi, J.; Drachman, Richard J.

    2012-01-01

    While carrying out investigations on Ps-He scattering we realized that it would be possible to improve the results of a previous work on zero-energy scattering of ortho-positronium by helium atoms. The previous work used a model to account for exchange and also attempted to include the effect of short-range Coulomb interactions in the close-coupling approximation. The 3 terms that were then included did not produce a well-converged result but served to give some justification to the model. Now we improve the calculation by using a simple variational wave function, and derive a much better value of the scattering length. The new result is compared with other computed values, and when an approximate correction due to the van der Waals potential is included the total is consistent with an earlier conjecture.

  18. Excited-state positronium formation from positron--atomic-hydrogen collisions

    International Nuclear Information System (INIS)

    Mandal, C.R.; Mandal, M.; Mukherjee, S.C.

    1991-01-01

    Positronium formation into ground and n=2 levels has been studied in collisions of positrons with atomic hydrogen in the framework of an approximation called the boundary-corrected continuum-intermediate-state (BCCIS) approximation in the energy range of 0.08--2 keV. The conventional continuum-intermediate-state approximation does not satisfy the correct boundary condition. It has been shown that, with a suitable choice of the distorting potential, the boundary condition may be satisfied with a proper account of the intermediate continuum states. It has also been shown that the BCCIS approximation leads to the same transition amplitude as may be derived using the Vainshtein-Presnyakov-Sobelman approximation. The results obtained here are found to be in good agreement when compared with other theoretical results

  19. Evidence from n=2 fine structure transitions for the production of fast excited state positronium

    International Nuclear Information System (INIS)

    Ley, R.; Niebling, K.D.; Schwarz, R.; Werth, G.

    1990-01-01

    Fine structure transitions in the first excited state of positronium (Ps) have been measured using 'Backscatter Ps' production on a Mo surface by observation of a change in the emitted Lyman-α intensity under resonant microwave irradiation. Production, fine structure transitions and Lyman-α decay of the Ps atoms took place inside a waveguide designed to transmit the microwave frequencies of 8.6, 13.0 and 18.5 GHz for the transitions from the 2 3 S 1 state to the 2 3 P J , J=2, 1, 0, states, respectively. In the presence of a magnetic field, all transitions observed show a shift to higher frequencies, compared with earlier calculations and measurements in zero magnetic field. The deviations exceed the expected Zeeman shift significantly but may be explained by assuming a motional Stark effect for Ps with kinetic energies of several eV. (author)

  20. Development of a positronium atom diagnostic beam to study transport in tokamaks

    International Nuclear Information System (INIS)

    Surko, C.M.

    1992-01-01

    Anomalous transport is probably the key physics issue in magnetic confinement fusion. It severely limits our ability to create and maintain a dense, hot, fusion plasma. There is also good evidence that there is a fundamental lack of understanding in this area, namely the transport of particles and energy induced by waves and fluctuations in magnetically confined plasmas. The positronium atom beam diagnostic, if successful, can provide a qualitatively new and different way of studying transport in tokamak fusion plasmas. The use of the positron as a thermalized, electron-mass test particle will allow important new tests of current theories of plasma transport. In particular, it could provide unique insights into the potential role of magnetic fluctuations in producing anomalous transport. This is particularly significant in that, at present, there is essentially no in situ probe of these fluctuations or the transport which they produce. Some results of this study are summarized

  1. On the mobility of delocalized and self-trapped positronium states in ionic crystals

    CERN Document Server

    Bondarev, I V

    2003-01-01

    The temperature dependence of the diffusivity is studied for delocalized and self-trapped positronium (Ps) atoms in ionic crystals. Detailed calculations taking into account low-temperature and inelastic scattering corrections and a Ps scattering form-factor have been performed for delocalized Ps. Low-temperature and inelastic corrections to the delocalized Ps diffusivity are shown to be essential below several tens of K, while the form-factor contribution is negligibly small up to thousand K. The mobility of self-trapped Ps is analyzed within the framework of a small polaron approach. The hopping contribution to the self-trapped Ps diffusivity is shown to be adiabatic in its physical nature. The tunnel contribution is in general not small and may turn out to be dominating even at very high temperatures. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

  2. Reasons for the deviation of I1/I3 and τ1 from the expected lifetime parameters of positronium annihilation in polymers

    International Nuclear Information System (INIS)

    Dlubek, G.; Eichler, S.; Huebner, Ch.; Nagel, Ch.

    1999-01-01

    High quality positron lifetime spectra were taken for several amorphous polymers. The spectra were analysed using the routine MELT which assumes continuous lifetime distributions, as well as the discrete-term analysis routine LIFSPECFIT. Disagreements between the analysed lifetime parameters and theoretical expectations, I 1 /I 3 > I p-Ps /I o-Ps =1/3 and τ 1 >τ p-Ps , which are well known, also appear in our results. The disagreements are distinctly larger using a discrete-term routine than when applying MELT (or CONTIN). From the analysis of computer-generated spectra, we found that these disagreements may be well understood by assuming a distribution of e + lifetimes in addition to an o-Ps lifetime distribution, both of which can occur as consequence of size and shape distributions of free-volume holes in amorphous polymers (or of bubbles in molecular liquids). The disagreements appear to be due to the inability of the routines correctly to mirror very broad lifetime distributions. For broad distributions, MELT (and also CONTIN) delivers, as an artefact of the spectrum analysis, a distribution consisting of two narrow subpeaks instead of a single broad one. The lower subpeak of the e + lifetime distribution may mix with the p-Ps lifetime component resulting in artificially large values for τ 1 and I 1 . That is the reason for the unphysical increase of τ 1 and I 1 with decreasing I 3 observed in the analysed parameters of simulated as well as experimental spectra

  3. Reasons for the deviation of I1/I3 and τ1 from the expected lifetime parameters of positronium annihilation in polymers

    International Nuclear Information System (INIS)

    Dlubek, G.; Eichler, S.; Huebner, C.; Nagel, C.

    1999-01-01

    High quality positron lifetime spectra were taken for several amorphous polymers. The spectra were analysed using the routine MELT which assumes continuous lifetime distributions, as well as the discrete-term analysis routine LIFSPECFIT. Disagreements between the analysed lifetime parameters and theoretical expectations, I 1 /I 3 I p-Ps /I o-Ps =3D1/3 and τ 1 τ p-Ps , which are well known, also appear in our results. The disagreements are distinctly larger using a discrete-term routine than when applying MELT (or CONTIN). From the analysis of computer-generated spectra, we found that these disagreements may be well understood by assuming a distribution of e + lifetimes in addition to an o-Ps lifetime distribution, both of which can occur as consequence of size and shape distributions of free-volume holes in amorphous polymers (or of bubbles in molecular liquids). The disagreements appear to be due to the inability of the routines correctly to mirror very broad lifetime distributions. For broad distributions, MELT (and also CONTIN) delivers, as an artefact of the spectrum analysis, a distribution consisting of two narrow subpeaks instead of a single broad one. The lower subpeak of the e + lifetime distribution may mix with the p-Ps lifetime component resulting in artificially large values for τ 1 and I 1 . That is the reason for the unphysical increase of τ 1 and I 1 with decreasing I 3 observed in the analysed parameters of simulated as well as experimental spectra. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  4. PAES: Positron annihilation induced Auger electron spectrometer

    OpenAIRE

    Hugenschmidt, Christoph

    2015-01-01

    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.

  5. Radiation damage analysis by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Siegel, R.W.

    1982-01-01

    Positron annihilation spectroscopy (PAS) has in recent years become a valuable new tool for investigating defects in metals. The ability of the positron to localize in a trapped state at various defect sites, in which the positron annihilates with unique characteristics, has enabled the positron to be used as a localized probe of these defect sites. Several reviews of the application of PAS to the study of defects in metals have been published, as have more general treatises on the applications of positron annihilation to the study of solids. PAS has made, and has considerably greater potential for, a significant contribution to radiation damage analysis in two areas of importance: (1) the determination of atomic-defect properties, a knowledge of which is necessary for the modeling required to couple the results of model experiments using electron and ion irradiation with the expected irradiation conditions of reactor systems, and (2) the monitoring and characterization of irradiation-induced microstructure development. A unique aspect of PAS for radiation damage analysis is the defect specificity of the annihilation characteristics of a trapped positron. In addition to its value as an independent analytical tool, PAS can be a useful complement to more traditional techniques for defect studies

  6. 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.

  7. Positron annihilation studies on high temperature superconductors

    International Nuclear Information System (INIS)

    Sundar, C.S.; Bharathi, A.

    1991-01-01

    The results of positron annihilation measurements as a function of temperature, across Tc, in a variety of high temperature superconductors such as Y-Ba-Cu-O (Y1237), Y-Ba-Cu-O (Y1248), Bi-Sr-Ca-Cu-O, Tl-Ba-Ca-Cu-O, Ba-K-Bi-O and Nd-Ce-Cu-O are presented. It is shown that the variation of annihilation parameters in the superconducting state is correlated with the diposition of the positron density distribution with respect to the superconducting CuO planes. An increase in positron lifetime is observed below Tc when the positrons probe the CuO planes whereas a decrease in lifetime is observed when the positron density overlaps predominantly with the apical oxygen atom. With this correlation, the different temperature variation of annihilation parameters, seen in the various high temperature superconductors, is understood in terms of a local charge transfer from the planar oxygen atom to the apical oxygen atom. The significance of these results in the context of various theoretical models of high temperature superconductivity is discussed. In addition, the application of positron annihilation spectroscopy to the study of oxygen defects in the Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O and Nd-Ce-Cu-O is presented. (author). 53 refs., 17 figs., 2 tabs

  8. Antihydrogen annihilation reconstruction with the ALPHA silicon detector

    CERN Document Server

    Andresen, G B; Bertsche, W; Bowe, P D; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Deller, A; Eriksson, S; Fajans, J; Friesen, T; Fujiwara, M C; Gill, D.R; Gutierrez, A; Hangst, J S; Hardy, W N; Hayden, M E; Hayano, R S; Humphries, A J; Hydomako, R; Jonsell, S; Jorgensen, L V; Kurchaninov, L; Madsen, N; Menary, S; Nolan, P; Olchanski, K; Olin, A; Povilus, A; Pusa, P; Sarid, E; Seif el Nasr, S; Silveira, D M; So, C; Storey, J W; Thompson, R I; van der Werf, D P; Yamazaki, Y

    2012-01-01

    The ALPHA experiment has succeeded in trapping antihydrogen, a major milestone on the road to spectroscopic comparisons of antihydrogen with hydrogen. An annihilation vertex detector, which determines the time and position of antiproton annihilations, has been central to this achievement. This detector, an array of double-sided silicon microstrip detector modules arranged in three concentric cylindrical tiers, is sensitive to the passage of charged particles resulting from antiproton annihilation. This article describes the method used to reconstruct the annihilation location and to distinguish the annihilation signal from the cosmic ray background. Recent experimental results using this detector are outlined.

  9. Antihydrogen annihilation reconstruction with the ALPHA silicon detector

    Energy Technology Data Exchange (ETDEWEB)

    Andresen, G.B. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Ashkezari, M.D. [Department of Physics, Simon Fraser University, Burnaby, BC, Canada V5A 1S6 (Canada); Bertsche, W. [Department of Physics, Swansea University, Swansea SA2 8PP (United Kingdom); Bowe, P.D. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Butler, E. [European Laboratory for Particle Physics, CERN, CH-1211 Geneva 23 (Switzerland); Cesar, C.L. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-972 (Brazil); Chapman, S. [Department of Physics, University of California, Berkeley, CA 94720-7300 (United States); Charlton, M.; Deller, A.; Eriksson, S. [Department of Physics, Swansea University, Swansea SA2 8PP (United Kingdom); Fajans, J. [Department of Physics, University of California, Berkeley, CA 94720-7300 (United States); Friesen, T. [Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada T2N 1N4 (Canada); Fujiwara, M.C. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, Canada V6T 2A3 (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada T2N 1N4 (Canada); Gill, D.R. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, Canada V6T 2A3 (Canada); Gutierrez, A. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 (Canada); Hangst, J.S. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Hardy, W.N. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 (Canada); Hayden, M.E. [Department of Physics, Simon Fraser University, Burnaby, BC, Canada V5A 1S6 (Canada); Hayano, R.S. [Department of Physics, University of Tokyo, Tokyo 113-0033 (Japan); Humphries, A.J. [Department of Physics, Swansea University, Swansea SA2 8PP (United Kingdom); and others

    2012-08-21

    The ALPHA experiment has succeeded in trapping antihydrogen, a major milestone on the road to spectroscopic comparisons of antihydrogen with hydrogen. An annihilation vertex detector, which determines the time and position of antiproton annihilations, has been central to this achievement. This detector, an array of double-sided silicon microstrip detector modules arranged in three concentric cylindrical tiers, is sensitive to the passage of charged particles resulting from antiproton annihilation. This article describes the method used to reconstruct the annihilation location and to distinguish the annihilation signal from the cosmic ray background. Recent experimental results using this detector are outlined.

  10. 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.

  11. 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.

  12. Positronium formation in helium bubbles in 600 MeV proton-irradiated aluminium

    DEFF Research Database (Denmark)

    Jensen, K. O.; Eldrup, Morten Mostgaard; Singh, Bachu Narain

    1985-01-01

    Aluminium samples containing helium bubbles produced by 600 MeV proton irradiation at 430°C were investigated by positron annihilation; both lifetime and angular correlation measurements were made. The angular correlation curves contain an unusually narrow component. This component is associated...

  13. Calculation of the positronium formation differential cross section for collision of electron with anti-hydrogen atoms

    International Nuclear Information System (INIS)

    Ghanbari Adivi, E.; Kanjuri, F.; Bolorizadeh, M.

    2006-01-01

    The positronium formation differential cross sections in collision of the high-energy but non-relativistic electrons with anti-hydrogen atoms are calculated by using the three-body Faddeev-Watson-Lovelace formalism. In a second-order approximation, the inter-nuclear and nuclear-electronic partial amplitudes therein the Faddeev-Watson series are calculated, analytically, in the range of 0-180 degrees of the scattering angles. The presence of the T homas peak a t 45 d egree i s investigated. The results are discussed for 1 and 10 keV impact energies and for electron transition from anti-hydrogen ground state into the different states therein the K-, L- and M- shells of the positronium atoms.

  14. Low energy positron interactions with uracil—Total scattering, positronium formation, and differential elastic scattering cross sections

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, E. K.; Boadle, R. A.; Machacek, J. R.; Makochekanwa, C.; Sullivan, J. P. [ARC Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, The Australian National University, Canberra 0200 (Australia); Chiari, L. [ARC Centre for Antimatter-Matter Studies, Flinders University, GPO Box 2100, Adelaide, 5001 SA (Australia); Buckman, S. J., E-mail: Stephen.buckman@anu.edu.au [ARC Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, The Australian National University, Canberra 0200 (Australia); Institute of Mathematical Sciences, University of Malaya, Kuala Lumpur (Malaysia); Brunger, M. J. [ARC Centre for Antimatter-Matter Studies, Flinders University, GPO Box 2100, Adelaide, 5001 SA (Australia); Institute of Mathematical Sciences, University of Malaya, Kuala Lumpur (Malaysia); Garcia, G. [Instituto de Fısica Fundamental, Consejo Superior de Investigationes Cientıficas (CSIC), Serrano 113-bis, E-28006 Madrid (Spain); Blanco, F. [Departamento de Fısica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Ingolfsson, O. [Department of Chemistry, Science Institute, University of Iceland, Reykjavík 107 (Iceland)

    2014-07-21

    Measurements of the grand total and total positronium formation cross sections for positron scattering from uracil have been performed for energies between 1 and 180 eV, using a trap-based beam apparatus. Angular, quasi-elastic differential cross section measurements at 1, 3, 5, 10, and 20 eV are also presented and discussed. These measurements are compared to existing experimental results and theoretical calculations, including our own calculations using a variant of the independent atom approach.

  15. FISURAS LABIO PALATINAS. TRATAMIENTO MULTIDISCIPLINARIO

    Directory of Open Access Journals (Sweden)

    Dr. Luis Monasterio A.

    2016-01-01

    Full Text Available La fisura labio palatina es la segunda malformación congénita más frecuente. En su génesis hay factores genéticos (25% y ambientales siendo en general multifactorial. La incidencia en Chile es de aproximadamente 1 en 550 recién nacidos vivos. Las fisuras pueden afectar el labio a uno o ambos lados, el paladar o ambos. La evaluación genética es fundamental para descartar casos sindrómicos, siendo estos frecuentes en las fisuras asiladas de paladar (sindrome velocardiofacial, stickler. El tratamiento de esta enfermedad debe ser multidisciplinario e iniciarse en el periodo de recién nacido para garantizar los mejores resultados. El equipo debiera estar integrado por enfermera especialista, otorrinolaringólogo, odontólogos de diferentes especialidades, genetista, fonoaudióloga y cirujano plástico. Las cirugías primarias incluyen la plastia del labio(3-6 meses, plastia de velo del paladar (6 meses y el cierre de paladar óseo junto a plastia de velo (12 meses.

  16. Vector dark matter annihilation with internal bremsstrahlung

    Energy Technology Data Exchange (ETDEWEB)

    Bambhaniya, Gulab, E-mail: gulab@prl.res.in [Physical Research Laboratory, Ahmedabad 380009 (India); Kumar, Jason, E-mail: jkumar@hawaii.edu [Department of Physics & Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Marfatia, Danny, E-mail: dmarf8@hawaii.edu [Department of Physics & Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Nayak, Alekha C., E-mail: acnayak@iitk.ac.in [Department of Physics, Indian Institute of Technology, Kanpur 208016 (India); Tomar, Gaurav, E-mail: tomar@prl.res.in [Physical Research Laboratory, Ahmedabad 380009 (India)

    2017-03-10

    We consider scenarios in which the annihilation of self-conjugate spin-1 dark matter to a Standard Model fermion–antifermion final state is chirality suppressed, but where this suppression can be lifted by the emission of an additional photon via internal bremsstrahlung. We find that this scenario can only arise if the initial dark matter state is polarized, which can occur in the context of self-interacting dark matter. In particular, this is possible if the dark matter pair forms a bound state that decays to its ground state before the constituents annihilate. We show that the shape of the resulting photon spectrum is the same as for self-conjugate spin-0 and spin-1/2 dark matter, but the normalization is less heavily suppressed in the limit of heavy mediators.

  17. 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

  18. Application of positron annihilation in materials science

    International Nuclear Information System (INIS)

    Siegel, R.W.; Fluss, M.J.; Smedskjaer, L.C.

    1984-05-01

    Owing to the ability of the positron to annihilate from a variety of defect-trapped states, positron annihilation spectroscopy (PAS) has been applied increasingly to the characterization and study of defects in materials in recent years. In metals particularly, it has been demonstrated that PAS can yield defect-specific information which, by itself or in conjunction with more traditional experimental techniques, has already made a significant impact upon the determination of atomic-defect properties and the monitoring and characterization of vacancy-like microstructure development, as occurs during post-irradiation annealing. The applications of PAS are now actively expanding to the study of more complex defect-related phenomena in irradiated or deformed metals and alloys, phase transformations and structural disorder, surfaces and near-surface defect characterization. A number of these applications in materials science are reviewed and discussed with respect to profitable future directions

  19. Increased Elemental Specificity of Positron Annihilation Spectra

    International Nuclear Information System (INIS)

    Asoka-Kumar, P.; Alatalo, M.; Ghosh, V.J.; Kruseman, A.C.; Nielsen, B.; Lynn, K.G.

    1996-01-01

    Positron annihilation spectroscopy (PAS) is a sensitive probe for studying the electronic structure of defects in solids. We show that the high-momentum part of the Doppler-broadened annihilation spectra can be used to distinguish different elements. This is achieved by using a new two-detector coincidence system to examine the line shape variations originating from high-momentum core electrons. Because the core electrons retain their atomic character even when atoms form a solid, these results can be directly compared to simple theoretical predictions. The new approach adds increased elemental specificity to the PAS technique, and is useful in studying the elemental variations around a defect site. copyright 1996 The American Physical Society

  20. Radiative annihilation and isospin mixing in protonium

    International Nuclear Information System (INIS)

    Gutsche, T.; Faessler, A.; Vinh Mau, R.

    1999-01-01

    In recent experiments by the Crystal Barrel collaboration at CERN, a systematic study of reactions of the type p-bar p → γX where X γ,π 0 ,η , ω and η' were performed and the branching ratios are measured. Thereby, a sensitive test for different NN interaction models in the p-bar p atom can be performed. We evaluate the branching ratio for radiative proton-antiproton annihilation in the framework of the constituent quark model. In setting up the annihilation mechanism we adopt a two-step process where the p-bar p system first annihilates into two mesons π 0 ρ, π 0 ω, ωω, ρ 0 ρ 0 , ωρ 0 , ηρ, ηω and where the produced vector meson converts into a photon analogous to the vector dominance model (VDM). Both steps can be derived from the underlying quark mechanism. Amplitudes for the strong annihilation of p-bar p into two mesons are calculated in the framework of the so-called A 2 quark model. Radiative decay channels, in contrast to nonstrange mesonic decay channels, couple to the isospin I = 0 and I = 1 components of the atomic p-bar p initial states. The resulting transition amplitudes interfere in the predictions for the branching ratios. Combining experimental inputs with the outlined theoretical derivation we are able to extract the interference terms from the data, which are sizable and depend strongly on the initial atomic state considered. The interference terms are used to determine the isospin mixing effects in the p-bar p atomic wave functions. Radiative decays offer a unique window to study isospin mixing effects in the p-bar p system, which are strongly dependent on the NN-bar initial state interaction model. (authors)

  1. Positron annihilation studies in lysozyme and catalase

    International Nuclear Information System (INIS)

    Rohilla, Y.; Singh, K.P.; Roy Choudhury, S.; Jain, P.C.

    1992-01-01

    Positron annihilation studies have been carried out in two enzymes, lysozyme and catalase. Temperature dependence of the positron lifetimes in these two enzymes has been investigated. The results explained in terms of the free volume model and fluctuations between different conformational micro states of enzyme structures provide a new insight into the mechanism of bio-activity of these enzymes. (author). 15 refs., 4 figs

  2. Baryon production in e+e- annihilation

    International Nuclear Information System (INIS)

    Saxon, D.H.

    1988-11-01

    The phenomenology of baryon production in high energy e + e - annihilation is described. Much can be understood in terms of mass effects. Comparisons with the rates for different flavours and spins, with momentum and transverse momentum spectra and with particle correlations are used to confront models. Diquark models give good descriptions, except for the on/off Υ(1s) rates. Areas for experimental and theoretical development are indicated. (author)

  3. 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)

  4. 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).

  5. Temperature Dependence of the Inhibition of Positronium by Chlorine- Substituted Hydrocarbons in Non-Polar Liquids

    DEFF Research Database (Denmark)

    Wikander, G.; Mogensen, O.E.; Pedersen, Niels Jørgen

    1984-01-01

    Positron annihilation lifetime spectra were measured for solutions of 1,2,3,5-C6H2Cl4 in hexane, toluene, m-xylene and mesitylene, CCl4 in hexane and toluene, and C2HCl3 in n-hexane for concentrations below 1 M and at various temperatures between −30°C and 67°C. The Ps inhibition by C6H2Cl4 was r...

  6. Antiproton-helium annihilation around 45 MeV/c

    International Nuclear Information System (INIS)

    Balestra, F.; Bassolasco, S.; Bussa, M.P.; Busso, L.; Ferrero, L.; Panzieri, D.; Piragino, G.; Tosello, F.; Barbieri, R.; Bendiscioli, G.; Filippini, V.; Rotondi, A.; Salvini, P.; Zenoni, A.; Batusov, Yu.A.; Falomkin, I.V.; Pontecorvo, G.B.; Rozhdestvensky, A.M.; Sapozhnikov, M.G.; Tretyak, V.I.; Breivik, F.O.; Jacobsen, T.; Soerensen, S.O.

    1989-01-01

    The anti p 4 He annihilation cross section averaged over the interval 40-50 MeV/c has been measured using a streamer chamber in a magnetic field. The measured value is 1342±250 mb. It agrees with a behaviour like 1/p of the annihilation cross section. Our result has been obtained at the lowest momentum achieved till now in measurements of antiproton annihilation in flight. (orig.)

  7. Antiproton-helium annihilation around 45 MeV/c

    Energy Technology Data Exchange (ETDEWEB)

    Balestra, F.; Bassolasco, S.; Bussa, M.P.; Busso, L.; Ferrero, L.; Panzieri, D.; Piragino, G.; Tosello, F. (Turin Univ. (Italy). Ist. di Fisica Generale; Istituto Nazionale di Fisica Nucleare, Turin (Italy)); Barbieri, R.; Bendiscioli, G.; Filippini, V.; Rotondi, A.; Salvini, P.; Zenoni, A. (Pavia Univ. (Italy). Dipt. di Fisica Nucleare e Teorica; Istituto Nazionale di Fisica Nucleare, Pavia (Italy)); Batusov, Yu.A.; Falomkin, I.V.; Pontecorvo, G.B.; Rozhdestvensky, A.M.; Sapozhnikov, M.G.; Tretyak, V.I. (Joint Inst. for Nuclear Research, Dubna (USSR)); Breivik, F.O.; Jacobsen, T.; Soerensen, S.O. (Oslo Univ. (Norway). Fysisk Inst.); Guaraldo, C.; Maggiora, A. (Istituto Nazionale di Fisica Nucleare, Frascati (Italy). Lab. Nazionale di Frascati); Haatuft, A.; Halsteinslid, A.; Myklebost, K.; Olsen, J.M. (Bergen Univ. (Norway). Dept. of Physics); Lodi Rizzini, E. (Brescia Univ. (Italy). Dipt. di Automazione Industriale); Masala, M. (Brescia Univ. (Italy). Dipt. di Automazione Ind

    1989-10-26

    The anti p{sup 4}He annihilation cross section averaged over the interval 40-50 MeV/c has been measured using a streamer chamber in a magnetic field. The measured value is 1342+-250 mb. It agrees with a behaviour like 1/p of the annihilation cross section. Our result has been obtained at the lowest momentum achieved till now in measurements of antiproton annihilation in flight. (orig.).

  8. Evidence of isospin effects in antiproton-nucleus annihilation

    International Nuclear Information System (INIS)

    Balestra, F.; Bossolasco, S.; Bussa, M.P.; Busso, L.; Ferrero, L.; Panzieri, D.; Piragino, G.; Tosello, F.; Barbieri, R.; Bendiscioli, G.; Rotondi, A.; Salvini, P.; Venaglioni, A.; Zenoni, A.; Batusov, Yu.A.; Falomkin, I.V.; Pontecorvo, G.B.; Rozhdestvensky, A.M.; Sapozhnikov, M.G.; Tretyak, V.I.; Guaraldo, C.; Maggiora, A.; Haatuft, A.; Halsteinslid, A.; Myklebost, K.; Olsen, J.M.; Breivik, F.O.; Jacobsen, T.; Soerensen, S.O.

    1989-01-01

    Antiproton- 3 He annihilation events at rest have been detected using a self-shunted streamer chamber. The ratio of the cross section for annihilation on neutrons and on protons has been measured (0.467±0.035). It is compared with other results from annihilation on free nucleons, deuterium, 3 He and 4 He. The low value of the ratio seems to indicate a strong isospin dependence of the antinucleon-nucleon P-wave amplitude. (orig.)

  9. A new anti-neutrino detection technique based on positronium tagging with plastic scintillators

    Energy Technology Data Exchange (ETDEWEB)

    Consolati, G. [Department of Aerospace Science and Technology, Politecnico di Milano, via La Masa 34, 20156 Milano (Italy); Franco, D., E-mail: dfranco@in2p3.fr [APC, Univ. Paris Diderot, CNRS/IN2P3, CEA/Irfu, Obs. de Paris, Sorbonne Paris Cité, 75205 Paris (France); Jollet, C. [IPHC, Université de Strasbourg, CNRS/IN2P3, 67037 Strasbourg (France); Meregaglia, A., E-mail: amerega@in2p3.fr [IPHC, Université de Strasbourg, CNRS/IN2P3, 67037 Strasbourg (France); Minotti, A. [IPHC, Université de Strasbourg, CNRS/IN2P3, 67037 Strasbourg (France); Perasso, S.; Tonazzo, A. [APC, Univ. Paris Diderot, CNRS/IN2P3, CEA/Irfu, Obs. de Paris, Sorbonne Paris Cité, 75205 Paris (France)

    2015-09-21

    The main signature for anti-neutrino detection in reactor and geo-neutrino experiments based on scintillators is provided by the space–time coincidence of positron and neutron produced in the Inverse Beta Decay reaction. Such a signature strongly suppresses backgrounds and allows for measurements performed underground with a relatively high signal-to-background ratio. In an aboveground environment, however, the twofold coincidence technique is not sufficient to efficiently reject the high background rate induced by cosmogenic events. Enhancing the positron–neutron twofold coincidence efficiency may pave the way to future aboveground detectors for reactor monitoring. We propose a new detection scheme based on a threefold coincidence, among the positron ionization, the ortho-positronium (o-Ps) decay, and the neutron capture, in a sandwich detector with alternated layers of plastic scintillator and aerogel powder. We present the results of a set of dedicated measurements on the achievable light yield and on the o-Ps formation and lifetime. The efficiencies for signal detection and background rejection of a preliminary detector design are also discussed.

  10. Positronium formation in CS2 and C6F6 mixtures with triethylamine or tetrahydrofuran

    International Nuclear Information System (INIS)

    Zhicheng Zhang; Ito, Yasuo; Tabata, Yoneho

    1990-01-01

    Positronium (Ps) yields were measured for CS 2 /THF, CS 2 /TEA, C 6 F 6 THF and C 6 F 6 /TEA mixtures. Addition of C 6 F 6 or CS 2 into TEA or THF showed a similar influence which induces a decrease of Ps yield. This is ascribed to the non-dissociative electron scavenging by both CS 2 and C 6 F 6 . On the other hand, the effect of addition of TEA and THF has been found to be different for C 6 F 6 and CS 2 , i.e. both TEA and THF did not change Ps yield in CS 2 substantially, while they caused a sharp decrease of Ps yield in C 6 F 6 . The latter sharp decreases was ascribed to quenching of excited state of C 6 F 6 . This interpretation is supported by pulse radiolysis emission measurements for the same system, in which it was found that TEA quenches the excited state of C 6 F 6 efficiently. (author)

  11. Three-body dynamical interference in electron and positron collision with positronium atom

    Directory of Open Access Journals (Sweden)

    E Ghanbari Adivi

    2010-12-01

    Full Text Available In this project, the Faddeev-Watson-Lovelace (FWL formalism is generalized to large scattering angles. The angular range includes 0-180 degrees. Using this method, the charge transfer differential cross-sections are calculated, in a second-order approximation, for collision of energetic positrons and electrons with neutral positronium atoms. In this approximation, the rearrangement amplitude contains two first-order and three second-order partial amplitudes. The first first-order term is the Born amplitude in a first-order approximation. The second one corresponds to capturing the transferred particle without perturbing the state of this particle. This term, in fact, describes a knock-on process. Since the masses of the particles and the absolute values of their charges are equal, one expects that the second-order terms be similar in magnitude. This aspect causes the instructive interference of the partial amplitudes in some angles and destructive interference in some others. However, it is predicted that these amplitudes have local maxima in direction of the recoiling of the projectile. In order to investigate this situation, the second-order partial amplitudes are calculated and their relations with the parity of the initial and final states of the scattering system are analyzed. In particular, the role of dynamical interference of these partial amplitudes in creation of the kinematical peak and the peak corresponding to the knock-on scattering in angular distribution of the differential cross sections is investigated.

  12. Nuevas terapias en el tratamiento del VIH

    OpenAIRE

    Garrido Estévez, Julieta

    2017-01-01

    Desde hace décadas, los avances en el tratamiento del VIH han conseguido controlar la infección y disminuir su progresión hacia SIDA. La eliminación del VIH, virus capaz de evadir e incapacitar al sistema inmune, que es el que nos protege de otras infecciones, es en la actualidad uno de los retos más importantes en la investigación científica, pretendiendo con ello las ansiadas prevención y curación de la enfermedad. Objetivo: Definir la situación actual del tratamiento de la infección por...

  13. 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

  14. Positron annihilation imaging device having movable collimator

    International Nuclear Information System (INIS)

    Thompson, C.J.

    1981-01-01

    This patent application relates to a positron annihilation imaging device comprising two circular arrays of detectors disposed in spaced apart parallel planes and circumferentially offset by half the detector spacing, axially movable annular outer collimator rings, generally disposed in a pair of opposite planes outside the associated planes of the detectors, each collimator being movable toward the opposite collimator. An inner collimator of annular configuration is disposed between the two rows of detectors and is formed in two rings which may be separated axially. The outer and inner collimators serve to enhance data readout and imaging. (author)

  15. Hadronic physics in electron-positron annihilation

    International Nuclear Information System (INIS)

    Bethke, S.

    1993-01-01

    The author presents an introduction to the study of hadronic physics by means of e + e - processes. After an introduction to the theory of the strong interactions and QCD the current accelerator facilities for such studies are listed. Then the treatment of e + e - annihilation into hadrons by QCD is discussed. Thereafter the studies of hadronic event shapes, jet physics, the tests of the basic quantum numbers of quarks and gluons, the measurement of α S , and the studies of the differences between quark and gluon jets are described. Finally an outlook to further studies of such processes at higher energies is given. (HSI)

  16. 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

  17. Movable collimator for positron annihilation imaging device

    International Nuclear Information System (INIS)

    Thompson, C.J.

    1982-01-01

    A positron annihilation imaging device has two or more rings of detectors from which three or more slices through the object being scanned can be determined at once. A technique is provided for adjusting the slice widths. One slice may be imaged by all detectors in adjacent planes simultaneously, and reconstructed as if all detectors were in the same plane. The single slice facility is provided without the necessity of rotating the detector array or moving it in any way during data collection, allowing the possibility of doing physiologically gated imaging of a single slice

  18. 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

  19. Movable collimator for positron annihilation imaging device

    International Nuclear Information System (INIS)

    Thompson, C.J.

    1981-01-01

    A positron annihilation imaging device having two circular arrays of detectors disposed in spaced apart parallel planes wherein axially movable annular collimator rings are generally disposed in a pair of opposite planes outside the associated planes of the collimators to each collimator being movable toward the opposite collimator and a central collimator of annular configuration generally disposed between the two rows of detectors but being split into two rings which may be separated, the outer and inner collimators serving to enhance data readout and imaging

  20. Kinetics of fragmentation-annihilation processes

    OpenAIRE

    Filipe, JAN; Rodgers, GJ

    1996-01-01

    We investigate the kinetics of systems in which particles of one species undergo binary fragmentation and pair annihilation. In the latter, nonlinear process, fragments react at collision to produce an inert species, causing loss of mass. We analyze these systems in the reaction-limited regime by solving a continuous model within the mean-field approximation. The rate of fragmentation for a particle of mass x to break into fragments of masses y and x-y has the form x(lambda-1) (lambda > 0), a...

  1. The p-antip annihilation in the quark model

    International Nuclear Information System (INIS)

    Niskanen, J.A.

    1988-05-01

    After a concise review of the N-antiN annihilation in the quark rearrangement and 3 P 0 annihilation models, preliminary results are given for the case with an additional term where a q-antiq pair with the gluon quantum number 3 S 1

  2. Isospin effects in anti p3He annihilation at rest

    International Nuclear Information System (INIS)

    Balestra, F.; Barbieri, R.; Batusov, Yu.A.; Bendiscioli, G.; Breivik, F.O.; Bossolasco, S.; Bussa, M.P.; Busso, L.; Falomkin, I.V.; Ferrero, L.; Guaraldo, C.; Haatuft, A.; Halsteinslid, A.; Jacobsen, T.; Lodi Rizzini, E.; Maggiora, A.; Myklebost, K.; Olsen, J.M.; Panzieri, D.; Piragino, G.; Pontecorvo, G.B.; Rozhdestvensky, A.M.; Rotondi, A.; Salvini, P.; Sapozhnikov, M.G.; Soerensen, S.O.; Tosello, F.; Tretyak, V.I.; Venaglioni, A.; Zenoni, A.

    1989-01-01

    The analysis of anti p 3 He annihilation events at rest (from the PS 179 experiment at LEAR) gives the value 0.467±0.035 for the ratio between the annihilation cross sections on n and on p. This low value indicates a strong isospin dependence of the anti NN amplitude in P wave. (orig.)

  3. 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

  4. 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...

  5. 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

  6. 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

  7. Tratamiento acortado estrictamente supervisado para tuberculosis pulmonar

    Directory of Open Access Journals (Sweden)

    Alvarez-Gordillo Guadalupe del Carmen

    1998-01-01

    Full Text Available Objetivo. Evaluar la posibilidad de aplicar el tratamiento acortado estrictamente supervisado (TAES en el Programa de Control de la Tuberculosis en Chiapas, México. Material y métodos. Se evaluó la eficacia y la eficiencia del tratamiento en una cohorte de pacientes con tuberculosis pulmonar confirmada por baciloscopía, que ingresaron a tratamiento con esquemas de autoadministración semisupervisión y estricta supervisión, de enero a junio de 1996. Resultados. La eficacia fue de 90.9. 97.7 y 100% para los esquemas de tratamiento autoadministrado, semisupervisado y TAES, respectivamente, mientras que la eficiencia fue de 68.1. 77.6 y 88.5% en el mismo orden. Conclusiones. Para la salud pública el TAES demostró ser la actividad más importante en el control de la tuberculosis, al elevar las tasas de curación y disminuir, por lo tanto, las fuentes de transmisión de la enfermedad.

  8. Positron-annihilation-radiation transmission gauge

    International Nuclear Information System (INIS)

    Padawer, G.M.

    1984-01-01

    A radiographic method and apparatus for nondestructively monitoring a specimen for density variations are disclosed. A positron-annihilation-radiation-emitting point source is situated approximately midway along the axis separating two detectors sensitive to positron-annihilation (0.511-MeV photon) radiation. The outputs of the two detectors are fed to an electronic circuit that reckons only time-coincident events that are sensed simultaneously in the two detectors. The specimen to be measured is positioned between the source and one of the detectors such that the cone of detected, i.e., coincident, photons intercepts the region of interest. The number of coincidences that are counted in a preset time interval are recorded, or, alternatively, the coincidence count rate is monitored directly with a ratemeter. A linear scan of the region of interest is performed by the sequential displacing of the source/detectors axis with respect to the measured specimen, or the specimen with respect to the source/detectors axis. The number of coincidence counts accumulated within a preset time interval are recorded for each displacement. The spatial variation of density within the specimen is inferred from corresponding variations in the coincidence count rate

  9. Tratamiento conservador en pacientes con retinoblastoma bilateral

    Directory of Open Access Journals (Sweden)

    Juan C. Suárez

    2008-11-01

    Full Text Available OBJETIVO: comparar el tratamiento convencional del retinoblastoma bilateral, usado hasta hace algunos años, consistente en radioterapia o enucleación bilateral, con el tratamiento conservador actual que incluye termoterapia transpupilar (TTT o TTT/quimioterapia al menos en un ojo, en niños con diagnóstico de retinoblastoma bilateral. DISEÑO: estudio retrospectivo descriptivo. MUESTRA: 20 pacientes con diagnóstico de retinoblastoma bilateral que consultaron al Hospital Universitario San Vicente de Paúl, de Medellín, Colombia, entre 1997 y 2007. MÉTODO: se hizo enucleación del ojo con el tumor de mayor tamaño. En el otro ojo se hizo tratamiento con TTT, con el láser diodo (810 nm, spot amplio, solo o combinado con otras terapias. RESULTADOS: se dividió a los pacientes en dos grupos: 16 pacientes (32 ojos en el grupo 1 tratados conservadoramente y 4 pacientes (8 ojos en el grupo 2 con tratamiento convencional. El rango de edad fue de 1-72 meses en el grupo 1 y de 1-12 meses en el grupo 2. El tiempo de seguimiento fue de 7-67 meses para el grupo 1 y de 13-73 meses para el grupo 2. En el grupo 1 se hizo enucleación de 16 ojos (50%, radioterapia externa de uno (3,1%, quimioterapia más termoterapia de 5 (15,6% y quimioterapia más termoterapia más crioterapia de 10 (31,3%. En todos los pacientes se logró preservar al menos un ojo. En el grupo 2, se enuclearon 7 ojos (87,5% y se hizo radioterapia externa más enucleación en un paciente (12.5%. Además, todos los pacientes recibieron quimioterapia. CONCLUSIÓN: la terapia conservadora actual consistente en tratamiento local (termoterapia, crioterapia o braquiterapia y quimiorreducción permite preservar al menos un ojo y en algunos casos de los dos, muchas veces con buena agudeza visual, en niños con retinoblastoma bilateral; se evitan así la enucleación bilateral y la radioterapia externa usada en el tratamiento convencional con todos sus efectos secundarios. La enucleación contin

  10. Measurements of Positronium Formation Cross Sections for Positron-Kr, Xe Scattering

    Science.gov (United States)

    Kauppila, W. E.; Kwan, C. K.; Li, H.; Stein, T. S.; Zhou, S.

    1997-04-01

    Our experimental approach(S. Zhou et al., Phys. Rev. Lett. 73, 236 (1994).) for measuring Ps formation cross sections (Q_Ps) involves passing a variable energy positron beam through a gas scattering cell and detecting the 511 keV annihilation gamma rays resulting from the decay of para-Ps and from the interaction of ortho-Ps with the walls of the scattering cell. It is found that the Q_Ps curves for both Kr and Xe rise rapidly from their formation threshold energies of 7.2 and 5.3 eV, reach maxima within about 10 eV of their thresholds and then decrease to become rather small (less than 10% of the peak heights) above 100 eV. At the maxima Q_Ps accounts for more than 50% of the total scattering cross sections. There is some evidence of possible small scale structure in the Q_Ps curves between 10 and 100 eV. The present results are consistent with the prior measurements of Diana et al.( L.M. Diana et al., in "Atomic Physics with Positrons", edited by J.W. Humberston and E.A.G. Armour (Plenum, New York and London, 1987), p. 55; and in "Positron Annihilation", edited by L. Dorikens-Vanpraet et al. (World Scientific, Singapore, 1989), p. 311.) from near threshold to 70 eV for Kr and from 15 to 100 eV for Xe.

  11. Trilateration-based reconstruction of ortho-positronium decays into three photons with the J-PET detector

    International Nuclear Information System (INIS)

    Gajos, A.; Kamińska, D.; Czerwiński, E.; Alfs, D.; Bednarski, T.; Białas, P.; Głowacz, B.; Gorgol, M.; Jasińska, B.; Kapłon, Ł.; Korcyl, G.; Kowalski, P.; Kozik, T.; Krzemień, W.; Kubicz, E.; Mohammed, M.; Niedźwiecki, Sz.; Pałka, M.; Pawlik-Niedźwiecka, M.

    2016-01-01

    This work reports on a new reconstruction algorithm allowing us to reconstruct the decays of ortho-positronium atoms into three photons using the places and times of photons recorded in the detector. The method is based on trilateration and allows for a simultaneous reconstruction of both location and time of the decay. Results of resolution tests of the new reconstruction in the J-PET detector based on Monte Carlo simulations are presented, which yield a spatial resolution at the level of 2 cm (FWHM) for X and Y and at the level of 1 cm (FWHM) for Z available with the present resolution of J-PET after application of a kinematic fit. Prospects of employment of this method for studying angular correlations of photons in decays of polarized ortho-positronia for the needs of tests of CP and CPT discrete symmetries are also discussed. The new reconstruction method allows for discrimination of background from random three-photon coincidences as well as for application of a novel method for determination of the linear polarization of ortho-positronium atoms, which is also introduced in this work.

  12. A feasibility study of ortho-positronium decays measurement with the J-PET scanner based on plastic scintillators

    International Nuclear Information System (INIS)

    Kaminska, D.; Gajos, A.; Czerwinski, E.; Alfs, D.; Bednarski, T.; Bialas, P.; Dulski, K.; Glowacz, B.; Gupta-Sharma, N.; Korcyl, G.; Krawczyk, N.; Kubicz, E.; Mohammed, M.; Niedzwiecki, Sz.; Pawlik-Niedzwiecka, M.; Rudy, Z.; Wieczorek, A.; Zielinski, M.; Moskal, P.; Curceanu, C.; Silarski, M.; Gorgol, M.; Jasinska, B.; Zgardzinska, B.; Hiesmayr, B.C.; Kowalski, P.; Raczynski, L.; Wislicki, W.; Krzemien, W.

    2016-01-01

    We present a study of the application of the Jagiellonian positron emission tomograph (J-PET) for the registration of gamma quanta from decays of ortho-positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of ortho-positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the o-Ps → 3γ decays with angular and energy resolution equal to σ(θ) ∼ 0.4 circle and σ(E) ∼ 4.1 keV, respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pile-ups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities. (orig.)

  13. A feasibility study of ortho-positronium decays measurement with the J-PET scanner based on plastic scintillators

    Energy Technology Data Exchange (ETDEWEB)

    Kaminska, D.; Gajos, A.; Czerwinski, E.; Alfs, D.; Bednarski, T.; Bialas, P.; Dulski, K.; Glowacz, B.; Gupta-Sharma, N.; Korcyl, G.; Krawczyk, N.; Kubicz, E.; Mohammed, M.; Niedzwiecki, Sz.; Pawlik-Niedzwiecka, M.; Rudy, Z.; Wieczorek, A.; Zielinski, M.; Moskal, P. [Jagiellonian University, Faculty of Physics, Astronomy and Applied Computer Science, Krakow (Poland); Curceanu, C.; Silarski, M. [INFN, Laboratori Nazionali di Frascati, CP 13, Frascati (Italy); Gorgol, M.; Jasinska, B.; Zgardzinska, B. [Maria Curie-Sklodowska University, Department of Nuclear Methods, Institute of Physics, Lublin (Poland); Hiesmayr, B.C. [University of Vienna, Faculty of Physics, Vienna (Austria); Kowalski, P.; Raczynski, L.; Wislicki, W. [Swierk Computing Centre, National Centre for Nuclear Research, Otwock-Swierk (Poland); Krzemien, W. [National Centre for Nuclear Research, High Energy Department, Otwock-Swierk (Poland)

    2016-08-15

    We present a study of the application of the Jagiellonian positron emission tomograph (J-PET) for the registration of gamma quanta from decays of ortho-positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of ortho-positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the o-Ps → 3γ decays with angular and energy resolution equal to σ(θ) ∼ 0.4 {sup circle} and σ(E) ∼ 4.1 keV, respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pile-ups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities. (orig.)

  14. A feasibility study of ortho-positronium decays measurement with the J-PET scanner based on plastic scintillators

    Science.gov (United States)

    Kamińska, D.; Gajos, A.; Czerwiński, E.; Alfs, D.; Bednarski, T.; Białas, P.; Curceanu, C.; Dulski, K.; Głowacz, B.; Gupta-Sharma, N.; Gorgol, M.; Hiesmayr, B. C.; Jasińska, B.; Korcyl, G.; Kowalski, P.; Krzemień, W.; Krawczyk, N.; Kubicz, E.; Mohammed, M.; Niedźwiecki, Sz.; Pawlik-Niedźwiecka, M.; Raczyński, L.; Rudy, Z.; Silarski, M.; Wieczorek, A.; Wiślicki, W.; Zgardzińska, B.; Zieliński, M.; Moskal, P.

    2016-08-01

    We present a study of the application of the Jagiellonian positron emission tomograph (J-PET) for the registration of gamma quanta from decays of ortho-positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of ortho-positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the { o-Ps }→ 3γ decays with angular and energy resolution equal to σ (θ ) ≈ {0.4°} and σ (E) ≈ 4.1 {keV}, respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pile-ups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities.

  15. Trilateration-based reconstruction of ortho-positronium decays into three photons with the J-PET detector

    Energy Technology Data Exchange (ETDEWEB)

    Gajos, A.; Kamińska, D. [Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Cracow (Poland); Czerwiński, E., E-mail: eryk.czerwinski@uj.edu.pl [Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Cracow (Poland); Alfs, D.; Bednarski, T.; Białas, P.; Głowacz, B. [Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Cracow (Poland); Gorgol, M.; Jasińska, B. [Department of Nuclear Methods, Institute of Physics, Maria Curie-Skłodowska University, 20-031 Lublin (Poland); Kapłon, Ł. [Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Cracow (Poland); Institute of Metallurgy and Materials Science of Polish Academy of Sciences, Cracow (Poland); Korcyl, G. [Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Cracow (Poland); Kowalski, P. [Świerk Computing Centre, National Centre for Nuclear Research, 05-400 Otwock-Świerk (Poland); Kozik, T. [Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Cracow (Poland); Krzemień, W. [High Energy Department, National Centre for Nuclear Research, 05-400 Otwock-Świerk (Poland); Kubicz, E.; Mohammed, M.; Niedźwiecki, Sz.; Pałka, M.; Pawlik-Niedźwiecka, M. [Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Cracow (Poland); and others

    2016-05-21

    This work reports on a new reconstruction algorithm allowing us to reconstruct the decays of ortho-positronium atoms into three photons using the places and times of photons recorded in the detector. The method is based on trilateration and allows for a simultaneous reconstruction of both location and time of the decay. Results of resolution tests of the new reconstruction in the J-PET detector based on Monte Carlo simulations are presented, which yield a spatial resolution at the level of 2 cm (FWHM) for X and Y and at the level of 1 cm (FWHM) for Z available with the present resolution of J-PET after application of a kinematic fit. Prospects of employment of this method for studying angular correlations of photons in decays of polarized ortho-positronia for the needs of tests of CP and CPT discrete symmetries are also discussed. The new reconstruction method allows for discrimination of background from random three-photon coincidences as well as for application of a novel method for determination of the linear polarization of ortho-positronium atoms, which is also introduced in this work.

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

    Science.gov (United States)

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

    2016-04-07

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

  17. 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

  18. 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)

  19. 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)

  20. 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)

  1. The scavenging of the precursors of the solvated electrons fom the positron lifetime spectroscopy and the Doppler broadening of annihilation line shape technique

    International Nuclear Information System (INIS)

    Abbe, J.C.; Duplatre, G.; Maddock, A.G.; Haessler, A.

    1979-01-01

    The electron scavenging properties in water of two series of solutes are investigated, using the positron as a probe. For a better interpretation of the data, both the lifetime specroscopy and the Doppler broadening of annihilation line shape technique are used. All solutes inhibit the positronium (Ps) formation, by the scavenging of electron. The first series consists of the halate ions, that should follow the Hunt linear relation between the rate constant for reaction with the solvated electrons, ksub(e - sub(aq)+S) and that for its precursors(s), 1/C 37 . The Ps inhibition constants, k, are 0.14, 1.44 and 3.45M -1 for ClO 3 - , BrO 3 - and IO 3 - respectively. This sequence is quantitatively consistent with that of the respective ksub(e - sub(aq)+S). The second series includes the SeO 4 -- , Te(OH) 6 and BrO 4 - species, and the Ps inhibition constants are 5.62, 10.5 and 14.3 respectively. Theses values are much higher than expected from the ksub(e - sub(aq)+S) constants, on basis of the Hunt relation, in agreement with previous results from pulse radiolysis experiments

  2. Dark matter annihilation in the local group

    International Nuclear Information System (INIS)

    Pieri, Lidia; Branchini, Enzo

    2004-01-01

    Under the hypothesis of a dark matter composed by supersymmetric particles such as neutralinos, we investigate the possibility that their annihilation in the halos of nearby galaxies could produce detectable fluxes of γ photons. Expected fluxes depend on several, poorly known quantities such as the density profiles of dark matter halos, the existence and prominence of central density cusps and the presence of a population of subhalos. We find that, for all reasonable choices of dark matter halo models, the intensity of the γ-ray flux from some of the nearest extragalactic objects, such as M31, is comparable to or higher than the diffuse galactic foreground. We show that next generation ground-based experiments could have the sensitivity to reveal such fluxes which could help us to unveil the nature of dark matter particles

  3. Positron annihilation and Wheeler complexes in semiconductors

    International Nuclear Information System (INIS)

    Prokop'ev, E.P.

    1995-01-01

    Properties of Ps-Ex (positron-exciton) complex nature Wheeler complexes that may be formed at irradiation of semiconductors and ion crystals by positrons at low temperature under conditions of optical excitation by excitons are studied. Binding energy of similar and more complex systems regarding decomposition in Ps and Ex and/or Ex ± exceeds, at least, 0.1 eV, while lifetime regarding biquantum-self-annihilation constitutes τ 2γ ∼5.02x10 - 10 κ c 3 c (κ c -phenomenological parameter of the effective mass method). The lifetime estimations enabled to conclude that Ps-Ex complexes may be detected in some oxide semiconductors, in zinc sulfide, as well as, in alkaline-haloid crystals. At the same time, in silicon, gallium arsenide and in other semiconductors of A 3 B 5 and A 2 B 6 it is highly improbable to observe these complexes. 27 refs

  4. Resonance analysis of e+e- annihilation

    International Nuclear Information System (INIS)

    Horn, D.; Novoseller, D.E.

    1978-01-01

    We present a formalism of overlapping resonances with variable channel structure which is suitable for the analysis of inclusive and exclusive data in e + e - annihilation into hadrons. We use it in a discussion of the psi' (3.86) and iota'' (3.77) states, in a fit to SPEAR data in the range 3.9--4.1 GeV and a fit to DESY data in the range 4.0--4.3 GeV. Two fits to the SPEAR data are used as examples of various features of the resonance system. Special attention is paid to the contraint that a very strong channel (D*D-bar*) opens up in the middle of the resonance structure. Both inclusive and exclusive quantities are displayed and the correlation between them is discussed

  5. Positron annihilation studies on high temperature superconductors

    International Nuclear Information System (INIS)

    Sundar, C.S.; Bharathi, A.

    1996-01-01

    A survey of the positron annihilation studies on high temperature superconductors (HTSC), with results drawn mainly from our work, is presented. These include results of the studies on the temperature dependence of positron lifetime across T c , which have been carried out in the whole gamut of oxide superconductors. These experimental results are discussed in conjunction with the results of theoretically calculated positron density distribution, and it is shown that the observed temperature dependence of lifetime is intimately linked to the probing of the Cu-O network by the positrons. Results on the investigation of oxygen defects, which play a crucial role in HTSC, are presented. The most significant contribution of positrons to HTSC relates to the investigation of Fermi surface and the results of these studies, drawn from literature, are indicated. Some of our recent results in other novel superconducting materials, viz., the fullerenes and borocarbides are also presented. (author). 69 refs., 15 figs

  6. Generalized quantum operators of creation and annihilation

    International Nuclear Information System (INIS)

    Kuryshkin, Vassili

    1980-01-01

    Generalized permutation relation determined by a set of coefficients μ=(μ 1 ,...,μsub(k)) are under consideration for a pair of operators a and a + conjugated to each other. The totality of operator functions of a and a + (the μ-algebra) is investigated. It is shown that a and a + can be interpreted as the annihilation and creation operators of some 'particles'. Unlike the well known types of the quantization of Bose-Einstein and Fermi-Dirac the μ-quantization generally violates the proportionality between the energy of a state and its number of 'particles', a fact which is treated as a certain interaction between the 'particles'. All the particular cases of μ-quantization free from interaction are determined [fr

  7. Positron annihilation study of hydrogen storage alloys

    International Nuclear Information System (INIS)

    Shirai, Yasuharu; Araki, Hideki; Sakaki, Kouji

    2003-01-01

    Some AB 5 and AB 2 hydrogen storage alloys have been characterized by using positron-annihilation lifetime spectroscopy. It has been shown that they contain no constitutional vacancies and that deviations from the stoichiometric compositions are all compensated by antistructure atoms. Positron lifetimes in fully-annealed LaNi 5-x Al x and MmNi 5-x Al x alloys show good correlation with their hydrogen desorption pressures. On the other hand, surprising amounts of vacancies together with dislocations have been found to be generated during the first hydrogen absorption process of LaNi 5 and ZrMn 2 . These lattice defects play important role in hydrogen absorption-desorption processes of hydrogen storage alloys. (author)

  8. 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

  9. 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...... the trapped state iri the defect. The annihilation characteristics (e.g., the lifetime of the positron) can be measured and provide information about the nature of the defect (e.g., size, density, morphology). The technique is sensitive to both defect size (in the range from monovacancies up to cavities...

  10. 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)

  11. éste durante el tratamiento

    Directory of Open Access Journals (Sweden)

    José Miguel Martínez González

    2005-01-01

    Full Text Available El objetivo de esta investigación fue estudiar si las creencias relacionadas con la vivencia del acompañamiento de un familiar en el tratamiento de un drogodependiente, y las del mismo paciente, varían en función de aspectos como el tiempo de abstinencia, el tiempo dedicado al tratamiento, la presencia de patología dual en el drogodependiente, la gravedad de ajuste psicológico del acompañante, los años de evolución de la drogodependencia y el tiempo transcurrido desde que se conoce el problema. La muestra estuvo compuesta por 130 personas, 65 familiares y 65 drogodependientes en tratamiento en centros ambulatorios. Para el análisis de los datos, obtenidos éstos, mediante distintos diseños cuasi-experimentales de grupos no aleatorios, se aplicó la prueba “t-Student” para un nivel de significación del 0,05. Se analizaron las relaciones bivariadas entre las variables descritas y las diferentes creencias tanto en los pacientes como en los familiares de éstos. Los resultados mostraron que las creencias evaluadas están presentes en la experiencia del adicto y del familiar, cambiando éstas a través de los valores de las variables manipuladas ya mencionadas.

  12. Detector for positronium temperature measurements by two-photon angular correlation

    Science.gov (United States)

    Cecchini, G. G.; Jones, A. C. L.; Fuentes-Garcia, M.; Adams, D. J.; Austin, M.; Membreno, E.; Mills, A. P.

    2018-05-01

    We report on the design and characterization of a modular γ-ray detector assembly developed for accurate and efficient detection of coincident 511 keV back-to-back γ-rays following electron-positron annihilation. Each modular detector consists of 16 narrow lutetium yttrium oxyorthosilicate scintillators coupled to a multi-anode Hamamatsu H12700B photomultiplier tube. We discuss the operation and optimization of 511 keV γ-ray detection resulting from testing various scintillators and detector arrangements concluding with an estimate of the coincident 511 keV detection efficiency for the intended experiment and a preliminary test representing one-quarter of the completed array.

  13. Positron annihilation and tribological studies of nano-embedded Al ...

    Indian Academy of Sciences (India)

    Administrator

    Positron annihilation studies of aluminium alloys with nanodispersions of insoluble elements, i.e.,. In, Sn, Pb and Au ... potential objects of different studies and applications. ... dence Doppler broadening spectroscopy is the high sensi- tivity to ...

  14. Inclusive quarkonium production in e+e- annihilation

    International Nuclear Information System (INIS)

    Bayer, V.N.; Grozin, A.G.

    1981-03-01

    The inclusive production of S-wave state mesons composed of identical heavy quarks in e + e - annihilation at an energy high as compared with the meson mass, is considered. Exclusive production of meson pairs is also considered. (orig.)

  15. Automation of low temperature positron annihilation spectroscopy system

    International Nuclear Information System (INIS)

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

    1997-01-01

    This paper describes the automation implemented in the low temperature measurements in positron annihilation spectroscopic studies. This has not only widened the scope of the positron research, but also helps achieve result with better precision. (author). 3 refs., 1 fig

  16. Baryon production in e+e--annihilation at PETRA

    International Nuclear Information System (INIS)

    Bartel, W.; Cords, D.; Dittmann, P.; Eichler, R.; Felst, R.; Krehbiel, H.; Meier, K.; Naroska, B.; O'Neill, L.H.

    1981-06-01

    Data on anti p and anti Λ production by e + e - -annihilation at CM energies between 30 and 36 GeV are presented. Indication for an angular anticorrelation in events with baryon antibaryon pairs is seen. (orig.)

  17. Exclusive channels in bar pp annihilation at rest

    International Nuclear Information System (INIS)

    Bluem, P.

    1992-01-01

    Exclusive channels in bar pp annihilation at rest provide a powerful tool for studying the meson spectrum below the bar pp threshold. The mesons can be classified in SU(3) multiplets according to their quantum numbers. The states which do not fit into this classification are candidates for new forms of hadronic matter like glueballs, hybrids, and multi-quark states. Recent results on the search for exotic states in exclusive channels of bar pp annihilation at rest are discussed. No less important is the study of the annihilation mechanism. In particular, high-statistic measurements of bar pp annihilation at rest into two-meson final states are an excellent tool for studying quark dynamics. Examples of two-body reactions are presented. 24 refs., 9 figs., 3 tabs

  18. Neutrinos from WIMP annihilations in the Sun including neutrino oscillations

    International Nuclear Information System (INIS)

    Blennow, Mattias; Edsjö, Joakim; Ohlsson, Tommy

    2011-01-01

    The prospects to detect neutrinos from the Sun arising from dark matter annihilations in the core of the Sun are reviewed. Emphasis is placed on new work investigating the effects of neutrino oscillations on the expected neutrino fluxes.

  19. Neutrinos from WIMP annihilations in the Sun including neutrino oscillations

    International Nuclear Information System (INIS)

    Blennow, Mattias; Edsjoe, Joakim; Ohlsson, Tommy

    2006-01-01

    The prospects for detecting neutrinos from the Sun arising from dark matter annihilations in the core of the Sun are reviewed. Emphasis is placed on new work investigating the effects of neutrino oscillations on the expected neutrino fluxes

  20. 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.

  1. Alternative method for reconstruction of antihydrogen annihilation vertices

    CERN Document Server

    Amole, C; Andresen , G B; Baquero-Ruiz, M; Bertsche, W; Bowe, P D; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Deller, A; Eriksson, S; Fajans, J; Friesen, T; Fujiwara, M C; Gill, D R; Gutierrez, A; Hangst, J S; Hardy, W N; Hayano, R S; Hayden, M E; Humphries, A J; Hydomako, R; Jonsell, S; Kurchaninov, L; Madsen, N; Menary, S; Nolan, P; Olchanski, K; Olin, A; Povilus, A; Pusa, P; Robicheaux, F; Sarid, E; Silveira, D M; So, C; Storey, J W; Thompson, R I; van der Werf, D P; Wurtele, J S; Yamazaki,Y

    2012-01-01

    The ALPHA experiment, located at CERN, aims to compare the properties of antihydrogen atoms with those of hydrogen atoms. The neutral antihydrogen atoms are trapped using an octupole magnetic trap. The trap region is surrounded by a three layered silicon detector used to reconstruct the antiproton annihilation vertices. This paper describes a method we have devised that can be used for reconstructing annihilation vertices with a good resolution and is more efficient than the standard method currently used for the same purpose.

  2. Alternative method for reconstruction of antihydrogen annihilation vertices

    Energy Technology Data Exchange (ETDEWEB)

    Amole, C., E-mail: chanpreet.amole@cern.ch [York University, Department of Physics and Astronomy (Canada); Ashkezari, M. D. [Simon Fraser University, Department of Physics (Canada); Andresen, G. B. [Aarhus University, Department of Physics and Astronomy (Denmark); Baquero-Ruiz, M. [University of California, Department of Physics (United States); Bertsche, W. [Swansea University, Department of Physics (United Kingdom); Bowe, P. D. [Aarhus University, Department of Physics and Astronomy (Denmark); Butler, E. [CERN, Physics Department (Switzerland); Cesar, C. L. [Universidade Federal do Rio de Janeiro, Instituto de Fisica (Brazil); Chapman, S. [University of California, Department of Physics (United States); Charlton, M.; Deller, A.; Eriksson, S. [Swansea University, Department of Physics (United Kingdom); Fajans, J. [University of California, Department of Physics (United States); Friesen, T.; Fujiwara, M. C. [University of Calgary, Department of Physics and Astronomy (Canada); Gill, D. R. [TRIUMF (Canada); Gutierrez, A. [University of British Columbia, Department of Physics and Astronomy (Canada); Hangst, J. S. [Aarhus University, Department of Physics and Astronomy (Denmark); Hardy, W. N. [University of British Columbia, Department of Physics and Astronomy (Canada); Hayano, R. S. [University of Tokyo, Department of Physics (Japan); Collaboration: ALPHA Collaboration; and others

    2012-12-15

    The ALPHA experiment, located at CERN, aims to compare the properties of antihydrogen atoms with those of hydrogen atoms. The neutral antihydrogen atoms are trapped using an octupole magnetic trap. The trap region is surrounded by a three layered silicon detector used to reconstruct the antiproton annihilation vertices. This paper describes a method we have devised that can be used for reconstructing annihilation vertices with a good resolution and is more efficient than the standard method currently used for the same purpose.

  3. Defect Characterization in Semiconductors with Positron Annihilation Spectroscopy

    Science.gov (United States)

    Tuomisto, Filip

    Positron annihilation spectroscopy is an experimental technique that allows the selective detection of vacancy defects in semiconductors, providing a means to both identify and quantify them. This chapter gives an introduction to the principles of the positron annihilation techniques and then discusses the physics of some interesting observations on vacancy defects related to growth and doping of semiconductors. Illustrative examples are selected from studies performed in silicon, III-nitrides, and ZnO.

  4. 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

  5. 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

  6. 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.

  7. 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

  8. Development of mini linac-based positron source and an efficient positronium convertor for positively charged antihydrogen production

    Science.gov (United States)

    Muranaka, T.; Debu, P.; Dupré, P.; Liszkay, L.; Mansoulie, B.; Pérez, P.; Rey, J. M.; Ruiz, N.; Sacquin, Y.; Crivelli, P.; Gendotti, U.; Rubbia, A.

    2010-04-01

    We have installed in Saclay a facility for an intense positron source in November 2008. It is based on a compact 5.5 MeV electron linac connected to a reaction chamber with a tungsten target inside to produce positrons via pair production. The expected production rate for fast positrons is 5·1011 per second. The study of moderation of fast positrons and the construction of a slow positron trap are underway. In parallel, we have investigated an efficient positron-positronium convertor using porous silica materials. These studies are parts of a project to produce positively charged antihydrogen ions aiming to demonstrate the feasibility of a free fall antigravity measurement of neutral antihydrogen.

  9. Development of mini linac-based positron source and an efficient positronium convertor for positively charged antihydrogen production

    International Nuclear Information System (INIS)

    Muranaka, T; Debu, P; Dupre, P; Liszkay, L; Mansoulie, B; Perez, P; Rey, J M; Ruiz, N; Sacquin, Y; Crivelli, P; Gendotti, U; Rubbia, A

    2010-01-01

    We have installed in Saclay a facility for an intense positron source in November 2008. It is based on a compact 5.5 MeV electron linac connected to a reaction chamber with a tungsten target inside to produce positrons via pair production. The expected production rate for fast positrons is 5·10 11 per second. The study of moderation of fast positrons and the construction of a slow positron trap are underway. In parallel, we have investigated an efficient positron-positronium convertor using porous silica materials. These studies are parts of a project to produce positively charged antihydrogen ions aiming to demonstrate the feasibility of a free fall antigravity measurement of neutral antihydrogen.

  10. Development of mini linac-based positron source and an efficient positronium convertor for positively charged antihydrogen production

    Energy Technology Data Exchange (ETDEWEB)

    Muranaka, T; Debu, P; Dupre, P; Liszkay, L; Mansoulie, B; Perez, P; Rey, J M; Ruiz, N; Sacquin, Y [Irfu, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex (France); Crivelli, P; Gendotti, U; Rubbia, A, E-mail: tomoko.muranaka@cea.f [Institut fuer TelichenPhysik, ETHZ, CH-8093 Zuerich (Switzerland)

    2010-04-01

    We have installed in Saclay a facility for an intense positron source in November 2008. It is based on a compact 5.5 MeV electron linac connected to a reaction chamber with a tungsten target inside to produce positrons via pair production. The expected production rate for fast positrons is 5{center_dot}10{sup 11} per second. The study of moderation of fast positrons and the construction of a slow positron trap are underway. In parallel, we have investigated an efficient positron-positronium convertor using porous silica materials. These studies are parts of a project to produce positively charged antihydrogen ions aiming to demonstrate the feasibility of a free fall antigravity measurement of neutral antihydrogen.

  11. CrossRef Large numbers of cold positronium atoms created in laser-selected Rydberg states using resonant charge exchange

    CERN Document Server

    McConnell, R; Kolthammer, WS; Richerme, P; Müllers, A; Walz, J; Grzonka, D; Zielinski, M; Fitzakerley, D; George, MC; Hessels, EA; Storry, CH; Weel, M

    2016-01-01

    Lasers are used to control the production of highly excited positronium atoms (Ps*). The laser light excites Cs atoms to Rydberg states that have a large cross section for resonant charge-exchange collisions with cold trapped positrons. For each trial with 30 million trapped positrons, more than 700 000 of the created Ps* have trajectories near the axis of the apparatus, and are detected using Stark ionization. This number of Ps* is 500 times higher than realized in an earlier proof-of-principle demonstration (2004 Phys. Lett. B 597 257). A second charge exchange of these near-axis Ps* with trapped antiprotons could be used to produce cold antihydrogen, and this antihydrogen production is expected to be increased by a similar factor.

  12. A study of the solvent effect on the chemical interaction between ortho-positronium and iron(III)-chloride

    International Nuclear Information System (INIS)

    Vertes, A.

    1980-01-01

    The chemical rate constant (k) between ortho-positronium (o-Ps) and iron(III)-chloride was measured in donor solvents as benzene, acetone, pyridine and ethanol. The minimal k was obtained in benzene and the maximal one in acetone. The minimal k value was explained by the low dispersity of FeCl 3 in benzene, and the high rate of the interaction in acetone was considered to be the result of the presence of monomer and dimer iron(III)-species and of the chloride coordination to iron(III). The probability of Ps formation depended only on the character of the solvent and not on the concentration of the FeCl 3 solute. (author)

  13. Positron annihilation in superconducting 123 compounds

    International Nuclear Information System (INIS)

    Peter, M.; Manuel, A.A.; Erb, A.

    1998-01-01

    After a brief review of the theory of angular correlation of positron annihilation radiation (ACAR), the authors illustrate experimental principles and give examples of successful determination of electron momentum density (EMD) and of positron lifetime in solids. The central question which the authors try to answer concerns the contribution of positron spectroscopy to the knowledge and understanding of the new high temperature superconducting oxides. They find that in these oxides also, partially filled bands exist and they can observe parts of their Fermi surface and measure lifetimes in accordance with band theoretical calculations. There are characteristic differences, however. The intensity of the anisotropy of the ACAR signal is below theoretical expectation and signals depend on sample preparation. Recent studies by the Geneva group have concerned dependence of the signals on impurities, on oxygen content and on the thermal history of preparation. Of particular interest are correlations between the variations of these signals and between the variations of structural and transport properties in these substances. Besides deliberate additions of impurities, the Geneva group also reports progress in the preparations of samples of highest purity (barium zirconate crucibles). The alloy series Pr x Y 1-x Ba 2 Cu 3 O 7-δ is of special interest because of exceptional transport properties. The recent positron results on these materials will be presented and commented in the light of theoretical models and in the light of the reported superconductivity of the Pr-compound

  14. Jets in e+e- annihilation

    International Nuclear Information System (INIS)

    Hollebeek, R.

    1983-10-01

    We have a simple perturbative picture of the production of hadrons from e + e - annihilations which works quite well in predicting the main features of this interaction. It explains the magnitude of the total cross-section, the basic two-jet structure, and the final state angular distributions. It is also consistent with our present ideas about the structure of hadronic matter and the requirement that at high enough energies, the corrections due to strong interactions are small and hence treatable in a perturbative sense. We have seen, however, that to progress beyond this point requires a detailed model of fragmentation phenomena and that differences in models prevent us from making clean predictions about QCD. It is therefore important that we continue to study the fragmentation process and try to parameterize it as well as possible. Large amounts of experimental data are now available on this subject, and new tests will become available as experimenters look in more detail at the behavior of quantum number correlations and energy dependent effects. In doing this, it will be important to keep in mind that mass effects can yield significant energy variations in the model parameters. Our eventual goal should be to find ways of treating the data which will yield quantitative tests of QCD. Studies of three- and four-jet fractions, three-jet fragmentation properties, and energy-energy correlations have begun, and hopefully with improved understanding of fragmentation effects, will yield such tests. 48 references

  15. Annihilation of antiproton on deuteron at rest

    International Nuclear Information System (INIS)

    Grach, I.; Shmatikov, M.

    1982-01-01

    The system of Faddeev equations for amplitudes of anti pD iteraction at rest accounting for higher partial anti NN waves is derived. From its solution the total and elastic anti pD cross sections are calculated. Predictions for the missing-mass spectrum in the anti pD annihilation are made. The P-wave anti NN states give small contribution to the anti pD cross section at rest, the theoretical value of the latter being less than the experimental cross section extrapolated to the threshold. Let us emphasize that the total anti pD cross section depending weakly on the radii of anti NN interactions is sensitive to the values of the anti NN scattering lengths. Experimental data for anti pD cross sections at rest can be obtained only by extrapolation procedure. Henceforth it is very important to investigate the anti pD interactions at low but non-zero momenta where the direct comparison to the experiment is possible [ru

  16. Tratamientos psicologicos en la hipertension arterial

    Directory of Open Access Journals (Sweden)

    Lilia Mabel Labiano

    2002-01-01

    Full Text Available En vista que las evidencias obtenidas acerca del beneticio percibido por los sujetos hipertensos leves con los tratamientos farmacológicos resultan conflictivas, se ha considerado importante para estos pacientes, la aplicación de intervenciones psicológicas y comportamentales. Se presentan en este trabajo, distintos tipos de tratamientos psicológicos que en los últimos años han demostrado su efectividad en la reducción de la presión arterial esencial. Se consideraron importantes para individuos hipertensos leves, la implementación de procedimientos tales como: la relajación, el entrenamiento autógeno, la retroalimentación biológica, la meditación, el Hatha -Yoga, la reestructuración cognitiva y el entrenamiento en habilidades sociales, porque contribuyeron a la reducción, no solo de los niveles hipertensivos sino también de los efectos adversos de la medicación farmacológica que afectan la calidad de vida. Es necesario evidentemente que el individuo generalice las estrategias aprendidas en el contexto clínico-experimental, a los diferentes contextos vitales. La técnica empleada, las características del terapeuta y el tipo de personalidad del paciente son componentes principales en la determinación del éxito del tratamiento. La práctica diaria sostenida fuera del contexto clínico, es un elemento de crucial importancia para el mantenimiento de la mejoría lograda.

  17. Tratamiento cognitivo-conductual en la menopausia

    OpenAIRE

    Gutiérrez Gómez-Calcerrada, Sonia

    2012-01-01

    Dada la carencia de alternativas terapéuticas a la terapia hormonal sustitutiva que aborden la sintomatología menopáusica y los diferentes aspectos que influyen en esta etapa, y la incapacidad de los tratamientos hormonales para la remisión de la sintomatología psicológica en la etapa climatérica, se plantea como objetivo de la presente investigación: establecer un programa de intervención cognitivo-conductual eficaz para mujeres climatéricas con sintomatología menopáusica.

  18. Tratamiento de aguas contaminadas con cianuro

    OpenAIRE

    Aguilar Roca, Fernando; Aguilar Roca, Fernando; Aguilar Roca, Fernando

    2011-01-01

    El presente trabajo “Tratamiento de aguas contaminadas con cianuro" se divide en tres partes: química del contaminante, procesos de descontaminación estudiados y un procedimiento basado en una investigación reciente. Principales propiedades físico-químicas del ion cianuro y de sus principales compuestos, cianuros simples o complejos, en medio acuoso. Métodos y procesos que existen para la descontaminación de efluentes cianurados, tanto los que se dan de forma natural (degradación natu...

  19. Lesiones periapicales: diagnóstico y tratamiento

    OpenAIRE

    A. García-Rubio; A.L. Bujaldón-Daza; A. Rodríguez-Archilla

    2015-01-01

    Las lesiones periapicales resultado de la necrosis de la pulpa dental son las patologías que más frecuentemente ocurren encontradas en el hueso alveolar. El tratamiento consiste en la eliminación de los agentes infecciosos mediante el tratamiento del canal radicular, permitiendo la cicatrización de la lesión.

  20. Uso del aralen en el tratamiento de la teniasis

    Directory of Open Access Journals (Sweden)

    Carlos Arteaga Camargo

    1951-08-01

    Full Text Available En el presente trabajo se hace referencia al tratamiento de siete casos de Taeniasis (todos de Taenia saginata, por medio del "Aralen". Dicho tratamiento es de administración fácil, no produjo manifestaciones tóxicas y dio éxito en todos los casos tratados.

  1. Annihilation model of quasi-stellar objects

    International Nuclear Information System (INIS)

    Alfven, H.

    1979-01-01

    The possibility that annihilation is a major source of energy in cosmic physics is discussed. Since Klein suggested that the Universe might be matter-antimatter symmetric over two decades ago, there have been a significant number of papers developing the consequences of this view. These, however, have been largely ignored in the general literature. There have also been a number of papers claiming to prove that there cannot be antimatter anywhere in the observable Universe. In the first part of this paper an assessment of the differing views is given, and it is shown that none of the arguments against antimatter is convincing. The existence of antimatter is not in conflict with any observational fact. The reason for the negative attitude towards the existence of antimatter seems to be that this view is in conflict with a number of speculative but 'generally accepted' theories. However, recent magnetospheric and heliospheric research, including in situ measurements of cosmic plasmas, is now drastically changing cosmic plasma physics in a way that leads to growing scepticism about quite a few of the speculative theories. An attempt is made to develop a simple phenomenological model of QSOs based on star-antistar collisions. This model can account for such basic observational properties as the acceleration to very large (non-cosmological) velocities, the existence of broad emission lines, and at the same time narrow absorption lines with different redshifts. The absence of blueshifts is also explained. The model predicts that relatively young QSOs should be at cosmological distances whereas the old ones may very well be much closer to us than indicated by their redshift. (Auth.)

  2. 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

  3. Y PROCEDIMIENTOS QUIRÚRGICOS DE TRATAMIENTO

    Directory of Open Access Journals (Sweden)

    FBE Guevara

    2005-01-01

    Full Text Available La hemiplejía laríngea idiopática es la causa más común de insuficiencia de las vías respiratorias altas en equinos. La enfermedad está clasificada como una axonopatía distal que afecta el nervio laríngeo recurrente y que produce atrofia neurogénica de la musculatura intrínseca de la laringe. La enfermedad se manifiesta por la paresa o parálisis de los músculos abductores laríngeos (cricoaritenoides dorsal, lo que termina en la obstrucción de la vía aérea y en el colapso dinámico del cartílago aritenoideo afectado, durante el ejercicio. Su diagnóstico es realizado por medio de un examen endoscópico, en reposo o durante el ejercicio. Las técnicas quirúrgicas de tratamiento para caballos con grados III o IV de hemiplejía laríngea son principalmente la laringoplastia prostética, la aritenoidectomía, la ventriculectomía/cordectomía y los procedimientos de reinervación del músculo cricoaritenoideo dorsal. De las anteriores técnicas, la laringoplastia continúa siendo el tratamiento quirúrgico de primera elección.

  4. Hacia un tratamiento computacional del Aktionsart

    Directory of Open Access Journals (Sweden)

    Juan Aparicio

    2013-12-01

    Full Text Available En el área del Procesamiento del Lenguaje Natural (PLN, a la hora de crear aplicaciones inteligentes, el tratamiento semántico es fundamental. Sin embargo, la investigación que actualmente se está llevando a cabo en PLN está todavía lejos de conseguir niveles profundos de compresión del lenguaje. El objetivo principal de nuestra investigación es la representación del Aktionsart (la manera como se construye el evento expresado por un verbo en su desarrollo temporal. Una de las dificultades básicas que presenta el tratamiento semántico del lenguaje es el establecimiento de clases, debido principalmente a la naturaleza gradual del significado y la alta incidencia del contexto en la interpretación de las diferentes unidades. En este artículo nos centraremos en la presentación de las clases aspectuales léxicas de nuestra propuesta. El total de clases definidas se clasifica en dos grupos, las clases simples: estados, procesos y puntos, cuya combinación da lugar a las clases complejas: culminaciones, realizaciones y graduales. Esta presentación se llevará a cabo tanto desde el punto de vista teórico, como de su implementación computacional.

  5. 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.

  6. 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.

  7. Constraints on dark matter annihilation from CMB observations before Planck

    Energy Technology Data Exchange (ETDEWEB)

    Lopez-Honorez, Laura [Theoretische Natuurkunde, Vrije Universiteit Brussel and The International Solvay Institutes, Pleinlaan 2, B-1050 Brussels (Belgium); Mena, Olga; Palomares-Ruiz, Sergio; Vincent, Aaron C., E-mail: llopezho@vub.ac.be, E-mail: omena@ific.uv.es, E-mail: sergio.palomares.ruiz@ist.utl.pt, E-mail: vincent@ific.uv.es [Instituto de Física Corpuscular (IFIC), CSIC-Universitat de València, Apartado de Correos 22085, E-46071 Valencia (Spain)

    2013-07-01

    We compute the bounds on the dark matter (DM) annihilation cross section using the most recent Cosmic Microwave Background measurements from WMAP9, SPT'11 and ACT'10. We consider DM with mass in the MeV–TeV range annihilating 100% into either an e{sup +}e{sup −} or a μ{sup +}μ{sup −} pair. We consider a realistic energy deposition model, which includes the dependence on the redshift, DM mass and annihilation channel. We exclude the canonical thermal relic abundance cross section ((σv) = 3 × 10{sup −26}cm{sup 3}s{sup −1}) for DM masses below 30 GeV and 15 GeV for the e{sup +}e{sup −} and μ{sup +}μ{sup −} channels, respectively. A priori, DM annihilating in halos could also modify the reionization history of the Universe at late times. We implement a realistic halo model taken from results of state-of-the-art N-body simulations and consider a mixed reionization mechanism, consisting on reionization from DM as well as from first stars. We find that the constraints on DM annihilation remain unchanged, even when large uncertainties on the halo model parameters are considered.

  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. Bremsstrahlung Based Positron Annihilation Spectroscopy for Material Defect Analysis

    International Nuclear Information System (INIS)

    Selim, F.A.; Wells, D.P.; Harmon, F.; Kwofie, J.; Lancaster, G.; Jones, J.L.

    2003-01-01

    The Idaho Accelerator Center (IAC) has developed new techniques for Positron Annihilation Spectroscopy (PAS) using highly penetrating γ-rays to create positrons inside the material via pair production. γ-Ray induced positron annihilation spectroscopy can provide highly penetrating probes for material characterization and defect analysis. Bremsstrahlung beams from small, pulsed electron Linacs (6 MeV) have been used to bombard the materials to generate positrons, which annihilate with the material electrons emitting 511 keV radiation. We have also synchronized bremsstrahlung pulses with laser irradiation pulses to study dynamic structural changes in material. In addition, we have developed another method using (p,γ) reactions from a 2 MeV proton beam, which induce coincident γ-rays to perform positron life-time spectroscopy. We have showed the feasibility of extending PAS into thick samples and a wide variety of materials and industrial applications

  10. 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.

  11. Dynamics of an exclusion process with creation and annihilation

    International Nuclear Information System (INIS)

    Juhasz, Robert; Santen, Ludger

    2004-01-01

    We examine the dynamical properties of an exclusion process with creation and annihilation of particles in the framework of a phenomenological domain-wall theory, by scaling arguments and by numerical simulation. We find that the length and the time scales are finite in the maximum current phase for finite creation and annihilation rates as opposed to the algebraically decaying correlations of the totally asymmetric simple exclusion process (TASEP). Critical exponents of the transition to the TASEP are determined. The case where bulk creation and annihilation rates vanish faster than the inverse of the system size N is also analysed. We point out that shock localization is possible even for rates proportional to N -a , 1 < a < 2

  12. Dark matter annihilation with s-channel internal Higgsstrahlung

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Jason; Liao, Jiajun, E-mail: liaoj@hawaii.edu; Marfatia, Danny

    2016-08-10

    We study the scenario of fermionic dark matter that annihilates to standard model fermions through an s-channel axial vector mediator. We point out that the well-known chirality suppression of the annihilation cross section can be alleviated by s-channel internal Higgsstrahlung. The shapes of the cosmic ray spectra are identical to that of t-channel internal Higgsstrahlung in the limit of a heavy mediating particle. Unlike the general case of t-channel bremsstrahlung, s-channel Higgsstrahlung can be the dominant annihilation process even for Dirac dark matter. Since the s-channel mediator can be a standard model singlet, collider searches for the mediator are easily circumvented.

  13. Dark matter annihilation with s-channel internal Higgsstrahlung

    International Nuclear Information System (INIS)

    Kumar, Jason; Liao, Jiajun; Marfatia, Danny

    2016-01-01

    We study the scenario of fermionic dark matter that annihilates to standard model fermions through an s-channel axial vector mediator. We point out that the well-known chirality suppression of the annihilation cross section can be alleviated by s-channel internal Higgsstrahlung. The shapes of the cosmic ray spectra are identical to that of t-channel internal Higgsstrahlung in the limit of a heavy mediating particle. Unlike the general case of t-channel bremsstrahlung, s-channel Higgsstrahlung can be the dominant annihilation process even for Dirac dark matter. Since the s-channel mediator can be a standard model singlet, collider searches for the mediator are easily circumvented.

  14. 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)

  15. 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.

  16. Positron Annihilation in Thunderstorms Observed by ILDAS.

    Science.gov (United States)

    Kochkin, P.; Sarria, D., Sr.; Van Deursen, A.; de Boer, A.; Bardet, M.; Allasia, C.; Flourens, F.; Østgaard, N.

    2017-12-01

    Positron clouds within thunderstorms were for the first time reported in 2015 [Dwyer et al. 2015]. The observation was made by the Airborne Detector for Energetic Lightning Emissions (ADELE) in 2009 at 14.1 km altitude. Strong 511 keV line enhancement was recorded synchronously with nearby electrical activity. It lasted at least 0.2 s and was modeled as annihilation from disperse positron cloud more than a kilometer across. Different positron generation mechanisms were proposed in the paper. In January 2016 an Airbus A340 factory test aircraft was intentionally flying through thunderstorms over Northern Australia. The aircraft was equipped with a dedicated in-flight lightning detection system ILDAS (http://ildas.nlr.nl). The system contains two gamma-ray scintillation detectors each with 38x38 mm cylinder LaBr3 crystals. Total 9 video cameras were installed on-board to monitor the outer surfaces. When the aircraft flew at 12 km inside an active thundercloud, the ambient electric field was strong enough to trigger electrical discharges from the sharp edges. One sequence of such discharges was accompanied with enhancements of 511 keV line, each lasted for 0.5 - 1.0 s and total duration over 15 s. The video cameras recorded electrical discharges attached to the aircraft during this process. ILDAS reported brief 100 A current pulses in association with these discharges. Ground-based lightning location networks, i.e. WWLLN and local Australian LIAS, have not detected any sferics from this region. A detailed Geant4 model of the aircraft was created. The model was used to test different production mechanisms for the observed emission. In this presentation we will show a detailed reconstruction ofthe events with precise mapping on infrared cloud snapshot. Videos from the cameras at the positron detection moment will be shown. The results of the Geant4 simulation will be presented and discussed. References: 1. Dwyer, Joseph R., et al. "Positron clouds within thunderstorms

  17. 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

  18. Positron annihilation at the Si/SiO2 interface

    International Nuclear Information System (INIS)

    Leung, T.C.; Weinberg, Z.A.; Asoka-Kumar, P.; Nielsen, B.; Rubloff, G.W.; Lynn, K.G.

    1992-01-01

    Variable-energy positron annihilation depth-profiling has been applied to the study of the Si/SiO 2 interface in Al-gate metal-oxide-semiconductor (MOS) structures. For both n- and p-type silicon under conditions of negative gate bias, the positron annihilation S-factor characteristic of the interface (S int ) is substantially modified. Temperature and annealing behavior, combined with known MOS physics, suggest strongly that S int depends directly on holes at interface states or traps at the Si/SiO 2 interface

  19. Applications of positron annihilation spectroscopy to polymeric and biological systems

    International Nuclear Information System (INIS)

    Jean, Y.C.; Chen, Hongmin; Liu, Guang; Chakka, Lakshmi; Gadzia, Joseph E.

    2007-01-01

    Positron annihilation spectroscopy (PAS) is a novel radio-analytical technique which uses the positron (anti-electron) and is capable of probing the atomic and molecular scale (0.2-2 nm) free-volume and hole properties in polymeric and biological materials. Recently, we developed positron annihilation lifetime and Doppler broadening of energy spectroscopies coupled with a variable mono-energetic positron beam to measure the free-volume depth profile from the surface, interfaces, and to the bulk. This paper presents applications of PAS to determine multi-layer structures, glass transition temperatures in nano-scale polymeric films and to detect cancer in the human skin. (author)

  20. Modeling of positron states and annihilation in solids

    International Nuclear Information System (INIS)

    Puska, M.J.

    2003-01-01

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

  1. Short gamma ray bursts triggered by neutrino-antineutrino annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Yasin, Hannah; Perego, Albino [Institut fuer Kernphysik, TU Darmstadt (Germany); Arcones, Almudena [Institut fuer Kernphysik, TU Darmstadt (Germany); GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany)

    2016-07-01

    Gamma ray bursts (GRB) are one of the most energetic events in the universe. Neutron star mergers are the most favourable candidate for the subclass of GRBs that last less than two seconds. It has been suggested that the annihilation of neutrino-antineutrino pairs emitted by the hot and dense merger remnant could be enough to launch a relativistic jet, producing such a burst. We calculate the energy deposition by neutrino-antineutrino annihilation based on the results of a Newtonian simulation of the aftermath of a binary neutron star merger. In addition, we investigate the necessary requirements for launching a GRB and compare with our numerical results.

  2. Characterization of advanced semiconductor materials by positron annihilation

    International Nuclear Information System (INIS)

    Uedono, Akira; Suzuki, Ryoichi; Ohdaira, Toshiyuki; Ishibashi, Shoji

    2005-01-01

    Positron annihilation is an established technique for investigating vacancy-type defects near surfaces or interfaces. Using this technique, one can identify defect species in a nondestructive manner. Because there is no restriction of sample conductivity or temperature, this technique can be applied to a various materials, such as semiconductors, metals, metal oxides, and polymers. The positron annihilation has been applied to the studies of Si-technology related materials, which show that it can provide useful information for the development of semiconductor devices. In this article, we report the results obtained for electroplated Cu, strained Si and high-k materials. (author)

  3. 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

  4. Fractal studies on the positron annihilation in metals

    International Nuclear Information System (INIS)

    Lung, C.W.

    1994-06-01

    Traditionally, the Euclidean lines, circles and spheres have served as the basis of the intuitive understanding of the geometry of nature. Recently, the concept of fractals has caught the imagination of scientists in many fields. This paper is to continue our previous work on position annihilation near fractal surfaces to demonstrate that the concept of fractals provides a powerful tool for understanding the structure and properties of defects and rough surfaces in relation to positron annihilation studies. Some problems on Berry geometrical phase have also been discussed. (author). 15 refs, fig., 1 tab

  5. 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.

  6. Microemulsion systems studied by positron annihilation techniques. II

    International Nuclear Information System (INIS)

    Lopez, R.; Olea, O.; Fucugauchi, L.A.

    1982-01-01

    The positron annihilation technique was applied to assess the effect of the double bond of the surfactant molecule on the microemulsion formation mechanism by replacing sodium stearate by sodium oleate in surfactant-cosurfactant-solvent-water systems. Diameters of microemulsions were measured by dynamic laser light scattering, and the obtained values concur with the present positron annihilation data. Structures of these microemulsions have been assessed by considering the available conformation and shapes of the surfactant-cosurfactant-solvent-assemblies. Volumes of the same aggregates have been calculated by taking into consideration the packing constraint imposed upon kink formation. (Auth.)

  7. Polarization of photons in matter–antimatter annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Moskaliuk, S.S. [Bogolyubov Institute for Theoretical Physics, Metrolohichna Street, 14-b, Kyiv-143, Ukraine, UA-03143 e-mail: mss@bitp.kiev.ua (Ukraine)

    2015-03-10

    In this work we demonstrate the possibility of generation of linear polarization of the electromagnetic field (EMF) due to the quantum effects in matter-antimatter annihilation process for anisotropic space of the I type according to Bianchi. We study the dynamics of this process to estimate the degree of polarisation of the EMF in the external gravitational field of the anisotropic Bianchi I model. It has been established that the quantum effects in matter-antimatter annihilation process in the external gravitational field of the anisotropic Bianchi I model provide contribution to the degree of polarisation of the EMF in quadrupole harmonics.

  8. The annihilation spectrum of relatiVistic electron-positron plasma

    International Nuclear Information System (INIS)

    Aragonyan, F.A.; Atoyan, A.M.; Syunyaev, R.A.

    1980-01-01

    The annihilation spectrum of isotropically distributed monoenergetic electrons and positrons is obtained. The spectrum of the (e + e - ) plasma is analyzed in a large range of plasma temperatures. The comparison of transitions peratures. The comparison of transitions intensities of annihilation radiation and bremsstrahlung shows that for temperatures kT 2 (e + e - ) plasma is cooled mainly due to annihilation. The case of the fast positron annihilation on the rest electrons also considered. The possible astrophysical applications are discussed [ru

  9. Rabdomiolisis asociada al tratamiento con valaciclovir

    Directory of Open Access Journals (Sweden)

    Héctor Enríquez Gómez

    2012-03-01

    Full Text Available La rabdomiolisis es un efecto secundario asociado a un buen número de fármacos, entre ellos los antivirales. Describimos un caso de rabdomiolisis secundaria a valaciclovir, efecto no descrito anteriormente en laliteratura, en un contexto clínico muy especial. Se trata de un varón queingresa por un golpe de calor secundario a la realización de ejercicio físicoextremo. Durante su ingreso se comienza tratamiento con valaciclovir porun herpes nasolabial, observándose en los días siguientes una marcadaelevación de las cifras de CPK que desaparece con la suspensión del mismo. Proponemos, por tanto, que ante la administración de valaciclovir ensituaciones que puedan comportar daño mitocondrial habría que realizarmonitorización estrecha de los niveles de CPK

  10. Tratamiento de la obesidad con productos naturales

    Directory of Open Access Journals (Sweden)

    Lina Neri Espinosa Pire

    2016-12-01

    Full Text Available Los crecientes índices de obesidad alrededor del mundo, provocados principalmente por los excesos en la ingesta y la vida sedentaria, constituye uno de los grandes problemas de salud pública en nuestras sociedades. Entre otras formas como dietas y tratamientos que surgen cada día para combatir la obesidad, el uso de plantas medicinales conocido como fitoterapia, ha despertado gran interés. Existen ciertas plantas que poseen propiedades adelgazantes, sin embargo, lo mejor es ponerse en manos de especialistas en este campo, para recibir una correcta asesoría de acuerdo a las necesidades personales. Las plantas medicinales y los productos que de ellas se obtienen, constituyen remedios eficaces para combatir la obesidad, pues no tienen efectos adversos. No obstante el tratamiento debe combinarse con un cambio de hábitos alimentarios y actividad física y no conviene utilizarlos irresponsablemente, pues no todos tienen los mismos beneficios y efectos. La eficacia de la aplicación de plantas con la finalidad de bajar de peso ha sido comprobada en numerosos ensayos clínicos que se han realizado con determinadas especies vegetales. Las plantas medicinales se han utilizado tradicionalmente en forma de infusión, sin embargo esta forma de administración no permite controlar efectivamente las dosis administradas, por lo que es preferible hacerlo en preparados como cápsulas o comprimidos. Cada planta deberá administrarse de una manera específica y es importante que los preparados se tomen siempre en el mismo horario para potenciar su efectividad.

  11. 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, trappin...

  12. 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

  13. Applications of positron annihilation spectroscopy in materials research

    International Nuclear Information System (INIS)

    Singh, J.J.

    1988-01-01

    Positron Annihilation Spectroscopy (PAS) has emerged as a powerful technique for research in condensed matter. It has been used extensively in the study of metals, ionic crystals, glasses and polymers. The present review concentrates on applications of positron lifetime measurements for elucidation of the physicochemical structure of polymers. 10 references

  14. Applications of positron annihilation spectroscopy in materials research

    Science.gov (United States)

    Singh, Jag J.

    1988-01-01

    Positron Annihilation Spectroscopy (PAS) has emerged as a powerful technique for research in condensed matter. It has been used extensively in the study of metals, ionic crystals, glasses and polymers. The present review concentrates on applications of positron lifetime measurements for elucidation of the physicochemical structure of polymers.

  15. Examination of minor actinide annihilation by BWR core

    International Nuclear Information System (INIS)

    Hida, Kazuki

    1995-01-01

    From the viewpoint of reducing burden for disposing high level waste generated from spent fuel, the examination of recycling minor actinide (MA) to reactors and reducing its accumulation has been advanced. In this study, the possibility of annihilation in the case of recycling it to a BWR was examined. The main MAs are 237 Np, 241 Am, 243 Am, 242 Cm, and 244 Cm. However, as for Cm isotopes, the half life is short, the amount of generation is small, and the rate of neutron emission is high, therefore, those are disposed as waste, and 237 Np, 241 Am and 243 Am were taken as the objects of recycling. In order to grasp the basic characteristics in the case of recycling MAs to a BWR, MAs were added to UO 2 fuel, MOX fuel and HCR fuel and burned, and the nuclear conversion characteristics were examined. As the result, it was found that they were converted to short half life nuclides, and as the neutron spectra were softer, the rate of annihilation was higher. In the case of recycling MAs by concentrating to a specific reactor, reactivity loss, the degree of uranium enrichment required for compensating reactivity, and the rate of MA annihilation were calculated. Based on these data, the MA recycling system was set up, and the rate of MA annihilation was evaluated. This is reported. (K.I.)

  16. 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,

  17. anti ee annihilation into hadrons from dual unitarisation

    International Nuclear Information System (INIS)

    Hong-mo, C.

    1976-09-01

    By grafting to the dual unitarisation scheme for hadron reactions a quark-current coupling suggested by the parton model, a model is obtained for anti ee annihilations in which the conversion of quarks into final hadrons is specific. As a first application, the correction to the value of R given by the parton model is estimated. (author)

  18. e+e- annihilation into hadrons at SPEAR

    International Nuclear Information System (INIS)

    Feldman, G.J.

    1975-08-01

    The review of e + e - annihilation includes the detectors, total hadronic cross sections, charged multiplicity, and inclusive distributions. The new particles are excluded. Some results on the search for new particles, searches for monochromatic photons from the psi 1 , a search for nonleptonic decays of charmed mesons, and evidence for anomalous lepton production are also given. 20 references

  19. Source theory analysis of electron--positron annihilation experiments

    International Nuclear Information System (INIS)

    Schwinger, J.

    1975-01-01

    The phenomenological viewpoint already applied to deep inelastic scattering is extended to the discussion of electron-positron annihilation experiments. Some heuristic arguments lead to simple forms for the pion differential cross section that are in reasonable accord with the published experimental data in the energy interval 3 to 4.8 GeV

  20. Hybrid mesons (Q anti Qg) in N anti N annihilation

    International Nuclear Information System (INIS)

    Dover, C.B.; Gutsche, T.; Faessler, A.

    1993-09-01

    N anti N annihilation reactions provide exciting possibilities to study mesonic resonances beyond the usual Q anti Q spectrum. Particularly the search for Q anti Qg mesons containing an explicit dynamical excitation of the gluon field is not promising, since hybrids are predicted to display unique features: exotic quantum numbers (J πC ) and dynamical selection rules for their decay modes. The authors have investigated the possibility of producing hybrids from p anti p atomic states in reactions of the type N anti N(L= 0,1) → π + Q anti Qg. Production rates for hybrid mesons are found to display a strong dependence on the quantum numbers and kinematical factors associated with the transition. The dependence on the orbital angular momentum L of the p anti p atomic state, accessible in p anti p annihilation at rest, would provide a striking signature for the production of hybrids. In estimating branching ratios for the formation of Q anti Qg hybrid mesons in N anti N annihilation reactions at rest, the authors have employed a microscopic model with constituent quarks and gluons in analogy to the annihilation model for the production of Q anti Q mesons

  1. On hadron jet multiplicity in e+e- annihilation

    International Nuclear Information System (INIS)

    Kiselev, A.V.

    1982-01-01

    The Q 2 -dependence of the average hadron multiplicity in e + e - -annihilation jets is found in QCD within the framework of planar diagram approximation (Q-transfer momentum). It is shown that account for kinematical restrictions alters the result obtained previously by other authors

  2. 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

  3. 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)

  4. Calculation of positron annihilation in high Tc copper oxides

    International Nuclear Information System (INIS)

    Barbiellini, B.; Jarlborg, T.; Gauthier, M.; Shukla, A.

    1992-01-01

    LMTO calculations have been done in order to obtain electronic and positronic states in YBaCuO compounds. The annihilation rates have been calculated including the enhancement effects. Folded momentum density spectra are calculated and used for prediction of Fermi surface signals. The influence of lattice defects on the spectra is studied by the comparison between experimental and calculated positron lifetimes. (orig.)

  5. 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

  6. 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.)

  7. Violation of G-parity in antinucleon-nucleon annihilation

    International Nuclear Information System (INIS)

    Green, A.M.; Sainio, M.E.; Moussallam, B.; Niskanen, J.A.; Wycech, S.

    1991-01-01

    A strategy is proposed for investigating the violation of G-parity in the annihilation reaction anti np → π + π 0 . As illustrations π 0 -η mixing and the mass difference effects are considered. This leads to an asymmetry of about 1% in the cross section. (orig.)

  8. Calculation of gamma spectra for positron annihilation on molecules

    Energy Technology Data Exchange (ETDEWEB)

    Green, Dermot G; Gribakin, G F [Centre for Theoretical Atomic, Molecular and Optical Physics, Queen' s University Belfast, BT7 1NN (United Kingdom); Wang, F [Centre for Molecular Simulation, Sinburne University of Technology, Melbourne, Victoria 3122 (Australia); Surko, C M, E-mail: dgreen09@qub.ac.u [Physics Department, University of California, San Diego, La Jolla, California 92093-0319 (United States)

    2009-11-01

    Gamma spectra for positron annihilation on molecules are calculated based on molecular electron momentum densities and using an atomic adjustment factor that accounts for the positron. Results for H{sub 2} agree well with experiment. Analysis of methane and larger alkanes and their substitutes is underway.

  9. 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

  10. 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)

  11. Positron annihilation studies on BeO powders

    International Nuclear Information System (INIS)

    Brauer, G.; Kerbe, F.; Kajcsos, Z.; Ashry, A.

    1984-01-01

    The sintering behaviour of two differently produced BeO powders is studied by positron annihilation. The positron lifetime in dislocations is found to be tau/sub d/ = (185 +- 2) ps, whereas for the perfect lattice tau/sub c/ = (130 +- 2) ps. (author)

  12. 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.)

  13. Positron annihilation imaging device using multiple offset rings of detectors

    International Nuclear Information System (INIS)

    Thompson, C.J.

    1981-01-01

    This patent application relates to a positron annihilation imaging device comprising two or more coaxial circular arrays of detectors (2,2'), with the detectors in one array angularly offset with respect to the detectors in the adjacent array to detect more than one tomographic image simultaneously through different cross-sections of a patient. (author)

  14. Pseudoscalar boson production in e+e- annihilation

    International Nuclear Information System (INIS)

    Grigoryan, S.G.; Chatrchyan, S.A.

    1987-01-01

    A mechanism of pseudoscalar boson production by the heavy quark-antiquark pair via one-photon exchange in e + e - annihilation is studied. The total cross sections of this reaction and energy distributions of produced p 0 -boson are obtained

  15. Characteristics of the positron annihilation process in the matter

    International Nuclear Information System (INIS)

    Dryzek, J.

    2000-01-01

    In this report the positrons annihilation spectroscopy, as a method for the matter study is described. The interaction of positrons of high as well as thermal energies are discussed and different models of mentioned interactions are presented. Special attention is paid for positrons interaction with crystal lattice and its defects. The influence of positron beams characteristics on measured values are also discussed

  16. Production of φ-Mesons in anti NN-Annihilation

    International Nuclear Information System (INIS)

    Sapozhnikov, M.G.

    1994-01-01

    Recent results from the experiments on the φ-meson production in the annihilation of stopped antiprotons have demonstrated a significant (by a factor of 30-50) violation of the OZI rule. Experimental information on the φ-meson production is discussed and possible theoretical explanations of the strong OZI rule violation are reviewed. 37 refs., 4 figs., 2 tabs

  17. On the simulation of annihilation process of positrons in flight

    International Nuclear Information System (INIS)

    Dobrynin, Yu.L.

    1988-01-01

    The process of annihilation (AN) of positrons with the energy lower than 50 MeV in flight is sequentially considered.Formulae and data tables necessary for calculating probabilities and kinematics of AN process are presented in a suitable for computerized simulation algorithmic form

  18. Positronium formation in NaY-zeolites studied by lifetime, positron beam Doppler broadening and 3-gamma detection techniques

    CERN Document Server

    Schut, H; Kolar, Z I; Veen, A V; Clet, G

    2000-01-01

    Results of positron annihilation measurements on NaY pressed powders and deposited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external sup sup 2 sup sup 2 Na source an averaged long lifetime of 1.8 ns with a sum intensity of 27% was observed in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled alpha or beta cages Habrowska, A.M., Popiel, E.S., 1987. Positron annihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic exchange some of the Na was replaced by sup sup 2 sup sup 2 Na. These powders showed a long lifetime component of 7-8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200 deg. C. No significant increase of the shorter (1.5 ns) lifetime was observed, while its intensity dropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water from alpha cages onl...

  19. Contribution from S and P waves in pp annihilation at rest

    CERN Document Server

    Bendiscioli, G; Fontana, A; Montagna, P; Rotondi, A; Salvini, P; Bertin, A; Bruschi, M; Capponi, M; De Castro, S; Donà, R; Galli, D; Giacobbe, B; Marconi, U; Massa, I; Piccinini, M; Cesari, N S; Spighi, R; Vecchi, S; Vagnoni, V M; Villa, M; Vitale, A; Zoccoli, A; Bianconi, A; Bonomi, G; Lodi-Rizzini, E; Venturelli, L; Zenoni, A; Cicalò, C; De Falco, A; Masoni, A; Puddu, G; Serci, S; Usai, G L; Gorchakov, O E; Prakhov, S N; Rozhdestvensky, A M; Tretyak, V I; Poli, M; Gianotti, P; Guaraldo, C; Lanaro, A; Lucherini, V; Petrascu, C; Kudryavtsev, A E; Balestra, F; Bussa, M P; Busso, L; Cerello, P G; Denisov, O Yu; Ferrero, L; Grasso, A; Maggiora, A; Panzarasa, A; Panzieri, D; Tosello, F; Botta, E; Bressani, Tullio; Calvo, D; Costa, S; D'Isep, D; Feliciello, A; Filippi, A; Marcello, S; Mirfakhraee, N; Agnello, M; Iazzi, F; Minetti, B; Tessaro, S

    2001-01-01

    The annihilation frequencies of 19 pp annihilation reactions at rest obtained in different target densities are analysed in order to determine the values of the P-wave annihilation percentage at each target density and the average hadronic branching ratios from P- and S-states. Both the assumptions of linear dependence of the annihilation frequencies on the P-wave annihilation percentage of the protonium state and the approach with the enhancement factors of Batty (1989) are considered. Furthermore the cases of incompatible measurements are discussed. (55 refs).

  20. Light mesons and separated J(PC) sources in N-antiN annihilations at rest

    International Nuclear Information System (INIS)

    Lucaci-Timoce, Angela; Lazanu, I.

    2002-01-01

    N-antiN annihilations at rest and in flight are the most productive physics tools to investigate the spectroscopy of light mesons. The annihilations proceed from more sources of initial states, with different J (PC) quantum numbers. This makes the interpretation of the experimental data much more difficult than in the case of other annihilation process, as for example the e + e - annihilations, and introduces ambiguities in the results. In this talk, the possibilities to separate the N-antiN contributions of initial quantum states in different annihilation channels, are analyzed. The interference phenomena that appear are also discussed. (authors)

  1. Fitoterapia como coadyuvante en el tratamiento de la obesidad

    Directory of Open Access Journals (Sweden)

    López-Regueiro S

    2013-03-01

    Full Text Available La obesidad es uno de los problemas de salud más importantes a nivel mundial debido a su relación con numerosas patologías como la diabetes mellitus tipo 2, la hipertensión y el aumento importante en el riesgo cardiovascular. La base del tratamiento es la dieta y el ejercicio físico, pero en muchos casos no es sufi ciente y es necesario combinarlo con tratamiento farmacológico. Recientemente se ha retirado sibutramina del mercado por lo que sólo se dispone de orlistat, que no está exento de contraindicaciones y efectos secundarios. Ante esta situación, se ha vuelto a retomar el tratamiento fi toterápico, aunque, en muchas ocasiones, con numerosas dudas. Esta revisión pretende aportar la información necesaria sobre las principales plantas utilizadas en este tratamiento.

  2. Fitoterapia como coadyuvante en el tratamiento de la obesidad

    Directory of Open Access Journals (Sweden)

    López-Regueiro S

    2012-12-01

    Full Text Available La obesidad es uno de los problemas de salud más importantes a nivel mundial debido a su relación con numerosas patologías como la diabetes mellitus tipo 2, la hipertensión y el aumento importante en el riesgo cardiovascular. La base del tratamiento es la dieta y el ejercicio físico, pero en muchos casos no es suficiente y es necesario combinarlo con tratamiento farmacológico. Recientemente se ha retirado sibutramina del mercado por lo que sólo se dispone de orlistat, que no está exento de contraindicaciones y efectos secundarios. Ante esta situación, se ha vuelto a retomar el tratamiento fitoterápico, aunque, en muchas ocasiones, con numerosas dudas. Esta revisión pretende aportar la información necesaria sobre las principales plantas utilizadas en este tratamiento.

  3. Amebiasis: Epidemiología y Tratamiento

    Directory of Open Access Journals (Sweden)

    Alberto Albornoz Plata

    1986-08-01

    Full Text Available

    Introducción

    El concepto que se tenía hace varios años de “Enfermedades Tropicales” (se pensaba en un tipo de medicina exótica, como se llamaban en Europa, la malaria y amebiasis ha cambiado totalmente en la actualidad y específicamente para la amebiasis en el sentido de considerarla como enfermedad universal a la que puede ser susceptible cualquier ser humano que viva en cualquier sitio del mundo. Actualmente esta parasitosis cobra especial interés por los estudios inmunológicos, enzimáticos, epidemiológicos, metabólicos y terapéuticos que se desarrollan en centros muy especializados y se supone, con fundamento lógico, que no estará lejos el día en que se disponga de una vacuna eficaz contra esta enfermedad que ataca a muchas gentes, es causa de ausentismo al trabajo, incapacita por períodos largos a muchos pacientes por la complicación hepática y muchas veces es causa de mortalidad en los llamados casos de amebiasis invasora-fulminante.

    En este escrito solo se explicará lo referen te al aspecto epidemiológico y preventivo y, además, se hará énfasis para combatir ideas diagnósticas equivocadas con la entidad colon irritable.

    Al final se explicará el tratamiento actual de la amebiasis.

    Prevalencia y Susceptibilidad
    La amebiasis se considera como una enfermedad mundial, pero la mayor frecuencia es en aquellos lugares en donde las condiciones higiénicas ambientales son defectuosas, en especial lo referente al correcto suministro de agua potable, al buen tratamiento de las excretas y al control sanitario de los alimentos; por este motivo, en los países sub-desarrollados, o mejor subprivilegiados, y en las clases socio-económicas débiles, es donde más se encunetra esta enfermedad.

    Se ha calculado que en el mundo, el 20%de la población alberga la Endamoeba histolytica (l pero la gran mayoría no se consideran enfermos ya que son simplemente

  4. Fobia social: Naturaleza, evaluación y tratamiento (2015)

    OpenAIRE

    Bados López, Arturo

    2015-01-01

    Se abordan diversos aspectos de la fobia social: naturaleza, edad de comienzo y curso, frecuencia, problemas asociados, génesis y mantenimiento, métodos e instrumentos de evaluación, y eficacia y utilidad clínica del tratamiento psicológico y farmacológico. Además, se ofrecen guías para aplicar los tratamientos psicológicos más eficaces.

  5. Tratamiento Quirúrgico de las Esclerosis Faciales.

    Directory of Open Access Journals (Sweden)

    Ricardo Salazar López

    2006-06-01

    En este estudio se hará una descripción del cuadro clínico y evolución de esta entidad, un análisis de su fisiopatología, una historia de la descripción y tratamiento de la misma, posteriormente se propone el tratamiento quirúrgico mediante colgajos musculares y se presentan varios casos clínicos...

  6. Cervicoartrosis: efectividad de un tratamiento fisioterápico convencional

    OpenAIRE

    Pérez Navarro, Mario; García Madrid, José Luis; Pérez Albert, José María; Martínez Fuentes, Juan

    2005-01-01

    El objetivo de este estudio consiste en valorar la efectividad de un tratamiento de fisioterapia convencional para la cervicoartrosis (microondas, tracción cervical, movilización activa, masaje e higiene postural). Para su realización, se han seleccionado 32 pacientes (26 mujeres y 6 hombres) diagnosticados de cervicoartrosis. Se han valorado factores como el dolor y el balance articular. Tras analizar los resultados, concluimos que el tratamiento planteado es efectivo en la patol...

  7. Las quemaduras : su tratamiento por injertos de piel

    Directory of Open Access Journals (Sweden)

    Juan Ruiz Mora

    1947-09-01

    Full Text Available Uno de los problemas médicos más discutidos y apasionantes, es el relativo al tratamiento de las quemaduras. Desde los mas remotos tiempos, el hombre en su lucha contra los elementos adversos, uso el calor en distintas formas; los guerreros desde las épocas mas primitivas lo emplearon como medio de destrucción del enemigo, castigo o mutilación de los vencidos, y así tenemos que el problema que vamos a tratar y en el cual se han hecho avances notorios, es tan viejo como la historia misma de la humanidad. Aunque es la intención de este trabajo, llamar la atención de los colegas, hacia el tratamiento de las quemaduras mediante los injertos de piel, es sin embargo indispensable pasar una revista al tratamiento de las quemaduras en general, puesto que dicho tratamiento no se- inicia inmediatamente después de acaecida esta y antes de emprender el tratamiento quirúrgico, es necesario llevar a cabo un tratamiento medico adecuado.

  8. 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.

  9. Analysis of sub-nano spaces by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Jean, Y.C.; Liu, J.; Huang, C.M.; Dai, G.H.; Yuan, J.P.

    1994-01-01

    Positron annihilation spectroscopy (PAS) has been realized to be a novel and potentially powerful tool to evolve the open spaces in the range 1-20 angstrom in molecular systems. Due to the repulsive force between the positron (the anti-particle of the electron) and the cores, annihilation signals are solely contributed from the open spaces, such as vacancies, holes, and voids in the molecular subtracts under study. By further developing two PAS techniques, positron lifetime (PAL), and angular correlation (ACAR), the authors are able to obtain useful and important information of: hole sizes, distributions, hole fractions, and anisotropic structures at sub-nano scales. Applications of PAS to chemical analysis, surface chemistry of inner pores, and polymer sciences are discussed

  10. Positron annihilation spectroscopy for chemical analysis (PASCA). Chapter 9

    International Nuclear Information System (INIS)

    Cheng, K.L.; Jean, Y.C.

    1988-01-01

    This chapter gives an up to date overview of positron annihilation spectroscopy for chemical analysis (PASCA). As an in situ technique PASCA is especially suitable for studying processes occurring at surfaces. The in situ characteristics of PASCA are treated. The principes of positron annihilation life time spectroscopy (PAL) are discussed and some important analytical applications such as, in determining of total surface areas and cavity volumes in chemical reactions, in the study of chemisorption and catalytic reactions on porous surfaces, in the analysis of bulk materials, in determining molecular association constants in biological systems, in proton and neutron activation analysis, in thin layer chromatography and in tracer technology. 28 refs.; 15 figs.; 8 tabs

  11. Positron annihilation studies on structural materials for nuclear reactors

    International Nuclear Information System (INIS)

    Rajaraman, R.; Amarendra, G.; Sundar, C.S.

    2012-01-01

    Structural steels for nuclear reactors have renewed interest owing to the future advanced fission reactor design with increased burn-up goals as well as for fusion reactor applications. While modified austenitic steels continue to be the main cladding materials for fast breeder reactors, Ferritic/martensitic steels and oxide dispersion strengthened ferritic steels are the candidate materials for future reactors applications in India. Sensitivity and selectivity of positron annihilation spectroscopy to open volume type defects and nano clusters have been extensively utilized in studying reactor materials. We have recently reviewed the application of positron techniques to reactor structural steels. In this talk, we will present successful application of positron annihilation spectroscopy to probe various structural materials such as D9, ferritic/martensitic, oxide dispersion strengthened (ODS) steels and related model alloys, highlighting our recent studies. (author)

  12. Application of positron annihilation techniques for semiconductor studies

    International Nuclear Information System (INIS)

    Karwasz, G.P.; Zecca, A.; Brusa, R.S.; Pliszka, D.

    2004-01-01

    Positron annihilation techniques, being non-destructive, allowing depth profiling down to a few micrometers and detecting open-volume defects (vacancies, dislocations etc.) at single ppm concentrations constitute a valuable and complementary method, compared to other solid-state-physics studies. We give examples of investigation in the field of semiconductors with different techniques, both with and without use of positron low-energy beams. The Doppler broadening of the 511 keV annihilation line method and the slow positron beam were used to study helium-implanted silicon and the surface reduction processes in semiconducting glasses. The positron lifetime technique and coincidence spectra of the Doppler broadening were used for systematic studies of metals and semiconductors. Doppler-coincidence method was then used to identify the kinetics of oxygen precipitates in Czochralski-grown silicon

  13. Dark matter annihilations search in dwarf spheroidal galaxies with fermi

    International Nuclear Information System (INIS)

    Farnier, C.; Nuss, E.; Cohen-Tanugi, J.

    2011-01-01

    Launched in June 2008, the Fermi Gamma-ray Telescope includes a pair conversion detector designed for the 20 MeV to ∼300GeV gamma-ray sky study, the Large Area Telescope (LAT). Operating in all-sky survey mode, its excellent sensitivity and angular resolution will allow either to discover or constrain a signal coming through the annihilation of dark matter particles. Predicted by cold dark matter scenarios as the largest clumps, dwarf spheroidal galaxies are amongst the most attractive targets for indirect search of dark matter by gamma-ray experiments. We present here an overview of the Fermi LAT Dark Matter and New Physics Working Group efforts in the searches of gamma-ray fluxes coming from WIMP pair annihilations in dwarf spheroidal galaxies.

  14. 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

  15. Annihilation and gravitational clumping of monopoles in the early universe

    International Nuclear Information System (INIS)

    Izawa, Mizuo; Sato, Katsuhiko.

    1983-01-01

    In order to avoid the overproduction of magnetic monopoles in the early Universe, we investigate how monopoles evolve in the Big Bang Universe for arbitrary mass of monopoles and the arbitrary initial abundance. First, we calculate pair annihilation of monopoles by taking into account the entropy production due to the annihilations. Second, we investigate the formation of monopole stars and black holes due to gravitational clumping of monopoles. In particular, we take into account the entropy and baryon number generation by black hole evaporation. It is shown, however, that the burning of monopole stars or the evaporation of black holes cannot dilute the monopole abundance sufficiently without conflicts with present baryon/entropy ratio and primordial nucleosynthesis regardless of monopole mass. (author)

  16. Strong CMB constraint on P-wave annihilating dark matter

    Directory of Open Access Journals (Sweden)

    Haipeng An

    2017-10-01

    Full Text Available We consider a dark sector consisting of dark matter that is a Dirac fermion and a scalar mediator. This model has been extensively studied in the past. If the scalar couples to the dark matter in a parity conserving manner then dark matter annihilation to two mediators is dominated by the P-wave channel and hence is suppressed at very low momentum. The indirect detection constraint from the anisotropy of the Cosmic Microwave Background is usually thought to be absent in the model because of this suppression. In this letter we show that dark matter annihilation via bound state formation occurs through the S-wave and hence there is a constraint on the parameter space of the model from the Cosmic Microwave Background.

  17. Positron annihilation lifetime spectroscopy source correction determination: A simulation study

    Energy Technology Data Exchange (ETDEWEB)

    Kanda, Gurmeet S.; Keeble, David J., E-mail: d.j.keeble@dundee.ac.uk

    2016-02-01

    Positron annihilation lifetime spectroscopy (PALS) can provide sensitive detection and identification of vacancy-related point defects in materials. These measurements are normally performed using a positron source supported, and enclosed by, a thin foil. Annihilation events from this source arrangement must be quantified and are normally subtracted from the spectrum before analysis of the material lifetime components proceeds. Here simulated PALS spectra reproducing source correction evaluation experiments have been systematically fitted and analysed using the packages PALSfit and MELT. Simulations were performed assuming a single lifetime material, and for a material with two lifetime components. Source correction terms representing a directly deposited source and various foil supported sources were added. It is shown that in principle these source terms can be extracted from suitably designed experiments, but that fitting a number of independent, nominally identical, spectra is recommended.

  18. Moisture dependence of positron annihilation rates in molecular substances

    International Nuclear Information System (INIS)

    Singh, J.J.; Holt, W.H.

    1982-01-01

    Positron annihilation rates have been studied in polymers and graphite-polymer composites as a function of their moisture content. The annihilation rates have been found to increase linearly with increasing moisture content in epoxies and polyamides, whereas no definite trends have been observed in polyimides. These experimental results have been used as the basis for the calculation of moisture content of several polymeric test specimens. For example, the directly measured moisture content of a Kevlar specimen was 45.5 + or - 5.0% of saturation value, whereas the moisture content on the basis of the decrease in positron lifetime was calculated to be 46.5 + or - 3.5%. Similarly, the directly measured moisture content of a graphite-epoxy composite (55 v/o fiber) was 19.2 + or - 0.6% of saturation value as opposed to a calculated value of 16.0 + or - 5.0%

  19. Moisture dependence of positron annihilation rates in molecular substances

    International Nuclear Information System (INIS)

    Singh, J.J.; Holt, W.H.; Mock, W. Jr.

    1982-01-01

    Positron annihilation rates have been studied in polymers and graphite-polymer composites as a function of their moisture content. The annihilation rates have been found to increase linearly with increasing moisture content in epoxies and polyamides, whereas no definite trends have been observed in the polymides. These experimental results have been used as the basis for the calculation of moisture content of several polymeric test specimens. For example, the directly measured moisture content of a Kevlar/epoxy specimen (55 v/o fiber) was 45.5 +- 5.0% of saturation value, whereas the moisture content on the basis of the decrease in positron lifetime was calculated to be 46.5 +- 3.5%. Similarly, the directly measured moisture content of a graphite/epoxy composite (55 v/o fiber) was 19.2 +- 0.6% of saturation value as opposed to a calculated value of 16.0 +- 5.0%. (orig.)

  20. Positron annihilation studies on nasicon analogues containing cation vacancies

    International Nuclear Information System (INIS)

    Sreeramalu, V.; Sreepad, H.R.; Chandrashekara, A.; Ravindrachary, V.; Gopal, S.

    1990-01-01

    Positron annihilation studies were carried out on the Nasicon analogue Na 2 (La, Al)Zr(PO 4 ) 3 compound for three different concentrations (2.2, 2.8 and 5.2 by wt.%) of ZrO 2 in the nutrient. Angular correlation study of annihilated photons reveals that the defect concentration is maximum for 2.8(wt.%) of ZrO 2 . Further, positron lifetime studies indicate that the positrons are trapped at cation vacancies. Application of a two state trapping model to this system made it possible to evaluate the lifetime of positrons in the Bloch state and of positrons trapped at cation vacancies. (author). 16 refs., 4 figs