WorldWideScience

Sample records for electron-positron annihilation coincidence

  1. 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)

  2. 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

  3. 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

  4. 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)

  5. 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

  6. Jet cross sections in electron-positron annihilation

    International Nuclear Information System (INIS)

    Sharpe, S.R.

    1983-08-01

    There are few, if any, detailed tests of QCD at present. I disucss the problems associated with testing QCD and argue that the three jet angular distribution in electron-positron annihilation is a good quantity to use because it minimizes the sensitivity to nonperturbative effects and provides a test of the detailed structure of QCD. However, for such a test to be possible, the perturbation expansion must be well behaved. I present a calculation of the perturbative corrections using two different generalizations of the Sterman-Weinberg two-jet cross section. I argue that because of the uncertainties in our understanding of hadronization it is necessary that the corrections to both these cross sections be small. In presenting the results I use the recent proof of Mukti and Sterman that all the logarithms can be resummed. I find that at Z-factory energies there is a substantial region of parameters defining the jets for which the correction is small, but that there is no such region at PEP/PETRA energies. This problem at PEP/PETRA energies is made worse by the results of a study of the effects of hadronization. Using a simple model I find very significant effects at PEP/PETRA energies that would make a test difficult. These effects do not, however, present problems at Z-factory energies. I conclude that, even if there are further theoretical advances, testing QCD at PEP/PETRA energies using the three-jet angular distribution will be very difficult. However, this distribution can be used to test QCD in a detailed way at Z-factory energies. The corrected results, furthermore, show a systematic difference from the lowest order result that may be measurable at Z-factory energies. If this effect could be measured it would provide a yet more detailed test of QCD, testing, for example, the three gluon coupling. 66 references

  7. Angular correlations of coincident electron-positron pairs in heavy ion collisions

    International Nuclear Information System (INIS)

    Graf, O.

    1988-10-01

    In the present thesis angular correlations of coincident electron-positron pairsnin heavy ion collisions are studied. It is meant as a contribution to the answer of fundamental questions in the quantum electrodynamics of strong fields. (orig./HSI) [de

  8. Electron-positron annihilation at high luminosity colliding beams

    International Nuclear Information System (INIS)

    Grigoryan, G.V.; Khodzhamiryan, A.Yu.

    1977-01-01

    Experiments are discussed, which can be carried out at the electron-positron storage rings with increased luminosity (up to 10 34 cm -2 sec -1 ) and corresponding improvement of detectors at total energy region up to 10 GeV. This improvement of the experimental conditions may provide valuable physical information from the theoretical point of view. The comparison is made with analogous experimental possibilities of the projected high energy e + e - storage rings with luminosity up to 10 32 cm -2 sec -1

  9. 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

  10. Development of an Electron-Positron Source for Positron Annihilation Lifetime Spectroscopy

    Science.gov (United States)

    2009-12-19

    REPORT Development of an electron- positron source for positron annihilation lifetime spectroscopy : FINAL REPORT 14. ABSTRACT 16. SECURITY...to generate radiation, to accelerate particles, and to produce electrons and positrons from vacuum. From applications using existing high-repetition...theoretical directions. This report reviews work directed toward the application of positron generation from laser interaction with matter 1. REPORT DATE

  11. Experimental study of jets in electron-positron-annihilation

    International Nuclear Information System (INIS)

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

    1981-02-01

    Data on hadron production by e + e - -annihilation at c.m. energies between 30 GeV and 36 GeV are presented and compared with two models both based on first order QCD but using different schemes for the fragmentation of quarks and gluons into hadrons. In one model the fragmentation proceeds along the parton momenta, in the other along the colour-anticolour axes. The data are reproduced better by fragmentation along the colour axes. (orig.)

  12. Importance of non-local electron-positron correlations for positron annihilation characteristics in solids

    International Nuclear Information System (INIS)

    Rubaszek, A.

    2001-01-01

    Several methods to describe the electron-positron (e-p) correlation effects are used in calculations of positron annihilation characteristics in solids. The weighted density approximation (WDA), giving rise to the non-local, state-selective e-p correlation functions, is applied to calculate positron annihilation rates and e-p momentum densities in a variety of metals and silicon. The WDA results are compared to the results of other methods such as the independent particle model, local density approximation, generalised gradient approximation, and also to experiments. The importance of non-locality and state-dependence of the e-p correlation functions is discussed. (orig.)

  13. Measurement of anomalous dimuons produced in electron-positron annihilations

    International Nuclear Information System (INIS)

    Seidman, K.M.

    1979-01-01

    An experimental search for anomalous events of the type μ + μ - + (missing energy and momentum) produced in e + e - annihilation at center-of-mass energies between 6.4 and 7.4 GeV is presented. Analysis of the data reveals 12 events, of which only 6 can be readily explained as background. It is concluded that anomalous dimuon events were found. Furthermore, these events are most simply interpreted as the production and subsequent decay of a pair of heavy leptons, tau +- , each with a mass of about 1.8 GeV/c 2 , and a muonic branching ratio, B(tau → ν/sub tau/μν/tau → all), = 0.21 +0 07 - 0 08 . Because the known family of leptons is so small, and because these leptons seem to be truly elementary particles, the discovery of new lepton is a major event in physics. This discovery can be viewed as a hint of a needed revision in the current paradigm of elementary particle physics. The historical, logical, and technological development of physics in progressing towards fields of increasingly abstract nature is noted. The experimental search, analysis, and interpretation presented here is considered an example of a model problem and solution within the current paradigm of high energy physics. This paradigm is not considered to be complete. On the basis of the Transcendental Meditation technique it is proposed that the systematic and precise exploration of consciousness and its relationship to physical matter is now feasible. It is proposed that the expansion of the current paradigm to include the pure consciousness state as a dynamical element in both the physical description of nature, and the experience of one's own inner nature is a necessity to accomplish the goal and fulfill the purpose of physics

  14. 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.

  15. Measurement of the hadronic cross section in electron-positron annihilation

    International Nuclear Information System (INIS)

    Clearwater, S.

    1983-11-01

    This thesis describes the most precise measurement to date of the ratio R, the hadronic cross section in lowest order electron-positron annihilation to the cross section for muon pair production in lowest order electron-positron annihilation. This experiment is of interest because R is a fundamental parameter that tests in a model independent way the basic assumptions of strong interaction theories. According to the assumptions of one of these theories the value of R is determined simply from the electric charges, spin, and color assignments of the produced quark-pairs. The experiment was carried out with the MAgnetic Calorimeter using collisions of 14.5 GeV electrons and positrons at the 2200m circumference PEP storage ring at SLAC. The MAC detector is one of the best-suited collider detectors for measuring R due to its nearly complete coverage of the full angular range. The data for this experiment were accumulated between February 1982 and April 1983 corresponding to a total event sample of about 40,000 hadronic events. About 5% of the data were taken with 14 GeV beams and the rest of the data were taken with 14.5 GeV beams. A description of particle interactions and experimental considerations is given

  16. Charged Particles Multiplicity and Scaling Violation of Fragmentation Functions in Electron-Positron Annihilation

    International Nuclear Information System (INIS)

    Ghaffary, Tooraj

    2016-01-01

    By the use of data from the annihilation process of electron-positron in AMY detector at 60 GeV center of mass energy, charged particles multiplicity distribution is obtained and fitted with the KNO scaling. Then, momentum spectra of charged particles and momentum distribution with respect to the jet axis are obtained, and the results are compared to the different models of QCD; also, the distribution of fragmentation functions and scaling violations are studied. It is being expected that the scaling violations of the fragmentation functions of gluon jets are stronger than the quark ones. One of the reasons for such case is that splitting function of quarks is larger than splitting function of gluon.

  17. Electron-positron annihilation into hadrons at the higher-loop levels

    Energy Technology Data Exchange (ETDEWEB)

    Nesterenko, A.V. [Joint Institute for Nuclear Research, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation)

    2017-12-15

    The strong corrections to the R-ratio of electron-positron annihilation into hadrons are studied at the higher-loop levels. Specifically, the derivation of a general form of the commonly employed approximate expression for the R-ratio (which constitutes its truncated re-expansion at high energies) is delineated, the appearance of the pertinent π{sup 2}-terms is expounded, and their basic features are examined. It is demonstrated that the validity range of such approximation is strictly limited to √(s)/Λ > exp(π/2) ≅ 4.81 and that it converges rather slowly when the energy scale approaches this value. The spectral function required for the proper calculation of the R-ratio is explicitly derived and its properties at the higher-loop levels are studied. The developed method of calculation of the spectral function enables one to obtain the explicit expression for the latter at an arbitrary loop level. By making use of the derived spectral function the proper expression for the R-ratio is calculated up to the five-loop level and its properties are examined. It is shown that the loop convergence of the proper expression for the R-ratio is better than that of its commonly employed approximation. The impact of the omitted higher-order π{sup 2}-terms on the latter is also discussed. (orig.)

  18. On-ground detection of an electron-positron annihilation line from thunderclouds.

    Science.gov (United States)

    Umemoto, D; Tsuchiya, H; Enoto, T; Yamada, S; Yuasa, T; Kawaharada, M; Kitaguchi, T; Nakazawa, K; Kokubun, M; Kato, H; Okano, M; Tamagawa, T; Makishima, K

    2016-02-01

    Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of gamma-ray emission lasting for ∼60 s. The spectrum of this prolonged emission reached ∼10 MeV, and contained a distinct line emission at 508±3(stat.)±5(sys.) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (∼80keV), and contained 520±50 photons which amounted to ∼10% of the total signal photons of 5340±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons.

  19. Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas

    International Nuclear Information System (INIS)

    Andreev, Pavel A.

    2015-01-01

    We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction

  20. The Effects of Surface Reconstruction and Electron-Positron Correlation on the Annihilation Characteristics of Positrons Trapped at Semiconductor Surfaces

    International Nuclear Information System (INIS)

    Fazleev, N. G.; Jung, E.; Weiss, A. H.

    2009-01-01

    Experimental positron annihilation induced Auger electron spectroscopy (PAES) data from Ge(100) and Ge(111) surfaces display several strong Auger peaks corresponding to M 4,5 N 1 N 2,3 , M 2,3 M 4,5 M 4,5 , M 2,3 M 4,5 V, and M 1 M 4,5 M 4,5 Auger transitions. The integrated peak intensities of Auger transitions have been used to obtain experimental annihilation probabilities for the Ge 3d and 3p core electrons. The experimental data were analyzed by performing theoretical studies of the effects of surface reconstructions and electron-positron correlations on image potential induced surface states and annihilation characteristics of positrons trapped at the reconstructed Ge(100) and Ge(111) surfaces. Calculations of positron surface states and annihilation characteristics have been performed for Ge(100) surface with (2x1), (2x2), and (4x2) reconstructions, and for Ge(111) surface with c(2x8) reconstruction. Estimates of the positron binding energy and annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of the semiconductor and to the approximations used to describe electron-positron correlations. The results of these theoretical studies are compared with the ones obtained for the reconstructed Si(100)-(2x1) and Si(111)-(7x7) surfaces.

  1. Search for the sixth quark in hadronic final states of the electron-positron annihilation at PETRA

    International Nuclear Information System (INIS)

    Rykaczewski, H.

    1981-08-01

    Using the MARK-J detector at the PETRA storage ring hadronic final states of the electron-positron annihilation were studied. One aim of these measurements is mainly the search for a further quark, the top quark. The results yield no indications for bound state of the top quark in the energy range between 29.90 and 37.72 GeV. From the analysis of the spatial energy distribution of hadronic final states as well the rate of inclusive muon events also the result is obtained that top quarks are not produced below an energy of W=36.72 GeV. (orig./HSI) [de

  2. 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

  3. Electron-positron annihilation: unitarity, scaling and electrodynamics at high energies

    Energy Technology Data Exchange (ETDEWEB)

    Karl, G [Guelph Univ., Ontario (Canada); European Organization for Nuclear Research, Geneva (Switzerland))

    1974-01-01

    The work on e/sup +/e/sup -/ annihilation by Cabibbo, Wolfenstein and the author is reviewed. The restrictions of unitarity are analyzed and the connection between the cross sections sigmasub(h) (into hadrons) and sigmasub(..mu..) (into muons) is derived. The possibility of non-scaling in e/sup +/e/sup -/ annihilation is studied and it is pointed out that it leads to no contradiction with presently available information. It is further pointed out that non-scaling could provide a cut-off mechanism for quantum electrodynamics.

  4. Electron positron annihilation from 3 to 11 GeV. ARGUS progress report 1984

    International Nuclear Information System (INIS)

    Darden, C. III.

    1985-01-01

    The ARGUS detector and the e + e - storage ring DORIS at DESY are used to investigate particles produced by the mutual annihilation of the e + and e - , including members of the upsilon family of mesons which are produced resonantly in the ring, and charm mesons, baryons, and charged leptons, which are produced nonresonantly. The ring delivered luminosity at the UPSILON(2S), UPSILON(4S), UPSILON(1S), and a small amount in the continuum. Results are briefly reviewed on the decay of D* +- and F +- mesons. It was found that antideuterons were produced in e + e - annihilation at 10 GeV. Evidence was found for the F* meson. Evidence was sought for the zeta particle. A fast processor was added to reduce dead time. The performance of the vertex drift chamber, beam pipe, inner compensation coils, main drift chamber, time of flight, shower and muon counters, and the storage ring are reviewed

  5. 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

  6. Multi-photon creation and single-photon annihilation of electron-positron pairs

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Huayu

    2011-04-27

    In this thesis we study multi-photon e{sup +}e{sup -} pair production in a trident process, and singlephoton e{sup +}e{sup -} pair annihilation in a triple interaction. The pair production is considered in the collision of a relativistic electron with a strong laser beam, and calculated within the theory of laser-dressed quantum electrodynamics. A regularization method is developed systematically for the resonance problem arising in the multi-photon process. Total production rates, positron spectra, and relative contributions of different reaction channels are obtained in various interaction regimes. Our calculation shows good agreement with existing experimental data from SLAC, and adds further insights into the experimental findings. Besides, we study the process in a manifestly nonperturbative domain, whose accessibility to future all-optical experiments based on laser acceleration is shown. In the single-photon e{sup +}e{sup -} pair annihilation, the recoil momentum is absorbed by a spectator particle. Various kinematic configurations of the three incoming particles are examined. Under certain conditions, the emitted photon exhibits distinct angular and polarization distributions which could facilitate the detection of the process. Considering an equilibrium relativistic e{sup +}e{sup -} plasma, it is found that the single-photon process becomes the dominant annihilation channel for plasma temperatures above 3 MeV. Multi-particle correlation effects are therefore essential for the e{sup +}e{sup -} dynamics at very high density. (orig.)

  7. Multi-photon creation and single-photon annihilation of electron-positron pairs

    International Nuclear Information System (INIS)

    Hu, Huayu

    2011-01-01

    In this thesis we study multi-photon e + e - pair production in a trident process, and singlephoton e + e - pair annihilation in a triple interaction. The pair production is considered in the collision of a relativistic electron with a strong laser beam, and calculated within the theory of laser-dressed quantum electrodynamics. A regularization method is developed systematically for the resonance problem arising in the multi-photon process. Total production rates, positron spectra, and relative contributions of different reaction channels are obtained in various interaction regimes. Our calculation shows good agreement with existing experimental data from SLAC, and adds further insights into the experimental findings. Besides, we study the process in a manifestly nonperturbative domain, whose accessibility to future all-optical experiments based on laser acceleration is shown. In the single-photon e + e - pair annihilation, the recoil momentum is absorbed by a spectator particle. Various kinematic configurations of the three incoming particles are examined. Under certain conditions, the emitted photon exhibits distinct angular and polarization distributions which could facilitate the detection of the process. Considering an equilibrium relativistic e + e - plasma, it is found that the single-photon process becomes the dominant annihilation channel for plasma temperatures above 3 MeV. Multi-particle correlation effects are therefore essential for the e + e - dynamics at very high density. (orig.)

  8. INTEGRAL SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane

    DEFF Research Database (Denmark)

    Teegarden, B. J.; Watanabe, K.; Jean, P.

    2005-01-01

    ‐Ray Astrophysics Laboratory) mission, launched in 2002 October, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high‐resolution, coded‐aperture gamma‐ray telescope with an unprecedented combination of sensitivity, angular resolution, and energy resolution. We report results from...... the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic plane. No positive annihilation flux was detected outside of the central region () of our Galaxy. In this paper we describe the observations and data analysis methods...

  9. Lambda production in electron-positron annihilation at 29 GeV

    International Nuclear Information System (INIS)

    Baden, A.R.

    1986-08-01

    The inclusive cross-secton for the production of the singly-strange baryons λ and anti λ, along with the differential cross-sections in momentum and energy, are measured by e + e - annihilation at a center-of-mass energy of 29GeV. The charged decay mode λ → pπ is used in a search for polarization. Such a polarization may be used as a check of CP invariance in λ production. The sample of events with two detected decays is analyzed for correlations in production angle. 43 refs., 44 figs

  10. Lambda production in electron-positron annihilation at 29 GeV

    International Nuclear Information System (INIS)

    Baden, A.R.

    1986-01-01

    The inclusive cross-section for the production of the singly-strange baryons Lambda and anti Lambda, along with the differential cross-sections in momentum and energy, are measured by e + e - annihilation at a center-of-mass energy of 29 GeV. The charged decay mode Lambda → pπ is used in a search for polarization. Such a polarization may be used as a check of CP invariance in Lambda production. The sample of events with two detected decays is analyzed for correlations in production angle. All results are summarized in the conclusion of this thesis

  11. Quark decay functions as measured in electron positron annihilation and semi-inclusive process in electron proton collisions

    International Nuclear Information System (INIS)

    Meng, R.

    1988-01-01

    The modern theory describing the strong interaction, which holds the quarks together in the hadrons, is quantum chromodynamics (QCD), in which the interaction is mediated by the exchange of spin 1 particles called gluons. Today good qualitative agreement between the theory and experimental results has been found in the investigation of the interactions in which there is a large momentum transfer. This situation has prompted us to look for other detailed tests of the theory. We study the order α s measurement of the MS parton decay functions, which play an important role in the application of high order perturbative QCD calculations. We calculate the hard scattering cross section for e + + e - → parton + anything. Then, by carefully analyzing the electron positron annihilation data, we obtain the order α s MS quark decay function. We also study the gluon bremsstrahlung effects predicted by QCD in a semi-inclusive process at the future HERA electron proton collider, p + e - → h + e - + X. In analogy to studies of Drell-Yan process we study the transverse momentum distribution and angular distribution of the final state hadrons, which are sensitive to the gluon bremsstrahlung effects. Then we investigate the general structure of the hadronic tensor, which appears in the formula for the cross section, including both the parity conserving and parity violating terms. Using the soft gluon resummation technique, the singular and the nonsingular structure functions are all calculated for the process p + e - → γ → h + e - + X

  12. Generalized threshold resummation in inclusive DIS and semi-inclusive electron-positron annihilation

    International Nuclear Information System (INIS)

    Almasy, A.A.; Lo Presti, N.A.; Vogt, A.

    2015-11-01

    We present analytic all-order results for the highest three threshold logarithms of the space-like and time-like off-diagonal splitting functions and the corresponding coefficient functions for inclusive deep-inelastic scattering (DIS) and semi-inclusive e + e - annihilation. All these results, obtained through an order-by-order analysis of the structure of the corresponding unfactorized quantities in dimensional regularization, can be expressed in terms of the Bernoulli functions introduced by one of us and leading-logarithmic soft-gluon exponentials. The resulting numerical corrections are small for the splitting functions but large for the coefficient functions. In both cases more terms in the threshold expansion need to be determined in order to arrive at quantitatively reliable results.

  13. Study on the coherent emission of gluons in QCD jets from electron-positron annihilation

    International Nuclear Information System (INIS)

    Kreutzmann, H.

    1990-11-01

    The inclusive momentum distribution of charged particles is studied with the OPAL detector at LEP in multihadronic events produced in e + e - -annihilations at E cm ≅ M(Z 0 ). Agreement is found with analytical formulae for gluon production that include the phenomena of soft gluon interference. Using data from c.m. energies between 14 GeV and 91 GeV, the dependence of the inclusive momentum distribution on the centre of momentum energy E cm is investigated. The analytic predictions derived from perturbative energy E cm ≅ M(Z 0 ) and its change with E cm are also described by QCD shower Monte Carlo programs which include either coherent gluon branchings or string fragmentation. Simple incoherent models with independent fragmentation fail to reproduce the energy dependence and the momentum spectra. A detailed simulation of the OPAL Jet Chamber and a reconstruction program for jet chamber tracks were developed and applied in this analysis. The essential features of both programs are presented. (orig.) [de

  14. 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.

  15. 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)

  16. Contributions of scalar leptoquarks to the cross sections for the production of quark-antiquark pairs in electron-positron annihilation

    International Nuclear Information System (INIS)

    Povarov, A.V.; Smirnov, A.D.

    2003-01-01

    The contributions of scalar-leptoquark doublets to the cross sections σ QQ-tilde ' for the production of quark-antiquark pairs in electron-positron annihilation are calculated within the minimal model based on the four-color symmetry of quarks and leptons. These contributions are analyzed versus the scalar-leptoquark masses and the mixing parameters of the model at colliding-particle energies in the range 250-1000 GeV. It is shown that the contributions in question are of greatest importance for processes leading to t-quark production. In particular, it is found that, with allowance for the contribution of the scalar leptoquark of charge 5/3 and mass in the range 250-500 GeV, the cross section σ tt-tilde calculated at a mixing-parameter value of k t ∼ 1 may be severalfold larger than the corresponding cross section σ tt-tilde (SM) within the Standard Model. The possibility of setting constraints on the scalar-leptoquark masses and on the mixing parameters by measuring such contributions at future electron-positron colliders is indicated

  17. Calculation of the Doppler broadening of the electron-positron annihilation radiation in defect-free bulk materials

    International Nuclear Information System (INIS)

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

    2000-01-01

    Results of a calculation of the Doppler broadening of the positron-electron annihilation radiation and positron lifetimes in a large number of elemental defect-free materials are presented. A simple scheme based on the method of superimposed atoms is used for these calculations. Calculated values of the Doppler broadening are compared with experimental data for a number of elemental materials, and qualitative agreement is obtained. These results provide a database which can be used for characterizing materials and identifying impurity-vacancy complexes. (c) 2000 The American Physical Society

  18. 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

  19. Analysis of electron-positron momentum spectra of metallic alloys as supported by first-principles calculations

    OpenAIRE

    Folegati, P.; Makkonen, I.; Ferragut, R.; Puska, Martti J.

    2007-01-01

    Electron-positron momentum distributions measured by the coincidence Doppler broadening method can be used in the chemical analysis of the annihilation environment, typically a vacancy-impurity complex in a solid. In the present work, we study possibilities for a quantitative analysis, i.e., for distinguishing the average numbers of different atomic species around the defect. First-principles electronic structure calculations self-consistently determining electron and positron densities and i...

  20. Positron probes of the Ge(1 0 0) surface: The effects of surface reconstructions and electron-positron correlations on positron trapping and annihilation characteristics

    International Nuclear Information System (INIS)

    Fazleev, N.G.; Jung, E.; Weiss, A.H.

    2007-01-01

    Positron annihilation induced Auger electron spectroscopy (PAES) has been applied to study the Ge(1 0 0) surface. The high-resolution PAES spectrum from the Ge(1 0 0) surface displays several strong Auger peaks corresponding to M 4,5 N 1 N 2,3 , M 2,3 M 4,5 M 4,5 , M 2,3 M 4,5 V and M 1 M 4,5 M 4,5 Auger transitions. The integrated peak intensities of Auger transitions are used to obtain experimental annihilation probabilities for the Ge 3d and 3p core level electrons. These experimental results are analyzed by performing calculations of positron surface states and annihilation characteristics of surface trapped positrons with relevant Ge core-level electrons for the non-reconstructed and reconstructed Ge(1 0 0)-p(2 x 1), Ge(1 0 0)-p(2 x 2) and Ge(1 0 0)-c(4 x 2) surfaces. It is found that the positron surface state wave function extends into the Ge lattice in the regions where atoms are displaced from their ideal terminated positions due to reconstructions. Estimates of the positron binding energy and the positron annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of Ge(1 0 0). A comparison with PAES data reveals an agreement with theoretical core annihilation probabilities for the Auger transitions considered

  1. Positron probes of the Ge(1 0 0) surface: The effects of surface reconstructions and electron-positron correlations on positron trapping and annihilation characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Fazleev, N.G. [Department of Physics, University of Texas at Arlington, Box 19059, Arlington, TX 76019-0059 (United States) and Department of Physics, Kazan State University, Kazan 420008 (Russian Federation)]. E-mail: Fazleev@uta.edu; Jung, E. [Department of Physics, University of Texas at Arlington, Box 19059, Arlington, TX 76019-0059 (United States); Weiss, A.H. [Department of Physics, University of Texas at Arlington, Box 19059, Arlington, TX 76019-0059 (United States)

    2007-08-15

    Positron annihilation induced Auger electron spectroscopy (PAES) has been applied to study the Ge(1 0 0) surface. The high-resolution PAES spectrum from the Ge(1 0 0) surface displays several strong Auger peaks corresponding to M{sub 4,5}N{sub 1}N{sub 2,3}, M{sub 2,3}M{sub 4,5}M{sub 4,5}, M{sub 2,3}M{sub 4,5}V and M{sub 1}M{sub 4,5}M{sub 4,5} Auger transitions. The integrated peak intensities of Auger transitions are used to obtain experimental annihilation probabilities for the Ge 3d and 3p core level electrons. These experimental results are analyzed by performing calculations of positron surface states and annihilation characteristics of surface trapped positrons with relevant Ge core-level electrons for the non-reconstructed and reconstructed Ge(1 0 0)-p(2 x 1), Ge(1 0 0)-p(2 x 2) and Ge(1 0 0)-c(4 x 2) surfaces. It is found that the positron surface state wave function extends into the Ge lattice in the regions where atoms are displaced from their ideal terminated positions due to reconstructions. Estimates of the positron binding energy and the positron annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of Ge(1 0 0). A comparison with PAES data reveals an agreement with theoretical core annihilation probabilities for the Auger transitions considered.

  2. Total cross section for hadron production by electron-positron annihilation between 2.4 and 5.0 GeV center-of-mass energy

    International Nuclear Information System (INIS)

    Augustin, J.; Boyarski, A.M.; Breidenbach, M.; Bulos, F.; Dakin, J.T.; Feldman, G.J.; Fischer, G.E.; Fryberger, D.; Hanson, G.; Jean-Marie, B.; Larsen, R.R.; Luth, V.; Lynch, H.L.; Lyon, D.; Morehouse, C.C.; Paterson, J.M.; Perl, M.L.; Richter, B.; Schwitters, R.F.; Vannucci, F.; Abrams, G.S.; Briggs, D.; Chinowsky, W.; Friedberg, C.E.; Goldhaber, G.; Hollebeek, R.J.; Kadyk, J.A.; Trilling, G.H.; Whitaker, J.S.; Zipse, J.E.

    1975-01-01

    The total cross section for hadron production by e + e - annihilation has been measured at center-of-mass energies between 2.4 and 5.0 GeV. Aside from the very narrow resonances psi (3105) and psi (3695), the cross section varies between 32 and 17 nb over this region with structure in the vicinity of 4.1 GeV

  3. Electron-positron interactions

    International Nuclear Information System (INIS)

    Wiik, B.; Wolf, G.

    1979-01-01

    This book is an introduction into the physics of electron-positron interactions. After a description of electron-positron storage rings pure electromagnetic e + e - interactions, and the total cross section are considered. Then low energy processes, the production of the J/psi and psi' particles including their radiative decay as well as the search for other narrow vector states are described. Then after the quark model interpretation of J/psi and psi' charmed mesons, the heavy lepton t, and the upsilon resonances are described. Thereafter inclusive hadron production and jet formation is discussed. Finally the next generation of e + e - colliding rings is described, and the first results from PETRA are presented. This book is suited for all physicists, who want to get a general review about e + e - physics. (HSI) 891 HSI/HSI 892 RKD

  4. Inclusive momentum and angular distributions from electron positron annihilation at √s = 3.0, 3.8, and 4.8 GeV

    International Nuclear Information System (INIS)

    Hollebeek, R.

    1975-05-01

    Inclusive features of multi-hadron final states produced in the annihilations of electrons and positrons are presented. Data were taken at the colliding beam machine, SPEAR, at center-of-mass energies 3.0 GeV, 3.8 GeV, and 4.8 GeV. Reaction products were detected in an approximately 20 m 3 collection of spark chambers and counters, cylindrically arranged, in an axial magnetic field of approximately 4 KG, around the e + e - intersection region. Distributions of single-particle momenta and production angle and two-particle correlations are presented and compared with dynamical models. The results are in disagreement with expectations based on the successful parton--quark model of hadron structure. No generally satisfactory interpretation is available. (U.S.)

  5. Electron-positron annihilation from 3 to 11 GeV. First progress report, 18 August 1980-15 Mar 1981

    International Nuclear Information System (INIS)

    Darden, C.W.

    1981-01-01

    The ARGUS collaboration started forming in mid 1978. It was a natural outgrowth of the CASP II collaboration which had grown up to run the old DASP detector in late 1977. That was the year that the Upsilon meson was discovered at Fermilab. Both the PLUTO and DASP II collaborations were able to see the Upsilon in e + e - annihilations the following year and to confirm that it was indeed a narrow resonance. Late in 1978 the ARGUS collaboration submitted a proposal to the DESY Directorium to build a new universal magnetic solenoid detector that would allow the investigation of reactions of the type e + e - > anything at energies that could be reached by the storage ring DORIS. This energy range included the Charm region and the first two Upsilon states, 1S and 2S. At the same time, the Directorium was urged to rebuild the storage ring DORIS to increase its luminosity and raise its maximum energy so that Upsilon spectroscopy could be done. Following the approval of the ARGUS detector, the finishing touches were put on its design and various parts either put out for bid or spoken for by different groups in the collaboration. Progress toward completion has been satisfactory and the status of each is discussed

  6. A calorimetric measurement of the strong coupling constant in electron-positron annihilation at a center-of-mass energy of 91.6 GeV

    International Nuclear Information System (INIS)

    Martirena, S.G.

    1994-04-01

    In this work, a measurement of the strong coupling constant α s in e + e - annihilation at a center-of-mass energy of 91.6 GeV is presented. The measurement was performed with the SLD at the Stanford Linear Collider facility located at the Stanford Linear Accelerator Center in California. The procedure used consisted of measuring the rate of hard gluon radiation from the primary quarks in a sample of 9,878 hadronic events. After defining the asymptotic manifestation of partons as 'jets', various phenomenological models were used to correct for the hadronization process. A value for the QCD scale parameter Λ bar MS , defined in the bar MS renormalization convention with 5 active quark flavors, was then obtained by a direct fit to O(α s 2 ) calculations. The value of α s obtained was α s (M z0 ) = 0.122 ± 0.004 -0.007 +0.008 where the uncertainties are experimental (combined statistical and systematic) and theoretical (systematic) respectively. Equivalently, Λ bar MS = 0.28 -0.10 +0.16 GeV where the experimental and theoretical uncertainties have been combined

  7. Digital spectrometer for coincidence measurement of Doppler broadening of positron annihilation radiation

    International Nuclear Information System (INIS)

    Cizek, J.; Vlcek, M.; Prochazka, I.

    2010-01-01

    High-resolution digital coincidence Doppler broadening spectrometer equipped with two high-purity Ge detectors and two-channel 12-bit fast digitizer was developed and tested in this work. Two configurations were compared: (i) semi-digital setup which uses active analogue shaping of detector pulses prior to digitization to improve signal-to-noise ratio, and (ii) pure-digital setup which samples detector pulses directly. Software procedure developed for analysis of sampled waveforms, i.e. precise determination of energy of detected photon and rejection of distorted pulses, is described. Performance of digital coincidence spectrometer was compared with traditional analogue setup connected to the same detectors. It was found that digital spectrometer enables to achieve better energy resolution than in traditional analogue setup. Moreover, in digital configuration one has better control over shape of the signal. This allows efficient elimination of undesired distorted or damaged waveforms and to obtain spectrum of better clarity. The superior parameters of new digital coincidence Doppler broadening spectrometer are demonstrated by benchmark measurements of well defined Fe and Al specimens and also by the detection of rare annihilation in flight events.

  8. WORKSHOP: Electron-positron mystery

    International Nuclear Information System (INIS)

    Bokemeyer, H.; Mueller, B.

    1989-01-01

    The tightly correlated electron-positron pairs seen in experiments at the GSI Darmstadt heavy ion Laboratory and elsewhere have yet to be explained. New particle or new effect? The question was highlighted at a recent Moriond workshop held at Les Arcs in the French Alps in January

  9. Next generation of electron-positron colliding beam machines

    International Nuclear Information System (INIS)

    Richter, B.

    1979-03-01

    The contribution of electron-positron colliding beam experiments to high-energy physics in the 1970's has been prodigious. From the research done with the two highest-energy e + e - machines of the present generation of these devices, have come such things as the discovery and illumination of the properties of the psi family, charmed particles, a new heavy lepton, non-ambigious evidence for hadronic jets, etc. The rapid pace of new developments in physics from such machines comes about for two reasons. First, the electron-positron annihilation process at present energies is particularly simple and well understood, making the problem of determining the quantum numbers and properties of new particles particularly simple. Second, in electron-positron annihilation all final states are on a relatively equal footing, and small production cross sections are compensated for by a lack of confusing background. For example, the rate of production of charmed particles at the SPEAR storage ring at SLAC and the DORIS storage ring at DESY is 3 or 4 orders of magnitude less than the rate of production at FNAL and the SPS. Yet these particles were first found at the storage rings where the background cross sections are comparable to the signal cross section, and have not yet been observed directly by their hadronic decays at the proton machines where the background cross sections are 4 orders of magnitude larger than the signal cross sections. The machines PEP at SLAC and PETRA at DESY will soon be operating at 35 to 40 GeV cm to explore new regions of energy. Studies of electron-positron annihilation at much higher energies than presently planned have a great deal to teach, not only about particle structure and dynamics, but also about the nature of the weak interaction. Some of the physics which can be done with such machines is discussed with a view toward getting an idea of the minimum required energy for the new generation of colliding beam devices

  10. 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.

  11. Electron-positron pairs in physics and astrophysics: From heavy nuclei to black holes

    Science.gov (United States)

    Ruffini, Remo; Vereshchagin, Gregory; Xue, She-Sheng

    2010-02-01

    +e- annihilation to hadronic channels, in addition to the Dirac electromagnetic channel; (B) ongoing Earth-based experiments to detect electron-positron production in strong fields by focusing coherent laser beams and by electron-beam-laser collisions; and (C) the multiyear attempts to detect electron-positron production in Coulomb fields for a large atomic number Z>137 in heavy-ion collisions. These attempts follow the classical theoretical work of Popov and Zeldovich, and Greiner and their schools. We then turn to astrophysics. We first review the basic work on the energetics and electrodynamical properties of an electromagnetic black hole and the application of the Schwinger formula around Kerr-Newman black holes as pioneered by Damour and Ruffini. We only focus on black hole masses larger than the critical mass of neutron stars, for convenience assumed to coincide with the Rhoades and Ruffini upper limit of 3.2 M⊙. In this case the electron Compton wavelength is much smaller than the space-time curvature and all previous results invariantly expressed can be applied following well established rules of the equivalence principle. We derive the corresponding rate of electron-positron pair production and introduce the concept of dyadosphere. We review the recent progress in describing the evolution of optically thick electron-positron plasma in the presence of supercritical electric field, which is relevant both in astrophysics as well as in ongoing laser beam experiments. In particular we review the recent progress based on the Vlasov-Boltzmann-Maxwell equations to study the feedback of the created electron-positron pairs on the original constant electric field. We evidence the existence of plasma oscillations and its interaction with photons leading to energy and number equipartition of photons, electrons and positrons. We finally review the recent progress obtained by using the Boltzmann equations to study the evolution of an electron-positron-photon plasma towards thermal

  12. Wake field in electron-positron plasmas

    International Nuclear Information System (INIS)

    Avinash, K.; Berezhiani, V.I.

    1993-03-01

    We study the creation of wake field in cold electron positron plasma by electron bunches. In the resulting plasma inhomogeneity we study the propagation of short electromagnetic pulse. In is found that wake fields can change the frequency of the radiation substantially. (author). 7 refs, 1 fig

  13. LEP - Large Electron Positron Exhibition LEPFest 2000

    CERN Multimedia

    2000-01-01

    The Large Electron-Positron Collider (LEP) is 27 km long. Its four detectors (ALEPH, DELPHI, L3, OPAL) measure precisely what happens in the collisions of electrons and positrons. These conditions only exist-ed in the Universe when it was about 10 -10 sec old.

  14. Quark flavor identification in electron-positron annihilation

    International Nuclear Information System (INIS)

    Kaye, H.S.

    1983-09-01

    The theoretical issues relevant to inclusive muon analysis, the MAC detector and its data flow structure, the identification of muons in hadronic events and the measurement of their momenta, and the selection of events so as to minimize background are described. Experimental results are presented describing the fragmentation of heavy quarks into hadrons, the semimuonic branching fractions of the heavy quarks, the asymmetry in the angular distribution of the heavy quarks, and the invariant mass and charged multiplicity of heavy quark jets. In addition, lower limits are set on the masses of certain proposed particles that are expected to decay semileptonically. Finally, events containing two muons are analyzed in order to investigate the possibility of mixing in the B-B system and whether the b might form its own SU(2) singlet

  15. Theory of electron--positron annihilation into hadrons

    International Nuclear Information System (INIS)

    Gilman, F.J.

    1975-01-01

    The total cross section for e + e - → hadrons and R, its ratio to the muon pair cross section, the physics below and above the threshold near 4 GeV cms with particular attention to what is changing there and exactly where it happens, and inclusive distributions and jets of final state hadrons are treated

  16. Approach to asymptopia in electron-positron annihilation into hadrons

    International Nuclear Information System (INIS)

    Choudhury, D.K.

    1975-01-01

    Assuming CEA/SPEAR energies to be nonasymptotic and from the positivity of the parton mass squared, it is derived that the asymptotic ratio Rsub(infinity) should lie within the interval [6.69+-1.00,7.77+-1.00]. Rsub(infinity) is the limit ratio of the cross sections of the reactions e + e - →hadrons and e + e - →μ + μ - respectively, as s tends to infinity. Present estimate is based on the application of leading-order finite-mass correction to the light-cone algebra/parton model in the non-asymptotic region

  17. Cosmological Implications of the Electron-Positron Aether

    Science.gov (United States)

    Rothwarf, Allen

    1997-04-01

    An aether is not prohibited on theoretical nor experimental grounds; only a credible physical model for it is lacking.By assuming that the particles and anti-particles created during the "big-bang" origin of the universe have not annihilated one another, but instead, form a bound state plasma, we have a model for a real aether.This aether is dominated by electron-positron pairs at very high density(10**30/cm3),in close analogy with electron-hole droplets formed in laser irradiated semiconductors. The Fermi velocity of this plasma is the speed of light, and the plasma expands at this speed. This gives results for the expanding universe in agreement with the Einstein-deSitter result for a universe dominated by radiation.The speed of light varies with time as do the other fundamental constants.This leads to an alternate explanation for cosmological redshifts. Independent,mini big bangs can occur and account for observed anomalous redshifts. The model can be tested using LIGO apparatus.

  18. The PEP electron-positron ring

    International Nuclear Information System (INIS)

    Rees, J.R.

    1988-01-01

    The first stage of the positron-electron-proton (PEP) colliding-beam system which has been under joint study by a Lawrence Berkeley Laboratory-Stanford Linear Accelerator Center team for the past two years, will be the electron-positron storage ring. The physics justification for the e + e/sup minus/ ring is summarized briefly and the proposed facility is described. The ring will have six arcs having gross radii of about 220 m and six interaction regions located at the centers of straight sections about 130 m long. The longitudinal distance left free for experimental apparatus at the intersection regions will be 20 m. The range of operating beam energies will be from 5 GeV to 15 GeV. The design luminosity at 15 GeV will be 10 32 cm/sup minus 2/s/sup minus 1/, and the luminosity will vary approximately as the square of the beam energy. Alternative methods under consideration for adjusting the beam cross-section are discussed. The designs of the storage ring subsystems and of the conventional facilities including the experimental halls at the interaction regions are described

  19. Electron-positron plasma generation in a pulsar magnetosphere

    International Nuclear Information System (INIS)

    Gurevich, A.V.; Istomin, Ya.N.

    1985-01-01

    The generation of an electron-positron plasma in vacuum (vacuum ''breakdown'') in the presence of an inhomogeneous electric field and strong curvilinear magnetic field is considered. A situation of this type may occur in the magnetosphere of a rotating neutron star. A general set of kinetic equations for electrons, positrons and γ quanta in a curvilinear magnetic field is derived by taking into account electron-positron pair production and emission of curvicur and synchrotron photons. The conditions for appearance of ''breakdown'' are determined and the threshold value of the elec tric field discontinuity at the surface of the star is found. Multiplication of particles in the magnetosphere is investigated and the electron, positron and γ quantum distribution functions are found. The extinction limit of pulsars is determined. The theory is shown to be in accordance with the observation results

  20. Study of electron-positron interactions

    International Nuclear Information System (INIS)

    Abashian, A.; Gotow, K.; Philonen, L.

    1990-01-01

    For the past seven years, this group has been interested in the study of tests of the Standard Model of Electroweak interactions. The program has centered about the AMY experiment which examines the nature of the final state products in electron-positron collisions in the center of mass energy range near 60 GeV. Results of these measurements have shown a remarkable consistency with the predictions of the minimal model of 3 quark and lepton generations and single charged and neutral intermediate bosons. No new particles or excited states have been observed nor has any evidence for departures in cross sections or angular asymmetries from expectations been observed. These conclusions have been even more firmly established by the higher energy results from the LEP and SLC colliders at center of mass energies of about 90 GeV. Our focus is shifting to the neutrino as a probe to electroweak interactions. The relative merit of attempting to observe neutrinos from point sources versus observing neutrinos generally is not easy to predict. The improved ability to interpret is offset by the probably episodic nature of the emission and irreproducibility of the results. In this phase of development, it is best to be sensitive to both sources of neutrinos. As a second phase of our program at Virginia Tech, we are studying the feasibility of detecting cosmic ray neutrinos in a proposed experiment which we have called NOVA. the results of the test setup will be instrumental in developing an optimum design. A third program we are involved in is the MEGA experiment at Los Alamos, an experiment to place a limit on the rate of muon decay to electron plus photon which is forbidden by the Standard Model

  1. Laser driven electron-positron pair creation-kinetic theory versus analytical approximations

    International Nuclear Information System (INIS)

    Smolyansky, S.A.; Prozorkevich, A.V.; Bonitz, M.

    2013-01-01

    The dynamical Schwinger effect of vacuum pair creation driven by an intense external laser pulse is studied on the basis of quantum kinetic theory. The numerical solutions of these kinetic equations exhibit a complex time dependence which makes an analysis of the physical processes difficult. In particular, the question of secondary effects, such as creation of secondary annihilation photons from the focus spot of the colliding laser beams, remains an important open problem. In the present work we, therefore, develop a perturbation theory which is able to capture the dominant time dependence of the produced electron-positron pair density. The theory shows excellent agreement with the exact kinetic results during the laser pulse, but fails to reproduce the residual pair density remaining in the system after termination of the pulse. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Investigation of induced radioactivity in the CERN Large Electron Positron collider for its decommissioning

    CERN Document Server

    Silari, Marco

    2004-01-01

    The future installation of the Large Hadron Collider in the tunnel formerly housing the Large Electron Positron collider (LEP) required the dismantling of the latter after 11-year operation. As required by the French legislation, an extensive theoretical study was conducted before decommissioning to establish the possible activation paths both in the accelerator and in the four experiments (L3, ALEPH, OPAL and DELPHI) installed around the ring. The aim was to define which areas may contain activated material and which ones would be completely free of activation. The four major sources of activation in LEP, i.e., distributed and localized beam losses, synchrotron radiation and the super-conducting RF cavities, were investigated. Conversion coefficients from unit lost beam power to induced specific activity were established for a number of materials. A similar study was conducted for the four experiments, evaluating the four potential sources of induced radioactivity, namely e**+e **- annihilation events, two-p...

  3. Topics in electron-positron interactions

    International Nuclear Information System (INIS)

    Soeding, P.

    1983-01-01

    This chapter investigates the collision of an electron and a positron in a high energy storage ring in which a large energy Q=W=√s=2 E /SUB beam/ is dumped into a tiny region of space-time. If the electron and positron annihilate each other almost all of this energy becomes concentrated in a single field quantum. Points out 3 consequences: 1) all flavored particles existing in nature are expected to be pair-produced provided their mass is not larger than W/2; 2) the pair production process acts as an effective ''filter'' for fundamental (i.e. pointlike) particles; and 3) particles without flavor (i.e. the gluons) are not directly pair-produced in e - e + interactions. Discusses basic processes; probing QED and lepton structure; hadron production at high energies; resonances; e - e + storage rings; detectors; electroweak interaction and new particles (leptons, quarks); restrictions on a more general weak interaction scenario; limits on pair production of scalar particles; and jets and QCD tests

  4. Electron-positron pair creation in heavy ion collisions

    International Nuclear Information System (INIS)

    Kienle, P.

    1987-01-01

    The authors review the status of experiments to study the electron positron pair creation in heavy ion atom collisions at bombarding energies close to the Coulomb barrier. The disentanglement and characterization of various sources of positrons observed in such collisions are described with a focus on the monoenergetic electron positron pairs observed. They seem to originate from the two-body decay of a family of neutral particles with masses of about 3m and lifetimes in the range of 6 x 10 - 14 s, produced by high Coulomb fields. First attempts were made to create these particles by resonant Bhabha scattering

  5. Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.

    Science.gov (United States)

    Adamová, D; Agakichiev, G; Appelshäuser, H; Belaga, V; Braun-Munzinger, P; Cherlin, A; Damjanović, S; Dietel, T; Dietrich, L; Drees, A; Esumi, S I; Filimonov, K; Fomenko, K; Fraenkel, Z; Garabatos, C; Glässel, P; Hering, G; Holeczek, J; Kushpil, V; Lenkeit, B; Maas, A; Marín, A; Milosević, J; Milov, A; Miśkowiec, D; Panebrattsev, Yu; Petchenova, O; Petrácek, V; Pfeiffer, A; Rak, J; Ravinovich, I; Rehak, P; Richter, M; Sako, H; Schmitz, W; Sedykh, S; Seipp, W; Sharma, A; Shimansky, S; Slívová, J; Specht, H J; Stachel, J; Sumbera, M; Tilsner, H; Tserruya, I; Wessels, J P; Wienold, T; Windelband, B; Wurm, J P; Xie, W; Yurevich, S; Yurevich, V

    2003-07-25

    We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

  6. Electron-positron pair production in Coulomb collisions at ultrarelativistic energies

    International Nuclear Information System (INIS)

    Vane, C.R.; Datz, S.; Dittner, P.F.; Krause, H.F.; Bottcher, C.; Strayer, M.; Schuch, R.; Gao, H.; Hutton, R.

    1993-01-01

    We have measured angular and momentum distributions for electrons and positrons created as pairs in peripheral collisions of 6.4 TeV bare sulfur ions with fixed targets of Al, Pd, and Au. Singly- and doubly-differential cross sections have been determined for 1--17 MeV/c electrons and positrons detected independently and in coincidence as pairs. Integrated yields for pair production are found to vary as the square of the target nuclear charge. Relative angular and momentum differential cross sections are effectively target independent. Probability distributions for the pair total momentum, the positron fraction of the pair momentum, and the pair traverse momentum have been derived from the coincident electron-positron data

  7. Electron-positron colliders: looking at future physics

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    1991-12-15

    With research and development work underway throughout the world towards high energy electron-positron linear colliders, interest turns to the new physics these machines would open up. The first International Workshop on Physics and Experiments with Linear Colliders was held recently in Selkirk's in Finnish Lapland - some 300 kilometres north of the Arctic Circle.

  8. Simulation of tail distributions in electron-positron circular colliders

    International Nuclear Information System (INIS)

    Irwin, J.

    1992-02-01

    In addition to the Gaussian shaped core region, particle bunches in electron-positron circular colliders have a rarefied halo region of importance in determining beam lifetimes and backgrounds in particle detectors. A method is described which allows simulation of halo particle distributions

  9. Electromagnetic pulses in a strongly magnetized electron-positron plasma

    International Nuclear Information System (INIS)

    Yu, M.Y.; Rao, N.N.

    1985-01-01

    The conditions for the existence of large-amplitude localized electromagnetic wave pulses in an electron-positron plasma penetrated by a very strong ambient magnetic field are obtained. It is shown that such pulses can exist in pulsar polar magnetospheres. 12 references

  10. A relativistic solitary wave in electron positron plasma

    International Nuclear Information System (INIS)

    Berezhiani, V.I.; Skarka, V.; Mahajan, S.

    1993-09-01

    The relativistic solitary wave propagation is studied in cold electron-positron plasma embedded in an external arbitrary strong magnetic field. The exact, analytical soliton-like solution corresponding to a localized, purely electromagnetic pulse with arbitrary big amplitude is found. (author). 7 refs, 1 fig

  11. Electron-positron colliders: looking at future physics

    International Nuclear Information System (INIS)

    Anon.

    1991-01-01

    With research and development work underway throughout the world towards high energy electron-positron linear colliders, interest turns to the new physics these machines would open up. The first International Workshop on Physics and Experiments with Linear Colliders was held recently in Selkirk's in Finnish Lapland - some 300 kilometres north of the Arctic Circle

  12. Bruno Touschek: From Betatrons to Electron-Positron Colliders

    Science.gov (United States)

    Bernardini, Carlo; Pancheri, Giulia; Pellegrini, Claudio

    Bruno Touschek’s life as a physicist spanned the period from World War II to the 1970s. He was a key figure in the developments of electron-positron colliders and storage rings, and made important contributions to theoretical high energy physics. Storage rings, initially developed for high energy physics, are being widely used in many countries as synchrotron radiation sources and are a tool for research in physics, chemistry, biology, environmental sciences and cultural heritage studies. We describe Touschek’s life in Austria, where he was born, in Germany, where he participated in the construction of a betatron during WWII, and in Italy, where he proposed and led to completion the first electron-positron storage ring in 1960, in Frascati. We highlight how his central European culture influenced his lifestyle and work, and his main contributions to physics, such as the discovery of the Touschek effect and beam instabilities in the larger storage ring ADONE.

  13. Electron-positron pair creation in heavy ion collisions

    International Nuclear Information System (INIS)

    Kienle, P.

    1987-08-01

    We review here the status of experiments to study the electron positron pair creation in heavy ion atom collisions at bombarding energies close to the Coulomb barrier. The disentanglement and characterisation of various sources of positrons observed in such collisions are described with a focus on the monoenergetic electron positron pairs observed. They seem to originate from the two-body decay of a family of neutral particles with masses of about 3 m e and life times in the range of 6x10 -14 s -10 s, produced by high Coulomb fields. First attempts were made to create these particles by resonant Bhabha scattering. First we present some experimental methods for high efficiency positron spectroscopy in heavy ion collisions. Then we describe the discovery of positron creation induced by strong time changing Coulomb fields. (orig./HSI)

  14. Classical-quantum correspondence in electron-positron pair creation

    International Nuclear Information System (INIS)

    Chott, N. I.; Su, Q.; Grobe, R.

    2007-01-01

    We examine the creation of electron-positron pairs in a very strong force field. Using numerical solutions to quantum field theory we calculate the spatial and momentum probability distributions for the created particles. A comparison with classical mechanical phase space calculations suggests that despite the fully relativistic and quantum mechanical nature of the matter creation process, most aspects can be reproduced accurately in terms of classical mechanics

  15. Electrostatic stability of electron-positron plasmas in dipole geometry

    OpenAIRE

    Mishchenko, Alexey; Plunk, Gabriel; Helander, Per

    2017-01-01

    The electrostatic stability of electron-positron plasmas is investigated in the point-dipole and Z-pinch limits of dipole geometry. The kinetic dispersion relation for sub-bounce-frequency instabilities is derived and solved. For the zero-Debye-length case, the stability diagram is found to exhibit singular behavior. However, when the Debye length is non-zero, a fluid mode appears, which resolves the observed singularity, and also demonstrates that both the temperature and density gradients c...

  16. Vortex structures in dense electron-positron-ion plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Haque, Q [Theoretical Plasma Physics Division, PINSTECH, P O Nilore, Islamabad (Pakistan)], E-mail: qamar_haque@hotmail.com

    2009-11-15

    A linear dispersion relation for electrostatic quantum drift and acoustic waves has been found for dense electron-positron-ion magnetoplasmas. Both the fermion and thermal temperature effects have been considered for electrons and positrons. In the nonlinear regime, a stationary solution in the form of dipolar vortices has been obtained. For illustration, the results were applied to the astrophysical plasma of the atmosphere of neutron stars/pulsars.

  17. ''Heavy light bullets'' in electron-positron plasma

    International Nuclear Information System (INIS)

    Berezhiani, V.I.; Mahajan, S.M.

    1995-03-01

    The nonlinear propagation of circularly polarized electromagnetic waves with relativistically strong amplitudes in an unmagnetized hot electron-positron plasma with a small fraction of ions is investigated. The possibility of finding localized solutions in such a plasma is explored. It is shown that these plasmas support the propagation of ''heavy light bullets''; nondiffracting and nondispersive electromagnetic (EM) pulses with large density bunching. (author). 24 refs, 12 figs

  18. Electron-positron correlations in an electron liquid

    International Nuclear Information System (INIS)

    Stachowiak, H.

    1980-01-01

    The importance of studying electron-positron interaction for the interpretation of angular correlation data obtained for metallic systems is emphasized. The most successful approaches to electron-positron correlations in jellium are presented. Those include the Bethe-Goldstone two-body equation proposed by Kahana, the charge-density-dielectric function approach connected with the names of Singwi, Sjolander, Stott and Bhattacharyya and the Sawada boson-generalized Tamm-Dancoff approach elaborated recently by Arponen and Pajanne. In conclusion, it is reported that one can consider that the behaviour of a positron at rest in jellium is relatively well understood, though the problem of the optimal choice of a two-body electron-positron phenomenological equation is still open. Also, the behaviour of a positron in a real metal is not well understood and so far, serious calculations in this field have been performed only on very simple models while realistic calculations of the ACPAQ curves tend to minimize the importance of the problems which remain to be solved. (K.B.)

  19. Research of the internal electron-positron pair production

    International Nuclear Information System (INIS)

    Fenyes, Tibor

    1985-01-01

    The phenomenon of internal electron-positron pair production by excited nuclei is briefly reviewed. The advantages of this phenomenon in nuclear structure investigations are pointed. The new Si(Li)-Si(Li) electron spectrometer with superconducting magnetic transporter (SMS) built at ATOMKI, Hungary, was tested for detection of internal electron-positron pair production events. Proton beam of a Van de Graaff accelerator of 5 MV was used to excite the target nuclei of sup(27)Al, sup(42)Ca and sup(19)F. The internal pair production coefficients were measured and compared with the data of literature. The detection efficiency of SMS is calculated to be (37+-7)%. The test proved that the SMS is suitable for nuclear structure investigations producing electron-positron pairs. The SMS of ATOMKI is recently the top instrument all over the world in this field: its detection efficiency, energy resolution and applicability for multipolarity identification are much better than these properties of other detectors. (D.Gy.)

  20. 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)

  1. Precise tests of QCD in e+e- annihilation

    International Nuclear Information System (INIS)

    Burrows, P.N.

    1997-03-01

    A pedagogical review is given of precise tests of QCD in electron-positron annihilation. Emphasis is placed on measurements that have served to establish QCD as the correct theory of strong interactions, as well as measurements of the coupling parameter α s . An outlook is given for future important tests at a high-energy e + e - collider

  2. A magnetic-lens - mini-orange coincidence spectrometer

    International Nuclear Information System (INIS)

    Bargholtz, C.; Holmberg, L.; Ruus, N.; Tegner, P.E.; Weiss, G.

    1997-04-01

    A coincidence spectrometer consisting of a Gerholm type magnetic lens and a permanent magnet mini-orange spectrometer is described. Electron-electron or electron-positron coincidences may be registered in various angular settings. The spectrometer has been developed mainly to search for anomalous contributions to Bhabha scattering or positrons and is at present used for such studies. 6 refs

  3. A study of electron-positron pair equilibria in models of compact X- and gamma-ray sources

    International Nuclear Information System (INIS)

    Bjoernsson, G.

    1990-01-01

    Thermal electron-positron pair equilibria in two temperature models of compact x ray and gamma ray sources are studied. The pairs are assumed to be heated by Coulomb interaction with the much hotter protons and cooled by bremsstrahlung emission, Compton scattering, and annihilation. Two parameters, the proton optical depth and the compactness, characterize each equilibrium state. It is shown that a careful account of the energy balance is very important when the stability properties of the pair equilibria in a spherical plasma cloud are determined. The equilibria are found to be unstable in a very limited range of compactness and proton optical depth. This particular instability is unlikely to be the cause of the observed variability of the compact sources and implies that it is possible to build up high pair densities by a thermal mechanism in two temperature environments. The most important result considers the effects of pairs on the structure of geometrically and effectively optically thin accretion disks. A new approach for solving for the equilibrium structure of the disks is presented. In effect, the pair equilibrium states are projected into the space spanned by the disk structure parameters. This allows a direct visualization of all possible disk solutions at once. Each solution profile needs to be calculated only once and a complete disk solution is obtained by a simple radial coordinate transformation. The disk solutions are thus seen to be scale free in terms of the radial coordinate as well as in terms of the mass of the central object and the accretion rate. Two particular disk solutions are given. It is shown that including electron-positron pairs in the disk structure calculations leads to a breakdown of the thin disk assumptions and that more detailed disk modeling is required before electron-positron pairs can be self-consistently included

  4. Recoil effects in multiphoton electron-positron pair creation

    International Nuclear Information System (INIS)

    Krajewska, K.; Kaminski, J. Z.

    2010-01-01

    Triply differential probability rates for electron-positron pair creation in laser-nucleus collisions, calculated within the S-matrix approach, are investigated as functions of the nuclear recoil. Pronounced enhancements of differential probability rates of multiphoton pair production are found for a nonzero momentum transfer from the colliding nucleus. The corresponding rates show a very dramatic dependence on the polarization of the laser field impinging on the nucleus; only for a linearly polarized light are the multiphoton rates for electron-positron pair production considerably large. We focus therefore on this case. Our numerical results for different geometries of the reaction particles demonstrate that, for the linearly polarized laser field of an infinite extent (which is a good approximation for femtosecond laser pulses), the pair creation is far more efficient if the nucleus is detected in the direction of the laser-field propagation. The corresponding angular distributions of the created particles show that the high-energy pairs are predominantly produced in the plane spanned by the polarization vector and the laser-field propagation direction, while the low-energy pairs are rather spread around the latter of the two directions. The enhancement of differential probability rates at each energy sector, defined by the four-momentum conservation relation, is observed with varying the energy of the produced particles. The total probability rates of pair production are also evaluated and compared with the corresponding results for the case when one disregards the recoil effect. A tremendous enhancement of the total probability rates of the electron-positron pair creation is observed if one takes into account the nuclear recoil.

  5. Optical distortions in electron/positron storage rings

    International Nuclear Information System (INIS)

    Brown, K.L.; Donald, M.; Servranckx, R.

    1983-01-01

    We have studied the optical distortions in the PEP electron/positron storage ring for various optical configurations using the computer programs DIMAT, HARMON, PATRICIA, and TURTLE. The results are shown graphically by tracing several thousand trajectories from one interaction region to the next using TURTLE and by tracing a few selected rays several hundred turns using the programs DIMAT and PATRICIA. The results show an interesting correlation between the calculated optical cleanliness of a particular lattice configuration and the observed operating characteristics of the machine

  6. The Cornell electron-positron storage ring - CESR

    International Nuclear Information System (INIS)

    DeWire, J.W.

    1977-01-01

    At the Laboratory of Nuclear Studies of Cornell University we are working on a project to convert the present 12 GeV electron synchrotron complex into the Cornell Electron-Positron Storage Ring - CESR. The design studies for this new device were begun in early 1975. During the past eighteen months the National Science Foundation has supported a program of research and development on CESR and funds to begin construction are included in the NSF budget now before the U.S. Congress. Our goal is to have CESR in operation in the fall of 1979. (orig.) [de

  7. Relativistic current sheets in electron-positron plasmas

    International Nuclear Information System (INIS)

    Zenitani, S.

    2008-01-01

    The current sheet structure with magnetic field reversal is one of the fundamental structure in space and astrophysical plasmas. It draws recent attention in high-energy astrophysical settings, where relativistic electron-positron plasmas are considered. In this talk we will review the recent progress of the physical processes in the relativistic current sheet. The kinetic stability of a single current sheet, the nonlinear behavior of these instabilities, and recent challenges on the multi current sheet systems are introduced. We will also introduce some problems of magnetic reconnection in these relativistic environments. (author)

  8. Electron--positron storage ring PETRA: plans and status

    International Nuclear Information System (INIS)

    Voss, G.A.

    1977-01-01

    Construction of the Electron-Positron Storage Ring PETRA was authorized October 20, 1975. At present most of the civil engineering work is completed and ring installation work is under way. All major components are on order and series production of bending magnets, quadrupoles, vacuum chambers and rf-resonators has started. Start-up of the machine is planned with a fourfold symmetry configuration with four active beam-beam interaction points. Five experimental facilities have been recommended for the first round of experiments scheduled to begin mid 79

  9. Four Pion Final States with Tagged Photons at Electron Positron Colliders

    CERN Document Server

    Czyz, H

    2001-01-01

    A Monte Carlo generator has been constructed to simulate the reaction e^+e^- \\to \\gamma + 4 \\pi, where the photon is assumed to be observed in the detector. Isospin relations between the amplitudes governing tau decays into four pions and electron positron annihilation into four pions respectively have been found which allow to determine all four modes after the amplitude for the \\pi^+\\pi^-2\\pi^0 channel has been fixed. The kinematic breaking of these isospin relations as a consequence of the \\pi^- -- \\pi^0 mass difference has also been investigated. The program is constructed in analogy to an earlier one simulating e^+e^- \\to \\gamma + 2 \\pi. However, it does not include final state radiation from the charged pions. Additional collinear photon radiation has been incorporated with the technique of structure functions. Predictions are presented for cms energies of 1GeV, 3GeV and 10GeV, corresponding to the energies of DAPHNE, BEBC and of B-meson factories. Using this program it is demonstrated that, even after ...

  10. Electron-positron pair creation from vacuum induced by variable electric field

    International Nuclear Information System (INIS)

    Marinov, M.S.; Popov, V.S.

    1977-01-01

    Problem is considered of spontaneous creation of electron-positron pairs from the vacuum induced by external electric field, that is homogeneous and depends on time in an arbitrary way. The Heisenberg equations of motion are obtained for the creation-annihilation operators. The solution is a linear canonical transformation. The problem is reduced to a set of differential equations for the second-order matrices determining this transformation. A consequence of the CP symmetry of the Dirac equation with an external electric field is that the e + e - pair is created from the vacuum in a state with total spin 1. The case when the variating electric field conserves its direction, is considered in more detail. In this case the equations are much simplified and may be reduced to the Riccati equation or to problem of oscillator with variable frequency, so the problem is equivalent to the one-dimensional quantal problem of a barrier penetration. Two approximate methods to calculate the pair creation probabilities are discussed: the quasiclassical approach and the antidiabatical method, applicable for sharp variations of the external field. Numerical estimates are obtained for the number of e + e - pairs produced by the field E(t) = E cos ωt. Group-theoretical aspects of the problem are also considered. (author)

  11. Kinetics of electron-positron pair plasmas using an adaptive Monte Carlo method

    International Nuclear Information System (INIS)

    Pilla, R.P.; Shaham, J.

    1997-01-01

    A new algorithm for implementing the adaptive Monte Carlo method is given. It is used to solve the Boltzmann equations that describe the time evolution of a nonequilibrium electron-positron pair plasma containing high-energy photons. These are coupled nonlinear integro-differential equations. The collision kernels for the photons as well as pairs are evaluated for Compton scattering, pair annihilation and creation, bremsstrahlung, and Coulomb collisions. They are given as multidimensional integrals which are valid for all energies. For an homogeneous and isotropic plasma with no particle escape, the equilibrium solution is expressed analytically in terms of the initial conditions. For two specific cases, for which the photon and the pair spectra are initially constant or have a power-law distribution within the given limits, the time evolution of the plasma is analyzed using the new method. The final spectra are found to be in a good agreement with the analytical solutions. The new algorithm is faster than the Monte Carlo scheme based on uniform sampling and more flexible than the numerical methods used in the past, which do not involve Monte Carlo sampling. It is also found to be very stable. Some astrophysical applications of this technique are discussed. copyright 1997 The American Astronomical Society

  12. Faraday rotation in an electron-positron plasma containing a fraction of ions

    International Nuclear Information System (INIS)

    Hall, J.O.; Shukla, P.K.

    2005-01-01

    The Faraday rotation in a magnetized electron-positron plasma containing a fraction of ions is investigated by using a multifluid description. It is shown that the Faraday rotation for circularly polarized electromagnetic waves with frequencies much larger than the electron/positron plasma and electron gyrofrequencies is proportional to the ion number density and the magnitude of the ambient magnetic-field strength. The results are relevant for astrophysical observations and diagnostics of laboratory electron-positron-ion magnetoplasmas

  13. Velocity shear generated Alfven waves in electron-positron plasmas

    International Nuclear Information System (INIS)

    Rogava, A.D.; Berezhiani, V.I.; Mahajan, S.M.

    1996-01-01

    Linear MHD modes in cold, nonrelativistic electron-positron plasma shear flow are considered. The general set of differential equations, describing the evolution of perturbations in the framework of the nonmodal approach is derived. It is found, that under certain circumstances, the compressional and shear Alfven perturbations may exhibit large transient growth fuelled by the mean kinetic energy of the shear flow. The velocity shear also induces mode coupling allowing the exchange of energy as well as the possibility of a strong mutual transformation of these modes into each other. The compressional Alfven mode may extract the energy of the mean flow and transfer it to the shear Alfven mode via this coupling. The relevance of these new physical effects to provide a better understanding of the laboratory e + e - plasma is emphasized. It is speculated that the shear-induced effects in the electron-positron plasmas could also help solve some astrophysical puzzles (e.g., the generation of pulsar radio emission). Since most astrophysical plasma are relativistic, it is shown that the major results of the study remain valid for weakly sheared relativistic plasmas. (author). 21 refs, 4 figs

  14. Experiments using coincidence methods

    International Nuclear Information System (INIS)

    Anwar Dhani.

    1978-01-01

    Experiments on γ spectroscopy using the simple coincidence techniques, including investigation of angular distribution of γ radiation from annihilation process in decay of Na 22 , γ - γ angular correlation technique in decay of Co 60 , decay scheme study of Bi 207 and life time measurement of nuclear Pb 207 excited state have been carried out. (author)

  15. A Test of QED in Electron-Positron Annihilation at Energies around the Z Mass

    CERN Document Server

    Spartiotis, C

    1992-01-01

    A study of the reaction e+ e- -t 11( /) at center-of-mass energies around the mass of the z 0 boson(91.2Ge V) has been performed. The total and differential cross sections have been measured cor- responding to an integrated luminosity of 14.42pb- 1 . The results are in good agreement with QED predictions. Lower limits were set , at 95% confidence level, on the QED cutoff parameters of A+ >130 GeV, A_ >112 GeV and on the mass of an excited elec- tron of me* > 120 Ge V. z 0 rare decays with photonic signatures in the final state were also searched for. Upper limits, at 953 confi- dence level, for the branching ratio of z 0 decaying into 7ro/ /11, TJI and /// are 1.2 x 10-4, 1.7 x 10-4, 3.3 x 10- 5 respectively.

  16. Charmed and strange baryon production in 29 GeV electron positron annihilation

    International Nuclear Information System (INIS)

    Klein, S.R.

    1988-06-01

    This dissertation presents measurements of the production rates of baryons with different strangeness and spin. The analyses presented here use data taken with the Mark III detector at the PEP storage ring, operating at a center of mass energy of 29 GeV. The Ξ/sup /minus// production rate is measured to be 0.017 +- 0.004 +- 0.004 per hadronic event, Ω/sup /minus// production is measured to be 0.014 +- 0.006 +- 0.004 per hadronic event, and Ξ* 0 production is less than 0.006 per hadronic event at a 90% confidence level. These measurements place strong constraints on models of baryon production. In particular, the unexpectedly high rate of Ω/sup /minus// production is difficult to explain in any diquark based model. Semileptonic Λ/sub c/ + decays have also been observed. Because neither the branching ratios nor the production rate are well known, it is difficult to interpret these results. However, they do indicate that the branching ratio for Λ/sub c/ + → Λlν may be higher than previous experimental measurements. 85 refs., 45 figs., 12 tabs

  17. Charmed and strange baryon production in 29 GeV electron positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Klein, S.R.

    1988-06-01

    This dissertation presents measurements of the production rates of baryons with different strangeness and spin. The analyses presented here use data taken with the Mark III detector at the PEP storage ring, operating at a center of mass energy of 29 GeV. The ..xi../sup /minus// production rate is measured to be 0.017 +- 0.004 +- 0.004 per hadronic event, ..cap omega../sup /minus// production is measured to be 0.014 +- 0.006 +- 0.004 per hadronic event, and ..xi..*/sup 0/ production is less than 0.006 per hadronic event at a 90% confidence level. These measurements place strong constraints on models of baryon production. In particular, the unexpectedly high rate of ..cap omega../sup /minus// production is difficult to explain in any diquark based model. Semileptonic ..lambda../sub c//sup +/ decays have also been observed. Because neither the branching ratios nor the production rate are well known, it is difficult to interpret these results. However, they do indicate that the branching ratio for ..lambda../sub c//sup +/ ..-->.. ..lambda..l..nu.. may be higher than previous experimental measurements. 85 refs., 45 figs., 12 tabs.

  18. Energy-energy correlation in electron-positron annihilation at NNLL + NNLO accuracy

    Energy Technology Data Exchange (ETDEWEB)

    Tulipant, Zoltan; Kardos, Adam; Somogyi, Gabor [University of Debrecen, MTA-DE Particle Physics Research Group, Debrecen (Hungary)

    2017-11-15

    We present the computation of energy-energy correlation in e{sup +}e{sup -} collisions in the back-to-back region at next-to-next-to-leading logarithmic accuracy matched with the next-to-next-to-leading order perturbative prediction. We study the effect of the fixed higher-order corrections in a comparison of our results to LEP and SLC data. The next-to-next-to-leading order correction has a sizable impact on the extracted value of α{sub S}(M{sub Z}), hence its inclusion is mandatory for a precise measurement of the strong coupling using energy-energy correlation. (orig.)

  19. DIANA and applications to fermion production in electron-positron annihilation

    International Nuclear Information System (INIS)

    Fleischer, J.; Lorca, A.; Tentyukov, M.

    2004-01-01

    A demonstration of the use of DIANA has been given. As an example, the process e+e-->tt-bar was selected. Recent developments are indicated: automation of momenta distribution, the status of parallelization of FORM jobs, handling of topologies and new features for the implementation of fermions

  20. A search for single electron production in electron positron annihilation at E = 29 GeV

    International Nuclear Information System (INIS)

    Steele, T.R.

    1989-09-01

    This thesis presents experimental results from the ASP detector which took data on e + e - interactions in the PEP storage ring at SLAC. Its design was particularly suitable for searching for production of supersymmetric particles. The motivations for and phenomenology of Supersymmetry are discussed. In particular, the production of a single supersymmetric electron (''selectron'', e) in combination with a supersymmetric photon (''photino'', γ) would result in events in which a single electron and no other particles are observed in the detector at an e + e - collider such as PEP, provided the masses of these particles are not too large. Such events would also result from the production of a single supersymmetric W-boson (''wino'', W) in combination with a supersymmetric neutrino (''sneutrino'', ν). These processes make it possible to search for electrons and winos with masses greater than the beam energy. Observation of these unusual events would distinctly indicate the production of new particles. The ASP detector was designed to be hermetic and to provide efficient event reconstruction for low multiplicity events. The detector is described and its performance is evaluated; it is found to be well-suited to this study. The data sample collected with the detector was thoroughly analyzed for evidence of single-electron events. The various possible background processes are considered and Monte Carlo calculations of the distributions from single selectron and single wino production are presented. Using this information an efficient off-line event selection process was developed, and it is described in detail. 82 refs., 41 figs., 4 tabs

  1. Lectures in electron--positron annihilation. Part II. Anomalous lepton production

    International Nuclear Information System (INIS)

    Perl, M.L.

    1975-06-01

    Data and an analysis in progress of these data are presented for events of the type e + + e - → e/sup +-/ + μ/sup +-/ + missing mass in which no other particles are detected. Heavy leptons and bosons, the intermediate boson, other elementary bosons, and other interpretations are considered. Other anomalous lepton production processes are also discussed briefly. 12 references

  2. Energy-energy correlation in electron-positron annihilation at NNLL + NNLO accuracy

    Science.gov (United States)

    Tulipánt, Zoltán; Kardos, Adam; Somogyi, Gábor

    2017-11-01

    We present the computation of energy-energy correlation in e^+e^- collisions in the back-to-back region at next-to-next-to-leading logarithmic accuracy matched with the next-to-next-to-leading order perturbative prediction. We study the effect of the fixed higher-order corrections in a comparison of our results to LEP and SLC data. The next-to-next-to-leading order correction has a sizable impact on the extracted value of α S(M_Z), hence its inclusion is mandatory for a precise measurement of the strong coupling using energy-energy correlation.

  3. Pumping Electron-Positron Pairs from a Well Potential.

    Science.gov (United States)

    Wang, Qiang; Liu, Jie; Fu, Li-Bin

    2016-04-29

    In the presence of very deep well potential, electrons will spontaneously occupy the empty embedded bound states and electron-positron pairs are created by means of a non-perturbative tunneling process. In this work, by slowly oscillating the width or depth, the population transfer channels are opened and closed periodically. We find and clearly show that by the non-synchronous ejections of particles, the saturation of pair number in a static super-critical well can be broken, and electrons and positrons can be pumped inexhaustibly from vacuum with a constant production rate. In the adiabatic limit, final pair number after a single cycle has quantized values as a function of the upper boundary of the oscillating, and the critical upper boundaries indicate the diving points of the bound states.

  4. Search for excited charged leptons in electron positron collisions

    CERN Document Server

    Vachon, Brigitte Marie Christine; Sobie, Randall

    2002-01-01

    A search for evidence that fundamental particles are made of smaller subconstituents is performed. The existence of excited states of fundamental particles would be an unambiguous indication of their composite nature. Experimental signatures compatible with the production of excited states of charged leptons in electron-positron collisions are studied. The data analysed were collected by the OPAL detector at the LEP collider. No evidence for the existence of excited states of charged leptons was found. Upper limits on the product of the cross-section and the electromagnetic branching fraction are inferred. Using results from the search for singly produced excited leptons, upper limits on the ratio of the excited lepton coupling constant to the compositeness scale are calculated. From pair production searches, 95% confidence level lower limits on the masses of excited electrons, muons and taus are determined to be 103.2 GeV.

  5. Nonlinear electromagnetic waves in a degenerate electron-positron plasma

    Energy Technology Data Exchange (ETDEWEB)

    El-Labany, S.K., E-mail: skellabany@hotmail.com [Department of Physics, Faculty of Science, Damietta University, New Damietta (Egypt); El-Taibany, W.F., E-mail: eltaibany@hotmail.com [Department of Physics, College of Science for Girls in Abha, King Khalid University, Abha (Saudi Arabia); El-Samahy, A.E.; Hafez, A.M.; Atteya, A., E-mail: ahmedsamahy@yahoo.com, E-mail: am.hafez@sci.alex.edu.eg, E-mail: ahmed_ateya2002@yahoo.com [Department of Physics, Faculty of Science, Alexandria University, Alexandria (Egypt)

    2015-08-15

    Using the reductive perturbation technique (RPT), the nonlinear propagation of magnetosonic solitary waves in an ultracold, degenerate (extremely dense) electron-positron (EP) plasma (containing ultracold, degenerate electron, and positron fluids) is investigated. The set of basic equations is reduced to a Korteweg-de Vries (KdV) equation for the lowest-order perturbed magnetic field and to a KdV type equation for the higher-order perturbed magnetic field. The solutions of these evolution equations are obtained. For better accuracy and searching on new features, the new solutions are analyzed numerically based on compact objects (white dwarf) parameters. It is found that including the higher-order corrections results as a reduction (increment) of the fast (slow) electromagnetic wave amplitude but the wave width is increased in both cases. The ranges where the RPT can describe adequately the total magnetic field including different conditions are discussed. (author)

  6. Electrostatic stability of electron-positron plasmas in dipole geometry

    Science.gov (United States)

    Mishchenko, Alexey; Plunk, Gabriel G.; Helander, Per

    2018-04-01

    The electrostatic stability of electron-positron plasmas is investigated in the point-dipole and Z-pinch limits of dipole geometry. The kinetic dispersion relation for sub-bounce-frequency instabilities is derived and solved. For the zero-Debye-length case, the stability diagram is found to exhibit singular behaviour. However, when the Debye length is non-zero, a fluid mode appears, which resolves the observed singularity, and also demonstrates that both the temperature and density gradients can drive instability. It is concluded that a finite Debye length is necessary to determine the stability boundaries in parameter space. Landau damping is investigated at scales sufficiently smaller than the Debye length, where instability is absent.

  7. Nonlinear electrostatic solitary waves in electron-positron plasmas

    Science.gov (United States)

    Lazarus, I. J.; Bharuthram, R.; Moolla, S.; Singh, S. V.; Lakhina, G. S.

    2016-02-01

    The generation of nonlinear electrostatic solitary waves (ESWs) is explored in a magnetized four component two-temperature electron-positron plasma. Fluid theory is used to derive a set of nonlinear equations for the ESWs, which propagate obliquely to an external magnetic field. The electric field structures are examined for various plasma parameters and are shown to yield sinusoidal, sawtooth and bipolar waveforms. It is found that an increase in the densities of the electrons and positrons strengthen the nonlinearity while the periodicity and nonlinearity of the wave increases as the cool-to-hot temperature ratio increases. Our results could be useful in understanding nonlinear propagation of waves in astrophysical environments and related laboratory experiments.

  8. Magnetohydrodynamic spin waves in degenerate electron-positron-ion plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Mushtaq, A. [TPPD, PINSTECH Nilore, 44000 Islamabad (Pakistan); National Center for Physics, Shahdrah Valley Road, 44000 Islamabad (Pakistan); Maroof, R.; Ahmad, Zulfiaqr [Institute of Physics and Electronics, University of Peshawar, 25000 Peshawar (Pakistan); Qamar, A. [National Center for Physics, Shahdrah Valley Road, 44000 Islamabad (Pakistan); Institute of Physics and Electronics, University of Peshawar, 25000 Peshawar (Pakistan)

    2012-05-15

    Low frequency magnetosonic waves are studied in magnetized degenerate electron-positron-ion plasmas with spin effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, and spin magnetization energy, a generalized dispersion relation for oblique magnetosonic waves is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. For three different values of angle {theta}, the generalized dispersion relation is reduced to three different relations under the low frequency magnetohydrodynamic assumptions. It is found that the effect of quantum corrections in the presence of positron concentration significantly modifies the dispersive properties of these modes. The importance of the work relevant to compact astrophysical bodies is pointed out.

  9. Hot accretion disks with electron-positron pairs

    International Nuclear Information System (INIS)

    White, T.R.; Lightman, A.P.

    1989-01-01

    The hot thermal accretion disks of the 1970s are studied and consideration is given to the effects of electron-positron pairs, which were originally neglected. It is found that disks cooled by internally produced photons have a critical accretion rate above which equilibrium is not possible in a radial annulus centered around r = 10 GM/c-squared, where M is the mass of the central object. This confirms and extends previous work by Kusunose and Takahara. Above the critical rate, pairs are created more rapidly than they can be destroyed. Below the critical rate, there are two solutions to the disk structure, one with a high pair density and one with a low pair density. Depending on the strength of the viscosity, the critical accretion rate corresponds to a critical luminosity of about 3-10 percent of the Eddington limit. 32 refs

  10. Electron-positron collision physics: 1 MeV to 2 TeV

    International Nuclear Information System (INIS)

    Perl, M.L.

    1988-07-01

    An overview of electron-positron collision physics is presented. It begins at 1 MeV, the energy region of positronium formation, and extends to 2 TeV, the energy region which requires an electron- positron linear collider. In addition, the concept of searching for a lepton-specific forces is discussed. 18 refs., 15 figs., 1 tab

  11. Electron-positron pair production in ultrarelativistic atomic collisions: 6.4 TeV S16+ with Au, Pd and Al

    International Nuclear Information System (INIS)

    Datz, S.; Vane, C.R.; Dittner, P.F.; Krause, H.F.; Schuch, R.; Gao, H.; Hutton, R.

    1994-01-01

    Angular and momentum distributions have been measured for electron-positron pairs created in peripheral collisions of 6.4 TeV bare sulfur ions with thin targets of Al, Pd, and Au. Singly- and doubly-differential cross sections are presented for 1--17 MeV/c electrons and positrons detected independently and in coincidence as pairs. Various physical parameters are deduced from the coincident electron and positron data, including probability distributions for the pair transverse momentum, the pair total energy, and the positron fraction of the pair energy

  12. Characterisation of Ion Implantation-induced Defects in Certain Technologically Important Materials by Positron Annihilation (Review Paper)

    OpenAIRE

    P.M.G. Nambissan

    2009-01-01

    The application of positron annihilation spectroscopy for the studies of defects produced by different types of charged particles and ions in a variety of materials is discussed with specific examples. The ability to detect and quantify the information through the characteristic parameters of the annihilation radiation in a totally non-destructive method has made the fundamental process of electron-positron annihilation a powerful spectroscopic probe for investigating the structure and proper...

  13. Coincidence detection of photons of 511 keV from positon annihilation on a conventional gamma camera: optimization and analysis of potentialities

    International Nuclear Information System (INIS)

    Brasse, David

    1999-01-01

    The feasibility of acquiring clinical oncology studies on a gamma camera designed for the imaging of low energy single photons was investigated. The first prototype used two Nal(Tl) detectors of 40 cm by 30 cm with a 3/8 inch height and the second prototype was equipped with two large Nal(Tl) detectors of 40 cm by 54 cm with a 4/8 inch height. The optimization of such devices was mainly an optimization of the count rates obtained for reconstruct an image as a function of the angular axial aperture of the projections, with and without axial collimators. This optimization was performed experimentally using an anthropomorphic whole body phantom and the noise equivalent count rate as the figure of merit. An original correction for the random coincidences was also designed in order to optimize the contrast recovery and the contrast to noise ratio of small tumors (16 mm and 19 mm diameter). Finally, the optimal dose of FDG that can be injected to the subjects for an acquisition of that machine was determined and data acquired on an ECAT HR+ were compared with those acquired on the gamma camera for five subjects. (author) [fr

  14. A Model of Electron-Positron Pair Formation

    Directory of Open Access Journals (Sweden)

    Lehnert B.

    2008-01-01

    Full Text Available The elementary electron-positron pair formation process is consideredin terms of a revised quantum electrodynamic theory, with specialattention to the conservation of energy, spin, and electric charge.The theory leads to a wave-packet photon model of narrow line widthand needle-radiation properties, not being available from conventionalquantum electrodynamics which is based on Maxwell's equations. Themodel appears to be consistent with the observed pair productionprocess, in which the created electron and positron form two raysthat start within a very small region and have original directionsalong the path of the incoming photon. Conservation of angular momentum requires the photon to possess a spin, as given by the present theory but not by the conventional one. The nonzero electric field divergence further gives rise to a local intrinsic electric charge density within the photon body, whereas there is a vanishing total charge of the latter. This may explain the observed fact that the photon decays on account of the impact from an external electric field. Such a behaviour should not become possible for a photon having zero local electric charge density.

  15. Electrostatic solitons in unmagnetized hot electron-positron-ion plasmas

    International Nuclear Information System (INIS)

    Mahmood, S.; Ur-Rehman, H.

    2009-01-01

    Linear and nonlinear electrostatic waves in unmagnetized electron-positron-ion (e-p-i) plasmas are studied. The electrons and positrons are assumed to be isothermal and dynamic while ions are considered to be stationary to neutralize the plasma background only. It is found that both upper (fast) and lower (slow) Langmuir waves can propagates in such a type of pair (e-p) plasma in the presence of ions. The small amplitude electrostatic Korteweg-de Vries (KdV) solitons are also obtained using reductive perturbation method. The electrostatic potential hump structures are found to exist when the temperature of the electrons is larger than the positrons, while the electrostatic potential dips are obtained in the reverse temperature conditions for electrons and positrons in e-p-i plasmas. The numerical results are also shown for illustration. The effects of different ion concentration and temperature ratios of electrons and positrons, on the formation of nonlinear electrostatic potential structures in e-p-i plasmas are also discussed.

  16. Transient beam loading in electron-positron storage rings

    International Nuclear Information System (INIS)

    Wilson, P.B.

    1978-01-01

    In this note the fundamental of transient beam loading in electron-positron storage rings will be reviewed. The notation, and some of the material, has been introduced previously. The present note is, however, more tutorial in nature, and in addition the analysis is extended to include the transient behaviour of the cavity fields and reflected power between bunch passages. Since we are not bound here by the rigid space limitations of a paper for publication, an attempt is made to give a reasonably coherent and complete discussion of transient beam loading that can hopefully be followed even by the uninitiated. The discussion begins with a consideration of the beam-cavity interaction in the ''single-pass'' limit. In this limit it is assumed that the fields induced in the cavity by the passage of a bunch have decayed essentially to zero by the time the next bunch has arrived. The problem of the maximum energy that can be extracted from a cavity by a bunch is given particular attention, since this subject seems to be the source of some confusion. The analysis is then extended to the ''multiple-pass'' case, where the beam-induced fields do not decay to zero between bunches, and to a detailed consideration of the transient variation of cavity fields and reflected power. The note concludes with a brief discussion of the effect of transient beam loading on quantum lifetime

  17. Electron-positron pair production in inhomogeneous electromagnetic fields

    International Nuclear Information System (INIS)

    Kohlfürst, C.

    2015-01-01

    The process of electron-positron pair production is investigated within the phase-space Wigner formalism. The similarities between atomic ionization and pair production for homogeneous, but time-dependent linearly polarized electric fields are examined mainly in the regime of multiphoton absorption (field-dependent threshold, above-threshold pair production). Characteristic signatures in the particle spectra are identified (effective mass, channel closing). The non-monotonic dependence of the particle yield on the carrier frequency is discussed as well. The investigations are then extended to spatially inhomogeneous electric fields. New effects arising due to the spatial dependence of the effective mass are discussed in terms of a semi-classical interpretation. An increase in the normalized particle yield is found for various field configurations.Pair production in inhomogeneous electric and magnetic fields is also studied. The influence of a time-dependent spatially inhomogeneous magnetic field on the momentum spectrum and the particle yield is investigated. The Lorentz invariants are identified to be crucial in order to understand pair production by strong electric fields in the presence of strong magnetic fields. (author) [de

  18. Production of an electron-positron plasma in a pulsar magnetosphere

    International Nuclear Information System (INIS)

    Gurevich, A.V.; Istomin, Y.N.

    1985-01-01

    A study is made of the production of electron-positron plasma in the vacuum state (''breakdown'' of the vacuum) in the presence of an inhomogeneous electric field and a strong curvilinear magnetic field. Such conditions are encountered in the magnetosphere of a rotating neutron star. A general system of kinetic equations is derived for the electrons, positrons, and γ photons in the curvilinear magnetic field with allowance for the production of electron-positron pairs and the emission of curvature and synchrotron photons. The conditions of occurrence of ''breakdown'' are determined, and the threshold value of the jump in the value of the electric field at the surface of the star is found. The process of multiplication of particles in the magnetosphere is investigated, and the distribution functions of the electrons, positrons, and photons are found. The extinction limit of pulsars is determined. It is shown that the theory is in agreement with observational data

  19. Cross section formulae on single W and Z boson productions in electron-positron collisions

    International Nuclear Information System (INIS)

    Katuya, Mituaki

    1987-01-01

    The formulae are given for the transverse momentum distributions and total cross sections for the single W boson and Z boson productions in electron-positron collisions by using the equivalent photon approximation. (author)

  20. A Monte Carlo model to produce baryons in e+e- annihilation

    International Nuclear Information System (INIS)

    Meyer, T.

    1981-08-01

    A simple model is described extending the Field-Feynman model to baryon production in quark fragmentation. The model predicts baryon baryon correlations within jets and in opposite jets produced in electron-positron annihilation. Existing data is well described by the model. (orig.)

  1. Vector mesons in reactions with colliding electron-positron beams

    International Nuclear Information System (INIS)

    Rekalo, M.P.; Gakh, G.I.

    1980-01-01

    Polarization phenomena in the processes of vector meson production in reactions with colliding electron-positron beams e + e - → V+X, where V is a vector meson, X is a nondetected set of particles are investigated. For the one-photon mechanism of the process, where V and X are hadrons, the mutually unambiguous correspondence between the structural functions is found. The dependence of the e + e - → VX differential cross section upon the electron and positron polarizations is calculated using the virtual photon density matrix in the helicity basis. This formalism permits to take explicitly into account the P-invariance consequences for the angular distribution of the V-meson decay products. For the processes e + e - → πA 1 , and e + e - → rho + rho - the structural functions are calculated in terms of the corresponding electromagnetic form factors. It is noted that six functions out ten real structural functions describing the e + e - → VX reaction can be determined by means of investigation of the angular distribution of the V-meson decay products which is produced in collisions of unpolarized leptons. To study the collision of polarized leptons one more structural function can be determined. The formation of the X system with definite values of parity and spin is characterized by seven structural functions, five of which can be found while studying the angular distribution of the V-meson decay products produced in e + e - collisions with unpolarized (polarized) particles. If the spin of the X state is 1, in experiments with polarized beams all structural functions can be determined while investigating the angular distribution of the V-meson decay products

  2. Two-site Hubbard molecule with a spinless electron-positron pair

    KAUST Repository

    Cossu, Fabrizio

    2012-12-19

    We determine the eigenvalues of the two-site Hubbard molecule with one electron and one positron to describe the characteristics of electron-positron interactions in solids. While the effect of hopping is, in general, opposite to the effect of on-site interaction, we find a complex scenario for the electron-positron pair with a non-vanishing potential drop. We give analytical solutions and discuss the combined effects of the model parameters.

  3. Two-site Hubbard molecule with a spinless electron-positron pair

    KAUST Repository

    Cossu, Fabrizio; Schuster, Cosima; Schwingenschlö gl, Udo

    2012-01-01

    We determine the eigenvalues of the two-site Hubbard molecule with one electron and one positron to describe the characteristics of electron-positron interactions in solids. While the effect of hopping is, in general, opposite to the effect of on-site interaction, we find a complex scenario for the electron-positron pair with a non-vanishing potential drop. We give analytical solutions and discuss the combined effects of the model parameters.

  4. Electron-positron momentum density in TTF-TCNQ

    DEFF Research Database (Denmark)

    Ishibashi, S.; Manuel, A.A.; Hoffmann, L.

    1997-01-01

    We present measurements of the positron two-dimensional angular correlation of annihilation radiation (2D-ACAR) in TTF-TCNQ. We report also theoretical simulations of the 2D-ACAR in which the electron wave functions were expressed as TTF or TCNQ molecular orbitals obtained from self-consistent qu...... from a study of the Kohn anomaly. We investigate also the shape and position of the Fermi surface and conclude that a simple planar Fermi surface is consistent with our measurements....

  5. 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

  6. Electromagnetic cascade in high-energy electron, positron, and photon interactions with intense laser pulses

    Science.gov (United States)

    Bulanov, S. S.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.

    2013-06-01

    The interaction of high-energy electrons, positrons, and photons with intense laser pulses is studied in head-on collision geometry. It is shown that electrons and/or positrons undergo a cascade-type process involving multiple emissions of photons. These photons can consequently convert into electron-positron pairs. As a result charged particles quickly lose their energy developing an exponentially decaying energy distribution, which suppresses the emission of high-energy photons, thus reducing the number of electron-positron pairs being generated. Therefore, this type of interaction suppresses the development of the electromagnetic avalanche-type discharge, i.e., the exponential growth of the number of electrons, positrons, and photons does not occur in the course of interaction. The suppression will occur when three-dimensional effects can be neglected in the transverse particle orbits, i.e., for sufficiently broad laser pulses with intensities that are not too extreme. The final distributions of electrons, positrons, and photons are calculated for the case of a high-energy e-beam interacting with a counterstreaming, short intense laser pulse. The energy loss of the e-beam, which requires a self-consistent quantum description, plays an important role in this process, as well as provides a clear experimental observable for the transition from the classical to quantum regime of interaction.

  7. Linear electrostatic waves in a three-component electron-positron-ion plasma

    Energy Technology Data Exchange (ETDEWEB)

    Mugemana, A., E-mail: mugemanaa@gmail.com; Moolla, S. [School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4000 (South Africa); Lazarus, I. J. [Department of Mathematics, Statistics and Physics, Durban University of Technology, Durban 4000 (South Africa)

    2014-12-15

    Analytical linear electrostatic waves in a magnetized three-component electron-positron-ion plasma are studied in the low-frequency limit. By using the continuity and momentum equations with Poisson's equation, the dispersion relation for the electron-positron-ion plasma consisting of cool ions, and hot Boltzmann electrons and positrons is derived. In the linear regime, the propagation of two possible modes and their evolution are studied. In the cases of parallel and perpendicular propagation, it is shown that these two possible modes are always stable. The present investigation contributes to nonlinear propagation of electrostatic waves in space and the laboratory.

  8. Electron-positron-paircreation in heavy ion collisions

    International Nuclear Information System (INIS)

    Kienle, P.

    1987-09-01

    Recent experiments to study e + -e - paircreation in heavy ion atom collisions at energies close to the Coulomb barrier are reviewed. For high combined charges of the collision system Z u = Z 1 +Z 2 one finds pairs produced by the strong time changing Coulomb field with cross sections rising proportional to Z u 16 . The characteristics of the e + production line Z u and scattering angle dependence as well as their spectral distribution is well understood theoretically. Superimposed on the e + continua, e + lines were discovered with energies independent on Z u but with cross sections which rise with Z u 22 . The line energies are grouped around 250 and 340 keV for all systems with 164 u + -e - pairs. This is indicated by e + -e - coincidence experiments which show evidence for energy and angle correlated e + -e - emission expected for a particle decay. (orig.)

  9. Coupled channel calculations for electron-positron pair production in collisions of heavy ions

    CERN Document Server

    Gail, M; Scheid, W

    2003-01-01

    Coupled channel calculations are performed for electron-positron pair production in relativistic collisions of heavy ions. For this purpose the wavefunction is expanded into different types of basis sets consisting of atomic wavefunctions centred around the projectile ion only and around both of the colliding nuclei. The results are compared with experimental data from Belkacem et al (1997 Phys. Rev. A 56 2807).

  10. The beam energy measurement system for the Beijing electron-positron collider

    International Nuclear Information System (INIS)

    Zhang, J.Y.; Abakumova, E.V.; Achasov, M.N.; Blinov, V.E.; Cai, X.; Dong, H.Y.; Fu, C.D.; Harris, F.A.; Kaminsky, V.V.; Krasnov, A.A.; Liu, Q.; Mo, X.H.; Muchnoi, N.Yu.; Nikolaev, I.B.; Qin, Q.; Qu, H.M.; Olsen, S.L.; Pyata, E.E.; Shamov, A.G.; Shen, C.P.

    2012-01-01

    The beam energy measurement system (BEMS) for the upgraded Beijing electron-positron collider BEPC-II is described. The system is based on measuring the energies of Compton back-scattered photons. The relative systematic uncertainty of the electron and positron beam energy determination is estimated as 2⋅10 -5 .

  11. Relativistic total and differential cross section proton--proton electron--positron pair production calculation

    International Nuclear Information System (INIS)

    Rubinstein, J.E.

    1976-01-01

    Circle Feynman diagrams for a specific permutation of variables along with their corresponding algebraic expressions are presented to evaluate [H] 2 for proton-proton electron-positron pair production. A Monte Carlo integration technique is introduced and is used to set up the multiple integral expression for the total pair production cross section. The technique is first applied to the Compton scattering problem and then to an arbitrary multiple integral. The relativistic total cross section for proton-proton electron-positron pair production was calculated for eight different values of incident proton energy. A variety of differential cross sections were calculated for the above energies. Angular differential cross section distributions are presented for the electron, positron, and proton. Invariant mass differential cross section distributions are done both with and without the presence of [H] 2 . Both WGHT and log 10 (TOTAL) distributions were also obtained. The general behavioral trends of the total and differential cross sections for proton-proton electron-positron pair production are presented. The range of validity for this calculation is from 0 to about 200 MeV

  12. Large Amplitude Low Frequency Waves in a Magnetized Nonuniform Electron-Positron-Ion Plasma

    Institute of Scientific and Technical Information of China (English)

    Q. Haque; H. Saleem

    2004-01-01

    @@ It is shown that the large amplitude low-frequency electromagnetic drift waves in electron-positron-ion plasmas might give rise to dipolar vortices. A linear dispersion relation of several coupled electrostatic and electromagnetic low-frequency modes is obtained. The relevance of this work to both laboratory and astrophysical situations is pointed out.

  13. Progress in measurement and understanding of beam polarization in electron positron storage rings

    International Nuclear Information System (INIS)

    Barber, D.P.; Bremer, H.D.; Kewisch, J.; Lewin, H.C.; Limberg, T.; Mais, H.; Ripken, G.; Rossmanith, R.; Schmidt, R.

    1983-07-01

    A report is presented on the status of attempts to obtain and measure spin polarization in electron-positron storage rings. Experimental results are presented and their relationship to predictions of calculations discussed. Examples of methods for decoupling orbital and spin motion and thus improving polarization are discussed. (orig.)

  14. Electron-positron pair production in relativistic ion-atom collisions

    International Nuclear Information System (INIS)

    Eichler, Joerg

    2005-01-01

    The creation of electron-positron pairs constitutes an example for the conversion of energy into mass. We here give a brief outline of the various processes and theoretical approaches in a simple fashion. We point out some recent results and difficulties that have yet to be overcome

  15. Towards TeV-scale electron-positron collisions: the Compact Linear Collider (CLIC)

    Science.gov (United States)

    Doebert, Steffen; Sicking, Eva

    2018-02-01

    The Compact Linear Collider (CLIC), a future electron-positron collider at the energy frontier, has the potential to change our understanding of the universe. Proposed to follow the Large Hardron Collider (LHC) programme at CERN, it is conceived for precision measurements as well as for searches for new phenomena.

  16. Localized structures of electromagnetic waves in hot electron-positron plasma

    International Nuclear Information System (INIS)

    Kartal, S.; Tsintsadze, L.N.; Berezhiani, V.I.

    1995-08-01

    The dynamics of relatively strong electromagnetic (EM) wave propagation in hot electron-positron plasma is investigated. The possibility of finding localized stationary structures of EM waves is explored. It it shown that under certain conditions the EM wave forms a stable localized soliton-like structures where plasma is completely expelled from the region of EM field location. (author). 9 refs, 2 figs

  17. The beam energy measurement system for the Beijing electron-positron collider

    International Nuclear Information System (INIS)

    Abakumova, E.V.; Achasov, M.N.; Blinov, V.E.; Cai, X.; Dong, H.Y.; Fu, C.D.; Harris, F.A.; Kaminsky, V.V.; Krasnov, A.A.; Liu, Q.; Mo, X.H.; Muchnoi, N.Yu.; Nikolaev, I.B.; Qin, Q.; Qu, H.M.; Olsen, S.L.; Pyata, E.E.; Shamov, A.G.; Shen, C.P.; Todyshev, K.Yu.

    2011-01-01

    The beam energy measurement system (BEMS) for the upgraded Beijing electron-positron collider BEPC-II is described. The system is based on measuring the energies of Compton back-scattered photons. The relative systematic uncertainty of the electron and positron beam energy determination is estimated as 2×10 -5 . The relative uncertainty of the beam's energy spread is about 6%.

  18. On the average luminosity of electron positron collider and positron-producing energy

    International Nuclear Information System (INIS)

    Xie Jialin

    1985-01-01

    In this paper, the average luminosity of linac injected electron positron collider is investigated from the positron-producing energy point of view. When the energy of the linac injector is fixed to be less than the operating energy of the storage ring, it has been found that there exists a positron-producing energy to give optimum average luminosity. Two cases have been studied, one for an ideal storage ring with no single-beam instability and the other for practical storage ring with fast head-tail instability. The result indicates that there is a positron-producing energy corresponding to the minimum injection time, but this does not correspond to the optimum average luminosity for the practical storage rings. For Beijing Electron Positron Collider (BEPC), the positron-producing energy corresponding to the optimum average luminosity is about one tenth of the total injector energy

  19. Nonlinear interaction of photons and phonons in electron-positron plasmas

    International Nuclear Information System (INIS)

    Tajima, T.; Taniuti, T.

    1990-03-01

    Nonlinear interaction of electromagnetic waves and acoustic modes in an electron-positron plasma is investigated. The plasma of electrons and positrons is quite plastic so that the imposition of electromagnetic (EM) waves causes depression of the plasma and other structural imprints on it through either the nonresonant or resonant interaction. Our theory shows that the nonresonant interaction can lead to the coalescence of photons and collapse of plasma cavity in higher (≥ 2) dimensions. The resonant interaction, in which the group velocity of EM waves is equal to the phase velocity of acoustic waves, is analyzed and a set of basic equations of the system is derived via the reductive perturbation theory. We find new solutions of solitary types: bright solitons, kink solitons, and dark solitons as the solutions to these equations. Our computation hints their stability. An impact of the present theory on astrophysical plasma settings is expected, including the cosmological relativistically hot electron-positron plasma. 20 refs., 9 figs

  20. Nonlinear screening effect in an ultrarelativistic degenerate electron-positron gas

    International Nuclear Information System (INIS)

    Tsintsadze, N. L.; Rasheed, A.; Shah, H. A.; Murtaza, G.

    2009-01-01

    Nonlinear screening process in an ultrarelativistic degenerate electron-positron gas has been investigated by deriving a generalized nonlinear Poisson equation for the electrostatic potential. In the simple one-dimensional case, the nonlinear Poisson equation leads to Debye-like (Coulomb-like) solutions at distances larger (less) than the characteristic length. When the electrostatic energy is larger than the thermal energy, this nonlinear Poisson equation converts into the relativistic Thomas-Fermi equation whose asymptotic solution in three dimensions shows that the potential field goes to zero at infinity much more slowly than the Debye potential. The possibility of the formation of a bound state in electron-positron plasma is also indicated. Further, it is investigated that the strong spatial fluctuations of the potential field may reduce the screening length and that the root mean square of this spatial fluctuating potential goes to zero for large r rather slowly as compared to the case of the Debye potential.

  1. Renormalization theory of beam-beam interaction in electron-positron colliders

    International Nuclear Information System (INIS)

    Chin, Y.H.

    1989-07-01

    This note is devoted to explaining the essence of the renormalization theory of beam-beam interaction for carrying out analytical calculations of equilibrium particle distributions in electron-positron colliding beam storage rings. Some new numerical examples are presented such as for betatron tune dependence of the rms beam size. The theory shows reasonably good agreements with the results of computer simulations. 5 refs., 6 figs

  2. The design, construction and commissioning of the CERN Large Electron-Positron collider

    International Nuclear Information System (INIS)

    Myers, S.; Picasso, E.

    1990-01-01

    A description is given of the most important parameters considered in the design of the CERN Large Electron-Positron collider. It is shown how these parameters affect the collider performance and how they have been optimised with respect to the cost of the project. The functioning of each major subsystem is described with respect to its role as part of the collider. Finally, the planning, testing and initial commissioning of LEP is described and possible future developments are outlined. (author)

  3. Theoretical calculations of positron annihilation characteristics in inorganic solids -- Recent advances and problems

    Science.gov (United States)

    Sob, M.; Sormann, H.; Kuriplach, J.

    Principles and applications of positron annihilation spectroscopy to electronic structure and defect studies are briefly reviewed and some recent advances and pending problems are illustrated by specific examples. In particular, it turns out that the sensitivity of calculated momentum densities of electron-positron annihilation pairs (MDAP) to the choice of electron crystal potential is higher or comparable to its sensitivity with respect to the choice of description of the electron-positron interaction. As a result, it is very hard to distinguish between various electron-positron interaction theories on the basis of the comparison of theoretical and experimental MDAPs. Furthermore, the positron affinity is determined theorttically for several systems having a band gap (semiconductors, insulators). It appears that the calculated positron affinities are significantly underestimated when compared to experimental data and, apparently, electron-positron interactions in such systems are not described satisfactorily by contemporary theoretical approaches. The above examples are related rather to electronic structure studies, but positrons are often used to investigate various open-volume defects in solids, which is dealt with in the last illustration. A non-selfconsistent computational technique suitable for the theoretical examination of configurations having large number (thousands) of non-equivalent atoms has been updated recently to treat non-periodic solids. It is based on the superposition of atomic densities in order to approximate the electronic density of the system studied. Though the charge redistribution due to selfconsistency effects is neglected, positron annihilation characteristics are determined quite reasonably. This allows for studying properties of extended defects like grain boundaries (and other interfaces), dislocations, precipitates, etc., which is very helpful when interpreting experimental positron annihilation data. Our technique is

  4. Relativistic description of pair production of doubly heavy baryons in e+e− annihilation

    International Nuclear Information System (INIS)

    Martynenko, A. P.; Trunin, A. M.

    2015-01-01

    Relativistic corrections in the pair production of S-wave doubly heavy diquarks in electron-positron annihilation were calculated on the basis of perturbative QCD and the quark model. The relativistic corrections to the wave functions for quark bound states were taken into account with the aid of the Breit potential in QCD. Relativistic effects change substantially the nonrelativistic cross sections for pair diquark production. The yield of pairs of (ccq) doubly heavy baryons at B factories was estimated

  5. Precise tests of QCD in e{sup +}e{sup {minus}} annihilation

    Energy Technology Data Exchange (ETDEWEB)

    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 {alpha}{sub s}. An outlook is given for future important tests at a high-energy e{sup +}e{sup {minus}} collider.

  6. Electron-positron pair production by two identical photons in the nuclear field

    International Nuclear Information System (INIS)

    Smirnov, A.I.

    1977-01-01

    In the Born approximation of the perturbation theory considered is a nonlinear effect of the electron-positron pair production by two identical photons in the Coulomb field of an atomic nucleus. The kinematic version of identical photons is studied. All the particles are considered to be nonpolarized. The calculation of the differential probability of the effect has been carried out earlier by the Feynman method. The total probability of the effect in limiting energy ranges is determined by integrating the formulas of the pair component distribution over energies. The probabilities of the electron-positron pair production and fusion of two photons into one in the nucleus field have been compared for the case of identical quanta. From the comparison of the results of analyzing both the nonlinear effects it follows that in the high-energy range the electron-positron pair production by two identical photons in the nucleus field extremely predominates over the fusion of two photons into one photon in the same field

  7. Electron/positron measurements obtained with the Mars Science Laboratory Radiation Assessment Detector on the surface of Mars

    Energy Technology Data Exchange (ETDEWEB)

    Koehler, J.; Wimmer-Schweingruber, R.F.; Appel, J. [Kiel Univ. (Germany). Inst. of Experimental and Applied Physics; and others

    2016-04-01

    The Radiation Assessment Detector (RAD), on board the Mars Science Laboratory (MSL) rover Curiosity, measures the energetic charged and neutral particles and the radiation dose rate on the surface of Mars. Although charged and neutral particle spectra have been investigated in detail, the electron and positron spectra have not been investigated yet. The reason for that is that they are difficult to separate from each other and because of the technical challenges involved in extracting energy spectra from the raw data. We use GEANT4 to model the behavior of the RAD instrument for electron/positron measurements.We compare Planetocosmics predictions for different atmospheric pressures and different modulation parameters Φ with the obtained RAD electron/positron measurements.We find that the RAD electron/positron measurements agree well with the spectra predicted by Planetocosmics. Both RAD measurements and Planetocosmics simulation show a dependence of the electron/positron fluxes on both atmospheric pressure and solar modulation potential.

  8. Positron annihilation study in La2CuO4

    International Nuclear Information System (INIS)

    Kubo, Y.; Asano, S.

    1992-01-01

    The positron annihilation study for La 2 CuO 4 are performed using the full-potential linearized augmented-plane-wave(FLAPW) calculated electron and positron densities. The electron-positron momentum density(EPMD) is computed, and the well known Lock-Crisp-West(LCW) zone folding of the EPMD is produced. In the LCW analysis, small residual variations of order about 3 % are observed. The calculations show that the relative weights of the Fermi surface discontinuities are substantially altered due to the positron preferentially sampling the Cu-O plane region

  9. e+e- annihilation in the Weinberg-Salam model

    International Nuclear Information System (INIS)

    Davier, M.

    1980-01-01

    Electron-positron annihilation at high energies is a good probe of the neutral weak interaction and it is foreseen to be a privileged tool for the study of the neutral weak and electromagnetic currents. In these lectures, we analyse in detail the various tests of the gauge structure of these currents with particular emphasis on the SU(2) X U(1) Salam-Weinberg group. These tests include: study of the coupling of all fermions (leptons and quarks) to the neutral weak current, vector boson (Z 0 and W +- ) production. Higgs meson production and finally 3 and 4 boson couplings - a critical test of non-abelian group structure [fr

  10. Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

    Science.gov (United States)

    Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.

    2005-01-01

    Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by tine Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron s (positron s) transverse deflection behind the jet head. This

  11. Multi-messenger constraints and pressure from dark matter annihilation into e--e+ pairs

    International Nuclear Information System (INIS)

    Wechakama, Maneenate

    2013-01-01

    Despite striking evidence for the existence of dark matter from astrophysical observations, dark matter has still escaped any direct or indirect detection until today. Therefore a proof for its existence and the revelation of its nature belongs to one of the most intriguing challenges of nowadays cosmology and particle physics. The present work tries to investigate the nature of dark matter through indirect signatures from dark matter annihilation into electron-positron pairs in two different ways, pressure from dark matter annihilation and multi-messenger constraints on the dark matter annihilation cross-section. We focus on dark matter annihilation into electron-positron pairs and adopt a model-independent approach, where all the electrons and positrons are injected with the same initial energy E 0 ∝m dm c 2 . The propagation of these particles is determined by solving the diffusion-loss equation, considering inverse Compton scattering, synchrotron radiation, Coulomb collisions, bremsstrahlung, and ionization. The first part of this work, focusing on pressure from dark matter annihilation, demonstrates that dark matter annihilation into electron-positron pairs may affect the observed rotation curve by a significant amount. The injection rate of this calculation is constrained by INTEGRAL, Fermi, and H.E.S.S. data. The pressure of the relativistic electron-positron gas is computed from the energy spectrum predicted by the diffusion-loss equation. For values of the gas density and magnetic field that are representative of the Milky Way, it is estimated that the pressure gradients are strong enough to balance gravity in the central parts if E 0 0 . By comparing the predicted rotation curves with observations of dwarf and low surface brightness galaxies, we show that the pressure from dark matter annihilation may improve the agreement between theory and observations in some cases, but it also imposes severe constraints on the model parameters (most notably, the

  12. Neutrino (antineutrino) effective charge in a magnetized electron-positron plasma

    International Nuclear Information System (INIS)

    Serbeto, A.; Rios, L.A.; Mendonca, J.T.; Shukla, P.K.

    2004-01-01

    Using dynamical techniques of the plasma physics, the neutrino (antineutrino) effective charge in a magnetized dense electron-positron plasma is determined here. It shown that its value, which is determined by the plasma collective processes, depends mainly on the propagation direction of plasma waves and neutrinos against the external magnetic field direction. The direction dependence of the effective charge occurs due to the fact that the magnetic field breaks the plasma isotropy. The present theory gives a unified picture of the problem which is valid for an external magnetic field below the Landau-Schwinger critical value. Comparison with some of the results from the quantum field theory has been made

  13. Positron-acoustic waves in an electron-positron plasma with an electron beam

    International Nuclear Information System (INIS)

    Nejoh, Y.N.

    1996-01-01

    The nonlinear wave structures of large-amplitude positron-acoustic waves are studied in an electron-positron plasma in the presence of an electron beam with finite temperature and hot electrons and positrons. The region where positron-acoustic waves exist is presented by analysing the structure of the pseudopotential. The region depends sensitively on the positron density, the positron temperature and the electron beam temperature. It is shown that the maximum amplitude of the wave decreases as the positron temperature increases, and the region of positron-acoustic waves spreads as the positron temperature increases. 11 refs., 5 figs

  14. Langmuir wave phase-mixing in warm electron-positron-dusty plasmas

    Science.gov (United States)

    Pramanik, Sourav; Maity, Chandan

    2018-04-01

    An analytical study on nonlinear evolution of Langmuir waves in warm electron-positron-dusty plasmas is presented. The massive dust grains of either positively or negatively charged are assumed to form a fixed charge neutralizing background. A perturbative analysis of the fluid-Maxwell's equations confirms that the excited Langmuir waves phase-mix and eventually break, even at arbitrarily low amplitudes. It is shown that the nature of the dust-charge as well as the amount of dust grains can significantly influence the Langmuir wave phase-mixing process. The phase-mixing time is also found to increase with the temperature.

  15. Equation of state for electron gas in the presence of electron-positron pairs

    Energy Technology Data Exchange (ETDEWEB)

    Sugimoto, D; Nomoto, K [Tokyo Univ. (Japan). Coll. of General Education

    1975-12-01

    Fermi-Dirac integrals for partially relativistic, partially degenerate, electron gas are tabulated, especially for the region of electron-positron pair-creation in equilibrium with radiation field. Electrons are treated to be non-interacting particles. Independent entries for the table are non-dimensional temperature and a degeneracy parameter which is related directly with matter density. Thermodynamical quantities and their partial derivatives with respect to density and temperature are also given in table, which are intended for use in computing stellar evolution by means of a Henyey-type technique. This table is a supplement to one published earlier, in which only electrons were taken into account explicitly.

  16. Two-temperature accretion disks with electron-positron pairs - Effects of Comptonized external soft photons

    Science.gov (United States)

    Kusunose, Masaaki; Takahara, Fumio

    1990-01-01

    The present account of the effects of soft photons from external sources on two-temperature accretion disks in electron-positron pair equilibrium solves the energy-balance equation for a given radial distribution of the input rate of soft photons, taking into account their bremsstrahlung and Comptonization. Critical rate behavior is investigated as a function of the ratio of the energy flux of incident soft photons and the energy-generation rate. As in a previous study, the existence of a critical accretion rate is established.

  17. Beam-beam interaction in high energy linear electron-positron colliders

    International Nuclear Information System (INIS)

    Ritter, S.

    1985-04-01

    The interaction of high energy electron and positron beams in a linear collider has been investigated using a macroparticle Monte Carlo method based on a Cloud-In-Cells plasma simulation scheme. Density evolutions, luminosities, energy and angular distributions for electrons (positrons) and synchrotron photons are calculated. Beside beams with a symmetric transverse profile also flat beams are considered. A reasonably good agreement to alternative computer calculations as well as to an analytical approximation for the energy spectrum of synchrotron photons has been obtained. (author)

  18. Polarization effects in the reaction of charm baryon production on colliding electron-positron beams

    International Nuclear Information System (INIS)

    Rekalo, M.P.; Korzh, A.P.; Barannik, V.P.

    1980-01-01

    To calculate energy and angular distributions of various decay products of charm baAyons, which are prodUced in reactions on colliding e + e - beams, it is necessary to know the differential cross sections of the e + e - → C+anti C process which correspond to different polarized states of produced C and anti C (C - charm baryon). These differential cross sections are calculated for a single-photon mechanism with respect to the contribution of the anapole and electric dipole form factors of C-baryon. Polarizations of colliding electron-positron beams are taken into account in a full volume

  19. [Experiment studies of electron-positron interactions at the Stanford Linear Accelerator Center

    International Nuclear Information System (INIS)

    Hertzbach, S.S.; Kofler, R.R.

    1993-01-01

    The High Energy Physics group at the University of Massachusetts has continued its' program of experimental studies of electron-positron interactions at the Stanford Linear Accelerator Center (SLAC). The group activities have included: analysis of data taken between 1982 and 1990 with the TPC detector at the PEP facility, continuing data collection and data analysis using the SLC/SLD facility, planning for the newly approved B-factory at SLAC, and participation in design studies for future high energy linear colliders. This report will briefly summarize these activities

  20. Development of a stripline-type position monitor for the KEK electron/positron linac

    International Nuclear Information System (INIS)

    Suwada, T.; Urano, T.; Lazos, A.; Kobayashi, H.

    1994-01-01

    A stripline-type beam-position monitor (BPM) is under development at the KEK electron/positron linac. This monitor will be installed in order to easily handle the orbit of a high-current electron beam (∼10 nC/pulse) generating a positron beam in the B-factory. The prototype BPM was tested at a test bench and then in the linac using a single-bunch electron beam. In this report some basic characteristics and the experimental results of the BPM are presented

  1. Online beam energy measurement of Beijing electron positron collider II linear accelerator

    Science.gov (United States)

    Wang, S.; Iqbal, M.; Liu, R.; Chi, Y.

    2016-02-01

    This paper describes online beam energy measurement of Beijing Electron Positron Collider upgraded version II linear accelerator (linac) adequately. It presents the calculation formula, gives the error analysis in detail, discusses the realization in practice, and makes some verification. The method mentioned here measures the beam energy by acquiring the horizontal beam position with three beam position monitors (BPMs), which eliminates the effect of orbit fluctuation, and is much better than the one using the single BPM. The error analysis indicates that this online measurement has further potential usage such as a part of beam energy feedback system. The reliability of this method is also discussed and demonstrated in this paper.

  2. Improving the equivalent-photon approximation in electron-positron collisions

    CERN Document Server

    Schuler, G A

    1996-01-01

    The validity of the equivalent-photon approximation for two-photon processes in electron--positron collisions is critically examined. Commonly used forms to describe hadronic two-photon production are shown to lead to sizeable errors. An improved two-photon luminosity function is presented, which includes beyond-leading-logarithmic effects and scalar-photon contributions. Comparisons of various approximate expressions with the exact calculation in the case of the total hadronic cross section are given. Furthermore, effects of the poorly known low-Q2 behaviour of the virtual hadronic cross sections are discussed.

  3. CERN: TeV Electron-Positron Linear Collider Studies; More polarization in LEP

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    1993-09-15

    The world's highest energy electronpositron collider - CERN's LEP, with a circumference of 27 kilometres - will also be the last such machine to be built as a storage ring. With interest growing in electronpositron physics at energies beyond those attainable at LEP, the next generation of electron-positron colliders must be linear if prohibitive synchrotron radiation power losses are to be avoided. Very high energy linear colliders present many technical challenges but mastery of SLC at Stanford, the world's first electron-positron linear collider, is encouraging. The physics issues of a linear collider have been examined by the international community in ICFA workshops in Saariselka, Finland (September 1991) and most recently in Hawaii (April 1993). The emerging consensus is for a collider with an initial collision energy around 500 GeV, and which can be upgraded to over 1 TeV. A range of very different collider designs are being studied at Laboratories in Europe, the US, Japan and Russia. Following the report of the 1987 CERN Long Range Planning Committee chaired by Carlo Rubbia, studies for a 2 TeV linear collider have progressed at CERN alongside work towards the Laboratory's initial objective - the LHC high energy proton-proton collider in the LEP tunnel.

  4. Electroweak Measurements in Electron-Positron Collisions at W-Boson-Pair Energies at LEP

    CERN Document Server

    Schael, S.; Bruneliere, R.; Buskulic, D.; De Bonis, I.; Decamp, D.; Ghez, P.; Goy, C.; Jezequel, S.; Lees, J.P.; Lucotte, A.; Martin, F.; Merle, E.; Minard, M.N.; Nief, J.Y.; Odier, P.; Pietrzyk, B.; Trocme, B.; Bravo, S.; Casado, M.P.; Chmeissani, M.; Comas, P.; Crespo, J.M.; Fernandez, E.; Fernandez-Bosman, M.; Garrido, Ll.; Grauges, E.; Juste, A.; Martinez, M.; Merino, G.; Miquel, R.; Mir, Ll. M.; Orteu, S.; Pacheco, A.; Park, I.C.; Perlas, J.; Riu, I.; Ruiz, H.; Sanchez, F.; Colaleo, A.; Creanza, D.; De Filippis, N.; De Palma, M.; Iaselli, G.; Maggi, G.; Maggi, M.; Nuzzo, S.; Ranieri, A.; Raso, G.; Ruggieri, F.; Selvaggi, G.; Silvestris, L.; Tempesta, P.; Tricomi, A.; Zito, G.; Huang, X.; Lin, J.; Ouyang, Q.; Wang, T.; Xie, Y.; Xu, R.; Xue, S.; Zhang, J.; Zhang, L.; Zhao, W.; Abbaneo, D.; Bazarko, A.; Becker, U.; Boix, G.; Bird, F.; Blucher, E.; Bonvicini, B.; Bright-Thomas, P.; Barklow, T.; Buchmuller, O.; Cattaneo, M.; Cerutti, F.; Ciulli, V.; Clerbaux, B.; Drevermann, H.; Forty, R.W.; Frank, M.; Greening, T.C.; Hagelberg, R.; Halley, A.W.; Gianotti, F.; Girone, M.; Hansen, J.B.; Harvey, J.; Jacobsen, R.; Hutchcroft, D.E.; Janot, P.; Jost, B.; Knobloch, J.; Kado, M.; Lehraus, I.; Lazeyras, P.; Maley, P.; Mato, P.; May, J.; Moutoussi, A.; Pepe-Altarelli, M.; Ranjard, F.; Rolandi, L.; Schlatter, D.; Schmitt, B.; Schneider, O.; Tejessy, W.; Teubert, F.; Tomalin, I.R.; Tournefier, E.; Veenhof, R.; Valassi, A.; Wiedenmann, W.; Wright, A.E.; Ajaltouni, Z.; Badaud, F.; Chazelle, G.; Deschamps, O.; Dessagne, S.; Falvard, A.; Ferdi, C.; Fayolle, D.; Gay, P.; Guicheney, C.; Henrard, P.; Jousset, J.; Michel, B.; Monteil, S.; Montret, J.C.; Pallin, D.; Pascolo, J.M.; Perret, P.; Podlyski, F.; Bertelsen, H.; Fernley, T.; Hansen, J.D.; Hansen, J.R.; Hansen, P.H.; Kraan, A.C.; Lindahl, A.; Mollerud, R.; Nilsson, B.S.; Rensch, B.; Waananen, A.; Daskalakis, G.; Kyriakis, A.; Markou, C.; Simopoulou, E.; Siotis, I.; Vayaki, A.; Zachariadou, K.; Blondel, A.; Bonneaud, G.; Brient, J.C.; Machefert, F.; Rouge, A.; Rumpf, M.; Swynghedauw, M.; Tanaka, R.; Verderi, M.; Videau, H.; Ciulli, V.; Focardi, E.; Parrini, G.; Zachariadou, K.; Corden, M.; Georgiopoulos, C.; Antonelli, A.; Antonelli, M.; Bencivenni, G.; Bologna, G.; Bossi, F.; Campana, P.; Capon, G.; Cerutti, F.; Chiarella, V.; Felici, G.; Laurelli, P.; Mannocchi, G.; Murtas, G.P.; Passalacqua, L.; Picchi, P.; Colrain, P.; ten Have, I.; Hughes, I.S.; Kennedy, J.; Knowles, I.G.; Lynch, J.G.; Morton, W.T.; Negus, P.; O'Shea, V.; Raine, C.; Reeves, P.; Scarr, J.M.; Smith, K.; Thompson, A.S.; Turnbull, R.M.; Wasserbaech, S.; Buchmuller, O.; Cavanaugh, R.; Dhamotharan, S.; Geweniger, C.; Hanke, P.; Hansper, G.; Hepp, V.; Kluge, E.E.; Putzer, A.; Sommer, J.; Stenzel, H.; Tittel, K.; Werner, W.; Wunsch, M.; Beuselinck, R.; Binnie, D.M.; Cameron, W.; Davies, G.; Dornan, P.J.; Goodsir, S.; Marinelli, N.; Martin, E.B.; Nash, J.; Nowell, J.; Rutherford, S.A.; Sedgbeer, J.K.; Thompson, J.C.; White, R.; Williams, M.D.; Ghete, V.M.; Girtler, P.; Kneringer, E.; Kuhn, D.; Rudolph, G.; Bouhova-Thacker, E.; Bowdery, C.K.; Buck, P.G.; Clarke, D.P.; Ellis, G.; Finch, A.J.; Foster, F.; Hughes, G.; Jones, R.W.L.; Keemer, N.R.; Pearson, M.R.; Robertson, N.A.; Sloan, T.; Smizanska, M.; Snow, S.W.; Williams, M.I.; van der Aa, O.; Delaere, C.; Leibenguth, G.; Lemaitre, V.; Bauerdick, L.A.T.; Blumenschein, U.; van Gemmeren, P.; Giehl, I.; Holldorfer, F.; Jakobs, K.; Kasemann, M.; Kayser, F.; Kleinknecht, K.; Muller, A.S.; Quast, G.; Renk, B.; Rohne, E.; Sander, H.G.; Schmeling, S.; Wachsmuth, H.; Wanke, R.; Zeitnitz, C.; Ziegler, T.; Aubert, J.J.; Benchouk, C.; Bonissent, A.; Carr, J.; Coyle, P.; Curtil, C.; Ealet, A.; Etienne, F.; Fouchez, D.; Motsch, F.; Payre, P.; Rousseau, D.; Tilquin, A.; Talby, M.; Thulasidas, M.; Aleppo, M.; Antonelli, M.; Ragusa, F.; Buscher, V.; David, A.; Dietl, H.; Ganis, G.; Huttmann, K.; Lutjens, G.; Mannert, C.; Manner, W.; Moser, H.G.; Settles, R.; Seywerd, H.; Stenzel, H.; Villegas, M.; Wiedenmann, W.; Wolf, G.; Azzurri, P.; Boucrot, J.; Callot, O.; Chen, S.; Cordier, A.; Davier, M.; Duflot, L.; Grivaz, J.F.; Heusse, Ph.; Jacholkowska, A.; Le Diberder, F.; Lefrancois, J.; Mutz, A.M.; Schune, M.H.; Serin, L.; Veillet, J.J.; Videau, I.; Zerwas, D.; Azzurri, P.; Bagliesi, G.; Bettarini, S.; Boccali, T.; Bozzi, C.; Calderini, G.; Dell'Orso, R.; Fantechi, R.; Ferrante, I.; Fidecaro, F.; Foa, L.; Giammanco, A.; 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Koetke, D.S.; Kokott, T.P.; Kolrep, M.; Komamiya, S.; Kowalewski, R.V.; Kramer, T.; Krasznahorkay, A., Jr.; Kress, T.; Krieger, P.; von Krogh, J.; Kuhl, T.; Kupper, M.; Kyberd, P.; Lafferty, G.D.; Lahmann, R.; Lai, W.P.; Landsman, H.; Lanske, D.; Lauber, J.; Lautenschlager, S.R.; Lawson, I.; Layter, J.G.; Lazic, D.; Lee, A.M.; Lefebvre, E.; Leins, A.; Lellouch, D.; Letts, J.; Levinson, L.; Lewis, C.; Liebisch, R.; Lillich, J.; List, B.; List, J.; Littlewood, C.; Lloyd, A.W.; Lloyd, S.L.; Loebinger, F.K.; Long, G.D.; Losty, M.J.; Lu, J.; Ludwig, A.; Ludwig, J.; Macchiolo, A.; Macpherson, A.; Mader, W.; Mannelli, M.; Marcellini, S.; Marchant, T.E.; Markus, C.; Martin, A.J.; Martin, J.P.; Martinez, G.; Mashimo, T.; Matthews, W.; Mattig, P.; McDonald, W.J.; McKenna, J.; Mckigney, E.A.; McMahon, T.J.; McNab, A.I.; McPherson, R.A.; Mendez-Lorenzo, P.; Meijers, F.; Menges, W.; Menke, S.; Merritt, F.S.; Mes, H.; Meyer, N.; Meyer, J.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Mir, R.; Mohr, W.; Montanari, A.; Mori, T.; Morii, M.; Muller, U.; Mutter, A.; Nagai, K.; Nakamura, I.; Nanjo, H.; Neal, H.A.; Nellen, B.; Nijjhar, B.; Nisius, R.; O'Neale, S.W.; Oakham, F.G.; Odorici, F.; Ogren, H.O.; Oh, A.; Okpara, A.; Oldershaw, N.J.; Omori, T.; Oreglia, M.J.; Orito, S.; Pahl, C.; Palinkas, J.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Patt, J.; Pearce, M.J.; Petzold, S.; Pfeifenschneider, P.; Pilcher, J.E.; Pinfold, J.; Plane, D.E.; Poffenberger, P.; Polok, J.; Poli, B.; Pooth, O.; Posthaus, A.; Przybycien, M.; Przysiezniak, H.; Quadt, A.; Rabbertz, K.; Rees, D.L.; Rembser, C.; Renkel, P.; Rick, H.; Rigby, D.; Robertson, S.; Robins, S.A.; Rodning, N.; Roney, J.M.; Rooke, A.; Ros, E.; Rosati, S.; Roscoe, K.; Rossi, A.M.; Rosvick, M.; Routenburg, P.; Rozen, Y.; Runge, K.; Runolfsson, O.; Ruppel, U.; Rust, D.R.; Rylko, R.; Sachs, K.; Saeki, T.; Sahr, O.; Sarkisyan, E.K.G.; Sasaki, M.; Sbarra, C.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schenk, P.; Schieck, J.; Schmitt, S.; Schorner-Sadenius, T.; Schroder, M.; Schultz-Coulon, H.C.; Schulz, M.; Schumacher, M.; Schutz, P.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Shepherd-Themistocleous, C.H.; Sherwood, P.; Siroli, G.P.; Sittler, A.; Skillman, A.; Skuja, A.; Smith, A.M.; Smith, T.J.; Snow, G.A.; Sobie, R.; Soldner-Rembold, S.; Spagnolo, S.; Spano, F.; Springer, R.W.; Sproston, M.; Stahl, A.; Steiert, M.; Stephens, K.; Steuerer, J.; Stockhausen, B.; Stoll, K.; Strom, D.; Strohmer, R.; Strumia, F.; Stumpf, L.; Surrow, B.; Szymanski, P.; Tafirout, R.; Talbot, S.D.; Tanaka, S.; Taras, P.; Tarem, S.; Taylor, R.J.; Tasevsky, M.; Teuscher, R.; Thiergen, M.; Thomas, J.; Thomson, M.A.; von Torne, E.; Torrence, E.; Towers, S.; Toya, D.; Trefzger, T.; Trigger, I.; Trocsanyi, Z.; Tsukamoto, T.; Tsur, E.; Turcot, A.S.; Turner-Watson, M.F.; Ueda, I.; Ujvari, B.; Utzat, P.; Vachon, B.; Van Kooten, R.; Vannerem, P.; Vertesi, R.; Verzocchi, M.; Vikas, P.; Vincter, M.; Vokurka, E.H.; Vollmer, C.F.; Voss, H.; Vossebeld, J.; Wackerle, F.; Wagner, A.; Waller, D.; Ward, C.P.; Ward, D.R.; Ward, J.J.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wetterling, D.; White, J.S.; Wilkens, B.; Wilson, G.W.; Wilson, J.A.; Wolf, G.; Wotton, S.; Wyatt, T.R.; Yamashita, S.; Yekutieli, G.; Zacek, V.; Zer-Zion, D.; Zivkovic, L.

    2013-01-01

    Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3~fb$^{-1}$ collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from $130~GeV$ to $209~GeV$. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron-positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose-Einstein correlations between the two W decay systems arising ...

  5. CERN: TeV Electron-Positron Linear Collider Studies; More polarization in LEP

    International Nuclear Information System (INIS)

    Anon.

    1993-01-01

    The world's highest energy electronpositron collider - CERN's LEP, with a circumference of 27 kilometres - will also be the last such machine to be built as a storage ring. With interest growing in electronpositron physics at energies beyond those attainable at LEP, the next generation of electron-positron colliders must be linear if prohibitive synchrotron radiation power losses are to be avoided. Very high energy linear colliders present many technical challenges but mastery of SLC at Stanford, the world's first electron-positron linear collider, is encouraging. The physics issues of a linear collider have been examined by the international community in ICFA workshops in Saariselka, Finland (September 1991) and most recently in Hawaii (April 1993). The emerging consensus is for a collider with an initial collision energy around 500 GeV, and which can be upgraded to over 1 TeV. A range of very different collider designs are being studied at Laboratories in Europe, the US, Japan and Russia. Following the report of the 1987 CERN Long Range Planning Committee chaired by Carlo Rubbia, studies for a 2 TeV linear collider have progressed at CERN alongside work towards the Laboratory's initial objective - the LHC high energy proton-proton collider in the LEP tunnel

  6. Multi-GeV electron-positron beam generation from laser-electron scattering.

    Science.gov (United States)

    Vranic, Marija; Klimo, Ondrej; Korn, Georg; Weber, Stefan

    2018-03-16

    The new generation of laser facilities is expected to deliver short (10 fs-100 fs) laser pulses with 10-100 PW of peak power. This opens an opportunity to study matter at extreme intensities in the laboratory and provides access to new physics. Here we propose to scatter GeV-class electron beams from laser-plasma accelerators with a multi-PW laser at normal incidence. In this configuration, one can both create and accelerate electron-positron pairs. The new particles are generated in the laser focus and gain relativistic momentum in the direction of laser propagation. Short focal length is an advantage, as it allows the particles to be ejected from the focal region with a net energy gain in vacuum. Electron-positron beams obtained in this setup have a low divergence, are quasi-neutral and spatially separated from the initial electron beam. The pairs attain multi-GeV energies which are not limited by the maximum energy of the initial electron beam. We present an analytical model for the expected energy cutoff, supported by 2D and 3D particle-in-cell simulations. The experimental implications, such as the sensitivity to temporal synchronisation and laser duration is assessed to provide guidance for the future experiments.

  7. Nonlinear dust-acoustic structures in space plasmas with superthermal electrons, positrons, and ions

    Energy Technology Data Exchange (ETDEWEB)

    Saberian, E., E-mail: e.saberian@neyshabur.ac.ir [University of Neyshabur, Department of Physics, Faculty of Basic Sciences (Iran, Islamic Republic of); Esfandyari-Kalejahi, A.; Afsari-Ghazi, M. [Azarbaijan Shahid Madani University, Department of Physics, Faculty of Sciences (Iran, Islamic Republic of)

    2017-01-15

    Some features of nonlinear dust-acoustic (DA) structures are investigated in a space plasma consisting of superthermal electrons, positrons, and positive ions in the presence of negatively charged dust grains with finite-temperature by employing a pseudo-potential technique in a hydrodynamic model. For this purpose, it is assumed that the electrons, positrons, and ions obey a kappa-like (κ) distribution in the background of adiabatic dust population. In the linear analysis, it is found that the dispersion relation yield two positive DA branches, i.e., the slow and fast DA waves. The upper branch (fast DA waves) corresponds to the case in which both (negatively charged) dust particles and (positively charged) ion species oscillate in phase with electrons and positrons. On the other hand, the lower branch (slow DA waves) corresponds to the case in which only dust particles oscillate in phase with electrons and positrons, while ion species are in antiphase with them. On the other hand, the fully nonlinear analysis shows that the existence domain of solitons and their characteristics depend strongly on the dust charge, ion charge, dust temperature, and the spectral index κ. It is found that the minimum/maximum Mach number increases as the spectral index κ increases. Also, it is found that only solitons with negative polarity can propagate and that their amplitudes increase as the parameter κ increases. Furthermore, the domain of Mach number shifts to the lower values, when the value of the dust charge Z{sub d} increases. Moreover, it is found that the Mach number increases with an increase in the dust temperature. Our analysis confirms that, in space plasmas with highly charged dusts, the presence of superthermal particles (electrons, positrons, and ions) may facilitate the formation of DA solitary waves. Particularly, in two cases of hydrogen ions H{sup +} (Z{sub i} = 1) and doubly ionized Helium atoms He{sup 2+} (Z{sub i} = 2), the mentioned results are the same

  8. Exploring fermionic dark matter via Higgs boson precision measurements at the Circular Electron Positron Collider

    Science.gov (United States)

    Xiang, Qian-Fei; Bi, Xiao-Jun; Yin, Peng-Fei; Yu, Zhao-Huan

    2018-03-01

    We study the impact of fermionic dark matter (DM) on projected Higgs precision measurements at the Circular Electron Positron Collider (CEPC), including the one-loop effects on the e+e-→Z h cross section and the Higgs boson diphoton decay, as well as the tree-level effects on the Higgs boson invisible decay. As illuminating examples, we discuss two UV-complete DM models, whose dark sector contains electroweak multiplets that interact with the Higgs boson via Yukawa couplings. The CEPC sensitivity to these models and current constraints from DM detection and collider experiments are investigated. We find that there exist some parameter regions where the Higgs measurements at the CEPC will be complementary to current DM searches.

  9. Multiple electromagnetic electron-positron pair production in relativistic heavy-ion collisions

    International Nuclear Information System (INIS)

    Alscher, A.; Hencken, K.; Trautmann, D.; Baur, G.

    1997-01-01

    We calculate the cross sections for the production of one and more electron-positron pairs due to the strong electromagnetic fields in relativistic heavy-ion collisions. We derive the N-pair amplitude using the generating functional of fermions in an external field and the path-integral formalism. The N-pair production probability is found to be an approximate Poisson distribution. We calculate total cross sections for the production of one pair in lowest order, including corrections from the Poisson distribution up to third order. Furthermore, we calculate cross sections for the production of up to five pairs including corrections from the Poisson distribution. copyright 1997 The American Physical Society

  10. Electron-positron pair production in a hot accretion plasma around a massive black hole

    International Nuclear Information System (INIS)

    Takahara, Fumio; Kusunose, Masaaki.

    1985-01-01

    We investigate the electron-positron pair production in a hot accretion plasma around a supermassive black hole in connection with active galactic nuclei. Assuming that an optically thin two-temperature plasma is produced in the vicinity of the central black hole, we examine the condition for the significant pair production by comparing relevant time scales. Since the pair production is dominated by collisions between hard photons, the conditions for significant pair production depend on the production rate of hard photons. We examine the case where the unsaturated Comptonization of soft photons produces hard photons as well as that of bremsstrahlung. We show that significant pair production occurs for a moderately high accretion rate with relatively slow accretion flow as compared to the free fall velocity in both cases. Possible consequences of pair production are briefly discussed. (author)

  11. Neutron dosimetry at a high-energy electron-positron collider

    Science.gov (United States)

    Bedogni, Roberto

    Electron-positron colliders with energy of hundreds of MeV per beam have been employed for studies in the domain of nuclear and sub-nuclear physics. The typical structure of such a collider includes an LINAC, able to produce both types of particles, an accumulator ring and a main ring, whose diameter ranges from several tens to hundred meters and allows circulating particle currents of several amperes per beam. As a consequence of the interaction of the primary particles with targets, shutters, structures and barriers, a complex radiation environment is produced. This paper addresses the neutron dosimetry issues associated with the operation of such accelerators, referring in particular to the DAΦ NE complex, operative since 1997 at INFN-Frascati National Laboratory (Italy). Special attention is given to the active and passive techniques used for the spectrometric and dosimetric characterization of the workplace neutron fields, for radiation protection dosimetry purposes.

  12. Particle flow oriented electromagnetic calorimeter optimization for the circular electron positron collider

    Science.gov (United States)

    Zhao, H.; Fu, C.; Yu, D.; Wang, Z.; Hu, T.; Ruan, M.

    2018-03-01

    The design and optimization of the Electromagnetic Calorimeter (ECAL) are crucial for the Circular Electron Positron Collider (CEPC) project, a proposed future Higgs/Z factory. Following the reference design of the International Large Detector (ILD), a set of silicon-tungsten sampling ECAL geometries are implemented into the Geant4 simulation, whose performance is then scanned using Arbor algorithm. The photon energy response at different ECAL longitudinal structures is analyzed, and the separation performance between nearby photon showers with different ECAL transverse cell sizes is investigated and parametrized. The overall performance is characterized by a set of physics benchmarks, including νν H events where Higgs boson decays into a pair of photons (EM objects) or gluons (jets) and Z→τ+τ- events. Based on these results, we propose an optimized ECAL geometry for the CEPC project.

  13. Small amplitude Kinetic Alfven waves in a superthermal electron-positron-ion plasma

    Science.gov (United States)

    Adnan, Muhammad; Mahmood, Sahahzad; Qamar, Anisa; Tribeche, Mouloud

    2016-11-01

    We are investigating the propagating properties of coupled Kinetic Alfven-acoustic waves in a low beta plasma having superthermal electrons and positrons. Using the standard reductive perturbation method, a nonlinear Korteweg-de Vries (KdV) type equation is derived which describes the evolution of Kinetic Alfven waves. It is found that nonlinearity and Larmor radius effects can compromise and give rise to solitary structures. The parametric role of superthermality and positron content on the characteristics of solitary wave structures is also investigated. It is found that only sub-Alfvenic and compressive solitons are supported in the present model. The present study may find applications in a low β electron-positron-ion plasma having superthermal electrons and positrons.

  14. Drift-Alfven eigenmodes in inhomogeneous electron-positron-ion plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Haque, Q; Ahmad, Ali [Theoretical Plasma Physics Division, PINSTECH, PO Nilore, Islamabad (Pakistan); Yamin, S, E-mail: qamar@pinstech.org.pk [Physics Division, PO Nilore, Islamabad (Pakistan)

    2011-03-15

    An analytical description of drift-Alfven modes in nonuniform bounded magnetized electron-positron-ion plasmas is presented here. In the linear domain, linearized equations are solved by considering the Gaussian density profile in the radial direction. For this bounded plasma, the condition for the quantization of the modes is found. We note that the condition depends upon the density ratios of different plasma species. The full set of nonlinear equations is also solved, yielding stationary rotating solutions in terms of Bessel functions. We also note that the behavior of the nonlinear structures can be affected by the concentration of the positrons in the system. The importance of the present results with respect to astrophysical plasmas is pointed out.

  15. Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

    Science.gov (United States)

    Warwick, J.; Dzelzainis, T.; Dieckmann, M. E.; Schumaker, W.; Doria, D.; Romagnani, L.; Poder, K.; Cole, J. M.; Alejo, A.; Yeung, M.; Krushelnick, K.; Mangles, S. P. D.; Najmudin, Z.; Reville, B.; Samarin, G. M.; Symes, D. D.; Thomas, A. G. R.; Borghesi, M.; Sarri, G.

    2017-11-01

    We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (≥1 T ) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of ɛB≈10-3 is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.

  16. Feedback for suppression of single-bunch transverse instability in electron-positron storage rings

    International Nuclear Information System (INIS)

    Smaluk, V; Sukhanov, D; Oreshonok, V; Cherepanov, V; Kiselev, V

    2012-01-01

    Transverse head-tail instability is a severe limitation of a single-bunch beam current in circular accelerators. Applicability and efficiency of feedbacks for suppression of the instability is analyzed. Both chromatic and nonlinear effects have been taken into account to understand the processes of excitation and damping of the instability. Analytical estimations are compared with the results of experiments and numerical simulations. A feedback system has been developed, installed and commissioned at the VEPP-4M electron-positron collider. An original scheme of the kicker powering has been developed to provide the necessary performance with minimal expenses. Real-time digital data processing performed by a code running in an FPGA module provides high efficiency and flexibility of the system. During the system commissioning, a more than threefold increase of intensity of the VEPP-4M single-bunch beam has been achieved.

  17. Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam.

    Science.gov (United States)

    Warwick, J; Dzelzainis, T; Dieckmann, M E; Schumaker, W; Doria, D; Romagnani, L; Poder, K; Cole, J M; Alejo, A; Yeung, M; Krushelnick, K; Mangles, S P D; Najmudin, Z; Reville, B; Samarin, G M; Symes, D D; Thomas, A G R; Borghesi, M; Sarri, G

    2017-11-03

    We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (≥1  T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of ε_{B}≈10^{-3} is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.

  18. Electron/positron measurements obtained with the Mars Science Laboratory Radiation Assessment Detector on the surface of Mars

    Directory of Open Access Journals (Sweden)

    J. Köhler

    2016-01-01

    Full Text Available The Radiation Assessment Detector (RAD, on board the Mars Science Laboratory (MSL rover Curiosity, measures the energetic charged and neutral particles and the radiation dose rate on the surface of Mars. Although charged and neutral particle spectra have been investigated in detail, the electron and positron spectra have not been investigated yet. The reason for that is that they are difficult to separate from each other and because of the technical challenges involved in extracting energy spectra from the raw data. We use GEANT4 to model the behavior of the RAD instrument for electron/positron measurements. We compare Planetocosmics predictions for different atmospheric pressures and different modulation parameters Φ with the obtained RAD electron/positron measurements. We find that the RAD electron/positron measurements agree well with the spectra predicted by Planetocosmics. Both RAD measurements and Planetocosmics simulation show a dependence of the electron/positron fluxes on both atmospheric pressure and solar modulation potential.

  19. Gamma-induced positron annihilation spectroscopy and application to radiation-damaged alloys

    International Nuclear Information System (INIS)

    Wells, D.P.; Hunt, A.W.; Tchelidze, L.; Kumar, J.; Smith, K.; Thompson, S.; Selim, F.; Williams, J.; Harmon, J.F.; Maloy, S.; Roy, A.

    2006-01-01

    Radiation damage and other defect studies of materials are limited to thin samples because of inherent limitations of well-established techniques such as diffraction methods and traditional positron annihilation spectroscopy (PAS) [P. Hautojarvi, et al., Positrons in Solids, Springer, Berlin, 1979, K.G. Lynn, et al., Appl. Phys. Lett. 47 (1985) 239]. This limitation has greatly hampered industrial and in-situ applications. ISU has developed new methods that use pair-production to produce positrons throughout the volume of thick samples [F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 192 (2002) 197, F.A. Selim, D.P. Wells, et al., Nucl. Instru. Meth. A 495 (2002) 154, F.A. Selim, et al., J. Rad. Phys. Chem. 68 (2004) 427, F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 241 (2005) 253, A.W. Hunt, D.P. Wells, et al., Nucl. Instr. and Meth. B. 241 (2005) 262]. Unlike prior work at other laboratories that use bremsstrahlung beams to create positron beams (via pair-production) that are then directed at a sample of interest, we produce electron-positron pairs directly in samples of interest, and eliminate the intermediate step of a positron beam and its attendant penetrability limitations. Our methods include accelerator-based bremsstrahlung-induced pair-production in the sample for positron annihilation energy spectroscopy measurements (PAES), coincident proton-capture gamma-rays (where one of the gammas is used for pair-production in the sample) for positron annihilation lifetime spectroscopy (PALS), or photo-nuclear activation of samples for either type of measurement. The positrons subsequently annihilate with sample electrons, emitting coincident 511 keV gamma-rays [F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 192 (2002) 197, F.A. Selim, D.P. Wells, et al., Nucl. Instru. Meth. A 495 (2002) 154, F.A. Selim, et al., J. Rad. Phys. Chem. 68 (2004) 427, F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 241 (2005) 253, A.W. Hunt, D

  20. Study of the density of electrons in momentum space in the Al-Li-Cu icosahedral phase by means of positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, Yoshikazu; Nanao, Susumu [Institute of Industrial Science, The University of Tokyo, Roppongi, Minato, Tokyo 106 (Japan); Tanigawa, Shoichiro [Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305 (Japan)

    1997-12-15

    The three-dimensional momentum density of annihilating electron - positron pairs has been studied for a single Al-Li-Cu icosahedral quasicrystal. A direct Fourier transform method is employed to reconstruct the three-dimensional momentum density from measurements of the two-dimensional angular correlation of positron annihilation radiation (2 D-ACAR). The crystallographic anisotropy in the momentum density is observed to be very small. The asphericity of the Fermi surface is not found explicitly within the experimental resolution in the momentum space. The features of the three-dimensional electron - positron momentum density agree with those obtained by means of Compton profile measurement. It is suggested that a strong lattice - electron interaction at the Fermi level occurs in this icosahedral phase. (author)

  1. Correlations in electron-positron, lepton-hadron and hadron-hadron collisions

    International Nuclear Information System (INIS)

    Koch, W.

    1982-11-01

    Recent results on two-particle correlations in rapidity space, forward-backward multiplicity correlations, charge correlations, flavour and baryon number correlations as well as Bose-Einstein correlations of identical particles are reviewed. Particular emphasis is given to the data from e + e - annihilation which serve in many respects as reference point in the interpretation of correlation phenomena observed in hadronic reactions. (orig.)

  2. Effects of new neutral currents at linear electron-positron colliders

    International Nuclear Information System (INIS)

    Pankov, A.A.

    2002-01-01

    Effects that are induced by contact four-fermion interactions in the processes e + e - → μ + μ - , b-barb, and c-barc at √(s) = 0.5 TeV linear electron-positron colliders are investigated for the case of longitudinally polarized initial beams. This analysis employs new integrated observables constructed from the polarized cross sections for the scattering of final fermions into the forward (σ F ) and the backward (σ B ) hemisphere in such a way that they single out the helicity cross sections for the processes in question. This property of the observables makes it possible to perform, in the most general form, a model-independent analysis of contact four-fermion interactions and to set constraints on their parameters. It is also shown that the sensitivity of new polarization observables to contact interactions is noticeably higher than the corresponding sensitivity of canonical observables like σ, A FB , A LR , and A LR,FB

  3. Simulation Study of Invisible Decays of the Higgs Boson with the Circular Electron Positron Collider

    Science.gov (United States)

    Jyotishmati, Susmita

    A Higgs-like boson has been discovered by the experiments ATLAS and CMS at the LHC. We need to verify that it is the Standard Model (SM) Higgs and understand its nature. A Circular Electron Positron Collider (CEPC), has been proposed as a Higgs factory for detailed study of the Higgs boson. In this dissertation we study the feasibility of measuring the H → Invisible decays at the CEPC. Dark Matter (DM) interacts with matter by gravity, thus appears to be invisible in the CEPC experiment. If Higgs boson couples to DM it could be an important "portal" to New Physics. A Monte Carlo analysis of H → Invisible optimized to achieve high signal significance, and low backgrounds in the e +e- → ZH, Z → mu +mu- channel based on an integrated luminosity of 5 ab-1 expected for ten years run of the CEPC, is performed. Precision on the Higgs to invisible branching ratio at the input values of 0.1%(SM) and Beyond Standard Model (BSM) cases 0%, 1%, 5% and 10% is determined. Two approaches have been employed. They are the cut-based analysis and the multivariate analysis. Based on this dissertation study a baseline analysis approach is recommended for future CEPC design and studies.

  4. The PEP [positron-electron-proton] electron-positron ring: PEP Stage I

    International Nuclear Information System (INIS)

    Rees, J.R.

    1974-01-01

    The first stage of the positron-electron-proton (PEP) colliding-beam system which has been under joint study by a Lawrence Berkeley Laboratory-Stanford Linear Accelerator Center team for the past two years, will be the electron-positron storage ring. The physics justification for the e/sup /plus//e/sup /minus// ring is summarized briefly and the proposed facility is described. The ring will have six arcs having gross radii of about 220 m and six interaction regions located at the centers of straight sections about 130 m long. The longitudinal distance left free for experimental apparatus around the interaction regions will be 20 m. The range of operating beam energies will be from 5 GeV to 15 GeV. The design luminosity at 15 GeV will be 10 32 cm/sup /minus/2/s/sup/minus/1/, and the luminosity will vary approximately as the square of the beam energy. Alternative methods under consideration for adjusting the beam cross-section are discussed. The designs of the storage ring subsystems and of the conventional facilities including the experimental halls at the interaction regions are described. 7 refs., 8 figs., 3 tabs

  5. Effect of nonthermal electrons on oblique electrostatic excitations in a magnetized electron-positron-ion plasma

    Energy Technology Data Exchange (ETDEWEB)

    Alinejad, H. [Department of Physics, Faculty of Basic Science, Babol University of Technology, Babol 47148-71167 (Iran, Islamic Republic of)

    2012-05-15

    The linear and nonlinear propagation of ion-acoustic waves are investigated in a magnetized electron-positron-ion (e-p-i) plasma with nonthermal electrons. In the linear regime, the propagation of two possible modes and their evolution are studied via a dispersion relation. In the cases of parallel and perpendicular propagation, it is shown that these two possible modes are always stable. Then, the Korteweg-de Vries equation describing the dynamics of ion-acoustic solitary waves is derived from a weakly nonlinear analysis. The influence on the solitary wave characteristics of relevant physical parameters such as nonthermal electrons, magnetic field, obliqueness, positron concentration, and temperature ratio is examined. It is observed that the increasing nonthermal electrons parameter makes the solitary structures much taller and narrower. Also, it is revealed that the magnetic field strength makes the solitary waves more spiky. The present investigation contributes to the physics of the nonlinear electrostatic ion-acoustic waves in space and laboratory e-p-i plasmas in which wave damping produces an electron tail.

  6. Ion-acoustic nonlinear periodic waves in electron-positron-ion plasma

    International Nuclear Information System (INIS)

    Chawla, J. K.; Mishra, M. K.

    2010-01-01

    Ion-acoustic nonlinear periodic waves, namely, ion-acoustic cnoidal waves have been studied in electron-positron-ion plasma. Using reductive perturbation method and appropriate boundary condition for nonlinear periodic waves, the Korteweg-de Vries (KdV) equation is derived for the system. The cnoidal wave solution of the KdV equation is discussed in detail. It is found that the frequency of the cnoidal wave is a function of its amplitude. It is also found that the positron concentration modifies the properties of the ion-acoustic cnoidal waves. The existence regions for ion-acoustic cnoidal wave in the parameters space (p,σ), where p and σ are the positron concentration and temperature ratio of electron to positron, are discussed in detail. In the limiting case these ion-acoustic cnoidal waves reduce to the ion-acoustic soliton solutions. The effect of other parameters on the characteristics of the nonlinear periodic waves is also discussed.

  7. Collisionless magnetic reconnection in large-scale electron-positron plasmas

    International Nuclear Information System (INIS)

    Daughton, William; Karimabadi, Homa

    2007-01-01

    One of the most fundamental questions in reconnection physics is how the dynamical evolution will scale to macroscopic systems of physical relevance. This issue is examined for electron-positron plasmas using two-dimensional fully kinetic simulations with both open and periodic boundary conditions. The resulting evolution is complex and highly dynamic throughout the entire duration. The initial phase is distinguished by the coalescence of tearing islands to larger scale while the later phase is marked by the expansion of diffusion regions into elongated current layers that are intrinsically unstable to plasmoid generation. It appears that the repeated formation and ejection of plasmoids plays a key role in controlling the average structure of a diffusion region and preventing the further elongation of the layer. The reconnection rate is modulated in time as the current layers expand and new plasmoids are formed. Although the specific details of this evolution are affected by the boundary and initial conditions, the time averaged reconnection rate remains fast and is remarkably insensitive to the system size for sufficiently large systems. This dynamic scenario offers an alternative explanation for fast reconnection in large-scale systems

  8. c-Axis projected electron-positron momentum density in YBa2Cu3O7

    International Nuclear Information System (INIS)

    Bansil, A.; Smedskjaer, L.C.

    1990-11-01

    The authors present the theoretical c-axis projected electron-positron momentum density N 2γ (P x ,p y ) in YBa 2 Cu 3 O 7 based on the local density approximation (LDA) framework along various lines in momentum space. The calculations use the Korringa-Kohn-Rostoker (KKR) band structure formalism. The anisotropic distribution defined by taking cuts through the calculated spectra along different lines in the (p x ,p y ) plane possesses complex structures which arise from both Fermi surface effects and the anisotropy of the smoothly varying underlying background from filled bands; the maximum size of the anisotropy is about 10% of N 2γ (0,0). The theoretically predicted N 2γ (p x , y ) distribution is compared with the measured 2D-ACAR spectrum. The considerations suggest that in interpreting the 2D-ACAR data on YBa 2 Cu 3 O 7 in terms of a band theory LDA picture, a substantial, largely isotropic, background should be subtracted from both the 2D-ACAR's and the associated LCW-folded spectra

  9. Modulation of a compressional electromagnetic wave in a magnetized electron-positron quantum plasma.

    Science.gov (United States)

    Amin, M R

    2015-09-01

    Amplitude modulation of a compressional electromagnetic wave in a strongly magnetized electron-positron pair plasma is considered in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the external strong magnetic field, Fermi quantum degeneracy pressure, particle exchange potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to collision of the charged carriers. A modified-nonlinear Schödinger equation is developed for the compressional magnetic field of the electromagnetic wave by employing the standard reductive perturbation technique. The linear and nonlinear dispersions of the electromagnetic wave are discussed in detail. For some parameter ranges, relevant to dense astrophysical objects such as the outer layers of white dwarfs, neutron stars, and magnetars, etc., it is found that the compressional electromagnetic wave is modulationally unstable and propagates as a dissipated electromagnetic wave. It is also found that the quantum effects due to the particle exchange potential and the Bohm potential are negligibly small in comparison to the effects of the Fermi quantum degeneracy pressure. The numerical results on the growth rate of the modulation instability is also presented.

  10. Phase-mixing of Langmuir oscillations in cold electron-positron-ion plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Maity, Chandan [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700 064 (India)

    2014-07-15

    Space-time evolution of Langmuir oscillations in a cold homogeneous electron-positron-ion plasma has been analyzed by employing a straightforward perturbation expansion method, showing phase-mixing and, thus, wave-breaking of excited oscillations at arbitrary amplitudes. Within an assumption of infinitely massive ions, an approximate phase-mixing time is found to scale as ω{sub pe}t{sub mix}∼[(6/δ{sup 2})((2−α){sup 5/2}/(1−α))]{sup 1/3}, where “δ” and “α” (= n{sub 0i}/n{sub 0e}) are the amplitude of perturbation and the ratio of equilibrium ion density to equilibrium electron density, respectively, and ω{sub pe}∼√(4πn{sub 0e}e{sup 2}/m) is the electron plasma frequency. The results presented on phase-mixing of Langmuir modes in multispecies plasmas are expected to be relevant to laboratory and astrophysical environments.

  11. Coupled ion acoustic and drift waves in magnetized superthermal electron-positron-ion plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Adnan, Muhammad; Qamar, Anisa [Institute of Physics and Electronics, University of Peshawar, Peshawar 25000 (Pakistan); National Center for Physics, Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Mahmood, S. [National Center for Physics, Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Theoretical Physics Division, PINSTECH P.O. Nilore Islamabad 44000 (Pakistan); Physics Institute, Federal University of Rio Grande do Sul (UFRGS), 915051-970, Porto Alegre, RS (Brazil)

    2014-09-15

    Linear and nonlinear coupled drift-ion acoustic waves are investigated in a nonuniform magnetoplasma having kappa distributed electrons and positrons. In the linear regime, the role of kappa distribution and positron content on the dispersion relation has been highlighted; it is found that strong superthermality (low value of κ) and addition of positrons lowers the phase velocity via decreasing the fundamental scalelengths of the plasmas. In the nonlinear regime, first, coherent nonlinear structure in the form of dipoles and monopoles are obtained and the boundary conditions (boundedness) in the context of superthermality and positron concentrations are discussed. Second, in case of scalar nonlinearity, a Korteweg–de Vries-type equation is obtained, which admit solitary wave solution. It is found that both compressive and rarefactive solitons are formed in the present model. The present work may be useful to understand the low frequency electrostatic modes in inhomogeneous electron positron ion plasmas, which exist in astrophysical plasma situations such as those found in the pulsar magnetosphere.

  12. Coupled ion acoustic and drift waves in magnetized superthermal electron-positron-ion plasmas

    Science.gov (United States)

    Adnan, Muhammad; Mahmood, S.; Qamar, Anisa

    2014-09-01

    Linear and nonlinear coupled drift-ion acoustic waves are investigated in a nonuniform magnetoplasma having kappa distributed electrons and positrons. In the linear regime, the role of kappa distribution and positron content on the dispersion relation has been highlighted; it is found that strong superthermality (low value of κ) and addition of positrons lowers the phase velocity via decreasing the fundamental scalelengths of the plasmas. In the nonlinear regime, first, coherent nonlinear structure in the form of dipoles and monopoles are obtained and the boundary conditions (boundedness) in the context of superthermality and positron concentrations are discussed. Second, in case of scalar nonlinearity, a Korteweg-de Vries-type equation is obtained, which admit solitary wave solution. It is found that both compressive and rarefactive solitons are formed in the present model. The present work may be useful to understand the low frequency electrostatic modes in inhomogeneous electron positron ion plasmas, which exist in astrophysical plasma situations such as those found in the pulsar magnetosphere.

  13. The PEP [positron-electron-proton] electron-positron ring: An update

    International Nuclear Information System (INIS)

    1975-03-01

    The first stage of the positron-electron-protron (PEP) colliding-beam system, which has been under joint study by a Lawrence Berkeley Laboratory--Stanford Linear Accelerator Center team for the past two years, will be the electron-positron storage ring. The physics justification for the e + e/sup /minus// ring is summarized briefly and the proposed facility is described. The ring will have six arcs having gross radii of about 220 m and six interaction regions located at the centers of straight sections about 130 m long. The longitudinal distance left free for experimental apparatus around the interaction regions was set provisionally at 20 m. The range of operating beam energies will be from 5 GeV to 15 GeV. The design luminosity at 15 GeV will be 10 32 cm/sup /minus/2/s/sup /minus/1/, and the luminosity will vary approximately as the square of the beam energy. Alternative methods under consideration for adjusting the beam cross section are discussed. The designs of the storage ring subsystems and of the conventional facilities including the experimental halls at the interaction regions are described. 7 figs., 3 tabs

  14. Radiation problems in the design of the large electron-positron collider (LEP)

    International Nuclear Information System (INIS)

    Fasso, A.; Goebel, K.; Hoefert, M.; Rau, G.; Schoenbacher, H.; Stevenson, G.R.; Sullivan, A.H.; Swanson, W.P.; Tuyn, J.W.N.

    1984-01-01

    This is a comprehensive review of the radiation problems taken into account in the design studies for the Large Electron-Positron collider (LEP) now under construction at CERN. It provides estimates and calculations of the magnitude of the most important hazards, including those from non-ionizing radiations and magnetic fields as well as from ionizing radiation, and describes the measures to be taken in the design, construction, and operation to limit them. Damage to components is considered as well as the risk to people. More general explanations are given of the physical processes and technical parameters that influence the production and effects of radiation, and a comprehensive bibliography provides access to the basic theories and other discussions of the subject. The report effectively summarizes the findings of the Working Group on LEP radiation problems and parallels the results of analogous studies made for the previous large accelerator. The concluding chapters describe the LEP radiation protection system, which is foreseen to reduce doses far below the legal limits for all those working with the machine or living nearby, and summarize the environmental impact. Costs are also briefly considered. (orig.)

  15. Coincidence summing corrections for positron emitters in germanium gamma spectrometry

    International Nuclear Information System (INIS)

    Richardson, A.E.; Sallee, W.W.; New Mexico State Univ., Las Cruces

    1990-01-01

    For positron emitters, 511 keV annihilation quanta are in coincidence with other gamma rays in the decay scheme. If the positrons are not localized at the point of decay, annihilation quanta will be produced at a site some distance from the point of emission. The magnitude of the summing coincidence effect will depend upon the position of annihilation. A method for determining the magnitude of the summing effect for a single gamma of energy E in coincidence with the annihilation gammas from non-localized positrons has been developed which makes use of the counting data for the full energy peaks for both the gamma ray (E) and the 511 keV annihilation gammas. With this data and efficiency calibration data one can determine the average total efficiency for the annihilation positions from which 511 keV gammas originate, and thereby obtain the summing correction factor, SCF, for gamma ray (E). Application of the method to a 22 Na NIST standard gave excellent agreement of observed emission rates for the 1275 keV gamma with the NIST value for wide ranging degrees of positron localization having summing correction factors ranging from 1.021 to 1.505. The method was also applied successfully to 58 Co in neutron-irradiated nickel foils. The method shows promise as a check on the accuracy of the efficiency calibration for a particular detector geometry at the 511 keV energy and energies for other gammas associated with positron emission. (orig.)

  16. Simulating TGF and gamma ray emission above and within stormclouds due to the interaction of TeV cosmic ray shower electrons/positrons/photons with plausible electric field geometries generated in stormclouds.

    Science.gov (United States)

    Connell, P. H.

    2017-12-01

    The University of Valencia has developed a software simulator LEPTRACK to simulate lepton and photon scattering in any kind of media with a variable density, and permeated by electric/magnetic fields of any geometry, and which can handle an exponential runaway avalanche. Here we show results of simulating the interaction of electrons/positrons/photons in an incoming TeV cosmic ray shower with the kind of electric fields expected in a stormcloud after a CG discharge which removes much of the positive charge build up at the centre of the cloud. The point is to show not just a Relativistic Runaway Electron Avalanche (RREA) above the upper negative shielding layer at 12 km but other gamma ray emission due to electron/positron interaction in the remaining positive charge around 9km and the lower negative charge at 6km altitude. We present here images, lightcurves, altitude profiles, spectra and videos showing the different ionization, excitation and photon density fields produced, their time evolution, and how they depend critically on where the cosmic ray shower beam intercepts the electric field geometry. We also show a new effect of incoming positrons, which make up a significant fraction of the shower, where they appear to "orbit" within the high altitude negative shielding layer, and which has been conjectured to produce significant microwave emission, as well as a short range 511 keV annihilation line. The interesting question is if this conjectured emission can be observed and correlated with TGF orbital observations to prove that a TGF originates in the macro-fields of stormclouds or the micro-fields of light leaders and streamers where this "positron orbiting" is not likely to occur.

  17. 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

  18. A scanning Auger electron spectrometer for internal surface analysis of Large Electron Positron 2 superconducting radio-frequency cavities

    Science.gov (United States)

    Benvenuti, C.; Cosso, R.; Genest, J.; Hauer, M.; Lacarrère, D.; Rijllart, A.; Saban, R.

    1996-08-01

    A computer-controlled surface analysis instrument, incorporating static Auger electron spectroscopy, scanning Auger mapping, and secondary electron imaging, has been designed and built at CERN to study and characterize the inner surface of superconducting radio-frequency cavities to be installed in the Large Electron Positron collider. A detailed description of the instrument, including the analytical head, the control system, and the vacuum system is presented. Some recent results obtained from the cavities provide examples of the instrument's capabilities.

  19. Jet production in the CoLoRFulNNLO method: event shapes in electron-positron collisions

    CERN Document Server

    Del Duca, Vittorio

    2016-01-01

    We present the CoLoRFulNNLO method to compute higher order radiative corrections to jet cross sections in perturbative QCD. We apply our method to the computation of event shape observables in electron-positron collisions at NNLO accuracy and validate our code by comparing our predictions to previous results in the literature. We also calculate for the first time jet cone energy fraction at NNLO.

  20. Three-Jet Production in Electron-Positron Collisions at Next-to-Next-to-Leading Order Accuracy

    Science.gov (United States)

    Del Duca, Vittorio; Duhr, Claude; Kardos, Adam; Somogyi, Gábor; Trócsányi, Zoltán

    2016-10-01

    We introduce a completely local subtraction method for fully differential predictions at next-to-next-to-leading order (NNLO) accuracy for jet cross sections and use it to compute event shapes in three-jet production in electron-positron collisions. We validate our method on two event shapes, thrust and C parameter, which are already known in the literature at NNLO accuracy and compute for the first time oblateness and the energy-energy correlation at the same accuracy.

  1. Three-jet production in electron-positron collisions using the CoLoRFulNNLO method

    CERN Document Server

    Del Duca, Vittorio

    2016-01-01

    We introduce a subtraction method for jet cross sections at next-to-next-to-leading order (NNLO) accuracy in the strong coupling and use it to compute event shapes in three-jet production in electron-positron collisions. We validate our method on two event shapes, thrust and C-parameter, which are already known in the literature at NNLO accuracy and compute for the first time oblateness and the energy-energy correlation at the same accuracy.

  2. Gamma and pizero production in e+e- annihilation

    International Nuclear Information System (INIS)

    Fong, A.

    1980-01-01

    Inclusive cross sections of γ's and π 0 mesons in hadronic events produced by electron-positron annihilation for the center-of-mass energy range 4.9 to 7.4 GeV are presented. Scale invariance of the inclusive spectra is exhibited in this energy range, and their normalization and shape are seen to be consistent with those of spectra arising from the decay of the π 0 . The fraction of center-of-mass energy carried away by the γ's at high energies is found to be = 0.24 +- 0.01. The π 0 inclusive cross section is seen to be consistent in normalization and shape with half the charged-π cross section between x = 0.15 and 0.75, with an integrated inclusive cross-section ratio of sigma(π 0 )/[sigma(π + ) + sigma(π - )] = 0.48 +- 0.05. 60 figures, 7 tables

  3. Signature of crystal symmetry in positron annihilation data

    International Nuclear Information System (INIS)

    Adam, G.; Adam, S.

    1994-12-01

    While the technique of two-dimensional angular correlation of the electron-positron annihilation radiation (2D-ACAR) yields data in a reference frame related to detectors, data interpretation is made in a reference frame related to the crystal. The paper shows that consistent reformulation of the 2D-ACAR data in the crystal frame can be obtained from the knowledge of the signature of crystal symmetry (SCS) in the data. Derivation of the SCS over variations M-Umklapp areas of the reciprocal lattice from a rigorous definition also results in an improved a posteriori criterion concerning the twinned or untwinned nature of the crystal under investigation. The analysis of a c-projected 2D-ACAR spectrum on Y Ba 2 Cu 3 O 7-δ , accurately establishes the untwinned nature of the used crystals and yields better resolved Fermi surface ridge signatures at 2- and 3- Umklapp processes. (author). 32 refs, 4 figs, 2 tabs

  4. Dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons

    Science.gov (United States)

    Saha, Asit; Pal, Nikhil; Chatterjee, Prasanta

    2014-10-01

    The dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons has been investigated in the framework of perturbed and non-perturbed Kadomtsev-Petviashili (KP) equations. Applying the reductive perturbation technique, we have derived the KP equation in electron-positron-ion magnetoplasma with kappa distributed electrons and positrons. Bifurcations of ion acoustic traveling waves of the KP equation are presented. Using the bifurcation theory of planar dynamical systems, the existence of the solitary wave solutions and the periodic traveling wave solutions has been established. Two exact solutions of these waves have been derived depending on the system parameters. Then, using the Hirota's direct method, we have obtained two-soliton and three-soliton solutions of the KP equation. The effect of the spectral index κ on propagations of the two-soliton and the three-soliton has been shown. Considering an external periodic perturbation, we have presented the quasi periodic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas.

  5. Dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons

    Energy Technology Data Exchange (ETDEWEB)

    Saha, Asit, E-mail: asit-saha123@rediffmail.com, E-mail: prasantachatterjee1@rediffmail.com [Department of Mathematics, Sikkim Manipal Institute of Technology, Majitar, Rangpo, East-Sikkim 737136 (India); Department of Mathematics, Siksha Bhavana, Visva Bharati University, Santiniketan-731235 (India); Pal, Nikhil; Chatterjee, Prasanta, E-mail: asit-saha123@rediffmail.com, E-mail: prasantachatterjee1@rediffmail.com [Department of Mathematics, Siksha Bhavana, Visva Bharati University, Santiniketan-731235 (India)

    2014-10-15

    The dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons has been investigated in the framework of perturbed and non-perturbed Kadomtsev-Petviashili (KP) equations. Applying the reductive perturbation technique, we have derived the KP equation in electron-positron-ion magnetoplasma with kappa distributed electrons and positrons. Bifurcations of ion acoustic traveling waves of the KP equation are presented. Using the bifurcation theory of planar dynamical systems, the existence of the solitary wave solutions and the periodic traveling wave solutions has been established. Two exact solutions of these waves have been derived depending on the system parameters. Then, using the Hirota's direct method, we have obtained two-soliton and three-soliton solutions of the KP equation. The effect of the spectral index κ on propagations of the two-soliton and the three-soliton has been shown. Considering an external periodic perturbation, we have presented the quasi periodic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas.

  6. Charmed and strange baryon production in 29-GeV electron positron collisions

    International Nuclear Information System (INIS)

    Klein, S.R.

    1988-01-01

    Baryon production is one of the least understood areas of hadron production in electron positron collisions. Early models of hadronization predicted that very few baryons should be produced. However, experiments have shown a very substantial rate of baryon production, and many different models have been proposed to explain this. One way to test these models, and to further probe the hadronization process is to measure the production rates of different types of baryons. This dissertation presents measurements of the production rates of baryons with different strangeness and spin. The analyses presented here use data taken with the Mark II detector at the PEP storage ring, operating at a center of mass energy of 29 GeV. The Ξ - production rate is measured to be 0.017 ± 0.004 ± 0.004 per hadronic event, Ω - production is measured to be 0.014 ± 0.006 ± 0.004 per hadronic event, and Ξ *0 production is less than 0.006 per hadronic event at a 90% confidence level. These measurements place strong constraints on models of baryon production. In particular, the unexpectedly high rate of Ω - production is difficult to explain in any disquark based model. Semileptonic Λ c + decays have also been observed, with σ(e + e - → Λ c X) * Br(Λ c → eΛX) = 0.0031 ± 0.0012 ± 0.0010 per hadronic event, and σ(e + e - → Λ c X) * Br(Λ c → μΛX) = 0.0024 ± 0.0024 ± 0.0007 per hadronic event. Because neither the branching ratios nor the production rate are well known, it is difficult to interpret these results

  7. Electron-positron momentium distribution measurements of high-Tc superconductors and related systems

    International Nuclear Information System (INIS)

    Wachs, A.L.; Turchi, P.E.A.; Howell, R.H.; Jean, Y.C.; Fluss, M.J.; West, R.N.; Kaiser, J.H.; Rayner, S.; Haghighi, H.; Merkle, K.L.; Revcolevshi, A.; Wang, Z.Z.

    1989-01-01

    The authors discuss measurements of the 2D-angular correlation of positron annihilation radiation (ACAR) in La 2 CuO 4 , YBa 2 Cu 3 O 7 (YBCO), and NiO. The measurements for NiO are the first such 2D-ACAR measurements; the YBCO results are of a higher statistical quality than previously reported. The data are compared with complementary theoretical calculations and with each other. The authors discuss the implication of this analysis for ACAR studies of similar and related systems

  8. Intrinsic spatial resolution limitations due to differences between positron emission position and annihilation detection localization

    International Nuclear Information System (INIS)

    Perez, Pedro; Malano, Francisco; Valente, Mauro

    2012-01-01

    Since its successful implementation for clinical diagnostic, positron emission tomography (PET) represents the most promising medical imaging technique. The recent major growth of PET imaging is mainly due to its ability to trace the biologic pathways of different compounds in the patient's body, assuming the patient can be labeled with some PET isotope. Regardless of the type of isotope, the PET imaging method is based on the detection of two 511-keV gamma photons being emitted in opposite directions, with almost 180 deg between them, as a consequence of electron-positron annihilation. Therefore, this imaging method is intrinsically limited by random uncertainties in spatial resolutions, related with differences between the actual position of positron emission and the location of the detected annihilation. This study presents an approach with the Monte Carlo method to analyze the influence of this effect on different isotopes of potential implementation in PET. (author)

  9. 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

  10. Effect of μe universality violation in muon pair production on colliding electron-positron beams

    International Nuclear Information System (INIS)

    Guliev, N.A.; Dzhafarov, I.G.; Mekhtiev, B.I.

    1981-01-01

    The muonic pair production in colliding electron-positron beams is treated assuming the electron and muon weak interaction constants to be different. General formulae for the differential and total cross sections applicable at arbitrary energies of the colliding beams are obtained taking simultaneously into account arbitrary polarizations of the incident particles and longitudinal polarization of the muon (μ - ). It is shown that study of some polarization characteristics of a given reaction allows to distinguish possible weak interaction μe universality breaking effects. The revealing effects are analysed in the framework of unified gauge SU(2)xU(1) models, of weak and electromagnetic interactions [ru

  11. Measurement of the cross-section of electron-positron scattering at high energy and quantum electrodynamics testing; Mesure de la section efficace de diffusion electron-positron a haute energie et validite de l'electrodynamique quantique

    Energy Technology Data Exchange (ETDEWEB)

    Lalanne, D.

    1970-07-17

    The experiment we have performed on the ACO (Orsay Collider Ring) is one of the most accurate tests of quantum electrodynamics over very short interaction distances (10{sup -14} cm). We have studied the electron-positron elastic scattering at very wide angle. This work is divided into 4 parts. The first part reviews recent tests of quantum electrodynamics and presents the electron-positron elastic scattering. The second part describes the measurement of brightness: the experimental device, data analysis and accuracy. The measurement of brightness has been performed by detecting the photons emitted in the double Bremsstrahlung reaction: e{sup +}e{sup -} → e{sup +}e{sup -}γγ. The third part deals with the measurement of the number of Bhabha events. The last part compares the experimental value of the Bhabha scattering with the theoretically expected value. We have got the following results: the number of Bhabha events: 757 events, the experimental value for Bhabha scattering cross-section: [1.97 ± 0.09 (stat.) ± 0.10 (syst.)]*10{sup -31} cm{sup 2}. The comparison of this experimental value with the expected value has allowed us to set the lower limit of the cutting parameter Λ: Λ > 2 GeV.

  12. Recent results in electron-positron and lepton-hadron interactions

    International Nuclear Information System (INIS)

    Wiik, B.H.; Mess, K.H.

    1982-03-01

    These lectures will start with a few remarks on detectors and beams used to study e + e - annihilation and deep inelastic lepton-nucleon interactions. The main part of the lectures will discuss recent results obtained from a study of these processes including a discussion on the result of recent particle searches. The picture which emerges from these data is consistant with what has become known as the standard model. However, it is important to bear in mind that the experiments so far have only investigated masses which are small compared to 100 GeV/c 2 , the characteristic mass of the weak interaction. The new generation of e + e - and ep collider will allow us to extend these measurements into a mass range above 100 GeV/c 2 , and thus provide answers to many of the questions confronting the standard model. (orig./HSI)

  13. Application of coincidence Doppler-broadening spectroscopy to different carbon phases

    International Nuclear Information System (INIS)

    Ito, Y.; Djourelov, N.; Suzuki, T.; Kondo, K.; Ito, Y.; Shantarovich, V.; Onoe, J.

    2004-01-01

    Coincidence Doppler-broadening spectroscopy was applied to C60 and C70 fullerenes and other carbon phases, such as nanotubes and graphites. Remarkable differences were observed in the Doppler-broadening of the positron annihilation γ-rays in these materials, which reflect the different densities distribution of the momentum for electrons annihilated with positrons. This would be caused by the different composition of the π and σ electrons in annihilation with positrons. This result shows the sensitivity of the coincidence Doppler-broadening method to determine the density distribution of electrons sampled by positrons. (orig.)

  14. Analysis of the energy weighted angular correlations in hadronic e+e- annihilations at 22 and 34 GeV

    International Nuclear Information System (INIS)

    Behrend, H.J.; Chen, C.; Fenner, H.; Field, J.H.; Schroeder, V.; Sindt, H.; D'Agostini, G.; Apel, W.D.; Banerjee, S.; Bodenkamp, J.

    1982-04-01

    Measurements of energy weighted angular correlations in electron positron annihilations at c.m. energies of 22 GeV and 34 GeV are presented. The data are compared with perturbative QCD predictions. The theoretical predictions which refer to the partons describe the data reasonably well, depending on the approximations chosen. The effective strong coupling constant αsub(s) has been evaluated using a method where the effect of fragmentation is minimal. At large acolinearity angles QCD calculations going beyond the Leading Double Log approximation appear to be quite successful. The agreement is improved when the smearing effect of heavy resonance decays is taken out of the data. (orig.)

  15. Fermi surface ridge at second and third Umklapp positron annihilations in Y Ba2Cu3Oτ-γ

    International Nuclear Information System (INIS)

    Adam, G.; Adam, S.; Barbiellini, B.; Hoffmann, L.; Manuel, A.A.; Peter, M.

    1993-06-01

    Results of statistical noise smoothing of the electron momentum distribution got by two-dimensional angular correlation of the electron-positron annihilation radiation technique on untwinned Y Ba 2 Cu 3 O τ-γ single crytals are reported. Two distinct signatures of the sheet of Fermi surface related to the CuO chains (the ridge) are resolved. The first occurs at second Umklapp processes, in agreement with previous evidence. The second one, identified for the first time, occurs at third Umklapp processes. Comparison with FLAPW calculations confirms this results. (author). 13 refs, 7 figs

  16. Study of four-lepton final states in electron-positron interactions at 29 GeV

    International Nuclear Information System (INIS)

    Petradza, A.

    1989-08-01

    This thesis presents a study of electron-positron scattering to four light leptons. The motivations behind it are twofold. Firstly, the study is a test of the theory of electron-positron interactions to 4th order in the fine structure constant α. A deviation from the theory could indicate the existence of a heavy new particle. Secondly, a measurement of these processes may prove useful in the understanding of other QED-type reactions. The method for simulating the four-lepton processes by the Monte Carlo event generator of Berends, Daverveldt and Kleiss is described. Theoretical predictions are compared to data from the Mark II and HRS experiments at the PEP storage ring. The observed events consist of four leptons at large angles. Data for all three e + e - e + e - , e + e - μ + μ - and μ + μ - μ + μ - processes are well described by the QED Monte Carlo calculation. The various kinematical distributions are in good agreement with QED to order α 4 . 18 refs., 64 figs., 19 tabs

  17. Measurement of the cross-section of electron-positron scattering at high energy and quantum electrodynamics testing

    International Nuclear Information System (INIS)

    Lalanne, D.

    1970-01-01

    The experiment we have performed on the ACO (Orsay Collider Ring) is one of the most accurate tests of quantum electrodynamics over very short interaction distances (10 -14 cm). We have studied the electron-positron elastic scattering at very wide angle. This work is divided into 4 parts. The first part reviews recent tests of quantum electrodynamics and presents the electron-positron elastic scattering. The second part describes the measurement of brightness: the experimental device, data analysis and accuracy. The measurement of brightness has been performed by detecting the photons emitted in the double Bremsstrahlung reaction: e + e - → e + e - γγ. The third part deals with the measurement of the number of Bhabha events. The last part compares the experimental value of the Bhabha scattering with the theoretically expected value. We have got the following results: the number of Bhabha events: 757 events, the experimental value for Bhabha scattering cross-section: [1.97 ± 0.09 (stat.) ± 0.10 (syst.)]*10 -31 cm 2 . The comparison of this experimental value with the expected value has allowed us to set the lower limit of the cutting parameter Λ: Λ > 2 GeV

  18. 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.)

  19. 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

  20. 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

  1. Electron-positron annihilation from 3 to 11 GeV. Second progress report, 15 March 1981-15 March 1982

    International Nuclear Information System (INIS)

    Darden, C.W.

    1982-01-01

    The ARGUS collaboration started forming in mid 1978 to build and operate a new magnetic solenoid detector at the storage ring DORIS in Hamburg. With this detector and a rebuilt storage ring it would be possible to unravel the complicated multiparticle decays of charmed baryons and, more exciting, those of the recently discovered Tau mesons. By March of 1981, construction of the detector was well underway. The progress since then to 15 March 1982 is covered in the pages that follow

  2. 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

  3. 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

  4. Results of a search for double positron decay and electron-positron conversion of 78Kr

    International Nuclear Information System (INIS)

    Saenz, C.; Cerezo, E.; Garcia, E.; Morales, A.; Morales, J.; Nunez-Lagos, R.; Ortiz de Solorzano, A.; Puimedon, J.; Salinas, A.; Sarsa, M.L.; Villar, J.A.; Klimenko, A.; Kuzminov, V.; Metlinsky, N.; Novikov, V.; Pomansky, A.; Pritychenko, B.

    1994-01-01

    The results of a search for the 2β + and Kβ + decay modes of 78 Kr, in a coincidence experiment using a high pressure ionization chamber of enriched 78 Kr inside an array of sodium iodine scintillators, are presented. After 4434 h of counting time, the half-life lower limits obtained are T 1/2 (Kβ + ) 0ν ≥5.1x10 21 yr and T 1/2 (2β + ) 0ν+2ν ≥2.0x10 21 yr at 68% C.L

  5. Results of a search for double positron decay and electron-positron conversion of 78Kr

    International Nuclear Information System (INIS)

    Saenz, C.; Garcia, E.; Klimenko, A.; Kuzminov, V.; Metlinsky, N.; Morales, A.; Morales, J.; Novikov, V.; Nunez-Lagos, R.; Ortiz de Solorzano, A.; Pomansky, A.; Pritytchenko, V.; Puimedon, J.; Salinas, A.; Sarsa, M.L.; Villar, J.A.

    1994-01-01

    The results of a search for the 2β + and Kβ + decay modes of 78 Kr, in a coincidence experiment using a high pressure ionization chamber of enriched 78 Kr inside an enceinte of sodium iodine scintillators, are presented. After 4434 hours of counting time, the half-life lower limits obtained are T 1/2 (Kβ + ) 0ν ≥qslant5.8x10 21 y and T 1/2 (2β + ) 0ν+2ν ≥qslant2.0x10 21 y at 68%C.L. ((orig.))

  6. Polarization of electron-positron vacuum by strong magnetic field in theory with fundamental mass

    International Nuclear Information System (INIS)

    Kadyshevskij, V.G.; ); Rodionov, V.N.

    2003-01-01

    The exact Lagrangian function of the intensive constant magnetic field, replacing the Heisenberg-Euler Lagrangian in the traditional quantum electrodynamics, is calculated within the frames of the theory with the fundamental mass in the single-loop approximation. It is established that the obtained generalization of the Lagrangian function is substantial by arbitrary values of the magnetic field. The calculated Lagrangian in the weak field coincides with the known Heisenberg-Euler formula. The Lagrangian dependence on the field in the extremely strong fields completely disappears and it tends in this area to the threshold value, which is determined by the fundamental and lepton mass ratio [ru

  7. Elliptically polarized electromagnetic waves in a magnetized quantum electron-positron plasma with effects of exchange-correlation

    Energy Technology Data Exchange (ETDEWEB)

    Shahmansouri, M., E-mail: mshmansouri@gmail.com [Department of Physics, Faculty of Science, Arak University, Arak 38156-8 8349 (Iran, Islamic Republic of); Misra, A. P., E-mail: apmisra@visva-bharati.ac.in, E-mail: apmisra@gmail.com [Department of Mathematics, Siksha Bhavana, Visva-Bharati University, Santiniketan 731 235, West Bengal (India)

    2016-07-15

    The dispersion properties of elliptically polarized electromagnetic waves in a magnetized electron-positron-pair (EP-pair) plasma are studied with the effects of particle dispersion associated with the Bohm potential, the Fermi degenerate pressure, and the exchange-correlation force. Two possible modes of the extraordinary or X wave, modified by these quantum effects, are identified and their propagation characteristics are investigated numerically. It is shown that the upper-hybrid frequency and the cutoff and resonance frequencies are no longer constants but are dispersive due to these quantum effects. It is found that the particle dispersion and the exchange-correlation force can have different dominating roles on each other depending on whether the X waves are of short or long wavelengths (in comparison with the Fermi Debye length). The present investigation should be useful for understanding the collective behaviors of EP plasma oscillations and the propagation of extraordinary waves in magnetized dense EP-pair plasmas.

  8. Electrostatic instabilities and nonlinear structures of low-frequency waves in nonuniform electron-positron-ion plasmas with shear flow

    International Nuclear Information System (INIS)

    Mirza, Arshad M.; Hasan, Asma; Azeem, M.; Saleem, H.

    2003-01-01

    It is found that the low-frequency ion acoustic and electrostatic drift waves can become unstable in uniform electron-ion and electron-positron-ion plasmas due to the ion shear flow. In a collisional plasma a drift-dissipative instability can also take place. In the presence of collisions the temporal behavior of nonlinear drift-dissipative mode can be represented in the form of well-known Lorenz and Stenflo type equations that admit chaotic trajectories. On the other hand, a quasi-stationary solution of the mode coupling equations can be represented in the form of monopolar vortex. The results of the present investigation can be helpful in understanding electrostatic turbulence and wave phenomena in laboratory and astrophysical plasmas

  9. Report of Snowmass 2001 Working Group E2: Electron-Positron Colliders from the Phi to the Z

    Energy Technology Data Exchange (ETDEWEB)

    Decker, Franz-Josef

    2002-08-07

    We report on the status and plans of experiments now running or proposed for electron-positron colliders at energies between the {phi} and the Z. The e{sup +}e{sup -} B and charm factories we considered were PEP-II/BABAR, KEKB/Belle, superKEK, SuperBABAR, and CESR-c/CLEO-c. We reviewed the programs at the {phi} factory at Frascati and the proposed PEP-N facility at Stanford Linear Accelerator Center. We studied the prospects for B physics with a dedicated linear collider Z factory, associated with the TESLA high energy linear collider. In all cases, we compared the physics reach of these facilities with that of alternative experiments at hadron colliders or fixed target facilities.

  10. Superconducting snake with the field of 75 kGs for the VEPP-2M electron-positron storage ring

    International Nuclear Information System (INIS)

    Anashin, V.V.; Vasserman, I.B.; Vlasov, A.M.

    1985-01-01

    Superconducting ''snake'' with the field of 75 kG is established in the VEPP-2M electron-positron storage ring for increase of colliding beam luminosity up to 2x10 31 cmsup(-2)sdup(-1) in the energy range from 2x200 to 2x700 MeV. The ''snake'' comprises three central magnets with the field of 75 kG and two side ones with the field of 45 kG and it is placed in one of rectilinear experimental gaps. Description of design peculiarities of the ''snake'' and its parameters are given. Parameters of beams with switched on and switched off ''snake'' as well as parameters of coils and superconducting wire are presented

  11. Top-quark pair production at next-to-next-to-leading order QCD in electron positron collisions

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Long [Institut für Theoretische Teilchenphysik und Kosmologie, RWTH Aachen University,52056 Aachen (Germany); Dekkers, Oliver [PRISMA Cluster of Excellence and Institut für Physik,Johannes-Gutenberg-Universität Mainz,55099 Mainz (Germany); Heisler, Dennis; Bernreuther, Werner [Institut für Theoretische Teilchenphysik und Kosmologie, RWTH Aachen University,52056 Aachen (Germany); Si, Zong-Guo [School of Physics, Shandong University,Jinan, Shandong 250100 (China)

    2016-12-19

    We set up a formalism, within the antenna subtraction framework, for computing the production of a massive quark-antiquark pair in electron positron collisions at next-to-next-to-leading order in the coupling α{sub s} of quantum chromodynamics at the differential level. Our formalism applies to the calculation of any infrared-safe observable. We apply this set-up to the production of top-quark top antiquark pairs in the continuum. We compute the production cross section and several distributions. We determine, in particular, the top-quark forward-backward asymmetry at order α{sub s}{sup 2}. Our result agrees with previous computations of this observable.

  12. Propagation of localized structures in relativistic magnetized electron-positron plasmas using particle-in-cell simulations

    Energy Technology Data Exchange (ETDEWEB)

    López, Rodrigo A. [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Concepción, Concepción 4070386 (Chile); Muñoz, Víctor [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Viñas, Adolfo F. [Geospace Physics Laboratory, Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Valdivia, Juan A. [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Centro para el Desarrollo de la Nanociencia y la Nanotecnología (CEDENNA), Santiago 9170124 (Chile)

    2015-09-15

    We use a particle-in-cell simulation to study the propagation of localized structures in a magnetized electron-positron plasma with relativistic finite temperature. We use as initial condition for the simulation an envelope soliton solution of the nonlinear Schrödinger equation, derived from the relativistic two fluid equations in the strongly magnetized limit. This envelope soliton turns out not to be a stable solution for the simulation and splits in two localized structures propagating in opposite directions. However, these two localized structures exhibit a soliton-like behavior, as they keep their profile after they collide with each other due to the periodic boundary conditions. We also observe the formation of localized structures in the evolution of a spatially uniform circularly polarized Alfvén wave. In both cases, the localized structures propagate with an amplitude independent velocity.

  13. Propagation of localized structures in relativistic magnetized electron-positron plasmas using particle-in-cell simulations

    International Nuclear Information System (INIS)

    López, Rodrigo A.; Muñoz, Víctor; Viñas, Adolfo F.; Valdivia, Juan A.

    2015-01-01

    We use a particle-in-cell simulation to study the propagation of localized structures in a magnetized electron-positron plasma with relativistic finite temperature. We use as initial condition for the simulation an envelope soliton solution of the nonlinear Schrödinger equation, derived from the relativistic two fluid equations in the strongly magnetized limit. This envelope soliton turns out not to be a stable solution for the simulation and splits in two localized structures propagating in opposite directions. However, these two localized structures exhibit a soliton-like behavior, as they keep their profile after they collide with each other due to the periodic boundary conditions. We also observe the formation of localized structures in the evolution of a spatially uniform circularly polarized Alfvén wave. In both cases, the localized structures propagate with an amplitude independent velocity

  14. Modulational instability: Conservation laws and bright soliton solution of ion-acoustic waves in electron-positron-ion-dust plasmas

    Science.gov (United States)

    EL-Kalaawy, O. H.

    2018-02-01

    We consider the nonlinear propagation of non-planar (cylindrical and spherical) ion-acoustic (IA) envelope solitary waves in an unmagnetized plasma consisting of electron-positron-ion-dust plasma with two-electron temperature distributions in the context of the non-extensive statistics. The basic set of fluid equations is reduced to the modified nonlinear Schrödinger (MNLS) equation in cylindrical and spherical geometry by using the reductive perturbation method (RPM). It is found that the nature of the modulational instabilities would be significantly modified due to the effects of the non-extensive and other plasma parameters as well as cylindrical and spherical geometry. Conservation laws of the MNLS equation are obtained by Lie symmetry and multiplier method. A new exact solution (envelope bright soliton) is obtained by the extended homogeneous balance method. Finally, we study the results of this article.

  15. Search for ψ(2S) production in e+e- annihilations at 4.03GeV

    International Nuclear Information System (INIS)

    Bai, J.Z.; Bian, J.G.; Chai, Z.W.; Chen, G.P.; Chen, J.C.; Chen, Y.; Chen, Y.B.; Chen, Y.Q.; Cheng, B.S.; Cui, X.Z.; Ding, H.L.; Ding, L.Y.; Dong, L.Y.; Du, Z.Z.; Feng, S.; Gao, C.S.; Gao, M.L.; Gao, S.Q.; Gu, J.H.; Gu, S.D.; Gu, W.X.; Gu, Y.F.; Guo, Y.N.; Han, S.W.; Han, Y.; He, J.; He, J.T.; Hu, G.Y.; Hu, H.M.; Hu, J.L.; Hu, Q.H.; Hu, T.; Hu, X.Q.; Huang, J.D.; Huang, Y.Z.; Jiang, C.H.; Jin, Y.; Ke, Z.J.; Lai, Y.F.; Lang, P.F.; Li, C.G.; Li, D.; Li, H.B.; Li, J.; Li, P.Q.; Li, R.B.; Li, W.; Li, W.D.; Li, W.G.; Li, X.H.; Li, X.N.; Liu, H.M.; Liu, J.; Liu, J.H.; Liu, R.G.; Liu, Y.; Lu, F.; Lu, J.G.; Lu, J.Y.; Lu, L.C.; Luo, C.H.; Ma, A.M.; Ma, E.C.; Ma, J.M.; Mao, H.S.; Mao, Z.P.; Meng, X.C.; Nie, J.; Qi, N.D.; Qi, X.R.; Qiu, J.F.; Qu, Y.H.; Que, Y.K.; Rong, G.; Shao, Y.Y.; Shen, B.W.; Shen, D.L.; Shen, H.; Shen, X.Y.; Sheng, H.Y.; Shi, H.Z.; Song, X.F.; Sun, F.; Sun, H.S.; Tang, S.Q.; Tong, G.L.; Wang, F.; Wang, L.S.; Wang, L.Z.; Wang, M.; Wang, M.; Wang, P.; Wang, P.L.; Wang, S.M.; Wang, T.J.; Wang, Y.Y.; Wei, C.L.; Wu, Y.G.; Xi, D.M.; Xia, X.M.; Xie, P.P.; Xie, Y.; Xie, Y.H.; Xiong, W.J.; Xu, C.C.; Xu, G.F.; Xue, S.T.; Yan, J.; Yan, W.G.; Yang, C.M.; Yang, C.Y.; Yang, J.; Yang, X.F.; Ye, M.H.; Yi, K.; Yu, C.S.; Yu, C.X.; Yu, Z.Q.; Yu, Z.T.; Yuan, C.Z.; Yuan, Y.; Zhang, B.Y.; Zhang, C.C.; Zhang, D.H.; Zhang, D.; Zhang, H.L.; Zhang, J.; Zhang, J.L.; Zhang, J.W.; Zhang, L.S.; Zhang, Q.J.; Zhang, S.Q.; Zhang, Y.; Zhang, Y.Y.; Zhao, D.X.; Zhao, H.W.; Zhao, J.W.; Zhao, M.; Zhao, W.R.; Zheng, J.P.; Zheng, L.S.; Zheng, Z.P.; Zhou, G.P.; Zhou, H.S.; Zhou, L.; Zhu, Q.M.; Zhu, Y.C.; Zhu, Y.S.; Zhuang, B.A.; Hitlin, D.G.; Kelsey, M.H.; Oyang, J.; Panetta, J.; Porter, F.; Weaver, M.; Chen, J.; Malchow, R.; Toki, W.; Yang, W.; Yu, Y.H.

    1998-01-01

    A search is performed for the production of the ψ(2S) in e + e - annihilation at a center-of-mass energy of 4.03 GeV using the BES detector operated at the Beijing Electron Positron Collider (BEPC). The kinematic features of the reconstructed ψ(2S) signal are consistent with its being produced only in association with an energetic photon resulting from initial state radiation (ISR). Limits are placed on ψ(2S) production from the decay of unknown charmonia or metastable hybrids that might be produced in e + e - annihilations at 4.03GeV. Under the assumption that the observed cross section for ψ(2S) production is due entirely to ISR, the partial width Γ ee of the ψ(2S) is measured to be 2.07±0.32keV. copyright 1998 The American Physical Society

  16. Simulation of triple coincidences in PET

    International Nuclear Information System (INIS)

    Cal-González, J; Herranz, E; Vicente, E; Udias, J M; Lage, E; Dave, S R; Parot, V; Herraiz, J L; Moore, S C; Park, M-A

    2015-01-01

    Although current PET scanners are designed and optimized to detect double coincidence events, there is a significant amount of triple coincidences in any PET acquisition. Triple coincidences may arise from causes such as: inter-detector scatter (IDS), random triple interactions (R T ), or the detection of prompt gamma rays in coincidence with annihilation photons when non-pure positron-emitting radionuclides are used (β + γ events). Depending on the data acquisition settings of the PET scanner, these triple events are discarded or processed as a set of double coincidences if the energy of the three detected events is within the scanner’s energy window. This latter option introduces noise in the data, as at most, only one of the possible lines-of-response defined by triple interactions corresponds to the line along which the decay occurred. Several novel works have pointed out the possibility of using triple events to increase the sensitivity of PET scanners or to expand PET imaging capabilities by allowing differentiation between radiotracers labeled with non-pure and pure positron-emitting radionuclides. In this work, we extended the Monte Carlo simulator PeneloPET to assess the proportion of triple coincidences in PET acquisitions and to evaluate their possible applications. We validated the results of the simulator against experimental data acquired with a modified version of a commercial preclinical PET/CT scanner, which was enabled to acquire and process triple-coincidence events. We used as figures of merit the energy spectra for double and triple coincidences and the triples-to-doubles ratio for different energy windows and radionuclides. After validation, the simulator was used to predict the relative quantity of triple-coincidence events in two clinical scanners assuming different acquisition settings. Good agreement between simulations and preclinical experiments was found, with differences below 10% for most of the observables considered. For

  17. Integrated coincidence circuits

    International Nuclear Information System (INIS)

    Borejko, V.F.; Grebenyuk, V.M.; Zinov, V.G.

    1976-01-01

    The description is given of two coincidence units employing integral circuits in the VISHNYA standard. The units are distinguished for the coincidence selection element which is essentially a combination of a tunnel diode and microcircuits. The output fast response of the units is at least 90 MHz in the mode of the output signal unshaped in duration and 50 MHz minimum in the mode of the output signal shaping. The resolution time of the units is dependent upon the duration of input signals

  18. 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)

  19. Window least squares method applied to statistical noise smoothing of positron annihilation data

    International Nuclear Information System (INIS)

    Adam, G.; Adam, S.; Barbiellini, B.; Hoffmann, L.; Manuel, A.A.; Peter, M.

    1993-06-01

    The paper deals with the off-line processing of experimental data obtained by two-dimensional angular correlation of the electron-positron annihilation radiation (2D-ACAR) technique on high-temperature superconductors. A piecewise continuous window least squares (WLS) method devoted to the statistical noise smoothing of 2D-ACAR data, under close control of the crystal reciprocal lattice periodicity, is derived. Reliability evaluation of the constant local weight WLS smoothing formula (CW-WLSF) shows that consistent processing 2D-ACAR data by CW-WLSF is possible. CW-WLSF analysis of 2D-ACAR data collected on untwinned Y Ba 2 Cu 3 O 7-δ single crystals yields significantly improved signature of the Fermi surface ridge at second Umklapp processes and resolves, for the first time, the ridge signature at third Umklapp processes. (author). 24 refs, 9 figs

  20. Effects of TMD evolution and partonic flavor on e"+e"− annihilation into hadrons

    International Nuclear Information System (INIS)

    Bacchetta, Alessandro; Echevarria, Miguel G.; Mulders, Piet J.G.; Radici, Marco; Signori, Andrea

    2015-01-01

    We calculate the transverse momentum dependence in the production of two back-to-back hadrons in electron-positron annihilations at the medium/large energy scales of Bes-III and Belle experiments. We use the parameters of the transverse-momentum-dependent (TMD) fragmentation functions that were recently extracted from the semi-inclusive deep-inelastic-scattering multiplicities at low energy from Hermes. TMD evolution is applied according to different approaches and using different parameters for the nonperturbative part of the evolution kernel, thus exploring the sensitivity of our results to these different choices and to the flavor dependence of parton fragmentation functions. We discuss how experimental measurements could discriminate among the various scenarios.

  1. Annihilation momentum density of positrons trapped at vacancy-type defects in metals and alloys

    International Nuclear Information System (INIS)

    Bansil, A.; Prasad, R.; Benedek, R.

    1988-01-01

    Positron annihilation, especially the angular correlation of annihilation radiation, is a powerful tool for investigating the electronic spectra of ordered as well as defected materials. The tendency of positrons to trap at vacancy-type defects should enable this technique to study the local environment of such defects. However, we need to develop a theoretical basis for calculating the two-photon annihilation momentum density rho/sub 2gamma/(p-vector). We have recently formulated and implemented a theory of rho/sub 2gamma/(p-vector) from vacancy-type defects in metals and alloys. This article gives an outline of our approach together with a few of our results. Section 2 summarizes the basic equations for evaluating rho/sub 2gamma/(p-vector). Our Green's function-based approach is nonperturbative and employs a realistic (one-particle) muffin-tin Hamiltonian for treating electrons and positrons. Section 3 presents and discusses rho/sub 2gamma/(p-vector) results for a mono-vacancy in Cu. We have neglected the effects of electron-positron correlations and of lattice distortion around the vacancy. Section 4 comments briefly on the question of treating defects such as divacancies and metal-impurity complexes in metals and alloys. Finally, in Section 5, we remark on the form of rho/sub 2gamma/(p-vector) for a mono-vacancy in jellium. 2 figs

  2. 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

  3. Constraints on the dark matter annihilation from Fermi-LAT observation of M31

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhengwei; Yuan, Qiang [Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing, 210008 (China); Huang, Xiaoyuan [Physik-Department T30d, Technische Universität München, James-Franck-Straße, Garching, D-85748 Germany (Germany); Xu, Yupeng, E-mail: lizw@ihep.ac.cn, E-mail: huangxiaoyuan@gmail.com, E-mail: yuanq@pmo.ac.cn, E-mail: xuyp@ihep.ac.cn [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing, 100049 (China)

    2016-12-01

    Gamma-ray is a good probe of dark matter (DM) particles in the Universe. We search for the DM annihilation signals in the direction of the Andromeda galaxy (M31) using 7.5 year Fermi-LAT pass 8 data. Similar to Pshirkov et al. (2016), we find that there is residual excess emission from the direction of M31 if only the galactic disk as traced by the far infrared emission is considered. Adding a point-like source will improve the fitting effectively, although additional slight improvements can be found if an extended component such as a uniform disk or two bubbles is added instead. Taking the far infrared disk plus a point source as the background model, we search for the DM annihilation signals in the data. We find that there is strong degeneracy between the emission from the galaxy and that from 10s GeV mass DM annihilation in the main halo with quark final state. However, the required DM annihilation cross section is about 10{sup −25}–10{sup −24} cm{sup 3}s{sup −1}, orders of magnitude larger than the constraints from observations of dwarf spheroidal galaxies, indicating a non-DM origin of the emission. If DM subhalos are taken into account, the degeneracy is broken. When considering the enhancement from DM subhalos, the constraints on DM model parameters are comparable to (or slightly weaker than) those from the population of dwarf spheroidal galaxies. We also discuss the inverse Compton scattering component from DM annihilation induced electrons/positrons. For the first time we include an energy dependent template of the inverse Compton emission (i.e., a template cube) in the data analysis to take into account the effect of diffusion of charged particles. We find a significant improvement of the constraints in the high mass range of DM particles after considering the inverse Compton emission.

  4. Coincidence studies with antiprotons

    Energy Technology Data Exchange (ETDEWEB)

    McGovern, M; Walters, H R J [Department of Applied Mathematics and Theoretical Physics, Queen' s University, Belfast BT7 1NN (United Kingdom); Assafrao, D; Mohallem, J 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); Whelan, Colm T, E-mail: mmcgovern06@qub.ac.u [Department of Physics, Old Dominion University, Norfolk, VA 23529-0116 (United States)

    2010-02-01

    We present a short overview of a new method for calculating fully differential cross sections that is able to describe any aspect of coincidence measurements involving heavy projectiles. The method is based upon impact parameter close coupling with pseudostates. Examples from antiproton impact ionization are shown.

  5. A β - γ coincidence

    International Nuclear Information System (INIS)

    Agullo, F.

    1960-01-01

    A β - γ coincidence method for absolute counting is given. The fundamental principles are revised and the experimental part is detailed. The results from 1 98 Au irradiated in the JEN 1 Swimming pool reactor are given. The maximal accuracy is 1 per cent. (Author) 11 refs

  6. A Monte-Carlo simulation of the equilibrium beam polarization in ultra-high energy electron (positron) storage rings

    International Nuclear Information System (INIS)

    Duan, Zhe; Bai, Mei; Barber, Desmond P.; Qin, Qing

    2015-04-01

    With the recently emerging global interest in building a next generation of circular electron-positron colliders to study the properties of the Higgs boson, and other important topics in particle physics at ultra-high beam energies, it is also important to pursue the possibility of implementing polarized beams at this energy scale. It is therefore necessary to set up simulation tools to evaluate the beam polarization at these ultra-high beam energies. In this paper, a Monte-Carlo simulation of the equilibrium beam polarization based on the Polymorphic Tracking Code(PTC) (Schmidt et al., 2002) is described. The simulations are for a model storage ring with parameters similar to those of proposed circular colliders in this energy range, and they are compared with the suggestion (Derbenev et al., 1978) that there are different regimes for the spin dynamics underlying the polarization of a beam in the presence of synchrotron radiation at ultra-high beam energies. In particular, it has been suggested that the so-called ''correlated'' crossing of spin resonances during synchrotron oscillations at current energies, evolves into ''uncorrelated'' crossing of spin resonances at ultra-high energies.

  7. Observation of Electron Cloud Instabilities and Emittance Dilution at the Cornell Electron-Positron Storage Ring Test Accelerator

    International Nuclear Information System (INIS)

    Holtzapple, R.L.; Campbell, R.C.; McArdle, K.E.; Miller, M.I.; Totten, M.M.; Tucker, S.L.; Billing, M.G.; Dugan, G.F.; Ramirez, G.A.; Sonnad, K.G.; Williams, H.A.; Flanagan, J.; Palmer, M.A.

    2016-01-01

    Electron cloud related emittance dilution and instabilities of bunch trains limit the performance of high intensity circular colliders. One of the key goals of the Cornell electron-positron storage ring Test Accelerator (CesrTA) research program is to improve our understanding of how the electron cloud alters the dynamics of bunches within the train. Single bunch beam diagnotics have been developed to measure the beam spectra, vertical beam size, two important dynamical effects of beams interacting with the electron cloud, for bunch trains on a turn-by-turn basis. Experiments have been performed at CesrTA to probe the interaction of the electron cloud with stored positron bunch trains. The purpose of these experiments was to characterize the dependence of beam-electron cloud interactions on the machine parameters such as bunch spacing, vertical chromaticity, and bunch current. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains; 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this paper we report on the observations from these experiments and analyze the effects of the electron cloud on the stability of bunches in a train under many different operational conditions

  8. Lattice design and beam optics calculations for the new large-scale electron-positron collider FCC-ee

    CERN Document Server

    Haerer, Bastian; Prof. Dr. Schmidt, Ruediger; Dr. Holzer, Bernhard

    Following the recommendations of the European Strategy Group for High Energy Physics, CERN launched the Future Circular Collider Study (FCC) to investigate the feasibility of large-scale circular colliders for future high energy physics research. This thesis presents the considerations taken into account during the design process of the magnetic lattice in the arc sections of the electron-positron version FCC-ee. The machine is foreseen to operate at four different centre-of-mass energies in the range of 90 to 350 GeV. Different beam parameters need to be achieved for every energy, which requires a flexible lattice design in the arc sections. Therefore methods to tune the horizontal beam emittance without re-positioning machine components are implemented. In combination with damping and excitation wigglers a precise adjustment of the emittance can be achieved. A very first estimation of the vertical emittance arising from lattice imperfections is performed. Special emphasis is put on the optimisation of the ...

  9. Oblique Propagation of Electrostatic Waves in a Magnetized Electron-Positron-Ion Plasma in the Presence of Heavy Particles

    Science.gov (United States)

    Sarker, M.; Hossen, M. R.; Shah, M. G.; Hosen, B.; Mamun, A. A.

    2018-06-01

    A theoretical investigation is carried out to understand the basic features of nonlinear propagation of heavy ion-acoustic (HIA) waves subjected to an external magnetic field in an electron-positron-ion plasma that consists of cold magnetized positively charged heavy ion fluids and superthermal distributed electrons and positrons. In the nonlinear regime, the Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations describing the propagation of HIA waves are derived. The latter admits a solitary wave solution with both positive and negative potentials (for K-dV equation) and only positive potential (for mK-dV equation) in the weak amplitude limit. It is observed that the effects of external magnetic field (obliqueness), superthermal electrons and positrons, different plasma species concentration, heavy ion dynamics, and temperature ratio significantly modify the basic features of HIA solitary waves. The application of the results in a magnetized EPI plasma, which occurs in many astrophysical objects (e.g. pulsars, cluster explosions, and active galactic nuclei) is briefly discussed.

  10. Kinetic transverse dispersion relation for relativistic magnetized electron-positron plasmas with Maxwell-Jüttner velocity distribution functions

    Energy Technology Data Exchange (ETDEWEB)

    López, Rodrigo A. [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Concepción, Concepción (Chile); Moya, Pablo S. [NASA Goddard Space Flight Center, Heliophysics Science Division, Geospace Physics Laboratory, Mail Code 673, Greenbelt, Maryland 20771 (United States); Department of Physics, Catholic University of America, Washington DC, DC 20064 (United States); Muñoz, Víctor [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Viñas, Adolfo F. [NASA Goddard Space Flight Center, Heliophysics Science Division, Geospace Physics Laboratory, Mail Code 673, Greenbelt, Maryland 20771 (United States); Valdivia, J. Alejandro [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Centro para el Desarrollo de la Nanociencia y la Nanotecnología, CEDENNA, Santiago (Chile)

    2014-09-15

    We use a kinetic treatment to study the linear transverse dispersion relation for a magnetized isotropic relativistic electron-positron plasma with finite relativistic temperature. The explicit linear dispersion relation for electromagnetic waves propagating along a constant background magnetic field is presented, including an analytical continuation to the whole complex frequency plane for the case of Maxwell-Jüttner velocity distribution functions. This dispersion relation is studied numerically for various temperatures. For left-handed solutions, the system presents two branches, the electromagnetic ordinary mode and the Alfvén mode. In the low frequency regime, the Alfvén branch has two dispersive zones, the normal zone (where ∂ω/∂k > 0) and an anomalous zone (where ∂ω/∂k < 0). We find that in the anomalous zone of the Alfvén branch, the electromagnetic waves are damped, and there is a maximum wave number for which the Alfvén branch is suppressed. We also study the dependence of the Alfvén velocity and effective plasma frequency with the temperature. We complemented the analytical and numerical approaches with relativistic full particle simulations, which consistently agree with the analytical results.

  11. Amplitude modulation of quantum-ion-acoustic wavepackets in electron-positron-ion plasmas: Modulational instability, envelope modes, extreme wavesa)

    Science.gov (United States)

    Rahman, Ata-ur-; Kerr, Michael Mc; El-Taibany, Wael F.; Kourakis, Ioannis; Qamar, A.

    2015-02-01

    A semirelativistic fluid model is employed to describe the nonlinear amplitude modulation of low-frequency (ionic scale) electrostatic waves in an unmagnetized electron-positron-ion plasma. Electrons and positrons are assumed to be degenerated and inertialess, whereas ions are warm and classical. A multiscale perturbation method is used to derive a nonlinear Schrödinger equation for the envelope amplitude, based on which the occurrence of modulational instability is investigated in detail. Various types of localized ion acoustic excitations are shown to exist, in the form of either bright type envelope solitons (envelope pulses) or dark-type envelope solitons (voids, holes). The plasma configurational parameters (namely, the relativistic degeneracy parameter, the positron concentration, and the ionic temperature) are shown to affect the conditions for modulational instability significantly, in fact modifying the associated threshold as well as the instability growth rate. In particular, the relativistic degeneracy parameter leads to an enhancement of the modulational instability mechanism. Furthermore, the effect of different relevant plasma parameters on the characteristics (amplitude, width) of these envelope solitary structures is also presented in detail. Finally, the occurrence of extreme amplitude excitation (rogue waves) is also discussed briefly. Our results aim at elucidating the formation and dynamics of nonlinear electrostatic excitations in superdense astrophysical regimes.

  12. Amplitude modulation of quantum-ion-acoustic wavepackets in electron-positron-ion plasmas: Modulational instability, envelope modes, extreme waves

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, Ata-ur-, E-mail: ata797@yahoo.com [Department of Physics, University of Peshawar, Peshawar 25000 (Pakistan); Department of Physics, Islamia College Peshawar, Khyber Pakhtunkhwa (Pakistan); Kerr, Michael Mc, E-mail: mjamckerr@gmail.com; Kourakis, Ioannis, E-mail: IoannisKourakisSci@gmail.com [Centre for Plasma Physics, Department of Physics and Astronomy, Queen' s University Belfast, BT7 1NN Northern Ireland (United Kingdom); El-Taibany, Wael F., E-mail: eltaibany@hotmail.com [Department of Physics, Faculty of Science, Damietta University, New Damietta, P.O. Box 34517 (Egypt); Department of Physics, College of Science for Girls in Abha, King Khalid University, P.O. Box 960, Abha (Saudi Arabia); Qamar, A., E-mail: anisaqamar@gmail.com [Department of Physics, University of Peshawar, Peshawar 25000 (Pakistan)

    2015-02-15

    A semirelativistic fluid model is employed to describe the nonlinear amplitude modulation of low-frequency (ionic scale) electrostatic waves in an unmagnetized electron-positron-ion plasma. Electrons and positrons are assumed to be degenerated and inertialess, whereas ions are warm and classical. A multiscale perturbation method is used to derive a nonlinear Schrödinger equation for the envelope amplitude, based on which the occurrence of modulational instability is investigated in detail. Various types of localized ion acoustic excitations are shown to exist, in the form of either bright type envelope solitons (envelope pulses) or dark-type envelope solitons (voids, holes). The plasma configurational parameters (namely, the relativistic degeneracy parameter, the positron concentration, and the ionic temperature) are shown to affect the conditions for modulational instability significantly, in fact modifying the associated threshold as well as the instability growth rate. In particular, the relativistic degeneracy parameter leads to an enhancement of the modulational instability mechanism. Furthermore, the effect of different relevant plasma parameters on the characteristics (amplitude, width) of these envelope solitary structures is also presented in detail. Finally, the occurrence of extreme amplitude excitation (rogue waves) is also discussed briefly. Our results aim at elucidating the formation and dynamics of nonlinear electrostatic excitations in superdense astrophysical regimes.

  13. 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 ...

  14. 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.

  15. 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

  16. 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

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

    Science.gov (United States)

    Tuomisto, Filip

    2015-03-01

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

  18. 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

  19. Response to ''Comment on 'Interaction of two solitary waves in quantum electron-positron-ion plasma''' [Phys. Plasmas 18, 084701 (2011)

    International Nuclear Information System (INIS)

    Xu Yanxia; Lin Maimai; Shi Yuren; Duan Wenshan; Liu Zongming

    2011-01-01

    According to the comments of Akbari-Moghanjoughi that the electron-positron-ion(e-p-i) plasmas parameters σ representing the ratio of the positron to electron Fermi-temperature and p standing for the positron to electron number-density ratio are related by the equation of p σ 3/2 . Based on this conclusion, we have replaced the Figs. 1-6 (Ref. 1) in the present paper.

  20. 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)

  1. Digital coincidence counting

    International Nuclear Information System (INIS)

    Buckman, S.M.; Ius, D.

    1996-01-01

    This paper reports on the development of a digital coincidence-counting system which comprises a custom-built data acquisition card and associated PC software. The system has been designed to digitise the pulse-trains from two radiation detectors at a rate of 20 MSamples/s with 12-bit resolution. Through hardware compression of the data, the system can continuously record both individual pulse-shapes and the time intervals between pulses. Software-based circuits are used to process the stored pulse trains. These circuits are constructed simply by linking together icons representing various components such as coincidence mixers, time delays, single-channel analysers, deadtimes and scalers. This system enables a pair of pulse trains to be processed repeatedly using any number of different methods. Some preliminary results are presented in order to demonstrate the versatility and efficiency of this new method. (orig.)

  2. Digital coincidence counting

    Science.gov (United States)

    Buckman, S. M.; Ius, D.

    1996-02-01

    This paper reports on the development of a digital coincidence-counting system which comprises a custom-built data acquisition card and associated PC software. The system has been designed to digitise the pulse-trains from two radiation detectors at a rate of 20 MSamples/s with 12-bit resolution. Through hardware compression of the data, the system can continuously record both individual pulse-shapes and the time intervals between pulses. Software-based circuits are used to process the stored pulse trains. These circuits are constructed simply by linking together icons representing various components such as coincidence mixers, time delays, single-channel analysers, deadtimes and scalers. This system enables a pair of pulse trains to be processed repeatedly using any number of different methods. Some preliminary results are presented in order to demonstrate the versatility and efficiency of this new method.

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

    International Nuclear Information System (INIS)

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

    1992-01-01

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

  4. Prospects in coincidence experiments

    International Nuclear Information System (INIS)

    Laget, J.M.

    1984-01-01

    The sensitivity of virtual photons to the local variations of the charge and magnetization densities is exploited to study the short-range part of the nucleon-nucleon interaction inside the nucleus. The possibility of varying energy, squared mass and longitudinal polarization of the photons independently enables us to disentangle the mechanisms related to the internal structure of the nucleon (e.g. quark interchange) and the contribution due to meson exchange. Coincidence experiments of the type (e,e'N) and (e,e'NN) are performed to suppress the meson contribution to the longitudinal part of the quasi-elastic peak. Four typical examples of coincidence experiments induced by virtual photons are discussed: experiments (1) on the spectroscopic structure of the quasi-elastic peak and the problem of deep lying hole states; (2) on the structure of the continuum; (3) on the low energy side of the quasi-elastic peak; and finally a three-arm coincidence experiment. (Auth.)

  5. 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...

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

    International Nuclear Information System (INIS)

    Wiktor, Julia

    2015-01-01

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

  7. Constraints on dark matter annihilation in clusters of galaxies with the Fermi large area telescope

    International Nuclear Information System (INIS)

    Ackermann, M.; Ajello, M.; Allafort, A.; Bechtol, K.; Blanford, R.D.; Bloom, E.D.; Borgland, A.W.; Bouvier, A.; Buehler, R.; Cameron, R.A.; Charles, E.; Chiang, J.; Claus, R.; Do Couto E Silva, E.; Drell, P.S.; Drlica-Wagner, A.; Dubois, R.; Edmonds, Y.; Glanzman, T.; Godfrey, G.; Hayashida, M.; Johannesson, G.; Johnson, A.S.; Kamae, T.; Lande, J.; Lee, S.H.; Madejski, G.M.; Michelson, P.F.; Mitthumsiri, W.; Monzani, M.E.; Moskalenko, I.V.; Murgia, S.; Nolan, P.L.; Omodei, N.; Panetta, J.H.; Porter, T.A.; Tanaka, T.; Thayer, J.B.; Thayer, J.G.; Waite, A.P.; Wang, P.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Kuss, M.; Latronico, L.; Pesce-Rollins, M.; Razzano, M.; Sgro, C.; Spandre, G.; Ballet, J.; Casandjian, J.M.; Grenier, I.A.; Starck, J.L.; Tibaldo, L.

    2010-01-01

    Nearby clusters and groups of galaxies are potentially bright sources of high-energy gamma-ray emission resulting from the pair-annihilation of dark matter particles. However, no significant gamma-ray emission has been detected so far from clusters in the first 11 months of observations with the Fermi Large Area Telescope. We interpret this non-detection in terms of constraints on dark matter particle properties. In particular for leptonic annihilation final states and particle masses greater than similar to 200 GeV, gamma-ray emission from inverse Compton scattering of CMB photons is expected to dominate the dark matter annihilation signal from clusters, and our gamma-ray limits exclude large regions of the parameter space that would give a good fit to the recent anomalous Pamela and Fermi-LAT electron-positron measurements. We also present constraints on the annihilation of more standard dark matter candidates, such as the lightest neutralino of supersymmetric models. The constraints are particularly strong when including the fact that clusters are known to contain substructure at least on galaxy scales, increasing the expected gamma-ray flux by a factor of similar to 5 over a smooth-halo assumption. We also explore the effect of uncertainties in cluster dark matter density profiles, finding a systematic uncertainty in the constraints of roughly a factor of two, but similar overall conclusions. In this work, we focus on deriving limits on dark matter models; a more general consideration of the Fermi-LAT data on clusters and clusters as gamma-ray sources is forthcoming. (authors)

  8. Impact-parameter dependence of the total probability for electromagnetic electron-positron pair production in relativistic heavy-ion collisions

    International Nuclear Information System (INIS)

    Hencken, K.; Trautmann, D.; Baur, G.

    1995-01-01

    We calculate the impact-parameter-dependent total probability P total (b) for the electromagnetic production of electron-positron pairs in relativistic heavy-ion collisions in lowest order. We study expecially impact parameters smaller than the Compton wavelength of the electron, where the equivalent-photon approximation cannot be used. Calculations with and without a form factor for the heavy ions are done; the influence is found to be small. The lowest-order results are found to violate unitarity and are used for the calculation of multiple-pair production probabilities with the help of the approximate Poisson distribution already found in earlier publications

  9. Use of positron annihilation spectroscopy for the study and characterization of materials

    International Nuclear Information System (INIS)

    Somoza, Alberto

    1998-01-01

    In this work the potentiality of positron annihilation spectroscopy (PAS) for the study and characterization of materials is presented, the physical principles of the electron-positron annihilation process is described, as well as the experimental techniques to measure such process. The greatest application fields of positron techniques are the study of electronic structures and defects in condensed matter. The quality of the information obtained suggests that PAS techniques could turn into an alternative of great importance to undertake the study of different material properties. During the development of this work, special emphasis was put on PAS application to the study of defects in metals and alloys, where it was shown the great sensibility of positrons to vacancies type-defects covering the range between mono vacancies and clusters that contain between 50 and 100 vacancies, for a concentration range between 10 -4 and 10 -7 at. -1 . Such range is below the sizes that can be visualized through electron microscopy. This high sensibility is, in turn, one of PAS limitations for the study of greater size defects. Also the positrons are insensible to defects such as interstitials, which present an electron density greater than the average. The development of slow positron beams that enable the study of spatial distribution of defects has permitted to complement PAS conventional techniques. In this way the joint use of the different positron techniques provides complete information about the nature, concentration and distribution of defects in solids

  10. 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.

  11. 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).

  12. Triple-coincidence with automatic chance coincidence correction

    International Nuclear Information System (INIS)

    Chase, R.L.

    1975-05-01

    The chance coincidences in a triple-coincidence circuit are of two types--partially correlated and entirely uncorrelated. Their relative importance depends on source strength and source and detector geometry so that the total chance correction cannot, in general, be calculated. The system described makes use of several delays and straightforward integrated circuit logic to provide independent evaluation of the two components of the chance coincidence rate. (auth)

  13. Search for high mass resonances decaying into electron-positron pairs in proton-proton collisions at √(s)=7 TeV with the ATLAS detector

    International Nuclear Information System (INIS)

    Goeringer, Christian

    2013-01-01

    The Standard Model of particle physics was developed to describe the fundamental particles, which form matter, and their interactions via the strong, electromagnetic and weak force. Although most measurements are described with high accuracy, some observations indicate that the Standard Model is incomplete. Numerous extensions were developed to solve these limitations. Several of these extensions predict heavy resonances, so-called Z' bosons, that can decay into an electron positron pair. The particle accelerator Large Hadron Collider (LHC) at CERN in Switzerland was built to collide protons at unprecedented center-of-mass energies, namely 7 TeV in 2011. With the data set recorded in 2011 by the ATLAS detector, a large multi-purpose detector located at the LHC, the electron positron pair mass spectrum was measured up to high masses in the TeV range. The properties of electrons and the probability that other particles are mis-identified as electrons were studied in detail. Using the obtained information, a sophisticated Standard Model expectation was derived with data-driven methods and Monte Carlo simulations. In the comparison of the measurement with the expectation, no significant deviations from the Standard Model expectations were observed. Therefore exclusion limits for several Standard Model extensions were calculated. For example, Sequential Standard Model (SSM) Z' bosons with masses below 2.10 TeV were excluded with 95% Confidence Level (C.L.).

  14. Search for high mass resonances decaying into electron-positron pairs in proton-proton collisions at {radical}(s)=7 TeV with the ATLAS detector

    Energy Technology Data Exchange (ETDEWEB)

    Goeringer, Christian

    2013-04-25

    The Standard Model of particle physics was developed to describe the fundamental particles, which form matter, and their interactions via the strong, electromagnetic and weak force. Although most measurements are described with high accuracy, some observations indicate that the Standard Model is incomplete. Numerous extensions were developed to solve these limitations. Several of these extensions predict heavy resonances, so-called Z' bosons, that can decay into an electron positron pair. The particle accelerator Large Hadron Collider (LHC) at CERN in Switzerland was built to collide protons at unprecedented center-of-mass energies, namely 7 TeV in 2011. With the data set recorded in 2011 by the ATLAS detector, a large multi-purpose detector located at the LHC, the electron positron pair mass spectrum was measured up to high masses in the TeV range. The properties of electrons and the probability that other particles are mis-identified as electrons were studied in detail. Using the obtained information, a sophisticated Standard Model expectation was derived with data-driven methods and Monte Carlo simulations. In the comparison of the measurement with the expectation, no significant deviations from the Standard Model expectations were observed. Therefore exclusion limits for several Standard Model extensions were calculated. For example, Sequential Standard Model (SSM) Z' bosons with masses below 2.10 TeV were excluded with 95% Confidence Level (C.L.).

  15. Study of Doppler broadened annihilation spectra in zinc and zinc-containing 0.05 at. % iron

    International Nuclear Information System (INIS)

    Troev, T.; Zolov, R.; Dimova, V.; Levay, B.

    1979-01-01

    The Doppler broadening of annihilation gamma spectra obtained from positron-electron annihilation in pure polycrystalline zinc and zinc-containing 0.05 at. % iron have been investigated. The line shapes were measured by a Ge(Li) detector in coincidence with a NaI(Tl) scintillation detector. The results are quite consistent with those expected from the trapping model. The positrons are trapped by impurity atoms and vacancy-impurity pairs in zinc containing 0.05 at. % iron. (author)

  16. Coincidence counting corrections for dead time losses and accidental coincidences

    International Nuclear Information System (INIS)

    Wyllie, H.A.

    1987-04-01

    An equation is derived for the calculation of the radioactivity of a source from the results of coincidence counting taking into account the dead-time losses and accidental coincidences. The derivation is an extension of the method of J. Bryant [Int. J. Appl. Radiat. Isot., 14:143, 1963]. The improvement on Bryant's formula has been verified by experiment

  17. Directional Pair-Production Spectrometer Design for Airborne Stand-Off Detection of Special Nuclear Material

    Science.gov (United States)

    2011-03-01

    detectors arranged as shown in Figure 5. When the incoming gamma deposits its energy in the central detector, the resulting positron annihilates ...Compton detectors. Each pair of detectors can accomplish both spectroscopy and detection through application of energy filtering. The detectors are...electron- positron annihilation have three other detectors to interact with. Coincident techniques are used to provide real-time determination of

  18. Application of a digital data acquisition system for time of flight Positron annihilation-induced Auger Electron Spectroscopy

    Science.gov (United States)

    Gladen, R. W.; Chirayath, V. A.; McDonald, A. D.; Fairchild, A. J.; Chrysler, M. D.; Imam, S. K.; Koymen, A. R.; Weiss, A. H.

    We describe herein a digital data acquisition system for a time-of-flight Positron annihilation-induced Auger Electron Spectrometer. This data acquisition system consists of a high-speed digitizer collecting signals induced by Auger electrons and annihilation gammas in a multi-channel plate electron detector and a BaF2 gamma detector, respectively. The time intervals between these two signals is used to determine the times of flight of the Auger electrons, which are analyzed by algorithms based on traditional nuclear electronics methods. Ultimately, this digital data acquisition system will be expanded to incorporate the first coincidence measurements of Auger electron and annihilation gamma energies.

  19. An application of the coincidence Doppler spectroscopy for substances of chemical interest: phthalocyanine and acetylacetonate complexes

    International Nuclear Information System (INIS)

    Ito, Y.; Suzuki, T.

    2000-01-01

    Coincidence Doppler spectroscopy, which is particularly powerful when one is concerned with high momentum components of positron annihilation gamma-rays, has been applied to two different kinds of organo-metallic ligands: metal phthalocyanines and metal acetylacetonates. The energy (momentum) profiles of the annihilation gamma-rays were the same for metal phthalocyanines indicating that positron and/or positronium are not interacting with the metal ions. However, the profiles for the metal acetylacetonates evidently showed a dependence on the kind of metal ions. Discussion is made on the features of positron interaction which are different for phthalocyanines and acetylacetonates.

  20. 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

  1. New positron annihilation spectroscopy techniques for thick materials

    International Nuclear Information System (INIS)

    Selim, F.A.; Wells, D.P.; Harmon, J.F.; Kwofie, J.; Erikson, G.; Roney, T.

    2003-01-01

    The Idaho Accelerator Center (IAC) has developed new techniques for positron annihilation spectroscopy (PAS) by using highly penetrating γ-rays to create positrons inside the material via pair production. Two sources of γ-rays have been employed. Bremsstrahlung beams from small-electron linacs (6 MeV) were used to generate positrons inside the material to perform Doppler-broadening spectroscopy. A 2 MeV proton beam was used to obtain coincident γ-rays from 27 Al target and enable lifetime and Doppler-broadening spectroscopy. This technique successfully measured stress/strain in thick samples, and showed promise to extend PAS into a variety of applications

  2. Intrinsic spatial resolution limitations due to differences between positron emission position and annihilation detection localization; Limitacoes da resolucao espacial intrinseca devido as diferencas entre a posicao da emissao do positron e a deteccao da localizacao de aniquilacao

    Energy Technology Data Exchange (ETDEWEB)

    Perez, Pedro; Malano, Francisco; Valente, Mauro, E-mail: valente@famaf.unc.edu.ar [Universidad Nacional de Cordoba, Cordoba (Argentina). Fac. de Matematica, Astronomia y Fisica (FaMAF)

    2012-07-01

    Since its successful implementation for clinical diagnostic, positron emission tomography (PET) represents the most promising medical imaging technique. The recent major growth of PET imaging is mainly due to its ability to trace the biologic pathways of different compounds in the patient's body, assuming the patient can be labeled with some PET isotope. Regardless of the type of isotope, the PET imaging method is based on the detection of two 511-keV gamma photons being emitted in opposite directions, with almost 180 deg between them, as a consequence of electron-positron annihilation. Therefore, this imaging method is intrinsically limited by random uncertainties in spatial resolutions, related with differences between the actual position of positron emission and the location of the detected annihilation. This study presents an approach with the Monte Carlo method to analyze the influence of this effect on different isotopes of potential implementation in PET. (author)

  3. 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...

  4. 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

  5. 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.

  6. Measurement of the Z boson differential cross-section in transverse momentum in the electron-positron channel with the ATLAS detector at LHC

    International Nuclear Information System (INIS)

    Martinez, Homero

    2013-01-01

    This work presents the measurement of the Z boson differential cross section in transverse momentum (p T Z ), in the electron-positron decay channel, using the ATLAS detector at the LHC. The measurement is done using 4.64 fb -1 of proton-proton collision data, collected in 2011 at a center-of-mass energy of 7 TeV. The result is combined with an independent measurement done in the muon-anti-muon decay channel. The measurement is done up to p T Z = 800 GeV, and has a typical uncertainty of 0.5 % for transverse momentum below 60 GeV, rising up to 5 % towards the end of the spectrum. The measurement is compared to theoretical models and Monte Carlo generators predictions. (author) [fr

  7. Search for new physics in high-mass electron-positron events in pp[over] collisions at square root s = 1.96 TeV.

    Science.gov (United States)

    Aaltonen, T; Abulencia, A; Adelman, J; Affolder, T; Akimoto, T; Albrow, M G; Amerio, S; Amidei, D; Anastassov, A; Anikeev, K; Annovi, A; Antos, J; Aoki, M; Apollinari, G; Arisawa, T; Artikov, A; Ashmanskas, W; Attal, A; Aurisano, A; Azfar, F; Azzi-Bacchetta, P; Azzurri, P; Bacchetta, N; Badgett, W; Barbaro-Galtieri, A; Barnes, V E; Barnett, B A; Baroiant, S; Bartsch, V; Bauer, G; Beauchemin, P-H; Bedeschi, F; Behari, S; Bellettini, G; Bellinger, J; Belloni, A; Benjamin, D; Beretvas, A; Beringer, J; Berry, T; Bhatti, A; Binkley, M; Bisello, D; Bizjak, I; Blair, R E; Blocker, C; Blumenfeld, B; Bocci, A; Bodek, A; Boisvert, V; Bolla, G; Bolshov, A; Bortoletto, D; Boudreau, J; Boveia, A; Brau, B; Brigliadori, L; Bromberg, C; Brubaker, E; Budagov, J; Budd, H S; Budd, S; Burkett, K; Busetto, G; Bussey, P; Buzatu, A; Byrum, K L; Cabrera, S; Campanelli, M; Campbell, M; Canelli, F; Canepa, A; Carrillo, S; Carlsmith, D; Carosi, R; Carron, S; Casal, B; Casarsa, M; Castro, A; Catastini, P; Cauz, D; Cavalli-Sforza, M; Cerri, A; Cerrito, L; Chang, S H; Chen, Y C; Chertok, M; Chiarelli, G; Chlachidze, G; Chlebana, F; Cho, I; Cho, K; Chokheli, D; Chou, J P; Choudalakis, G; Chuang, S H; Chung, K; Chung, W H; Chung, Y S; Cilijak, M; Ciobanu, C I; Ciocci, M A; Clark, A; Clark, D; Coca, M; Compostella, G; Convery, M E; Conway, J; Cooper, B; Copic, K; Cordelli, M; Cortiana, G; Crescioli, F; Cuenca Almenar, C; Cuevas, J; Culbertson, R; Cully, J C; DaRonco, S; Datta, M; D'Auria, S; Davies, T; Dagenhart, D; de Barbaro, P; De Cecco, S; Deisher, A; De Lentdecker, G; De Lorenzo, G; Dell'Orso, M; Delli Paoli, F; Demortier, L; Deng, J; Deninno, M; De Pedis, D; Derwent, P F; Di Giovanni, G P; Dionisi, C; Di Ruzza, B; Dittmann, J R; D'Onofrio, M; Dörr, C; Donati, S; Dong, P; Donini, J; Dorigo, T; Dube, S; Efron, J; Erbacher, R; Errede, D; Errede, S; Eusebi, R; Fang, H C; Farrington, S; Fedorko, I; Fedorko, W T; Feild, R G; Feindt, M; Fernandez, J P; Field, R; Flanagan, G; Forrest, R; Forrester, S; Franklin, M; Freeman, J C; Furic, I; Gallinaro, M; Galyardt, J; Garcia, J E; Garberson, F; Garfinkel, A F; Gay, C; Gerberich, H; Gerdes, D; Giagu, S; Giannetti, P; Gibson, K; Gimmell, J L; Ginsburg, C; Giokaris, N; Giordani, M; Giromini, P; Giunta, M; Giurgiu, G; Glagolev, V; Glenzinski, D; Gold, M; Goldschmidt, N; Goldstein, J; Golossanov, A; Gomez, G; Gomez-Ceballos, G; Goncharov, M; González, O; Gorelov, I; Goshaw, A T; Goulianos, K; Gresele, A; Grinstein, S; Grosso-Pilcher, C; Grundler, U; Guimaraes da Costa, J; Gunay-Unalan, Z; Haber, C; Hahn, K; Hahn, S R; Halkiadakis, E; Hamilton, A; Han, B-Y; Han, J Y; Handler, R; Happacher, F; Hara, K; Hare, D; Hare, M; Harper, S; Harr, R F; Harris, R M; Hartz, M; Hatakeyama, K; Hauser, J; Hays, C; Heck, M; Heijboer, A; Heinemann, B; Heinrich, J; Henderson, C; Herndon, M; Heuser, J; Hidas, D; Hill, C S; Hirschbuehl, D; Hocker, A; Holloway, A; Hou, S; Houlden, M; Hsu, S-C; Huffman, B T; Hughes, R E; Husemann, U; Huston, J; Incandela, J; Introzzi, G; Iori, M; Ivanov, A; Iyutin, B; James, E; Jang, D; Jayatilaka, B; Jeans, D; Jeon, E J; Jindariani, S; Johnson, W; Jones, M; Joo, K K; Jun, S Y; Jung, J E; Junk, T R; Kamon, T; Karchin, P E; Kato, Y; Kemp, Y; Kephart, R; Kerzel, U; Khotilovich, V; Kilminster, B; Kim, D H; Kim, H S; Kim, J E; Kim, M J; Kim, S B; Kim, S H; Kim, Y K; Kimura, N; Kirsch, L; Klimenko, S; Klute, M; Knuteson, B; Ko, B R; Kondo, K; Kong, D J; Konigsberg, J; Korytov, A; Kotwal, A V; Kraan, A C; Kraus, J; Kreps, M; Kroll, J; Krumnack, N; Kruse, M; Krutelyov, V; Kubo, T; Kuhlmann, S E; Kuhr, T; Kulkarni, N P; Kusakabe, Y; Kwang, S; Laasanen, A T; Lai, S; Lami, S; Lammel, S; Lancaster, M; Lander, R L; Lannon, K; Lath, A; Latino, G; Lazzizzera, I; Lecompte, T; Lee, J; Lee, J; Lee, Y J; Lee, S W; Lefèvre, R; Leonardo, N; Leone, S; Levy, S; Lewis, J D; Lin, C; Lin, C S; Lindgren, M; Lipeles, E; Lister, A; Litvintsev, D O; Liu, T; Lockyer, N S; Loginov, A; Loreti, M; Lu, R-S; Lucchesi, D; Lujan, P; Lukens, P; Lungu, G; Lyons, L; Lys, J; Lysak, R; Lytken, E; Mack, P; Macqueen, D; Madrak, R; Maeshima, K; Makhoul, K; Maki, T; Maksimovic, P; Malde, S; Malik, S; Manca, G; Manousakis, A; Margaroli, F; Marginean, R; Marino, C; Marino, C P; Martin, A; Martin, M; Martin, V; Martínez, M; Martínez-Ballarín, R; Maruyama, T; Mastrandrea, P; Masubuchi, T; Matsunaga, H; Mattson, M E; Mazini, R; Mazzanti, P; McFarland, K S; McIntyre, P; McNulty, R; Mehta, A; Mehtala, P; Menzemer, S; Menzione, A; Merkel, P; Mesropian, C; Messina, A; Miao, T; Miladinovic, N; Miles, J; Miller, R; Mills, C; Milnik, M; Mitra, A; Mitselmakher, G; Miyamoto, A; Moed, S; Moggi, N; Mohr, B; Moon, C S; Moore, R; Morello, M; Fernandez, P Movilla; Mülmenstädt, J; Mukherjee, A; Muller, Th; Mumford, R; Murat, P; Mussini, M; Nachtman, J; Nagano, A; Naganoma, J; Nakamura, K; Nakano, I; Napier, A; Necula, V; Neu, C; Neubauer, M S; Nielsen, J; Nodulman, L; Norniella, O; Nurse, E; Oh, S H; Oh, Y D; Oksuzian, I; Okusawa, T; Oldeman, R; Orava, R; Osterberg, K; Pagliarone, C; Palencia, E; Papadimitriou, V; Papaikonomou, A; Paramonov, A A; Parks, B; Pashapour, S; Patrick, J; Pauletta, G; Paulini, M; Paus, C; Pellett, D E; Penzo, A; Phillips, T J; Piacentino, G; Piedra, J; Pinera, L; Pitts, K; Plager, C; Pondrom, L; Portell, X; Poukhov, O; Pounder, N; Prakoshyn, F; Pronko, A; Proudfoot, J; Ptohos, F; Punzi, G; Pursley, J; Rademacker, J; Rahaman, A; Ramakrishnan, V; Ranjan, N; Redondo, I; Reisert, B; Rekovic, V; Renton, P; Rescigno, M; Richter, S; Rimondi, F; Ristori, L; Robson, A; Rodrigo, T; Rogers, E; Rolli, S; Roser, R; Rossi, M; Rossin, R; Roy, P; Ruiz, A; Russ, J; Rusu, V; Saarikko, H; Safonov, A; Sakumoto, W K; Salamanna, G; Saltó, O; Santi, L; Sarkar, S; Sartori, L; Sato, K; Savard, P; Savoy-Navarro, A; Scheidle, T; Schlabach, P; Schmidt, E E; Schmidt, M P; Schmitt, M; Schwarz, T; Scodellaro, L; Scott, A L; Scribano, A; Scuri, F; Sedov, A; Seidel, S; Seiya, Y; Semenov, A; Sexton-Kennedy, L; Sfyrla, A; Shalhout, S Z; Shapiro, M D; Shears, T; Shepard, P F; Sherman, D; Shimojima, M; Shochet, M; Shon, Y; Shreyber, I; Sidoti, A; Sinervo, P; Sisakyan, A; Slaughter, A J; Slaunwhite, J; Sliwa, K; Smith, J R; Snider, F D; Snihur, R; Soderberg, M; Soha, A; Somalwar, S; Sorin, V; Spalding, J; Spinella, F; Spreitzer, T; Squillacioti, P; Stanitzki, M; Staveris-Polykalas, A; St Denis, R; Stelzer, B; Stelzer-Chilton, O; Stentz, D; Strologas, J; Stuart, D; Suh, J S; Sukhanov, A; Sun, H; Suslov, I; Suzuki, T; Taffard, A; Takashima, R; Takeuchi, Y; Tanaka, R; Tecchio, M; Teng, P K; Terashi, K; Thom, J; Thompson, A S; Thomson, E; Tipton, P; Tiwari, V; Tkaczyk, S; Toback, D; Tokar, S; Tollefson, K; Tomura, T; Tonelli, D; Torre, S; Torretta, D; Tourneur, S; Trischuk, W; Tsuno, S; Tu, Y; Turini, N; Ukegawa, F; Uozumi, S; Vallecorsa, S; van Remortel, N; Varganov, A; Vataga, E; Vazquez, F; Velev, G; Vellidis, C; Veramendi, G; Veszpremi, V; Vidal, M; Vidal, R; Vila, I; Vilar, R; Vine, T; Vogel, M; Vollrath, I; Volobouev, I; Volpi, G; Würthwein, F; Wagner, P; Wagner, R G; Wagner, R L; Wagner, J; Wagner, W; Wallny, R; Wang, S M; Warburton, A; Waters, D; Weinberger, M; Wester, W C; Whitehouse, B; Whiteson, D; Wicklund, A B; Wicklund, E; Williams, G; Williams, H H; Wilson, P; Winer, B L; Wittich, P; Wolbers, S; Wolfe, C; Wright, T; Wu, X; Wynne, S M; Yagil, A; Yamamoto, K; Yamaoka, J; Yamashita, T; Yang, C; Yang, U K; Yang, Y C; Yao, W M; Yeh, G P; Yoh, J; Yorita, K; Yoshida, T; Yu, G B; Yu, I; Yu, S S; Yun, J C; Zanello, L; Zanetti, A; Zaw, I; Zhang, X; Zhou, J; Zucchelli, S

    2007-10-26

    We report the results of a search for a narrow resonance in electron-positron events in the invariant mass range of 150-950 GeV/c(2) using 1.3 fb(-1) of pp[over] collision data at square root s = 1.96 TeV collected by the CDF II detector at Fermilab. No significant evidence of such a resonance is observed and we interpret the results to exclude the standard-model-like Z' with a mass below 923 GeV/c(2) and the Randall-Sundrum graviton with a mass below 807 GeV/c(2) for k/M[over](pl) = 0.1, both at the 95% confidence level. Combining with diphoton data excludes the Randall-Sundrum graviton for masses below 889 GeV/c(2) for k/M[over](pl) = 0.1.

  8. Positron-annihilation-induced ion desorption from TiO2(110)

    Science.gov (United States)

    Tachibana, T.; Hirayama, T.; Nagashima, Y.

    2014-05-01

    We have investigated the positron-stimulated desorption of ions from a TiO2(110) surface. Desorbed O+ ions were detected in coincidence with the emission of annihilation γ rays. The energy dependence of the ion yields shows that the O+ ions were detected at energies much lower than the previously reported threshold for electron impact desorption corresponding to the excitation energy of Ti(3p) core electrons. These results provide evidence that core-hole creation by positron annihilation with electrons in the core levels leads to ion desorption.

  9. Positron annihilation studies in ZnO nanoparticles

    Science.gov (United States)

    Sharma, S. K.; Pujari, P. K.; Sudarshan, K.; Dutta, D.; Mahapatra, M.; Godbole, S. V.; Jayakumar, O. D.; Tyagi, A. K.

    2009-04-01

    We report results on positron annihilation spectroscopic (PAS) studies using lifetime and coincidence Doppler broadening techniques in zinc oxide (ZnO) nanoparticles (4 to 40 nm) synthesized by solid state pyrolytic reaction followed by annealing in the temperature range of 200 ∘C to 800 ∘C. Positron lifetime in the nanoparticles are observed to be higher than bulk lifetime in all the cases. Theoretical calculation of lifetime indicates the presence of either Zn or (Zn, O) vacancy clusters which migrate and anneal out at high temperature. Comparison of ratio spectra from coincidence Doppler broadening measurement and calculated electron momentum distribution indicates the presence of either Zn or (Zn, O) vacancies. In addition, photoluminescence (PL) measurements have been carried out to examine the role of defects on the intensity of emission in the visible region.

  10. Channel coincidence counter: version 1

    International Nuclear Information System (INIS)

    Krick, M.S.; Menlove, H.O.

    1980-06-01

    A thermal neutron coincidence counter has been designed for the assay of fast critical assembly fuel drawers and plutonium-bearing fuel rods. The principal feature of the detector is a 7-cm by 7-cm by 97-cm detector channel, which provides a uniform neutron detection efficiency of 16% along the central 40 cm of the channel. The electronics system is identical to that used for the High-Level Neutron Coincidence Counter

  11. 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.

  12. 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

  13. 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)

  14. The influence of radiation and light on Ps formation in PMMA and PE studied by coincidence Doppler-broadening spectroscopy

    CERN Document Server

    Suzuki, T; Shantarovich, V; Kondo, K; Hamada, E; Matso, M; Ma Li; Ito, Y

    2003-01-01

    Using two Ge detectors, the high-resolution Doppler-broadening energy spectra of positron annihilation gamma rays has been obtained by measuring the coincidences of the two photons. Light bleaching and oxygen effects on positron annihilation were investigated in this way. A large enhancement of the high-momentum part of the coincidence Doppler spectra was observed in poly(methylmethacrylate) (PMMA), which contains oxygen atoms in the polymer structure. Bleaching experiments in PMMA and in copolymer ethylene-methylmethacrylate EMMA (LDPE+MMA 3 mol%) have demonstrated that the enhancement effect may be due to the trapping of positrons by the polar -C sup + 6-O sup - groups, followed by positron annihilation with the electrons belonging to oxygen.

  15. [Commissioning of the newly constructed Beijing electron-positron collider BEPC, Beijing, China, and visit to SRRC to discuss magnet manufacturing and measurement methods, Taipei, Taiwan, November 11--27, 1988]: Foreign trip report

    International Nuclear Information System (INIS)

    Weng, W.T.

    1988-01-01

    The traveller was invited to IHEP to participate in the commissioning of the newly constructed Beijing electron-positron collider BEPC, give a status report on the AGS Booster Project and to assess the feasibility of sub-contracting booster sextupoles to IHEP. The trip to SRRC was undertaken to discuss magnet manufacturing and measurement methods

  16. Application of positron-electron annihilation method for determination of dislocation splitting width in d-transition metals

    International Nuclear Information System (INIS)

    Dekhtyar, A.I.; Kozyrskij, G.Ya.; Kononenko, V.A.

    1978-01-01

    A method for the study of the dislocation structure in d-transition metals with the application of experimental data on annihilation of electron-positron pairs is suggested. The method is based on finding the density of partially collectivized d- electrons using the technique of expanding the angular distribution of the positron-electron annihilation. In the wave vectors space, the concept of a pseudosphere was introduced, whose radius k'sub(F) is determined by the number of d-electrons. It was assumed that k'sub(F) is a parameter of the potential of effective atomic interaction in d-metals. The interaction energy between nuclei of partial dislocations was accounted for as an oscillating potential between parallel atom rows. Such a consideration makes it possible to correct the position of a partial dislocation in the neighbourhood of a wide minimum of interaction energy. The possibilities of the method for determining the splitting width of edge dislocations in various d-metals and their alloys (Mo, Ni, Fe, Nb) is shown. Using pure and doped Ni, the decrease of the packing defect energy was traced with the increase of Al content

  17. Materials characterization of free volume and void properties by two-dimensional positron annihilation lifetime spectroscopy

    Science.gov (United States)

    Chen, Hongmin; Van Horn, J. David; Jean, Y. C.; Hung, Wei-Song; Lee, Kueir-Rarn

    2013-04-01

    Positron annihilation lifetime spectroscopy (PALS) has been widely used to determine the free volume and void properties in polymeric materials. Recently, a two dimensional positron annihilation lifetime spectroscopy (2DPALS) system has been developed for membrane applications. The system measures the coincident signals between the lifetime and the energy which could separate the 2γ and 3γ annihilations and improve the accuracy in the determination of the free volume and void properties. When 2D-PALS is used in coupling with a variable mono-energy slow positron beam, it could be applied to a variety of material characterization. Results of free volumes and voids properties in a multi-layer polymer membrane characterized using 2D-PALS are presented.

  18. Multiple gamma lines from semi-annihilation

    International Nuclear Information System (INIS)

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

    2013-01-01

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

  19. Antinucleon-nucleon annihilation dynamics

    International Nuclear Information System (INIS)

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

    1989-01-01

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

  20. Positron annihilation spectroscopic characterization of defects in wide band gap oxide semiconductors

    Science.gov (United States)

    Sarkar, A.; Luitel, Homnath; Gogurla, N.; Sanyal, D.

    2017-03-01

    Annealing effect of granular ZnO has been studied by Doppler broadened electron positron annihilated γ-ray (0.511 MeV) line shape measurement. Ratio curve analysis shows that granular ZnO samples contain both Zn and O vacancies. Such defects exist as agglomerates of several vacancies and start to recover above 400 °C annealing. It has also been observed that due to annealing temperature difference of 125 °C (from 325 °C to 450 °C), huge change occurs in low temperature photoluminescence (PL) of ZnO. Significant reduction of free to bound (FB) transition ~3.315 eV is observed for increasing the annealing temperature. It has been conjectured that ~3.315 eV PL in ZnO is related to particular decoration (unknown) of both Zn and O vacancies. The methodology of revealing defect-property correlation as employed here can also be applied to other types of semiconductors.

  1. Off-line analysis of positron annihilation spectra. I. Signature of crystal symmetry

    International Nuclear Information System (INIS)

    Adam, Gh.; Adam, S.

    1997-01-01

    While the technique of 2-D angular correlation of the electron-positron annihilation radiation (2D-ACAR) yields data in the laboratory frame, consistent off-line data analysis requires their reformulation in the crystal frame. In the case of an n-axis projected 2D-ACAR spectrum (where n denotes a principal crystallographic axis) of a high-T c superconductor, the crystal frame derivation needs enhancement of information on spectrum symmetry. The concept of signature of crystal symmetry (SCS) in a 2D-ACAR histogram discussed in this paper is a basic ingredient to the consistent solution of the problem. The SCS in a row 2D-ACAR histogram is defined as a collection of chi-square sums over M max + 1 sets of sites inside the detector-defined histogram plane. The number M max is fixed by choice of the principal crystallographic axis n-vector and the angular aperture of the setup. The necessity of this concept is discussed in Section 2. The correct understanding of the meaning of the SCS results heavily relies of that of the various sources contributing to the symmetry a 2D-ACAR spectrum. This point is discussed in Section 3. The quantitative definition of the SCS is detailed in Section 4. Finally, Section 5 is devoted to a short consideration of the computation of the SCS numerical values

  2. Superstring Z' bozon in e-e+ → ff-bar annihilation

    International Nuclear Information System (INIS)

    Abdullaev, S.K.; Mukhtarov, A.I.

    1989-01-01

    An influence of an additional neutral Z' bozon on characteristics of e - e + →ff-bar processes is studied, where ff-bar is a pair of arbitrary particles (leptons, nucleons, hyperons, pseudoscalar or vector mesons etc.). The general expression for the differential cross sections of e - e + →ff-bar processes is obtained with arbitrary polarizations of an electron-positron pair by introducing of structure functions, and the following integral characteristics are considered: polarized forward A F (λ 2 ) and backward A B (λ 2 ) assymmetries; right-left asymmetry A RL ; forward-backward asymmetry in the case of longitudinal polarized e - e + pair annihilation A BH (λ 2 ); transversal spin assymmetries A Φ (1) and A Φ (2) ; the degree of longitudinal polarization of r lepton P in e - e + → r - r + r - r + process. The general expressions for these characteristics are found and their quantitative estimates are given in the framework of superstring E 6 -model. 20 refs.; 5 figs.; 2 tabs

  3. 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

  4. Video Histories, Memories, and Coincidences

    DEFF Research Database (Denmark)

    Kacunko, Slavko

    2012-01-01

    Looping images allows us to notice things that we have never noticed before. Looping a small but exquisite selection of the video tapes of Marcel Odenbach, Dieter Kiessling and Matthias Neuenhofer may allow the discovering of Histories, Coincidences, and Infinitesimal Aesthetics inscribed...

  5. 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...

  6. Positron Annihilation Induced Auger and Gamma Spectroscopy of Catalytically Important Surfaces

    Science.gov (United States)

    Weiss, A. H.; Nadesalingam, M. P.; Sundaramoorthy, R.; Mukherjee, S.; Fazleev, N. G.

    2006-10-01

    The annihilation of positrons with core electrons results in unique signatures in the spectra of Auger-electron and annihilation-gamma rays that can be used to make clear chemical identification of atoms at the surface. Because positrons implanted at low energies are trapped with high efficiency in the image-correlation well where they are localized just outside the surface it is possible to use annihilation induced Auger and Gamma signals to probe the surfaces of solids with single atomic layer depth resolution. In this talk we will report recent applications of Positron Annihilation Induced Auger Electron Spectroscopy (PAES) and Auger-Gamma Coincidence Spectroscopy (AGCS) to the study of surface structure and surface chemistry. Our research has demonstrated that PAES spectra can provide new information regarding the composition of the top-most atomic layer. Applications of PAES to the study of catalytically important surfaces of oxides and wide band-gap semiconductors including TiO2, SiO2,Cu2O, and SiC will be presented. We conclude with a discussion of the use of Auger-Gamma and Gamma-Gamma coincidence spectroscopy for the study of surfaces at pressures closer to those found in practical chemical reactors. Research supported by the Welch Foundation Grant Number Y-1100.

  7. Annihilation gamma ray background characterization and rejection for a positron camera

    International Nuclear Information System (INIS)

    Levin, C.S.; Tornai, M.P.; MacDonald, L.R.

    1996-01-01

    We have developed a miniature (1.2 cm 2 ) beta-ray camera prototype to assist a surgeon in locating and removing the margins of a resected tumor. When imaging positron emitting radiopharmaceuticals, annihilation gamma ray interactions in the detector can mimic those of the betas. The extent of the background contamination depends on the detector, geometry and tumor specificity of the radiopharmaceutical. We have characterized the effects that annihilation gamma rays have on positron imaging with the camera. We studied beta and gamma ray detection rates and imaging using small positron or electron sources directly exposed to the detector to simulate hot tumor remnants and a cylinder filled with 18 F to simulate annihilation background from the brain. For various ratios of phantom brain/tumor activity, a annihilation gamma rate of 1.8 cts/sec/gCi was measured in the CaF 2 (Eu) detector. We present two gamma-ray background rejection schemes that use a β-γ coincidence. Results show that the coincidence methods works with ∼99% gamma ray rejection efficiency

  8. Optimized coincidence Doppler broadening spectroscopy using deconvolution algorithms

    International Nuclear Information System (INIS)

    Ho, K.F.; Ching, H.M.; Cheng, K.W.; Beling, C.D.; Fung, S.; Ng, K.P.

    2004-01-01

    In the last few years a number of excellent deconvolution algorithms have been developed for use in ''de-blurring'' 2D images. Here we report briefly on one such algorithm we have studied which uses the non-negativity constraint to optimize the regularization and which is applied to the 2D image like data produced in Coincidence Doppler Broadening Spectroscopy (CDBS). The system instrumental resolution functions are obtained using the 514 keV line from 85 Sr. The technique when applied to a series of well annealed polycrystalline metals gives two photon momentum data on a quality comparable to that obtainable using 1D Angular Correlation of Annihilation Radiation (ACAR). (orig.)

  9. Development and Testing of a New Positron Identification by Coincident Annihilation Photons (PICAP) System Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The objective of the proposed research is to develop and test a prototype of an innovative and simple detector technique to identify moderate energy (a few MeV)...

  10. 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.)

  11. Positron annihilation study of yttria-stabilized zirconia nanopowders containing Cr2O3 additive

    International Nuclear Information System (INIS)

    Prochazka, I; Cizek, J; Melikhova, O; Kuriplach, J; Konstantinova, T E; Danilenko, I A

    2011-01-01

    Yttria-stabilized zirconia compacted nanopowders, doped with trivalent chromium oxide, were studied by means of high-resolution positron lifetime and coincidence Doppler broadening techniques. The observed data suggest that positrons annihilate mainly in vacancylike defects at grain boundaries or in larger open volumes most likely located at triple points. The results also show that an addition of Cr 2 O 3 leads to a decrease in grain size.

  12. High-Mass Drell-Yan Cross-Section and Search for New Phenomena in Multi-Electron/Positron Final States with the ATLAS Detector

    CERN Document Server

    Wollstadt, Simon

    The Standard Model of particle physics is a very successful theory which describes nearly all known processes of particle physics very precisely. Nevertheless, there are several observations which cannot be explained within the existing theory. In this thesis, two analyses with high energy electrons and positrons using data of the ATLAS detector are presented. One, probing the Standard Model of particle physics and another searching for phenomena beyond the Standard Model. The production of an electron-positron pair via the Drell-Yan process leads to a very clean signature in the detector with low background contributions. This allows for a very precise measurement of the cross-section and can be used as a precision test of perturbative quantum chromodynamics (pQCD) where this process has been calculated at next-to-next-to-leading order (NNLO). The invariant mass spectrum $m_{ee}$ is sensitive to parton distribution functions (PFDs), in particular to the poorly known distribution of antiquarks at large moment...

  13. Electron-positron pairs creation in the field of two strong counterpropagating laser beams and the nonlocality of the photon-photon interaction

    International Nuclear Information System (INIS)

    Gainutdinov, R.Kh.; Khamadeev, M.A.; Mutygullina, A.A.

    2010-01-01

    Complete text of publication follows. We discuss various approaches to problem of the electron-positron pair creation in the strong external field. Special interest presents the circuit, in which the interaction of two strong counterpropagating laser beams in vacuum is considered. For the calculation of the probability of the creation the following formula is usually applied: W = 2Im(L (E-H) (ρ L )) = 2m 4 /(2π) 3 ρ L 2 Σ n=1 -∞ 1/n 2 e -nπ /ρ L where ρ L = E L / E cr and E cr = m 2 /e = 1.3 x 10 16 V/cm is the Schwinger field limit. However this expression was obtained even in pioneer works dedicated to vacuum nonlinearity and it based on some approximations. Attempt of the strict analysis has been made in work by introducing the nonlocal form-factor into the Lagrangian. But, as it is well known, such procedure leads to the loss of Lorenz invariance or unitarity. We show that the formalism of generalized quantum dynamic (GQD) opens new opportunities to solve such problems. We show also how it can be made proceeding from nonlocal interaction operator obtained earlier within the framework of the formalism of GQD. Acknowledgements. This work was supported by the Grant of Federal Agency on Education, Russia (Contract number 02.740.11.0428) and by the Grant of Russian President No. NSh 2965.2008.2.

  14. Studies of electroweak interactions and searches for new physics using photonic events with missing energy at the Large Electron-Positron Collider

    CERN Document Server

    Gataullin, Marat I

    2006-01-01

    In this thesis I study the production of photonic events with missing energy in e+e- collisions at the Large Electron-Positron (LEP) Collider. My analysis was based on 619 inverse picobarns of data collected by the L3 detector during 1998--2000 at center-of-mass energies between 189 and 208 GeV, the highest energies ever attained in an e+e- collider. I selected a high-purity sample of 2,022 well-reconstructed single- and multi-photon events with missing energy. I used this sample to study the pair-production of neutrinos accompanied by the emission of one or more photons. The average ratio of the measured to expected cross section was found to be R = 0.987±0.022(stat)±0.014 (syst). The number of light neutrino species was measured to be 2.98±0.05(stat)±0.04(syst), and the first direct evidence for the pair-production of electron neutrinos was found. The experimental errors in these results are smaller than those of comparable previous measurements. The selection results are also given in the form of table...

  15. Design of an 18 MW vortex flow water beam dump for 500 GeV electrons/positrons of an international linear collider

    International Nuclear Information System (INIS)

    Satyamurthy, Polepalle; Rai, Pravin; Tiwari, Vikas; Kulkarni, Kiran; Amann, John; Arnold, Raymond G.; Walz, Dieter; Seryi, Andrei; Davenne, Tristan; Caretta, Ottone; Densham, Chris; Appleby, Robert B.

    2012-01-01

    Beam dumps are essential components of any accelerator system. They are usually located at the end of the beam delivery systems and are designed to safely absorb and dissipate the particle energy. In the second stage of the proposed International Linear Collider (ILC), the electron and positron beams are accelerated to 500 GeV each (1 TeV total). Each bunch will have 2×10 10 electrons/positrons, and 2820 bunches form one beam bunch train with time duration of 0.95 ms and 4 Hz frequency. The average beam power will be 18 MW with a peak power of 4.5 GW. The FLUKA code was used to determine the power deposited by the beam at all critical locations. This data forms the input into the thermal hydraulic analysis CFD code for detailed flow and thermal evaluation. Both 2D and 3D flow analyses were carried out at all the critical regions to arrive at optimum geometry and flow parameters of the beam dump. The generation and propagation of pressure waves due to rapid deposition of heat has also been analyzed.

  16. IR spectroscopy and electron-positron annihilation study of microstructure of polymer materials under low-intensity irradiation; Issledovanie mikrostruktury polimernykh materialov pri nizkointensivnom obluchenii s ispol`zovaniem IK-spektroskopii i ehlektron-pozimtronnoj annigilyatsii

    Energy Technology Data Exchange (ETDEWEB)

    Valeev, R S; Kononenko, A.I.

    1994-12-31

    A model of oxidation destruction of polymer materials under a low-intensity gamma irradiation is considered. The results obtained allow one to determine conditions for conducting accelerated testings, which the mechanism of polymer material aging under their utilization at NPPs is realized.

  17. 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

  18. 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

  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. 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)

  1. 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

  2. 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)

  3. 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.

  4. 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

  5. Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS

    CERN Document Server

    Adamova, D; Appelshäuser, H; Belaga, V; Braun-Munzinger, P; Cherlin, A; Damjanovic, S; Dietel, T; Dietrich, L; Drees, A; Esumi, S I; Filimonov, K; Fomenko, K; Fraenkel, Zeev; Garabatos, C; Glässel, P; Hering, G; Holeczek, J; Kushpil, V; Lenkeit, B C; Maas, A; Marin, A; Milosevic, J; Milov, A; Miskowiec, D; Panebratsev, Yu A; Petchenova, O Yu; Petracek, V; Pfeiffer, A; Rak, J; Ravinovich, I; Rehak, P; Richter, M; Sako, H; Schmitz, W; Sedykh, S; Seipp, W; Sharma, A; Shimansky, S S; Slivova, J; Specht, H J; Stachel, J; Sumbera, M; Tilsner, H; Tserruya, Itzhak; Wessels, J P; Wienold, T; Windelband, B; Wurm, J P; Xie, W; Yurevich, S; Yurevich, V I

    2003-01-01

    We report on first measurements of low-mass electron pairs in Pb-Au collisions at the lower SPS beam energy of 40 AGeV. The pair yield integrated over the range of invariant masses 0.2 e+ e- annihilation with a modified rho-propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

  6. Multiple channel programmable coincidence counter

    Science.gov (United States)

    Arnone, Gaetano J.

    1990-01-01

    A programmable digital coincidence counter having multiple channels and featuring minimal dead time. Neutron detectors supply electrical pulses to a synchronizing circuit which in turn inputs derandomized pulses to an adding circuit. A random access memory circuit connected as a programmable length shift register receives and shifts the sum of the pulses, and outputs to a serializer. A counter is input by the adding circuit and downcounted by the seralizer, one pulse at a time. The decoded contents of the counter after each decrement is output to scalers.

  7. Detection of tokamak plasma positrons using annihilation photons

    Energy Technology Data Exchange (ETDEWEB)

    Guanying, Yu; Liu, Jian; Xie, Jinlin [University of Science and Technology, Hefei, Anhui, 230027 (China); Li, Jiangang, E-mail: j_li@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China)

    2017-05-15

    Highlights: • A design for detection of tokamak plasma positrons is given. • Identify the main obstacle toward experimental confirmation of fusion plasma positrons. • Signal to noise ratio in a plasma disruption is estimated. • Unique potential applications of fusion plasma positrons are discussed. - Abstract: A massive amount of positrons (plasma positrons), produced by the collision between runaway electrons and nuclei during fusion plasma disruption, was first predicted theoretically in 2003. To help confirm this prediction, we report here the design of an experimental system to detect tokamak plasma positrons. Because a substantial amount of positrons (material positrons) are produced when runaway electrons impact plasma-facing materials, we proposed maximizing the ratio of plasma to material positrons by inserting a thin carbon target at the plasma edge as a plasma positron bombing target and producing a plasma disruption scenario triggered by massive gas injection. Meanwhile, the coincidence detection of positron annihilation photons was used to filter out the noise of annihilation photons from locations other than the carbon target and that of bremsstrahlung photons near 511 keV. According to our simulation, the overall signal-to-noise ratio should be more than 10:1.

  8. Polarisation-based coincidence event discrimination: an in silico study towards a feasible scheme for Compton-PET

    Science.gov (United States)

    Toghyani, M.; Gillam, J. E.; McNamara, A. L.; Kuncic, Z.

    2016-08-01

    Current positron emission tomography (PET) systems use temporally localised coincidence events discriminated by energy and time-of-flight information. The two annihilation photons are in an entangled polarisation state and, in principle, additional information from the polarisation correlation of photon pairs could be used to improve the accuracy of coincidence classification. In a previous study, we demonstrated that in principle, the polarisation correlation information could be transferred to an angular correlation in the distribution of scattered photon pairs in a planar Compton camera system. In the present study, we model a source-phantom-detector system using Geant4 and we develop a coincidence classification scheme that exploits the angular correlation of scattered annihilation quanta to improve the accuracy of coincidence detection. We find a 22% image quality improvement in terms of the peak signal-to-noise ratio when scattered coincidence events are discriminated solely by their angular correlation, thus demonstrating the feasibility of this novel classification scheme. By integrating scatter events (both single-single and single-only) with unscattered coincidence events discriminated using conventional methods, our results suggest that Compton-PET may be a promising candidate for optimal emission tomographic imaging.

  9. Positron annihilation spectroscopy using high-energy photons

    International Nuclear Information System (INIS)

    Butterling, Maik; Jungmann, Marco; Krause-Rehberg, Reinhard; Krille, Arnold; Anwand, Wolfgang; Brauer, Gerhard; Cowan, Thomas E.; Hartmann, Andreas; Kosev, Krasimir; Schwengner, Ronald; Wagner, Andreas

    2010-01-01

    The superconducting electron accelerator ELBE (Electron Linac with high Brilliance and low Emittance) at the Research Centre Dresden-Rossendorf (Germany) serves as a high-intensity bremsstrahlung photon-source delivering a pulsed beam (26 MHz) with very short bunches (<5 ps). The photons are being converted into positrons by means of pair production inside the target material thus forming an intense positron source. The accelerator machine pulse is used as time reference allowing positron lifetime spectroscopy. We performed positron annihilation spectroscopy by pair production in different sample materials and used coincidence techniques to reduce the background due to scattered photons significantly in order resulting in spectra of extraordinary high quality. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

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

    International Nuclear Information System (INIS)

    Sharshar, T.

    2004-01-01

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

  11. Electron-positron pair production by gamma-rays in an anisotropic flux of soft photons, and application to pulsar polar caps

    Science.gov (United States)

    Voisin, Guillaume; Mottez, Fabrice; Bonazzola, Silvano

    2018-02-01

    Electron-positron pair production by collision of photons is investigated in view of application to pulsar physics. We compute the absorption rate of individual gamma-ray photons by an arbitrary anisotropic distribution of softer photons, and the energy and angular spectrum of the outgoing leptons. We work analytically within the approximation that 1 ≫ mc2/E > ɛ/E, with E and ɛ the gamma-ray and soft-photon maximum energy and mc2 the electron mass energy. We give results at leading order in these small parameters. For practical purposes, we provide expressions in the form of Laurent series which give correct reaction rates in the isotropic case within an average error of ˜ 7 per cent. We apply this formalism to gamma-rays flying downward or upward from a hot neutron star thermally radiating at a uniform temperature of 106 K. Other temperatures can be easily deduced using the relevant scaling laws. We find differences in absorption between these two extreme directions of almost two orders of magnitude, much larger than our error estimate. The magnetosphere appears completely opaque to downward gamma-rays while there are up to ˜ 10 per cent chances of absorbing an upward gamma-ray. We provide energy and angular spectra for both upward and downward gamma-rays. Energy spectra show a typical double peak, with larger separation at larger gamma-ray energies. Angular spectra are very narrow, with an opening angle ranging from 10-3 to 10-7 radians with increasing gamma-ray energies.

  12. Differential coincidence circuit in the 10{sup -10} second region (1960); Circuit de coincidence differentiel dans le domaine de 10{sup -10} seconde (1960)

    Energy Technology Data Exchange (ETDEWEB)

    Van Zurk, R [Commissariat a l' Energie Atomique, Lab. de Physique Nucleaire, Grenoble (France).Centre d' Etudes Nucleaires; [Grenoble-1 Univ., 38 (France); [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1960-07-01

    A coincidence circuit of low resolution time using the differential coincidence Bay principle is described. It uses three 6BN6 tubes ordered to chronotron structure. Results with Radiotechnique 56 AVP photomultipliers and for {sup 60}Co {gamma}-{gamma} coincidences are 4,6.10{sup -10} s (full width at half maximum) if the efficiency is {epsilon} = 40 per cent and also 7,2.10{sup -10} s if {epsilon} = 85 per cent. (author) [French] Un circuit de coincidence differentiel du type de Bay, utilise en selecteur en temps a canal mobile, a ete construit pour la mesure des periodes {gamma} et des periodes d'annihilation du positon dans differents materiaux. Il comporte trois tubes 6BN6 disposes en structure chronotron. On a utilise les nouveaux photomultiplicateurs 56 AVP avec scintillateur plastique. Avec les coincidences {gamma}-{gamma} du {sup 60}Co, on obtient 2T 4,6.10{sup -10} s avec une efficacite de 40 pour cent et 2T = 7,2.10{sup -10} s avec une efficacite de 85 pour cent. (auteur)

  13. 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.)

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

    KAUST Repository

    Vlach, Martin; Cizek, Jakub; Melikhova, Oksana; Stulikova, Ivana; Smola, Bohumil; Kekule, Tomas; Kudrnova, Hana; Gemma, Ryota; Neubert, Volkmar

    2015-01-01

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

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

    KAUST Repository

    Vlach, Martin

    2015-01-29

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

  16. 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.

  17. 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)

  18. Numerical coincidences and 'tuning' in cosmology

    OpenAIRE

    Rees, Martin J.

    2004-01-01

    Fred Hoyle famously drew attention to the significance of apparent coincidences in the energy levels of the carbon and oxygen nucleus. This paper addresses the possible implications of other coincidences in cosmology.

  19. 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

  20. Coincident photoelectron spectroscopy on superconductors

    International Nuclear Information System (INIS)

    Voss, Stefan

    2011-01-01

    Aim of the performed experiments of this thesis was to attempt to detect Cooper pairs as carriers of the superconducting current directly by means of the photoelectric effect. The method of the coincident photoelectron spectroscopy aims thereby at the detection of two coherently emitted electrons by the interaction with a photon. Because electrostatic analyzers typically cover only a very small spatial angle, which goes along with very low coincidence rates, in connection with this thesis a time-of-flight projection system has been developed, which maps nearly the whole spatial angle on a position-resolving detector. The pulsed light source in form of special synchrotron radiation necessary for the measurement has been adjusted so weak, that only single photons could arrive at the sample. Spectroscoped were beside test measurements on silver layers both a lead monocrystal as representative of the classical BCS superconductors and monocrystalline Bi 2 Sr 2 CaCu 2 O 8 from the family of the high-temperature superconductors. With excitation energies up to 40 eV could be shown that sufficiently smooth and clean surfaces in the superconducting phase exhibit within the resolving power of about 0.5 eV no recognizable differences in comparison to the normally conducting phase. Beside these studies furthermore the simple photoemission at the different samples and especially in the case of the lead crystal is treated, because here no comparable results are known. Thereby the whole momentum space is discussed and the Fermi surface established as three-dimensional model, by means of which the measurement results are discussed. in the theoretical descriptions different models for the Cooper-pair production are presented, whereby to the momentum exchange with the crystal a special role is attributed, because this can only occur in direct excitations via discrete lattice vectors.

  1. High energy electron positron physics

    International Nuclear Information System (INIS)

    Ali, A.; Soding, P.

    1987-01-01

    With the termination of the physics program at PETRA in a year from now, and with the start of TRISTAN and the SLC and later LEP, an era of e/sup +/e/sup -/ physics will come to an end and a new one begins. The field is changing from a field of a few specialists, to becoming one of the mainstream efforts of the high energy community. It seems appropriate at this moment to summarize what has been learned over the past years, in a way more useful to any high energy physicist in particular to newcomers in the e/sup +/e/sup -/ field. This is the purpose of the book. This book should be used as a reference for future workers in the field of e/sup +/e/sup -/ interactions. It includes the most relevant data, parametrizations, theoretical background, and a chapter on detectors. Contents: Foreword; Detectors for High Energy e/sup +/e/sup -/ Physics; Lepton Pair Production and Electroweak Parameters; Hadron Production, Strong and Electroweak Properties; tau Physics; Recent Results on the Charm Sector; Bottom Physics; Lifetime Measurements of tau, Charmed and Beauty Hadrons; Υ Spectroscopy; Hadronic Decays of the Υ; Quark and Gluon Fragmentation in the e/sup +/e/sup -/ Continuum; Jet Production and QCD; Two Photon Physics; Search for New Particles

  2. Electron-Positron Accumulator (EPA)

    CERN Multimedia

    Photographic Service

    1986-01-01

    After acceleration in the low-current linac LIL-W, the electrons and positrons are accumulated in EPA to obtain a sufficient intensity and a suitable time-structure, before being passed on to the PS for further acceleration to 3.5 GeV. Electrons circulate from right to left, positrons in the other direction. Dipole bending magnets are red, focusing quadrupoles blue, sextupoles for chromaticity-control orange. The vertical tube at the left of the picture belongs to an optical transport system carrying the synchrotron radiation to detectors for beam size measurement. Construction of EPA was completed in spring 1986. LIL-W and EPA were conceived for an energy of 600 MeV, but operation was limited to 500 MeV.

  3. Observation of relaxation on time scale of core hole decay by coincidence photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Ohno, Masahide

    2007-01-01

    It is shown by a many-body theory that when the relaxation time of a metastable core hole state(s) to the most stable one is comparable to or shorter than core hole decay time of the former state(s), a comparison between the singles (noncoincidence) photoelectron spectroscopy (PES) spectrum and the coincidence one provides a direct evidence of the relaxation. In principle the variation with photoelectron kinetic energy of relaxation (or charge transfer (CT)) time can be determined. By singles measurement the correlation of a photoelectron generated by creation of the metastable states not only with an Auger electron generated by annihilation of the same core hole state but also with an Auger electron generated by annihilation of the stable state via relaxation of the metastable state, is completely lost, unless only the metastable state is observed by PES, whereas the correlation often manifests directly in the coincidence spectra. Thus, compared to the coincidence spectroscopy the singles one is often much less capable of elucidating the competition between relaxation and core hole decay of a metastable state. Such examples are discussed

  4. Oxygen vacancies in oxides studied by annihilation of mono-energetic positrons

    Energy Technology Data Exchange (ETDEWEB)

    Hugenschmidt, Christoph; Pikart, Philip [ZWE FRM II, Technische Universitaet Muenchen, Lichtenbergstrasse 1, 85747 Garching (Germany); Physik-Department E21, Technische Universitaet Muenchen, James-Franck-Strasse, 85748 Garching (Germany); Schreckenbach, Klaus [Physik-Department E21, Technische Universitaet Muenchen, James-Franck-Strasse, 85748 Garching (Germany)

    2009-07-01

    Oxygen vacancies play a fundamental role for the material properties of various oxides, e.g. charge carrier density in high-Tc superconductors, magnetic properties of diluted magnetic semiconductors or paramagnetic properties of SiO{sub 2}. In this study, open volume defects in (metal) oxides are investigated by Doppler-broadening spectroscopy (DBS) of the positron annihilation. More detailed information about the chemical surrounding at the positron annihilation site is gained by additional coincident DBS experiments, where a signature of positrons annihilating with electrons from oxygen is observed. The mono-energetic positron beam at NEPOMUC was used which allows depth dependent measurements, and hence the investigation of thin oxide layers. Recent results for metallic oxides such as ZnO are presented and compared with various non-metallic oxides such as amorphous and crystalline SiO{sub 2}, oxygen terminated Si-surface, and ice. The role of neutral and charged oxygen vacancies and the application of the positron annihilation technique to study oxygen vacancies will be discussed.

  5. Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud

    Science.gov (United States)

    Drlica-Wagner, Alex; Gomez-Vargas, German A.; Hewitt, John W.; Linden, Tim; Tibaldo, Luigi

    2014-01-01

    Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use gamma-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant gamma-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (approximately 3 x 10 (sup -26) cubic centimeters per second) for dark matter masses less than or approximately 30 gigaelectronvolts annihilating via the B/B- bar oscillation or tau/antitau channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

  6. Searching for dark matter annihilation in the Smith high-velocity cloud

    International Nuclear Information System (INIS)

    Drlica-Wagner, Alex; Gómez-Vargas, Germán A.; Hewitt, John W.; Linden, Tim; Tibaldo, Luigi

    2014-01-01

    Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use γ-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant γ-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (∼ 3 × 10 –26 cm 3 s –1 ) for dark matter masses ≲ 30 GeV annihilating via the b b-bar or τ + τ – channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

  7. Searching for dark matter annihilation in the Smith high-velocity cloud

    Energy Technology Data Exchange (ETDEWEB)

    Drlica-Wagner, Alex [Center for Particle Astrophysics, Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States); Gómez-Vargas, Germán A. [Departamento de Fisíca, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Santiago (Chile); Hewitt, John W. [CRESST, University of Maryland, Baltimore County, Baltimore, MD 21250 (United States); Linden, Tim [The Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637 (United States); Tibaldo, Luigi [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)

    2014-07-20

    Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use γ-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant γ-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (∼ 3 × 10{sup –26} cm{sup 3} s{sup –1}) for dark matter masses ≲ 30 GeV annihilating via the b b-bar or τ{sup +}τ{sup –} channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

  8. 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.)

  9. 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.

  10. Recovering the triple coincidence of non-pure positron emitters in preclinical PET

    Science.gov (United States)

    Lin, Hsin-Hon; Chuang, Keh-Shih; Chen, Szu-Yu; Jan, Meei-Ling

    2016-03-01

    Non-pure positron emitters, with their long half-lives, allow for the tracing of slow biochemical processes which cannot be adequately examined by the commonly used short-lived positron emitters. Most of these isotopes emit high-energy cascade gamma rays in addition to positron decay that can be detected and create a triple coincidence with annihilation photons. Triple coincidence is discarded in most scanners, however, the majority of the triple coincidence contains true photon pairs that can be recovered. In this study, we propose a strategy for recovering triple coincidence events to raise the sensitivity of PET imaging for non-pure positron emitters. To identify the true line of response (LOR) from a triple coincidence, a framework utilizing geometrical, energy and temporal information is proposed. The geometrical criterion is based on the assumption that the LOR with the largest radial offset among the three sub pairs of triple coincidences is least likely to be a true LOR. Then, a confidence time window is used to test the valid LOR among those within triple coincidence. Finally, a likelihood ratio discriminant rule based on the energy probability density distribution of cascade and annihilation gammas is established to identify the true LOR. An Inveon preclinical PET scanner was modeled with GATE (GEANT4 application for tomographic emission) Monte Carlo software. We evaluated the performance of the proposed method in terms of identification fraction, noise equivalent count rates (NECR), and image quality on various phantoms. With the inclusion of triple coincidence events using the proposed method, the NECR was found to increase from 11% to 26% and 19% to 29% for I-124 and Br-76, respectively, when 7.4-185 MBq of activity was used. Compared to the reconstructed images using double coincidence, this technique increased the SNR by 5.1-7.3% for I-124 and 9.3-10.3% for Br-76 within the activity range of 9.25-74 MBq, without compromising the spatial resolution or

  11. Evaluation of scintillators and semiconductor detectors to image three-photon positron annihilation for positron emission tomography

    International Nuclear Information System (INIS)

    Abuelhia, E.; Spyrou, N.M.; Kacperski, K.; College University, Middlesex Hospital, London

    2008-01-01

    Positron emission tomography (PET) is rapidly becoming the main nuclear imaging modality of the present century. The future of PET instrumentation relies on semiconductor detectors because of their excellent characteristics. Three-photon positron annihilation has been recently investigated as a novel imaging modality, which demands the crucial high energy resolution of semiconductor detector. In this work the evaluation of the NaI(Tl) scintillator and HPGe and CdZTe semiconductor detectors, to construct a simple three-photon positron annihilation scanner has been explored. The effect of detector and scanner size on spatial resolution (FWHM) is discussed. The characteristics: energy resolution versus count rate and point-spread function of the three-photon positron annihilation image profile from triple coincidence measurements were investigated. (author)

  12. 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

  13. A portable neutron coincidence counter

    Energy Technology Data Exchange (ETDEWEB)

    Peurrung, A.J.; Bowyer, S.M.; Craig, R.A.; Dudder, G.B.; Knopf, M.A.; Panisko, M.E.; Reeder, P.L.; Stromswold, D.C.; Sunberg, D.S.

    1996-11-01

    Pacific Northwest National Laboratory has designed and constructed a prototype portable neutron coincidence counter intended for use in a variety of applications, such as the verification and inspection of weapons components, safety measurements for novel and challenging situations, portable portal deployment to prevent the transportation of fissile materials, uranium enrichment measurements in hard-to-reach locations, waste assays for objects that cannot be measured by existing measurement systems, and decontamination and decommissioning. The counting system weighs less than 40 kg and is composed of parts each weighing no more than 5 kg. In addition, the counter`s design is sufficiently flexible to allow rapid, reliable assembly around containers of nearly arbitrary size and shape. The counter is able to discern the presence of 1 kg of weapons-grade plutonium within an ALR-8 (30-gal drum) in roughly 100 seconds and 10 g in roughly 1000 seconds. The counter`s electronics are also designed for maximum adaptability, allowing operation under a wide variety of circumstances, including exposure to gamma-ray fields of 1 R/h. This report provides a detailed review of the design and construction process. Finally, preliminary experimental measurements that confirm the performance capabilities of this counter are discussed. 6 refs., 18 figs., 3 tabs.

  14. Multiverse understanding of cosmological coincidences

    International Nuclear Information System (INIS)

    Bousso, Raphael; Hall, Lawrence J.; Nomura, Yasunori

    2009-01-01

    There is a deep cosmological mystery: although dependent on very different underlying physics, the time scales of structure formation, of galaxy cooling (both radiatively and against the CMB), and of vacuum domination do not differ by many orders of magnitude, but are all comparable to the present age of the universe. By scanning four landscape parameters simultaneously, we show that this quadruple coincidence is resolved. We assume only that the statistical distribution of parameter values in the multiverse grows towards certain catastrophic boundaries we identify, across which there are drastic regime changes. We find order-of-magnitude predictions for the cosmological constant, the primordial density contrast, the temperature at matter-radiation equality, the typical galaxy mass, and the age of the universe, in terms of the fine structure constant and the electron, proton and Planck masses. Our approach permits a systematic evaluation of measure proposals; with the causal patch measure, we find no runaway of the primordial density contrast and the cosmological constant to large values.

  15. Experimental tests of QCD: Deep inelastic scattering, e+e- annihilation and hard hadron-hadron scattering

    International Nuclear Information System (INIS)

    Hansl-Kozanecka, T.

    1992-01-01

    In this set of lectures the author examines phenomenological aspects of quantum chromodynamics (QCD) which are relevant for lepton-hadron, electron-positron, and hadron-hadron collisions. He points how the strength of the strong coupling constant, αs, makes QCD calculations converge much more slowly in powers of αs, and missing higher order terms must be carefully estimated. The most stringent test of QCD can be performed in deep inelastic lepton scattering and in e + e - annihilation. In deep inelastic scattering the virtual γ or W/Z are used as a probe of the nucleon structure. They couple to quarks, not gluons. Only the incoming and outgoing lepton have to be measured. The hadronic fluid state does not have to be analyzed. In e + e - annihilation the virtual γ or Z 0 decays to lepton and quark pairs. The branching ratio into quarks is a counter for the number of colours available, the detailed structure of the final state reflects the radiation of gluons as the initial quark-antiquark separate from each other. Quarks and gluons are observed here, though in the presence of hadron formation. Hard hadron-hadron, or parton-parton collisions provide cross sections dominated by the gluon component, which is only weakly measured in deep inelastic collisions. Recent experimental results in these three areas are reviewed, and compared to QCD calculations. Scaling violations and analysis of structure functions in deep inelastic scattering are reviewed. QCD in e + e - branching to hadrons is reviewed near the Z 0 resonance, and a number of cross sections and jet related properties which can be calculated as a function of the single parameter αs are reviewed. Hadron-hadron collisions are reviewed for three processes; jet production, direct photon production, and high p perpendicular W/Z boson production

  16. Deconvolution of 2D coincident Doppler broadening spectroscopy using the Richardson-Lucy algorithm

    International Nuclear Information System (INIS)

    Zhang, J.D.; Zhou, T.J.; Cheung, C.K.; Beling, C.D.; Fung, S.; Ng, M.K.

    2006-01-01

    Coincident Doppler Broadening Spectroscopy (CDBS) measurements are popular in positron solid-state studies of materials. By utilizing the instrumental resolution function obtained from a gamma line close in energy to the 511 keV annihilation line, it is possible to significantly enhance the quality of the CDBS spectra using deconvolution algorithms. In this paper, we compare two algorithms, namely the Non-Negativity Least Squares (NNLS) regularized method and the Richardson-Lucy (RL) algorithm. The latter, which is based on the method of maximum likelihood, is found to give superior results to the regularized least-squares algorithm and with significantly less computer processing time

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

    Science.gov (United States)

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

    2018-02-01

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

  18. Positron annihilation in sodium and copper β-vanadium oxide bronzes

    International Nuclear Information System (INIS)

    Dryzek, J.; Rogowska, E.

    1990-01-01

    Studies of copper and sodium β-vanadium oxide bronzes are performed using positron annihilation measured with a long slit angular correlation apparatus. The dependences of peak coincidence rate on temperature (40 to 310deg C) are obtained for different concentrations of donor atoms in the case of copper vanadium oxide bronzes. A three-states model corresponding to the annihilation of positrons in donor atom sublattice is applied for the description of the experimental data. The creation enthalpy of vacancies for that sublattice is equal to (0.60 ± 0.01) eV for Na 0.33 V 2 O 5 and equal to (0.64 ± 0.01) eV for Cu x V 2 O 5 . (author)

  19. Photoion spectroscopy of atoms using coincidence techniques

    International Nuclear Information System (INIS)

    Hayaishi, Tatsuji

    1990-01-01

    Interaction of atoms or molecules with photons causes many effects which are often obscured because of many decay paths from the event. To pick up an effect in the mixed-up ones, it is necessary to observe the decay path arising the effect alone. There is a coincidence technique in one of experimental means for the purpose of observing the decay path. In this article, two coincidence measurements are presented; a photoelectron-photoion coincidence technique and a threshold photoelectron-photoion coincidence technique. Furthermore, experimental facts of rare gases atoms obtained by the techniques are reviewed. (author)

  20. High-mass Drell-Yan cross-section and search for new phenomena in multi-electron/positron final states with the ATLAS detector

    International Nuclear Information System (INIS)

    Wollstadt, Simon

    2015-01-01

    The Standard Model of particle physics is a very successful theory which describes nearly all known processes of particle physics very precisely. Nevertheless, there are several observations which cannot be explained within the existing theory. In this thesis, two analyses with high energy electrons and positrons using data of the ATLAS detector are presented. One, probing the Standard Model of particle physics and another searching for phenomena beyond the Standard Model. The production of an electron-positron pair via the Drell-Yan process leads to a very clean signature in the detector with low background contributions. This allows for a very precise measurement of the cross-section and can be used as a precision test of perturbative quantum chromodynamics (pQCD) where this process has been calculated at next-to-next-to-leading order (NNLO). The invariant mass spectrum mee is sensitive to parton distribution functions (PFDs), in particular to the poorly known distribution of antiquarks at large momentum fraction (Bjoerken x). The measurement of the high-mass Drell-Yan cross-section in proton-proton collisions at a center-of-mass energy of √(s)=7 TeV is performed on a dataset collected with the ATLAS detector, corresponding to an integrated luminosity of 4.7 fb -1 . The differential cross-section of pp→Z 0 /γ * +X→e + e - +X is measured as a function of the invariant mass in the range 116 GeV

  1. 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.

  2. 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

  3. Production bias and cluster annihilation: Why necessary?

    DEFF Research Database (Denmark)

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

    1994-01-01

    the primary cluster density is high. Therefore, a sustained high swelling rate driven by production bias must involve the annihilation of primary clusters at sinks. A number of experimental observations which are unexplainable in terms of the conventional dislocation bias for monointerstitials is considered......-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....

  4. 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

  5. Vacancy identification in Co+ doped rutile TiO2 crystal with positron annihilation spectroscopy

    Science.gov (United States)

    Qin, X. B.; Zhang, P.; Liang, L. H.; Zhao, B. Z.; Yu, R. S.; Wang, B. Y.; Wu, W. M.

    2011-01-01

    Co-doped rutile TiO2 films were synthesized by ion implantation. Variable energy positron annihilation Doppler broadening spectroscopy and coincidence Doppler broadening measurements were performed for identification of the vacancies. A newly formed type of vacancy can be concluded by the S-W plot and the CDB results indicated that the oxygen vacancy (VO) complex Ti-Co-VO and/or Ti-VO are formed with Co ions implantation and the vacancy concentration is increased with increase of dopant dose.

  6. Studies of martensitic transformation in Cu-Al alloys by positron annihilation

    International Nuclear Information System (INIS)

    Kojima, T.; Kuribayashi, K.; Doyama, M.

    1977-01-01

    The reverse martensitic transformations in Cu-23.5 at-%Al, and Cu-25.3 at-%Al have been studied by means of positron annihilation. The coincidence counting rates of angular correlation were measured as a function of the specimen temperature. The change of counting rates in heating run was rather different from that in cooling run due to the influence of tempering of martensitic structure. The results were interpreted by the change of the formation energy of a vacancy with phase transition. Influence of heating rate is also discussed. (orig.) [de

  7. Defect studies in annealed ZnO by positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sanyal, D; Roy, Tapatee Kundu; Chakrabarti, Mahuya; Dechoudhury, Siddhartha; Bhowmick, Debasis; Chakrabarti, Alok [Variable Energy Cyclotron Centre, 1/AF, Bidhannagar, Kolkata 700064 (India)

    2008-01-30

    Coincidence Doppler broadening of the positron annihilation technique has been employed to identify the defects in thermally annealed 'as-received' ZnO and thermally annealed ball-milled nanocrystalline ZnO. Results indicate that a significant amount of oxygen vacancy has been created in ZnO due to annealing at about 500 deg. C and above. The results also indicate that the Zn vacancy created during the ball milling process can be easily removed by annealing the sample at about 500 deg. C and above. The defect characterization has also been correlated with the magnetic properties of ZnO.

  8. Defect studies in annealed ZnO by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Sanyal, D; Roy, Tapatee Kundu; Chakrabarti, Mahuya; Dechoudhury, Siddhartha; Bhowmick, Debasis; Chakrabarti, Alok

    2008-01-01

    Coincidence Doppler broadening of the positron annihilation technique has been employed to identify the defects in thermally annealed 'as-received' ZnO and thermally annealed ball-milled nanocrystalline ZnO. Results indicate that a significant amount of oxygen vacancy has been created in ZnO due to annealing at about 500 deg. C and above. The results also indicate that the Zn vacancy created during the ball milling process can be easily removed by annealing the sample at about 500 deg. C and above. The defect characterization has also been correlated with the magnetic properties of ZnO

  9. Study on grown-in defects in CZ-Si by positron annihilation

    International Nuclear Information System (INIS)

    Nakagawa, S.; Hori, F.; Oshima, R.

    2004-01-01

    In order to study the nature of grown-in microdefects of a silicon wafer taken from a czochralski-grown single crystal (CZ-Si) in which ring oxidation-induced stacking faults (ring-OSF) are formed after oxidation heat treatment, positron annihilation coincidence Doppler broadening experiments (CDB) have been performed. Vacancy-type defects were detected in the central region of a wafer of an as-grown crystal, and they were changed with annealing. It was confirmed that different types of defects were formed in the regions of outside and inside of the ring-OSF. (orig.)

  10. Sensitivity to coincidences and paranormal belief.

    Science.gov (United States)

    Hadlaczky, Gergö; Westerlund, Joakim

    2011-12-01

    Often it is difficult to find a natural explanation as to why a surprising coincidence occurs. In attempting to find one, people may be inclined to accept paranormal explanations. The objective of this study was to investigate whether people with a lower threshold for being surprised by coincidences have a greater propensity to become believers compared to those with a higher threshold. Participants were exposed to artificial coincidences, which were formally defined as less or more probable, and were asked to provide remarkability ratings. Paranormal belief was measured by the Australian Sheep-Goat Scale. An analysis of the remarkability ratings revealed a significant interaction effect between Sheep-Goat score and type of coincidence, suggesting that people with lower thresholds of surprise, when experiencing coincidences, harbor higher paranormal belief than those with a higher threshold. The theoretical aspects of these findings were discussed.

  11. 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

  12. 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.)

  13. 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)

  14. 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)

  15. 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)

  16. Chemical analysis using coincidence Doppler broadening and supporting first-principles theory: Applications to vacancy defects in compound semiconductors

    International Nuclear Information System (INIS)

    Makkonen, I.; Rauch, C.; Mäki, J.-M.; Tuomisto, F.

    2012-01-01

    The Doppler broadening of the positron annihilation radiation contains information on the chemical environment of vacancy defects trapping positrons in solids. The measured signal can, for instance, reveal impurity atoms situated next to vacancies. As compared to integrated quantities such as the positron annihilation rate or the annihilation line shape parameters, the full Doppler spectrum measured in the coincidence mode contains much more useful information for defect identification. This information, however, is indirect and complementary understanding is needed to fully interpret the results. First-principles calculations are a valuable tool in the analysis of measured spectra. One can construct an atomic-scale model for a given candidate defect, calculate from first principles the corresponding Doppler spectrum, and directly compare results between experiment and theory. In this paper we discuss recent examples of successful combinations of coincidence Doppler broadening measurements and supporting first-principles calculations. These demonstrate the predictive power of state-of-the-art calculations and the usefulness of such an approach in the chemical analysis of vacancy defects.

  17. Statistical data filtration in neutron coincidence counting

    International Nuclear Information System (INIS)

    Beddingfield, D.H.; Menlove, H.O.

    1992-11-01

    We assessed the effectiveness of statistical data filtration to minimize the contribution of matrix materials in 200-ell drums to the nondestructive assay of plutonium. Those matrices were examined: polyethylene, concrete, aluminum, iron, cadmium, and lead. Statistical filtration of neutron coincidence data improved the low-end sensitivity of coincidence counters. Spurious data arising from electrical noise, matrix spallation, and geometric effects were smoothed in a predictable fashion by the statistical filter. The filter effectively lowers the minimum detectable mass limit that can be achieved for plutonium assay using passive neutron coincidence counting

  18. 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.

  19. 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

  20. 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.

  1. 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)

  2. 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

  3. 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...

  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. Vacancy identification in Co+ doped rutile TiO2 crystal with positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Ma Minyang; Qin Xiubo; Wang Baoyi; Wu Weiming

    2013-01-01

    Background: Room temperature Diluted Magnetic Semiconductor (DMS) is a critical path in the study of spin-electronic devices, but there are many disputes in the intrinsic properties and origin of the room temperature ferromagnetism. Positron annihilation spectroscopy (PAS) is a powerful technique for evaluating vacancy-type defects. Purpose: We aim to establish the relationship between the defect structure and ferromagnetism of the materials by analyzing the parameters of positron annihilation. Methods: Co-doped rutile TiO 2 films were synthesized by ion implantation and extensively studied by variable energy positron annihilation Doppler broadening spectroscopy (DBS) and coincidence Doppler broadening (CDB) measurements with variable energy slow positron beam for identification of the vacancies. Results: The results of DBS showed that a newly formed type of vacancy could be concluded by the S-W plot and the CDB results indicated that the oxygen vacancy (Vo) complex Ti-Co-Vo and/or Ti-Vo were formed with Co ions implantation and the vacancy concentration increased with increasing dopant dose. Conclusion: We identify that the generation of Ti-Vo and/or Ti-Co-Vo vacancy complex are induced by the existence of excess Ti 3d electrons around the oxygen vacancy. (authors)

  6. 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

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

    International Nuclear Information System (INIS)

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

    2008-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-05-31

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

  9. Positron annihilation spectroscopic studies of solvothermally synthesized ZnO nanobipyramids and nanoparticles

    Science.gov (United States)

    Ghoshal, Tandra; Biswas, Subhajit; Kar, Soumitra; Chaudhuri, Subhadra; Nambissan, P. M. G.

    2008-02-01

    Zinc oxide (ZnO) samples in the form of hexagonal-based bipyramids and particles of nanometer dimensions were synthesized through solvothermal route and characterized by x-ray diffraction and transmission electron microscopy. Positron annihilation experiments were performed to study the structural defects such as vacancies and surfaces in these nanosystems. From coincidence Doppler broadening measurements, the positron trapping sites were identified as Zn vacancies or Zn-O-Zn trivacancy clusters. The positron lifetimes, their relative intensities, and the Doppler broadened lineshape parameter S all showed characteristic changes across the nanobipyramid size corresponding to the thermal diffusion length of positrons. In large nanobipyramids, vacancies within the crystallites also trapped positrons and the effects of agglomeration of such vacancies due to increased temperatures of synthesis were reflected in the variation of the annihilation parameters with their base diameters. The sizes of the nanoparticles used were all in the limit of thermal diffusion length of positrons and the annihilation characteristics were in accordance with the decreasing contribution from surfaces with increasing particle size.

  10. 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.

  11. 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.

  12. Coincident effect characteristic in a thermoacoustic regenerator

    International Nuclear Information System (INIS)

    Liu Yicai; Xin Tianlong; Huang Qian; Shi Xiangnan; Chen Siming; Chen Lixin

    2011-01-01

    Many previous studies on characteristics of thermoacoustic regenerator are based on fluid micro-groups and their compression-expansion cycle. In this paper, coincident frequency is introduced to evaluate its acoustic characteristics by combining structural acoustic with structural vibration theories. The relationship among structure wave radiation and regenerator position, slab thickness, and properties of material are analyzed by numerical calculation. The results show that in the low-frequency thermoacoustic system, the coincident effect generated by higher frequency wave weakens the fundamental sound wave. While in the high-frequency thermoacoustic system, where the oscillating fundamental frequency is higher than the coincident frequency, the sound field strength is enhanced by stronger structure wave radiation because of the coincident effect.

  13. A versatile fast coincidence system with memory

    International Nuclear Information System (INIS)

    Pouthas, J.

    1976-01-01

    A versatile fast coincidence system has been studied for experiments using several detectors. In this system, all the coincidence events are produced with an associated code, and thus, different kinds of events can be processed with the same experimental set-up. Also, the classification of the logical pulses gives the possibility of using a large number of ways (30 in this system). The setting of the system is very simple: there are only two time windows to adjust. (Auth.)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-07-01

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

  15. Measures of gamma rays between 0,3 MeV and 3,0 MeV and of the 0,511 MeV annihilation line coming from Galactic Center Region

    International Nuclear Information System (INIS)

    Jardim, M.V.A.

    1982-04-01

    The detection of the flux of the electron-positron annihilation line coming from the Galactic Center direction allows one to estimate the rate of positrons production and the corresponding luminosity. The results of measurements of the annihilation line flux intensity at 0.511 MeV, obtained with a balloon borne experiment to measure gamma rays in the energy interval 0.3 to 3 MeV are presented. The detector looked at the galactic disk in the longitude interval -31 0 0 and observed a flux intensity of (6.70 +- 0.85) x 10 -3 photons cm -2 s -1 , which is in good agreement with the flux value estimated assuming that the Galactic Center is a line source emitting uniformly. Some likely sources of positrons and annhilation regions are also discussed. The results for the continuum spectrum emitted from the Galactic Center in the energy interval 0.3 to 0.67 MeV are presented and compared with measurements had already made. (Author) [pt

  16. Coincidence method for determination of radionuclides activities

    International Nuclear Information System (INIS)

    Andrukhovich, S.K.; Berestov, A.V.; Rudak, E.A.

    2004-01-01

    The radon and radium activity measurements using six-crystal gamma-gamma coincidence, 4 -spectrometer PRIPJAT and radioactivity measurements in different samples of meat and vegetation by 32-crystal spectrometer ARGUS, are described. Radiation detector with 4 -geometry provides higher efficiency, and therefore shorter counting time than a detector without such geometry. However, its application is limited by the fact that obtained spectrum contains summing peaks of all γ-quanta registered in coincidence. Multiparameter information on coincident photon emission can be obtained only by a detection system where the 4 -geometry is made by many detectors, such are both the PRIPJAT and the ARGUS - γ-coincidence spectrometer of the Crystal Ball type in the Institute of Physics, Minsk [1,2]. There are other characteristics, as background conditions, energy and time resolution, makes it ve suitable for investigation of rare decays and interactions, cascade transitions, k intensity radiations etc. We are developing a method of 2 26R a and 2 26 Rn measurement by a multidetector 4 -spectrometer. The method is based on coincidence counting of γ-rays from two step cascade transitions that follow - decay of 2 14 Bi. Its application to the PRIPL spectrometer, which has 6 Nal(Tl) detectors, is presented here, as well as the method of the determination of radionuclide activities based on the registration of the cascades intensity of γ-rays of different multiplicity using ARGUS

  17. 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.

  18. 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

  19. 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

  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. Quintessence, Cosmic Coincidence, and the Cosmological Constant

    International Nuclear Information System (INIS)

    Zlatev, I.; Wang, L.; Steinhardt, P.J.; Steinhardt, P.J.

    1999-01-01

    Recent observations suggest that a large fraction of the energy density of the Universe has negative pressure. One explanation is vacuum energy density; another is quintessence in the form of a scalar field slowly evolving down a potential. In either case, a key problem is to explain why the energy density nearly coincides with the matter density today. The densities decrease at different rates as the Universe expands, so coincidence today appears to require that their ratio be set to a specific, infinitesimal value in the early Universe. In this paper, we introduce the notion of a open-quotes tracker field,close quotes a form of quintessence, and show how it may explain the coincidence, adding new motivation for the quintessence scenario. copyright 1999 The American Physical Society

  4. 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

  5. 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)

  6. Slow coincidences for CAMAC multiparameter analysis

    International Nuclear Information System (INIS)

    Akimov, Yu.K.; Kalinin, A.I.; Tissol'd, E.; Fromm, V.D.; Ekstein, P.

    1978-01-01

    A coincidence circuit with controlled parameters is described. The circuit has six coincidence inputs and one input for anticoincidences. A pulse duration in channels is changed from 0.25 to 5 μs and delay time, within 8 μs. The circuit is developed for multiparameter spectrometric analysis with the use of amplitude-digital and time-digital convertors. Its introduction permits one to diminish considerably the ''dead'' time of apparatus and to select rapidly and reliably strictly correlated digital information from convertors

  7. Coincidence-counting corrections for accidental coincidences, set dead time and intrinsic dead time

    International Nuclear Information System (INIS)

    Wyllie, H.A.

    1998-01-01

    An equation is derived for calculating the radioactivity of a source from the results of coincidence counting, taking into account dead-time losses and accidental coincidences. The corrections allow for the extension of the set dead time in the p channel by the intrinsic dead time. Experimental verification shows improvement over a previous equation. (author)

  8. 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.

  9. 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).

  10. Determining chance coincidence, survival factor and decay factor in 220Rn delayed coincidence measurement

    International Nuclear Information System (INIS)

    Huang Derong; Yan Yongjun; Zhou Jianliang; Qiu Shoukang

    2013-01-01

    The method and calculation formulas to determine the chance coincidence in the 220 Rn coincidence measurement are introduced in this paper. The poisson distribution is introduced to correct the chance coincidence. The relative deviation of the true coincidence between the method and the Giffin's is within 5% after the correction of the cohance coincidence. The measurement of 220 Rn is done by comparative measurement with RAD7. The results shows that 220 Rn can be measured by the method with a relative deviation of 14%. Mean while, for the 220 Rn flow regime is difficult to meet the condition of calculation formulas, a solution to solve the survival factor and decay factor is proposed and the error come from the useage of theoretical calculation formula is avoided. (authors)

  11. 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.)

  12. 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.).

  13. 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.)

  14. 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

  15. Tachyon driven solution to Cosmic Coincidence Problrm

    OpenAIRE

    Srivastaca, S. K.

    2004-01-01

    Here, non-minimally coupled tachyon to gravity is considered as a source of "dark energy". It is demonstrated that with expansion of the universe, tachyon dark energy decays to "dark matter" providing a solution to "cosmic coincidence problem".Moreover, it is found that universe undergoes accelerated expansion simultaneously.

  16. 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

  17. Using Compton scattering for random coincidence rejection

    International Nuclear Information System (INIS)

    Kolstein, M.; Chmeissani, M.

    2016-01-01

    The Voxel Imaging PET (VIP) project presents a new approach for the design of nuclear medicine imaging devices by using highly segmented pixel CdTe sensors. CdTe detectors can achieve an energy resolution of ≈ 1% FWHM at 511 keV and can be easily segmented into submillimeter sized voxels for optimal spatial resolution. These features help in rejecting a large part of the scattered events from the PET coincidence sample in order to obtain high quality images. Another contribution to the background are random events, i.e., hits caused by two independent gammas without a common origin. Given that 60% of 511 keV photons undergo Compton scattering in CdTe (i.e. 84% of all coincidence events have at least one Compton scattering gamma), we present a simulation study on the possibility to use the Compton scattering information of at least one of the coincident gammas within the detector to reject random coincidences. The idea uses the fact that if a gamma undergoes Compton scattering in the detector, it will cause two hits in the pixel detectors. The first hit corresponds to the Compton scattering process. The second hit shall correspond to the photoelectric absorption of the remaining energy of the gamma. With the energy deposition of the first hit, one can calculate the Compton scattering angle. By measuring the hit location of the coincident gamma, we can construct the geometric angle, under the assumption that both gammas come from the same origin. Using the difference between the Compton scattering angle and the geometric angle, random events can be rejected.

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

    International Nuclear Information System (INIS)

    Dryzek, E.

    2008-01-01

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

  19. Suitability study of using a coincidence monitor for room air radioactivity monitoring in a PET center

    International Nuclear Information System (INIS)

    Roellig, D.; Reichelt, C.; Iwatschenko-Borho, M.

    2001-01-01

    The application of radioactive nuclides in medicine may cause as well radioactive exposure of personnel (Medical Technical Assistants). In the present case the exposure of personnel in the area of medical positron-emission tomography (PET) within the Research Center of Rossendorf due to exhalation of the injected activity by the patient shall be investigated. For this purpose it is necessary to measure the activity concentration of the room air. Conventional methods such as collecting samples on special filters are not suitable due to the short half-life time of the used nuclides. Standard type continuous monitors are hardly suitable as well, because the injected activity of the patient and various radioactive sources required for the calibration of the PET-Camera produce an increased gamma background. In order to eliminate these disturbing influences a monitor has been constructed which uses CCM (cobalt coincidence method) developed by the company Thermo Eberline ESM. This method is specially suitable because upon each radioactive decay of PET nuclides positrons are emitted which in turn annihilate via the simultaneous emission of two 511 keV gamma quanta under an angle of 180 . The air to be measured is sucked through a cavity with two scintillation detectors on opposite sides. The coincident pulses produced by annihilating positrons inside the cavity are counted by a suitable electronic. Gamma quanta from outside the cavity can produce a pulse only in one detector and are rejected. Therefore no heavy lead shielding is required. Besides the mechanical construction of the monitor optimization and calibration for different PET-nuclides had to be performed. Special attention was paid to the sampling system. The air intake had to be close to the breathing zone of the MTA. The hose to the monitor had to be as short as possible. The target of the work was to design a model for an industrial monitor. (orig.) [de

  20. 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

  1. Method and apparstus for determining random coincidence count rate in a scintillation counter utilizing the coincidence technique

    International Nuclear Information System (INIS)

    Horrocks, D.L.

    1980-01-01

    A method and apparatus for the reliable determination of a random coincidence count attributable to chance coincidences of single-photon events which are each detected in only a single detector of a scintillation counter utilizing two detectors in a coincidence counting technique are described. A firstdelay device is employed to delay output pulses from one detector, and then the delayed signal is compared with the undelayed signal from the other detector in a coincidence circuit, to obtain an approximate random coincidence count. The output of the coincidence circuit is applied to an anti-coincidence circuit, where it is corrected by elimination of pulses coincident with, and attributable to, conventionally detected real coincidences, and by elimination of pulses coincident with, and attributable to, real coincidences that have been delayed by a second delay device having the same time parameter as the first. 8 claims

  2. 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)

  3. 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)

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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...

  9. Development of coincidence processing module for PEM

    International Nuclear Information System (INIS)

    Feng Baotong; Shuai Lei; Li Ke

    2011-01-01

    For the breast cancer diagnosis and therapy, a prototype of positron emission mammography (PEM) was developed in Institute of High Energy Physics, Chinese Academy of Sciences. In this paper, the design of coincidence processing module (CPM) for this PEM was presented. Both the hardware architecture and the software logic were introduced. In this design, the CPM used the Rocket IO fast interface in FPGA and fiber technology to acquire the preprocessed data from the continuous sampling module (CSM) and then selected the valid event with the coincidence timing window method, which was performed in the FPGA on the daughter board. The CPM transmits the processed data to host computer via gigabit Ethernet. The whole system was controlled by CAN bus. The primary tests indicate that the performance of this design is good. (authors)

  10. Recent progress with digital coincidence counting

    International Nuclear Information System (INIS)

    Butcher, K.S.A.; Watt, G.C.; Alexiev, D.

    1999-01-01

    Digital Coincidence Counting (DCC) is a new technique, based on the older method of analogue coincidence counting. It has been developed by ANSTO as a faster more reliable means of determining the activity of ionising radiation samples. The technique employs a dual channel analogue to digital converter acquisition system for collecting pulse information from a 4Π beta detector and a NaI(Tl) gamma detector. The digitised pulse information is stored on a high speed hard disk and timing information for both channels is also stored. The data may subsequently be recalled and analysed using software based algorithms. The system is operational and results are now being routinely collected and analysed. Some of the early work is presented for Co-60, Na-22 and Sm-153

  11. New way on designing majorant coincidence circuits

    International Nuclear Information System (INIS)

    Gajdamaka, R.I.; Kalinnikov, V.A.; Nikityuk, N.M.; Shirikov, V.P.

    1982-01-01

    A new way of designing fast devices of combinatorial selection by the number of particles passing through a multichannel charged particle detector is decribed. The algorithm of their operation is based on modern algebraic coding theory. By application of analytical computational methods Boolean expressions can be obtianed for designing basic circuits for a large number of inputs. An example of computation of 15 inputs majorant coincidence circuit is considered

  12. Kinematical coincidence method in transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Acosta, L.; Amorini, F. [INFN—Laboratori Nazionali del Sud, Via S. Sofia, Catania (Italy); Auditore, L. [INFN Gruppo Collegato di Messina and Dipartimento di Fisica, Università di Messina (Italy); Berceanu, I. [Institute for Physics and Nuclear Engineering, Bucharest (Romania); Cardella, G., E-mail: cardella@ct.infn.it [INFN—Sezione di Catania, Via S. Sofia, 95123 Catania (Italy); Chatterjiee, M.B. [Saha Institute for Nuclear Physics, Kolkata (India); De Filippo, E. [INFN—Sezione di Catania, Via S. Sofia, 95123 Catania (Italy); Francalanza, L.; Gianì, R. [INFN—Laboratori Nazionali del Sud, Via S. Sofia, Catania (Italy); Dipartimento di Fisica e Astronomia, Università di Catania, Via S. Sofia, Catania (Italy); Grassi, L. [INFN—Sezione di Catania, Via S. Sofia, 95123 Catania (Italy); Rudjer Boskovic Institute, Zagreb (Croatia); Grzeszczuk, A. [Institut of Physics, University of Silesia, Katowice (Poland); La Guidara, E. [INFN—Sezione di Catania, Via S. Sofia, 95123 Catania (Italy); Centro Siciliano di Fisica Nucleare e Struttura della Materia, Catania (Italy); Lanzalone, G. [INFN—Laboratori Nazionali del Sud, Via S. Sofia, Catania (Italy); Facoltà di Ingegneria e Architettura, Università Kore, Enna (Italy); Lombardo, I. [INFN—Laboratori Nazionali del Sud, Via S. Sofia, Catania (Italy); Dipartimento di Scienze Fisiche, Università Federico II and INFN Sezione di Napoli (Italy); Loria, D.; Minniti, T. [INFN Gruppo Collegato di Messina and Dipartimento di Fisica, Università di Messina (Italy); Pagano, E.V. [INFN—Laboratori Nazionali del Sud, Via S. Sofia, Catania (Italy); Dipartimento di Fisica e Astronomia, Università di Catania, Via S. Sofia, Catania (Italy); and others

    2013-07-01

    A new method to extract high resolution angular distributions from kinematical coincidence measurements in binary reactions is presented. Kinematics is used to extract the center of mass angular distribution from the measured energy spectrum of light particles. Results obtained in the case of {sup 10}Be+p→{sup 9}Be+d reaction measured with the CHIMERA detector are shown. An angular resolution of few degrees in the center of mass is obtained. The range of applicability of the method is discussed.

  13. Coincident-inclusive electrofission angular correlations

    International Nuclear Information System (INIS)

    Arruda Neto, J.D.T.

    1983-08-01

    A method for the joint analysis of coincident and inclusive electrofission data, in order to minimize effects of the model dependence of data interpretation, is developed. Explicit calculations of the (e,e'f) angular correlations are presented. The potentialities of the method to the study of sub- and near-barrier properties of the fission process, and to the study of the giant resonances fission mode, are discussed. (Author) [pt

  14. Timing coincidence studies with fast photomultipliers

    International Nuclear Information System (INIS)

    Raoof, M.A.; Raoof, S.A.

    1981-01-01

    The time response of RCA C70045D photomultipliers was studied using a subnanosecond light flasher. The tubes, which have an output rise time of approximately 0.5 ns, were used in coincidence to study the variations in the fwhm of the time spectrum over a certain dynamic range of pulse amplitudes for both leading edge and constant fraction discrimination. A comparison has also been made for the measured time resolutions with some of the other fast photomultipliers. (orig.)

  15. Fast coincidence counting with active inspection systems

    Science.gov (United States)

    Mullens, J. A.; Neal, J. S.; Hausladen, P. A.; Pozzi, S. A.; Mihalczo, J. T.

    2005-12-01

    This paper describes 2nd and 3rd order time coincidence distributions measurements with a GHz processor that synchronously samples 5 or 10 channels of data from radiation detectors near fissile material. On-line, time coincidence distributions are measured between detectors or between detectors and an external stimulating source. Detector-to-detector correlations are useful for passive measurements also. The processor also measures the number of times n pulses occur in a selectable time window and compares this multiplet distribution to a Poisson distribution as a method of determining the occurrence of fission. The detectors respond to radiation emitted in the fission process induced internally by inherent sources or by external sources such as LINACS, DT generators either pulsed or steady state with alpha detectors, etc. Data can be acquired from prompt emission during the source pulse, prompt emissions immediately after the source pulse, or delayed emissions between source pulses. These types of time coincidence measurements (occurring on the time scale of the fission chain multiplication processes for nuclear weapons grade U and Pu) are useful for determining the presence of these fissile materials and quantifying the amount, and are useful for counter terrorism and nuclear material control and accountability. This paper presents the results for a variety of measurements.

  16. Coincidence measurements of FFTF breeder fuel subassemblies

    International Nuclear Information System (INIS)

    Eccleston, G.W.; Foley, J.E.; Krick, M.; Menlove, H.O.; Goris, P.; Ramalho, A.

    1984-04-01

    A prototype coincidence counter developed to assay fast breeder reactor fuel was used to measure four fast-flux test facility subassemblies at the Hanford Engineering Development Laboratory in Richland, Washington. Plutonium contents in the four subassemblies ranged between 7.4 and 9.7 kg with corresponding 240 Pu-effective contents between 0.9 and 1.2 kg. Large count rates were observed from the measurements, and plots of the data showed significant multiplication in the fuel. The measured data were corrected for deadtime and multiplication effects using established formulas. These corrections require accurate knowledge of the plutonium isotopics and 241 Am content in the fuel. Multiplication-corrected coincidence count rates agreed with the expected count rates based on spontaneous fission-neutron emission rates. These measurements indicate that breeder fuel subassemblies with 240 Pu-effective contents up to 1.2 kg can be nondestructively assayed using the shift-register electronics with the prototype counters. Measurements using the standard Los Alamos National Laboratory shift-register coincidence electronics unit can produce an assay value accurate to +-1% in 1000 s. The uncertainty results from counting statistics and deadtime-correction errors. 3 references, 8 figures, 8 tables

  17. Fast coincidence counting with active inspection systems

    International Nuclear Information System (INIS)

    Mullens, J.A.; Neal, J.S.; Hausladen, P.A.; Pozzi, S.A.; Mihalczo, J.T.

    2005-01-01

    This paper describes 2nd and 3rd order time coincidence distributions measurements with a GHz processor that synchronously samples 5 or 10 channels of data from radiation detectors near fissile material. On-line, time coincidence distributions are measured between detectors or between detectors and an external stimulating source. Detector-to-detector correlations are useful for passive measurements also. The processor also measures the number of times n pulses occur in a selectable time window and compares this multiplet distribution to a Poisson distribution as a method of determining the occurrence of fission. The detectors respond to radiation emitted in the fission process induced internally by inherent sources or by external sources such as LINACS, DT generators either pulsed or steady state with alpha detectors, etc. Data can be acquired from prompt emission during the source pulse, prompt emissions immediately after the source pulse, or delayed emissions between source pulses. These types of time coincidence measurements (occurring on the time scale of the fission chain multiplication processes for nuclear weapons grade U and Pu) are useful for determining the presence of these fissile materials and quantifying the amount, and are useful for counter terrorism and nuclear material control and accountability. This paper presents the results for a variety of measurements

  18. 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

  19. 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.)

  20. 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...

  1. 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

  2. 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

  3. 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

  4. A Fokker-Planck treatment of stochastic particle motion within the framework of a fully coupled 6-dimensional formalism for electron-positron storage rings including classical spin motion in linear approximation

    International Nuclear Information System (INIS)

    Barber, D.P.; Heinemann, K.; Mais, H.; Ripken, G.

    1991-12-01

    In the following report we investigate stochastic particle motion in electron-positron storage ring in the framework of a Fokker-Planck treatment. The motion is described by using the canonical variables χ, p χ , z, p z , σ = s - cxt, p σ = ΔE/E 0 of the fully six-dimensional formalism. Thus synchrotron- and betatron-oscillations are treated simultaneously taking into account all kinds of coupling (synchro-betatron coupling and the coupling of the betatron oscillations by skew quadrupoles and solenoids). In order to set up the Fokker-Planck equation, action-angle variables of the linear coupled motion are introduced. The averaged dimensions of the bunch, resulting from radiation damping of the synchro-betatron oscillations and from an excitation of these oscillations by quantum fluctuations, are calculated by solving the Fokker-Planck equation. The surfaces of constant density in the six-dimensional phase space, given by six-dimensional ellipsoids, are determined. It is shown that the motion of such an ellipsoid under the influence of external fields can be described by six generating orbit vectors which may be combined into a six-dimenional matrix B(s). This 'bunch-shape matrix', B(s), contains complete information about the configuration of the bunch. Classical spin diffusion in linear approximation has also been included so that the dependence of the polarization vector on the orbital phase space coordinates can be studied and another derivation of the linearized depolarization time obtained. (orig.)

  5. Investigations of the coherent hard photon yields from (50-300) GeV/c electrons/positrons in the strong crystalline fields of diamond, Si, and Ge crystals

    CERN Multimedia

    The aim of this experiment is to measure the influence of strong fields on QED-processes like: Emission of coherent radiation and pair-production when multi-hundred GeV electrons/positrons and photons penetrate single crystals near axial/planar directions. The targets will be diamond, Si, Ge and W crystals.\\\\\\\\ QED is a highly developed theory and has been investigated experimentally in great detail. In recent years it has become technically possible to investigate QED-processes in very strong electromagnetic fields around the characteristic strong field E$_{0}$ = m$^{2}$c$^{3}$/eh = 1.32.10$^{16}$ V/cm. The work of such a field over the Compton length equals the electron mass. The theoretical description of QED in such fields is beyond the framework of perturbation theory. Such fields are only obtained in laboratories for a) heavy ion collisions b) interactions of multi-GeV electrons with extremely intense laser fields and in oriented crystals. In fact it turns out that crystals are unique for this type of e...

  6. Measurement of the forward-backward asymmetry ($A_\\textit{FB}$) of $Z$ boson decays in electron-positron pairs with the ATLAS detector in proton-proton collisions at $\\sqrt{s}$ = 7 TeV at the LHC

    CERN Document Server

    König, Sebastian

    In this thesis the measurement of the effective weak mixing angle $\\sin^2{\\theta_W^{\\mathrm{eff}}}$ in proton-proton collisions is described. The results are extracted from the forward-backward asymmetry ($A_\\textit{FB}$) in electron-positron final states at the ATLAS experiment at the LHC. The $A_\\textit{FB}$ is defined upon the distribution of the polar angle between the incoming quark and outgoing lepton. The signal process used in this study is the reaction $pp\\to Z/\\gamma^*+X\\to e^+e^-+X$ taking a total integrated luminosity of 4.8 fb$^{-1}$ of data into account. The data was recorded at a proton-proton center-of-mass energy of $\\sqrt{s}=7$ TeV. The weak mixing angle is a central parameter of the electroweak theory of the Standard Model (SM) and relates the neutral current interactions of electromagnetism and weak force. The higher order corrections on $\\sin^2{\\theta_W^{\\mathrm{eff}}}$ are related to other SM parameters like the mass of the Higgs boson. Because of the symmetric initial...

  7. 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)

  8. 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)

  9. Coincidence corrections for a multi-detector gamma spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Britton, R., E-mail: r.britton@surrey.ac.uk [University of Surrey, Guildford GU2 7XH (United Kingdom); AWE, Aldermaston, Reading, Berkshire RG7 4PR (United Kingdom); Burnett, J.L.; Davies, A.V. [AWE, Aldermaston, Reading, Berkshire RG7 4PR (United Kingdom); Regan, P.H. [University of Surrey, Guildford GU2 7XH (United Kingdom)

    2015-01-01

    List-mode data acquisition has been utilised in conjunction with a high-efficiency γ–γ coincidence system, allowing both the energetic and temporal information to be retained for each recorded event. Collected data is re-processed multiple times to extract any coincidence information from the γ-spectroscopy system, correct for the time-walk of low-energy events, and remove accidental coincidences from the projected coincidence spectra. The time-walk correction has resulted in a reduction in the width of the coincidence delay gate of 18.4±0.4%, and thus an equivalent removal of ‘background’ coincidences. The correction factors applied to ∼5.6% of events up to ∼500 keV for a combined {sup 137}Cs and {sup 60}Co source, and are crucial for accurate coincidence measurements of low-energy events that may otherwise be missed by a standard delay gate. By extracting both the delay gate and a representative ‘background’ region for the coincidences, a coincidence background subtracted spectrum is projected from the coincidence matrix, which effectively removes ∼100% of the accidental coincidences (up to 16.6±0.7% of the total coincidence events seen during this work). This accidental-coincidence removal is crucial for accurate characterisation of the events seen in coincidence systems, as without this correction false coincidence signatures may be incorrectly interpreted.

  10. 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

  11. Nano sulfide and oxide semiconductors as promising materials for studies by positron annihilation

    International Nuclear Information System (INIS)

    Nambissan, P M G

    2013-01-01

    A number of wide band gap sulfide and oxide semiconducting nanomaterial systems were investigated using the experimental techniques of positron lifetime and coincidence Doppler broadening measurements. The results indicated several features of the nanomaterial systems, which were found strongly related to the presence of vacancy-type defects and their clusters. Quantum confinement effects were displayed in these studies as remarkable changes in the positron lifetimes and the lineshape parameters around the same grain sizes below which characteristic blue shifts were observed in the optical absorption spectra. Considerable enhancement in the band gap and significant rise of the positron lifetimes were found occurring when the particle sizes were reduced to very low sizes. The results of doping or substitutions by other cations in semiconductor nanosystems were also interesting. Variously heat-treated TiO 2 nanoparticles were studied recently and change of positron annihilation parameters across the anatase to rutile structural transition are carefully analyzed. Preliminary results of positron annihilation studies on Eu-doped CeO nanoparticles are also presented.

  12. Nano sulfide and oxide semiconductors as promising materials for studies by positron annihilation

    Science.gov (United States)

    Nambissan, P. M. G.

    2013-06-01

    A number of wide band gap sulfide and oxide semiconducting nanomaterial systems were investigated using the experimental techniques of positron lifetime and coincidence Doppler broadening measurements. The results indicated several features of the nanomaterial systems, which were found strongly related to the presence of vacancy-type defects and their clusters. Quantum confinement effects were displayed in these studies as remarkable changes in the positron lifetimes and the lineshape parameters around the same grain sizes below which characteristic blue shifts were observed in the optical absorption spectra. Considerable enhancement in the band gap and significant rise of the positron lifetimes were found occurring when the particle sizes were reduced to very low sizes. The results of doping or substitutions by other cations in semiconductor nanosystems were also interesting. Variously heat-treated TiO2 nanoparticles were studied recently and change of positron annihilation parameters across the anatase to rutile structural transition are carefully analyzed. Preliminary results of positron annihilation studies on Eu-doped CeO nanoparticles are also presented.

  13. Damping kinetics of annihilation slowed fluorescence of aromatic molecules in Langmuir films

    International Nuclear Information System (INIS)

    Ibraev, N.Kh.; Latonin, V.A.; Satybaldina, D.Zh.

    1996-01-01

    The paper is devoted to study of decay mechanism of phosphors molecules triplet states in the Langmuir-Blogett (L-B) films. The L-B-films have being prepared on the base of anthracene, pyrene, 3,4-benzopyrene and 1,2-benzanthracene molecules. Spectral and kinetic investigations were carried out in photons counting regime. Long-lived luminescence was observed under excitation of the LB-film by nitrogen laser radiation (λ=337 nm) .Spectrum of the long-lived luminescence coincides with spectrum of fast fluorescence of same film. Received spectral data indicate on similarity of LB-films structure of aromatic molecules and its crystals. It was defined, that deactivation of triplet states of aromatic molecules in LB-films has being carried out mainly in the result of annihilation of triplet excitation. 14 refs., 2 tabs., 5 figs

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

    International Nuclear Information System (INIS)

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

    2007-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-09-08

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

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

    International Nuclear Information System (INIS)

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

    2008-01-01

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

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

    Science.gov (United States)

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

    2010-04-01

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

  18. Coincidence logic modules for criticality alarming

    International Nuclear Information System (INIS)

    Schaief, C.C. III.

    1977-04-01

    A coincidence Logic Module and a companion contact closure Relay Module utilizing the NIM Standard have been developed for criticality alarming. The units provide an ALARM whenever two or more out of N detectors become activated. In addition, an ALERT is generated whenever one or more detectors is activated or when certain electronic component failures occur. The number of detector inputs (N) can be expanded in groups of six by adding modules. Serial and parallel redundancy were used to reduce the probability of system failure

  19. 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.

  20. Quark seesaw mechanism, dark U (1 ) symmetry, and the baryon-dark matter coincidence

    Science.gov (United States)

    Gu, Pei-Hong; Mohapatra, Rabindra N.

    2017-09-01

    We attempt to understand the baryon-dark matter coincidence problem within the quark seesaw extension of the standard model where parity invariance is used to solve the strong C P problem. The S U (2 )L×S U (2 )R×U (1 )B -L gauge symmetry of this model is extended by a dark U (1 )X group plus inclusion of a heavy neutral vector-like fermion χL ,R charged under the dark group which plays the role of dark matter. All fermions are Dirac type in this model. Decay of heavy scalars charged under U (1 )X leads to simultaneous asymmetry generation of the dark matter and baryons after sphaleron effects are included. The U (1 )X group not only helps to stabilize the dark matter but also helps in the elimination of the symmetric part of the dark matter via χ -χ ¯ annihilation. For dark matter mass near the proton mass, it explains why the baryon and dark matter abundances are of similar magnitude (the baryon-dark matter coincidence problem). This model is testable in low threshold (sub-keV) direct dark matter search experiments.

  1. 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)

  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. Monte Carlo calculations of the neutron coincidence gate utilisation factor for passive neutron coincidence counting

    CERN Document Server

    Bourva, L C A

    1999-01-01

    The general purpose neutron-photon-electron Monte Carlo N-Particle code, MCNP sup T sup M , has been used to simulate the neutronic characteristics of the on-site laboratory passive neutron coincidence counter to be installed, under Euratom Safeguards Directorate supervision, at the Sellafield reprocessing plant in Cumbria, UK. This detector is part of a series of nondestructive assay instruments to be installed for the accurate determination of the plutonium content of nuclear materials. The present work focuses on one aspect of this task, namely, the accurate calculation of the coincidence gate utilisation factor. This parameter is an important term in the interpretative model used to analyse the passive neutron coincidence count data acquired using pulse train deconvolution electronics based on the shift register technique. It accounts for the limited proportion of neutrons detected within the time interval for which the electronics gate is open. The Monte Carlo code MCF, presented in this work, represents...

  9. 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

  10. 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...

  11. 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)

  12. Poster – 02: Positron Emission Tomography (PET) Imaging Reconstruction using higher order Scattered Photon Coincidences

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Hongwei; Pistorius, Stephen [Department of Physics and Astronomy, University of Manitoba, CancerCare, Manitoba (Canada)

    2016-08-15

    PET images are affected by the presence of scattered photons. Incorrect scatter-correction may cause artifacts, particularly in 3D PET systems. Current scatter reconstruction methods do not distinguish between single and higher order scattered photons. A dual-scattered reconstruction method (GDS-MLEM) that is independent of the number of Compton scattering interactions and less sensitive to the need for high energy resolution detectors, is proposed. To avoid overcorrecting for scattered coincidences, the attenuation coefficient was calculated by integrating the differential Klein-Nishina cross-section over a restricted energy range, accounting only for scattered photons that were not detected. The optimum image can be selected by choosing an energy threshold which is the upper energy limit for the calculation of the cross-section and the lower limit for scattered photons in the reconstruction. Data was simulated using the GATE platform. 500,000 multiple scattered photon coincidences with perfect energy resolution were reconstructed using various methods. The GDS-MLEM algorithm had the highest confidence (98%) in locating the annihilation position and was capable of reconstructing the two largest hot regions. 100,000 photon coincidences, with a scatter fraction of 40%, were used to test the energy resolution dependence of different algorithms. With a 350–650 keV energy window and the restricted attenuation correction model, the GDS-MLEM algorithm was able to improve contrast recovery and reduce the noise by 7.56%–13.24% and 12.4%–24.03%, respectively. This approach is less sensitive to the energy resolution and shows promise if detector energy resolutions of 12% can be achieved.

  13. The influence of photon depth of interaction and non-collinear spread of annihilation photons on PET image spatial resolution

    International Nuclear Information System (INIS)

    Sanchez-Crespo, Alejandro; Larsson, Stig A.

    2006-01-01

    The quality of PET imaging is impaired by parallax errors. These errors produce misalignment between the projected location of the true origin of the annihilation event and the line of response determined by the coincidence detection system. Parallax errors are due to the varying depths of photon interaction (DOI) within the scintillator and the non-collinear (NC) emission of the annihilation photons. The aim of this work was to address the problems associated with the DOI and the NC spread of annihilation photons and to develop a quantitative model to assess their impact on image spatial resolution losses for various commonly used scintillators and PET geometries. A theoretical model based on Monte Carlo simulations was developed to assess the relative influence of DOI and the NC spread of annihilation photons on PET spatial resolution for various scintillator materials (BGO, LSO, LuAP, GSO, NaI) and PET geometries. The results demonstrate good agreement between simulated, experimental and published overall spatial resolution for some commercial systems, with maximum differences around 1 mm in both 2D and 3D mode. The DOI introduces an impairment of non-stationary spatial resolution along the radial direction, which can be very severe at peripheral positions. As an example, the radial spatial resolution loss due to DOI increased from 1.3 mm at the centre to 6.7 mm at 20 cm from the centre of a BGO camera with a 412-mm radius in 2D mode. Including the NC, the corresponding losses were 3.0 mm at the centre and 7.3 mm 20 cm from the centre. Without a DOI detection technique, it seems difficult to improve PET spatial resolution and increase sensitivity by reducing the detector ring radius or by extending the detector in the axial direction. Much effort is expended on the design and configuration of smaller detector elements but more effort should be devoted to the DOI complexity. (orig.)

  14. Coincident Detection Significance in Multimessenger Astronomy

    Science.gov (United States)

    Ashton, G.; Burns, E.; Dal Canton, T.; Dent, T.; Eggenstein, H.-B.; Nielsen, A. B.; Prix, R.; Was, M.; Zhu, S. J.

    2018-06-01

    We derive a Bayesian criterion for assessing whether signals observed in two separate data sets originate from a common source. The Bayes factor for a common versus unrelated origin of signals includes an overlap integral of the posterior distributions over the common-source parameters. Focusing on multimessenger gravitational-wave astronomy, we apply the method to the spatial and temporal association of independent gravitational-wave and electromagnetic (or neutrino) observations. As an example, we consider the coincidence between the recently discovered gravitational-wave signal GW170817 from a binary neutron star merger and the gamma-ray burst GRB 170817A: we find that the common-source model is enormously favored over a model describing them as unrelated signals.

  15. A generalized model for coincidence counting

    International Nuclear Information System (INIS)

    Lu, Ming-Shih; Teichmann, T.

    1992-01-01

    The aim of this paper is to provide a description of the multiplicative processes associated with coincidence counting techniques, for example in the NDA of plutonium bearing materials. The model elucidates both the physical processes and the underlying mathematical formalism in a relatively simple but comprehensive way. In particular, it includes the effect of absorption by impurities or poisons, as well as that of neutron leakage on a parallel basis to the treatment of induced fission itself. The work thus parallels and generalizes the methods of Boehnel of Hage and Cifarelli, and more recently of Yanjushkin. This paper introduces the concept of a dual probability generating function to account for both the basic physical multiplication phenomena, as well as the detection phenomena. The underlying approach extends the idea of a simple probability generating function, due to De Moivre. The basic mathematical background may be found, for example, in Feller 1966

  16. Electron-electron coincidence spectroscopies at surfaces

    International Nuclear Information System (INIS)

    Stefani, G.; Iacobucci, S.; Ruocco, A.; Gotter, R.

    2002-01-01

    In the past 20 years, a steadily increasing number of electron-electron coincidence experiments on atoms and molecules have contributed to a deeper understanding of electron-electron correlation effects. In more recent years this technique has been extended to the study of solid surfaces. This class of one photon IN two electrons OUT experiments will be discussed with an emphasis on grazing incidence geometry, that is expected to be particularly suited for studying surfaces. The crucial question of which is the dominant mechanism that leads to ejection of pairs of electron from the surface will be addressed. It will be shown that, depending on the kinematics chosen, the correlated behaviour of the pairs of electrons detected might be singled out from independent particle one

  17. More accurate thermal neutron coincidence counting technique

    International Nuclear Information System (INIS)

    Baron, N.

    1978-01-01

    Using passive thermal neutron coincidence counting techniques, the accuracy of nondestructive assays of fertile material can be improved significantly using a two-ring detector. It was shown how the use of a function of the coincidence count rate ring-ratio can provide a detector response rate that is independent of variations in neutron detection efficiency caused by varying sample moderation. Furthermore, the correction for multiplication caused by SF- and (α,n)-neutrons is shown to be separable into the product of a function of the effective mass of 240 Pu (plutonium correction) and a function of the (α,n) reaction probability (matrix correction). The matrix correction is described by a function of the singles count rate ring-ratio. This correction factor is empirically observed to be identical for any combination of PuO 2 powder and matrix materials SiO 2 and MgO because of the similar relation of the (α,n)-Q value and (α,n)-reaction cross section among these matrix nuclei. However the matrix correction expression is expected to be different for matrix materials such as Na, Al, and/or Li. Nevertheless, it should be recognized that for comparison measurements among samples of similar matrix content, it is expected that some function of the singles count rate ring-ratio can be defined to account for variations in the matrix correction due to differences in the intimacy of mixture among the samples. Furthermore the magnitude of this singles count rate ring-ratio serves to identify the contaminant generating the (α,n)-neutrons. Such information is useful in process control

  18. Minicomputer system for radiochemical analysis by coincidence spectrometry

    International Nuclear Information System (INIS)

    Brauer, F.P.; Fager, J.E.

    1979-01-01

    Minicomputer-based coincidence analysis methods have been developed for use in performing radiochemical analysis by high-resolution x- and gamma-ray coincidence spectrometry. This paper describes the data-acquisition and analysis methods develolped for qualitative and quantitative analyses of coincidence spectrometric data. Data-acquisition capabilities include both direct multiparameter pulse-height analysis and buffered list-mode acquisition

  19. Monte Carlo calculations of the neutron coincidence gate utilisation factor for passive neutron coincidence counting

    International Nuclear Information System (INIS)

    Bourva, L.C.A.; Croft, S.

    1999-01-01

    The general purpose neutron-photon-electron Monte Carlo N-Particle code, MCNP TM , has been used to simulate the neutronic characteristics of the on-site laboratory passive neutron coincidence counter to be installed, under Euratom Safeguards Directorate supervision, at the Sellafield reprocessing plant in Cumbria, UK. This detector is part of a series of nondestructive assay instruments to be installed for the accurate determination of the plutonium content of nuclear materials. The present work focuses on one aspect of this task, namely, the accurate calculation of the coincidence gate utilisation factor. This parameter is an important term in the interpretative model used to analyse the passive neutron coincidence count data acquired using pulse train deconvolution electronics based on the shift register technique. It accounts for the limited proportion of neutrons detected within the time interval for which the electronics gate is open. The Monte Carlo code MCF, presented in this work, represents a new evaluation technique for the estimation of gate utilisation factors. It uses the die-away profile of a neutron coincidence chamber generated either by MCNP TM , or by other means, to simulate the neutron detection arrival time pattern originating from independent spontaneous fission events. A shift register simulation algorithm, embedded in the MCF code, then calculates the coincidence counts scored within the electronics gate. The gate utilisation factor is then deduced by dividing the coincidence counts obtained with that obtained in the same Monte Carlo run, but for an ideal detection system with a coincidence gate utilisation factor equal to unity. The MCF code has been benchmarked against analytical results calculated for both single and double exponential die-away profiles. These results are presented along with the development of the closed form algebraic expressions for the two cases. Results of this validity check showed very good agreement. On this

  20. 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 ...

  1. 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

  2. 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.)

  3. 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

  4. 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.)

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. Soudan 2 muons in coincidence with BATSE bursts

    International Nuclear Information System (INIS)

    DeMuth, D.M.; Marshak, M.L.; Wagner, G.L.

    1994-01-01

    We explore the possibilities of statistically significant temporal and spatial coincidences between underground muons at Soudan 2 and Gamma Ray Bursts at the GRO-BATSE detector. Our search uses data from the April 91 to March 92 BATSE burst catalog to seek correlations within a 100 second window of coincidence. Sixteen of 180 BATSE triggers have temporally and spatially coincident muons in the Soudan 2 detector. We estimate the chance probability of each coincidence assuming the null hypothesis on the basis of a study of the multiplicities of spatially coincident muons observed over a two day period centered on the time of burst

  14. 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

  15. 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.

  16. 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

  17. 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

  18. TRISTAN, electron-positron colliding beam project

    International Nuclear Information System (INIS)

    1987-03-01

    In this report e + e - colliding beam program which is now referred to as TRISTAN Project will be described. A brief chronology and outline of TRISTAN Project is given in Chapter 1. Chapter 2 of this article gives a discussion of physics objectives at TRISTAN. Chapter 3 treats the overall description of the accelerators. Chapter 4 describes design of each of the accelerator systems. In Chapter 5, detector facilities are discussed in some detail. A description of accelerator tunnels, experimental areas, and utilities are given in Chapter 6. In the Appendix, the publications on the TRISTAN Project are listed. (author)

  19. The Story of Large Electron Positron Collider

    Indian Academy of Sciences (India)

    Institute of Fundamental. Research ... standard model of the fundamental particles of nature. .... the particle 'a' now refers to the energy in the lab system, we have denoted it by E!ab ..... Hanlburg, Germany, operating at centre of mass energy.

  20. Electron-positron scattering and gauge theories

    International Nuclear Information System (INIS)

    Davier, M.

    1983-07-01

    Recent results from high-energy e + e - colliding facilities are reviewed in the context of gauge theories. First QCD analyses are discussed and difficulties are seen to arise from the interplay between perturbative QCD and non-perturbative fragmentation processes. Many results have been recently obtained on weak electromagnetic interference, strengthening our faith in the standard SU(2) x U(1) theory: however some pieces are still missing and looked for. Finally, vigourous searches are pursued to find clues for physics beyond the SU(3) x SU(2) x U(1) framework: among those supersymmetric particles are being actively hunted in a large variety of situations