Generation and application of slow positrons based on a electron LINAC

CERN Document Server

Kurihara, T

2002-01-01

History of slow positron in Institute of Materials Structure Science High Energy Accelerator Research Organization is explained. The principle of generation and application of intense positron beam is mentioned. Two sources of intense positron are radioactive decay of radioactive isotopes emitting positron and electron-positron pair creation. The radioactive decay method uses sup 5 sup 8 Co, sup 6 sup 4 Cu, sup 1 sup 1 C, sup 1 sup 3 N, sup 1 sup 5 O and sup 1 sup 8 F. The electron-positron pair creation method uses nuclear reactor or electron linear accelerator (LINAC). The positron experimental facility in this organization consists of electron LINAC, slow positron beam source, positron transport and experimental station. The outline of this facility is started. The intense slow positron beam is applied to research positronium work function, electron structure of surface. New method such as combination of positron lifetime measurement and slow positron beam or Auger electron spectroscopy by positron annihil...

A transmission positron microscope and a scanning positron microscope being built at KEK, Japan

International Nuclear Information System (INIS)

Doyama, M.; Inoue, M.; Kogure, Y.; Kurihara, T.; Yagishita, A.; Shidara, T.; Nakahara, K.; Hayashi, Y.; Yoshiie, T.

2001-01-01

This paper reports the plans of positron microscopes being built at KEK (High Energy Accelerator Research Organization), Tsukuba, Japan improving used electron microscopes. The kinetic energies of positron produced by accelerators or by nuclear decays have not a unique value but show a spread over in a wide range. Positron beam will be guided near electron microscopes, a transmission electron microscope (JEM100S) and a scanning electron microscope (JSM25S). Positrons are slowed down by a tungsten foil, accelerated and focused on a nickel sheet. The monochromatic focused beam will be injected into an electron microscope. The focusing of positrons and electrons is achieved by magnetic system of the electron microscopes. Imaging plates are used to record positron images for the transmission electron microscope. (orig.)

Decaying dark matter and the PAMELA anomaly

International Nuclear Information System (INIS)

Ibarra, Alejandro; Tran, David

2009-01-01

Astrophysical and cosmological observations do not require the dark matter particles to be absolutely stable. If they are indeed unstable, their decay into positrons might occur at a sufficiently large rate to allow the indirect detection of dark matter through an anomalous contribution to the cosmic positron flux. In this paper we discuss the implications of the excess in the positron fraction recently reported by the PAMELA collaboration for the scenario of decaying dark matter. To this end, we have performed a model-independent analysis of possible signatures by studying various decay channels in the case of both a fermionic and a scalar dark matter particle. We find that the steep rise in the positron fraction measured by PAMELA at energies larger than 10 GeV can naturally be accommodated in several realizations of the decaying dark matter scenario. The data point toward a rather heavy dark matter particle, m DM ∼> 300 GeV, which preferentially decays directly into first or second generation charged leptons with a lifetime τ DM ∼ 10 26 s

The positron excess as a smoking gun for dynamical dark matter?

Energy Technology Data Exchange (ETDEWEB)

Dienes, Keith R. [Department of Physics, University of Arizona, Tucson, AZ 85721 USA and Department of Physics, University of Maryland, College Park, MD 20742 (United States); Kumar, Jason [Department of Physics, University of Hawaii, Honolulu, HI 96822 (United States); Thomas, Brooks [Department of Physics, Carleton University, Ottawa, Ontario, K1S 5B6 (Canada)

2014-06-24

One of the most puzzling aspects of recent data from the AMS-02 experiment is an apparent rise in the cosmic-ray positron fraction as a function of energy. This feature is observed out to energies of approximately 350 GeV. One explanation of these results interprets the extra positrons as arising from the decays of dark-matter particles. This in turn typically requires that such particles have rather heavy TeV-scale masses and not undergo simple two-body decays to leptons. In this talk, by contrast, we show that Dynamical Dark Matter (DDM) can not only match existing AMS-02 data on the positron excess, but also accomplish this feat with significantly lighter dark-matter constituents undergoing simple two-body decays to leptons. We also demonstrate that the Dynamical Dark Matter framework makes a fairly robust prediction that the positron fraction should level off and then remain roughly constant out to approximately 1 TeV, without experiencing any sharp downturns. Thus, if we interpret the positron excess in terms of decaying dark matter, the existence of a plateau in the positron fraction at energies less than 1 TeV may be taken as a “smoking gun” of Dynamical Dark Matter.

The positron excess as a smoking gun for dynamical dark matter?

International Nuclear Information System (INIS)

Dienes, Keith R.; Kumar, Jason; Thomas, Brooks

2014-01-01

One of the most puzzling aspects of recent data from the AMS-02 experiment is an apparent rise in the cosmic-ray positron fraction as a function of energy. This feature is observed out to energies of approximately 350 GeV. One explanation of these results interprets the extra positrons as arising from the decays of dark-matter particles. This in turn typically requires that such particles have rather heavy TeV-scale masses and not undergo simple two-body decays to leptons. In this talk, by contrast, we show that Dynamical Dark Matter (DDM) can not only match existing AMS-02 data on the positron excess, but also accomplish this feat with significantly lighter dark-matter constituents undergoing simple two-body decays to leptons. We also demonstrate that the Dynamical Dark Matter framework makes a fairly robust prediction that the positron fraction should level off and then remain roughly constant out to approximately 1 TeV, without experiencing any sharp downturns. Thus, if we interpret the positron excess in terms of decaying dark matter, the existence of a plateau in the positron fraction at energies less than 1 TeV may be taken as a “smoking gun” of Dynamical Dark Matter

Late decaying 2-component dark matter scenario as an explanation of the AMS-02 positron excess

Energy Technology Data Exchange (ETDEWEB)

Buch, Jatan; Ralegankar, Pranjal; Rentala, Vikram, E-mail: jatan_buch@brown.edu, E-mail: pranjal6@illinois.edu, E-mail: rentala@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology - Bombay, Powai, Mumbai 400076 (India)

2017-10-01

The long standing anomaly in the positron flux as measured by the PAMELA and AMS-02 experiments could potentially be explained by dark matter (DM) annihilations. This scenario typically requires a large 'boost factor' to be consistent with a thermal relic dark matter candidate produced via freeze-out. However, such an explanation is disfavored by constraints from CMB observations on energy deposition during the epoch of recombination. We discuss a scenario called late-decaying two-component dark matter (LD2DM), where the entire DM consists of two semi-degenerate species. Within this framework, the heavier species is produced as a thermal relic in the early universe and decays to the lighter species over cosmological timescales. Consequently, the lighter species becomes the DM which populates the universe today. We show that annihilation of the lighter DM species with an enhanced cross-section, produced via such a non-thermal mechanism, can explain the observed AMS-02 positron flux while avoiding CMB constraints. The observed DM relic density can be correctly reproduced as well with simple s -wave annihilation cross-sections. We demonstrate that the scenario is safe from CMB constraints on late-time energy depositions during the cosmic 'dark ages'. Interestingly, structure formation constraints force us to consider small mass splittings between the two dark matter species. We explore possible cosmological and particle physics signatures in a toy model that realizes this scenario.

Late decaying 2-component dark matter scenario as an explanation of the AMS-02 positron excess

International Nuclear Information System (INIS)

Buch, Jatan; Ralegankar, Pranjal; Rentala, Vikram

2017-01-01

The long standing anomaly in the positron flux as measured by the PAMELA and AMS-02 experiments could potentially be explained by dark matter (DM) annihilations. This scenario typically requires a large 'boost factor' to be consistent with a thermal relic dark matter candidate produced via freeze-out. However, such an explanation is disfavored by constraints from CMB observations on energy deposition during the epoch of recombination. We discuss a scenario called late-decaying two-component dark matter (LD2DM), where the entire DM consists of two semi-degenerate species. Within this framework, the heavier species is produced as a thermal relic in the early universe and decays to the lighter species over cosmological timescales. Consequently, the lighter species becomes the DM which populates the universe today. We show that annihilation of the lighter DM species with an enhanced cross-section, produced via such a non-thermal mechanism, can explain the observed AMS-02 positron flux while avoiding CMB constraints. The observed DM relic density can be correctly reproduced as well with simple s -wave annihilation cross-sections. We demonstrate that the scenario is safe from CMB constraints on late-time energy depositions during the cosmic 'dark ages'. Interestingly, structure formation constraints force us to consider small mass splittings between the two dark matter species. We explore possible cosmological and particle physics signatures in a toy model that realizes this scenario.

Fundamentals of positron emission tomography

International Nuclear Information System (INIS)

Ostertag, H.

1989-01-01

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

Constraining decaying dark matter with FERMI-LAT gamma rays

International Nuclear Information System (INIS)

Maccione, L.

2011-01-01

High energy electron sand positrons from decaying dark matter can produce a significant flux of gamma rays by inverse Compton of low energy photons in the interstellar radiation field. This possibility is inevitably related with the dark matter interpretation of the observed PAMELA and FERMI excesses. We will describe a simple and universal method to constrain dark matter models which produce electrons and positrons in their decay by using the FERMI-LAT gamma-ray observations in the energy range between 0.5 GeV and 300 GeV, by exploiting universal response functions that, once convolved with a specific dark matter model, produce the desired constraint. The response functions contain all the astrophysical inputs. Here is discussed the uncertainties in the determination of the response functions and apply them to place constraints on some specific dark matter decay models that can well fit the positron and electron fluxes observed by PAMELA and FERMI LAT, also taking into account prompt radiation from the dark matter decay. With the available data decaying dark matter can not be excluded as source of the PAMELA positron excess.

Matrix Isolation Spectroscopy Applied to Positron Moderatioin in Cryogenic Solids

Science.gov (United States)

2011-07-01

Current Positron Applications • 2-γ decay exploited in Positron Emission Tomography (PET) scanners. • Positrons localize & annihilate preferentially at...Air Force  Eglin Air Force Base AFRL-RW-EG-TP-2011-024 Matrix Isolation Spectroscopy Applied to Positron Moderation in Cryogenic Solids Distribution... Spectroscopy Applied to Positron Moderation in Cryogenic Solids 5a. CONTRACT NUMBER 5b. GRANT NUMBER 62602F 5c. PROGRAM ELEMENT NUMBER 6

Decaying fermionic dark matter search with CALET

Energy Technology Data Exchange (ETDEWEB)

Bhattacharyya, S.; Torii, S. [Graduate School of Advanced Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo, 169-8555 (Japan); Motz, H. [International Center for Science and Engineering Programs, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo, 169-8555 (Japan); Asaoka, Y., E-mail: saptashwab@ruri.waseda.jp, E-mail: motz@aoni.waseda.jp, E-mail: torii.shoji@waseda.jp, E-mail: yoichi.asaoka@aoni.waseda.jp [Research Institute for Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo, 169-8555 (Japan)

2017-08-01

The ISS-based CALET (CALorimetric Electron Telescope) detector can play an important role in indirect search for Dark Matter (DM), measuring the electron+positron flux in the TeV region for the first time directly. With its fine energy resolution of approximately 2% and good proton rejection ratio (1:10{sup 5}) it has the potential to search for fine structures in the Cosmic Ray (CR) electron spectrum. In this context we discuss the ability of CALET to discern between signals originating from astrophysical sources and DM decay. We fit a parametrization of the local interstellar electron and positron spectra to current measurements, with either a pulsar or 3-body decay of fermionic DM as the extra source causing the positron excess. The expected CALET data for scenarios in which DM decay explains the excess are calculated and analyzed. The signal from this particular 3-body DM decay which can explain the recent measurements from the AMS−02 experiment is shown to be distinguishable from a single pulsar source causing the positron excess by 5 years of observation with CALET, based on the shape of the spectrum. We also study the constraints from diffuse γ-ray data on this DM-only explanation of the positron excess and show that especially for the possibly remaining parameter space a clearly identifiable signature in the CR electron spectrum exists.

Positron range in PET imaging: an alternative approach for assessing and correcting the blurring

DEFF Research Database (Denmark)

Jødal, Lars; Le Loirec, Cindy; Champion, Christophe

2012-01-01

Background: Positron range impairs resolution in PET imaging, especially for high-energy emitters and for small-animal PET. De-blurring in image reconstruction is possible if the blurring distribution is known. Further, the percentage of annihilation events within a given distance from the point...... on allowed-decay isotopes. Methods: It is argued that blurring at the detection level should not be described by positron range r, but instead the 2D-projected distance δ (equal to the closest distance between decay and line-of-response). To determine these 2D distributions, results from a dedicated positron...... is important for improved resolution in PET imaging. Relevant distributions for positron range have been derived for seven isotopes. Distributions for other allowed-decay isotopes may be estimated with the above formulas....

Design of a transmission electron positron microscope

International Nuclear Information System (INIS)

Doyama, Masao; Inoue, M.; Kogure, Y.; Hayashi, Y.; Yoshii, T.; Kurihara, T.; Tsuno, K.

2003-01-01

This paper reports the plans and design of positron-electron microscopes being built at KEK (High Energy Accelerator Research Organization), Tsukuba, Japan. A used electron microscope is altered. The kinetic energies of positrons produced by accelerators or by nuclear decays are not a unique value but show a spread over in a wide range. Positron beam is guided to a transmission electron microscope (JEM100SX). Positrons are moderated by a tungsten foil, are accelerated and are focused on a nickel sheet. The monochromatic focused beam is injected into an electron microscope. The focusing and aberration of positrons are the same as electrons in a magnetic system which are used in commercial electron microscopes. Imaging plates are used to record positron images for the transmission electron microscope. (author)

Galactic signatures of decaying dark matter

International Nuclear Information System (INIS)

Zhang, Le; Sigl, Guenter

2009-05-01

If dark matter decays into electrons and positrons, it can affect Galactic radio emissions and the local cosmic ray fluxes. We propose a new, more general analysis of constraints on dark matter. The constraints can be obtained for any decaying dark matter model by convolving the specific dark matter decay spectrum with a response function. We derive this response function from full-sky radio surveys at 408 MHz, 1.42 GHz and 23 GHz, as well as from the positron flux recently reported by PAMELA. We discuss the influence of astrophysical uncertainties on the response function, such as from propagation and from the profiles of the dark matter and the Galactic magnetic field. As an application, we find that some widely used dark matter decay scenarios can be ruled out under modest assumptions. (orig.)

Galactic signatures of decaying dark matter

Energy Technology Data Exchange (ETDEWEB)

Zhang, Le; Sigl, Guenter [Hamburg Univ. (Germany). II. Inst. fuer Theoretische Physik; Redondo, Javier [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

2009-05-15

If dark matter decays into electrons and positrons, it can affect Galactic radio emissions and the local cosmic ray fluxes. We propose a new, more general analysis of constraints on dark matter. The constraints can be obtained for any decaying dark matter model by convolving the specific dark matter decay spectrum with a response function. We derive this response function from full-sky radio surveys at 408 MHz, 1.42 GHz and 23 GHz, as well as from the positron flux recently reported by PAMELA. We discuss the influence of astrophysical uncertainties on the response function, such as from propagation and from the profiles of the dark matter and the Galactic magnetic field. As an application, we find that some widely used dark matter decay scenarios can be ruled out under modest assumptions. (orig.)

Development of slow positron beam lines and applications

Science.gov (United States)

Mondal, Nagendra Nath

2018-05-01

A positron is an antiparticle of an electron that can be formed in diverse methods: natural or artificial β-decay process, fission and fusion reactions, and a pair production of electron-positron occurred in the reactor and the high energy accelerator centers. Usually a long-lifetime radio isotope is customized for the construction of a slow positron beam lines in many laboratories. The typical intensity of this beam depends upon the strength of the positron source, moderator efficiency, and guiding, pulsing, focusing and detecting systems. This article will review a few positron beam lines and their potential applications in research, especially in the Positronium Bose-Einstein Condensation.

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

Energy Technology Data Exchange (ETDEWEB)

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

2013-01-15

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

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

International Nuclear Information System (INIS)

Boyko, Olha; Shpotyuk, Yaroslav; Filipecki, Jacek

2013-01-01

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

The MEG positron spectrometer

International Nuclear Information System (INIS)

Nishiguchi, Hajime

2007-01-01

We have been developing an innovative spectrometer for the MEG experiment at the Paul Scherrer Institute (PSI) in Switzerland. This experiment searches for a lepton flavour violating decay μ + →e + γ with a sensitivity of 10 -13 in order to explore the region predicted by supersymmetric extensions of the standard model. The MEG positron spectrometer consists of a specially designed superconducting solenoidal magnet with a highly graded field, an ultimate low-mass drift chamber system, and a precise time measuring counter system. This innovative positron spectrometer is described here focusing on the drift chamber system

Constraining decaying dark matter with Fermi LAT gamma-rays

International Nuclear Information System (INIS)

Zhang, Le; Sigl, Günter; Weniger, Christoph; Maccione, Luca; Redondo, Javier

2010-01-01

High energy electrons and positrons from decaying dark matter can produce a significant flux of gamma rays by inverse Compton off low energy photons in the interstellar radiation field. This possibility is inevitably related with the dark matter interpretation of the observed PAMELA and FERMI excesses. The aim of this paper is providing a simple and universal method to constrain dark matter models which produce electrons and positrons in their decay by using the Fermi LAT gamma-ray observations in the energy range between 0.5 GeV and 300 GeV. We provide a set of universal response functions that, once convolved with a specific dark matter model produce the desired constraints. Our response functions contain all the astrophysical inputs such as the electron propagation in the galaxy, the dark matter profile, the gamma-ray fluxes of known origin, and the Fermi LAT data. We study the uncertainties in the determination of the response functions and apply them to place constraints on some specific dark matter decay models that can well fit the positron and electron fluxes observed by PAMELA and Fermi LAT. To this end we also take into account prompt radiation from the dark matter decay. We find that with the available data decaying dark matter cannot be excluded as source of the PAMELA positron excess

Decaying dark matter in light of the PAMELA and Fermi LAT data

International Nuclear Information System (INIS)

Ibarra, Alejandro; Tran, David

2009-06-01

A series of experiments measuring high-energy cosmic rays have recently reported strong indications for the existence of an exotic source of high-energy electrons and positrons. If interpreted in terms of the decay of dark matter particles, the PAMELA measurements of the positron fraction and the Fermi LAT measurements of the total electron plus positron flux restrict the possible decaying dark matter scenarios to a few cases. Pursuing a model-independent approach, we identify some promising scenarios of dark matter decay and calculate the predictions for the diffuse extragalactic gamma-ray flux, including the contributions from inverse Compton scattering with the interstellar radiation field. (orig.)

Positron production in heavy ion-atom collisions

International Nuclear Information System (INIS)

Kienle, P.

1985-08-01

Following an introduction into the concept of an atom with an overcritical field, established by a nucleus with a charge larger than 173, the spontaneous positron emission from such an atom with an 1s binding energy exceeding 2mc 2 is presented. Such a process, in which an electron is bound and a monoenergetic positron emitted turns the neutral into a charged vacuum. In a U-U di-nuclear system (Z=184) the spontaneous positron emission proceeds with an energy of about 300 keV corresponding to a decay time of 3x10 -19 sec. (orig./WL)

Positronic complexes with unnatural parity

International Nuclear Information System (INIS)

Bromley, M. W. J.; Mitroy, J.; Varga, K.

2007-01-01

The structure of the unnatural parity states of PsH, LiPs, NaPs, and KPs are investigated with the configuration interaction and stochastic variational methods. The binding energies (in hartree) are found to be 8.17x10 -4 , 4.42x10 -4 , 15.14x10 -4 , and 21.80x10 -4 , respectively. These states are constructed by first coupling the two electrons into a configuration which is predominantly 3 P e , and then adding a p-wave positron. All the active particles are in states in which the relative angular momentum between any pair of particles is at least L=1. The LiPs state is Borromean since there are no three-body bound subsystems (of the correct symmetry) of the (Li + , e - , e - , e + ) particles that make up the system. The dominant decay mode of these states will be radiative decay into a configuration that autoionizes or undergoes positron annihilation

Beta spectra. II-Positron spectra

International Nuclear Information System (INIS)

Grau, A.; Garcia-Torano, E.

1981-01-01

Using the Fermi theory of beta decay, the beta spectra for 30 positron emitters have been computed, introducing a correction factor for unique forbidden transitions. The spectra are ploted vs. energy, once normalised, and tabulated with the related Fermi functions. The average and median energies are calculated. (author)

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

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)

Positron range in PET imaging: an alternative approach for assessing and correcting the blurring

Science.gov (United States)

Jødal, L.; Le Loirec, C.; Champion, C.

2012-06-01

Positron range impairs resolution in PET imaging, especially for high-energy emitters and for small-animal PET. De-blurring in image reconstruction is possible if the blurring distribution is known. Furthermore, the percentage of annihilation events within a given distance from the point of positron emission is relevant for assessing statistical noise. This paper aims to determine the positron range distribution relevant for blurring for seven medically relevant PET isotopes, 18F, 11C, 13N, 15O, 68Ga, 62Cu and 82Rb, and derive empirical formulas for the distributions. This paper focuses on allowed-decay isotopes. It is argued that blurring at the detection level should not be described by the positron range r, but instead the 2D projected distance δ (equal to the closest distance between decay and line of response). To determine these 2D distributions, results from a dedicated positron track-structure Monte Carlo code, Electron and POsitron TRANsport (EPOTRAN), were used. Materials other than water were studied with PENELOPE. The radial cumulative probability distribution G2D(δ) and the radial probability density distribution g2D(δ) were determined. G2D(δ) could be approximated by the empirical function 1 - exp(-Aδ2 - Bδ), where A = 0.0266 (Emean)-1.716 and B = 0.1119 (Emean)-1.934, with Emean being the mean positron energy in MeV and δ in mm. The radial density distribution g2D(δ) could be approximated by differentiation of G2D(δ). Distributions in other media were very similar to water. The positron range is important for improved resolution in PET imaging. Relevant distributions for the positron range have been derived for seven isotopes. Distributions for other allowed-decay isotopes may be estimated with the above formulas.

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

ALEPH: Decay of Z0 to two jets

CERN Multimedia

1991-01-01

This track is an example of real data collected from the ALEPH detector on the Large Electron-Positron (LEP) collider at CERN. Here a Z0 particle is produced in the collision between an electron and positron, which then decays into a quark-antiquark pair. The quark pair is seen as a pair of hadron jets in the detector.

Positrons and positronium in grainy and porous solids

International Nuclear Information System (INIS)

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

2001-01-01

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

Decay of the vacuum in heavy ion collisions

International Nuclear Information System (INIS)

Mueller, B.

1984-10-01

The neutral electron-positron vacuum state becomes unstable in very strong electric fields of nuclei with Z>173 and decays into a charged vacuum by spontaneous positron emission. Such giant nuclear systems can be formed in collisions of very heavy ions (U+U, U+Cm, etc.) for a period of 10 -20 s or more. Recent experimental results revealing line structures in the positron spectra observed in these collisions are discussed and their implications for quantum electrodynamics and nuclear physics are pointed out. (orig.)

ALEPH: Decay of Z0 to two jets

CERN Multimedia

1991-01-01

This track is an example of real data collected from the ALEPH detector on the Large Electron-Positron (LEP) collider at CERN, which ran between 1989 and 2000. Here a Z0 particle in the collision between an electron and positron, which then decays into a quark-antiquark pair. The quark pair is seen as a pair of hadron jets in the detector.

Basic principles of 18F-fluoro-deoxyglucose positron emission tomography

International Nuclear Information System (INIS)

Standke, R.

2002-01-01

Positron emission tomography uses photons to receive regional information about dynamic, physiologic, and biochemical processes in the living body. A positron decay is measured indirectly by the simultaneous registration of both gamma rays created by the annihilation. The event is counted, if two directly opposite located detectors register gamma rays in coincidence. Unfortunately the detectors of a positron emission tomography system do not register only true coincident events. There are also scattered and random coincidences. Different types of positron tomographs are presented and scintillation crystals, which are in use for positron emission tomography are discussed. The 2D- and 3D-acquisition methods are described as well as preprocessing methods, such as correction for attenuation, scatter and dead time. For quantification the relative parameter standard uptake value (SUV) is explained. Finally hybrid systems, such as combined positron emission tomography/computed tomography scanners and the use of computed tomography data for attenuation correction are introduced. (author)

Development of a cone-geometry positron moderator

International Nuclear Information System (INIS)

Lynn, K.G.; Gramsch, E.; Usmar, S.G.; Sferlazzo, P.

1989-01-01

Results are presented on a new cone-shaped positron moderator which shows a high moderator efficiency (i.e., conversion of beta decay to emitted slow positrons). The moderator efficiencies for the cone moderators studied were found to be up to 0.14% compared to thin-foil measurements of 0.06% in the same experimental system including identical source and holder. These moderators are rugged and easily fabricated, however, they have a lower brightness than single-crystal foil moderators. Comparison of various geometries is presented as well as suggestions for further improvements to increase the total efficiencies

Time reversal violation in radiative beta decay: experimental plans

Science.gov (United States)

Behr, J. A.; McNeil, J.; Anholm, M.; Gorelov, A.; Melconian, D.; Ashery, D.

2017-01-01

Some explanations for the excess of matter over antimatter in the universe involve sources of time reversal violation (TRV) in addition to the one known in the standard model of particle physics. We plan to search for TRV in a correlation between the momenta of the beta, neutrino, and the radiative gamma sometimes emitted in nuclear beta decay. Correlations involving three (out of four) momenta are sensitive at lowest order to different TRV physics than observables involving spin, such as electric dipole moments and spin-polarized beta decay correlations. Such experiments have been done in radiative kaon decay, but not in systems involving the lightest generation of quarks. An explicit low-energy physics model being tested produces TRV effects in the Fermi beta decay of the neutron, tritium, or some positron-decaying isotopes. We will present plans to measure the TRV asymmetry in radiative beta decay of laser-trapped 38mK at better than 0.01 sensitivity, including suppression of background from positron annihilation. Supported by NSERC, D.O.E., Israel Science Foundation. TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada.

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.)

Decaying dark matter in supersymmetric SU(5) models

International Nuclear Information System (INIS)

Luo Mingxing; Wang Liucheng; Wu Wei; Zhu Guohuai

2010-01-01

Motivated by recent observations from PAMELA, Fermi and H.E.S.S., we consider dark matter decays in the framework of supersymmetric SU(5) grand unification theories. An SU(5) singlet S is assumed to be the main component of dark matters, which decays into visible particles through dimension six operators suppressed by the grand unification scale. Under certain conditions, S decays dominantly into a pair of sleptons with universal coupling for all generations. Subsequently, electrons and positrons are produced from cascade decays of these sleptons. These cascade decay chains smooth the e + +e - spectrum, which permit naturally a good fit to the Fermi-LAT data. The observed positron fraction upturn by PAMELA can be reproduced simultaneously. We have also calculated diffuse gamma-ray spectra due to the e ± excesses and compared them with the preliminary Fermi-LAT data from 0.1 GeV to 10 GeV in the region 0 deg. ≤l≤ 360 deg., 10 deg. ≤|b|≤20 deg. The photon spectrum of energy above 100 GeV, mainly from final state radiations, may be checked in the near future.

High-resolution positron Q-value measurements and nuclear-structure studies far from the stability line. Progress report

International Nuclear Information System (INIS)

Avignone, F.T. III.

1981-01-01

Extensive data analysis and theoretical analysis has been done to complete the extensive decay scheme investigation of 206 208 Fr and the level structures of 206 208 Rn. A final version of a journal article is presented in preprint form. Extensive Monte Carlo calculations have been made to correct the end point energies of positron spectra taken with intrinsic Ge detectors for annihilation radiation interferences. These calculations were tested using the decay of 82 Sr which has previously measured positron branches. This technique was applied to the positron spectra collected at the on-line UNISOR isotope separator. The reactions used were 60 Ni( 20 Ne;p2n) 77 Rb and 60 Ni( 20 Ne;pn) 78 Rb. Values for 5, γ-β + coincidence positron end point energies are given for the decay of 77 Rb. The implied Q-value is 5.075 +- 0.010 MeV. A complete paper on the calculated corrections is presented. A flow chart of a more complete program which accounts for positrons scattering out of the detector and for bremsstralung radiation is also presented. End-point energies of four β + branches in 77 Rb are given as well as a proposed energy level scheme of 75 Kr based on γ-γ coincidence data taken at UNISOR

ALEPH: Decay of Z0 to two jets

CERN Multimedia

1991-01-01

This track is an example of real data collected from the ALEPH detector on the Large Electron-Positron (LEP) collider at CERN, which ran between 1989 and 2000. Here a Z0 particle is produced in the collision between an electron and positron, which then decays into a quark-antiquark pair. The quark pair is seen as a pair of hadron jets in the detector.

OPAL: Decay of Z0 to two jets

CERN Multimedia

1990-01-01

This track is an example of real data collected from the OPAL detector on the Large Electron-Positron (LEP) collider at CERN, which ran between 1989 and 2000. Here a Z0 particle is produced in the collision between an electron and positron that then decays into a quark-antiquark pair. The quark pair is seen as a pair of hadron jets in the detector.

OPAL: Decay of Z0 to three jets

CERN Multimedia

1990-01-01

This track is an example of real data collected from the OPAL detector on the Large Electron-Positron (LEP) collider at CERN, which ran between 1989 and 2000. A Z0 particle is produced in the electron-positron collision which decays into a quark and an antiquark, one of which emits a gluon. Both quarks and gluons appear in the detector as jets of hadrons.

Mass of decaying wino from AMS-02 2014

Energy Technology Data Exchange (ETDEWEB)

Ibe, Masahiro [Tokyo Univ. (Japan). Inst. for Cosmic Ray Research; Univ. Tokyo (Japan). Kavli Inst. for the Physics and Mathematics of the Universe; Matsumoto, Shigeki; Yanagida, Tsutomu T. [Univ. Tokyo (Japan). Kavli Inst. for the Physics and Mathematics of the Universe; Shirai, Satoshi [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

2014-09-15

We revisit the decaying wino dark matter scenario in the light of the updated positron fraction, electron and positron fluxes in cosmic ray recently reported by the AMS-02 collaboration. We show the AMS-02 results favor the mass of the wino dark matter at around a few TeV, which is consistent with the prediction on the wino mass in the pure gravity mediation model.

Mass of decaying wino from AMS-02 2014

Energy Technology Data Exchange (ETDEWEB)

Ibe, Masahiro, E-mail: ibe@icrr.u-tokyo.ac.jp [Institute for Cosmic Ray Research (ICRR), Theory Group, University of Tokyo, Kashiwa, Chiba 277-8568 (Japan); Kavli Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, Kashiwa, Chiba 277-8568 (Japan); Matsumoto, Shigeki [Kavli Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, Kashiwa, Chiba 277-8568 (Japan); Shirai, Satoshi [Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg (Germany); Yanagida, Tsutomu T. [Kavli Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, Kashiwa, Chiba 277-8568 (Japan)

2015-02-04

We revisit the decaying wino dark matter scenario in the light of the updated positron fraction, electron and positron fluxes in cosmic ray recently reported by the AMS-02 collaboration. We show the AMS-02 results favor the mass of the wino dark matter at around a few TeV, which is consistent with the prediction on the wino mass in the pure gravity mediation model.

Mass of decaying wino from AMS-02 2014

International Nuclear Information System (INIS)

Ibe, Masahiro

2014-09-01

We revisit the decaying wino dark matter scenario in the light of the updated positron fraction, electron and positron fluxes in cosmic ray recently reported by the AMS-02 collaboration. We show the AMS-02 results favor the mass of the wino dark matter at around a few TeV, which is consistent with the prediction on the wino mass in the pure gravity mediation model.

Positron imaging in the evaluation of ischemia and myocardial infarction

International Nuclear Information System (INIS)

Goldstein, R.A.

1985-01-01

Positron emission tomography (PET) is a unique imaging approach since it allows quantification of regional myocardial radioactivity by virtue of its decay characteristics. Studies of regional myocardial metabolism are possible since there are positron emitting isotopes of carbon, oxygen and nitrogen that can be used to synthesize labeled fatty acids, amino acids or carbohydrate. Recent studies from the author's group have focused on Rb-82, a diffusible cation with a short half-life that is obtained from a generator and thus, has the potential for routine clinical use without a cyclotron. In this chapter, the basic principles of positron imaging and their application to imaging of acute myocardial infarction are discussed

Cosmic Ray Electron and Positron Excesses from a Fourth Generation Heavy Majorana Neutrino

DEFF Research Database (Denmark)

Masina, Isabella; Sannino, Francesco

2011-01-01

and positrons originated in the heavy Majorana neutrino decay modes, also including polarization effects. We then compare the prediction of this model with the experimental data, exploiting both the standard direct method and our recently proposed Sum Rules method. We find that the decay modes involving the tau...

Scintillators for positron emission tomography

International Nuclear Information System (INIS)

Moses, W.W.; Derenzo, S.E.

1995-09-01

Like most applications that utilize scintillators for gamma detection, Positron Emission Tomography (PET) desires materials with high light output, short decay time, and excellent stopping power that are also inexpensive, mechanically rugged, and chemically inert. Realizing that this ''ultimate'' scintillator may not exist, this paper evaluates the relative importance of these qualities and describes their impact on the imaging performance of PET. The most important PET scintillator quality is the ability to absorb 511 keV photons in a small volume, which affects the spatial resolution of the camera. The dominant factor is a short attenuation length (≤ 1.5 cm is required), although a high photoelectric fraction is also important (> 30% is desired). The next most important quality is a short decay time, which affects both the dead time and the coincidence timing resolution. Detection rates for single 511 keV photons can be extremely high, so decay times ≤ 500 ns are essential to avoid dead time losses. In addition, positron annihilations are identified by time coincidence so ≤5 ns fwhm coincidence pair timing resolution is required to identify events with narrow coincidence windows, reducing contamination due to accidental coincidences. Current trends in PET cameras are toward septaless, ''fully-3D'' cameras, which have significantly higher count rates than conventional 2-D cameras and so place higher demands on scintillator decay time. Light output affects energy resolution, and thus the ability of the camera to identify and reject events where the initial 511 keV photon has undergone Compton scatter in the patient. The scatter to true event fraction is much higher in fully-3D cameras than in 2-D cameras, so future PET cameras would benefit from scintillators with a 511 keV energy resolution < 10--12% fwhm

Beta-decay of 56Cu

International Nuclear Information System (INIS)

Ramdhane, M.; Baumann, P.; Knipper, A.; Walter, G.; Janas, Z.; Plochocki, A.; Liu, W.; Grawe, H.; Hu, Z.; Kirchner, R.; Klepper, O.; Roeckl, E.; Gorska, M.; Fujita, Y.; Brown, B.A.

1998-02-01

By measuring positrons and β-delayed γ-rays emitted from mass-separated sources, the decay of 56 Cu(4 + ,T z =-1,T=1) to states in the doubly-magic nucleus 56 Ni was studied for the first time. The half-life of 56 Cu was measured to be 78(15) ms, and four β-delayed γ-rays were assigned to its decay. The resulting experimental data on Fermi and Gamow-Teller strength are compared with shell-model predictions. (orig.)

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

Science.gov (United States)

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

2017-12-01

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

Cosmic Ray Signatures of Decaying Dark Matter

International Nuclear Information System (INIS)

Ibarra, Alejandro

2011-01-01

Astrophysical and cosmological observations do not require the dark matter particles to be absolutely stable. If they are indeed unstable, their decay into Standard Model particles might occur at a sufficiently large rate to allow the indirect detection of dark matter through an anomalous contribution to the high energy cosmic ray fluxes. We analyze the implications of the excess in the total electron plus positron flux and the positron fraction reported by the Fermi and PAMELA collaborations, respectively, for the scenario of decaying dark matter. We also discuss the constraints on this scenario from measurements of other cosmic ray species and the predictions for the diffuse gamma ray flux and the neutrino flux. In particular, we expect a sizable dipole-like anisotropy which may be observed in the near future by the Fermi-LAT.

The MAJORANA Experiment

Energy Technology Data Exchange (ETDEWEB)

Aguayo Navarrete, Estanislao; Avignone, F. T.; Back, Henning O.; Barabash, Alexander S.; Bergevin, M.; Bertrand, F.; Boswell, M.; Brudanin, V.; Busch, Matthew; Chan, Yuen-Dat; Christofferson, Cabot-Ann; Collar, J. I.; Combs, Dustin C.; Cooper, R. J.; Detwiler, Jason A.; Doe, Peter J.; Efremenko, Yuri; Egorov, Viatcheslav; Ejiri, H.; Elliott, Steven R.; Esterline, James H.; Fast, James E.; Fields, N.; Finnerty, P.; Fraenkle, Florian; Gehman, Victor M.; Giovanetti, G. K.; Green, Matthew P.; Guiseppe, Vincente; Gusey, K.; Hallin, A. L.; Hazama, R.; Henning, R.; Hime, Andrew; Hoppe, Eric W.; Horton, Mark; Howard, Stanley; Howe, M. A.; Johnson, R. A.; Keeter, K.; Keillor, Martin E.; Keller, C.; Kephart, Jeremy D.; Kidd, Mary; Knecht, A.; Kochetov, Oleg; Konovalov, S.; Kouzes, Richard T.; LaFerriere, Brian D.; LaRoque, B. H.; Leon, Jonathan D.; Leviner, L.; Loach, J. C.; MacMullin, S.; Marino, Michael G.; Martin, R. D.; Mei, Dong-Ming; Merriman, Jason H.; Miller, M. L.; Mizouni, Leila; Nomachi, Masaharu; Orrell, John L.; Overman, Nicole R.; Phillips, D.; Poon, Alan; Perumpilly, Gopakumar; Prior, Gersende; Radford, D. C.; Rielage, Keith; Robertson, R. G. H.; Ronquest, M. C.; Schubert, Alexis G.; Shima, T.; Shirchenko, M.; Snavely, Kyle J.; Sobolev, V.; Steele, David; Strain, J.; Thomas, K.; Timkin, V.; Tornow, W.; Vanyushin, I.; Varner, R. L.; Vetter, Kai; Vorren, Kris R.; Wilkerson, John; Wolfe, B. A.; Yakushev, E.; Young, A.; Yu, Chang-Hong; Yumatov, Vladimir; Zhang, C.

2011-10-01

The Majorana collaboration is actively pursuing research and development aimed at a tonne-scale {sup 76}Ge neutrinoless double-beta decay ({beta}{beta}(0{nu})-decay) experiment. The current, primary focus is the construction of the Majorana Demonstrator experiment, an R and D effort that will field approximately 40 kg of germanium detectors with mixed enrichment levels. This article provides a status update on the construction of the Demonstrator.

On the cosmic-ray spectra of three-body lepton-flavor-violating dark matter decays

International Nuclear Information System (INIS)

Carone, Christopher D.; Cukierman, Ari; Primulando, Reinard

2011-01-01

We consider possible leptonic three-body decays of spin-1/2, charge-asymmetric dark matter. Assuming a general Dirac structure for the four-fermion contact interactions of interest, we study the cosmic-ray electron and positron spectra and show that good fits to the current data can be obtained for both charged-lepton-flavor-conserving and flavor-violating decay channels. We find that different choices for the Dirac structure of the underlying decay operator can be significantly compensated by different choices for the dark matter mass and lifetime. The decay modes we consider provide differing predictions for the cosmic-ray positron fraction at energies higher than those currently probed at the PAMELA experiment; these predictions might be tested at cosmic-ray detectors like AMS-02.

Positron emission tomography: a new paradigm in cancer management

International Nuclear Information System (INIS)

Paez Gutierrez, Diana Isabel; De los Reyes, Amelia; Llamas Olier, Augusto

2007-01-01

The National Cancer Institute (NCI) is currently building a positron emission tomography facility that will house a cyclotron and a PET fusion scanner. lt should be operational as of december 2007, being a cancer dedicated national referral center, the NCI should provide both positron-emitting radiopharmaceuticals and medical services to institutions and patients nationwide. PET technology provides metabolic information that has been documented to be useful in patient care. The properties of positron decay allow accurate imaging of the in vivo distribution of positron-emitting radiopharmaceuticals. a wide array of positron-emitting radiopharmaceuticals has been used to characterize multiple physiologic and pathologic states. The major clinical PET applications are in cancer patients using fluorine-18 fluorodeoxyglucose (FDG). FDG, an analogue of glucose, accumulates in most tumors in a greater amount than it does in normal tissue. PET is being used in diagnosis and follow-up of several malignancies, and the list of articles supporting its use continues to grow. in this article, the instrumentation aspects of PET are described and most of the clinical applications in oncology are described

Suppressing proton decay in theories with localised fermions

International Nuclear Information System (INIS)

Acharya, B.S.; Valandro, R.

2005-12-01

We calculate the contribution to the proton decay amplitude from Kaluza-Klein lepto-quarks in theories with extra dimensions, localised fermions and gauge fields which propagate in the bulk. Such models naturally occur within the context of M theory. In SU(5) models we show that carefully including all such modes gives a distinctive pattern of decays through various channels including a strong suppression of decays into neutrinos or right handed positrons. By contrast there is no such suppression for SO(10). (author)

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

Micropolyelectrons as possible sources of the anomalous positron peaks in heavy-ion reactions

International Nuclear Information System (INIS)

Wong, Cheuk-Yin.

1988-01-01

We propose that aggregates of electrons and positrons in a small assembly [micropolyelectrons (e + e - ) n ], held together by their own electromagnetic interactions, are probably the sources of the anomalous positron peaks observed in heavy-ion reactions. The quasistability of the micropolyelectrons arises from a strong noncentral, short-range, attractive interaction between an electron and a positron in their 0 ++ state, which may be supercritical and may lead to a condensation of such pairs. These entities are strongly attracted to a nucleus with a large charge, due to the quadratic Coulomb interaction between the nucleus and the constituents, and may therefore have binding energies greater than their rest masses to render them spontaneously produced in a strong Coulomb field. Final-state interactions between the produced micropolyelectrons and the receding nuclei may lead to their being nearly at rest and back-to-back decay into e + and e - in some cases, and their being captured into stationary orbits and asymmetrical decay in some other cases

Constraints on decaying dark matter from the extragalactic gamma-ray background

International Nuclear Information System (INIS)

Ando, Shin'ichiro

2015-02-01

If dark matter is unstable and the mass is within GeV-TeV regime, its decays produce high-energy photons that give contribution to the extragalactic gamma-ray background (EGRB). We constrain dark matter decay by analyzing the 50-month EGRB data measured with Fermi satellite, for different decay channels motivated with several supersymmetric scenarios featuring R-parity violation. We adopt the latest astrophysical models for various source classes such as active galactic nuclei and star-forming galaxies, and take associated uncertainties properly into account. The lower limits for the lifetime are very stringent for a wide range of dark matter mass, excluding the lifetime shorter than 10 28 s for mass between a few hundred GeV and ∝1TeV, e.g., for b anti b decay channel. Furthermore, most dark matter models that explain the anomalous positron excess are also excluded. These constraints are robust, being little dependent on astrophysical uncertainties, unlike other probes such as Galactic positrons or anti-protons.

Alternative positron emission tomography with non-conventional positron emitters: effects of their physical properties on image quality and potential clinical applications

International Nuclear Information System (INIS)

Pagani, M.; Stone-Elander, S.; Larsson, S.A.

1997-01-01

The increasing amount of clinically relevant information obtained by positron emission tomography (PET), primarily with fluorine-18 labelled 2-deoxy-2-fluoro-d-glucose, has generated a demand for new routes for the widespread and cost-efficient use of positron-emitting radiopharmaceuticals. New dual-head single-photon emission tomography (SPET) cameras are being developed which offer coincidence detection with camera heads lacking a collimator or SPET imaging with specially designed collimators and additional photon shielding. Thus, not only satellite PET imaging units but also nuclear medicine units investing in these new SPET/PET systems need to examine all available alternatives for rational radionuclide supplies from host cyclotrons. This article examines 25 ''alternative'' positron-emitting radionuclides, discusses the impact of their decay properties on image quality and reviews methods for their production as well as for their application in imaging techniques. (orig.)

Neutrino signals from dark matter decay

International Nuclear Information System (INIS)

Covi, Laura; Grefe, Michael; Ibarra, Alejandro; Tran, David

2009-12-01

We investigate different neutrino signals from the decay of dark matter particles to determine the prospects for their detection, and more specifically if any spectral signature can be disentangled from the background in present and future neutrino observatories. If detected, such a signal could bring an independent confirmation of the dark matter interpretation of the dramatic rise in the positron fraction above 10 GeV recently observed by the PAMELA satellite experiment and offer the possibility of distinguishing between astrophysical sources and dark matter decay or annihilation. In combination with other signals, it may also be possible to distinguish among different dark matter decay channels. (orig.)

Neutrino signals from dark matter decay

Energy Technology Data Exchange (ETDEWEB)

Covi, Laura; Grefe, Michael [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Ibarra, Alejandro; Tran, David [Technische Univ. Muenchen, Garching (Germany). Physik-Department T30d

2009-12-15

We investigate different neutrino signals from the decay of dark matter particles to determine the prospects for their detection, and more specifically if any spectral signature can be disentangled from the background in present and future neutrino observatories. If detected, such a signal could bring an independent confirmation of the dark matter interpretation of the dramatic rise in the positron fraction above 10 GeV recently observed by the PAMELA satellite experiment and offer the possibility of distinguishing between astrophysical sources and dark matter decay or annihilation. In combination with other signals, it may also be possible to distinguish among different dark matter decay channels. (orig.)

The stationary non-equilibrium plasma of cosmic-ray electrons and positrons

Science.gov (United States)

Tomaschitz, Roman

2016-06-01

The statistical properties of the two-component plasma of cosmic-ray electrons and positrons measured by the AMS-02 experiment on the International Space Station and the HESS array of imaging atmospheric Cherenkov telescopes are analyzed. Stationary non-equilibrium distributions defining the relativistic electron-positron plasma are derived semi-empirically by performing spectral fits to the flux data and reconstructing the spectral number densities of the electronic and positronic components in phase space. These distributions are relativistic power-law densities with exponential cutoff, admitting an extensive entropy variable and converging to the Maxwell-Boltzmann or Fermi-Dirac distributions in the non-relativistic limit. Cosmic-ray electrons and positrons constitute a classical (low-density high-temperature) plasma due to the low fugacity in the quantized partition function. The positron fraction is assembled from the flux densities inferred from least-squares fits to the electron and positron spectra and is subjected to test by comparing with the AMS-02 flux ratio measured in the GeV interval. The calculated positron fraction extends to TeV energies, predicting a broad spectral peak at about 1 TeV followed by exponential decay.

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

International Nuclear Information System (INIS)

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

1982-01-01

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

The MEG detector for {mu} {sup +}{yields}e{sup +} {gamma} decay search

Energy Technology Data Exchange (ETDEWEB)

Adam, J.; Schneebeli, M. [Paul Scherrer Institut PSI, Villigen (Switzerland); Swiss Federal Institute of Technology ETH, Zurich (Switzerland); Bai, X.; Fujii, Y.; Hisamatsu, Y.; Iwamoto, T.; Kaneko, D.; Mori, T.; Natori, H.; Nishimura, Y.; Ootani, W.; Ozone, K.; Sawada, R.; Yamashita, S. [University of Tokyo 7-3-1 Hongo, ICEPP, Bunkyo-ku, Tokyo (Japan); Baldini, A.M.; Cerri, C.; Del Frate, L.; Galeotti, S.; Grassi, M.; Morsani, F.; Raffaelli, F.; Sergiampietri, F.; Signorelli, G. [INFN Sezione di Pisa, Pisa (Italy); Baracchini, E. [University of Tokyo 7-3-1 Hongo, ICEPP, Bunkyo-ku, Tokyo (Japan); University of California, Irvine, CA (United States); KEK, High Energy Accelerator Research Organization, Tsukuba, Ibaraki (Japan); Bemporad, C.; Cei, F.; Corbo, M.; Curalli, N.; Gallucci, G.; Nicolo, D.; Pazzi, R.; Tenchini, F. [INFN Sezione di Pisa, Pisa (Italy); Universita di Pisa, Dipartimento di Fisica, Pisa (Italy); Boca, G.; De Bari, A.; Nardo, R. [INFN Sezione di Pavia, Pavia (Italy); Universita di Pavia, Dipartimento di Fisica, Pavia (Italy); Cattaneo, P.W.; Rossella, M. [INFN Sezione di Pavia, Pavia (Italy); Cavoto, G.; Graziosi, A.; Piredda, G.; Voena, C.; Zanello, D. [INFN Sezione di Roma, Rome (Italy); De Gerone, M. [Paul Scherrer Institut PSI, Villigen (Switzerland); INFN Sezione di Roma, Rome (Italy); Universita di Roma ' ' Sapienza' ' , Dipartimento di Fisica, Rome (Italy); INFN Sezione di Genova, Genoa (Italy); Universita degli Studi di Genova, Dipartimento di Fisica, Genoa (Italy); Doke, S.; Suzuki, S. [Waseda University, Research Institute for Science and Engineering, Shinjuku-ku, Tokyo (Japan); Dussoni, S. [INFN Sezione di Pisa, Pisa (Italy); Universita di Pisa, Dipartimento di Fisica, Pisa (Italy); INFN Sezione di Genova, Genoa (Italy); Universita degli Studi di Genova, Dipartimento di Fisica, Genoa (Italy); Egger, J.; Hildebrandt, M.; Kettle, P.R.; Kiselev, O.; Ritt, S. [Paul Scherrer Institut PSI, Villigen (Switzerland); Fratini, K.; Gatti, F.; Valle, R. [INFN Sezione di Genova, Genoa (Italy); Universita degli Studi di Genova, Dipartimento di Fisica, Genoa (Italy); Galli, L.; Papa, A. [Paul Scherrer Institut PSI, Villigen (Switzerland); INFN Sezione di Pisa, Pisa (Italy); Universita di Pisa, Dipartimento di Fisica, Pisa (Italy); Golden, B.; Lim, G.; Molzon, W.; Topchyan, C.; Xiao, F. [University of California, Irvine, CA (United States); Grigoriev, D.N. [Budker Institute of Nuclear Physics of Siberian Branch of Russian Academy of Sciences, Novosibirsk (Russian Federation); Novosibirsk State Technical University, Novosibirsk (Russian Federation); Haruyama, T.; Kasami, K.; Maki, A.; Mihara, S.; Nishiguchi, H.; Yamada, S.; Yamamoto, S. [KEK, High Energy Accelerator Research Organization, Tsukuba, Ibaraki (Japan); Ignatov, F.; Khazin, B.I.; Popov, A.; Yudin, Yu.V. [Budker Institute of Nuclear Physics of Siberian Branch of Russian Academy of Sciences, Novosibirsk (Russian Federation); Korenchenko, A.; Kravchuk, N.; Mzavia, D. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Panareo, M. [INFN Sezione di Lecce, Lecce (Italy); Universita del Salento, Dipartimento di Matematica e Fisica, Lecce (Italy); Renga, F. [Paul Scherrer Institut PSI, Villigen (Switzerland); INFN Sezione di Roma, Rome (Italy); Universita di Roma ' ' Sapienza' ' , Dipartimento di Fisica, Rome (Italy); Ripiccini, E. [INFN Sezione di Roma, Rome (Italy); Universita di Roma ' ' Sapienza' ' , Dipartimento di Fisica, Rome (Italy); Uchiyama, Y. [Paul Scherrer Institut PSI, Villigen (Switzerland); University of Tokyo 7-3-1 Hongo, ICEPP, Bunkyo-ku, Tokyo (Japan)

2013-04-15

The MEG (Mu to Electron Gamma) experiment has been running at the Paul Scherrer Institut (PSI), Switzerland since 2008 to search for the decay {mu} {sup +}{yields}e{sup +} {gamma} by using one of the most intense continuous {mu} {sup +} beams in the world. This paper presents the MEG components: the positron spectrometer, including a thin target, a superconducting magnet, a set of drift chambers for measuring the muon decay vertex and the positron momentum, a timing counter for measuring the positron time, and a liquid xenon detector for measuring the photon energy, position and time. The trigger system, the read-out electronics and the data acquisition system are also presented in detail. The paper is completed with a description of the equipment and techniques developed for the calibration in time and energy and the simulation of the whole apparatus. (orig.)

Beta-decay of {sup 56}Cu

Energy Technology Data Exchange (ETDEWEB)

Ramdhane, M.; Baumann, P.; Knipper, A.; Walter, G. [Institute de Recherches Subatomiques, 67 - Strasbourg (France); Janas, Z.; Plochocki, A. [Warsaw Univ. (Poland). Inst. of Experimental Physics; Aeystoe, J.; Dendooven, P.; Jokinen, A.; Oinonen, M.; Pentilae, H. [Jyvaeskylae Univ. (Finland); Liu, W.; Grawe, H.; Hu, Z.; Kirchner, R.; Klepper, O.; Roeckl, E. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Gorska, M. [Warsaw Univ. (Poland). Inst. of Experimental Physics]|[Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Fujita, Y. [Osaka Univ. (Japan); Brown, B.A. [Michigan State Univ., East Lansing, MI (United States)

1998-02-01

By measuring positrons and {beta}-delayed {gamma}-rays emitted from mass-separated sources, the decay of {sup 56}Cu(4{sup +},T{sub z}=-1,T=1) to states in the doubly-magic nucleus {sup 56}Ni was studied for the first time. The half-life of {sup 56}Cu was measured to be 78(15) ms, and four {beta}-delayed {gamma}-rays were assigned to its decay. The resulting experimental data on Fermi and Gamow-Teller strength are compared with shell-model predictions. (orig.)

Decaying Dark Atom Constituents and Cosmic Positron Excess

DEFF Research Database (Denmark)

Belotsky, K.; Khlopov, M.; Kouvaris, C.

2014-01-01

We present a scenario where dark matter is in the form of dark atoms that can accommodate the experimentally observed excess of positrons in PAMELA and AMS-02 while being compatible with the constraints imposed on the gamma-ray ux from Fermi/LAT. This scenario assumes that the dominant component...... of dark matter is in the form of a bound state between a helium nucleus and a -2 particle and a small component is in the form of a WIMP-like dark atom compatible with direct searches in underground detectors. One of the constituents of this WIMP-like state is a +2 metastable particle with a mass of 1 Te...... baryons in the universe to be close to -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.

New detector developments for high resolution positron emission tomography

International Nuclear Information System (INIS)

Ziegler, S.I.; Pichler, B.; Lorenz, E.

1998-01-01

The strength of quantitative, functional imaging using positron emission tomography, specially in small animals, is limited due to the spatial resolution. Therefore, various tomograph designs employing new scintillators, light sensors, or coincidence electronic are investigated to improve resolution without losses in sensitivity. Luminous scintillators with short light decay time in combination with novel readout schemes using photomultipliers or semiconductor detectors are currently tested by several groups and are implemented in tomographs for small animals. This review summarises the state of development in high resolution positron emission tomography with a detailed description of a system incorporating avalanche photodiode arrays and small scintillation crystals. (orig.) [de

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.

Rare psi decays

International Nuclear Information System (INIS)

Partridge, R.

1986-01-01

Slightly more than ten years have passed since the psi was discovered, yet the study of psi decays continues to be an active and fruitful area of research. One reason for such longevity is that each successive experiment has increased their sensitivity over previous experiments either by improving detection efficiency or by increasing statistics. This has allowed the observation and, in some cases, detailed studies of rare psi decays. Branching ratios of ≅10-/sup 4/ are now routinely studied, while certain decay channels are beginning to show interesting effects at the 10-/sup 5/ level. Future experiments at the Beijing Electron Positron Collider (BEPC) have the potential for increasing sensitivities by one or two orders of magnitude, thus enabling many interesting studies impossible with current data samples. The author first examines the extent to which psi decays can be used to study electroweak phenomena. The remainder of this work is devoted to the more traditional task of using the psi to study quarks, gluons, and the properties of the strong interaction. Of particular interest is the study of radioactive psi decays, where a number of new particles have been discovered. Recent results regarding two of these particles, the θ(1700) and iota(1450), are discussed, as well as a study of the quark content of the eta and eta' using decays of the psi to vector-pseudoscalar final states

Search for CP and P violating pseudoscalar decays into pi pi

NARCIS (Netherlands)

Ablikim, M.; Achasov, M. N.; Alberto, D.; An, Q.; An, Z. H.; Bai, J. Z.; Baldini, R.; Ban, Y.; Becker, J.; Berger, N.; Bertani, M.; Bian, J. M.; Bondarenko, O.; Boyko, I.; Briere, R. A.; Bytev, V.; Cai, X.; Calcaterra, A. C.; Cao, G. F.; Cao, X. X.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, J. C.; Chen, M. L.; Chen, S. J.; Chen, Y.; Chen, Y. B.; Cheng, H. P.; Chu, Y. P.; Cronin-Hennessy, D.; Dai, H. L.; Dai, J. P.; Dedovich, D.; Deng, Z. Y.; Denysenko, I.; Destefanis, M.; Ding, Y.; Dong, L. Y.; Dong, M. Y.; Du, S. X.; Fan, R. R.; Fang, J.; Fang, S. S.; Feng, C. Q.; Fu, C. D.; Fu, J. L.; Gao, Y.; Geng, C.; Goetzen, K.; Gong, W. X.; Greco, M.; Grishin, S.; Gu, M. H.; Gu, Y. T.; Guan, Y. H.; Guo, A. Q.; Guo, L. B.; Guo, Y. P.; Hao, X. Q.; Harris, F. A.; He, K. L.; He, M.; He, Z. Y.; Heng, Y. K.; Hou, Z. L.; Hu, H. M.; Hu, J. F.; Hu, T.; Huang, B.; Huang, G. M.; Huang, J. S.; Huang, X. T.; Huang, Y. P.; Hussain, T.; Ji, C. S.; Ji, Q.; Ji, X. B.; Ji, X. L.; Jia, L. K.; Jiang, L. L.; Jiang, X. S.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Jing, F. F.; Kalantar-Nayestanaki, N.; Kavatsyuk, M.; Komamiya, S.; Kuehn, W.; Lange, J. S.; Leung, J. K. C.; Li, Cheng; Li, Cui; Li, D. M.; Li, F.; Li, G.; Li, H. B.; Li, J. C.; Li, Lei; Li, N. B.; Li, Q. J.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. N.; Li, X. Q.; Li, X. R.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Liao, X. T.; Liu, B. J.; Liu, B. J.; Liu, C. L.; Liu, C. X.; Liu, C. Y.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, G. C.; Liu, H.; Liu, H. B.; Liu, H. M.; Liu, H. W.; Liu, J. P.; Liu, K.; Liu, K.; Liu, K. Y.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, X. H.; Liu, Y. B.; Liu, Y. W.; Liu, Yong; Liu, Z. A.; Liu, Z. Q.; Loehner, H.; Lu, G. R.; Lu, H. J.; Lu, J. G.; Lu, Q. W.; Lu, X. R.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Ma, C. L.; Ma, F. C.; Ma, H. L.; Ma, Q. M.; Ma, T.; Ma, X.; Ma, X. Y.; Maggiora, M.; Malik, Q. A.; Mao, H.; Mao, Y. J.; Mao, Z. P.; Messchendorp, J. G.; Min, J.; Mitchell, R. E.; Mo, X. H.; Muchnoi, N. Yu.; Nefedov, Y.; Nikolaev, I. B.; Ning, Z.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Pelizaeus, M.; Peters, K.; Ping, J. L.; Ping, R. G.; Poling, R.; Pun, C. S. J.; Qi, M.; Qian, S.; Qiao, C. F.; Qin, X. S.; Qiu, J. F.; Rashid, K. H.; Rong, G.; Ruan, X. D.; Sarantsev, A.; Schulze, J.; Shao, M.; Shen, C. P.; Shen, X. Y.; Sheng, H. Y.; Shepherd, M. R.; Song, X. Y.; Sonoda, S.; Spataro, S.; Spruck, B.; Sun, D. H.; Sun, G. X.; Sun, J. F.; Sun, S. S.; Sun, X. D.; Sun, Y. J.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tang, C. J.; Tang, X.; Tang, X. F.; Tian, H. L.; Toth, D.; Varner, G. S.; Wan, X.; Wang, B. Q.; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, Q.; Wang, S. G.; Wang, X. L.; Wang, Y. D.; Wang, Y. F.; Wang, Y. Q.; Wang, Z.; Wang, Z. G.; Wang, Z. Y.; Wei, D. H.; Wen, Q. G.; Wen, S. P.; Wiedner, U.; Wu, L. H.; Wu, N.; Wu, W.; Wu, Z.; Xiao, Z. J.; Xie, Y. G.; Xu, G. F.; Xu, G. M.; Xu, H.; Xu, Y.; Xu, Z. R.; Xu, Z. Z.; Xue, Z.; Yan, L.; Yan, W. B.; Yan, Y. H.; Yang, H. X.; Yang, M.; Yang, T.; Yang, Y.; Yang, Y. X.; Ye, M.; Ye, M. H.; Yu, B. X.; Yu, C. X.; Yu, L.; Yu, S. P. Yu; Yuan, C. Z.; Yuan, W. L.; Yuan, Y.; Zafar, A. A.; Zallo, A.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, L.; Zhang, S. H.; Zhang, T. R.; Zhang, X. J.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, H. S.; Zhao, Jiawei; Zhao, Jingwei; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, S. J.; Zhao, T. C.; Zhao, X. H.; Zhao, Y. B.; Zhao, Z. G.; Zhao, Z. L.; Zhemchugov, A.; Zheng, B.; Zheng, J. P.; Zheng, Y. H.; Zheng, Z. P.; Zhong, B.; Zhong, J.; Zhong, L.; Zhou, L.; Zhou, X. K.; Zhou, X. R.; Zhu, C.; Zhu, K.; Zhu, K. J.; Zhu, S. H.; Zhu, X. L.; Zhu, X. W.; Zhu, Y. S.; Zhu, Z. A.; Zhuang, J.; Zou, B. S.; Zou, J. H.; Zuo, J. X.

2011-01-01

Using a sample of (225.2 +/- 2.8) x 10(6) J/psi events collected with the Beijing Spectrometer at the Beijing Electron-Positron Collider, CP and P violating decays of eta, eta', and eta(c) into pi(+)pi(-) and pi(0)pi(0) are searched for in J/psi radiative decays. No significant eta, eta', or eta(c)

Dark matter "transporting" mechanism explaining positron excesses

Science.gov (United States)

Kim, Doojin; Park, Jong-Chul; Shin, Seodong

2018-04-01

We propose a novel mechanism to explain the positron excesses, which are observed by satellite-based telescopes including PAMELA and AMS-02, in dark matter (DM) scenarios. The novelty behind the proposal is that it makes direct use of DM around the Galactic Center where DM populates most densely, allowing us to avoid tensions from cosmological and astrophysical measurements. The key ingredients of this mechanism include DM annihilation into unstable states with a very long laboratory-frame life time and their "retarded" decay near the Earth to electron-positron pair(s) possibly with other (in)visible particles. We argue that this sort of explanation is not in conflict with relevant constraints from big bang nucleosynthesis and cosmic microwave background. Regarding the resultant positron spectrum, we provide a generalized source term in the associated diffusion equation, which can be readily applicable to any type of two-"stage" DM scenarios wherein production of Standard Model particles occurs at completely different places from those of DM annihilation. We then conduct a data analysis with the recent AMS-02 data to validate our proposal.

New results on multi-muon production in 250 GeV μ+ Fe interactions

International Nuclear Information System (INIS)

Best, C.H.

1981-05-01

Preliminary results on the contribution to the nucleon structure function F 2 from charm particle production are presented. The data consist of dimuon and trimuon events from a high statistics experiment for a beam energy of 250 GeV. Exotic trimuon events have been observed and are compared to predictions from BETABETA and tautau production and decay. (author)

Detecting gamma-ray anisotropies from decaying dark matter. Prospects for Fermi LAT

International Nuclear Information System (INIS)

Ibarra, Alejandro; Tran, David

2009-09-01

Decaying dark matter particles could be indirectly detected as an excess over a simple power law in the energy spectrum of the diffuse extragalactic gamma-ray background. Furthermore, since the Earth is not located at the center of the Galactic dark matter halo, the exotic contribution from dark matter decay to the diffuse gamma-ray flux is expected to be anisotropic, offering a complementary method for the indirect search for decaying dark matter particles. In this paper we discuss in detail the expected dipole-like anisotropies in the dark matter signal, taking also into account the radiation from inverse Compton scattering of electrons and positrons from dark matter decay. A different source for anisotropies in the gamma-ray flux are the dark matter density fluctuations on cosmic scales. We calculate the corresponding angular power spectrum of the gamma-ray flux and comment on observational prospects. Finally, we calculate the expected anisotropies for the decaying dark matter scenarios that can reproduce the electron/positron excesses reported by PAMELA and the Fermi LAT, and we estimate the prospects for detecting the predicted gamma-ray anisotropy in the near future. (orig.)

Measurements of $\\jpsi$ decays into $\\omega\\pio$, $\\omega\\eta$, and $\\omega\\etap$

OpenAIRE

Ablikim, M.

2005-01-01

Based on $5.8 \\times 10^7 \\jpsi$ events collected with BESII at the Beijing Electron-Positron Collider (BEPC), the decay branching fractions of $\\jpsi\\to\\omega\\pio$, $\\omega\\eta$, and $\\omega\\etap$ are measured using different $\\eta$ and $\\etap$ decay modes. The results are higher than previous measurements. The $\\omega\\pio$ electromagnetic form factor is also obtained.

Muon decay: Measurement of the integral asymmetry parameter

International Nuclear Information System (INIS)

Beltrami, I.; Burkard, H.; Dincklage, R.D. von; Fetscher, W.; Gerber, H.J.; Johnson, K.F.

1987-01-01

The positron directional distribution following muon decay is measured. The polarized muons are derived from pion decay in flight and are brought to rest in Be metal. Using the μSR-technique P μ ξ = 1.0027 ± 0.0084 is deduced. The integral asymmetry parameters ξ bears on the mass of the W tilde (wino, the supersymmetrical partner of the gauge boson W), mediating such decay as μ → eν tilde ν tilde. Assuming very light scalar neutrini msub(n tilde) μ a new lower limit on the wino mass msub(w tilde) > 270 GeV/c 2 (90% CL) is inferred. (orig.)

A Study of charm quark production in beauty quark decays with the OPAL detector at LEP

CERN Document Server

Waller, David

2003-01-01

The production of charm quarks in beauty quark decays has been studied with the OPAL detector at the Large Electron Positron collider near Geneva, Switzerland. The branching ratio Br(b -1 DDX) has been measured using hadronic zo decays collected between 1993 and 1995. Here b refers to the admixture of weakly decaying hadrons containing ab quark that are produced in electron-positron annihilations at a centre of mass energy equal to the mass of the zo boson. The impact parameter significance of tracks in tagged b-jets is used to differentiate b -1 DDX decays from other decays. The result is Br(b -1 DDX) = (10.0 ± 3.2(stat.)~~:~(syst. det.)~~~04 (syst. phys.))%. where syst. det. is the systematic uncertainty due to the modelling of the detector, and syst. phys. is the systematic uncertainty due to the modelling of the underlying particle physics. Using this result, the average number of charm and anti-charm quarks produced in a beauty quark decay, nc, is found to be l.12~8:i6- Ill

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

Electrons and kaons in charmed particle decays

International Nuclear Information System (INIS)

Feller, J.M.

1979-05-01

Inclusive studies of the electron content, kaon content, and associated electron-kaon content of the decays of D mesons and other charmed particles produced in electron-positron annihilation are presented. At the psi(3772) resonance the following inclusive branching ratios for D meson decays to charged kaons were measured. Also at the psi(3772) resonance the average semileptonic branching ratio for D 0 and D + decays to electrons has been measured to be .076 +- .028. The average semileptonic branching ratio of charmed particles produced in e + e - annihilation at center-of-mass energies from 3.9 to 7.4 GeV is found to be equal within errors to that of the D's. At all energies the electron momentum spectra are consistent with a combination of the decays D → Ke nu and D → K*e nu. 84 references

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

Science.gov (United States)

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

2016-08-01

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

Decay correction methods in dynamic PET studies

International Nuclear Information System (INIS)

Chen, K.; Reiman, E.; Lawson, M.

1995-01-01

In order to reconstruct positron emission tomography (PET) images in quantitative dynamic studies, the data must be corrected for radioactive decay. One of the two commonly used methods ignores physiological processes including blood flow that occur at the same time as radioactive decay; the other makes incorrect use of time-accumulated PET counts. In simulated dynamic PET studies using 11 C-acetate and 18 F-fluorodeoxyglucose (FDG), these methods are shown to result in biased estimates of the time-activity curve (TAC) and model parameters. New methods described in this article provide significantly improved parameter estimates in dynamic PET studies

Positron-molecule interactions and corresponding positron attachment to molecules. As a basis for positron emission tomography (PET)

International Nuclear Information System (INIS)

Tachikawa, Masanori; Kimura, Mineo; Pichl, Lukas

2007-01-01

Through positron and electron interactions, they annihilate emitting primarily two gamma rays with 180-degree opposite directions. Positron spectroscopy using the characteristics of these gamma rays has been employed for analyzing various properties of material as well as for positron emission tomography (PET). However, its fundamental physics of positron-electron interactions and resulting features of emitting gamma rays are not well understood. By obtaining better understanding of positron interactions, it should become possible to provide the firm bases for positron spectroscopy in finer accuracy and quality. Here, we propose a significant mechanism for positron annihilation through positron attachment process, which may help increase the quality of positron spectroscopy. (author)

Nuclear medicine and positron emission tomography: An overview

International Nuclear Information System (INIS)

McCarthy, T.J.; Schwarz, S.W.; Welch, M.J.

1994-01-01

Nuclear medicine is the field of medical practice that involves the oral or intravenous administration of radioactive materials for use in diagnosis and therapy. The majority of radiopharmaceutical available are used for diagnostic purposes. These involve the determination of organ function, shape, or position from an image of the radioactivity distribution within an organ or at a location within the body. After administration, the radiopharmaceutical localizes within an organ or target tissue due to its biological or physiologic characteristics. This diagnostic capability is usually the result of the emission of gamma radiation from the radiopharmaceutical localized within an organ. This allows for external detection and imaging using a special type of camera known as a gamma camera. When a positron-emitting radionuclide decays, a positron (positive electron) is emitted from the nucleus. The positron then annihilates with an electron, resulting in the release of energy in the form of two 511-KeV γ-rays at 180 degree to one another. The energy of these photons is sufficient to pass through tissue. Thus, placing a series of detectors around the patient allows technicians to monitor the emission of both of the photons that result from a single positron annihilation. this ultimately allows an accurate quantification of the distribution of radioactivity in the body not possible when only a single γ-ray is emitted

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

International Nuclear Information System (INIS)

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

2016-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-08-15

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

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.).

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.).

UA1: Z particle decay

CERN Multimedia

1992-01-01

A colour treated picture of the computer reconstruction of the real particle tracks emerging from a high energy proton-antiproton collision recorded in the UA1 detector at the SPS (converted to act as a collider). This picture shows the production of a Z particle that has decayed into a high energy electron and positron flying off in opposite directions (in yellow). The UA1 detector ran on the SPS accelerator at CERN between 1981 and 1993.

Investigation of granular impact using positron emission particle tracking

KAUST Repository

Marston, Jeremy O.

2015-04-01

We present results from an experimental study of granular impact using a combination of high-speed video and positron emission particle tracking (PEPT). The PEPT technique exploits the annihilation of photons from positron decay to determine the position of tracer particles either inside a small granular bed or attached to the object which impacts the bed. We use dense spheres as impactors and the granular beds are comprised of glass beads which are fluidised to achieve a range of different initial packing states. For the first time, we have simultaneously investigated both the trajectory of the sphere, the motion of particles in a 3-D granular bed and particles which jump into the resultant jet, which arises from the collapse of the cavity formed by the impacting sphere.

ZZ RADDECAY, Decay Data Library for Radiological Assessment

International Nuclear Information System (INIS)

2000-01-01

Description of program or function: - Format: special format defined in documentation. - Nuclides: 500 nuclides of interest in the nuclear fuel cycle, environmental problems, nuclear medicine, fusion reactor technology, and radiological protection assessment. - Origin: DLC-80/DRALIST. ZZ-RADDECAY is a data library of half-lives, radioactive daughter nuclides, probabilities per decay and decay product energies for alpha particles, positrons, electrons, X-rays, and gamma-rays. The current data base contains approximately 500 nuclides of interest in the nuclear fuel cycle, environmental problems, nuclear medicine, fusion reactor technology, and radiological protection assessment. RADIATION DECAY VERSION 2 March 1997: This application is being provided by Aptec as 'Freeware' with permission of the author Mr. Charles Hacker, Engineering and Applied Science, Griffith University, Australia

Positron-containing systems and positron diagnostics

International Nuclear Information System (INIS)

1978-01-01

The results of the experimental and theoretical investigations are presented. Considered are quantum-mechanical calculations of wave functions describing the states of positron-containing atomic systems and of cross-sections of the processes characterizing different interactions, and also the calculations of the behaviour of positrons in gases in the presence of an electric field. The results of experimental tests are presented by the data describing the behaviour of positrons and positronium in liquids, polymers and elastomers, complex oxides and in different solids. New equipment and systems developed on the basis of current studies are described. Examined is a possibility of applying the methods of model and effective potentials for studying the bound states of positron systems and for calculating cross-sections of elementary processes of elastic and inelastic collisions with a positron involved. The experimental works described indicate new possibilities of the positron diagnosis method: investigation of thin layers and films of semiconductor materials, defining the nature of chemical bonds in semiconductors, determination of the dislocation density in deformed semiconductors, derivation of important quantitative information of the energy states of radiation defects in them

Gamma-ray lines from radiative dark matter decay

International Nuclear Information System (INIS)

Garny, Mathias; Ibarra, Alejandro; Tran, David; Weniger, Christoph

2011-01-01

The decay of dark matter particles which are coupled predominantly to charged leptons has been proposed as a possible origin of excess high-energy positrons and electrons observed by cosmic-ray telescopes PAMELA and Fermi LAT. Even though the dark matter itself is electrically neutral, the tree-level decay of dark matter into charged lepton pairs will generically induce radiative two-body decays of dark matter at the quantum level. Using an effective theory of leptophilic dark matter decay, we calculate the rates of radiative two-body decays for scalar and fermionic dark matter particles. Due to the absence of astrophysical sources of monochromatic gamma rays, the observation of a line in the diffuse gamma-ray spectrum would constitute a strong indication of a particle physics origin of these photons. We estimate the intensity of the gamma-ray line that may be present in the energy range of a few TeV if the dark matter decay interpretation of the leptonic cosmic-ray anomalies is correct and comment on observational prospects of present and future Imaging Cherenkov Telescopes, in particular the CTA

Proton decay in a nucleus: Nonrelativistic treatment of nuclear effects

International Nuclear Information System (INIS)

Fernandez, L.A.; Alvarez-Estrada, R.F.; Sanchez-Gomez, J.L.

1983-01-01

In this paper, proton decay in a large nucleus is studied in the framework of SU(5) grand unification theory (GUT). By using a method based upon the Green's-function technique of many-body physics, nuclear effects on spectator and pole terms are computed. The decay width in the nucleus is found to be practically the same as in free space. However, nuclear effects are of considerable importance concerning the positron spectrum. A density-correlation expansion is introduced which is useful for carrying out a systematic study of nuclear effects in proton decay in a large nucleus. The method presented here can be easily extended to other GUT's or supersymmetric GUT's

Form factors in Kμ3 decay

International Nuclear Information System (INIS)

Wilke, W.G.

1976-01-01

The decay of 1.83 GeV/c K + mesons in flight was studied using a magnetic spectrometer with multi-wire proportional chambers for the charged particles and an array of lead glass to detect γ-rays from π 0 decay. For the decay mode K + yields π 0 μ + nu/sub μ/ the muons were stopped after the spectrometer in a polarimeter, an array of carbon blocks and scintillators in a 40 g magnetic field. Four scintillators surrounded each carbon clock. The pattern of polarimeter counters in coincidence with the entering muon, and the pattern in coincidence with the decay positron were recorded, as well as the time delay between the μ + and the e + . For events with two γ-rays striking the lead glass, the positions and energies of the γ-rays were also recorded. Each Kμ 3 decay with two detected γ-rays was a 2-C fit, with an additional constraint of range-momentum consistency for the muon. Polarization analysis on a final sample of 24,669 events gave a value Xi(q 2 )/sub avg./ = -.25 +- .25. The experiment also gave values for Xi(q 2 ) in each of four q 2 bins

Origin and annihilation physics of positrons in the Galaxy

International Nuclear Information System (INIS)

Alexis, Anthony

2014-01-01

(magnetic field of the galactic halo, structure of the interstellar medium, etc.), we implemented several models accounting for these uncertainties. In doing so, we tested the impact of each of these parameters on the propagation and the annihilation emission of positrons. With this code, we studied the positrons produced by β + -decays of 26 Al, 44 Ti and 56 Ni which are continuously synthesised in the Galaxy within massive stars and explosions of supernovae. We first studied these sources because they have often been cited in the past as the major contributors of the galactic annihilation emission. Regardless of the configuration of the modelled Galaxy, we showed that nucleosynthesis positrons could explain the annihilation emission from the disk but not the emission from the bulge. The main reason is simple: these MeV positrons do not propagate far away from their birth sites. In our framework, an additional source is thus needed in the bulge to explain the strong bulge emission. We showed that a transient source of MeV positrons located at the Galactic centre could account for the bulge emission. (author)

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.

Chargino production and decay in photon-photon collisions

International Nuclear Information System (INIS)

Mayer, T.; Bloechinger, C.; Franke, F.; Fraas, H.

2003-01-01

We discuss the pair production of charginos in collisions of polarized photons, γγ→χ i + χ i - (i=1,2), and the subsequent leptonic decay of the lighter chargino χ 1 + →χ 1 0 e + ν e including the complete spin correlations. Analytical formulae are given for the polarization and the spin-spin correlations of the charginos. Since the production is a pure QED process the decay dynamics can be studied separately. For high energy photons from Compton backscattering of polarized laser pulses off polarized electron beams numerical results are presented for the cross section, the angular distribution and the forward-backward asymmetry of the decay positron. Finally we study the dependence on the gaugino mass parameter M 1 and on the sneutrino mass for a gaugino-like MSSM scenario. (orig.)

Conceptual design of a high-intensity positron source for the Advanced Neutron Source

International Nuclear Information System (INIS)

Hulett, L.D.; Eberle, C.C.

1994-12-01

The Advanced Neutron Source (ANS) is a planned new basic and applied research facility based on a powerful steady-state research reactor that provides neutrons for measurements and experiments in the fields of materials science and engineering, biology, chemistry, materials analysis, and nuclear science. The useful neutron flux will be at least five times more than is available in the world's best existing reactor facility. Construction of the ANS provides a unique opportunity to build a positron spectroscopy facility (PSF) with very-high-intensity beams based on the radioactive decay of a positron-generating isotope. The estimated maximum beam current is 1000 to 5000 times higher than that available at the world's best existing positron research facility. Such an improvement in beam capability, coupled with complementary detectors, will reduce experiment durations from months to less than one hour while simultaneously improving output resolution. This facility will remove the existing barriers to the routine use of positron-based analytical techniques and will be a giant step toward realization of the full potential of the application of positron spectroscopy to materials science. The ANS PSF is based on a batch cycle process using 64 Cu isotope as the positron emitter and represents the status of the design at the end of last year. Recent work not included in this report, has led to a proposal for placing the laboratory space for the positron experiments outside the ANS containment; however, the design of the positron source is not changed by that relocation. Hydraulic and pneumatic flight tubes transport the source material between the reactor and the positron source where the beam is generated and conditioned. The beam is then transported through a beam pipe to one of several available detectors. The design presented here includes all systems necessary to support the positron source, but the beam pipe and detectors have not been addressed yet

Slow positrons in single-crystal samples of Al and Al-AlxOy

Science.gov (United States)

Lynn, K. G.; Lutz, H.

1980-11-01

Well-characterized Al(111) and Al(100) samples were studied with monoenergetic positrons before and after exposure to oxygen. Both positronium-formation and positron-emission curves were obtained for various incident positron energies at sample temperatures ranging from 160-900 K. The orthopositronium decay signal provides a unique signature that the positron has emerged from the surface region of a clean metal. In the clean Al crystals part of the positronium formed near the surface is found to be associated with a temperature-activated process described as the thermally activated detrapping of a positron from a surface state. A simple positron diffusion model, including surface and vacancy trapping, is fitted to the positronium data and an estimate of the binding energy of the positron in this trap is made. The positron diffusion constant is found to have a negative temperature dependence before the onset of positron trapping at thermally generated monovacancies (>500 K), in reasonable agreement with theoretical predictions. The depth of the positron surface state is reduced or positronium is formed in the chemisorbed layer as oxygen is adsorbed on both Al sample surfaces, thus increasing the positronium fraction and decreasing the positron emission. At higher oxygen exposures [>500 L (1 L = 10-6 torr sec)] positron or positronium traps are generated in the overlayer and the positronium fraction is reduced. The amorphous-to-crystalline surface transition of AlxOy on Al is observed between 650 and 800 K by the change in the positronium fraction and is interpreted as the removal of trapping centers in the metal-oxide overlayer. At the higher temperatures and incident energies vacancy trapping is observed by the decrease in the positron diffusion length in both the clean and the underlying Al of the oxygen-exposed samples. Similar vacancy formation enthalpies for Al are extracted in both the clean and oxygen-covered samples by a simple model and are in good

Planned Positron Factory project

International Nuclear Information System (INIS)

Okada, Sohei

1990-01-01

The Japan Atomic Energy Research Institute, JAERI, has started, drafting a construction plan for the 'Positron Factory', in which intense energy-controllable monoenergetic positron beams are produced from pair-production reactions caused by high-energy electrons from a linac. The JAERI organized a planning committee to provide a basic picture for the Positron Factory. This article presents an overview of the interactions of positrons, intense positron sources and the research program and facilities planned for the project. The interactions of positrons and intense positron sources are discussed focusing on major characteristics of positrons in different energy ranges. The research program for the Positron Factory is then outlined, focusing on advanced positron annihilation techniques, positron spectroscopy (diffraction, scattering, channeling, microscopy), basic positron physics (exotic particle science), and positron beam technology. Discussion is also made of facilities required for the Positron Factory. (N.K.)

Improved search for heavy neutrinos in the decay π →e ν

Science.gov (United States)

Aguilar-Arevalo, A.; Aoki, M.; Blecher, M.; Britton, D. I.; Vom Bruch, D.; Bryman, D. A.; Chen, S.; Comfort, J.; Cuen-Rochin, S.; Doria, L.; Gumplinger, P.; Hussein, A.; Igarashi, Y.; Ito, S.; Kettell, S.; Kurchaninov, L.; Littenberg, L. S.; Malbrunot, C.; Mischke, R. E.; Numao, T.; Protopopescu, D.; Sher, A.; Sullivan, T.; Vavilov, D.; Pienu Collaboration

2018-04-01

A search for massive neutrinos has been made in the decay π+→e+ν . No evidence was found for extra peaks in the positron energy spectrum indicative of pion decays involving massive neutrinos (π →e+νh ). Upper limits (90% C.L.) on the neutrino mixing matrix element |Ue i|2 in the neutrino mass region 60 - 135 MeV /c2 were set and are an order of magnitude improvement over previous results.

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

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

Energy Technology Data Exchange (ETDEWEB)

Krsjak, Vladimir, E-mail: vladimir.krsjak@psi.ch; Dai, Yong

2015-10-15

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

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

Science.gov (United States)

Krsjak, Vladimir; Dai, Yong

2015-10-01

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

Transmission positron microscopes

International Nuclear Information System (INIS)

Doyama, Masao; Kogure, Yoshiaki; Inoue, Miyoshi; Kurihara, Toshikazu; Yoshiie, Toshimasa; Oshima, Ryuichiro; Matsuya, Miyuki

2006-01-01

Immediate and near-future plans for transmission positron microscopes being built at KEK, Tsukuba, Japan, are described. The characteristic feature of this project is remolding a commercial electron microscope to a positron microscope. A point source of electrons kept at a negative high voltage is changed to a point source of positrons kept at a high positive voltage. Positional resolution of transmission microscopes should be theoretically the same as electron microscopes. Positron microscopes utilizing trapping of positrons have always positional ambiguity due to the diffusion of positrons

Simulation of the scattering in a thorium foil of 0.15-2.3 MeV electrons and positrons

International Nuclear Information System (INIS)

Bargholtz, Chr.; Holmberg, L.; Liljequist, D.; Tegner, P.E.

1993-01-01

Studies of the scattering in thorium of electrons emitted in the decay of 90 Sr, involving measurements of the coincidence spectra of electrons and positrons in the energy region 210-420 keV in search for anomalies, have previously been reported. In the analysis of the experimental results, computer simulations of the scattering and energy loss of the electrons and positrons were used. The present report describes the models and assumptions used in this simulation and the comparison with experimentally determined spectra

Search for right-handed currents in the decay chain of K+ → μ+νμ, μ+ → e+νeν-barμ

International Nuclear Information System (INIS)

Aoki, M.; Yamazaki, T.; Imazato, J.

1993-12-01

The asymmetry of positrons in the K + → μ + ν, μ + → e + ν e ν-bar μ decay chain was measured in a search for right-handed weak currents in ΔS = 1 semi-leptonic decay. High-intensity low-background monoenergetic polarized muons of 236 MeV/c momentum resulting from kaon decay at rest were directly extracted from a primary production target which was hit by a proton beam of the KEK 12-GeV proton synchrotron. Muons were stopped in a pure-aluminum plate, and the energy-integrated asymmetry of the decay positrons with respect to the incoming muon direction was determined to high precision. The observed asymmetry yielded ξP μ = -0.9996 ± 0.0030(stat) ± 0.0048(sys). This result revealed no evidence of right-handed currents in this kaon-decay chain, and set a stringent bound on the mass of the right-handed weak boson. (author) 52 refs

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.

Gamma-ray constraints on hadronic and leptonic activities of decaying dark matter

International Nuclear Information System (INIS)

Chen, Chuan-Ren; Mandal, Sourav K.; Takahashi, Fuminobu

2010-01-01

While the excess in cosmic-ray electrons and positrons reported by PAMELA and Fermi may be explained by dark matter decaying primarily into charged leptons, this does not necessarily mean that dark matter should not have any hadronic decay modes. In order to quantify the allowed hadronic activities, we derive constraints on the decay rates of dark matter into WW, ZZ, hh, q q-bar and gg using the Fermi and HESS gamma-ray data. We also derive gamma-ray constraints on the leptonic e + e − , μ + μ − and τ + τ − final states. We find that dark matter must decay primarily into μ + μ − or τ + τ − in order to simultaneously explain the reported excess and meet all gamma-ray constraints

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

DEFF Research Database (Denmark)

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

1980-01-01

Positron lifetime measurements are reported as a function of temperature for bis[m-(m-phenoxyphenoxy)phenyl] ether and m-phenoxyphenyl-m-(m-phenoxyphenoxy)phenyl ether. The decay curves were analysed in terms of three lifetime components; two short lifetimes of typically 200 and 500 ps associated...

Study of J/ψ decaying into ωp anti p

International Nuclear Information System (INIS)

Ablikim, M.; Bai, J.Z.; Cai, X.; Chen, H.S.; Chen, H.X.; Chen, J.C.; Chen, Jin; Chen, Y.B.; Chu, Y.P.; Deng, Z.Y.; Du, S.X.; Fang, J.; Fang, S.S.; Gao, C.S.; Gu, S.D.; Guo, Y.N.; He, K.L.; Heng, Y.K.; Hu, H.M.; Hu, T.; Huang, G.S.; Ji, X.B.; Jiang, X.S.; Jin, D.P.; Jin, S.; Lai, Y.F.; Li, G.; Li, H.B.; Li, J.; Li, R.Y.; Li, S.M.; Li, W.D.; Li, W.G.; Li, X.L.; Li, X.N.; Liao, H.B.; Liu, B.J.; Liu, C.X.; Liu, Fang; Liu, H.H.; Liu, H.M.; Liu, J.B.; Liu, Jian; Liu, R.G.; Liu, Z.A.; Lu, F.; Lu, J.G.; Ma, L.L.; Ma, Q.M.; Mao, Z.P.; Mo, X.H.; Nie, J.; Ping, R.G.; Qi, N.D.; Qin, H.; Qiu, J.F.; Ren, Z.Y.; Rong, G.; Shan, L.Y.; Shang, L.; Shen, D.L.; Shen, X.Y.; Sheng, H.Y.; Sun, H.S.; Sun, S.S.; Sun, Y.Z.; Sun, Z.J.; Tang, X.; Tong, G.L.; Wang, D.Y.; Wang, L.; Wang, L.L.; Wang, L.S.; Wang, M.; Wang, P.; Wang, P.L.; Wang, W.F.; Wang, Y.F.; Wang, Z.; Wang, Z.Y.; Wang, Zheng; Wei, C.L.; Wei, D.H.; Weng, Y.; Wu, N.; Xia, X.M.; Xie, X.X.; Xu, G.F.; Yang, H.X.; Yu, G.W.; Yuan, C.Z.; Yuan, Y.; Zang, S.L.; Zhang, B.X.; Zhang, B.Y.; Zhang, C.C.; Zhang, D.H.; Zhang, H.Q.; Zhang, H.Y.; Zhang, J.W.; Zhang, J.Y.; Zhang, S.H.; Zhao, D.X.; Zhao, J.W.; Zhao, M.G.; Zhao, P.P.; Zhao, W.R.; Zhao, Z.G.; Zheng, J.P.; Zheng, Z.P.; Zhou, L.; Zhu, K.J.; Zhu, Q.M.; Zhu, Y.C.; Zhu, Y.S.; Zhu, Z.A.; Zhuang, B.A.; Zhuang, X.A.; Zou, B.S.; Ban, Y.; Liu, J.; Zhang, Z.X.; Zheng, H.Q.; Chen, H.F.; Yan, M.L.; Ye, Y.X.; Zhang, Z.P.; Dai, Y.S.; Diao, L.Y.; Ma, F.C.; Dong, Q.F.; Fu, C.D.; Gao, Y.N.; Gu, Y.T.; Ruan, X.D.; Guo, Z.J.; Harris, F.A.; Liu, Q.; Olsen, S.L.; Shen, C.P.; Varner, G.S.; He, M.; Huang, X.T.; Jiao, J.B.; Zhang, X.Y.; Hou, J.; Li, X.Q.; Xu, Y.; Hu, J.H.; Yang, Y.X.; Jiang, X.Y.; Lou, Y.C.; Lu, G.R.; Liang, Y.F.; Zhang, Yiyun; Liu, F.; Xu, X.P.; Liu, J.P.; Luo, C.L.; Ma, H.L.; Ye, M.H.; Zeng, Y.

2008-01-01

The decay J/ψ→ωp anti p is studied using a 5.8 x 10 7 J/ψ event sample accumulated with the BES II detector at the Beijing Electron-Positron Collider. The decay branching fraction is measured to be B(J/ψ→ωp anti p)=(9.8±0.3±1.4) x 10 -4 . No significant enhancement near the pp mass threshold is observed, and an upper limit of B(J/ψ→ωX(1860))B(X(1860)→pp) -5 is determined at the 95% confidence level, where X(1860) designates the near-threshold enhancement seen in the p anti p mass spectrum in J/ψ→γp anti p decays. (orig.)

Study of charmonium rare decays

International Nuclear Information System (INIS)

Brient, J.C.

1986-09-01

This thesis presents the study of rare decays of charmonium states formed in the interaction of an antiproton beam with an hydrogen gas jet target. Electromagnetic final states are used to sign the charmonium state formation (e + e - , e + e - + Χ, γγ). The selection of events used a two arms non magnetic spectrometer, with a charged track system, a threshold Cerenkov counter to tag the electron (positron), and an e.m. calorimeter. Energy scan technic have been used to observe the resonant formation through the excitation curves. Parameters of the states (mass, total and partial widths) are extracted from these curves using a statistical analysis. Two types of decays have been studied in this thesis: 1 P 1 charmonium state decay to the ψ (signed by its e + e - decay). In the energy scan around the center of gravity of the P charmonium states, we observe a cluster of 5 events, in a narrow mass range. This cluster correspond to a 2.7 σ signal. The most probable interpretation of this signal is given by a narrow resonance, with a mass of 3526. MeV. Due to the properties (mass, width and decay) of this signal, this could be interpreted as the 1 P 1 charmonium state. 2 photons decay of the η c and Χ 2 . 22 γγ events are observed, 15 in the η c region, and 7 in the Χ 2 region. This sample is interpreted as a direct observation of η c and Χ 2 decay into γγ. Parameters of these decays, (γγ partial width), are extracted using a maximum likekihood analysis. Theoretical models of charmonium explain correctly the properties of the charmonium, including the results presented in this thesis. 57 refs [fr

Gross theory of beta-decay and half-lives of short-lived nuclei

International Nuclear Information System (INIS)

Yamada, Masami; Kondo, Norikatsu.

1976-01-01

The gross theory of beta-decay has been developed, and this theory offers the means of calculating directly the function of beta-decay intensity, then half-lives, complex beta spectra and so on are estimated from it. This paper presents the more refined theory by introducing the shell effect. The shell effect is considered in the intensity function. The half-lives in the electron decay of In with spin of 9/2 + , the positron decay of Bi, Po, At and Rn, and the decay of odd-odd nuclei were estimated. The introduction of the shell effect shows better agreement between the theory and the experimental data. The inequality relations of intensity functions and half-lives of two adjacent nuclei were obtained. When the spins and parities of two nuclei are same, the inequality relations hold especially good. (Kato, T.)

High resolution Cerenkov light imaging of induced positron distribution in proton therapy

Energy Technology Data Exchange (ETDEWEB)

Yamamoto, Seiichi, E-mail: s-yama@met.nagoya-u.ac.jp; Fujii, Kento; Morishita, Yuki; Okumura, Satoshi; Komori, Masataka [Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, Aichi 461-8673 (Japan); Toshito, Toshiyuki [Department of Proton Therapy Physics, Nagoya Proton Therapy Center, Nagoya City West Medical Center, Aichi 462-8508 (Japan)

2014-11-01

Purpose: In proton therapy, imaging of the positron distribution produced by fragmentation during or soon after proton irradiation is a useful method to monitor the proton range. Although positron emission tomography (PET) is typically used for this imaging, its spatial resolution is limited. Cerenkov light imaging is a new molecular imaging technology that detects the visible photons that are produced from high-speed electrons using a high sensitivity optical camera. Because its inherent spatial resolution is much higher than PET, the authors can measure more precise information of the proton-induced positron distribution with Cerenkov light imaging technology. For this purpose, they conducted Cerenkov light imaging of induced positron distribution in proton therapy. Methods: First, the authors evaluated the spatial resolution of our Cerenkov light imaging system with a {sup 22}Na point source for the actual imaging setup. Then the transparent acrylic phantoms (100 × 100 × 100 mm{sup 3}) were irradiated with two different proton energies using a spot scanning proton therapy system. Cerenkov light imaging of each phantom was conducted using a high sensitivity electron multiplied charge coupled device (EM-CCD) camera. Results: The Cerenkov light’s spatial resolution for the setup was 0.76 ± 0.6 mm FWHM. They obtained high resolution Cerenkov light images of the positron distributions in the phantoms for two different proton energies and made fused images of the reference images and the Cerenkov light images. The depths of the positron distribution in the phantoms from the Cerenkov light images were almost identical to the simulation results. The decay curves derived from the region-of-interests (ROIs) set on the Cerenkov light images revealed that Cerenkov light images can be used for estimating the half-life of the radionuclide components of positrons. Conclusions: High resolution Cerenkov light imaging of proton-induced positron distribution was possible. The

High resolution Cerenkov light imaging of induced positron distribution in proton therapy

International Nuclear Information System (INIS)

Yamamoto, Seiichi; Fujii, Kento; Morishita, Yuki; Okumura, Satoshi; Komori, Masataka; Toshito, Toshiyuki

2014-01-01

Purpose: In proton therapy, imaging of the positron distribution produced by fragmentation during or soon after proton irradiation is a useful method to monitor the proton range. Although positron emission tomography (PET) is typically used for this imaging, its spatial resolution is limited. Cerenkov light imaging is a new molecular imaging technology that detects the visible photons that are produced from high-speed electrons using a high sensitivity optical camera. Because its inherent spatial resolution is much higher than PET, the authors can measure more precise information of the proton-induced positron distribution with Cerenkov light imaging technology. For this purpose, they conducted Cerenkov light imaging of induced positron distribution in proton therapy. Methods: First, the authors evaluated the spatial resolution of our Cerenkov light imaging system with a 22 Na point source for the actual imaging setup. Then the transparent acrylic phantoms (100 × 100 × 100 mm 3 ) were irradiated with two different proton energies using a spot scanning proton therapy system. Cerenkov light imaging of each phantom was conducted using a high sensitivity electron multiplied charge coupled device (EM-CCD) camera. Results: The Cerenkov light’s spatial resolution for the setup was 0.76 ± 0.6 mm FWHM. They obtained high resolution Cerenkov light images of the positron distributions in the phantoms for two different proton energies and made fused images of the reference images and the Cerenkov light images. The depths of the positron distribution in the phantoms from the Cerenkov light images were almost identical to the simulation results. The decay curves derived from the region-of-interests (ROIs) set on the Cerenkov light images revealed that Cerenkov light images can be used for estimating the half-life of the radionuclide components of positrons. Conclusions: High resolution Cerenkov light imaging of proton-induced positron distribution was possible. The authors

EM reconstruction of dual isotope PET using staggered injections and prompt gamma positron emitters

International Nuclear Information System (INIS)

Andreyev, Andriy; Sitek, Arkadiusz; Celler, Anna

2014-01-01

Purpose: The aim of dual isotope positron emission tomography (DIPET) is to create two separate images of two coinjected PET radiotracers. DIPET shortens the duration of the study, reduces patient discomfort, and produces perfectly coregistered images compared to the case when two radiotracers would be imaged independently (sequential PET studies). Reconstruction of data from such simultaneous acquisition of two PET radiotracers is difficult because positron decay of any isotope creates only 511 keV photons; therefore, the isotopes cannot be differentiated based on the detected energy. Methods: Recently, the authors have proposed a DIPET technique that uses a combination of radiotracer A which is a pure positron emitter (such as 18 F or 11 C) and radiotracer B in which positron decay is accompanied by the emission of a high-energy (HE) prompt gamma (such as 38 K or 60 Cu). Events that are detected as triple coincidences of HE gammas with the corresponding two 511 keV photons allow the authors to identify the lines-of-response (LORs) of isotope B. These LORs are used to separate the two intertwined distributions, using a dedicated image reconstruction algorithm. In this work the authors propose a new version of the DIPET EM-based reconstruction algorithm that allows the authors to include an additional, independent estimate of radiotracer A distribution which may be obtained if radioisotopes are administered using a staggered injections method. In this work the method is tested on simple simulations of static PET acquisitions. Results: The authors’ experiments performed using Monte-Carlo simulations with static acquisitions demonstrate that the combined method provides better results (crosstalk errors decrease by up to 50%) than the positron-gamma DIPET method or staggered injections alone. Conclusions: The authors demonstrate that the authors’ new EM algorithm which combines information from triple coincidences with prompt gammas and staggered injections

EM reconstruction of dual isotope PET using staggered injections and prompt gamma positron emitters

Energy Technology Data Exchange (ETDEWEB)

Andreyev, Andriy, E-mail: andriy.andreyev-1@philips.com [Philips Healthcare, Highland Heights, Ohio 44143 (United States); Sitek, Arkadiusz [Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114 (United States); Celler, Anna [Department of Radiology, University of British Columbia, Vancouver V5Z 1M9 (Canada)

2014-02-15

Purpose: The aim of dual isotope positron emission tomography (DIPET) is to create two separate images of two coinjected PET radiotracers. DIPET shortens the duration of the study, reduces patient discomfort, and produces perfectly coregistered images compared to the case when two radiotracers would be imaged independently (sequential PET studies). Reconstruction of data from such simultaneous acquisition of two PET radiotracers is difficult because positron decay of any isotope creates only 511 keV photons; therefore, the isotopes cannot be differentiated based on the detected energy. Methods: Recently, the authors have proposed a DIPET technique that uses a combination of radiotracer A which is a pure positron emitter (such as{sup 18}F or {sup 11}C) and radiotracer B in which positron decay is accompanied by the emission of a high-energy (HE) prompt gamma (such as {sup 38}K or {sup 60}Cu). Events that are detected as triple coincidences of HE gammas with the corresponding two 511 keV photons allow the authors to identify the lines-of-response (LORs) of isotope B. These LORs are used to separate the two intertwined distributions, using a dedicated image reconstruction algorithm. In this work the authors propose a new version of the DIPET EM-based reconstruction algorithm that allows the authors to include an additional, independent estimate of radiotracer A distribution which may be obtained if radioisotopes are administered using a staggered injections method. In this work the method is tested on simple simulations of static PET acquisitions. Results: The authors’ experiments performed using Monte-Carlo simulations with static acquisitions demonstrate that the combined method provides better results (crosstalk errors decrease by up to 50%) than the positron-gamma DIPET method or staggered injections alone. Conclusions: The authors demonstrate that the authors’ new EM algorithm which combines information from triple coincidences with prompt gammas and

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

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.))

Measurements of Charmless Three-Body and Quasi-Two-Body B Decays

Energy Technology Data Exchange (ETDEWEB)

Barrera, Barbara

2000-08-28

The authors present preliminary results of a search for several exclusive charmless hadronic B decays from electron-positron annihilation data collected by the BaBar detector near the Upsilon(4S) resonance. These include three-body decay modes with final states h{+-}h{sup minus-plus}h{+-} and h{+-}h{sup minus-plus}pi{sup 0}, and quasi-two-body decay modes with final states X{sup 0}h and X{sup 0}K{sub S}{sup 0}, where h = pi or K and X{sup 0} = eta-prime or omega. They find beta(B{sup 0} --> rho{sup minus-plus}pi{sup {+-}}) = (49{+-}13{sub {minus}5}{sup +6}) x 10{sup {minus}6} and beta(B{sup +} --> eta-prime-K{sup +}) = (62{+-}18{+-}8) x 10{sup {minus}6} and present upper limits for right other decays.

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

Measurements of Neutral Kaon Decays to Two Electron Positron Pairs

Energy Technology Data Exchange (ETDEWEB)

Halkiadakis, Eva [Rutgers U., Piscataway

2001-01-01

We observed 441 $K_L \\to e^+ e^- e^+ e^-$ events with a background of 4.2 events in the KTeV/E799II experiment at Fermilab. We present here a measurement of the $K_L \\to e^+ e^- e^+ e^-$ branching ratio (B), a study of CP symmetry and the first detailed study of the $e^+ e^-$ invariant mass spectrum in this decay mode....

Positron emission tomography. Present status and Romanian perspectives

International Nuclear Information System (INIS)

Constantinescu, B.; Lungu, V.

1995-01-01

Basic principles of the positron emission tomography (PET) are summarised. The main PET methods using short-lived radioisotopes (i.e. 11 C, 13 N, 15 O, 18 F) are briefly reviewed. Three types of particle accelerators for radioisotopes production and medical uses (including radiotherapy), corresponding to the proton energy (E p p p < 200 MeV) are presented. PET imaging equipment and procedures are discussed. Main radiopharmaceuticals based on beta decay for PET studies and their role in medicine is also described. Finally, perspectives for a PET program in Romania (Cyclotron + Radiochemistry + Tomograph ) are discussed. (author)

Search for right-handed currents in muon decay

International Nuclear Information System (INIS)

Carr, J.

The experiment is motivated by the recent interest in left-right symmetric theories based on the gauge group SU(2)sub(R) x SU(2)sub(L) x U(1). Such theories are left-right symmetric at the Lagrangian level but account for the apparently maximal parity violation at present energies by assuming that the right-handed gauge boson Wsub(R) has acquired, through spontaneous symmetry breaking, a mass larger than its left-handed counterpart Wsub(L). A search is made for deviations from maximal parity violation by observing the muon decay rate when the decay positron is emitted with momentum close to the kinematic limit and opposite to the muon spin direction. This decay rate approaches zero at the kinematic limit for purely left-handed W's (V-A) but is large for right-handed W's (V+A). From the data, bounds on the right-handed gauge boson mass and also on non-(V or A) couplings can be set. (author)

Lepton polarization asymmetries in rare semi-tauonic b → s exclusive decays at FCC-ee

Energy Technology Data Exchange (ETDEWEB)

Kamenik, J.F. [Jozef Stefan Institute, Ljubljana (Slovenia); University of Ljubljana, Faculty of Mathematics and Physics, Ljubljana (Slovenia); Monteil, S. [Universite Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand (France); Semkiv, A. [Universite Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand (France); Taras Shevchenko National University of Kyiv, Kyiv (Ukraine); Silva, L.V. [Jozef Stefan Institute, Ljubljana (Slovenia)

2017-10-15

We consider measurements of exclusive rare semi-tauonic b-hadron decays, mediated by the b → sτ{sup +}τ{sup -} transition, at a future high-energy circular electron-positron collider (FCC-ee). We argue that the high boosts of b-hadrons originating from on-shell Z boson decays allow for a full reconstruction of the decay kinematics in hadronic τ decay modes (up to discrete ambiguities). This, together with the potentially large statistics of Z → b anti b, opens the door for the experimental determination of τ polarizations in these rare b-hadron decays. In the light of the current experimental situation on lepton flavor universality in rare semileptonic B decays, we discuss the complementary short-distance physics information carried by the τ polarizations and suggest suitable theoretically clean observables in the form of single- and double-τ polarization asymmetries. (orig.)

Reconstruction of photon conversions in {tau} lepton decays in the ATLAS experiment

Energy Technology Data Exchange (ETDEWEB)

Boehler, Michael

2009-04-15

The ATLAS experiment is one of the experiments at the Large Hadron Collider (LHC) which is designed for the search of new elementary particles. To discover the Higgs boson or precisely measure SUSY scenarios, {tau} lepton final states are very powerful decay channels. Therefore the {tau} lepton decay modes have to be identified correctly. Due to interactions between photons from hadronic decay products of the {tau} lepton and detector material electron-positron pairs (photon conversions) may be produced. These lead to additional charged tracks changing the reconstructed {tau} lepton track multiplicity. To avoid such missidentifications, this thesis introduces an explicit photon conversion identification in the very dense {tau} lepton decay environment. Existing tools had to be modified and a new electron identification method has been developed especially for this task. As a first result, the corrected {tau} lepton track multiplicity is presented. (orig.)

Reconstruction of photon conversions in τ lepton decays in the ATLAS experiment

International Nuclear Information System (INIS)

Boehler, Michael

2009-04-01

The ATLAS experiment is one of the experiments at the Large Hadron Collider (LHC) which is designed for the search of new elementary particles. To discover the Higgs boson or precisely measure SUSY scenarios, τ lepton final states are very powerful decay channels. Therefore the τ lepton decay modes have to be identified correctly. Due to interactions between photons from hadronic decay products of the τ lepton and detector material electron-positron pairs (photon conversions) may be produced. These lead to additional charged tracks changing the reconstructed τ lepton track multiplicity. To avoid such missidentifications, this thesis introduces an explicit photon conversion identification in the very dense τ lepton decay environment. Existing tools had to be modified and a new electron identification method has been developed especially for this task. As a first result, the corrected τ lepton track multiplicity is presented. (orig.)

Investigation of positron moderator materials for electron-linac-based slow positron beamlines

International Nuclear Information System (INIS)

Suzuki, Ryoichi; Ohdaira, Toshiyuki; Uedono, Akira

1998-01-01

Positron re-emission properties were studied on moderator materials in order to improve the positron moderation system of electron-linac-based intense slow positron beamlines. The re-emitted positron fraction was measured on tungsten, SiC, GaN, SrTiO 3 , and hydrogen-terminated Si with a variable-energy pulsed positron beam. The results suggested that tungsten is the best material for the primary moderator of the positron beamlines while epitaxially grown n-type 6H-SiC is the best material for the secondary moderator. Defect characterization by monoenergetic positron beams and surface characterization by Auger electron spectroscopy were carried out to clarify the mechanism of tungsten moderator degradation induced by high-energy electron irradiation. The characterization experiments revealed that the degradation is due to both radiation-induced vacancy clusters and surface carbon impurities. For the restoration of degraded tungsten moderators, oxygen treatment at ∼900degC is effective. Furthermore, it was found that oxygen at the tungsten surface inhibits positronium formation; as a result, it can increase the positron re-emission fraction. (author)

Positron emitting radionuclides for South Africa

International Nuclear Information System (INIS)

Wynchbank, S.; Van der Walt, T.N.; Sharpey-Shafer, J.

2004-01-01

Full text: In South Africa there are currently two projects underway to supply and utilise positron emitting radionuclides for imaging in clinical nuclear medicine facilities. The advantages and applications of such radio nuclides are numerous and well known. However the premier initial application will be to employ 1BF, at first in the compound fluorine-18 fluorodeoxyglucose ( 18 F)-FDG, for patients with cancers and neoplasms. The two projects are sited at iThemba LABS, where production of a generator supplying 66 Ga and the provision of ( 18 F]-FDG, are in an advanced state of planning; the former already fully financed by the Innovation Fund of the National Research Foundation. The two positron emitting radionuclides, 18 F and 68 Ge, will be produced using a cyclotron induced reaction on 1802 and Ga, respectively, at iThemba LABS. The 68 Ge/ 68 Ga generator consists of an anion exchanger loaded with 68 Ge, which decays to 68 Ga. The resulting radiopharmaceuticals, ( 18 F]-FDG and 68 Ga citrate, will be produced by the Radionuclide Production Group of iThemba LABS, using well described methods. However the structures and processes to be used in the generator to provide 68 Ga are novel and will be explained. Initially provision of the CBF]-FDG will be to selected clinical medicine facilities in the Western Cape and Gauteng. It should be noted that the logistical problems of providing this radiopharmaceutical (which are much complicated by its short half life of 109.7 min) to Gauteng, were shown to be surmountable in the 1970s, by a regular delivery of 18 F between Gauteng and Cape Town, after the advent of a commercial service using jet aircraft. The obvious requirement that there should be appropriate nuclear medicine facilities to image patients, at the sites to which the positron emitting radiopharmaceuticals will be supplied, has been addressed. Proposed solutions will be outlined, in terms of a dedicated positron emission tomography (PET) camera and a gamma

Determination of the CKM-matrix element |Vub| from the electron energy spectrum measured in inclusive B→Xueν decay with the BABAR detector

International Nuclear Information System (INIS)

Lueck, Thomas

2013-01-01

This document presents a measurement of the CKM matrix-element vertical stroke V ub vertical stroke in inclusive semileptonic B→X u eν events on a dataset of 471 million B anti B events recorded by the BABAR detector. Inclusive B→X u eν decays are selected by reconstructing a high energetic electron (positron). Background suppression is achieved by selecting events with electron (positron) energies near the kinematical allowed endpoint of B→X u eν decays. A B→D * eν veto is applied to further suppress background. This veto uses D * mesons which have been reconstructed with a partial reconstruction technique.

Recent results on D meson decays from the MARK III

International Nuclear Information System (INIS)

Coward, D.H.

1985-10-01

The MARK III Collaboration recently completed the analysis of a number of decay modes of charged and neutral D mesons produced in electron-positron collisions near the peak of the psi(3770) resonance at SLAC's SPEAR storage ring. The mesons were produced nearly at rest in pairs, either D + D - or D 0 anti D 0 , at a center-of-mass energy below the threshold for DD production. The unique kinematics of the production allow us to isolate the charmed meson signal clearly and unambiguously. The data were collected with the MARK III Spectrometer, a large solid angle magnetic detector. Our data sample corresponds to an integrated luminosity of approximately 9.3 inverse picobarns. New results will be presented on the absolute branching ratios of D mesons into hadronic final states, branching ratios for three body decays via pseudoscalar-vector intermediate states, and branching ratios for Cabibbo allowed and Cabibbo suppressed decays. Inclusive and exclusive branching ratios for the semi-leptonic decays of D mesons will be presented, as well as the first measurement of the vector form factor in the decay D 0 → K - e + nu, evidence for interference in D + decays, and new information on the contributions of W exchange diagrams to D 0 decays

Dark matter for excess of AMS-02 positrons and antiprotons

Directory of Open Access Journals (Sweden)

Chuan-Hung Chen

2015-07-01

Full Text Available We propose a dark matter explanation to simultaneously account for the excess of antiproton-to-proton and positron power spectra observed in the AMS-02 experiment while having the right dark matter relic abundance and satisfying the current direct search bounds. We extend the Higgs triplet model with a hidden gauge symmetry of SU(2X that is broken to Z3 by a quadruplet scalar field, rendering the associated gauge bosons stable weakly-interacting massive particle dark matter candidates. By coupling the complex Higgs triplet and the SU(2X quadruplet, the dark matter candidates can annihilate into triplet Higgs bosons each of which in turn decays into lepton or gauge boson final states. Such a mechanism gives rise to correct excess of positrons and antiprotons with an appropriate choice of the triplet vacuum expectation value. Besides, the model provides a link between neutrino mass and dark matter phenomenology.

Positron astrophysics and areas of relation to low-energy positron physics

Science.gov (United States)

Guessoum, Nidhal

2014-05-01

I briefly review our general knowledge of positron astrophysics, focusing mostly on the theoretical and modelling aspects. The experimental/observational aspects of the topic have recently been reviewed elsewhere [E. Churazov et al., Mon. Nat. R. Astron. Soc. 411, 1727 (2011); N. Prantazos et al., Rev. Mod. Phys. 83, 1001 (2011)]. In particular, I highlight the interactions and cross sections of the reactions that the positrons undergo in various cosmic media. Indeed, these must be of high interest to both the positron astrophysics community and the low-energy positron physics community in trying to find common areas of potential collaboration for the future or areas of research that will help the astrophysics community make further progress on the problem. The processes undergone by positrons from the moments of their birth to their annihilation (in the interstellar medium or other locations) are thus examined. The physics of the positron interactions with gases and solids (dust grains) and the physical conditions and characteristics of the environments where the processes of energy loss, positronium formation, and annihilation take place, are briefly reviewed. An explanation is given about how all the relevant physical information is taken into account in order to calculate annihilation rates and spectra of the 511 keV emission in the ISM; special attention is paid to positron interactions with dust and with polycyclic aromatic hydrocarbons. In particular, an attempt is made to show to what extent the interactions between positrons and interstellar dust grains are similar to laboratory experiments in which beams of low-energy positrons impinge upon solids and surfaces. Sample results are shown for the effect of dust grains on positron annihilation spectra in some phases of the ISM which, together with high resolution spectra measured by satellites, can be used to infer useful knowledge about the environment where the annihilation is predominantly taking place

Positron-atom collisions

International Nuclear Information System (INIS)

Drachman, R.J.

1984-01-01

The past decade has seen the field of positron-atom collisions mature into an important sub-field of atomic physics. Increasingly intense positron sources are leading towards a situation in which electron and positron collision experiments will be on almost an equal footing, challenging theory to analyze their similarities and differences. The author reviews the advances made in theory, including dispersion theory, resonances, and inelastic processes. A survey of experimental progress and a brief discussion of astrophysical positronics is also included. (Auth.)

Positron astrophysics and areas of relation to low-energy positron physics

International Nuclear Information System (INIS)

Guessoum, N.

2014-01-01

I briefly review our general knowledge of positron astrophysics, focusing mostly on the theoretical and modelling aspects. The experimental/observational aspects of the topic have recently been reviewed elsewhere [E. Churazov et al., Mon. Nat. R. Astron. Soc. 411, 1727 (2011); N. Prantazos et al., Rev. Mod. Phys. 83, 1001 (2011)]. In particular, I highlight the interactions and cross sections of the reactions that the positrons undergo in various cosmic media. Indeed, these must be of high interest to both the positron astrophysics community and the low-energy positron physics community in trying to find common areas of potential collaboration for the future or areas of research that will help the astrophysics community make further progress on the problem. The processes undergone by positrons from the moments of their birth to their annihilation (in the interstellar medium or other locations) are thus examined. The physics of the positron interactions with gases and solids (dust grains) and the physical conditions and characteristics of the environments where the processes of energy loss, positronium formation, and annihilation take place, are briefly reviewed. An explanation is given about how all the relevant physical information is taken into account in order to calculate annihilation rates and spectra of the 511 keV emission in the ISM; special attention is paid to positron interactions with dust and with polycyclic aromatic hydrocarbons. In particular, an attempt is made to show to what extent the interactions between positrons and interstellar dust grains are similar to laboratory experiments in which beams of low-energy positrons impinge upon solids and surfaces. Sample results are shown for the effect of dust grains on positron annihilation spectra in some phases of the ISM which, together with high resolution spectra measured by satellites, can be used to infer useful knowledge about the environment where the annihilation is predominantly taking place

Harvesting the decay energy of 26Al to drive lightning discharge in protoplanetary discs

Science.gov (United States)

Johansen, Anders; Okuzumi, Satoshi

2018-01-01

Chondrules in primitive meteorites likely formed by recrystallisation of dust aggregates that were flash-heated to nearly complete melting. Chondrules may represent the building blocks of rocky planetesimals and protoplanets in the inner regions of protoplanetary discs, but the source of ubiquitous thermal processing of their dust aggregate precursors remains elusive. Here we demonstrate that escape of positrons released in the decay of the short-lived radionuclide 26Al leads to a large-scale charging of dense pebble structures, resulting in neutralisation by lightning discharge and flash-heating of dust and pebbles. This charging mechanism is similar to a nuclear battery where a radioactive source charges a capacitor. We show that the nuclear battery effect operates in circumplanetesimal pebble discs. The extremely high pebble densities in such discs are consistent with conditions during chondrule heating inferred from the high abundance of sodium within chondrules. The sedimented mid-plane layer of the protoplanetary disc may also be prone to charging by the emission of positrons, if the mass density of small dust there is at least an order of magnitude above the gas density. Our results imply that the decay energy of 26Al can be harvested to drive intense lightning activity in protoplanetary discs. The total energy stored in positron emission is comparable to the energy needed to melt all solids in the protoplanetary disc. The efficiency of transferring the positron energy to the electric field nevertheless depends on the relatively unknown distribution and scale-dependence of pebble density gradients in circumplanetesimal pebble discs and in the protoplanetary disc mid-plane layer.

Positrons and positronium

International Nuclear Information System (INIS)

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

1988-01-01

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

Shape coexistence, Lanczos techniques, and large-basis shell-model calculations

Energy Technology Data Exchange (ETDEWEB)

Haxton, W C [Washington Univ., Seattle, WA (United States). Dept. of Physics

1992-08-01

I discuss numerical many-body techniques based on the Lanczos algorithm and their applications to nuclear structure problems. Examples include shape coexistence, inclusive response functions, and weak interaction rates in {sup 16}O; weak-coupling descriptions of the O{sup +} bands in isotopes of Ge and Se; and the evaluation of the nuclear Green`s functions that arise in two-neutrino {beta}{beta} decay and in nuclear anapole and electric dipole moment calculations. (author). 11 refs., 2 tabs., 4 figs.

The proposed INEL intense slow positron source, beam line, and positron microscope facility

International Nuclear Information System (INIS)

Makowitz, H.; Denison, A.B.; Brown, B.

1993-01-01

A program is currently underway at the Idaho National Engineering Laboratory (INEL) to design and construct an Intense Slow Positron Beam Facility with an associated Positron Microscope. Positron beams have been shown to be valuable research tools and have potential application in industrial processing and nondestructive evaluation (microelectronics, etc.). The limit of resolution or overall usefulness of the technique has been limited because of lack of sufficient intensity. The goal of the INEL positron beam is ≥ 10 12 slow e+/s over a 0.03 cm diameter which represents a 10 3 to 10 4 advancement in beam current over existing beam facilities. The INEL is an ideal site for such a facility because of the nuclear reactors capable of producing intense positron sources and the personnel and facilities capable of handling high levels of radioactivity. A design using 58 Co with moderators and remoderators in conjunction with electrostatic positron beam optics has been reached after numerous computer code studies. Proof-of-principle electron tests have demonstrated the feasibility of the large area source focusing optics. The positron microscope development is occurring in conjunction with the University of Michigan positron microscope group. Such a Beam Facility and associated Intense Slow Positron Source (ISPS) can also be utilized for the generation and study of positron, and positron electron plasmas at ≤ 10 14 particles/cm 3 with plasma temperatures ranging from an eV to many keV, as well as an intense x-ray source via positron channeling radiation. The possibility of a tunable x-ray laser based on channeling positron radiation also exists. In this discussion the authors will present a progress report on various activities associated with the INEL ISPS

Positron emission tomography

International Nuclear Information System (INIS)

Reivich, M.; Alavi, A.

1985-01-01

This book contains 24 selections. Some of the titles are: Positron Emission Tomography Instrumentation, Generator Systems for Positron Emitters, Reconstruction Algorithms, Cerebral Glucose Consumption: Methodology and Validation, Cerebral Blood Flow Tomography Using Xenon-133 Inhalation: Methods and Clinical Applications, PET Studies of Stroke, Cardiac Positron Emission Tomography, and Use of PET in Oncology

Double beta decay - physics beyond the standard model now, and in future (Genius)

Energy Technology Data Exchange (ETDEWEB)

Klapdor-Kleingrothaus, H.V.

1998-08-01

Nuclear double beta decay provides an extraordinarily broad potential to search for beyond standard model physics, probing already now the TeV scale, on which new physics should manifest itself. These possibilities are reviewed here. First, the results of present generation experiments are presented. The most sensitive one of them - the Heidelberg-Moscow experiment in the Gran Sasso - probes the electron mass now in the sub eV region and will reach a limit of {proportional_to}0.1 eV in a few years. Basing to a large extent on the theoretical work of the Heidelberg double beta group in the last two years, results are obtained also for SUSY models (R-parity breaking, sneutrino mass), leptoquarks (leptoquark-Higgs coupling), compositeness, right-handed W boson mass and others. These results are comfortably competitive to corresponding results from high-energy accelerators like TEVATRON, HERA, etc. Second, future perspectives of {beta}{beta} research are discussed. A new Heidelberg experimental proposal (GENIUS) is presented which would allow to increase the sensitivity for Majorana neutrino masses from the present level of at best 0.1 eV down to 0.01 or even 0.001 eV. Its physical potential would be a breakthrough into the multi-TeV range for many beyond standard models. Its sensitivity for neutrino oscillation parameters would be larger than of all present terrestrial neutrino oscillation experiments and of those planned for the future. (orig.)

Cardiac positron emission tomography

International Nuclear Information System (INIS)

Eftekhari, M.; Ejmalian, G.

2003-01-01

Positron emission tomography is an intrinsically tool that provide a unique and unparalleled approach for clinicians and researchers to interrogate the heart noninvasively. The ability to label substances of physiological interest with positron-emitting radioisotopes has permitted insight into normal blood flow and metabolism and the alterations that occur with disease states. Positron emission tomography of the heart has evolved as a unique, noninvasive approach for the assessment of myocardial perfusion, metabolism, and function. Because of the intrinsic quantitative nature of positron emission tomography measurements as well as the diverse compounds that can be labeled with positron- emitting radioisotopes, studies with positron emission tomography have provided rich insight into the physiology of the heart under diverse conditions

Search for right-handed currents in muon decay

International Nuclear Information System (INIS)

Gobbi, B.

1983-01-01

We report preliminary results of an experiment designed to measure the mass of the right-handed intermediate vector boson. The presence of such a particle in electroweak interactions is predicted by left-right symmetric gauge theories. The experiment measures the momentum spectrum of the positrons from the decay at rest of (1) longitudinally polarized muons produced in the decay at rest of π + → μ + nu (polarization P/sub μ/) and (2) unpolarized muons. The endpoints of these two spectra are used to determine the quantity xi P/sub μ/ where xi is a Michel parameter. This product is related to the ratio of the mass of left and right handed W and to the phase between the two helicity states. We measure, at the 90% CL, 1 - delta/rho 380 GeV/c 2

BEPC II positron source

International Nuclear Information System (INIS)

Pei Guoxi; Sun Yaolin; Liu Jintong; Chi Yunlong; Liu Yucheng; Liu Nianzong

2006-01-01

BEPC II-an upgrade project of the Beijing Electron Positron Collider (BEPC) is a factory type of e + e - collider. The fundamental requirements for its injector linac are the beam energy of 1.89 GeV for on-energy injection and a 40 mA positron beam current at the linac end with a low beam emittance of 1.6 μm and a low energy spread of ±0.5% so as to guarantee a higher injection rate (≥50 mA/min) to the storage ring. Since the positron flux is proportional to the primary electron beam power on the target, the authors will increase the electron gun current from 4A to 10A by using a new electron gun system and increase the primary electron energy from 120 MeV to 240 MeV. The positron source itself is an extremely important system for producing more positrons, including a positron converter target chamber, a 12kA flux modulator, the 7m focusing module with DC power supplies and the support. The new positron production linac from the electron gun to the positron source has been installed into the tunnel. In what follows, the authors will emphasize the positron source design, manufacture and tests. (authors)

Positron annihilation studies on bulk metallic glass and high intensity positron beam developments

International Nuclear Information System (INIS)

Asoka-Kumar, P.; Stoeffl, W.

2003-01-01

Positron annihilation spectroscopy is an ideal probe to examine atomic scale open-volume regions in materials. Below, we summarize the recent results on studies of open-volume regions of a multicomponent Zr-Ti-Ni-Cu-Be bulk metallic glass. Our studies establish two types of open-volume regions, one group that is too shallow to trap positrons at room temperature and becomes effective only at low temperatures and the other group that localizes positrons at room temperature and is large enough to accommodate hydrogen. The second half of the paper will concentrate on the high intensity positron program at Lawrence Livermore National Laboratory. A new positron production target is under development and we are constructing two experimental end stations to accommodate a pulsed positron microprobe and an experiment on positron diffraction and holography. Important design considerations of these experiments will be described. (author)

TPC spectrometer for measuring the e+ spectrum in μ decay

International Nuclear Information System (INIS)

Kinnison, W.W.

1983-01-01

The Time Projection Chamber (TPC) being used at the Los Alamos Meson Physics Facility (LAMPF) for a high-statistics normal muon-decay experiment is described. It is shown how the experiment will improve upon the limits of the weak-interaction coupling constants by a factor of 5 through the measurement of the positron momentum and direction of emission with respect to the muon-polarization vector for 10 8 decays of stopped, polarized, positive muons. The TPC apparatus is described, and it is shown that even though more work is to be done to improve the detector acceptance and individual coordinate resolutions, for certain track topologies, the TPC already has a momentum resolution of 0.7% (sigma)

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

Positron emission tomography

International Nuclear Information System (INIS)

Paans, A.M.J.

1981-01-01

Positron emitting radiopharmaceuticals have special applications in in-vivo studies of biochemical processes. The combination of a cyclotron for the production of radionuclides and a positron emission tomograph for the registration of the distribution of radioactivity in the body enables the measurement of local radioactivity concentration in tissues, and opens up new possibilities in the diagnosis and examination of abnormalities in the metabolism. The principles and procedures of positron emission tomography are described and the necessary apparatus considered, with emphasis on the positron camera. The first clinical applications using 55 Co bloemycine for tumor detection are presented. (C.F.)

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.)

Solvated Positron Chemistry - Positron Reactions with Pseudo-Halide Ions in Water

DEFF Research Database (Denmark)

Mogensen, O. E.; Pedersen, Niels Jørgen; Andersen, Jan Rud

1982-01-01

The hydrated positron e+aq reactions with SCN−, OCN−, CN−, S2− were studied by means of the angular correlation technique. The positron forms bound states with SCN−, CN−, and S2− but not with OCN−. Apparently, the e+aq reaction with SH− results in a positron bound state with S2−. It was difficult...

Hadronic decays of tau-leptons in the extended Nambu-Jona-Lasinio model

Energy Technology Data Exchange (ETDEWEB)

Kostunin, Dmitriy [Karlsruher Institut fuer Technologie (KIT), Karlsruhe (Germany). Inst. fuer Kernphysik (IKP); Volkov, Mikhail; Arbuzov, Andrey [Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research (JINR), Dubna (Russian Federation)

2013-07-01

Modern experiments have collected large statistics on tau-lepton decays and electron-positron annihilation into light hadrons. Therefore it is worthwhile to confront the experimental results with the corresponding theoretical predictions. The extended Nambu-Jona-Lasinio model is a good candidate for the theoretical description of these processes. Excited states of mesons in this version of the NJL model are described with the help of polynomial form-factors with minimal number of parameters. We worked out decays and cross-sections with ππ, ππ(1300), ωπ, ηπ, η'π, ηππ, η'ππ final states. Our calculations are in satisfactory agreement with the existing experimental results. Predictions for branching ratios of suppressed decays were obtained and compared with previous theoretical estimates.

Production and chemical isolation procedure of positron-emitting isotopes of arsenic for environmental and medical applications

Science.gov (United States)

Ellison, P. A.; Barnhart, T. E.; Engle, J. W.; Nickles, R. J.; DeJesus, O. T.

2012-12-01

The positron-emitting isotopes of arsenic have unique potential for imaging research in medical and environmental applications. The production and purification of radioarsenic from proton-irradiated natural GeO2 targets is reported. The separation procedure utilizes precipitation and anion exchange separation steps. Two anion exchange procedures were investigated. An overall arsenic decay-corrected separation yield of 80% was obtained.

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

International Nuclear Information System (INIS)

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

2016-01-01

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

Positron-Induced Luminescence

Science.gov (United States)

Stenson, E. V.; Hergenhahn, U.; Stoneking, M. R.; Pedersen, T. Sunn

2018-04-01

We report on the observation that low-energy positrons incident on a phosphor screen produce significantly more luminescence than electrons do. For two different wide-band-gap semiconductor phosphors (ZnS:Ag and ZnO:Zn), we compare the luminescent response to a positron beam with the response to an electron beam. For both phosphors, the positron response is significantly brighter than the electron response, by a factor that depends strongly on incident energy (0-5 keV). Positrons with just a few tens of electron-volts of energy (for ZnS:Ag) or less (for ZnO:Zn) produce as much luminescence as is produced by electrons with several kilo-electron-volts. We attribute this effect to valence band holes and excited electrons produced by positron annihilation and subsequent Auger processes. These results demonstrate a valuable approach for addressing long-standing questions about luminescent materials.

Search for massive neutrinos in π → eν decay

International Nuclear Information System (INIS)

Dixit, M.S.; Bryman, D.A.; Dubois, R.; Numao, T.; Olaniyi, B.; Olin, A.; Poutissou, J.-M.; Macdonald, J.A.

1982-11-01

The positron spectrum from π sup(+) → e sup(+)ν sub(e) decay has been examined for evidence of peaks arising from an admixture in the ν sub(e) weak eigenstate of massive neutrinos. Limits on the intensity of such peaks, together with the measured π → eν branching ratio, have been used to derive constraints on the neutrino mixing parameters over the range 4 MeV < m(ν) < 120 MeV

The final measurements of the muon decay parameters from the TWIST experiment

International Nuclear Information System (INIS)

Bayes, R

2013-01-01

The TWIST (TRIUMF Weak Interaction Symmetry Test) experiment probes the Lorentz structure of the weak interaction using muon decay. This structure has a very well defined form under the Standard Model (SM) which makes precise predictions for the shape of the decay positron spectrum with respect to momentum and angle. The shape of the spectrum may be described under some rather general assumptions using a set of decay parameters whose values according to the SM are ρ = δ = 3/4, η = 0, and ξ = 1. TWIST uses a large sample of muon decays in a large acceptance spectrometer to measure the decay parameters to an order of magnitude greater precision than previous measurements. This experiment saw its last year of data collection in 2007. As TWIST is a systematics dominated experiment, much effort has been spent on refinements of the estimates of the systematic uncertainties over previous TWIST results. These proceedings will discuss the measures taken to achieve the precision goal of parts in 10 4 , and the physics implications of the experiment.

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

International Nuclear Information System (INIS)

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

1975-01-01

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

Positron Factory project

Energy Technology Data Exchange (ETDEWEB)

Okada, Sohei; Sunaga, Hiromi; Kaneko, Hirohisa; Kawasuso, Atsuo; Masuno, Shin-ichi; Takizawa, Haruki; Yotsumoto, Keiichi [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan). Takasaki Radiation Chemistry Research Establishment

1997-03-01

We have started drafting a construction program for the Positron Factory, in which linac-based intense monoenergetic positron beams are planned to be applied for materials science, biotechnology and basic physics and chemistry. A technical survey study confirmed the feasibility of manufacturing a dedicated electron linac of 100 kW class with a beam energy of 100 MeV, which will produce a world-highest monoenergetic positron beam of more than 10{sup 10}/sec in intensity. A self-driven rotating converter (electrons to positrons and photons) suitable for the high power electron beam was devised and successfully tested. The practicability of simultaneous extraction of multi-channel monoenergetic positron beams with multiple moderator assemblies, which had been originated on the basis of a Monte Carlo simulation, was demonstrated by an experiment using an electron linac. An efficient moderator structure, which is composed of honeycomb-like assembled moderator foils and reflectors, is also proposed. (author)

KEK-IMSS Slow Positron Facility

Energy Technology Data Exchange (ETDEWEB)

Hyodo, T; Wada, K; Yagishita, A; Kosuge, T; Saito, Y; Kurihara, T; Kikuchi, T; Shirakawa, A; Sanami, T; Ikeda, M; Ohsawa, S; Kakihara, K; Shidara, T, E-mail: toshio.hyodo@kek.jp [High Energy Accelerator Research Organization (KEK) 1-1 Oho, Tsukuba, Ibaraki, 305-0801 (Japan)

2011-12-01

The Slow Positron Facility at the Institute of Material Structure Science (IMSS) of High Energy Accelerator Research Organization (KEK) is a user dedicated facility with an energy tunable (0.1 - 35 keV) slow positron beam produced by a dedicated 55MeV linac. The present beam line branches have been used for the positronium time-of-flight (Ps-TOF) measurements, the transmission positron microscope (TPM) and the photo-detachment of Ps negative ions (Ps{sup -}). During the year 2010, a reflection high-energy positron diffraction (RHEPD) measurement station is going to be installed. The slow positron generator (converter/ moderator) system will be modified to get a higher slow positron intensity, and a new user-friendly beam line power-supply control and vacuum monitoring system is being developed. Another plan for this year is the transfer of a {sup 22}Na-based slow positron beam from RIKEN. This machine will be used for the continuous slow positron beam applications and for the orientation training of those who are interested in beginning researches with a slow positron beam.

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

International Nuclear Information System (INIS)

Murphy, T.J.

1986-11-01

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

Resonant production of dark photons in positron beam dump experiments

Science.gov (United States)

Nardi, Enrico; Carvajal, Cristian D. R.; Ghoshal, Anish; Meloni, Davide; Raggi, Mauro

2018-05-01

Positrons beam dump experiments have unique features to search for very narrow resonances coupled superweakly to e+e- pairs. Due to the continued loss of energy from soft photon bremsstrahlung, in the first few radiation lengths of the dump a positron beam can continuously scan for resonant production of new resonances via e+ annihilation off an atomic e- in the target. In the case of a dark photon A' kinetically mixed with the photon, this production mode is of first order in the electromagnetic coupling α , and thus parametrically enhanced with respect to the O (α2)e+e-→γ A' production mode and to the O (α3)A' bremsstrahlung in e- -nucleon scattering so far considered. If the lifetime is sufficiently long to allow the A' to exit the dump, A'→e+e- decays could be easily detected and distinguished from backgrounds. We explore the foreseeable sensitivity of the Frascati PADME experiment in searching with this technique for the 17 MeV dark photon invoked to explain the Be 8 anomaly in nuclear transitions.

Addendum to ''Radiative corrections to the Dalitz plot of semileptonic decays of neutral baryons with light or charm quarks''

International Nuclear Information System (INIS)

Martinez, A.; Tun, D.M.; Garcia, A.; Sanchez-Colon, G.

1994-01-01

We show that the radiative corrections containing terms up to order αq/πM 1 for unpolarized semileptonic decays of baryons with positron emission can be obtained by simply reversing the sign of the axial-vector form factors in the corresponding final expressions of such decays with electron emission. This rule is valid regardless of the final kinematical variables chosen and of the particular Lorentz frame in which the final results are required

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.

Analysis of the radiative decay J/ψ → γωω at BESIII

Energy Technology Data Exchange (ETDEWEB)

Albrecht, Malte [Institut fuer Experimentalphysik I, Ruhr-Universitaet Bochum (Germany)

2015-07-01

Gluonic bound states like glueballs or hybrids are predicted to be copiously produced in the radiative decays of J/ψ. Especially the radiative decays into two vector mesons, J/ψ → γVV, have been intensively studied, since pseudoscalar (0{sup -}) enhancements have been observed in the ρρ, φφ and ωω final states with low statistics in the past. In this talk we show preliminary results of the analysis of the radiative decay J/ψ → γωω, using the world's largest data sample of ∼ 1.2.10{sup 9} J/ψ events collected with the Beijing Spectrometer III (BESIII) at the Beijing Electron-Positron Collider (BEPCII). The data selection, background analysis and preliminary results of a mass-independent partial wave analysis of the selected sample are presented.

Power Deposition due to Muon Decay Losses in a Neutrino Factory

CERN Document Server

Keil, Eberhard

2000-01-01

The power in the charged muon decay products, deposited per unit distance, depends on the muon energy only through the relativistic factor beta. For a typical neutrino factory it is about one Watt/m, multiplied by the number of passes through a particular component. The power is highest in the muon decay ring, where the muon lifetime cooresponds to about 150 turns. The electrons or positrons from muon decay in the long straight section may remain inside the vacuum chamber, until they are lost at the beginning of the arcs, because of their large energy errors, that are enhanced by synchrotron radiation losses. The power losses along the straight section and the arcs are studied by computer simulation, and the results are presented. About two thirds of the power ends up in the straight section, the remainder in the matching section and in the first half of the dispersion suppressor.

Positron emission computed tomography

International Nuclear Information System (INIS)

Grover, M.; Schelbert, H.R.

1985-01-01

Regional mycardial blood flow and substrate metabolism can be non-invasively evaluated and quantified with positron emission computed tomography (Positron-CT). Tracers of exogenous glucose utilization and fatty acid metabolism are available and have been extensively tested. Specific tracer kinetic models have been developed or are being tested so that glucose and fatty acid metabolism can be measured quantitatively by Positron-CT. Tracers of amino acid and oxygen metabolism are utilized in Positron-CT studies of the brain and development of such tracers for cardiac studies are in progress. Methods to quantify regional myocardial blood flow are also being developed. Previous studies have demonstrated the ability of Positron-/CT to document myocardial infarction. Experimental and clinical studies have begun to identify metabolic markers of reversibly ischemic myocardium. The potential of Positron-CT to reliably detect potentially salvageable myocardium and, hence, to identify appropriate therapeutic interventions is one of the most exciting applications of the technique

Theory, development, and applications of the scanning positron microbeam and positron reemission microscope

International Nuclear Information System (INIS)

Brandes, G.R.

1990-01-01

The theory, design, development, and applications of two new imaging instruments, the scanning positron microbeam (SPM) and positron reemission microscope (PRM), are discussed. The SPM consists of a sectored lens which focuses and rasters the positrons from the beam across the sample. The results of rastering the 10μm x 50μm beam across a test grid demonstrate the SPM's ability to scan a 500μm diameter region and to resolve features with ∼ 5μm resolution. The SPM was used to examine the location of defects in a Si-on-SiO 2 sample. Possible applications to three dimensional defect spectroscopy and the observation of small samples are considered. In the PRM, the positrons from the brightness-enhanced beam are focused at 5keV to an 8/Am diameter spot (FWHM) onto a thin metal single crystal. An image of the opposing side of the film is formed by accelerating and focusing the reemitted thermalized positrons with a cathode lens objective and a projector lens. The final image (real) is a record of the thermal positron emission intensity versus position. Images of surface and subsurface defect structures, taken at magnifications up to 4400x and with a resolution up to 80nm, are presented and discussed. The ultimate resolution capabilities and possible applications of the PRM are examined. The implantation and diffusion process of positrons was studied with the PRM by examining the positron emission profile of 3-9keV positrons implanted into a 2200 angstrom thick Ni single crystal

Positron studies in catalysis research

International Nuclear Information System (INIS)

1994-01-01

During the past eight months, the authors have made progress in several areas relevant to the eventual use of positron techniques in catalysis research. They have come closer to the completion of their positron microscope, and at the same time have performed several studies in their non-microscopic positron spectrometer which should ultimately be applicable to catalysis. The current status of the efforts in each of these areas is summarized in the following sections: Construction of the positron microscope (optical element construction, data collection software, and electronic sub-assemblies); Doppler broadening spectroscopy of metal silicide; Positron lifetime spectroscopy of glassy polymers; and Positron lifetime measurements of pore-sizes in zeolites

22 Na positron source for annihilation positron spectroscopy

International Nuclear Information System (INIS)

Cimpeanu, Catalina; Craciun, L.; Dragulescu, E.; Dudu, D.; Racolta, P. M.; Voiculescu, Dana; Miron, N.

2003-01-01

To extend the nuclear physics applications and to perform the study of vacancy - type defects in metals, semiconductors, polymers etc., we decided to promote positron annihilation techniques. In order to achieve this goal we started a project of dedicated positron sources produced at the IFIN-HH U-120 Cyclotron. We have used the nuclear reaction: 24 Mg(d,α) 22 Na with deuterons of 13 MeV energy. The paper presents the main characteristics of this procedure, as follows: general conditions asked for 22 NaCl sources, reactive chamber and characteristics of Mg target, parameters for the irradiation, radiochemical procedures for separating Na from Mg after the irradiation and geometrical or mechanical requirements for dedicated NaCl source for positron annihilation spectrometry. In the e + lifetime measurements, the e + end - start signals may be obtained from prompt γ -quanta emitted from the NaCl source (1. 275 MeV photons). The 22 NaCl stock solution obtained by radiochemical separation will be kept in quartz sealed ampoules in dry places and will be dropped between the study materials before the use in positron spectrometry. (authors)

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

Slow positron applications at slow positron facility of institute of materials structure science, KEK

Science.gov (United States)

Hyodo, Toshio; Mochizuki, Izumi; Wada, Ken; Toge, Nobukazu; Shidara, Tetsuo

2018-05-01

Slow Positron Facility at High Energy Accelerator Research Organization (KEK) is a user dedicated facility with an energy-tunable (0.1 - 35 keV) slow positron beam created by a dedicated ˜ 50 MeV linac. It operates in a short pulse (width 1-12 ns, variable, 5×106 e+/s) and a long pulse (width 1.2 µs, 5×107 e+/s) modes of 50 Hz. High energy positrons from pair creation are moderated by reemission after thermalization in W foils. The reemitted positrons are then electrostatically accelerated to a desired energy up to 35 keV and magnetically transported. A pulse-stretching section (pulse stretcher) is installed in the middle of the beamline. It stretches the slow positron pulse for the experiments where too many positrons annihilating in the sample at the same time has to be avoided. Four experiment stations for TRHEPD (total-reflection high-energy positron diffraction), LEPD (low-energy positron diffraction), Ps- (positronium negative ion), and Ps-TOF (positronium time-of-flight) experiments are connected to the beamline branches, SPF-A3, SPF-A4, SPF-B1 and SPF-B2, respectively. Recent results of these stations are briefly described.

Positron effective mass in silicon

International Nuclear Information System (INIS)

Panda, B.K.; Shan, Y.Y.; Fung, S.; Beling, C.D.

1995-01-01

The positron effective mass in Si is obtained from the first-principles calculations along various crystallographic directions. The effect of electron-positron correlation on the band mass is examined in this work. A positron pseudopotential scheme is worked out to calculate the isotropic band mass without explicitly solving the band energy. The effective mass 1.46m obtained as a sum of band mass and the positron-plasmon interaction compares very well with 1.5m obtained from the positron mobility data

Positron emission tomography

International Nuclear Information System (INIS)

Iio, Masahiro

1982-01-01

Utilization of positron emission tomography was reviewed in relation to construction and planned construction of small-size medical cyclotrons, planned construction of positron cameras and utilization of short-lived radionuclides. (Chiba, N.)

Contribution of the time of flight information to the positron tomographic imaging

International Nuclear Information System (INIS)

Laval, M.; Allemand, R.; Campagnolo, R.; Garderet, P.; Gariod, R.; Guinet, P.; Moszinski, M.; Tournier, E.; Vacher, J.

1982-09-01

The TOF measurement enables positrons to be localized along the line joining two detectors. The accuracy of this measurement is mainly controled by the scintillator performances: light yield, and decay time constant are the key parameters. The main advantage of using the TOF information can be expressed in terms of sensitivity gain: for example the ratio of the required total counts to obtain the same random noise in a positron image without and with the TOF information. This gain ranges from 1 to more than 10, depending on the TOF performance but also on the activity distribution. Other advantages are inherent on the TOF method: - the very high count rate capabilities of the detectors enables fast dymanic studies with for example O 15 ; - the random coincidences to be found in an imaged object are the lowest that can be achieved; - a small amount of radiation scattered by the object is rejected outside of the field of reconstruction

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

Energy Technology Data Exchange (ETDEWEB)

Piochacz, Christian

2009-11-20

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

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

International Nuclear Information System (INIS)

Piochacz, Christian

2009-01-01

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

Determination of the CKM-matrix element |V{sub ub}| from the electron energy spectrum measured in inclusive B→X{sub u}eν decay with the BABAR detector

Energy Technology Data Exchange (ETDEWEB)

Lueck, Thomas

2013-01-30

This document presents a measurement of the CKM matrix-element vertical stroke V{sub ub} vertical stroke in inclusive semileptonic B→X{sub u}eν events on a dataset of 471 million B anti B events recorded by the BABAR detector. Inclusive B→X{sub u}eν decays are selected by reconstructing a high energetic electron (positron). Background suppression is achieved by selecting events with electron (positron) energies near the kinematical allowed endpoint of B→X{sub u}eν decays. A B→D{sup *}eν veto is applied to further suppress background. This veto uses D{sup *} mesons which have been reconstructed with a partial reconstruction technique.

Pulse shape discrimination for Gerda Phase I data

Energy Technology Data Exchange (ETDEWEB)

Agostini, M.; Bode, T.; Budjas, D.; Janicsko Csathy, J.; Lazzaro, A.; Schoenert, S. [Technische Universitaet Muenchen, Physik Department and Excellence Cluster Universe, Muenchen (Germany); Allardt, M.; Barros, N.; Domula, A.; Lehnert, B.; Wester, T.; Zuber, K. [Technische Universitaet Dresden, Institut fuer Kern- und Teilchenphysik, Dresden (Germany); Andreotti, E. [Institute for Reference Materials and Measurements, Geel (Belgium); Eberhard Karls Universitaet Tuebingen, Physikalisches Institut, Tuebingen (Germany); Bakalyarov, A.M.; Belyaev, S.T.; Lebedev, V.I.; Zhukov, S.V. [National Research Centre ' ' Kurchatov Institute' ' , Moscow (Russian Federation); Balata, M.; Ioannucci, L.; Junker, M.; Laubenstein, M.; Macolino, C.; Nisi, S.; Pandola, L.; Zavarise, P. [LNGS, INFN Laboratori Nazionali del Gran Sasso, Assergi (Italy); Barabanov, I.; Bezrukov, L.; Gurentsov, V.; Inzhechik, L.V.; Kuzminov, V.V.; Lubsandorzhiev, B.; Yanovich, E. [Institute for Nuclear Research of the Russian Academy of Sciences, Moscow (Russian Federation); Barnabe Heider, M. [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Technische Universitaet Muenchen, Physik Department and Excellence Cluster Universe, Muenchen (Germany); Baudis, L.; Benato, G.; Ferella, A.; Guthikonda, K.K.; Tarka, M.; Walter, M. [Physik Institut der Universitaet Zuerich, Zuerich (Switzerland); Bauer, C.; Hampel, W.; Heisel, M.; Heusser, G.; Hofmann, W.; Kihm, T.; Kirsch, A.; Knoepfle, K.T.; Lindner, M.; Lubashevskiy, A.; Machado, A.A.; Maneschg, W.; Salathe, M.; Schreiner, J.; Schwingenheuer, B.; Simgen, H.; Smolnikov, A.; Strecker, H.; Wagner, V.; Wegmann, A. [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Becerici-Schmidt, N.; Caldwell, A.; Cossavella, F.; Liao, H.Y.; Liu, X.; Majorovits, B.; O' Shaughnessy, C.; Schulz, O.; Volynets, O. [Max-Planck-Institut fuer Physik, Muenchen (Germany); Bellotti, E.; Pessina, G. [Universita Milano Bicocca, Dipartimento di Fisica, Milano (Italy); INFN Milano Bicocca, Milano (Italy); Belogurov, S.; Kornoukhov, V.N. [Institute for Nuclear Research of the Russian Academy of Sciences, Moscow (Russian Federation); Institute for Theoretical and Experimental Physics, Moscow (Russian Federation); Bettini, A.; Brugnera, R.; Garfagnini, A.; Hemmer, S.; Sada, C. [Universita di Padova, Dipartimento di Fisica e Astronomia, Padova (Italy); INFN Padova, Padova (Italy); Brudanin, V.; Egorov, V.; Kochetov, O.; Nemchenok, I.; Rumyantseva, N.; Shevchik, E.; Zhitnikov, I.; Zinatulina, D. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Cattadori, C.; Gotti, C. [INFN Milano Bicocca, Milano (Italy); Chernogorov, A.; Demidova, E.V.; Kirpichnikov, I.V.; Vasenko, A.A. [Institute for Theoretical and Experimental Physics, Moscow (Russian Federation); Falkenstein, R.; Freund, K.; Grabmayr, P.; Hegai, A.; Jochum, J.; Schmitt, C. [Eberhard Karls Universitaet Tuebingen, Physikalisches Institut, Tuebingen (Germany); Frodyma, N.; Misiaszek, M.; Pelczar, K.; Wojcik, M.; Zuzel, G. [Jagiellonian University, Institute of Physics, Cracow (Poland); Gangapshev, A. [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Institute for Nuclear Research of the Russian Academy of Sciences, Moscow (Russian Federation); Gusev, K. [Joint Institute for Nuclear Research, Dubna (Russian Federation); National Research Centre ' ' Kurchatov Institute' ' , Moscow (Russian Federation); Technische Universitaet Muenchen, Physik Department and Excellence Cluster Universe, Muenchen (Germany); Hult, M.; Lutter, G. [Institute for Reference Materials and Measurements, Geel (Belgium); Klimenko, A. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Lippi, I.; Stanco, L.; Ur, C.A. [INFN Padova, Padova (Italy); Pullia, A.; Riboldi, S. [Universita degli Studi di Milano (IT); INFN Milano, Dipartimento di Fisica, Milano (IT); Shirchenko, M. [Joint Institute for Nuclear Research, Dubna (RU); National Research Centre ' ' Kurchatov Institute' ' , Moscow (RU); Sturm, K. von [Universita di Padova, Dipartimento di Fisica e Astronomia, Padova (IT); INFN Padova, Padova (IT); Eberhard Karls Universitaet Tuebingen, Physikalisches Institut, Tuebingen (DE)

2013-10-15

The Gerda experiment located at the Laboratori Nazionali del Gran Sasso of INFN searches for neutrinoless double beta (0{nu}{beta}{beta}) decay of {sup 76}Ge using germanium diodes as source and detector. In Phase I of the experiment eight semi-coaxial and five BEGe type detectors have been deployed. The latter type is used in this field of research for the first time. All detectors are made from material with enriched {sup 76}Ge fraction. The experimental sensitivity can be improved by analyzing the pulse shape of the detector signals with the aim to reject background events. This paper documents the algorithms developed before the data of Phase I were unblinded. The double escape peak (DEP) and Compton edge events of 2.615 MeV {gamma} rays from {sup 208}Tl decays as well as two-neutrino double beta (2{nu}{beta}{beta}) decays of {sup 76}Ge are used as proxies for 0{nu}{beta}{beta} decay. For BEGe detectors the chosen selection is based on a single pulse shape parameter. It accepts 0.92{+-}0.02 of signal-like events while about 80 % of the background events at Q{sub {beta}{beta}} =2039 keV are rejected. For semi-coaxial detectors three analyses are developed. The one based on an artificial neural network is used for the search of 0 {nu}{beta}{beta} decay. It retains 90 % of DEP events and rejects about half of the events around Q{sub {beta}{beta}}. The 2 {nu}{beta}{beta} events have an efficiency of 0.85 {+-}0.02 and the one for 0 {nu}{beta}{beta} decays is estimated to be 0.90{sup +0.05}{sub -0.09}. A second analysis uses a likelihood approach trained on Compton edge events. The third approach uses two pulse shape parameters. The latter two methods confirm the classification of the neural network since about 90 % of the data events rejected by the neural network are also removed by both of them. In general, the selection efficiency extracted from DEP events agrees well with those determined from Compton edge events or from 2{nu}{beta}{beta} decays. (orig.)

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

Science.gov (United States)

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

1997-04-01

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

ZnO Luminescence and scintillation studied via photoexcitation, X-ray excitation, and gamma-induced positron spectroscopy

Science.gov (United States)

Ji, J.; Colosimo, A. M.; Anwand, W.; Boatner, L. A.; Wagner, A.; Stepanov, P. S.; Trinh, T. T.; Liedke, M. O.; Krause-Rehberg, R.; Cowan, T. E.; Selim, F. A.

2016-08-01

The luminescence and scintillation properties of ZnO single crystals were studied by photoluminescence and X-ray-induced luminescence (XRIL) techniques. XRIL allowed a direct comparison to be made between the near-band emission (NBE) and trap emissions providing insight into the carrier recombination efficiency in the ZnO crystals. It also provided bulk luminescence measurements that were not affected by surface states. The origin of a green emission, the dominant trap emission in ZnO, was then investigated by gamma-induced positron spectroscopy (GIPS) - a unique defect spectroscopy method that enables positron lifetime measurements to be made for a sample without contributions from positron annihilation in the source materials. The measurements showed a single positron decay curve with a 175 ps lifetime component that was attributed to Zn vacancies passivated by hydrogen. Both oxygen vacancies and hydrogen-decorated Zn vacancies were suggested to contribute to the green emission. By combining scintillation measurements with XRIL, the fast scintillation in ZnO crystals was found to be strongly correlated with the ratio between the defect luminescence and NBE. This study reports the first application of GIPS to semiconductors, and it reveals the great benefits of the XRIL technique for the study of emission and scintillation properties of materials.

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

CERN Multimedia

CERN. Geneva

2008-01-01

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

Estimate of S-values for children due to six positron emitting radionuclides used in PET examinations

Science.gov (United States)

Belinato, Walmir; Santos, William S.; Perini, Ana P.; Neves, Lucio P.; Caldas, Linda V. E.; Souza, Divanizia N.

2017-11-01

Positron emission tomography (PET) has revolutionized the diagnosis of cancer since its conception. When combined with computed tomography (CT), PET/CT performed in children produces highly accurate diagnoses from images of regions affected by malignant tumors. Considering the high risk to children when exposed to ionizing radiation, a dosimetric study for PET/CT procedures is necessary. Specific absorbed fractions (SAF) were determined for monoenergetic photons and positrons, as well as the S-values for six positron emitting radionuclides (11C, 13N, 18F, 68Ga, 82Rb, 15O), and 22 source organs. The study was performed for six pediatric anthropomorphic hybrid models, including the newborn and 1 year hermaphrodite, 5 and 10-year-old male and female, using the Monte Carlo N-Particle eXtended code (MCNPX, version 2.7.0). The results of the SAF in source organs and S-values for all organs showed to be inversely related to the age of the phantoms, which includes the variation of body weight. The results also showed that radionuclides with higher energy peak emission produces larger auto absorbed S-values due to local dose deposition by positron decay. The S-values for the source organs are considerably larger due to the interaction of tissue with non-penetrating particles (electrons and positrons) and present a linear relationship with the phantom body masses. The results of the S-values determined for positron-emitting radionuclides can be used to assess the radiation dose delivered to pediatric patients subjected to PET examination in clinical settings. The novelty of this work is associated with the determination of auto absorbed S-values, in six new pediatric virtual anthropomorphic phantoms, for six emitting positrons, commonly employed in PET exams.

High current pulsed positron microprobe

International Nuclear Information System (INIS)

Howell, R.H.; Stoeffl, W.; Kumar, A.; Sterne, P.A.; Cowan, T.E.; Hartley, J.

1997-01-01

We are developing a low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopy to provide a new defect analysis capability at the 10 10 e + s -l beam at the Lawrence Livermore National Laboratory electron linac. When completed, the pulsed positron microprobe will enable defect specific, 3-dimensional maps of defect concentrations with sub-micron resolution of defect location. By coupling these data with first principles calculations of defect specific positron lifetimes and positron implantation profiles we will both map the identity and concentration of defect distributions

Efficient Cryosolid Positron Moderators

Science.gov (United States)

2012-08-01

table layout Figure 21 shows the integration of the IR spectroscopy optics with the positron Moderation and Annihilation vacuum chambers on the...Characterization of Cryogenic Moderators The application of Matrix Isolation Spectroscopy (MIS) to characterizing cryogenic solid positron ...Matrix Isolation Spectroscopy capability into our Positron Moderation apparatus, which enables spectroscopic characterization of the cryogenic

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

Science.gov (United States)

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

1993-12-01

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

The beta decay asymmetry parameter of 35Ar

International Nuclear Information System (INIS)

Garnett, J.D.

1987-11-01

The beta decay asymmetry parameter for 35 Ar = 35 Cl + e + + nu/sub e/ has been remeasured in order to resolve a long standing puzzle. Previous asymmetry measurements, when combined with the comparative half-life, yield a value for the vector coupling constant, G/sub v/, that is in serious disagreement with the accepted value. We produced polarized 35 Ar by a (p,n) reaction on 35 Cl using the polarized proton beam provided by Lawrence Berkeley Laboratory's 88-Inch Cyclotron. The polarization of the 35 Ar was determined by measuring the asymmetry of the positrons produced in 35 Ar decay to the first excited state in 35 Cl (branching ratio = 1.3%) in coincidence with a 1219.4 keV gamma ray. Our result, A 0 = 0.49 +- 0.10, combined with the comparative half-life yields a value for G/sub v/ in agreement with the accepted value

The Search for a Non-Superallowed Branch in the β decay of ^38mK

Science.gov (United States)

Leach, Kyle; Bandyopadhyay, D.; Finlay, P.; Garrett, P. E.; Grinyer, G. F.; Phillips, A. A.; Schumaker, M. A.; Svensson, C. E.; Wong, J.; Ball, G. C.; Bassiachvilli, E.; Ettenauer, S.; Hackman, G.; Morton, A. C.; Mythili, S.; Newman, O.; Pearson, C. J.; Pearson, M. R.; Savajols, H.; Leslie, J. R.; Melconian, D.; Austin, R. A. E.; Barton, C.

2007-10-01

The study presented is part of an experimental program exploring the properties of superallowed Fermi β decays conducted at the Isotope Separator and Accelerator (ISAC) facility at TRIUMF in Vancouver, B.C. Canada. Using the 8π γ-ray spectrometer and the Scintillating Electron Positron Tagging Array (SCEPTAR), it was possible to set a new upper limit on an unobserved non-analogue branch in the decay of ^38mK. This branch is expected to be extremely weak, and the removal of contaminant isobaric decays and background radiation in the spectra was thus exceedingly important during the analysis. Our work has reduced the previous upper limit by approximately a factor of two and is approaching the theoretically predicted branching ratio.

22 Na positron source for annihilation positron spectroscopy

International Nuclear Information System (INIS)

Cimpeanu, Catalina; Craciun, L.; Dragulescu, E.; Dudu, D.; Racolta, P.M.; Voiculescu, Dana; Miron, N.

2002-01-01

To extend the nuclear physics applications and to perform the study of vacancy - type defects in metals, semiconductors, polymers etc., we decided to promote positron annihilation techniques. In order to achieve this goal we started a project of dedicated positron sources produced at the IFIN-HH U-120 Cyclotron. We have used the nuclear reaction 24 Mg(d,α) 22 Na and deuterons of 13 MeV energy. The paper presents the main steps of this procedure like: general conditions required for 22 NaCl sources, reactive chamber and characteristics of Mg target, parameters for the irradiation, radiochemical procedures to separate Na from Mg after the irradiation and geometrical or mechanical requirements for dedicated NaCl source for positron annihilation spectrometry. In the e + lifetime measurements the e + 'death - stop' signals are always provided by γ - quanta generated by the e + e - annihilation and the 'birth - start' signals may be obtained from 'prompt' γ - quanta emitted from the NaCl source (the 1.275 MeV photons). The 22 NaCl stock solution obtained by radiochemical separation will be kept in the sealed quartz vials in dry places and will be dropped between the studied materials before use in positron spectrometry. (authors)

Positron Beam Characteristics at NEPOMUC Upgrade

Science.gov (United States)

Hugenschmidt, C.; Ceeh, H.; Gigl, T.; Lippert, F.; Piochacz, C.; Reiner, M.; Schreckenbach, K.; Vohburger, S.; Weber, J.; Zimnik, S.

2014-04-01

In 2012, the new neutron induced positron source NEPOMUC upgrade was put into operation at FRMII. Major changes have been made to the source which consists of a neutron-γ-converter out of Cd and a Pt foil structure for electron positron pair production and positron moderation. The new design leads to an improvement of both intensity and brightness of the mono-energetic positron beam. In addition, the application of highly enriched 113Cd as neutron-γ-converter extends the lifetime of the positron source to 25 years. A new switching and remoderation device has been installed in order to allow toggling from the high-intensity primary beam to a brightness enhanced remoderated positron beam. At present, an intensity of more than 109 moderated positrons per second is achieved at NEPOMUC upgrade. The main characteristics are presented which comprise positron yield and beam profile of both the primary and the remoderated positron beam.

Study of thermochemically reduced and electron-irradiated LiNbO3 single crystals by positron annihilation and optical absorption measurements

International Nuclear Information System (INIS)

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

1984-01-01

Irradiation of LiNbO 3 single crystals using Van de Graaff electrons with an energy of 1.5 MeV introduces an optical absorption band similar to that observed in thermochemically reduced samples. As-grown, reduced, or irradiated crystals show single-component positron lifetime spectra with an average decay time of 234 ps. (author)

Positron emission tomography

International Nuclear Information System (INIS)

Wienhard, K.; Heiss, W.D.

1984-01-01

The principles and selected clinical applications of positron emission tomography are described. In this technique a chemical compound is labeled with a positron emitting isotope and its biochemical pathway is traced by coincidence detection of the two annihilation photons. The application of the techniques of computed tomography allows to reconstruct the spatial distribution of the radioactivity within a subject. The 18 F-deoxyglucose method for quantitative measurement of local glucose metabolism is discussed in order to illustrate the possibilities of positron emission tomography to record physiological processes in vivo. (orig.) [de

Application of mathematical removal of positron range blurring in positron emission tomography

International Nuclear Information System (INIS)

Haber, S.F.; Derenzo, S.E.; Uber, D.

1990-01-01

The range of positrons in tissue is an important limitation to the ultimate spatial resolution achievable in positron emission tomography. In this work the authors have applied a Fourier deconvolution technique to remove range blurring in images taken by the Donner 600-crystal positron tomograph. Using phantom data, the authors have found significant improvement in the image quality and the FWHM for both 68 Ga and 82 Rb. These were successfully corrected so that the images and FWHM almost matched those of 18 F which has negligible positron range. However, statistical noise was increased by the deconvolution process and it was not practical to recover the full spatial resolution of the tomograph

From superWIMPs to decaying dark matter. Models, bounds and indirect searches

International Nuclear Information System (INIS)

Weniger, Christoph

2010-06-01

Despite lots of observational and theoretical efforts, the particle nature of dark matter remains unknown. Beyond the paradigmatic WIMPs (Weakly Interacting Massive Particles), many theoretically well motivated models exist where dark matter interacts much more weakly than electroweak with Standard Model particles. In this case new phenomena occur, like the decay of dark matter or the interference with the standard cosmology of the early Universe. In this thesis we study some of these aspects of superweakly coupled dark matter in general, and in the special case of hidden U(1) X gauginos that kinetically mix with hypercharge. There, we will assume that the gauge group remains unbroken, similar to the Standard Model U(1) em . We study different kinds of cosmological bounds, including bounds from thermal overproduction, from primordial nucleosynthesis and from structure formation. Furthermore, we study the possible cosmic-ray signatures predicted by this scenario, with emphasis on the electron and positron channel in light of the recent observations by PAMELA and Fermi LAT. Moreover we study the cosmic-ray signatures of decaying dark matter independently of concrete particle-physics models. In particular we analyze in how far the rise in the positron fraction above 10 GeV, as observed by PAMELA, can be explained by dark matter decay. Lastly, we concentrate on related predictions for gamma-ray observations with the Fermi LAT, and propose to use the dipole-like anisotropy of the prompt gamma-ray dark matter signal to distinguish exotic dark matter contributions from the extragalactic gamma-ray background. (orig.)

From superWIMPs to decaying dark matter. Models, bounds and indirect searches

Energy Technology Data Exchange (ETDEWEB)

Weniger, Christoph

2010-06-15

Despite lots of observational and theoretical efforts, the particle nature of dark matter remains unknown. Beyond the paradigmatic WIMPs (Weakly Interacting Massive Particles), many theoretically well motivated models exist where dark matter interacts much more weakly than electroweak with Standard Model particles. In this case new phenomena occur, like the decay of dark matter or the interference with the standard cosmology of the early Universe. In this thesis we study some of these aspects of superweakly coupled dark matter in general, and in the special case of hidden U(1){sub X} gauginos that kinetically mix with hypercharge. There, we will assume that the gauge group remains unbroken, similar to the Standard Model U(1){sub em}. We study different kinds of cosmological bounds, including bounds from thermal overproduction, from primordial nucleosynthesis and from structure formation. Furthermore, we study the possible cosmic-ray signatures predicted by this scenario, with emphasis on the electron and positron channel in light of the recent observations by PAMELA and Fermi LAT. Moreover we study the cosmic-ray signatures of decaying dark matter independently of concrete particle-physics models. In particular we analyze in how far the rise in the positron fraction above 10 GeV, as observed by PAMELA, can be explained by dark matter decay. Lastly, we concentrate on related predictions for gamma-ray observations with the Fermi LAT, and propose to use the dipole-like anisotropy of the prompt gamma-ray dark matter signal to distinguish exotic dark matter contributions from the extragalactic gamma-ray background. (orig.)

Application of Monte Carlo simulation to the standardization of positron emitting radionuclides; Aplicacao do metodo de Monte Carlo na padronizacao de radionuclideos emissores de positrons

Energy Technology Data Exchange (ETDEWEB)

Tongu, Margareth Lika Onishi

2009-07-01

Since 1967, the Nuclear Metrology Laboratory (LNM) at the Nuclear and Energy Research (IPEN) in Sao Paulo, Brazil, has developed radionuclide standardization methods and measurements of the Gamma-ray emission probabilities per decay by means of 4{pi}{beta}-{gamma} coincidence system, a high accuracy primary method for determining disintegration rate of radionuclides of interest. In 2001 the LNM started a research field on modeling, based on Monte Carlo method, of all the system components, including radiation detectors and radionuclide decay processes. This methodology allows the simulation of the detection process in a 4{pi}{beta}-{gamma} system, determining theoretically the observed activity as a function of the 4{pi}{beta} detector efficiency, enabling the prediction of the behavior of the extrapolation curve and optimizing a detailed planning of the experiment before starting the measurements. One of the objectives of the present work is the improvement of the 4{pi} proportional counter modeling, presenting a detailed description of the source holder and radioactive source material, as well as absorbers placed around the source. The simulation of radiation transport through the detectors has been carried out using code MCNPX. The main focus of the present work is on Monte Carlo modeling of the standardization of positron emitting radionuclides associated (or not) with electron capture and accompanied (or not) by the emission of Gamma radiation. One difficulty in this modeling is to simulate the detection of the annihilation Gamma ray, which arise in the process of positron absorption within the 4{pi} detector. The methodology was applied to radionuclides {sup 18}F and {sup 22}Na. (author)

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

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

International Nuclear Information System (INIS)

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

2006-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2006-02-28

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

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

Energy Technology Data Exchange (ETDEWEB)

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

1996-02-20

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

LLNL pure positron plasma program

International Nuclear Information System (INIS)

Hartley, J.H.; Beck, B.R.; Cowan, T.E.; Howell, R.H.; McDonald, J.L.; Rohatgi, R.R.; Fajans, J.; Gopalan, R.

1995-01-01

Assembly and initial testing of the Positron Time-of-Flight Trap at the Lawrence Livermore National Laboratory (LLNL) Increase Pulsed Positron Facility has been completed. The goal of the project is to accumulate at high-density positron plasma in only a few seconds., in order to facilitate study that may require destructive diagnostics. To date, densities of at least 6 x 10 6 positrons per cm 3 have been achieved

Search for Physics Beyond the Standard Model via Positron Polarization Measurements with Polarized $ ^{17} $F.

CERN Multimedia

Versyck, S

2002-01-01

This proposal aims at measuring the longitudinal polarization of positrons emitted from polarized $^{17} $F~nuclei. The experiment will have a comparable sensitivity to possible right-handed current contributions in the weak interaction as the experiment which was recently carried out with $ ^{107} $In in Louvain-la-Neuve, but will provide a more stringent limit due to the fact that, since $ ^{17} $F decays through a superallowed $\\beta$ -transition, the recoil-order corrections to the allowed approximation can be taken into account very precisely. Furthermore, because $ ^{17} $F decays via a mixed Fermi/Gamow-Teller $\\beta$ -transition, this experiment will also yield a new limit on possible scalar contributions to the weak interaction. While the $^{17}$F beam is being developed, part of the beamtime was used to perform a similar experiment with $^{118}$ Sb. As this isotope decays via a pure GT $\\beta$ -transition, this experiment will yield new limits on the possible presence of both right-handed and tensor...

Potential advantages of a cesium fluoride scintillator for a time-of-flight positron camera

International Nuclear Information System (INIS)

Allemand, R.; Gresset, C.; Vacher, J.

1980-01-01

In order to improve the quality of positron tomographic imaging, a time-of-flight technique combined with a classical reconstruction method has been investigated. The decay time of NaI(Tl) and bismuth germanate (BGO) scintillators is too long for this application, and efficiency of the plastic scintillators is too low. Cesium fluoride appears to be a very promising detector material. This paper presents preliminary results obtained with a time-of-flight technique using CsF scintillators. The expected advantages were realized

Search for bosonic stop decays in R-parity violating supersymmetry in e+p collisions at HERA

International Nuclear Information System (INIS)

Aktas, A.; Andreev, V.; Anthonis, T.

2004-05-01

A search for scalar top quarks in R-parity violating supersymmetry is performed in e + p collisions at HERA using the H1 detector. The data, taken at √(s) = 319 GeV and 301 GeV, correspond to an integrated luminosity of 106 pb -1 . The resonant production of scalar top quarks t in positron quark fusion via an R-parity violating Yukawa coupling λ' is considered with the subsequent bosonic stop decay t→bW. The R-parity violating decay of the sbottom quark b→d anti ν e and leptonic and hadronic W decays are considered. No evidence for stop production is found in the search for bosonic stop decays nor in a search for the direct R-parity violating decay trightarrow eq. Mass dependent limits on λ' are obtained in the framework of the minimal supersymmetric standard model. Stop quarks with masses up to 275 GeV can be excluded at the 95% confidence level for a Yukawa coupling of electromagnetic strength. (orig.)

Limits on heavy neutrino mixing from the beta decay of 38mK confined in a magneto-optical trap

International Nuclear Information System (INIS)

Trinczek, M.C.

2001-01-01

This thesis details the search for mixing between electron neutrinos and possible heavy neutrinos using the positron decay of 38m K produced at ISAC, TRIUMF's new radioactive beam facility. Using the novel technique of laser atom trapping to confine 38m K, direct limits on such mixing in β-decay are determined for the mass range of 0.7 MeV/c 2 to 3.8 MeV/c 2 . The results, for part of this mass range, provide the best direct limits for the mixing of heavy neutrinos with the electron neutrino in the literature to date. The Standard Model of electroweak physics has been able to describe a wide range of experimental results, but an unresolved question arises in accounting for lepton masses. The charged leptons (electrons, muons and taus) have masses which vary enormously from one to another (m e = 0.511 MeV/c 2 , m μ = 106 MeV/c 2 , m τ = 1777 MeV/c 2 ), while their accompanying neutrinos appear to have no (or very little) mass. If neutrinos have finite mass, then mixing could occur among the different neutrino species. Thus, evidence of mixing would indicate the existence of non-zero neutrino mass and of the need to modify or extend the Standard Model. Consequently, this is a highly active field of physics. Evidence of possible neutrino mass and oscillation has been recently observed by the detection of energetic neutrinos from the atmosphere. The TRINAT collaboration at TRIUMF has searched for evidence of physics beyond the Standard Model using a radioactive source of 38m K atoms held in a neutral atom trap. The trap provides a source of several thousand atoms confined to a volume of less than a cubic millimeter, suspended in a vacuum vessel, in which the 38m K undergoes radioactive decay with the emission of a positron and a neutrino. This results in the creation of a daughter nucleus, 38 Ar , with momentum equal to the vector sum of the momenta of the positron and the neutrino. The unperturbed nucleus then recoils from the trap and is detected in coincidence

High resolution positron tomography

International Nuclear Information System (INIS)

Brownell, G.L.; Burnham, C.A.

1982-01-01

The limits of spatial resolution in practical positron tomography are examined. The four factors that limit spatial resolution are: positron range; small angle deviation; detector dimensions and properties; statistics. Of these factors, positron range may be considered the fundamental physical limitation since it is independent of instrument properties. The other factors are to a greater or lesser extent dependent on the design of the tomograph

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.; Giassi, A.; Gregorio, A.; Ligabue, F.; Lusiani, A.; Marrocchesi, P.S.; Messineo, A.; Palla, F.; Rizzo, G.; Sanguinetti, G.; Sciaba, A.; Sguazzoni, G.; Spagnolo, P.; Steinberger, J.; Tenchini, R.; Vannini, C.; Venturi, A.; Verdini, P.G.; Awunor, O.; Blair, G.A.; Cowan, G.; Garcia-Bellido, A.; Green, M.G.; Medcalf, T.; Misiejuk, A.; Strong, J.A.; Teixeira-Dias, P.; Botterill, D.R.; Clifft, R.W.; Edgecock, T.R.; Edwards, M.; Haywood, S.J.; Norton, P.R.; Tomalin, I.R.; Ward, J.J.; Bloch-Devaux, B.; Boumediene, D.; Colas, P.; Emery, S.; Fabbro, B.; Kozanecki, W.; Lancon, E.; Lemaire, M.C.; Locci, E.; Perez, P.; Rander, J.; Renardy, J.F.; Roussarie, A.; Schuller, J.P.; Schwindling, J.; Tuchming, B.; Vallage, B.; Black, S.N.; Dann, J.H.; Kim, H.Y.; Konstantinidis, N.; Litke, A.M.; McNeil, M.A.; Taylor, G.; Booth, C.N.; Cartwright, S.; Combley, F.; Hodgson, P.N.; Lehto, M.; Thompson, L.F.; Affholderbach, K.; Barberio, E.; Bohrer, A.; Brandt, S.; Burkhardt, H.; Feigl, E.; Grupen, C.; Hess, J.; Lutters, G.; Meinhard, H.; Minguet-Rodriguez, J.; Mirabito, L.; Misiejuk, A.; Neugebauer, E.; Ngac, A.; Prange, G.; Rivera, F.; Saraiva, P.; Schafer, U.; Sieler, U.; Smolik, L.; Stephan, F.; Trier, H.; Apollonio, M.; Borean, C.; Bosisio, L.; Della Marina, R.; Giannini, G.; Gobbo, B.; Musolino, G.; Pitis, L.; He, H.; Kim, H.; Putz, J.; Rothberg, J.; Armstrong, S.R.; Bellantoni, L.; Berkelman, K.; Cinabro, D.; Conway, J.S.; Cranmer, K.; Elmer, P.; Feng, Z.; Ferguson, D.P.S.; Gao, Y.; Gonzalez, S.; Grahl, J.; Harton, J.L.; Hayes, O.J.; Hu, H.; Jin, S.; Johnson, R.P.; Kile, J.; McNamara, P.A., III; Nielsen, J.; Orejudos, W.; Pan, Y.B.; Saadi, Y.; Scott, I.J.; Sharma, V.; Walsh, A.M.; Walsh, J.; Wear, J.; von Wimmersperg-Toeller, J.H.; Wiedenmann, W.; Wu, J.; Wu, S.L.; Wu, X.; Yamartino, J.M.; Zobernig, G.; Dissertori, G.; Abdallah, J.; Abreu, P.; Adam, W.; Adzic, P.; Albrecht, T.; Alemany-Fernandez, R.; Allmendinger, T.; Allport, P.P.; Amaldi, U.; Amapane, N.; Amato, S.; Anashkin, E.; Andreazza, A.; 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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 ...

Positron emission tomography

NARCIS (Netherlands)

Paans, AMJ

Positron Emission Tomography (PET) is a method for determining biochemical and physiological processes in vivo in a quantitative way by using radiopharmaceuticals labelled with positron emitting radionuclides as C-11, N-13, O-15 and F-18 and by measuring the annihilation radiation using a

Positron confinement in embedded lithium nanoclusters

Science.gov (United States)

van Huis, M. A.; van Veen, A.; Schut, H.; Falub, C. V.; Eijt, S. W.; Mijnarends, P. E.; Kuriplach, J.

2002-02-01

Quantum confinement of positrons in nanoclusters offers the opportunity to obtain detailed information on the electronic structure of nanoclusters by application of positron annihilation spectroscopy techniques. In this work, positron confinement is investigated in lithium nanoclusters embedded in monocrystalline MgO. These nanoclusters were created by means of ion implantation and subsequent annealing. It was found from the results of Doppler broadening positron beam analysis that approximately 92% of the implanted positrons annihilate in lithium nanoclusters rather than in the embedding MgO, while the local fraction of lithium at the implantation depth is only 1.3 at. %. The results of two-dimensional angular correlation of annihilation radiation confirm the presence of crystalline bulk lithium. The confinement of positrons is ascribed to the difference in positron affinity between lithium and MgO. The nanocluster acts as a potential well for positrons, where the depth of the potential well is equal to the difference in the positron affinities of lithium and MgO. These affinities were calculated using the linear muffin-tin orbital atomic sphere approximation method. This yields a positronic potential step at the MgO||Li interface of 1.8 eV using the generalized gradient approximation and 2.8 eV using the insulator model.

Studies of discrete symmetries in a purely leptonic system using the Jagiellonian Positron Emission Tomograph

Directory of Open Access Journals (Sweden)

Moskal P.

2016-01-01

Full Text Available Discrete symmetries such as parity (P, charge-conjugation (C and time reversal (T are of fundamental importance in physics and cosmology. Breaking of charge conjugation symmetry (C and its combination with parity (CP constitute necessary conditions for the existence of the asymmetry between matter and antimatter in the observed Universe. The presently known sources of discrete symmetries violations can account for only a tiny fraction of the excess of matter over antimatter. So far CP and T symmetries violations were observed only for systems involving quarks and they were never reported for the purely leptonic objects. In this article we describe briefly an experimental proposal for the test of discrete symmetries in the decays of positronium atom which is made exclusively of leptons. The experiments are conducted by means of the Jagiellonian Positron Emission Tomograph (J-PET which is constructed from strips of plastic scintillators enabling registration of photons from the positronium annihilation. J-PET tomograph together with the positronium target system enable to measure expectation values for the discrete symmetries odd operators constructed from (i spin vector of the ortho-positronium atom, (ii momentum vectors of photons originating from the decay of positronium, and (iii linear polarization direction of annihilation photons. Linearly polarized positronium will be produced in the highly porous aerogel or polymer targets, exploiting longitudinally polarized positrons emitted by the sodium 22Na isotope. Information about the polarization vector of orthopositronium will be available on the event by event basis and will be reconstructed from the known position of the positron source and the reconstructed position of the orthopositronium annihilation. In 2016 the first tests and calibration runs are planned, and the data collection with high statistics will commence in the year 2017.

New limits on 2ε, εβ{sup +} and 2β{sup +} decay of {sup 136}Ce and {sup 138}Ce with deeply purified cerium sample

Energy Technology Data Exchange (ETDEWEB)

Belli, P.; Bernabei, R. [INFN Sezione Roma ' ' Tor Vergata' ' , Rome (Italy); Universita di Roma ' ' Tor Vergata' ' , Dipartimento di Fisica, Rome (Italy); Boiko, R.S. [Institute for Nuclear Research, Kyiv (Ukraine); National University of Life and Environmental Sciences of Ukraine, Kyiv (Ukraine); Cappella, F. [INFN Sezione Roma, Rome (Italy); Cerulli, R.; Laubenstein, M. [INFN, Laboratori Nazionali del Gran Sasso, Assergi (Italy); Danevich, F.A.; Kropivyansky, B.N.; Polischuk, O.G.; Tretyak, V.I. [Institute for Nuclear Research, Kyiv (Ukraine); Incicchitti, A. [INFN Sezione Roma, Rome (Italy); Universita di Roma ' ' La Sapienza' ' , Dipartimento di Fisica, Rome (Italy); Mokina, V.M. [Institute for Nuclear Research, Kyiv (Ukraine); INFN Sezione Roma, Rome (Italy)

2017-08-15

A search for double electron capture (2ε), electron capture with positron emission (εβ{sup +}), and double positron emission (2β{sup +}) in {sup 136}Ce and {sup 138}Ce was realized with a 465 cm{sup 3} ultra-low background HP Ge γ spectrometer over 2299 h at the Gran Sasso underground laboratory. A 627 g sample of cerium oxide deeply purified by liquid-liquid extraction method was used as a source of γ quanta expected in double β decay of the cerium isotopes. New improved half-life limits were set on different modes and channels of double β decay of {sup 136}Ce and {sup 138}Ce at the level of T{sub 1/2} > 10{sup 17}-10{sup 18} yr. (orig.)

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)

Mining the bulk positron lifetime

International Nuclear Information System (INIS)

Aourag, H.; Guittom, A.

2009-01-01

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

Application of Monte Carlo simulation to the standardization of positron emitting radionuclides

International Nuclear Information System (INIS)

Tongu, Margareth Lika Onishi

2009-01-01

Since 1967, the Nuclear Metrology Laboratory (LNM) at the Nuclear and Energy Research (IPEN) in Sao Paulo, Brazil, has developed radionuclide standardization methods and measurements of the Gamma-ray emission probabilities per decay by means of 4πβ-γ coincidence system, a high accuracy primary method for determining disintegration rate of radionuclides of interest. In 2001 the LNM started a research field on modeling, based on Monte Carlo method, of all the system components, including radiation detectors and radionuclide decay processes. This methodology allows the simulation of the detection process in a 4πβ-γ system, determining theoretically the observed activity as a function of the 4πβ detector efficiency, enabling the prediction of the behavior of the extrapolation curve and optimizing a detailed planning of the experiment before starting the measurements. One of the objectives of the present work is the improvement of the 4π proportional counter modeling, presenting a detailed description of the source holder and radioactive source material, as well as absorbers placed around the source. The simulation of radiation transport through the detectors has been carried out using code MCNPX. The main focus of the present work is on Monte Carlo modeling of the standardization of positron emitting radionuclides associated (or not) with electron capture and accompanied (or not) by the emission of Gamma radiation. One difficulty in this modeling is to simulate the detection of the annihilation Gamma ray, which arise in the process of positron absorption within the 4π detector. The methodology was applied to radionuclides 18 F and 22 Na. (author)

Solvated Positron Chemistry. Competitive Positron Reactions with Halide Ions in Water

DEFF Research Database (Denmark)

Christensen, Palle; Pedersen, Niels Jørgen; Andersen, J. R.

1979-01-01

It is shown by means of the angular correlation technique that the binding of positrons to halides is strongly influenced by solvation effects. For aqueous solutions we find increasing values for the binding energies between the halide and the positron with increasing mass of the halide...

Dark matter vs. astrophysics in the interpretation of AMS-02 electron and positron data

Energy Technology Data Exchange (ETDEWEB)

Mauro, Mattia Di; Donato, Fiorenza; Fornengo, Nicolao; Vittino, Andrea, E-mail: mattia.dimauro@to.infn.it, E-mail: donato@to.infn.it, E-mail: fornengo@to.infn.it, E-mail: vittino@to.infn.it [Department of Physics, University of Torino, via P. Giuria 1, 10125 Torino (Italy)

2016-05-01

We perform a detailed quantitative analysis of the recent AMS-02 electron and positron data. We investigate the interplay between the emission from primary astrophysical sources, namely Supernova Remnants and Pulsar Wind Nebulae, and the contribution from a dark matter annihilation or decay signal. Our aim is to assess the information that can be derived on dark matter properties when both dark matter and primary astrophysical sources are assumed to jointly contribute to the leptonic observables measured by the AMS-02 experiment. We investigate both the possibility to set robust constraints on the dark matter annihilation/decay rate and the possibility to look for dark matter signals within realistic models that take into account the full complexity of the astrophysical background. Our results show that AMS-02 data enable to probe efficiently vast regions of the dark matter parameter space and, in some cases, to set constraints on the dark matter annihilation/decay rate that are comparable or even stronger than the ones derived from other indirect detection channels.

Dark matter vs. astrophysics in the interpretation of AMS-02 electron and positron data

International Nuclear Information System (INIS)

Mauro, Mattia Di; Donato, Fiorenza; Fornengo, Nicolao; Vittino, Andrea

2016-01-01

We perform a detailed quantitative analysis of the recent AMS-02 electron and positron data. We investigate the interplay between the emission from primary astrophysical sources, namely Supernova Remnants and Pulsar Wind Nebulae, and the contribution from a dark matter annihilation or decay signal. Our aim is to assess the information that can be derived on dark matter properties when both dark matter and primary astrophysical sources are assumed to jointly contribute to the leptonic observables measured by the AMS-02 experiment. We investigate both the possibility to set robust constraints on the dark matter annihilation/decay rate and the possibility to look for dark matter signals within realistic models that take into account the full complexity of the astrophysical background. Our results show that AMS-02 data enable to probe efficiently vast regions of the dark matter parameter space and, in some cases, to set constraints on the dark matter annihilation/decay rate that are comparable or even stronger than the ones derived from other indirect detection channels.

Development of a transmission positron microscope

Energy Technology Data Exchange (ETDEWEB)

Matsuya, M., E-mail: matsuya@jeol.co.jp [JEOL Ltd., 1-2 Musashino, 3-Chome, Akishima, Tokyo 196-8558 (Japan); Jinno, S. [Department of Applied Chemistry, Chiba University, Yayoi, Inage, Chiba, Chiba 263-8552 (Japan); Ootsuka, T.; Inoue, M. [JEOL Ltd., 1-2 Musashino, 3-Chome, Akishima, Tokyo 196-8558 (Japan); Kurihara, T. [High Energy Accelerator Research Organization, Oho, Tsukuba, Ibaraki 305-0801 (Japan); Doyama, M.; Inoue, M. [Teikyo University of Science and Technology, Uenohara, Yamanashi 409-0913 (Japan); Fujinami, M. [Department of Applied Chemistry, Chiba University, Yayoi, Inage, Chiba, Chiba 263-8552 (Japan)

2011-07-21

A practical transmission positron microscope (TPM) JEM-1011B has been developed to survey differences in the interaction of positron and electron beams with materials, and is installed in the Slow Positron Facility of High Energy Accelerator Research Organization (KEK). The TPM can share positron and electron beams, and can also be used as a transmission electron microscope (TEM). Positron transmission images up to magnification 10,000x (resolution: 50 nm) and positron diffraction patterns up to 044 family were successfully obtained by the TPM comparing them with those of electrons. The differences in material transmittances for both beams have been measured, and can be explained by the calculated results of the Monte Carlo simulation code PENELOPE-2008.

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)

Positron lifetimes in deformed copper

International Nuclear Information System (INIS)

Hinode, Kenji; Tanigawa, Shoichiro; Doyama, Masao

1976-01-01

Positron lifetime measurements were performed for Cu samples with different densities of lattice defects. The lifetime spectra were successfully resolved into two components with the help of the well established analysis program. Obtained results were quite consistent with those expected from the trapping model. The positron trapping mechanism from free to trapped states and the initial condition of the model were especially checked. Deduced values obtained for tau sub(c) (lifetime of free positrons) and tau sub(t) (lifetime of trapped positrons) were 122+-5 psec and 176+-5 psec, respectively. (auth.)

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

Positron annihilation method for {alpha} self radiation effect studies in doped actinide UO{sub 2} samples

Energy Technology Data Exchange (ETDEWEB)

Roudil, D.; Vella, F.; Bonnal, M.; Broudic, V. [CEA centre de Marcoule. BP 17171 30207 Bagnols sur ceze cedex (France); Barthe, M.F.; Gentils, A.; Moineau, V. [CNRS- CEMHTI 3A rue de la Ferollerie 45071 Orleans Cedex (France); Jolly, L. [CEA centre de Valduc 21120 Is-Sur Tille (France)

2008-07-01

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

High energy positron imaging

International Nuclear Information System (INIS)

Chen Shengzu

2003-01-01

The technique of High Energy Positron Imaging (HEPI) is the new development and extension of Positron Emission Tomography (PET). It consists of High Energy Collimation Imaging (HECI), Dual Head Coincidence Detection Imaging (DHCDI) and Positron Emission Tomography (PET). We describe the history of the development and the basic principle of the imaging methods of HEPI in details in this paper. Finally, the new technique of the imaging fusion, which combined the anatomical image and the functional image together are also introduced briefly

Device-dependent activity estimation and decay correction of radionuclide mixtures with application to Tc-94m PET studies

International Nuclear Information System (INIS)

Smith, Mark F.; Daube-Witherspoon, Margaret E.; Plascjak, Paul S.; Szajek, Lawrence P.; Carson, Richard E.; Everett, James R.; Green, Shielah L.; Territo, Paul R.; Balaban, Robert S.; Bacharach, Stephen L.; Eckelman, William C.

2001-01-01

Multi-instrument activity estimation and decay correction techniques were developed for radionuclide mixtures, motivated by the desire for accurate quantitation of Tc-94m positron emission tomography (PET) studies. Tc-94m and byproduct Tc isotopes were produced by proton irradiation of enriched Mo-94 and natural Mo targets. Mixture activities at the end of bombardment were determined with a calibrated high purity germanium detector. The activity fractions of the greatest mixture impurities relative to 100% for Tc-94m averaged 10.0% (Tc-94g) and 3.3% (Tc-93) for enriched targets and 10.1% (Tc-94g), 11.0% (Tc-95), 255.8% (Tc-96m), and 7.2% (Tc-99m) for natural targets. These radioisotopes have different half-lives (e.g., 52.5 min for Tc-94m, 293 min for Tc-94g), positron branching ratios (e.g., 0.72 for Tc-94m, 0.11 for Tc-94g) and gamma ray emissions for themselves and their short-lived, excited Mo daughters. This complicates estimation of injected activity with a dose calibrator, in vivo activity with PET and blood sample activity with a gamma counter. Decay correction using only the Tc-94m half-life overestimates activity and is inadequate. For this reason analytic formulas for activity estimation and decay correction of radionuclide mixtures were developed. Isotope-dependent sensitivity factors for a PET scanner, dose calibrator, and gamma counter were determined using theoretical sensitivity models and fits of experimental decay curves to sums of exponentials with fixed decay rates. For up to 8 h after the end of bombardment with activity from enriched and natural Mo targets, decay-corrected activities were within 3% of the mean for three PET studies of a uniform cylinder, within 3% of the mean for six dose calibrator decay studies, and within 6% of the mean for four gamma counter decay studies. Activity estimation and decay correction for Tc-94m mixtures enable routine use of Tc-94m in quantitative PET, as illustrated by application to a canine Tc-94m sestamibi

High intensity positron program at LLNL

International Nuclear Information System (INIS)

Asoka-Kumar, P.; Howell, R.; Stoeffl, W.; Carter, D.

1999-01-01

Lawrence Livermore National Laboratory (LLNL) is the home of the world's highest current beam of keV positrons. The potential for establishing a national center for materials analysis using positron annihilation techniques around this capability is being actively pursued. The high LLNL beam current will enable investigations in several new areas. We are developing a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with submicron resolution. Below we summarize the important design features of this microprobe. Several experimental end stations will be available that can utilize the high current beam with a time distribution determined by the electron linac pulse structure, quasi-continuous, or bunched at 20 MHz, and can operate in an electrostatic or (and) magnetostatic environment. Some of the planned early experiments are: two-dimensional angular correlation of annihilation radiation of thin films and buried interfaces, positron diffraction holography, positron induced desorption, and positron induced Auger spectroscopy

High intensity positron program at LLNL

International Nuclear Information System (INIS)

Asoka-Kumar, P.; Howell, R.H.; Stoeffl, W.

1998-01-01

Lawrence Livermore National Laboratory (LLNL) is the home of the world's highest current beam of keV positrons. The potential for establishing a national center for materials analysis using positron annihilation techniques around this capability is being actively pursued. The high LLNL beam current will enable investigations in several new areas. We are developing a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with submicron resolution. Below we summarize the important design features of this microprobe. Several experimental end stations will be available that can utilize the high current beam with a time distribution determined by the electron linac pulse structure, quasi-continuous, or bunched at 20 MHz, and can operate in an electrostatic or (and) magnetostatic environment. Some of the planned early experiments are: two-dimensional angular correlation of annihilation radiation of thin films and buried interfaces, positron diffraction holography, positron induced desorption, and positron induced Auger spectra

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

International Nuclear Information System (INIS)

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

2003-01-01

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

Positron astronomy with SPI/INTEGRAL

International Nuclear Information System (INIS)

Weidenspointner, G.; Diehl, R.; Strong, A.; Weidenspointner, G.; Skinner, G.K.; Skinner, G.K.; Jean, P.; Knoedlseder, J.; Von Ballmoos, P.; Cordier, B.; Schanne, S.; Winkler, C.

2008-01-01

We provide an overview of positron astronomy results that have been obtained using the INTEGRAL spectrometer SPI, and discuss their implications for the still mysterious origin of positrons in our Galaxy. It has long been known that the 511 keV positron annihilation emission is strongest from the central region of our Galaxy. Recently, it has been discovered with the SPI spectrometer that the weaker 511 keV line emission from the inner Galactic disk appears to be asymmetric, with the emission to the west of the Galactic center being about twice as strong than that to the east. This distribution of positron annihilation resembles that of low mass X-ray binaries as observed with the INTEGRAL imager IBIS at hard X-ray energies, suggesting that these systems could provide a significant portion of the positrons in our Galaxy. In addition, the spectrometer SPI has permitted unprecedented spectroscopy of annihilation radiation from the bulge and disk regions of the Galaxy, which commences to yield important insights into the conditions of the medium in which the positrons annihilate. (authors)

Positron implantation profile in kapton

International Nuclear Information System (INIS)

Plotkowski, K.; Panek, T.J.; Kansj, J.

1988-01-01

Measurements of positrons' implantation profile were made with geometry as in the majority of PAT experiments, making use of the difference in values of mean lifetimes of positrons in the absorber and in the detector. The function describing the absorption of positrons in the absorber taking into account measurement geometry was fitted to the experimental data. The correction to the exponential relation occurring in this function is the dominating factor for small thicknesses of the absorber. In this analysis various values of positrons' backscatter coefficients of the nickel and of the kapton were also taken into account

The Positron-Electron Correlation Energy In ZnO Calculated With The Modified Single Wave Function Of Positron

International Nuclear Information System (INIS)

Chau Van Tao; Trinh Hoa Lang; Le Hoang Chien; Nguyen Huu Loc; Nguyen Anh Tuan

2011-01-01

Positron-electron correlation energy of the ZnO - positron system is studied on assumption that positron binds with the outer shell electrons of Zinc and Oxygen to form the pseudo ZnO - positron molecule before it annihilates with one of these electrons. In this work, the single wave function for positron is form by LCAO approximation and is modified according to the principle of linear superposition, and by using Variational Quantum Monte Carlo method (VQMC) [7] the correlation energy of this system is estimated with the value E c e-p = - 9.3 ± 1.1 eV. In the theoretical aspect it turns out that this result is more reasonable and closer to those of other methods [3] than the one which is done without modifying the wave function of positron [1]. To confirm this legitimate approach, however, the further calculations of positron annihilation rate in ZnO have to be carried out in our next work. (author)

J/{psi} production and decay at the Z resonance

Energy Technology Data Exchange (ETDEWEB)

Vikas, P

1994-10-13

In the Large Electron Positron collider (LEP) bunches of electrons and positrons are brought in collision. At a collision energy of 91.2 GeV the Z resonance is excited. The Z boson, the uncharged mediator of the weak force, decays into a particle and an antiparticle almost instantaneously. The probability that in this process heavy quarks charm-anticharm(c anti c) and bottom-antibottom(b anti b) are formed is {approx}12% and {approx}15% respectively. Thus, LEP provides an ideal environment to make precision measurements in the heavy quark sector. The data for this thesis was collected with the L3 detector from 1990-1992. L3 is one of the four experiments at LEP. The integrated luminosity collected by L3 in this period is 43.5 pb{sup -1}. The L3 detector was designed to measure e{sup +}e{sup -} collisions up to 200 GeV with special emphasis on high resolution measurements of photons, electrons and muons. The detector is installed within a magnet providing 0.5 T field. It consists of subdetectors to detect and measure the direction and momentum/energy of charged particles, electromagnetic particles, hadrons and muons. In this thesis the production of the 1{sup 3} S{sub 1} (the j/{psi} meson) and the 2{sup 3} S{sub 1} (the {psi}` meson) and the c anti c bound states are investigated. The leptonic decays of the two mesons (J/{psi}, {psi}`{yields}l{sup +}l{sup -}, l=e, {mu}) provide the cleanest signals of heavy quarks. In this thesis, the {psi}` and J/{psi} mesons have been tagged via their decay into a muon pair. From the invariant mass distribution of the {mu}{sup +}{mu}{sup -} pairs the branching ratio for J/{psi} production at the Z, Br(Z{sup 0}{yields}J/{psi}+X), was determined to be 4.0{+-}0.6(stat.){+-}0.4(sys.)x10{sup -3} while the branching ratio for {psi}` production at the Z is smaller than <2x10{sup -3}. (orig./HSI).

J/ψ production and decay at the Z resonance

International Nuclear Information System (INIS)

Vikas, P.

1994-01-01

In the Large Electron Positron collider (LEP) bunches of electrons and positrons are brought in collision. At a collision energy of 91.2 GeV the Z resonance is excited. The Z boson, the uncharged mediator of the weak force, decays into a particle and an antiparticle almost instantaneously. The probability that in this process heavy quarks charm-anticharm(c anti c) and bottom-antibottom(b anti b) are formed is ∼12% and ∼15% respectively. Thus, LEP provides an ideal environment to make precision measurements in the heavy quark sector. The data for this thesis was collected with the L3 detector from 1990-1992. L3 is one of the four experiments at LEP. The integrated luminosity collected by L3 in this period is 43.5 pb -1 . The L3 detector was designed to measure e + e - collisions up to 200 GeV with special emphasis on high resolution measurements of photons, electrons and muons. The detector is installed within a magnet providing 0.5 T field. It consists of subdetectors to detect and measure the direction and momentum/energy of charged particles, electromagnetic particles, hadrons and muons. In this thesis the production of the 1 3 S 1 (the j/ψ meson) and the 2 3 S 1 (the ψ' meson) and the c anti c bound states are investigated. The leptonic decays of the two mesons (J/ψ, ψ'→l + l - , l=e, μ) provide the cleanest signals of heavy quarks. In this thesis, the ψ' and J/ψ mesons have been tagged via their decay into a muon pair. From the invariant mass distribution of the μ + μ - pairs the branching ratio for J/ψ production at the Z, Br(Z 0 →J/ψ+X), was determined to be 4.0±0.6(stat.)±0.4(sys.)x10 -3 while the branching ratio for ψ' production at the Z is smaller than -3 . (orig./HSI)

A Southern African positron beam

International Nuclear Information System (INIS)

Britton, D.T.; Haerting, M.; Teemane, M.R.B.; Mills, S.; Nortier, F.M.; Van der Walt, T.N.

1997-01-01

The first stage of a state of the art positron beam, being constructed at the University of Cape Town, is currently being brought into operation. This is the first positron beam on the African continent, as well as being the first positron beam dedicated to solid and surface studies in the southern hemisphere. The project also contains a high proportion of local development, including the encapsulated 22 Na positron source developed by our collaboration. Novel features in the design include a purely magnetic in-line deflector, working in the solenoidal guiding field, to eliminate unmoderated positrons and block the direct line of sight to the source. A combined magnetic projector and single pole probe forming lens is being implemented in the second phase of construction to achieve a spot size of 10 μm without remoderation

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.

Search for bosonic stop decays in R-parity violating supersymmetry in e$^{+}$ p collisions at HERA

CERN Document Server

Aktas, A.; Anthonis, T.; Asmone, A.; Babaev, A.; Backovic, S.; Bahr, J.; Baranov, P.; Barrelet, E.; Bartel, W.; Baumgartner, S.; Becker, J.; Beckingham, M.; Behnke, O.; Behrendt, O.; Belousov, A.; Berger, Ch.; Berger, N.; Berndt, T.; Bizot, J.C.; Bohme, J.; Boenig, M.-O.; Boudry, V.; Bracinik, J.; Brisson, V.; Broker, H.-B.; Brown, D.P.; Bruncko, D.; Busser, F.W.; Bunyatyan, A.; Buschhorn, G.; Bystritskaya, L.; Campbell, A.J.; Caron, S.; Cassol-Brunner, F.; Cerny, K.; Chekelian, V.; Contreras, J.G.; Coppens, Y.R.; Coughlan, J.A.; Cox, B.E.; Cozzika, G.; Cvach, J.; Dainton, J.B.; Dau, W.D.; Daum, K.; Delcourt, B.; Demirchyan, R.; De Roeck, A.; Desch, K.; De Wolf, E.A.; Diaconu, C.; Dingfelder, J.; Dodonov, V.; Dubak, A.; Duprel, C.; Eckerlin, Guenter; Efremenko, V.; Egli, S.; Eichler, R.; Eisele, F.; Ellerbrock, M.; Elsen, E.; Erdmann, M.; Erdmann, W.; Faulkner, P.J.W.; Favart, L.; Fedotov, A.; Felst, R.; Ferencei, J.; Fleischer, M.; Fleischmann, P.; Fleming, Y.H.; Flucke, G.; Flugge, G.; Fomenko, A.; Foresti, I.; Formanek, J.; Franke, G.; Frising, G.; Gabathuler, E.; Gabathuler, K.; Garutti, E.; Garvey, J.; Gayler, J.; Gerhards, R.; Gerlich, C.; Ghazaryan, Samvel; Ginzburgskaya, S.; Goerlich, L.; Gogitidze, N.; Gorbounov, S.; Grab, C.; Grassler, H.; Greenshaw, T.; Gregori, M.; Grindhammer, Guenter; Gwilliam, C.; Haidt, D.; Hajduk, L.; Haller, J.; Hansson, M.; Heinzelmann, G.; Henderson, R.C.W.; Henschel, H.; Henshaw, O.; Herrera, G.; Herynek, I.; Heuer, R.-D.; Hildebrandt, M.; Hiller, K.H.; Hoting, P.; Hoffmann, D.; Horisberger, R.; Hovhannisyan, A.; Ibbotson, M.; Ismail, M.; Jacquet, M.; Janauschek, L.; Janssen, X.; Jemanov, V.; Jonsson, L.; Johnson, D.P.; Jung, H.; Kant, D.; Kapichine, M.; Karlsson, M.; Katzy, J.; Keller, N.; Kennedy, J.; Kenyon, I.R.; Kiesling, Christian M.; Klein, M.; Kleinwort, C.; Klimkovich, T.; Kluge, T.; Knies, G.; Knutsson, A.; Koblitz, B.; Korbel, V.; Kostka, P.; Koutouev, R.; Kropivnitskaya, A.; Kroseberg, J.; Kruger, K.; Kuckens, J.; Kuhr, T.; Landon, M.P.J.; Lange, W.; Lastovicka, T.; Laycock, P.; Lebedev, A.; Leiner, B.; Lemrani, R.; Lendermann, V.; Levonian, S.; Lindfeld, L.; Lipka, K.; List, B.; Lobodzinska, E.; Loktionova, N.; Lopez-Fernandez, R.; Lubimov, V.; Lueders, H.; Luke, D.; Lux, T.; Lytkin, L.; Makankine, A.; Malden, N.; Malinovski, E.; Mangano, S.; Marage, P.; Marks, J.; Marshall, R.; Martisikova, M.; Martyn, H.-U.; Maxfield, S.J.; Meer, D.; Mehta, A.; Meier, K.; Meyer, A.B.; Meyer, H.; Meyer, J.; Mikocki, S.; Milcewicz-Mika, I.; Milstead, D.; Mohamed, A.; Moreau, F.; Morozov, A.; Morozov, I.; Morris, J.V.; Mozer, Matthias Ulrich; Muller, K.; Murin, P.; Nagovizin, V.; Nankov, K.; Naroska, B.; Naumann, J.; Naumann, Th.; Newman, Paul R.; Niebuhr, C.; Nikiforov, A.; Nikitin, D.; Nowak, G.; Nozicka, M.; Oganezov, R.; Olivier, B.; Olsson, J.E.; Ossoskov, G.; Ozerov, D.; Paramonov, A.; Pascaud, C.; Patel, G.D.; Peez, M.; Perez, E.; Perieanu, A.; Petrukhin, A.; Pitzl, D.; Placakyte, R.; Poschl, R.; Portheault, B.; Povh, B.; Raicevic, N.; Reimer, P.; Reisert, B.; Rimmer, A.; Risler, C.; Rizvi, E.; Robmann, P.; Roland, B.; Roosen, R.; Rostovtsev, A.; Rurikova, Z.; Rusakov, S.; Rybicki, K.; Sankey, D.P.C.; Sauvan, E.; Schatzel, S.; Scheins, J.; Schilling, F.-P.; Schleper, P.; Schmidt, S.; Schmitt, S.; Schneider, M.; Schoeffel, L.; Schoning, A.; Schroder, V.; Schultz-Coulon, H.-C.; Schwanenberger, C.; Sedlak, K.; Sefkow, F.; Sheviakov, I.; Shtarkov, L.N.; Sirois, Y.; Sloan, T.; Smirnov, P.; Soloviev, Y.; South, D.; Spaskov, V.; Specka, Arnd E.; Spitzer, H.; Stamen, R.; Stella, B.; Stiewe, J.; Strauch, I.; Straumann, U.; Tchoulakov, V.; Thompson, Graham; Thompson, P.D.; Tomasz, F.; Traynor, D.; Truoel, Peter; Tsipolitis, G.; Tsurin, I.; Turnau, J.; Tzamariudaki, E.; Uraev, A.; Urban, Marcel; Usik, A.; Utkin, D.; Valkar, S.; Valkarova, A.; Vallee, C.; Van Mechelen, P.; Van Remortel, N.; Vargas Trevino, A.; Vazdik, Y.; Veelken, C.; Vest, A.; Vinokurova, S.; Volchinski, V.; Wacker, K.; Wagner, J.; Weber, G.; Weber, R.; Wegener, D.; Werner, C.; Werner, N.; Wessels, M.; Wessling, B.; Winter, G.-G.; Wissing, Ch.; Woehrling, E.-E.; Wolf, R.; Wunsch, E.; Xella, S.; Yan, W.; Yeganov, V.; Zacek, J.; Zalesak, J.; Zhang, Z.; Zhelezov, A.; Zhokin, A.; Zohrabyan, H.; Zomer, F.

2004-01-01

A search for scalar top quarks in R-parity violating supersymmetry is performed in e^+ p collisions at HERA using the H1 detector. The data, taken at sqrt{s}=319 GeV and 301 GeV, correspond to an integrated luminosity of 106 pb^-1. The resonant production of scalar top quarks \\tilde{t} in positron quark fusion via an R-parity violating Yukawa coupling lambda' is considered with the subsequent bosonic stop decay \\tilde{t} -> \\tilde{b} W. The R-parity violating decay of the sbottom quark tilde{b} -> d \\bar{nu_e} and leptonic and hadronic W decays are considered. No evidence for stop production is found in the search for bosonic stop decays nor in a search for the direct R-parity violating decay \\tilde{t} -> eq. Mass dependent limits on lambda' are obtained in the framework of the Minimal Supersymmetric Standard Model. Stop quarks with masses up to 275 GeV can be excluded at the 95% confidence level for a Yukawa coupling of electromagnetic strength.

Positron emission tomography

International Nuclear Information System (INIS)

Yamamoto, Y.L.; Thompson, C.J.; Diksic, M.; Meyer, E.; Feindel, W.H.

1984-01-01

One of the most exciting new technologies introduced in the last 10 yr is positron emission tomography (PET). PET provides quantitative, three-dimensional images for the study of specific biochemical and physiological processes in the human body. This approach is analogous to quantitative in-vivo autoradiography but has the added advantage of permitting non-invasive in vivo studies. PET scanning requires a small cyclotron to produce short-lived positron emitting isotopes such as oxygen-15, carbon-11, nitrogen-13 and fluorine-18. Proper radiochemical facilities and advanced computer equipment are also needed. Most important, PET requires a multidisciplinary scientific team of physicists, radiochemists, mathematicians, biochemists and physicians. The most recent trends are reviewed in the imaging technology, radiochemistry, methodology and clinical applications of positron emission tomography. (author)

High intensity positron program at LLNL

International Nuclear Information System (INIS)

Asoka-Kumar, P.; Howell, R.; Stoeffl, W.; Carter, D.

1999-01-01

Lawrence Livermore National Laboratory (LLNL) is the home of the world close-quote s highest current beam of keV positrons. The potential for establishing a national center for materials analysis using positron annihilation techniques around this capability is being actively pursued. The high LLNL beam current will enable investigations in several new areas. We are developing a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with submicron resolution. Below we summarize the important design features of this microprobe. Several experimental end stations will be available that can utilize the high current beam with a time distribution determined by the electron linac pulse structure, quasi-continuous, or bunched at 20 MHz, and can operate in an electrostatic or (and) magnetostatic environment. Some of the planned early experiments are: two-dimensional angular correlation of annihilation radiation of thin films and buried interfaces, positron diffraction holography, positron induced desorption, and positron induced Auger spectroscopy. copyright 1999 American Institute of Physics

PF slow positron source

International Nuclear Information System (INIS)

Shirakawa, A.; Enomoto, A.; Kurihara, T.

1993-01-01

A new slow-positron source is under construction at the Photon Factory. Positrons are produced by bombarding a tantalum rod with high-energy electrons; they are moderated in multiple tungsten vanes. We report here the present status of this project. (author)

Positron spectroscopy of 2D materials using an advanced high intensity positron beam

Science.gov (United States)

McDonald, A.; Chirayath, V.; Lim, Z.; Gladen, R.; Chrysler, M.; Fairchild, A.; Koymen, A.; Weiss, A.

An advanced high intensity variable energy positron beam(~1eV to 20keV) has been designed, tested and utilized for the first coincidence Doppler broadening (CDB) measurements on 6-8 layers graphene on polycrystalline Cu sample. The system is capable of simultaneous Positron annihilation induced Auger electron Spectroscopy (PAES) and CDB measurements giving it unparalleled sensitivity to chemical structure at external surfaces, interfaces and internal pore surfaces. The system has a 3m flight path up to a micro channel plate (MCP) for the Auger electrons emitted from the sample. This gives a superior energy resolution for PAES. A solid rare gas(Neon) moderator was used for the generation of the monoenergetic positron beam. The positrons were successfully transported to the sample chamber using axial magnetic field generated with a series of Helmholtz coils. We will discuss the PAES and coincidence Doppler broadening measurements on graphene -Cu sample and present an analysis of the gamma spectra which indicates that a fraction of the positrons implanted at energies 7-60eV can become trapped at the graphene/metal interface. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

Positron depth profiling

International Nuclear Information System (INIS)

Coleman, P.

2001-01-01

Wide-ranging studies of defects below the surface of semiconductor structures have been performed at the University of Bath, in collaboration with the University of Surrey Centre for Ion Beam Applications and with members of research teams at a number of UK universities. Positron implantation has been used in conjunction with other spectroscopies such as RBS-channeling and SIMS, and electrical characterisation methods. Research has ranged from the development of a positron-based technique to monitor the in situ annealing of near-surface open-volume defects to the provision of information on defects to comprehensive diagnostic investigations of specific device structures. We have studied Si primarily but not exclusively; e.g., we have investigated ion-implanted SiC and SiO 2 /GaAs structures. Of particular interest are the applications of positron annihilation spectroscopy to ion-implanted semiconductors, where by linking ion dose to vacancy-type defect concentration one can obtain information on ion dose and uniformity with a sensitivity not achievable by standard techniques. A compact, user-friendly positron beam system is currently being developed at Bath, in collaboration with SCRIBA, with the intention of application in an industrial environment. (orig.)

Positron annihilation induced Auger electron spectroscopy and its implementation at accelerator based low energy positron factories

International Nuclear Information System (INIS)

Weiss, A.; Koeymen, A.R.; Mehl, D.; Lee, K.H.; Yang Gimo; Jensen, K.

1991-01-01

Positron annihilation induced auger electron spectroscopy (PAES) makes use of a beam of low energy positrons to excite Auger transitions by annihilating core electrons. The large secondary electron background usually present in Auger spectra can be eliminated by setting the positron beam energy well below the Auger electron energy. This allows true Auger lineshapes to be obtained. Further, because the positron is localized just outside the surface before it annihilates, PAES is extremely sensitive to the topmost atomic layer. Recent PAES results obtained at the University of Texas at Arlington will be presented. In addition, the use of high resolution energy analyzers with multichannel particle detection schemes to prevent problems due to the high data rates associated with accelerator based positron beams will be discussed. (orig.)

Nonlinear positron acoustic solitary waves

International Nuclear Information System (INIS)

Tribeche, Mouloud; Aoutou, Kamel; Younsi, Smain; Amour, Rabia

2009-01-01

The problem of nonlinear positron acoustic solitary waves involving the dynamics of mobile cold positrons is addressed. A theoretical work is presented to show their existence and possible realization in a simple four-component plasma model. The results should be useful for the understanding of the localized structures that may occur in space and laboratory plasmas as new sources of cold positrons are now well developed.

Positron emission tomography. Basic principles

International Nuclear Information System (INIS)

Rodriguez, Jose Luis; Massardo, Teresa; Gonzalez, Patricio

2001-01-01

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

Compressive effect of the magnetic field on the positron range in commonly used positron emitters simulated using Geant4

Science.gov (United States)

Li, Chong; Cao, Xingzhong; Liu, Fuyan; Tang, Haohui; Zhang, Zhiming; Wang, Baoyi; Wei, Long

2017-11-01

The compressive effect of a magnetic field on the positron range from commonly used positron emitters in PET (Positron Emission Tomography) was simulated using the Geant4 toolkit with H2O as the environmental material. The compression of the positron range, which was different in the directions parallel and perpendicular to the magnetic field, showed finite final variation of relative change rate versus the magnetic field. The variation greatly depended on the positron-emission energy spectrum in the same medium. Furthermore, the volume of the positron annihilation point was dramatically compressed as the magnetic field was set in the range of 3-6T. It was more prominent for 82Rb , which is generally used as a positron source in PET technology.

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

International Nuclear Information System (INIS)

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

2006-01-01

Positron annihilation lifetime spectra were measured for mesoporous silica films, which were synthesized using triblock copolymer (EO 106 PO 70 EO 106 ) as a structure-directing agent. Different positron lifetime spectra for the deposited and calcined films indicated the formation of meso-structure after calcination, which was confirmed by Fourier transform infrared (FTIR) spectra and field emission-scanning electron microscopy (FE-SEM) observation. Open porosity or pore interconnectivity of a silica film might be evaluated by a two-dimensional positron annihilation lifetime spectrum of an uncapped film. Pore sizes and their distributions in the silica films were found to be affected by thermal treatments

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

Positron Studies of Oxide-Semiconductor Structures

OpenAIRE

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

1995-01-01

The annihilation characteristics of positrons in SiO2 films grown on Si substrates were studied by using monoenergetic positron beams. Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured as a function of incident positron energy for SiO2/Si structures fabricated by various oxidation techniques. From the measurements, it was found that the formation probability of positronium (Ps) atoms in SiO2 films strongly depends on the growth condition...

Depth-dependent positron annihilation in different polymers

Energy Technology Data Exchange (ETDEWEB)

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

2013-09-01

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

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)

Experimentation with low-energy positron beams

International Nuclear Information System (INIS)

Mills, A.P. Jr.

1983-01-01

The capability of studying the interactions of positrons with surfaces has recently been exploited by using ultra-high-vacuum techniques. The result has been a new understanding of how positrons interact with surfaces and because of this we are now able to make much stronger fluxes of slow positrons. The higher beam strengths in turn are opening up new possibilities for experimentation on surfaces and solids and for studying the atomic physics of positronium and positron-molecule scattering at low energies. The lectures are intended to review some of the history of this subject and to outline the present state of our knowledge of experimentation with low-energy positron beams. (orig./TW)

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)

Positrons in ionic crystals

International Nuclear Information System (INIS)

Pareja, R.

1988-01-01

Positron annihilation experiments in ionic crystals are reviewed and their results are arranged. A discussion about the positron states in these materials is made in the light of these results and the different proposed models. The positronium in alkali halides is specially considered. (Author)

Design and evaluation of HEADTOME-IV, a whole-body positron emission tomograph

International Nuclear Information System (INIS)

Iida, H.; Miura, S.; Kanno, I.; Murakami, M.; Takahashi, K.; Uemura, K.

1989-01-01

A whole body positron emission tomograph HEADTOME-IV has been developed, and its physical performances were investigated. The in-plane spatial resolution of 4.5 mm was realized with stationary-sampling at the center of the field-of-view. The axial slice thickness was 9.5 and 9.0-mm for direct and cross planes, respectively. By moving the gantry framework axially, transaxial images of 14 or 21 slices are obtained quasi-simultaneously. The realtime-operation large-scale cache memory system was effective to realize realtime corrections for deadtime and radionuclide decay, and realtime weighted integration for the purpose of a rapid calculation of rate-constant images

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

Science.gov (United States)

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

2002-06-01

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

Search for the rare decays D →h (h('))e+e-

Science.gov (United States)

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M.; Alekseev, M.; Amoroso, A.; An, F. F.; An, Q.; Bai, J. Z.; Bai, Y.; Bakina, O.; Baldini Ferroli, R.; Ban, Y.; Begzsuren, K.; Bennett, D. W.; Bennett, J. V.; Berger, N.; Bertani, M.; Bettoni, D.; Bianchi, F.; Boger, E.; Boyko, I.; Briere, R. A.; Cai, H.; Cai, X.; Cakir, O.; Calcaterra, A.; Cao, G. F.; Cetin, S. A.; Chai, J.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, J. C.; Chen, M. L.; Chen, P. L.; Chen, S. J.; Chen, X. R.; Chen, Y. B.; Cheng, W.; Chu, X. K.; Cibinetto, G.; Cossio, F.; Dai, H. L.; Dai, J. P.; Dbeyssi, A.; Dedovich, D.; Deng, Z. Y.; Denig, A.; Denysenko, I.; Destefanis, M.; de Mori, F.; Ding, Y.; Dong, C.; Dong, J.; Dong, L. Y.; Dong, M. Y.; Dou, Z. L.; Du, S. X.; Duan, P. F.; Fang, J.; Fang, S. S.; Fang, Y.; Farinelli, R.; Fava, L.; Fegan, S.; Feldbauer, F.; Felici, G.; Feng, C. Q.; Fioravanti, E.; Fritsch, M.; Fu, C. D.; Gao, Q.; Gao, X. L.; Gao, Y.; Gao, Y. G.; Gao, Z.; Garillon, B.; Garzia, I.; Gilman, A.; Goetzen, K.; Gong, L.; Gong, W. X.; Gradl, W.; Greco, M.; Gu, M. H.; Gu, Y. T.; Guo, A. Q.; Guo, R. P.; Guo, Y. P.; Guskov, A.; Haddadi, Z.; Han, S.; Hao, X. Q.; Harris, F. A.; He, K. L.; He, X. Q.; Heinsius, F. H.; Held, T.; Heng, Y. K.; Hou, Z. L.; Hu, H. M.; Hu, J. F.; Hu, T.; Hu, Y.; Huang, G. S.; Huang, J. S.; Huang, X. T.; Huang, X. Z.; Huang, Z. L.; Hussain, T.; Ikegami Andersson, W.; Irshad, M.; Ji, Q.; Ji, Q. P.; Ji, X. B.; Ji, X. L.; Jiang, X. S.; Jiang, X. Y.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Jin, Y.; Johansson, T.; Julin, A.; Kalantar-Nayestanaki, N.; Kang, X. S.; Kavatsyuk, M.; Ke, B. C.; Keshk, I. K.; Khan, T.; Khoukaz, A.; Kiese, P.; Kiuchi, R.; Kliemt, R.; Koch, L.; Kolcu, O. B.; Kopf, B.; Kornicer, M.; Kuemmel, M.; Kuessner, M.; Kupsc, A.; Kurth, M.; Kühn, W.; Lange, J. S.; Larin, P.; Lavezzi, L.; Leithoff, H.; Li, C.; Li, Cheng; Li, D. M.; Li, F.; Li, F. Y.; Li, G.; Li, H. B.; Li, H. J.; Li, J. C.; Li, J. W.; Li, Jin; Li, K. J.; Li, Kang; Li, Ke; Li, Lei; Li, P. L.; Li, P. R.; Li, Q. Y.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. N.; Li, X. Q.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Liao, L. Z.; Libby, J.; Lin, C. X.; Lin, D. X.; Liu, B.; Liu, B. J.; Liu, C. X.; Liu, D.; Liu, D. Y.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, H. B.; Liu, H. L.; Liu, H. M.; Liu, Huanhuan; Liu, Huihui; Liu, J. B.; Liu, J. Y.; Liu, K.; Liu, K. Y.; Liu, Ke; Liu, L. D.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, Y. B.; Liu, Z. A.; Liu, Zhiqing; Long, Y. F.; Lou, X. C.; Lu, H. J.; Lu, J. G.; Lu, Y.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Lusso, S.; Lyu, X. R.; Ma, F. C.; Ma, H. L.; Ma, L. L.; Ma, M. M.; Ma, Q. M.; Ma, T.; Ma, X. N.; Ma, X. Y.; Ma, Y. M.; Maas, F. E.; Maggiora, M.; Maldaner, S.; Malik, Q. A.; Mangoni, A.; Mao, Y. J.; Mao, Z. P.; Marcello, S.; Meng, Z. X.; Messchendorp, J. G.; Mezzadri, G.; Min, J.; Mitchell, R. E.; Mo, X. H.; Mo, Y. J.; Morales Morales, C.; Muchnoi, N. Yu.; Muramatsu, H.; Mustafa, A.; Nefedov, Y.; Nerling, F.; Nikolaev, I. B.; Ning, Z.; Nisar, S.; Niu, S. L.; Niu, X. Y.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Pan, Y.; Papenbrock, M.; Patteri, P.; Pelizaeus, M.; Pellegrino, J.; Peng, H. P.; Peng, Z. Y.; Peters, K.; Pettersson, J.; Ping, J. L.; Ping, R. G.; Pitka, A.; Poling, R.; Prasad, V.; Qi, H. R.; Qi, M.; Qi, T. Y.; Qian, S.; Qiao, C. F.; Qin, N.; Qin, X. S.; Qin, Z. H.; Qiu, J. F.; Qu, S. Q.; Rashid, K. H.; Redmer, C. F.; Richter, M.; Ripka, M.; Rivetti, A.; Rolo, M.; Rong, G.; Rosner, Ch.; Sarantsev, A.; Savrié, M.; Schoenning, K.; Shan, W.; Shan, X. Y.; Shao, M.; Shen, C. P.; Shen, P. X.; Shen, X. Y.; Sheng, H. Y.; Shi, X.; Song, J. J.; Song, W. M.; Song, X. Y.; Sosio, S.; Sowa, C.; Spataro, S.; Sun, G. X.; Sun, J. F.; Sun, L.; Sun, S. S.; Sun, X. H.; Sun, Y. J.; Sun, Y. K.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tan, Y. T.; Tang, C. J.; Tang, G. Y.; Tang, X.; Tapan, I.; Tiemens, M.; Tsednee, B.; Uman, I.; Wang, B.; Wang, B. L.; Wang, D.; Wang, D. Y.; Wang, Dan; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, Meng; Wang, P.; Wang, P. L.; Wang, W. P.; Wang, X. F.; Wang, Y.; Wang, Y. F.; Wang, Z.; Wang, Z. G.; Wang, Z. Y.; Wang, Zongyuan; Weber, T.; Wei, D. H.; Weidenkaff, P.; Wen, S. P.; Wiedner, U.; Wolke, M.; Wu, L. H.; Wu, L. J.; Wu, Z.; Xia, L.; Xia, Y.; Xiao, D.; Xiao, Y. J.; Xiao, Z. J.; Xie, Y. G.; Xie, Y. H.; Xiong, X. A.; Xiu, Q. L.; Xu, G. F.; Xu, J. J.; Xu, L.; Xu, Q. J.; Xu, Q. N.; Xu, X. P.; Yan, F.; Yan, L.; Yan, W. B.; Yan, W. C.; Yan, Y. H.; Yang, H. J.; Yang, H. X.; Yang, L.; Yang, R. X.; Yang, Y. H.; Yang, Y. X.; Yang, Yifan; Yang, Z. Q.; Ye, M.; Ye, M. H.; Yin, J. H.; You, Z. Y.; Yu, B. X.; Yu, C. X.; Yu, J. S.; Yu, J. S.; Yuan, C. Z.; Yuan, Y.; Yuncu, A.; Zafar, A. A.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J.; Zhang, J. L.; Zhang, J. Q.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, K.; Zhang, L.; Zhang, T. J.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Y. T.; Zhang, Yang; Zhang, Yao; Zhang, Yu; Zhang, Z. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, J. W.; Zhao, J. Y.; Zhao, J. Z.; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, S. J.; Zhao, T. C.; Zhao, Y. B.; Zhao, Z. G.; Zhemchugov, A.; Zheng, B.; Zheng, J. P.; Zheng, W. J.; Zheng, Y. H.; Zhong, B.; Zhou, L.; Zhou, Q.; Zhou, X.; Zhou, X. K.; Zhou, X. R.; Zhou, X. Y.; Zhou, Xiaoyu; Zhou, Xu; Zhu, A. N.; Zhu, J.; Zhu, J.; Zhu, K.; Zhu, K. J.; Zhu, S.; Zhu, S. H.; Zhu, X. L.; Zhu, Y. C.; Zhu, Y. S.; Zhu, Z. A.; Zhuang, J.; Zou, B. S.; Zou, J. H.; Besiii Collaboration

2018-04-01

We search for rare decays of D mesons to hadrons accompanied by an electron-positron pair (h (h('))e+e-), using an e+e- collision sample corresponding to an integrated luminosity of 2.93 fb-1 collected with the BESIII detector at √{s }=3.773 GeV . No significant signals are observed, and the corresponding upper limits on the branching fractions at the 90% confidence level are determined. The sensitivities of the results are at the level of 10-5- 10-6 , providing a large improvement over previous searches.

Theoretical calculations of positron lifetimes for metal oxides

International Nuclear Information System (INIS)

Mizuno, Masataka; Araki, Hideki; Shirai, Yasuharu

2004-01-01

Our recent positron lifetime measurements for metal oxides suggest that positron lifetimes of bulk state in metal oxides are shorter than previously reported values. We have performed theoretical calculations of positron lifetimes for bulk and vacancy states in MgO and ZnO using first-principles electronic structure calculations and discuss the validity of positron lifetime calculations for insulators. By comparing the calculated positron lifetimes to the experimental values, it wa found that the semiconductor model well reproduces the experimental positron lifetime. The longer positron lifetime previously reported can be considered to arise from not only the bulk but also from the vacancy induced by impurities. In the case of cation vacancy, the calculated positron lifetime based on semiconductor model is shorter than the experimental value, which suggests that the inward relaxation occurs around the cation vacancy trapping the positron. (author)

Production and applications of positron microbeams

International Nuclear Information System (INIS)

Brandes, G.R.; Canter, K.F.; Horsky, T.N.; Lippel, P.H.; Mills, A.P. Jr.

1989-01-01

The production of a positron microbeam using the high-brightness beam developed at Brandeis University and possible applications of this microbeam to spatially resolved defect studies and positron microscopy are reviewed. The high-brightness beam consists of a W(110) primary moderator and two remoderation stages which provide a 500-fold increase in brightness. With this brightness increase and microbeam optics, we are able to form a 12 μm FWHM beam (48 mrad pencil half-angle) at 5 keV beam energy. The well characterised small-diameter beam is particularly adaptable for determining defect concentration and structure, both laterally and in a depth-profiling mode. In the case of a transmission positron microscope or a positron re-emission microscope operating in a high-magnification mode, efficient image formation requires the use of a microbeam to maximise the number of positrons in the area being imaged. Results of the scanning microbeam tests and the application of a microbeam to positron microscopy and defect studies are reviewed. (author)

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.

Time-dependent behavior of positrons in noble gases

International Nuclear Information System (INIS)

Wadehra, J.M.

1990-01-01

Both equilibrium and nonequilibrium behaviors of positrons in several noble gases are reviewed. Our novel procedure for obtaining the time-dependent behavior of various swarm parameters -- such as the positron drift velocity, average positron energy, positron annihilation rate (or equivalently Z eff ) etc. -- for positrons in pure ambient gases subjected to external electrostatic fields is described. Summaries of time-dependent as well as electric field-dependent results for positron swarms in various noble gases are presented. New time-dependent results for positron swarms in neon are also described in detail. 36 refs., 4 figs., 3 tabs

Solvated Positron Chemistry. II

DEFF Research Database (Denmark)

Mogensen, O. E.

1979-01-01

The reaction of the hydrated positron, eaq+ with Cl−, Br−, and I− ions in aqueous solutions was studied by means of positron The measured angular correlation curves for [Cl−, e+], [Br−, e+, and [I−, e+] bound states were in good agreement with th Because of this agreement and the fact...... that the calculated positron wavefunctions penetrate far outside the X− ions in the [X−, e+] sta propose that a bubble is formed around the [X−, e+] state, similar to the Ps bubble found in nearly all liquids. F−ions did not react w Preliminary results showed that CN− ions react with eaq+ while OH−ions are non...... in the Cl− case) at higher concentrations. This saturation and the high-concentration effects-in the angular correlation results were interpreted as caused by rather complicated spur effects, wh It is proposed that spur electrons may pick off the positron from the [X−, e+ states with an efficiency which...

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

International Nuclear Information System (INIS)

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

1995-01-01

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

Positron emission tomography: Physics, instrumentation, and image analysis

International Nuclear Information System (INIS)

Porenta, G.

1994-01-01

Positron emission tomography (PET) is a noninvasive diagnostic technique that permits reconstruction of cross-sectional images of the human body which depict the biodistribution of PET tracer substances. A large variety of physiological PET tracers, mostly based on isotopes of carbon, nitrogen, oxygen, and fluorine is available and allows the in vivo investigation of organ perfusion, metabolic pathways and biomolecular processes in normal and diseased states. PET cameras utilize the physical characteristics of positron decay to derive quantitative measurements of tracer concentrations, a capability that has so far been elusive for conventional SPECT (single photon emission computed tomography) imaging techniques. Due to the short half lives of most PET isotopes, an on-site cyclotron and a radiochemistry unit are necessary to provide an adequate supply of PET tracers. While operating a PET center in the past was a complex procedure restricted to few academic centers with ample resources. PET technology has rapidly advanced in recent years and has entered the commercial nuclear medicine market. To date, the availability of compact cyclotrons with remote computer control, automated synthesis units for PET radiochemistry, high-performance PET cameras, and userfriendly analysis workstations permits installation of a clinical PET center within most nuclear medicine facilities. This review provides simple descriptions of important aspects concerning physics, instrumentation, and image analysis in PET imaging which should be understood by medical personnel involved in the clinical operation of a PET imaging center. (author)

Reestimation of the production spectra of cosmic ray secondary positrons and electrons in the ISM

Science.gov (United States)

Wong, C. M.; Ng, L. K.

1985-01-01

A detailed calculation of the production spectra of charged hadrons produced by interactions of cosmic rays in the interstellar medium is presented along with a thorough treatment of pion and muon decays. Newly parameterized inclusive cross sections of hadrons were used and exact kinematic limitations were taken into account. Single parametrized expressions for the production spectra of both secondary positrons and electrons in the energy range .1 to 100 GeV are presented. The results are compared with other authors' predictions. Equilibrium spectra using various models are also presented.

Effects of positron density and temperature on large amplitude ion-acoustic waves in an electron-positron-ion plasma

International Nuclear Information System (INIS)

Nejoh, Y.N.

1997-01-01

The nonlinear wave structures of large amplitude ion-acoustic waves are studied in a plasma with positrons. We have presented the region of existence of the ion-acoustic waves by analysing the structure of the pseudopotential. The region of existence sensitively depends on the positron to electron density ratio, the ion to electron mass ratio and the positron to electron temperature ratio. It is shown that the maximum Mach number increases as the positron temperature increases and the region of existence of the ion-acoustic waves spreads as the positron temperature increases. 12 refs., 6 figs

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.)

Positron source based on the 48V isotope dedicated to positron lifetime spectroscopy

International Nuclear Information System (INIS)

Dryzek, Jerzy

2009-01-01

In the paper we consider application of the 48 V isotope as a source in the positron lifetime spectroscopy. The isotope was produced in the 48 Ti(p,n) 48 V reaction using 15 MeV proton beam. As a target the natural titanium thin plate was used. The measurements using the typical positron lifetime spectrometer have shown the usefulness of the source obtained for this application. Due to its properties, the source may be used for measurements of positron annihilation characteristics in high temperature or aggressive environments. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Applications of positron depth profiling

Energy Technology Data Exchange (ETDEWEB)

Hakvoort, R A

1993-12-23

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

Applications of positron depth profiling

International Nuclear Information System (INIS)

Hakvoort, R.A.

1993-01-01

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

Exotic decays of the 125 GeV Higgs boson at future e+e- colliders

Science.gov (United States)

Liu, Zhen; Wang, Lian-Tao; Zhang, Hao

2017-06-01

The discovery of unexpected properties of the Higgs boson would offer an intriguing opportunity to shed light on some of the most profound puzzles in particle physics. Beyond Standard Model (BSM) decays of the Higgs boson could reveal new physics in a direct manner. Future electron-positron lepton colliders operating as Higgs factories, including CEPC, FCC-ee and ILC, with the advantages of a clean collider environment and large statistics, could greatly enhance sensitivity in searching for these BSM decays. In this work, we perform a general study of Higgs exotic decays at future e+e- lepton colliders, focusing on the Higgs decays with hadronic final states and/or missing energy, which are very challenging for the High-Luminosity program of the Large Hadron Collider (HL-LHC). We show that with simple selection cuts, (10-3-10-5) limits on the Higgs exotic decay branching fractions can be achieved using the leptonic decaying spectator Z boson in the associated production mode e+e-→ ZH. We further discuss the interplay between detector performance and Higgs exotic decays, and other possibilities of exotic decays. Our work is a first step in a comprehensive study of Higgs exotic decays at future lepton colliders, which is a key area of Higgs physics that deserves further investigation. Supported by Fermi Research Alliance, LLC (DE-AC02-07CH11359) with the U.S. Department of Energy, DOE (DE-SC0013642), IHEP(Y6515580U1), and IHEP Innovation (Y4545171Y2)

Measurements of B{sup 0} Decays to pi{sup +}pi{sup -}pi{sup 0}

Energy Technology Data Exchange (ETDEWEB)

Harrison, Paul F.

2001-07-30

We present preliminary results of searches for exclusive B{sup 0} decays to {pi}{sup +}{pi}{sup -} {pi}{sup 0} among 22.7 million b{bar b} pairs collected by the BABAR experiment from electron-positron collisions near the {Upsilon}(4S) resonance. We measure {Beta}(B{sup 0} {yields} {pi}{sup {+-}}) = (28.9 {+-} 5.4 {+-} 4.3) x 10{sup 6}, and find no evidence for the presence of any other decay mode in the {pi}{sup +}{pi}{sup -} {pi}{sup 0} Dalitz plot. Upper limits are determined for the branching fractions of B{sup 0} {yields} {sup 0}{pi}{sup 0}, non-resonant B{sup 0} decays to {pi}{sup +}{pi}{sup -} {pi}{sup 0} and of several discrete regions of {pi}{sup +}{pi}{sup -} {pi}{sup 0} phase-space. We also measure the direct CP-violating asymmetry between the rates of untagged {sup +}{pi}{sup -} and {sup -}{pi}{sup +}, finding no significant evidence for an effect.

Positron emission tomography

International Nuclear Information System (INIS)

Lindback, Stig

1995-01-01

Positron Emission Tomography (PET) is an advanced nuclear medicine technique used for research at major centres. Unique diagnostic information is obtained from tomographic measurements of the biochemistry and physiology of tissues and organs. In theory, diseases are related to biochemical changes and these can be observed with PET long before any anatomical changes are detectable. In PET the radioactive component is a positron-emitting isotope or 'tracer'. The positrons annihilate with electrons in the body to produce two gamma rays 180° apart; coincidence detection of these gammas provides a very efficient method of determining the spatial distribution of the radioisotope tracer. Because physiological measurements are usually required in a single imaging session, very short-lived isotopes are used to label the tracer molecules; isotope production and labelling is usually carried out in situ. The most commonly used radionuclides are carbon- 11 (half-life 20 minutes), nitrogen-13 (10 minutes), oxygen-15 (2 minutes), and fluorine-18 (110 minutes). A PET system has three major components: - a particle accelerator with targets for production of the positron-emitting isotopes; - chemistry modules for synthesis and labelling of the desired tracers; - and a PET camera for in-vivo measurements of the distribution of the tracer in the body

Positron emission tomography

Energy Technology Data Exchange (ETDEWEB)

Lindback, Stig [GEMS PET Systems AB, Uppsala (Sweden)

1995-07-15

Positron Emission Tomography (PET) is an advanced nuclear medicine technique used for research at major centres. Unique diagnostic information is obtained from tomographic measurements of the biochemistry and physiology of tissues and organs. In theory, diseases are related to biochemical changes and these can be observed with PET long before any anatomical changes are detectable. In PET the radioactive component is a positron-emitting isotope or 'tracer'. The positrons annihilate with electrons in the body to produce two gamma rays 180° apart; coincidence detection of these gammas provides a very efficient method of determining the spatial distribution of the radioisotope tracer. Because physiological measurements are usually required in a single imaging session, very short-lived isotopes are used to label the tracer molecules; isotope production and labelling is usually carried out in situ. The most commonly used radionuclides are carbon- 11 (half-life 20 minutes), nitrogen-13 (10 minutes), oxygen-15 (2 minutes), and fluorine-18 (110 minutes). A PET system has three major components: - a particle accelerator with targets for production of the positron-emitting isotopes; - chemistry modules for synthesis and labelling of the desired tracers; - and a PET camera for in-vivo measurements of the distribution of the tracer in the body.

Determination of elemental tissue composition following proton treatment using positron emission tomography

International Nuclear Information System (INIS)

Cho, Jongmin; Ibbott, Geoffrey; Gillin, Michael; Gonzalez-Lepera, Carlos; Min, Chul Hee; Zhu, Xuping; El Fakhri, Georges; Paganetti, Harald; Mawlawi, Osama

2013-01-01

Positron emission tomography (PET) has been suggested as an imaging technique for in vivo proton dose and range verification after proton induced-tissue activation. During proton treatment, irradiated tissue is activated and decays while emitting positrons. In this paper, we assessed the feasibility of using PET imaging after proton treatment to determine tissue elemental composition by evaluating the resultant composite decay curve of activated tissue. A phantom consisting of sections composed of different combinations of 1 H, 12 C, 14 N, and 16 O was irradiated using a pristine Bragg peak and a 6 cm spread-out Bragg-peak (SOBP) proton beam. The beam ranges defined at 90% distal dose were 10 cm; the delivered dose was 1.6 Gy for the near monoenergetic beam and 2 Gy for the SOBP beam. After irradiation, activated phantom decay was measured using an in-room PET scanner for 30 min in list mode. Decay curves from the activated 12 C and 16 O sections were first decomposed into multiple simple exponential decay curves, each curve corresponding to a constituent radioisotope, using a least-squares method. The relative radioisotope fractions from each section were determined. These fractions were used to guide the decay curve decomposition from the section consisting mainly of 12 C + 16 O and calculate the relative elemental composition of 12 C and 16 O. A Monte Carlo simulation was also used to determine the elemental composition of the 12 C + 16 O section. The calculated compositions of the 12 C + 16 O section using both approaches (PET and Monte Carlo) were compared with the true known phantom composition. Finally, two patients were imaged using an in-room PET scanner after proton therapy of the head. Their PET data and the technique described above were used to construct elemental composition ( 12 C and 16 O) maps that corresponded to the proton-activated regions. We compared the 12 C and 16 O compositions of seven ROIs that corresponded to the vitreous humor, adipose

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

The cryogenic source of slow monochromatic positrons

International Nuclear Information System (INIS)

Meshkov, I.N.; Pavlov, V.N.; Sidorin, A.O.; Yakovenko, S.L.

2008-01-01

The cryogenic source of slow monochromatic positrons based on the 22 Na isotope has been designed and constructed at JINR. Positrons emitted from radioactive source 22 Na have a very broad energy spectrum up to 0.5 MeV. To generate monochromatic beam of slow positrons the solid neon is used as a moderator. The solid neon allows forming slow positron beam of the energy of 1.2 eV at the spectrum width of 1 eV. The efficiency of moderation is 1 % of total positron flux

Probing the positron moderation process using high-intensity, highly polarized slow-positron beams

Science.gov (United States)

Van House, J.; Zitzewitz, P. W.

1984-01-01

A highly polarized (P = 0.48 + or - 0.02) intense (500,000/sec) beam of 'slow' (Delta E = about 2 eV) positrons (e+) is generated, and it is shown that it is possible to achieve polarization as high as P = 0.69 + or - 0.04 with reduced intensity. The measured polarization of the slow e+ emitted by five different positron moderators showed no dependence on the moderator atomic number (Z). It is concluded that only source positrons with final kinetic energy below 17 keV contribute to the slow-e+ beam, in disagreement with recent yield functions derived from low-energy measurements. Measurements of polarization and yield with absorbers of different Z between the source and moderator show the effects of the energy and angular distributions of the source positrons on P. The depolarization of fast e+ transmitted through high-Z absorbers has been measured. Applications of polarized slow-e+ beams are discussed.

Development of a data acquisition architecture with distributed synchronization for a Positron Emission Tomography system with integrated front-end.

OpenAIRE

Aliaga Varea, Ramón José

2016-01-01

[EN] Positron Emission Tomography (PET) is a non-invasive nuclear medical imaging modality that makes it possible to observe the distribution of metabolic substances within a patient's body after marking them with radioactive isotopes and arranging an annular scanner around him in order to detect their decays. The main applications of this technique are the detection and tracing of tumors in cancer patients and metabolic studies with small animals. The Electronic Design for Nuclear Applic...

High efficiency positron moderation

International Nuclear Information System (INIS)

Taqqu, D.

1990-01-01

A new positron moderation scheme is proposed. It makes use of electric and magnetic fields to confine the β + emitted by a radioactive source forcing them to slow down within a thin foil. A specific arrangement is described where an intermediary slowed-down beam of energy below 10 keV is produced. By directing it towards a standard moderator optimal conversion into slow positrons is achieved. This scheme is best applied to short lived β + emitters for which a 25% moderation efficiency can be reached. Within the state of the art technology a slow positron source intensity exceeding 2 x 10 10 e + /sec is achievable. (orig.)

Positron emission tomography

International Nuclear Information System (INIS)

Chandrasekhar, Preethi; Himabindu, Pucha

2000-01-01

Positron Emission Tomography (PET) is a non-invasive nuclear imaging technique used to study different molecular pathways and anatomical structures. PET has found extensive applications in various fields of medicine viz. cardiology, oncology, psychiatry/psychology, neuro science and pulmonology. This study paper basically deals with the physics, chemistry and biology behind the PET technique. It discusses the methodology for generation of the radiotracers responsible for emission of positrons and the annihilation and detection techniques. (author)

Positron emission tomography

International Nuclear Information System (INIS)

Dvorak, O.

1989-01-01

The principle is briefly described of positron emission tomography, and its benefits and constraints are listed. It is emphasized that positron emission tomography (PET) provides valuable information on metabolic changes in the organism that are otherwise only very difficult to obtain, such as brain diagnosis including relationships between mental disorders and the physiology and pathophysiology of the brain. A PET machine is to be installed in Czechoslovakia in the near future. (L.O.)

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

International Nuclear Information System (INIS)

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

2006-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2006-02-28

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

Exact inclusion of the Coulomb field in the photobeta decay of a nucleus and problem of bypassed elements

International Nuclear Information System (INIS)

Kopytin, I.V.; Karelin, K.N.; Nekipelov, A.A.

2004-01-01

The probability of the endothermic β - decay of nuclei that is stimulated by an electromagnetic field of Planck frequency spectrum (photobeta decay) is calculated, the effect of the Coulomb field on a relativistic electron and a virtual relativistic positron being exactly taken into account in this calculation. It is shown that the inclusion of Coulomb effects is of paramount importance and that the results of the calculations may differ by an order of magnitude from those that were obtained previously in the plane-wave approximation, depending on the energy range being considered. A model for the synthesis of bypassed elements in the interior of massive stars is proposed on the basis of the mechanism of the photobeta decay of stable elements that originate from s and r processes

Three dimensional positron-CT: 3D-PET

International Nuclear Information System (INIS)

Ishii, K.

2000-01-01

Positron-CT, namely the positron emission tomograph (PET) provides us the metabolism images obtained by the administration of the drug labeled by the positron emission nuclide in the human body. For example, the carbohydrate metabolism image is obtained by the administration of glucose labelled by 18 F-radioisotopes, and it can be applied to early detection of the cancer and research of high-order function of the brain. As well as X-ray CT, the examine receives the exposure in the positron CT. 3D-PET is based on the solid measurement of γ-rays, therefore, the detection sensitivity of 3D-PET becomes very high and it is possible to drastically reduce the dose of the positron emission nuclide. Because the exposure is reduced to the utmost, the positron CT diagnosis would be possible for the child and the exposure of positron CT doctor in charge can be also reduced. This ideal functional diagnostic imaging equipment, namely, 3D-PET is introduced here. (author)

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

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

Positron lifetime technique with applications in materials science

International Nuclear Information System (INIS)

Vries, J. de.

1987-01-01

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

Results on positron diffusion in Si

International Nuclear Information System (INIS)

Nielsen, B.; Lynn, K.G.; Vehanen, A.; Schultz, P.J.

1984-10-01

Positron diffusion in Si(100) and Si(111) has been measured using a variable energy positron beam. The diffusion related parameter, E 0 is found to be 4.2 +- 0.2 keV, significantly longer than previously reported values. The positron diffusion coefficient is estimated at D/sub +/ = 2.3 +- 0.4 cm 2 /sec, the uncertainty arising mainly from the characteristics of the assumed positron implantation profile. A drastic reduction in E 0 is found after heating the sample to 1300 0 K, showing that previously reported low values of E 0 are associated with the thermal history of the sample. A high sensitivity to defects introduced by low energy ion bombardment is found, and the defect recovery was followed during heat treatments. Reconstruction of the Si(111) surface into the so-called 7 x 7 structure had no detectable influence on the positron diffusion behavior. No changes in the positron diffusion was observed after covering the surface with atomic hydrogen. However the yield of positronium formation at the surface was enhanced, attributed to an increased density of states at the surface

Positrons from supernova and the origin of the galactic-center positron-annihilation radiation

International Nuclear Information System (INIS)

Colgate, S.A.

1983-01-01

The emission of positrons from supernova ejecta is dicussed in terms of the galactic-center annihilation radiation. The positrons from the radioactive sequences 56 Ni→ 56 Co→ 56 Fe are the most numerous source from supernova. Only type I supernova will allow a significant fraction to escape the expanding ejecta. For a neutron star model of a type I SN a fraction 4 x 10 -3 of the escaped positron is enough to create the observed several year fluctuation of the annihilation radiation. The likelihood of this model is discussed in terms of other astrophysical evidence as well as the type I SN light curve

Theoretical aspects of positrons in imperfect solids

International Nuclear Information System (INIS)

Puska, M.J.

1987-01-01

The efficient use of positron annihilation in defect studies requires a deep understanding of the basic processes of positron-imperfect solid interaction. Three stages, i.e. thermalization, trapping by a defect, and the annihilation can be separated during the evolution of the interaction. The last two processes are the most relevant ones for the positron lifetime spectroscopy and they will be discussed in detail in this review. The complete solution of the problem of a localized positron interacting with the electrons around a defect requires the simultaneous self-consistent calculation of the electronic structure and the positron state. This is in principle possible in the two component density functional theory. However, the approximation, in which the electronic structure without the positron influence is used and the electron-positron correlation effects are described by local enhancement factors, has turned out to be feasible in practice and also accurate enough in predicting positron annihilation characteristics. Moreover, a non-self-consistent electron structure is sufficient in many cases. This enables an efficient calculation method in which the positron wave function can be solved in three dimensions for arbitrary defect geometries. Enhancement models for simple metals, transition metals, and semiconductors are represented. Thereafter, applications to vacancies, vacancy clusters, and vacancy-impurity complexes are shown. The positron trapping by defects is mediated by the transfer of the positron binding energy to the solid in the form of electron-hole pairs and phonons. The trapping phenomenon is discussed in the case of metals and semiconductors. Semiconductors are especially challenging because the existence of the energy gap makes the low energy electron-hole excitations impossible and because the defects have different charge states effecting strongly on the trapping rate. (author)

Positron deep level transient spectroscopy — a new application of positron annihilation to semiconductor physics

Science.gov (United States)

Beling, C. D.; Fung, S.; Au, H. L.; Ling, C. C.; Reddy, C. V.; Deng, A. H.; Panda, B. K.

1997-05-01

Recent positron mobility and lifetime measurements made on ac-biased metal on semi-insulating GaAs junctions, which have identified the native EL2 defect through a determination of the characteristic ionization energy of the donor level, are reviewed. It is shown that these measurements point towards a new spectroscopy, tentatively named positron-DLTS (deep level transient spectroscopy), that is the direct complement to conventional DLTS in that it monitors transients in the electric field of the depletion region rather than the inversely related depletion width, as deep levels undergo ionization. In this new spectroscopy, which may be applied to doped material by use of a suitable positron beam, electric field transients are monitored through the Doppler shift of the annihilation radiation resulting from the drift velocity of the positron in the depletion region. Two useful extensions of the new spectroscopy beyond conventional capacitance-DLTS are suggested. The first is that in some instances information on the microstructure of the defect causing the deep level may be inferred from the sensitivity of the positron to vacancy defects of negative and neutral charge states. The second is that the positron annihilation technique is intrinsically much faster than conventional DLTS with the capability of observing transients some 10 6 times faster, thus allowing deep levels (and even shallow levels) to be investigated without problems associated with carrier freeze-out.

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.

Investigation on the chirality of positrons from 22Na decay and their asymmetrical interactions with D-, L- and DL-alanines

International Nuclear Information System (INIS)

Conte, E.; Pieralice, M.

1987-01-01

An investigation on the chirality of the positrons from 22 Na and on their asymmetrical interactions with D-, L-, and DL-alanines was carried out. By using nuclear gamma-spectroscopy, the asymmetrical interaction was proved to be induced with a distinguishably asymmetrical effect

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.

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.

Study of B⁰ → $\\bar{D}$^*0 Decay and Measurement of sin(2β)

Energy Technology Data Exchange (ETDEWEB)

Bomben, Marco [Univ. of Trieste (Italy)

2007-09-18

This thesis describes a measurement of a CP violating asymmetry in neutral B meson decays, ⁰ → $\\bar{D}$^*0, where D^*0 is a charmed meson and h⁰ is a light meson, performed on data collected by the BABAR experiment at the SLAC asymmetric-energy electron-positron collider PEP-II.

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)

Positron probes for mechanical fatigue detection system

International Nuclear Information System (INIS)

Holt, W.H.; Mock, W. Jr.

1976-01-01

The invention comprises positron-emitting probes for use in testing samples of metals for fatique by positron annihilation techniques comprising a substrate made from the same material as the test sample, positron-emitting material supported by one surface of the substrate, and a cover for the emitting material, the cover is sealed to the substrate and is of such thinness and density as to provide a window through which positron passage is unimpeded

High-precision gamma-ray spectroscopy of 61Cu, an emerging medical isotope used in positron emission tomography

Science.gov (United States)

Nelson, N.; Ellison, P.; Nickles, R.; McCutchan, E.; Sonzogni, A.; Smith, S.; Greene, J.; Carpenter, M.; Zhu, S.; Lister, C.; Moran, K.

2017-09-01

61Cu (t1 / 2 = 3.339h) is an important medical isotope used in positron emission tomography (PET) tumor hypoxia imaging scans; however, its beta-plus decay and the subsequent gamma decay of 61Ni has not been studied in over 30 years. Therefore, high quality decay data of 61Cu is desired to determine the overall dose delivered to a patient. In this study, 61Cu was produced at the University of Wisconsin - Madison cyclotron and then assayed using the Gammasphere array at Argonne National Laboratory. Consisting of 70 Compton-suppressed high-purity germanium (HPGe) detectors, Gammasphere provides precise decay data that exceeds that of previous 61Cu studies. γ-ray singles and coincident data were recorded and then analyzed using Radware gf3m software. Through γ- γ coincidence techniques, new γ-ray transitions were identified and high precision determination of γ-ray intensities were made. These modifications and additions to the current decay scheme will be presented, and their impact on the resulting does estimates will be discussed. DOE Isotope Program is acknowledged for funding ST5001030. Work supported by the U.S. DOE under Grant No. DE-FG02-94ER40848 and Contract Nos. DE-AC02-98CH10946 and DE-AC02-06CH11357 and by the Science Undergraduate Laboratory Internship Program (SULI).

Simulation of decay processes and radiation transport times in radioactivity measurements

Energy Technology Data Exchange (ETDEWEB)

García-Toraño, E., E-mail: e.garciatorano@ciemat.es [Laboratorio de Metrología de Radiaciones Ionizantes, CIEMAT, Avda. Complutense 22, 28040 Madrid (Spain); Peyres, V. [Laboratorio de Metrología de Radiaciones Ionizantes, CIEMAT, Avda. Complutense 22, 28040 Madrid (Spain); Bé, M.-M.; Dulieu, C.; Lépy, M.-C. [CEA, LIST, Laboratoire National Henri Becquerel (LNE-LNHB), Bldg 602, PC111, 91191 Gif-sur-Yvette Cedex (France); Salvat, F. [Facultat de Física (FQA and ICC), Universitat de Barcelona, Diagonal 647, 08028 Barcelona (Spain)

2017-04-01

The Fortran subroutine package PENNUC, which simulates random decay pathways of radioactive nuclides, is described. The decay scheme of the active nuclide is obtained from the NUCLEIDE database, whose web application has been complemented with the option of exporting nuclear decay data (possible nuclear transitions, branching ratios, type and energy of emitted particles) in a format that is readable by the simulation subroutines. In the case of beta emitters, the initial energy of the electron or positron is sampled from the theoretical Fermi spectrum. De-excitation of the atomic electron cloud following electron capture and internal conversion is described using transition probabilities from the LLNL Evaluated Atomic Data Library and empirical or calculated energies of released X rays and Auger electrons. The time evolution of radiation showers is determined by considering the lifetimes of nuclear and atomic levels, as well as radiation propagation times. Although PENNUC is designed to operate independently, here it is used in conjunction with the electron-photon transport code PENELOPE, and both together allow the simulation of experiments with radioactive sources in complex material structures consisting of homogeneous bodies limited by quadric surfaces. The reliability of these simulation tools is demonstrated through comparisons of simulated and measured energy spectra from radionuclides with complex multi-gamma spectra, nuclides with metastable levels in their decay pathways, nuclides with two daughters, and beta plus emitters.

4.5 Tesla magnetic field reduces range of high-energy positrons -- Potential implications for positron emission tomography

International Nuclear Information System (INIS)

Wirrwar, A.; Vosberg, H.; Herzog, H.; Halling, H.; Weber, S.; Mueller-Gaertner, H.W.; Forschungszentrum Juelich GmbH

1997-01-01

The authors have theoretically and experimentally investigated the extent to which homogeneous magnetic fields up to 7 Tesla reduce the spatial distance positrons travel before annihilation (positron range). Computer simulations of a noncoincident detector design using a Monte Carlo algorithm calculated the positron range as a function of positron energy and magnetic field strength. The simulation predicted improvements in resolution, defined as full-width at half-maximum (FWHM) of the line-spread function (LSF) for a magnetic field strength up to 7 Tesla: negligible for F-18, from 3.35 mm to 2.73 mm for Ga-68 and from 3.66 mm to 2.68 mm for Rb-82. Also a substantial noise suppression was observed, described by the full-width at tenth-maximum (FWTM) for higher positron energies. The experimental approach confirmed an improvement in resolution for Ga-68 from 3.54 mm at 0 Tesla to 2.99 mm FWHM at 4.5 Tesla and practically no improvement for F-18 (2.97 mm at 0 Tesla and 2.95 mm at 4.5 Tesla). It is concluded that the simulation model is appropriate and that a homogeneous static magnetic field of 4.5 Tesla reduces the range of high-energy positrons to an extent that may improve spatial resolution in positron emission tomography

Photon pair spectrometers in a μ → eγ decay search with the MEGA experiment

International Nuclear Information System (INIS)

Dzemidzic, M.

1993-01-01

The MEGA experiment at LAMPF is conducting a search for the lepton family number violating decay μ + →e + γ with a branching ratio sensitivity of a few parts in 10 -13 . The detectors are contained in a 1.5 T solenoidal magnetic field. Positrons are confined to the central region and are measured by a set of cylindrical MWPCs. Photons are converted into e + e - pairs by one of three pair spectrometers in the outer region. Each pair spectrometer consists of an inner layer of plastic scintillator, two lead converters separated by a MWPC and three layers of drift chambers. The MEGA collaboration successfully concluded 1992 data taking with a set of positron MWPCs and two pair spectrometers. A brief overview of the pair spectrometer design and performance will be followed by a presentation of results to date of the data analysis

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

Atomic collisions involving pulsed positrons

DEFF Research Database (Denmark)

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

2000-01-01

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

Neutron emission from 9Be nucleus under the action of β+ and γ radiation emitted in radioactive decay

International Nuclear Information System (INIS)

Vo Dak Bang; Gangrskij, Yu.P.; Miller, M.B.; Mikhajlov, L.V.; Fam Zui Khien; Kharisov, I.F.

1980-01-01

The neutron yield from the 9 Be nucleus under the action of beta and gamma-radiation emitted at the radiative decay of 11 C, 62 Cu, 66 Ga, 74 Br isotopes is measured. These isotopes differ essentially by the emitted radiation spectra. The contribution of various processes ((γ, n)-reactions, inelastic scattering and positron nonradiative annihilation) to the neutron yield observed is determined [ru

Construction report of the PF slow-positron source. 1

International Nuclear Information System (INIS)

Enomoto, Atsushi; Kurihara, Toshikazu; Kobayashi, Hitoshi

1993-12-01

The slow positron source utilizing the electron beam of the 2.5 GeV electron beam accelerator which is the synchrotron radiation injector is being constructed. The outline of the project and the present state of construction are reported. As of November, 1993, by injecting the electron beam of about 10 W to the targets for producing positrons, the slow positrons of 4 x 10 4 e + /s has been obtained in the laboratory. Finally, with the electron beam of 30 kW, it is aimed at to obtain the slow positron beam of 2 x 10 9 e + /s. In the slow positron source, the electron beam from the 2.5 GeV linear accelerator is used as the primary beam. This beam is led to the target with electromagnets. Radiation shields were strengthened, and the electrostatic lens system was attached to efficiently extract and send out slow positrons. The conveying system for slow positrons is explained. Primary electron beam, target and moderator for producing slow positrons, the change to continuous current of pulsed slow positron beam and the heightening of luminance of slow positron beam, and the experiment on the utilization of slow positron beam, and the control system for positron conveyance path are reported. (K.I.)

A study of positron irradiated porous silicon

International Nuclear Information System (INIS)

Huang Yuanming; Xue Qing; Zhai Baogai; Xu Aijun; Liu Shewen; Yu Weizhong

1998-01-01

The effect of positron irradiation on photoluminescence (PL) of porous silicon has been studied. After four hour positron irradiation, the red PL spectrum of porous silicon blue shifts into greenish spectral region, and a higher energy luminescence band is introduced into this blueshifted spectrum. The fourier transform infrared absorption experiment shows that the positron irradiation can cause further oxidization of porous silicon. A possible mechanism causing this change of PL spectra after positron irradiation is suggested

Production and decay of heavy selectrons; Produktion und Nachweis schwerer Selektronen

Energy Technology Data Exchange (ETDEWEB)

Csallner, S.

2007-04-03

We investigate the production and the decay of selectrons with masses beyond the threshold for pair production at future linear colliders with center-of-mass energies of 500 GeV and 800 GeV. For this we study the production of left and right selectrons in association with the lightest neutralino or chargino, respectively, via electron-electron, electron-positron and electron-photon scattering in the framework of the MSSM. Furthermore we analyse the production via electron-electron scattering in two extended models, the NMSSM and an E6-model with an additional U(1) gauge factor. (orig.)

Nuclear-charge and positron-energy dependence of the single-quantum annihilation of positrons

International Nuclear Information System (INIS)

Palathingal, J.C.; Asoka-Kumar, P.; Lynn, K.G.; Wu, X.Y.

1995-01-01

We report an experimental study of the single-quantum annihilation of positrons in a number of elements having atomic numbers between 49 and 90, utilizing a monoenergetic positron beam. Measurements were made of the differential cross sections for the forward direction for the K, L, and M atomic shells in targets of Th, Pb, Au, Hf, Gd, and In, having thicknesses that vary between 2.7 and 4.4 mg/cm 2 . A shielded HPGe detector of high relative photopeak efficiency was used for recording the photon spectrum. Values for the individual atomic shells were obtained in the positron kinetic-energy range 1.02--2.24 MeV. It was observed that the differential cross sections measured for the forward direction varied with energy for each major shell almost alike so that the shell ratios appeared to remain constant while the positron energy varied. The dependence of the cross section on the atomic number Z of the target element was tested for each of the major shells at various energies of measurement. It was seen that the cross sections follow a Z ν relation with ν∼5.1 as the exponent for the K shell. For the higher shells, the exponent is approximately 6.4, which is significantly larger. It was also noted that this pattern is fairly independent of the positron energy. The results on the Z dependence are seen to be clearly at variance with the most updated theoretical predictions

Bulk Materials Analysis Using High-Energy Positron Beams

International Nuclear Information System (INIS)

Glade, S C; Asoka-Kumar, P; Nieh, T G; Sterne, P A; Wirth, B D; Dauskardt, R H; Flores, K M; Suh, D; Odette, G.R.

2002-01-01

This article reviews some recent materials analysis results using high-energy positron beams at Lawrence Livermore National Laboratory. We are combining positron lifetime and orbital electron momentum spectroscopic methods to provide electron number densities and electron momentum distributions around positron annihilation sites. Topics covered include: correlation of positron annihilation characteristics with structural and mechanical properties of bulk metallic glasses, compositional studies of embrittling features in nuclear reactor pressure vessel steel, pore characterization in Zeolites, and positron annihilation characteristics in alkali halides

Investigation and realization of a slow-positron beam

International Nuclear Information System (INIS)

Ruiz, Nicolas

2011-01-01

This research thesis first proposes a presentation of the GBAR project (Gravitational Behaviour of Anti-hydrogen at Rest) within which this research took place, and which aims at performing the first direct test of the Weak Equivalence Principle on anti-matter by studying the free fall of anti-hydrogen atoms in the Earth gravitational field. The author presents different aspects of this project: scientific objective, experiment principle and structure, detailed structure (positron beam, positron trap, positron/positronium conversion, anti-proton beam, trapping, slowing down and neutralisation of anti-hydrogen ions). The author then reports the design of the positron beam: study of source technology, studies related to the fast positron source, design of the low positron line (approach, functions, simulations, technology). The two last chapters report the construction and the characterization of the slow-positron line [fr

Ultrarelativistic electron and positron radiation in planar channeling

International Nuclear Information System (INIS)

Kalashnikov, N.P.; Olchack, A.S.

1980-01-01

The coherent electromagnetic radiation from channeling electrons and positrons is given by similar expression. However for the channeling positrons the close collisions are suppressed due to the fact that the positron wave function is exponentially small near the atoms of the crystal lattice. It follows that the coherent bremsstrahlung decreases for the channeling positrons. We have investigated the ultrarelativistic channeling electron and positron radiations, connected with the electromagnetic transitions from the continuum spectrum states to the quasi-bound spectrum states and between the different quasi-bound spectrum states. The radiation probabilities are calculated by using the model continuum planar potential. It is shown that the radiation from the channeling electrons is several orders of magnitude larger than the positron radiation, while the electron and positron radiation have similar characteristics such as frequency limitation and angular distribution of the radiation. (orig.)

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)

The rise in the positron fraction. Distance limits on positron point sources from cosmic ray arrival directions and diffuse gamma-rays

Energy Technology Data Exchange (ETDEWEB)

Gebauer, Iris; Bentele, Rosemarie [Karlsruhe Institute of Technology, Karlsruhe (Germany)

2016-07-01

The rise in the positron fraction as observed by AMS and previously by PAMELA, cannot be explained by the standard paradigm of cosmic ray transport in which positrons are produced by cosmic-ray-gas interactions in the interstellar medium. Possible explanations are pulsars, which produce energetic electron-positron pairs in their rotating magnetic fields, or the annihilation of dark matter. Here we assume that these positrons originate from a single close-by point source, producing equal amounts of electrons and positrons. The propagation and energy losses of these electrons and positrons are calculated numerically using the DRAGON code, the source properties are optimized to best describe the AMS data. Using the FERMI-LAT limits on a possible dipole anisotropy in electron and positron arrival directions, we put a limit on the minimum distance of such a point source. The energy losses that these energetic electrons and positrons suffer on their way through the galaxy create gamma ray photons through bremsstrahlung and Inverse Compton scattering. Using the measurement of diffuse gamma rays from Fermi-LAT we put a limit on the maximum distance of such a point source. We find that a single electron positron point source powerful enough to explain the locally observed positron fraction must reside between 225 pc and 3.7 kpc distance from the sun and compare to known pulsars.

Studies of positron induced luminescence from polymers

International Nuclear Information System (INIS)

Xu, J.; Hulett, L.D. Jr.; Lewis, T.A.; Tolk, N.H.

1994-01-01

Light emission from polymers (anthracene dissolved in polystryrene) induced by low-energy positrons and electrons has been studied. Results indicate a clear difference between optical emissions under positron and electron bombardment. The positron-induced luminescence spectrum is believed to be generated by both collisional and annihilation processes

Cardiac positron tomography

International Nuclear Information System (INIS)

Geltmann, E.M.; Roberts, R.; Sobel, B.E.

1980-01-01

Positron emission tomography (PET) performed after the administration of the positron-emitting radionuclides carbon-11 ( 11 C), nitrogen-13 ( 13 N), oxygen-15 ( 15 O) and fluorine-18 ( 18 F) has permitted the improved noninvasive assessment of the regional myocardial metabolism of normal physiologic substrates and intermediates and their cogeners. In experimental animals, the rate of oxidation of 11 C-palmitate correlates closely with other indexes of oxygen consumption, and the extraction of 11 C-palmitate (like that of 18 F-fatty acids and 18 F-fluoredoxyglucose) ist markedly diminished in regions of myocardial ischemia. In both experimental animals and in patients, myocardial infarct site and size, determined by positron emission tomography after the intravenous injection of 11 C-palmitate, correlate closely with the electrocardiographic infarct locus and enzymatically estimated infarct size as well as with the location and extent of regional left ventricular wall motion abnormalities. PET offers promise for assessment of flow as well despite the complexities involved. PET with 13 NH 3 appears to provide one useful qualitative index, although this tracer ist actively metabolized. Because of the quantitative capabilities of positron emission tomography and the rapid progress which is being made in the development of fast scan, multi-slice, and gated instrumentation, this technique is likely to facilitate improved understanding and characterization of regional myocardial metabolism and blood flow in man under physiological and pathophysiological conditions. (orig.) [de

Positron lifetime experiments in indium selenide

International Nuclear Information System (INIS)

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

1988-01-01

Positron lifetime experiments have been performed on as-grown samples which had been isochronally annealed up to 820 K and plastically deformed and these experiments yield a constant lifetime of 282 ± 2 ps which is attributed to bulk positron states in InSe. Electron-irradiated samples exhibit a two-component spectrum, revealing the presence of positron traps which anneal out at about 330 K. The nature of the native shallow donors in InSe is discussed in the light of the results, which support the idea that native donor centres are probably interstitial In atoms rather than Se vacancies. Positron trapping observed in the electron-irradiated samples is attributed to defects related to In vacancies. (author)

Cosmic Ray Positrons from Pulsars

Science.gov (United States)

Harding, Alice K.

2010-01-01

Pulsars are potential Galactic sources of positrons through pair cascades in their magnetospheres. There are, however, many uncertainties in establishing their contribution to the local primary positron flux. Among these are the local density of pulsars, the cascade pair multiplicities that determine the injection rate of positrons from the pulsar, the acceleration of the injected particles by the pulsar wind termination shock, their rate of escape from the pulsar wind nebula, and their propagation through the interstellar medium. I will discuss these issues in the context of what we are learning from the new Fermi pulsar detections and discoveries.

Undulator-based production of polarized positrons

Energy Technology Data Exchange (ETDEWEB)

Alexander, G. [Tel-Aviv Univ. (Israel); Barley, J. [Cornell Univ., Ithaca, NY (United States); Batygin, Y. [SLAC, Menlo Park, CA (US)] (and others)

2009-05-15

Full exploitation of the physics potential of a future International Linear Collider will require the use of polarized electron and positron beams. Experiment E166 at the Stanford Linear Accelerator Center (SLAC) has demonstrated a scheme in which an electron beam passes through a helical undulator to generate photons (whose first-harmonic spectrum extended to 7.9 MeV) with circular polarization, which are then converted in a thin target to generate longitudinally polarized positrons and electrons. The experiment was carried out with a one-meter-long, 400-period, pulsed helical undulator in the Final Focus Test Beam (FFTB) operated at 46.6 GeV. Measurements of the positron polarization have been performed at five positron energies from 4.5 to 7.5 MeV. In addition, the electron polarization has been determined at 6.7MeV, and the effect of operating the undulator with a ferrofluid was also investigated. To compare the measurements with expectations, detailed simulations were made with an upgraded version of GEANT4 that includes the dominant polarization-dependent interactions of electrons, positrons, and photons with matter. The measurements agree with calculations, corresponding to 80% polarization for positrons near 6 MeV and 90% for electrons near 7 MeV. (orig.)

Positron lifetime study of neutron-irradiated molybdenum

International Nuclear Information System (INIS)

Hinode, Kenji; Tanigawa, Shoichiro; Kumakura, Hiroaki; Doyama, Masao; Shiraishi, Kensuke.

1978-01-01

Annealing behavior of fast-neutron-irradiated molybdenum was studied by means of positron lifetime technique. It was found that Stage III annealing can be mainly identified as the vacancy migration process from the detailed analyses of data. The void growth after successive high temperature annealings was clearly detected through the changes of positron lifetime parameters. An attempt to analyse the size distribution of voids from positron lifetime spectra was presented, and discussions on the evaluation of void concentration from positron data are also given. (author)

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)

Digital positron annihilation spectrometer

International Nuclear Information System (INIS)

Cheng Bin; Weng Huimin; Han Rongdian; Ye Bangjiao

2010-01-01

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

Positron emission tomography imaging--technical considerations

International Nuclear Information System (INIS)

Muehllehner, G.; Karp, J.S.

1986-01-01

Positron imaging instrumentation has improved rapidly in the last few years. Scanners currently under development are beginning to approach fundamental limits set by positron range and noncolinearity effects. This report reviews the latest developments in positron emission tomography (PET) instrumentation, emphasizing the development of coding schemes that reduce the complexity and cost of high-resolution scanners. The relative benefits of using time-of-flight (TOF) information is discussed as well. 68 references

Experimental Study of a Positron\\\\ Source Using Channeling

CERN Multimedia

Gavrykov, V; Kulibaba, V; Baier, V; Beloborodov, K; Bojenok, A; Bukin, A; Burdin, S; Dimova, T; Druzhinin, V; Dubrovin, M; Seredniakov, S; Shary, V; Strakhovenko, V; Keppler, P; Major, J; Bogdanov, A V; Potylitsin, A; Vnoukov, I; Artru, X; Lautesse, P; Poizat, J-C; Remillieux, J

2002-01-01

Many simulations have predicted that the yield of positrons, resulting from the interaction of fast electrons in a solid target, increases if the target is a crystal oriented with a major axis parallel to the electron beam. Tests made at Orsay and Tokyo confirmed these expectations. The experiment WA 103 concerns the determination of the main characteristics (emittance, energy spread) of a crystal positron source which could replace advantageously the conventional positron converters foreseen in some linear collider projects. The main element of the set-up is a magnetic spectrometer, using a drift chamber, where the positron trajectories are reconstructed (see Figure 1) A first run has been operated in july 2000 and the first results showed, as expected, a significant enhancement in photon and positron generation along the $$ axis of the tungsten crystal. Indications about a significant increase in the number of soft photons and positrons were also gathered : this point is of importance for the positron colle...

Toward a European Network of Positron Laboratories

Directory of Open Access Journals (Sweden)

Karwasz Grzegorz P.

2015-12-01

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

Recent developments in the theory of positrons at surfaces

International Nuclear Information System (INIS)

Walker, A.B.

1989-01-01

Positron beams of ever brighter intensity are now establishing themselves as a novel surface probe enabling a wide variety of spectroscopies. The production of high positron intensities and exploitation of the beams depends critically on our understanding of the complex behaviour of positrons at and near surfaces. I will review progress on the theory of positron-surface interactions and of the implantation and diffusion of low energy positrons. Applications of this theory to a variety of experimental techniques such as ACAR (Angular Correlation by Annihilation Radiation) spectra, angle resolved positronium (Ps) spectroscopy, REPELS (Reemitted Positron Energy Loss Spectroscopy), LEPD (Low Energy Positron Diffraction) and measurements of defect profiles will be discussed. 24 refs. (author)

Cyclotrons and positron emitting radiopharmaceuticals

International Nuclear Information System (INIS)

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

1984-01-01

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

Positron emission tomography now and in the future

International Nuclear Information System (INIS)

Vaalburg, W.

1987-01-01

A survey is given of positron emission tomography used in nuclear medicine. The production of positron emitting radionuclides is discussed. The development of positron detectors is described. The application of positron emission tomography in cardiology, oncology and neurology is treated. The authors conclude that PET is a unique method to examine metabolic processes, although the method is still in its infancy. 7 refs.; 1 table

Positron creation in superheavy quasi-molecules

International Nuclear Information System (INIS)

Mueller, B.

1976-01-01

The review of positron creation in superheavy quasi-molecules includes spontaneous positron emission from superheavy atoms, supercritical quasi-molecules, background effects, and some implications of the new ground state. 66 references

Progress toward magnetic confinement of a positron-electron plasma: nearly 100% positron injection efficiency into a dipole trap

Science.gov (United States)

Stoneking, Matthew

2017-10-01

The hydrogen atom provides the simplest system and in some cases the most precise one for comparing theory and experiment in atomics physics. The field of plasma physics lacks an experimental counterpart, but there are efforts underway to produce a magnetically confined positron-electron plasma that promises to represent the simplest plasma system. The mass symmetry of positron-electron plasma makes it particularly tractable from a theoretical standpoint and many theory papers have been published predicting modified wave and stability properties in these systems. Our approach is to utilize techniques from the non-neutral plasma community to trap and accumulate electrons and positrons prior to mixing in a magnetic trap with good confinement properties. Ultimately we aim to use a levitated superconducting dipole configuration fueled by positrons from a reactor-based positron source and buffer-gas trap. To date we have conducted experiments to characterize and optimize the positron beam and test strategies for injecting positrons into the field of a supported permanent magnet by use of ExB drifts and tailored static and dynamic potentials applied to boundary electrodes and to the magnet itself. Nearly 100% injection efficiency has been achieved under certain conditions and some fraction of the injected positrons are confined for as long as 400 ms. These results are promising for the next step in the project which is to use an inductively energized high Tc superconducting coil to produce the dipole field, initially in a supported configuration, but ultimately levitated using feedback stabilization. Work performed with the support of the German Research Foundation (DFG), JSPS KAKENHI, NIFS Collaboration Research Program, and the UCSD Foundation.

Positron studies of metal-oxide-semiconductor structures

Science.gov (United States)

Au, H. L.; Asoka-Kumar, P.; Nielsen, B.; Lynn, K. G.

1993-03-01

Positron annihilation spectroscopy provides a new probe to study the properties of interface traps in metal-oxide semiconductors (MOS). Using positrons, we have examined the behavior of the interface traps as a function of gate bias. We propose a simple model to explain the positron annihilation spectra from the interface region of a MOS capacitor.

In-situ positron emission of CO oxidation

NARCIS (Netherlands)

Vonkeman, K.A.; Jonkers, G.; Wal, van der S.W.A.; Santen, van R.A.

1993-01-01

Using a Neuro ECAT positron tomog., the Positron Emission computed Tomog. (PET) was utilized to image the catalytic oxidn. of CO by using CO and CO2, labeled with short lived positron emitting nuclides. Studies were performed over highly dispersed CeO2/g-Al2O3 supported Pt and Rh catalysts. With a

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

Low-energy positron and electron diffraction and positron-stimulated secondary electron emission from Cu(100)

International Nuclear Information System (INIS)

Weiss, A.H.

1983-01-01

The results of two series of experiments are reported. In the first, an electrostatically guided beam of low-energy (40-400 eV) positrons, delta/sub p/ was used to study low-energy positron diffraction (LEPD) from a Cu(100) surface under ultrahigh-vacuum conditions. Low-energy electron diffraction (LEED) data were obtained from the same sample in the same apparatus. Comparison of LEPD and LEED intensity versus energy data with model calculations made using computer programs developed by C.B. Duke and collaborators indicated that: LEPD data is adequately modeled using potentials with no exchange-correlation term. The inelastic mean free path, lambda/sub ee/, is shorter for positrons than for electrons at low (< approx.80 eV). LEED is better than LEPD at making a determination of the first-layer spacing of Cu(100) for the particular data set reported. In the second set of experiments, the same apparatus and sample were used to compare positron- and electron-stimulated secondary-electron emission (PSSEE and ESSEE). The results were found to be consistent with existing models of secondary-electron production for metals. The energy distributions of secondary-electrons had broad low-energy (<10 eV) peaks for both positron and electron stimulation. But the PSEE distribution showed no elastic peak. Measurements of secondary-electron angular distributions, found to be cosine-like in both the PSSEE and ESSEE case, were used to obtain total secondary yield ratios, delta, at four beam energies ranging from 40-400 eV. The secondary yield ratio for primary positrons and the yield for primary electrons, delta/sub e/, were similar at these energies. For 400-eV primary particles the secondary yields were found to be delta/sub p/ = 0.94 +/- 0.12 and delta/sub e/ = 0.94 +/- 0./12, giving a ratio of unity for positron-stimulated secondary yield to electron-stimulated secondary yield

Positron emission tomography

International Nuclear Information System (INIS)

Bolwig, T.G.; Haunsoe, S.; Dahlgaard Hove, J.; Hesse, B.; Hoejgard, L.; Jensen, M.; Paulson, O.B.; Hastrup Svendsen, J.; Soelvsten Soerensen, S.

1994-01-01

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

Positron-attachment to small molecules: Vibrational enhancement of positron affinities with configuration interaction level of multi-component molecular orbital approach

Energy Technology Data Exchange (ETDEWEB)

Tachikawa, Masanori [Quantum Chemistry Division, Graduate School of NanoBioScience, Yokohama City University, 22-2 Seto, Kanazawa, Yokohama 236-0027 (Japan)

2015-12-31

To theoretically demonstrate the binding of a positron to small polarized molecules, we have calculated the vibrational averaged positron affinity (PA) values along the local vibrational contribution with the configuration interaction level of multi-component molecular orbital method. This method can take the electron-positron correlation contribution into account through single electronic - single positronic excitation configurations. The PA values are enhanced by including the local vibrational contribution from vertical PA values due to the anharmonicity of the potential.

Cyclotrons and positron emitting radiopharmaceuticals

Energy Technology Data Exchange (ETDEWEB)

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

1984-01-01

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

Automatic sup sup 1 sup sup 8 F positron source supply system for a monoenergetic positron beam

CERN Document Server

Saito, F; Itoh, Y; Goto, A; Fujiwara, I; Kurihara, T; Iwata, R; Nagashima, Y; Hyodo, T

2000-01-01

A system which supplies an intense sup sup 1 sup sup 8 F (half life 110 min) positron source produced by an AVF cyclotron through sup sup 1 sup sup 8 O(p,n) sup sup 1 sup sup 8 F reaction has been constructed. Produced sup sup 1 sup sup 8 F is transferred to a low background experiment hall through a capillary. It is electro-deposited on a graphite rod and used for a source of a slow positron beam. In the meantime the next batch of target sup sup 1 sup sup 8 O water is loaded and proton irradiation proceeds. This system makes it possible to perform continuous positron beam experiments using the 18 F positron source.

Positron emission tomography with Positome, 2

International Nuclear Information System (INIS)

Nukui, Hideaki; Yamamoto, Y.L.; Thompson, C.J.; Feindel, W.

1979-01-01

Positron emission tomography with Positome II using 68 Ga-EDTA was performed in cases with brain tumor and cerebral arteriovenous malformation. A significant focal uptake in static study and hemodynamic changes in dynamic study were noted in all cases except one case with intracranial lipoma. Comparing this method with sup(99m) Tc-pertechnetate cerebral image study and computerized axial tomography, the diagnostic rate for detecting brain tumor was almost equal in all of these three methods. However, detecting and localizing was easier and clearer in static positron emission tomography with 68 Ga-EDTA than in sup(99m) Tc-pertechnetate cerebral image and computerized axial tomography without infusion of contrast medium. Furthermore, static positron emission tomography with 68 Ga-EDTA was superior to computerized axial tomography without infusion of contrast medium for detecting cerebral arteriovenous malformation. Concerning dynamic positron emission tomography with 68 Ga-EDTA, semiquantitative values obtained by this method correlated well with findings of computerized axial tomography and was thought to be more precise and in detail than the findings of sup(99m) Tc-pertechnetate cerebral image study. Summation of the previous studies about dynamic positron emission tomography with 77 Kr in occlusive cerebrovascular disease is also reported. In conclusion, static positron emission tomography with 68 Ga-EDTA is a very useful diagnostic method for detecting and localizing brain tumor and cerebral arteriovenous malformation without any attendant complications. Furthermore, a good combination of static and dynamic positron emission tomography and computerized axial tomography appear to be outstandingly effective for not only detecting the lesion but also understanding the pathophysiological aspect in cases with various intracranial lesions. (author)

Simulation of a Positron Source for CEBAF

International Nuclear Information System (INIS)

S. Golge; A. Freyberger; C. Hyde-Wright

2007-01-01

A positron source for the 6 GeV (or the proposed 12 GeV upgrade) recirculating linacs at Jefferson Lab is presented. The proposed 100nA CW positron source has several unique characteristics; high incident beam power (100kW), 10 MeV incident electron beam energy, CW incident beam and CW production. Positron production with 10 MeV electrons has several advantages; the energy is below neutron threshold so the production target will not become activated during use and the absolute energy spread is bounded by the low incident energy. These advantages are offset by the large angular distribution of the outgoing positrons. Results of simulations of the positron production, capture, acceleration and injection into the recirculating linac are presented. Energy flow and thermal management of the production target present a challenge and are included in the simulations

Intense positron beam and its application to surface science

International Nuclear Information System (INIS)

Ito, Y.; Hirose, M.; Kanazawa, I.; Sueoka, O.; Takamura, S.; Okada, S.

1992-01-01

Intense pulsed slow positron beam has been produced using the 100 MeV electron LINAC of JAERI · Tokai. In order to use the beam for surface studies such as positron diffraction and positron microscopy, it was transferred from the solenoid magnetic field to field free region and then was brightness-enhanced. The beam size was reduced from 10 mmφ (in the magnetic field) to 0.5 mmφ after two stages of re-moderation. Using the intense brightness-enhanced positron beam we have observed for the first time RHEPD (Reflection High-Energy Positron Diffraction) patterns. A design of re-emission positron microscopy is also described. (author)

Simulation of complex detection systems in neutrinoless double beta decay experiments

International Nuclear Information System (INIS)

Larrea, A.; Morales, A.; Morales, J.; Nunez-Lagos, R.; Puimedon, J.; Villar, J.A.

1988-01-01

The estimated efficiency of several detection systems dedicated to the search of the neutrinoless double beta decay of 76 Ge is reported. In order to perform this work, we have developed the GEOM macro library system which can handle highly complex geometries in simulation problems, allowing to include an accurate description of the experimental setup in a very simple way. Also an internal mechanism for checking the correct location of every boundary defining the geometrical regions is included. The present version of GEOM is implemented in the EGS4 code of Monte Carlo simulation of photons and electron/positron showers, but it can be easily extended to other simulation codes. (orig.)

Formation of short-lived positron emitters in reactions of protons of energies up to 200 MeV with the target elements carbon, nitrogen and oxygen

CERN Document Server

Kettern, K; Qaim, S M; Shubin, Yu N; Steyn, G F; Van der Walt, T N; 10.1016/j.apradiso.2004.02.007

2004-01-01

Excitation functions were measured by the stacked-foil technique for proton induced reactions on carbon, nitrogen and oxygen leading to the formation of the short-lived positron emitters /sup 11/C (T/sub 1 /2/=20.38 min) and /sup 13/N (T/sub 1/2/=9.96 min). The energy region covered extended up to 200 MeV. The product activity was measured non-destructively via gamma -ray spectrometry. A careful decay curve analysis of the positron annihilation radiation was invariably performed. The experimental results were compared with theoretical data obtained using the modified hybrid nuclear model code ALICE-IPPE for intermediate energies. The agreement was found to be generally satisfactory. The data are of importance in proton therapy.

Study of a positron generation

International Nuclear Information System (INIS)

Nakahara, Kazuo; Enomoto, A.; Ikeda, M.; Ohsawa, S.; Kamitani, T.; Hosoyama, K.; Takei, H.; Emoto, T.; Tani, S.

1998-03-01

In the Power Reactor and Nuclear Fuel Development Corporation (PNC), the following are examined as part of an application technology using a high power electron linac: monochromatic gamma ray sources, free electron lasers, and intense positron sources. This report presents the study of an intense positron source, which has been developed jointly by High Energy Accelerator Research Organization (KEK) and PNC. In this report, we describe following items for an adaptive estimate of a superconducting magnet in order to efficiently converge a positron beam. (1) The cryostat which included the superconducting magnet is manufactured. (2) An excitement test of the superconducting magnet is carried out with a magnetic substance such as the electromagnet yoke. (author)

The influence of positron trapping at vacancies on a pattern of the Fermi surface of #betta#-brass studied by positron annihilation

International Nuclear Information System (INIS)

Rozenfeld, B.; Chabik, S.; Pajak, J.

1982-01-01

Angular correlations of positron annihilation quanta (ACPAQ) have been measured for differently oriented monocrystalline samples of the ordered #betta#-brass under conditions permitting the neglecting of the trapping of positrons at vacancies as well as in the case when almost all the positrons annihilate being trapped at vacancies. It has been shown that trapping of positrons at vacancies can make the observation of the directional anisotropy in electron momentum distribution impossible. (Auth.)

Selection of hadronic W-decays in DELPHI with feed forward neural networks - An update

CERN Document Server

Becks, K H; Müller, U; Wahlen, H

2003-01-01

Since 1998 feed forward neural networks have been successfully applied to select candidates of hadronic W-decays measured at different center of mass-energies by the DELPHI collaboration at the Large Electron Positron collider at CERN. To prepare the final publication, the neural network was adapted to all center of mass- energies. Detailed studies were performed concerning the level of preselection, the choice of network parameters and especially of the network architecture. The number of hidden nodes was optimized by testing different pruning methods. All studies and results will be discussed.

Selection of hadronic W-decays in DELPHI with feed forward neural networks - an update

International Nuclear Information System (INIS)

Becks, K.-H.; Drees, J.; Mueller, U.; Wahlen, H.

2003-01-01

Since 1998 feed forward neural networks have been successfully applied to select candidates of hadronic W-decays measured at different center of mass-energies by the DELPHI collaboration at the Large Electron Positron collider at CERN. To prepare the final publication, the neural network was adapted to all center of mass-energies. Detailed studies were performed concerning the level of preselection, the choice of network parameters and especially of the network architecture. The number of hidden nodes was optimized by testing different pruning methods. All studies and results will be discussed

Positron beam studies of transients in semiconductors

International Nuclear Information System (INIS)

Beling, C.D.; Ling, C.C.; Cheung, C.K.; Naik, P.S.; Zhang, J.D.; Fung, S.

2006-01-01

Vacancy-sensing positron deep level transient spectroscopy (PDLTS) is a positron beam-based technique that seeks to provide information on the electronic ionization levels of vacancy defects probed by the positron through the monitoring of thermal transients. The experimental discoveries leading to the concept of vacancy-sensing PDLTS are first reviewed. The major problem associated with this technique is discussed, namely the strong electric fields establish in the near surface region of the sample during the thermal transient which tend to sweep positrons into the contact with negligible defect trapping. New simulations are presented which suggest that under certain conditions a sufficient fraction of positrons may be trapped into ionizing defects rendering PDLTS technique workable. Some suggestions are made for techniques that might avoid the problematic electric field problem, such as optical-PDLTS where deep levels are populated using light and the use of high forward bias currents for trap filling

Positron lifetime measurements on electron irradiated amorphous alloys

International Nuclear Information System (INIS)

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

1981-08-01

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

Polarized positron sources for the future linear colliders

International Nuclear Information System (INIS)

Chaikovska, I.

2012-01-01

This thesis introduces the polarized positron source as one of the key element of the future Linear Collider (LC). In this context, the different schemes of the polarized positron source are described highlighting the main issues in this technology. In particular, the main focus is on the Compton based positron source adopted by the CLIC as a preferred option for the future positron source upgrade. In this case, the circularly polarized high energy gamma rays resulting from Compton scattering are directed to a production target where an electromagnetic cascade gives rise to the production of positrons by e + -e - pair conversion. To increase the efficiency of the gamma ray production stage, a multiple collision point line integrated in energy recovery linac is proposed. The simulations of the positron production, capture and primary acceleration allow to estimate the positron production efficiency and provide a simple parametrization of the Compton based polarized positron source in the view of the future LC requirements. The storage ring based Compton source option, so-called Compton ring, is also described. The main constraint of this scheme is given by the beam dynamics resulting in the large energy spread and increased bunch length affecting the gamma ray production rate. An original theoretical contribution is shown to calculate the energy spread induced by Compton scattering. Moreover, an experiment to test the gamma ray production by Compton scattering using a state-of-art laser system developed at LAL has been conducted in the framework of the 'Mighty Laser' project at the ATF, KEK. The experimental layout as well as the main results obtained are discussed in details. The studies carried out in this thesis show that the polarized positron source based on Compton scattering is a promising candidate for the future LC polarized positron source. (author)

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

International Nuclear Information System (INIS)

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

1977-02-01

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

New Possibilities of Positron-Emission Tomography

Science.gov (United States)

Volobuev, A. N.

2018-01-01

The reasons for the emergence of the angular distribution of photons generated as a result of annihilation of an electron and a positron in a positron-emission tomograph are investigated. It is shown that the angular distribution of the radiation intensity (i.e., the probability of photon emission at different angles) is a consequence of the Doppler effect in the center-of-mass reference system of the electron and the positron. In the reference frame attached to the electron, the angular distribution of the number of emitted photons does not exists but is replaced by the Doppler shift of the frequency of photons. The results obtained in this study make it possible to extend the potentialities of the positron-emission tomograph in the diagnostics of diseases and to obtain additional mechanical characteristics of human tissues, such as density and viscosity.

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

Development of dark disk model of positron anomaly origin

Science.gov (United States)

Belotsky, K. M.; Kirillov, A. A.; Solovyov, M. L.

Dark disk model could be a remedy for dark matter (DM) explanation of positron anomaly (PA) in cosmic rays (CR). The main difficulty in PA explanation relates to cosmic gamma-radiation which is inevitably produced in DM annihilation or decay leading to tension with respective observation data. Introduction of “active” (producing CR) DM component concentrating in galactic disk alleviates this tension. Earlier, we considered 2-lepton modes, with branching ratios being chosen to fit in the best way all the observation data. Here we considered, in the framework of the same dark disk model, two cases: 2-body final state annihilation and 4-body one, and in each case a quark mode is added to the leptonic ones. It is shown that 4-body mode case is a little better than 2-body one from viewpoint of quality of observation data description at the fixed all other parameters (of CR propagation, background, disk height). The values of DM particle mass around 350GeV and 500GeV are more favorable for 2- and 4-body modes, respectively. Higher values would improve description of data on positrons only but accounting for data on gamma-radiation prevents it because of unwanted more abundant high-energy gamma production. Inclusion of the quark modes improves a little fitting data in both 4- and 2-body mode cases, contrary to naive expectations. In fact, quark mode has a bigger gammas yield than that of most gamma-productive leptonic mode — tau, but they are softer due to bigger final state hadron multiplicity.

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)

New Developments in Positron Scintigraphy and the Application of Cyclotron-Produced Positron Emitters

Energy Technology Data Exchange (ETDEWEB)

Brownell, G. L.; Burnham, C. A.; Wilensky, S.; Aronow, S.; Kazemi, H.; Strieder, D. [Massachusetts General Hospital. Boston, MA (United States)

1969-01-15

The use of positron-emitting radioisotopes offers unique advantages inscintigraphy and dynamic function studies. The detection of the two annihilation quanta provides, in principle, the possibility of utilization of all the positron annihilations with good resolution. In practice, very high efficiencies can be achieved with large area annihilation quanta detectors. The use of multi-detector matrices as large area detectors permits high levels o f activity and yields very high data acquisition rates. The independence of attenuation with depth of a source offers marked advantages for quantitative measurement. The use of time-of-flight techniques opens the possibility of true three-dimensional visualization. Finally, a number of very short-lived positron emitting radioisotopes such as {sup 15}O, {sup 19}N and {sup 11}C are available. A hybrid positron scanner has been constructed and is undergoing tests for brain tumour localization using {sup 74}As. The scanner uses two rows of detectors each containing 9 Nal scintillators and phototubes. The detector array moves continuously in the horizontal direction and in steps in the vertical direction, producing a scintigram with no line structure. The data is recorded on tape for replay or for computer processing. In either case, the plane of best focus can be positioned at will. The techniques developed for the hybrid scanner will be used in a stationary device employing two two-dimensional arrays of detectors. The design will emphasize the very rapid collection of data and the sequential production of scintigrams. The advantages and techniques of positron annihilation detection are also applicable to devices for study of dynamic function. We have constructed and are testing a fast six-detector coincidence system for pulmonary function studies. The measurement of time-of-flight offers the possibility of three-dimensional visualization of a distribution of positron-emitting radioisotope. We a re studying systems with

Techniques for slow positron beam generation and the applications

International Nuclear Information System (INIS)

Okada, Sohei

1994-01-01

Slow positron beams have been expected to be a powerful tool for observation of nature in wide range of research fields from materials science to basic physics, chemistry and biology. In this paper, at first, the beam technology is reviewed, which includes the positron generation, the transformation to slow positron beams and the beam manipulation such as beam stretching, bunching and brightness enhancement. Next, the present status of the slow positron beam applications to a variety of fields is demonstrated in terms of special characteristics of positron, that is, depth controllability, surface sensitivity, unique ionization channels and elemental anti-particle properties. Finally, prospects to produce intense slow positron beams are described. (author) 65 refs

Physical conservation laws and the β-decay of nuclei

International Nuclear Information System (INIS)

Bagge, E.

1975-04-01

The law of conservation of energy is extended to the region of the Dirac states of negative energy. When particles are produced or disappear, energy changes occur in the negative energy region which can be seen in the positive energy region. The law of conservation of energy then says that the total change in energy is equal to naught. The same is valid for translations and angular momentum. The way in which completely occupied states change energy and momentum is not shown. The β-decay of the neutron is considered as pair production in which an electron is emitted and a positron is bonded to the neutron. Neutrinos are not produced. The latest results on neutrino experiments on accelerators are not discussed. (BJ/LH) [de

Positron emission tomography

CERN Document Server

Paans, A M J

2006-01-01

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

Low-energy positron interactions with atoms and molecules

International Nuclear Information System (INIS)

Surko, C M; Gribakin, G F; Buckman, S J

2005-01-01

This paper is a review of low-energy positron interactions with atoms and molecules. Processes of interest include elastic scattering, electronic and vibrational excitation, ionization, positronium formation and annihilation. An overview is presented of the currently available theoretical and experimental techniques to study these phenomena, including the use of trap-based positron beam sources to study collision processes with improved energy resolution. State-resolved measurements of electronic and vibrational excitation cross sections and measurement of annihilation rates in atoms and molecules as a function of incident positron energy are discussed. Where data are available, comparisons are made with analogous electron scattering cross sections. Resonance phenomena, common in electron scattering, appear to be less common in positron scattering. Possible exceptions include the sharp onsets of positron-impact electronic and vibrational excitation of selected molecules. Recent energy-resolved studies of positron annihilation in hydrocarbons containing more than a few carbon atoms provide direct evidence that vibrational Feshbach resonances underpin the anomalously large annihilation rates observed for many polyatomic species. We discuss open questions regarding this process in larger molecules, as well as positron annihilation in smaller molecules where the theoretical picture is less clear. (topical review)

Probing the defects in nano-semiconductors using positrons

Energy Technology Data Exchange (ETDEWEB)

Nambissan, P M G, E-mail: pmg.nambissan@saha.ac.in [Nuclear and Atomic Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India)

2011-01-10

Positron annihilation spectroscopy (PAS) is a very useful tool to study the defect properties of nanoscale materials. The ability of thermalized positrons to diffuse over to the surfaces of nanocrystallites prior to annihilation helps to explore the disordered atomic arrangement over there and is very useful in understanding the structure and properties of nanomaterials. As examples, the results of studies on FeS{sub 2} nanorods and ZnS nanoparticles are presented. In semiconductor nanoparticles, there are positron trapping sites within the grains also and these are characterised by using appropriate models on the measured positron lifetimes. We have observed vivid changes in the measured positron lifetimes and Doppler broadened gamma ray spectral lineshapes during structural transformations prompted by substitutional effects in Mn{sup 2+}-doped ZnS nanorods. Interestingly, the nanoparticles did not exhibit the transformation, implying the morphologies of the nanosystems playing a decisive role. Quantum confinement effect in CdS nanoparticles was another phenomenon that could be seen through positron annihilation experiments. Coincidence Doppler broadening measurements have been useful to identify the elemental environment around the vacancy clusters that trap positrons. Recent studies on nanocrystalline oxide and sulphide semiconductors are also discussed.

Probing the defects in nano-semiconductors using positrons

International Nuclear Information System (INIS)

Nambissan, P M G

2011-01-01

Positron annihilation spectroscopy (PAS) is a very useful tool to study the defect properties of nanoscale materials. The ability of thermalized positrons to diffuse over to the surfaces of nanocrystallites prior to annihilation helps to explore the disordered atomic arrangement over there and is very useful in understanding the structure and properties of nanomaterials. As examples, the results of studies on FeS 2 nanorods and ZnS nanoparticles are presented. In semiconductor nanoparticles, there are positron trapping sites within the grains also and these are characterised by using appropriate models on the measured positron lifetimes. We have observed vivid changes in the measured positron lifetimes and Doppler broadened gamma ray spectral lineshapes during structural transformations prompted by substitutional effects in Mn 2+ -doped ZnS nanorods. Interestingly, the nanoparticles did not exhibit the transformation, implying the morphologies of the nanosystems playing a decisive role. Quantum confinement effect in CdS nanoparticles was another phenomenon that could be seen through positron annihilation experiments. Coincidence Doppler broadening measurements have been useful to identify the elemental environment around the vacancy clusters that trap positrons. Recent studies on nanocrystalline oxide and sulphide semiconductors are also discussed.

Probing the defects in nano-semiconductors using positrons

Science.gov (United States)

Nambissan, P. M. G.

2011-01-01

Positron annihilation spectroscopy (PAS) is a very useful tool to study the defect properties of nanoscale materials. The ability of thermalized positrons to diffuse over to the surfaces of nanocrystallites prior to annihilation helps to explore the disordered atomic arrangement over there and is very useful in understanding the structure and properties of nanomaterials. As examples, the results of studies on FeS2 nanorods and ZnS nanoparticles are presented. In semiconductor nanoparticles, there are positron trapping sites within the grains also and these are characterised by using appropriate models on the measured positron lifetimes. We have observed vivid changes in the measured positron lifetimes and Doppler broadened gamma ray spectral lineshapes during structural transformations prompted by substitutional effects in Mn2+-doped ZnS nanorods. Interestingly, the nanoparticles did not exhibit the transformation, implying the morphologies of the nanosystems playing a decisive role. Quantum confinement effect in CdS nanoparticles was another phenomenon that could be seen through positron annihilation experiments. Coincidence Doppler broadening measurements have been useful to identify the elemental environment around the vacancy clusters that trap positrons. Recent studies on nanocrystalline oxide and sulphide semiconductors are also discussed.

New studies of nuclear decay γ-rays from novae

International Nuclear Information System (INIS)

Starrfield, S.; Truran, J.W.; Wiescher, M.C.; Sparks, W.M.

1997-01-01

The cause of the nova outburst is a thermonuclear runaway (TNR) in hydrogen rich material transferred by a companion onto a white dwarf. Studies of this phenomenon have shown that the TNR produces large concentrations of the short lived positron unstable isotopes of the CNO nuclei which are transported to the surface by convection so that early in the outburst we expect significant numbers of radioactive decays to occur at the surface. The resulting γ-ray emission may be detectable from nearby novae early in their outbursts. The TNR is also expected to produce substantial amounts of 7 Be and 22 Na. Their decays also yield potentially detectable levels of γ-ray emission for relatively nearby novae. We are also interested in the role played by novae in the production of the ∼2M circle-dot of 26 Al found in the galaxy. In order to improve our predictions of this phenomenon, we have performed a new set of calculations of TNR close-quote s on ONeMg and CO white dwarfs with an updated nuclear reaction network and opacities. copyright 1997 American Institute of Physics

Review of Non-Neutron and Neutron Nuclear Data, 2004

International Nuclear Information System (INIS)

Holden, Norman E.

2005-01-01

Review articles are in preparation for the 2004 edition of the CRC Handbook of Chemistry and Physics dealing with the evaluation of both non-neutron and neutron nuclear data. Data on the discovery of element 110, Darmstadtium, and element 111 have been officially accepted, while data on element 118 have been withdrawn. Data to be presented include revised values for very short-lived nuclides, long-lived nuclides, and beta-beta decay measurements. There has been a reassessment of the spontaneous fission (sf) half-lives, which distinguishes between sf decay half-lives and cluster decay half-lives, and with cluster-fission decay. New measurements of isotopic abundance values for many elements will be discussed with an emphasis on the minor isotopes of interest for use in neutron activation analysis measurements. Neutron resonance integrals will be discussed emphasizing the differences between the calculated values obtained from the analytical integration over neutron resonances and the measured values in a neutron reactor-spectrum, which does not quite conform to the assumed 1/E neutron energy spectrum. The method used to determine the neutron resonance integral from measurement, using neutron activation analysis, will be discussed

Descriptions of positron defect analysis capabilities

International Nuclear Information System (INIS)

Howell, R.H.

1994-10-01

A series of descriptive papers and graphics appropriate for distribution to potential collaborators has been assembled. These describe the capabilities for defect analysis using positron annihilation spectroscopy. The application of positrons to problems in the polymer and semiconductor industries is addressed

Quantum beats in positronium 3γ annihilation decay observed in an age dependent, magnetically perturbed angular distribution (ADPAD), experiment

International Nuclear Information System (INIS)

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

2005-01-01

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

IMPRINTS OF ELECTRON–POSITRON WINDS ON THE MULTIWAVELENGTH AFTERGLOWS OF GAMMA-RAY BURSTS

International Nuclear Information System (INIS)

Geng, J. J.; Huang, Y. F.; Dai, Z. G.; Wu, X. F.; Li, L.

2016-01-01

Optical rebrightenings in the afterglows of some gamma-ray bursts (GRBs) are unexpected within the framework of the simple external shock model. While it has been suggested that the central engines of some GRBs are newly born magnetars, we aim to relate the behaviors of magnetars to the optical rebrightenings. A newly born magnetar will lose its rotational energy in the form of Poynting-flux, which may be converted into a wind of electron–positron pairs through some magnetic dissipation processes. As proposed by Dai, this wind will catch up with the GRB outflow and a long-lasting reverse shock (RS) would form. By applying this scenario to GRB afterglows, we find that the RS propagating back into the electron–positron wind can lead to an observable optical rebrightening and a simultaneous X-ray plateau (or X-ray shallow decay). In our study, we select four GRBs (i.e., GRB 080413B, GRB 090426, GRB 091029, and GRB 100814A), of which the optical afterglows are well observed and show clear rebrightenings. We find that they can be well interpreted. In our scenario, the spin-down timescale of the magnetar should be slightly smaller than the peak time of the rebrightening, which can provide a clue to the characteristics of the magnetar.

Antideuteron production in Upsilon(nS) decays and in e(+)e(-) -> q(q) over bar at root s approximate to 10.58 GeV

NARCIS (Netherlands)

Lees, J. P.; Poireau, V.; Tisserand, V.; Grauges, E.; Palano, A.; Eigen, G.; Stugu, B.; Brown, D. N.; Kerth, L. T.; Kolomensky, Yu. G.; Lynch, G.; Schroeder, T.; Hearty, C.; Mattison, T. S.; McKenna, J. A.; So, R. Y.; Khan, A.; Blinov, V. E.; Buzykaev, A. R.; Druzhinin, V. P.; Golubev, V. B.; Kravchenko, E. A.; Onuchin, A. P.; Serednyakov, S. I.; Skovpen, Yu. I.; Solodov, E. P.; Todyshev, K. Yu.; Lankford, A. J.; Mandelkern, M.; Dey, B.; Gary, J. W.; Long, O.; Campagnari, C.; Sevilla, M. Franco; Hong, T. M.; Kovalskyi, D.; Richman, J. D.; West, C. A.; Eisner, A. M.; Lockman, W. S.; Vazquez, W. Panduro; Schumm, B. A.; Seiden, A.; Chao, D. S.; Echenard, B.; Flood, K. T.; Hitlin, D. G.; Miyashita, T. S.; Ongmongkolkul, P.; Andreassen, R.; Huard, Z.; Meadows, B. T.; Pushpawela, B. G.; Sokoloff, M. D.; Sun, L.; Bloom, P. C.; Ford, W. T.; Gaz, A.; Smith, J. G.; Wagner, S. R.; Ayad, R.; Toki, W. H.; Spaan, B.; Bernard, D.; Verderi, M.; Playfer, S.; Bettoni, D.; Bozzi, C.; Calabrese, R.; Cibinetto, G.; Fioravanti, E.; Garzia, I.; Luppi, E.; Piemontese, L.; Santoro, V.; Calcaterra, A.; de Sangro, R.; Finocchiaro, G.; Martellotti, S.; Patteri, P.; Peruzzi, I. M.; Piccolo, M.; Rama, M.; Zallo, A.; Contri, R.; Lo Vetere, M.; Monge, M. R.; Passaggio, S.; Patrignani, C.; Robutti, E.; Bhuyan, B.; Prasad, V.; Morii, M.; Adametz, A.; Uwer, U.; Lacker, H. M.; Dauncey, P. D.; Mallik, U.; Cochran, J.; Prell, S.; Ahmed, H.; Gritsan, A. V.; Arnaud, N.; Davier, M.; Derkach, D.; Grosdidier, G.; Le Diberder, F.; Lutz, A. M.; Malaescu, B.; Roudeau, P.; Stocchi, A.; Wormser, G.; Lange, D. J.; Wright, D. M.; Coleman, J. P.; Fry, J. R.; Gabathuler, E.; Hutchcroft, D. E.; Payne, D. J.; Touramanis, C.; Bevan, A. J.; Di Lodovico, F.; Sacco, R.; Cowan, G.; Bougher, J.; Brown, D. N.; Davis, C. L.; Denig, A. G.; Fritsch, M.; Gradl, W.; Griessinger, K.; Hafner, A.; Prencipe, E.; Schubert, K. R.; Barlow, R. J.; Lafferty, G. D.; Cenci, R.; Hamilton, B.; Jawahery, A.; Roberts, D. A.; Cowan, R.; Sciolla, G.; Cheaib, R.; Patel, P. M.; Robertson, S. H.; Neri, N.; Palombo, F.; Cremaldi, L.; Godang, R.; Sonnek, P.; Summers, D. J.; Simard, M.; Taras, P.; De Nardo, G.; Onorato, G.; Sciacca, C.; Martinelli, M.; Raven, G.; Jessop, C. P.; LoSecco, J. M.; Honscheid, K.; Kass, R.; Feltresi, E.; Margoni, M.; Morandin, M.; Posocco, M.; Rotondo, M.; Simi, G.; Simonetto, F.; Stroili, R.; Akar, S.; Ben-Haim, E.; Bomben, M.; Bonneaud, G. R.; Briand, H.; Calderini, G.; Chauveau, J.; Leruste, Ph.; Marchiori, G.; Ocariz, J.; Sitt, S.; Biasini, M.; Manoni, E.; Pacetti, S.; Rossi, A.; Angelini, C.; Batignani, G.; Bettarini, S.; Carpinelli, M.; Casarosa, G.; Cervelli, A.; Chrzaszcz, M.; Forti, F.; Giorgi, M. A.; Lusiani, A.; Oberhof, B.; Paoloni, E.; Perez, A.; Rizzo, G.; Walsh, J. J.; Pegna, D. Lopes; Olsen, J.; Smith, A. J. S.; Faccini, R.; Ferrarotto, F.; Ferroni, F.; Gaspero, M.; Gioi, L. Li; Piredda, G.; Buenger, C.; Dittrich, S.; Gruenberg, O.; Leddig, T.; Voss, C.; Waldi, R.; Adye, T.; Olaiya, E. O.; Wilson, F. F.; Emery, S.; Vasseur, G.; Anulli, F.; Aston, D.; Bard, D. J.; Cartaro, C.; Convery, M. R.; Dorfan, J.; Dubois-Felsmann, G. P.; Dunwoodie, W.; Ebert, M.; Field, R. C.; Fulsom, B. G.; Graham, M. T.; Hast, C.; Innes, W. R.; Kim, P.; Leith, D. W. G. S.; Lewis, P.; Lindemann, D.; Luitz, S.; Luth, V.; Lynch, H. L.; MacFarlane, D. B.; Muller, D. R.; Neal, H.; Perl, M.; Pulliam, T.; Ratcliff, B. N.; Roodman, A.; Salnikov, A. A.; Schindler, R. H.; Snyder, A.; Su, D.; Sullivan, M. K.; Va'vra, J.; Wisniewski, W. J.; Wulsin, H. W.; Purohit, M. V.; White, R. M.; Wilson, J. R.; Randle-Conde, A.; Sekula, S. J.; Bellis, M.; Burchat, P. R.; Puccio, E. M. T.; Alam, M. S.; Ernst, J. A.; Gorodeisky, R.; Guttman, N.; Peimer, D. R.; Soffer, A.; Spanier, S. M.; Ritchie, J. L.; Ruland, A. M.; Schwitters, R. F.; Wray, B. C.; Izen, J. M.; Lou, X. C.; Bianchi, F.; De Mori, F.; Filippi, A.; Gamba, D.; Lanceri, L.; Vitale, L.; Martinez-Vidal, F.; Oyanguren, A.; Villanueva-Perez, P.; Albert, J.; Banerjee, Sw.; Beaulieu, A.; Bernlochner, F. U.; Choi, H. H. F.; Kowalewski, R.; Lewczuk, M. J.; Lueck, T.; Nugent, I. M.; Roney, J. M.; Sobie, R. J.; Tasneem, N.; Gershon, T. J.; Harrison, P. F.; Latham, T. E.; Band, H. R.; Dasu, S.; Pan, Y.; Prepost, R.

2014-01-01

We present measurements of the inclusive production of antideuterons in e+e− annihilation into hadrons at ≈10.58  GeV center-of-mass energy and in Υ(1S,2S,3S) decays. The results are obtained using data collected by the BABAR detector at the PEP-II electron-positron collider. Assuming a fireball

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

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.)

Production of high energy η' in B meson decays from BaBar experiment

International Nuclear Information System (INIS)

Hicheur, A.

2003-04-01

The work presented in this thesis relies on the analysis of data collected between october 1999 and July 2002 by the BaBar experiment at the PEP-II collider located at SLAC (Stanford, California). Electron-positron collisions at a center of mass energy equal to the Υ(4S) resonance mass are used for the production of B meson pairs. In July 2001, the BaBar collaboration published the first measurement of CP violation in the neutral B mesons system. Since then, the precision of the measurement has been continually being improved with the increasing data sample. Two devices are dedicated to the reconstruction of charged particles: the Silicon Vertex Tracker and the Drift Chamber. The Silicon Vertex Tracker is crucial for the reconstruction of the B meson decay vertex. Its motion with regard to the Drift Chamber needs a rolling calibration of the corresponding alignment parameters roughly every two hours. The relation between the Drift Chamber geometry and the alignment has been studied. Beside CP violation, Heavy Flavour Physics is an other important issue of BaBar research program. Rare decays are of particular interest as they are sensible to a new physics beyond the Standard Model. The production of high energy η' in B decays has been studied through the two main contributions, B→ η' X s coming from the rare decay b → sg*, and B-bar 0 → η'D 0 coming from the internal tree color suppressed decay b → cud. The improvement of the measurement of the process B → η'X-s and the first. observation of the decay B-bar 0 → η'D 0 have led to the conclusion that the η' production is dominated by the decay b → sg* and enables to constrain its quark content. (author)

Development of positron emitting radionuclides for imaging with improved positron detectors

International Nuclear Information System (INIS)

Yano, Y.

1976-10-01

Recent advances in positron cameras and positron ring detectors for transverse section reconstruction have created renewed interest in positron emitting radionuclides. This paper reports on: generator-produced 82 Rb; cyclotron-produced 62 Zn; and reactor-produced 64 Cu. Investigation of the 82 Sr (25 d)-- 82 Rb (75 s) generator determined the elution characteristics for Bio-Rex 70, a weakly acidic carboxylic cation exchanger, using 2% NaCl as the eluent. The yield of 82 Rb and the breakthrough of 82 Sr were determined for newly prepared columns and for long term elution conditions. Spallation-produced 82 Sr was used to charge a compact 82 Rb generator to obtain multi-millicurie amounts of 82 Rb for myocardial imaging. Zinc accumulates in the islet cells of the pancreas and in the prostate. Zinc-62 was produced by protons on Cu foil and separated by column chromatography. Zinc-62 was administered as the amino acid chelates and as the ZnCl 2 to tumor and normal animals. Tissue distribution was determined for various times after intravenous injection. Pancreas-liver images of 62 Zn-histidine uptake were obtained in animals with the gamma camera and the liver uptake of /sup 99m/Tc sulfur colloid was computer subtracted to image the pancreas alone. The positron camera imaged uptake of 62 Zn-histidine in the prostate of a dog at 20 h. 64 Cu was chelated to asparagine, a requirement of leukemic cells, and administered to lymphoma mice. Uptake in tumor and various tissues was determined and compared with the uptake of 67 Ga citrate under the same conditions. 64 Cu-asparagine had better tumor-to-soft tissue ratios than 67 Ga-citrate

Positron Spectroscopy of Hydrothermally Grown Actinide Oxides

Science.gov (United States)

2014-03-27

actinide oxides . The work described here is an attempt to characterize the quality of crystals using positron annihilation spectroscopy (PALS). The...Upadhyaya, R. V. Muraleedharan, B. D. Sharma and K. G. Prasad, " Positron lifetime studies on thorium oxide powders," Philosohical Magazine A, vol. 45... crystals . A strong foundation for actinide PALS studies was laid, but further work is required to build a more effective system. Positron Spectroscopy

Positron beam studies of solids and surfaces: A summary

International Nuclear Information System (INIS)

Coleman, P.G.

2006-01-01

A personal overview is given of the advances in positron beam studies of solids and surfaces presented at the 10th International Workshop on Positron Beams, held in Doha, Qatar, in March 2005. Solids studied include semiconductors, metals, alloys and insulators, as well as biophysical systems. Surface studies focussed on positron annihilation-induced Auger electron spectroscopy (PAES), but interesting applications of positron-surface interactions in fields as diverse as semiconductor technology and studies of the interstellar medium serve to illustrate once again the breadth of scientific endeavour covered by slow positron beam investigations

Positron beam studies of solids and surfaces: A summary

Science.gov (United States)

Coleman, P. G.

2006-02-01

A personal overview is given of the advances in positron beam studies of solids and surfaces presented at the 10th International Workshop on Positron Beams, held in Doha, Qatar, in March 2005. Solids studied include semiconductors, metals, alloys and insulators, as well as biophysical systems. Surface studies focussed on positron annihilation-induced Auger electron spectroscopy (PAES), but interesting applications of positron-surface interactions in fields as diverse as semiconductor technology and studies of the interstellar medium serve to illustrate once again the breadth of scientific endeavour covered by slow positron beam investigations.

Low-energy positron-argon collisions by using parameter-free positron correlation polarization potentials

International Nuclear Information System (INIS)

Jain, A.

1990-01-01

We report differential, integral, and momentum-transfer cross sections and the scattering length (A 0 ) for positron (e + )-argon scattering at low energies below the positronium formation threshold. An optical-potential approach is employed in which the repulsive Coulombic interaction is calculated exactly at the Hartree-Fock level and the attractive polarization and correlation effects are included approximately via a parameter-free positron correlation polarization (PCP) potential recently proposed by us. The PCP model is based on the correlation energy var-epsilon corr of one positron in a homogeneous electron gas; in the outside region, the var-epsilon corr is joined smoothly with the correct asymptotic form of the polarization interaction (-α 0 /2r 4 , where α 0 is the target polarizability) where they cross each other for the first time. The total optical potential of the e + -argon system is treated exactly in a partial-wave analysis to extract the scattering parameters. It is found that the PCP potential gives much better qualitative results, particularly for the differential cross sections and the scattering length, than the corresponding results obtained from an electron polarization potential used as such for the positron case. We also discuss the ''critical'' points (representing the minima in the differential scattering) in the low-energy e + -Ar scattering. The present results involve no fitting procedure

Binding matter with antimatter: the covalent positron bond.

Science.gov (United States)

Charry, Jorge Alfonso; Varella, Marcio T Do N; Reyes, Andrés

2018-05-16

We report sufficient theoretical evidence of the energy stability of the e⁺H₂²⁻ molecule, formed by two H⁻ anions and one positron. Analysis of the electronic and positronic densities of the latter compound undoubtedly points out the formation of a positronic covalent bond between the otherwise repelling hydride anions. The lower limit for the bonding energy of the e⁺H₂²⁻ molecule is 74 kJ/mol (0.77 eV), accounting for the zero-point vibrational correction. The formation of a non electronic covalent bond is fundamentally distinct from positron attachment to stable molecules, as the latter process is characterized by a positron affinity, analogous to the electron affinity. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.)

Polymeric membrane studied using slow positron beam

International Nuclear Information System (INIS)

Hung, W.-S.; Lo, C.-H.; Cheng, M.-L.; Chen Hongmin; Liu Guang; Chakka, Lakshmi; Nanda, D.; Tung, K.-L.; Huang, S.-H.; Lee, Kueir-Rarn; Lai, J.-Y.; Sun Yiming; Yu Changcheng; Zhang Renwu; Jean, Y.C.

2008-01-01

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

A Magnetic Transport Middle Eastern Positron Beam

International Nuclear Information System (INIS)

Al-Qaradawi, I.Y.; Britton, D.T.; Rajaraman, R.; Abdulmalik, D.

2008-01-01

A magnetically guided slow positron beam is being constructed at Qatar University and is currently being optimised for regular operation. This is the first positron beam in the Middle East, as well as being the first Arabic positron beam. Novel features in the design include a purely magnetic in-line deflector, working in the solenoid guiding field, to eliminate un-moderated positrons and block the direct line of sight to the source. The impact of this all-magnetic transport on the Larmor radius and resultant beam characteristics are studied by SIMION simulations for both ideal and real life magnetic field variations. These results are discussed in light of the coupled effect arising from electrostatic beam extraction

Characteristics of the positron annihilation process in the matter

International Nuclear Information System (INIS)

Dryzek, J.

2000-01-01

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

Neutron- and muon-induced background in underground physics experiments

Energy Technology Data Exchange (ETDEWEB)

Kudryavtsev, V.A.; Tomasello, V. [University of Sheffield, Department of Physics and Astronomy, Sheffield (United Kingdom); Pandola, L. [Laboratori Nazionali del Gran Sasso, INFN, Assergi (Italy)

2008-05-15

Background induced by neutrons in deep underground laboratories is a critical issue for all experiments looking for rare events, such as dark matter interactions or neutrinoless {beta}{beta} decay. Neutrons can be produced either by natural radioactivity, via spontaneous fission or ({alpha}, n) reactions, or by interactions initiated by high-energy cosmic rays. In all underground experiments, Monte Carlo simulations of neutron background play a crucial role for the evaluation of the total background rate and for the optimization of rejection strategies. The Monte Carlo methods that are commonly employed to evaluate neutron-induced background and to optimize the experimental setup, are reviewed and discussed. Focus is given to the issue of reliability of Monte Carlo background estimates. (orig.)

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

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

Polarization Study for NLC Positron Source Using EGS4

Energy Technology Data Exchange (ETDEWEB)

Liu, James C

2000-09-20

SLAC is exploring a polarized positron source to study new physics for the NLC project. The positron source envisioned in this paper consists of a polarized electron source, a 50-MeV electron accelerator, a thin target less-than-or-equal-to 0.2 radiation length for positron production, and a capture system for high-energy, small angular divergence positrons. The EGS4 code was used to study the yield, energy spectra, emission-angle distribution, and the mean polarization of the positrons emanating from W-Re and Ti targets hit by longitudinally polarized electron and photon beams. To account for polarization within the EGS4 code a method devised by Flottmann was used, which takes into account polarization transfer for pair production, bremsstrahlung, and Compton interactions. A mean polarization of 0.85 for positrons with energies greater than 25 MeV was obtained. Most of the high-energy positrons were emitted within a forward angle of 20 degrees. The yield of positrons above 25 MeV per incident photon was 0.034, which was about 70 times higher than that obtained with an electron beam.

Generation of an intense pulsed positron beam and its applications

International Nuclear Information System (INIS)

Suzuki, Ryoichi; Mikado, Tomohisa; Ohgaki, Hideaki; Chiwaki, Mitsukuni; Yamazaki, Tetsuo; Kobayashi, Yoshinori.

1994-01-01

A positron pulsing system for an intense positron beam generated by an electron linac has been developed at the Electrotechnical Laboratory. The pulsing system generates an intense pulsed positron beam of variable energy and variable pulse period. The pulsed positron beam is used as a non destructive probe for various materials researches. In this paper, we report the present status of the pulsed positron beam and its applications. (author)

Estimates of Uncertainties in Analysis of Positron Lifetime Spectra for Metals

DEFF Research Database (Denmark)

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

1978-01-01

by excluding the peak regions of the spectra from the analysis. The influence of using incorrect source-surface components in the analysis may on the other hand be reduced by including the peak regions of the spectra. A main conclusion of the work is that extreme caution should be exercised to avoid......The effects of uncertainties and errors in various constraints used in the analysis of multi-component life-time spectra of positrons annihilating in metals containing defects have been investigated in detail using computer simulated decay spectra and subsequent analysis. It is found...... that the errors in the fitted values of the main components lifetimes and intensities introduced from incorrect values of the instrumental resolution function and of the source-surface components can easily exceed the statistical uncertainties. The effect of an incorrect resolution function may be reduced...

Advanced characterization of lithium battery materials with positrons

International Nuclear Information System (INIS)

Barbiellini, Bernardo; Kuriplach, Jan

2017-01-01

Cathode materials are crucial to improved battery performance, in part because there are not yet materials that can maintain high power and stable cycling with a capacity comparable to that of anode materials. Our parameter-free, gradient-corrected model for electron-positron correlations predicts that spectroscopies based on positron annihilation can be deployed to study the effect of lithium intercalation in the oxide matrix of the cathode. The positron characteristics in oxides can be reliably computed using methods based on first-principles. Thus, we can enable a fundamental characterization of lithium battery materials involving positron annihilation spectroscopy and first-principles calculations. The detailed information one can extract from positron experiments could be useful for understanding and optimizing both battery materials and bi-functional catalysts for oxygen reduction and evolution. (paper)

Defects in Czochralski-grown silicon crystals investigated by positron annihilation

Energy Technology Data Exchange (ETDEWEB)

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

1994-10-01

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

Stress evaluation at the ILC positron source

Energy Technology Data Exchange (ETDEWEB)

Ushakov, Andriy; Moortgat-Pick, Gudrid [Universitaet Hamburg, II. Institut fuer Theoretische Physik, Luruper Chaussee 149, 22761 Hamburg (Germany); Riemann, Sabine; Dietrich, Felix [Deutsches Elektronen-Synchrotron (DESY), Standort Zeuthen, Platanenallee 6, 15738 Zeuthen (Germany); Aulenbacher, Kurt; Tyukin, Valery; Heil, Philipp [Johannes Gutenberg-Universitaet Mainz, Institut fuer Kernphysik, Johann-Joachim-Becher-Weg 45, 55128 Mainz (Germany)

2016-07-01

High luminosity is required at future Linear Colliders which is particularly challenging for all corresponding positron sources. At the International Linear Collider (ILC), polarized positrons are obtained from electron-positron pairs by converting high-energy photons produced by passing the high-energy main electron beam through a helical undulator. The conversion target undergoes cyclic stress with high peak values. To distribute the thermal load, the target is designed as wheel spinning in vacuum with 100 m/s. However, the cyclic stress over long time at high target temperatures could exceed the fatigue stress limit. In the talk, an overview of the ILC positron source is given. The prospects to study material parameters under conditions as expected at the ILC are discussed.

Ionization and positron emission in giant quasiatoms

International Nuclear Information System (INIS)

Soff, G.; Reinhardt, J.; Reus, T. de; Wietschorke, K.H.; Schaefer, A.; Mueller, B.; Greiner, W.; Mueller, U.; Schlueter, P.

1985-07-01

Electron excitation processes in superheavy quasiatoms are treated within a relativistic framework. Theoretical results on K-hole production rates as well as delta-electron and positron spectra are compared with experimental data. It is demonstrated that the study of heavy ion collisions with nuclear time delay promises a signature for the spontaneous positron formation in overcritical systems. Corresponding experimental results are confronted with our theoretical hypothesis. Recent speculations on the origin of the observed peak structures in positron spectra are critically reviewed. Atomic excitations are also employed to obtain information on the course of a nuclear reaction. Using a semiclassical picture we calculate the emission of delta-electrons and positrons in deep-inelastic nuclear reactions. Furthermore some consequences of conversion processes in giant systems are investigated. (orig.)

Development of a Simple Positron Age-Momentum Setup

Science.gov (United States)

Sheffield, Thomas; Quarles, C. A.

2009-04-01

A positron age-momentum setup that uses NIM Bin electronic modules and a conventional multichannel analyzer (MCA) is described. The essential idea is to accumulate a Doppler broadened spectrum (sensitive to the annihilation electron momentum) using a high purity Germanium detector in coincidence with a BaF2 scintillation counter, which also serves as the stop signal in a conventional positron lifetime setup. The MCA that collects the Doppler spectrum is gated by a selected region of the lifetime spectrum. Thus we can obtain Doppler broadening spectra as a function of positron lifetime: an age-momentum spectrum. The apparatus has been used so far to investigate a ZnO sample where the size of different vacancy trapping sites may affect the positron lifetime and the Doppler broadening spectrum. We are also looking at polymer and rubber carbon-black composite samples where differences in the Doppler spectrum may arise from positron trapping or positronium formation in the samples. Correction for background and contribution from the positron source itself to the Doppler spectrum will be discussed.

Special features of the inverse-beta-decay reaction proceeding on a proton in a reactor-antineutrino flux

Energy Technology Data Exchange (ETDEWEB)

Kopeikin, V. I., E-mail: kopeikin46@yandex.ru; Skorokhvatov, M. D., E-mail: skorokhvatov-md@nrcki.ru [National Research Center Kurchatov Institute (Russian Federation)

2017-03-15

The evolution of the reactor-antineutrino spectrum and the evolution of the spectrum of positrons from the inverse-beta-decay reaction in the course of reactor operation and after reactor shutdown are considered. The present-day status in determining the initial reactor-antineutrino spectrum on the basis of spectra of beta particles from mixtures of products originating from uranium and plutonium fission is described. A local rise of the experimental spectrum of reactor antineutrinos with respect to the expected spectrum is studied.

Channeling crystals for positron production

International Nuclear Information System (INIS)

Decker, F.J.

1991-05-01

Particles traversing at small angles along a single crystal axis experience a collective scattering force of many crystal atoms. The enormous fields can trap the particles along an axis or plane, called channeling. High energy electrons are attracted by the positive nuclei and therefore produce strongly enhanced so called coherent bremsstrahlung and pair production. These effects could be used in a positron production target: A single tungsten crystal is oriented to the incident electron beam within 1 mrad. At 28 GeV/c the effective radiation length is with 0.9 mm about one quarter of the amorphous material. So the target length can be shorter, which yields a higher conversion coefficient and a lower emittance of the positron beam. This makes single crystals very interesting for positron production targets. 18 refs., 2 figs

Positron spectroscopy for materials characterization

International Nuclear Information System (INIS)

Schultz, P.J.; Snead, C.L. Jr.

1988-01-01

One of the more active areas of research on materials involves the observation and characterization of defects. The discovery of positron localization in vacancy-type defects in solids in the 1960's initiated a vast number of experimental and theoretical investigations which continue to this day. Traditional positron annihilation spectroscopic techniques, including lifetime studies, angular correlation, and Doppler broadening of annihilation radiation, are still being applied to new problems in the bulk properties of simple metals and their alloys. In addition new techniques based on tunable sources of monoenergetic positron beams have, in the last 5 years, expanded the horizons to studies of surfaces, thin films, and interfaces. In the present paper we briefly review these experimental techniques, illustrating with some of the important accomplishments of the field. 40 refs., 19 figs

50 years of positrons

International Nuclear Information System (INIS)

Anon.

1982-01-01

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

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)

PREFACE: The International Workshop on Positron Studies of Defects 2014

Science.gov (United States)

Sugita, Kazuki; Shirai, Yasuharu

2016-01-01

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

Positron annihilation in germanium in thermal equilibrium at high temperature

Energy Technology Data Exchange (ETDEWEB)

Uedono, Akira; Moriya, Tsuyoshi; Komuro, Naoyuki; Tanigawa, Shoichiro [Tsukuba Univ., Ibaraki (Japan). Inst. of Materials Science; Kawano, Takao; Ikari, Atsushi

1996-09-01

Annihilation characteristics of positrons in Ge in thermal equilibrium at high temperature were studied using a monoenergetic positron beam. Precise measurements of Doppler broadening profiles of annihilation radiation were performed in the temperature range between 300 K and 1211 K. The line shape parameters of Doppler broadening profiles were found to be almost constant at 300-600 K. The changes in these parameters were observed to start above 600 K. This was attributed to both the decrease in the fraction of positrons annihilating with core electrons and the lowering of the crystal symmetry around the region detected by positron-electron pairs. This suggests that behaviors of positrons are dominated by some form of positron-lattice coupling in Ge at high temperatures. The temperature dependence of the diffusion length of positrons was also discussed. (author)

A simulation study of a method to reduce positron annihilation spread distributions using a strong magnetic field in positron emission tomography

International Nuclear Information System (INIS)

Iida, H.; Kanno, I.; Miura, S.; Murakami, M.; Takahashi, V.; Kemura, K.

1986-01-01

The positron trajectories have been three-dimensionally simulated using a Monte-Carlo method under various strength of the magnetic field. More than 5 tesla of the field confined the positrons effectively, resulting in increase of the probability of the annihilation within a limited small region, hence the higher spatial resolution in positron emission tomography

Formation of a high intensity low energy positron string

Science.gov (United States)

Donets, E. D.; Donets, E. E.; Syresin, E. M.; Itahashi, T.; Dubinov, A. E.

2004-05-01

The possibility of a high intensity low energy positron beam production is discussed. The proposed Positron String Trap (PST) is based on the principles and technology of the Electron String Ion Source (ESIS) developed in JINR during the last decade. A linear version of ESIS has been used successfully for the production of intense highly charged ion beams of various elements. Now the Tubular Electron String Ion Source (TESIS) concept is under study and this opens really new promising possibilities in physics and technology. In this report, we discuss the application of the tubular-type trap for the storage of positrons cooled to the cryogenic temperatures of 0.05 meV. It is intended that the positron flux at the energy of 1-5 eV, produced by the external source, is injected into the Tubular Positron Trap which has a similar construction as the TESIS. Then the low energy positrons are captured in the PST Penning trap and are cooled down because of their synchrotron radiation in the strong (5-10 T) applied magnetic field. It is expected that the proposed PST should permit storing and cooling to cryogenic temperature of up to 5×109 positrons. The accumulated cooled positrons can be used further for various physics applications, for example, antihydrogen production.

Formation of a high intensity low energy positron string

International Nuclear Information System (INIS)

Donets, E.D.; Donets, E.E.; Syresin, E.M.; Itahashi, T.; Dubinov, A.E.

2004-01-01

The possibility of a high intensity low energy positron beam production is discussed. The proposed Positron String Trap (PST) is based on the principles and technology of the Electron String Ion Source (ESIS) developed in JINR during the last decade. A linear version of ESIS has been used successfully for the production of intense highly charged ion beams of various elements. Now the Tubular Electron String Ion Source (TESIS) concept is under study and this opens really new promising possibilities in physics and technology. In this report, we discuss the application of the tubular-type trap for the storage of positrons cooled to the cryogenic temperatures of 0.05 meV. It is intended that the positron flux at the energy of 1-5 eV, produced by the external source, is injected into the Tubular Positron Trap which has a similar construction as the TESIS. Then the low energy positrons are captured in the PST Penning trap and are cooled down because of their synchrotron radiation in the strong (5-10 T) applied magnetic field. It is expected that the proposed PST should permit storing and cooling to cryogenic temperature of up to 5x10 9 positrons. The accumulated cooled positrons can be used further for various physics applications, for example, antihydrogen production

Application of positron annihilation to polymer and development of a radioisotopes-based pulsed slow positron beam apparatus

International Nuclear Information System (INIS)

Suzuki, Takenori

2004-01-01

Positrons injected into polymer behave as nanometer probes, which can detect the size and amount of intermolecular spaces among polymer structures. Although positrons can probe the characteristics of polymer, they induce a radiation effect on polymer samples. At low temperature, the radiation effect induces free electrons, which can be trapped in a shallow potential created among intermolecular structures after freezing molecular motions. These trapped electrons can be released after the disappearance of the shallow potential due to the reappearance of molecular motion above the relaxation temperature. Thus, positrons can be used as a probe for relaxation studies. Coincidence of Doppler broadening spectroscopy (CDBS) can improve the S/N ratio to 10 7 , which makes it possible to detect trace elements, since CDBS can separate the high-momentum component of core electrons. A pulsed slow positron beam apparatus is necessary for measuring holes in the polymer film and allows the measurement of the characteristics of thin film coated on semiconductors used widely in electronics industries. (author)

Properties of low-lying intruder states in $^{34}$Al and $^{34}$Si sequentially populated in $\\beta$-decay of $^{34}$Mg

CERN Multimedia

A low-lying long-lived (26±1 ms) isomer in $^{34}$Al has been observed recently and assigned as 1$^{+}$ state of intruder character. It was populated in $^{36}$S fragmentation and feeds, in $\\beta$-decay, the 0$_{2}^{+}$ state in $^{34}$Si whose excitation energy and lifetime were determined in an electron-positron pairs spectroscopy experiment. In the present experiment we intend to measure for the first time the $\\gamma$-rays following the $\\beta$-decay of $^{34}$Mg. Despite the interest for $^{34}$Mg, the up-right corner of the “N$\\thicksim$20 island of inversion”, the only information on its $\\beta$-decay is the lifetime of 20±10 ms, determined from $\\beta$-neutron coincidences. As a result of the proposed experiment, we expect to place the first transitions in the level scheme of $^{34}$Al and to strongly populate the newly observed isomer, measuring its excitation energy, if the branching ratio to 4$^{−}$ ground state is significant. Theoretical estimations for the $\\beta$-decay of the new isome...

Ice and Atoms: experiments with laboratory-based positron beams

International Nuclear Information System (INIS)

Coleman, P G

2011-01-01

This short review presents results of new positron and positronium (Ps) experiments in condensed matter and atomic physics, as an illustration of the satisfying variety of scientific endeavours involving positron beams which can be pursued with relatively simple apparatus in a university laboratory environment. The first of these two studies - on ice films - is an example of how positrons and Ps can provide new insights into an important system which has been widely interrogated by other techniques. The second is an example of how simple positron beam systems can still provide interesting information - here on a current interesting fundamental problem in positron atomic physics.

Positron annihilation studies on nasicon analogues containing cation vacancies

International Nuclear Information System (INIS)

Sreeramalu, V.; Sreepad, H.R.; Chandrashekara, A.; Ravindrachary, V.; Gopal, S.

1990-01-01

Positron annihilation studies were carried out on the Nasicon analogue Na 2 (La, Al)Zr(PO 4 ) 3 compound for three different concentrations (2.2, 2.8 and 5.2 by wt.%) of ZrO 2 in the nutrient. Angular correlation study of annihilated photons reveals that the defect concentration is maximum for 2.8(wt.%) of ZrO 2 . Further, positron lifetime studies indicate that the positrons are trapped at cation vacancies. Application of a two state trapping model to this system made it possible to evaluate the lifetime of positrons in the Bloch state and of positrons trapped at cation vacancies. (author). 16 refs., 4 figs

Is the positron a light proton. Contrasts of positron/proton analogies in small molecules

International Nuclear Information System (INIS)

Cade, P.E.; Kao, C.-M.

1982-01-01

The nature of positron behavior in [M - :e + ] systems is explored. Here M - is a molecular anion which combines with a proton to form a stable system, HM. The sharp distinction between the positron and proton dynamics does not entirely remove common characteristics of these systems. Examples are given for HM versus [M - :e + ] systems with M - = (H - , SH - , CN - , and N 3- ). In addition, the possibilities of a 'positronium' bond versus a hydrogen bond are discussed. (Auth.)

Di-lepton yield from the decay of excited 28Si states

International Nuclear Information System (INIS)

Bacelar, J.C.; Buda, A.; Balanda, A.; Krasznahorkay, A.; Ploeg, H. van der; Sujkowski, Z.; Woude, A. van der

1994-01-01

The first dilepton yield measurements from excited nuclear states obtained with a new Positron-Electron Pair Spectroscopic Instrument (PEPSI) are reported. Nuclear states in 28 Si, with an initial excitation energy E * =50 MeV, were populated via the isospin T=0 reaction 4 He+ 24 Mg and the mixed-isospin 3 He+ 25 Mg reaction. In both reactions the dilepton (e + e - ) and photon decay yields were measured concurrently. An excess of counts in the e + e - spectrum, over the converted photon yield, is observed in the energy region above 15 MeV. An analyses is discussed whereby the observed excess counts are assumed to represent the isoscalar E0 strength in excited nuclear states. (orig.)

The generation and development of the moderators for slow positron beam

International Nuclear Information System (INIS)

Yu Weizhong; Yuan Jiaping

2001-01-01

The positron annihilation technique is a sensitive tool for studying microdefects and phase transitions in various materials. Usually the energy of positrons is on the order of MeV and the implantation depth about 100 microns, so the bulk average defect density can be studied. In a slow positron beam the positron energy is about keV and the implantation depth a few microns, so surface defects can be detected. Positron moderator is the key device for obtaining a slow positron beam. The authors review the history and development of the positron moderator, including four methods that convert fast positrons into slow mono-energetic positrons and five array types. The tungsten moderator is the most widely used one while the inert gas solid moderator is the most efficient. Field-enhanced moderators with their high efficiency have great potential but need to be developed. The vane arrangement is the most commonly found

Positron radiography of ignition-relevant ICF capsules

Science.gov (United States)

Williams, G. J.; Chen, Hui; Field, J. E.; Landen, O. L.; Strozzi, D. J.

2017-12-01

Laser-generated positrons are evaluated as a probe source to radiograph in-flight ignition-relevant inertial confinement fusion capsules. Current ultraintense laser facilities are capable of producing 2 × 1012 relativistic positrons in a narrow energy bandwidth and short time duration. Monte Carlo simulations suggest that the unique characteristics of such positrons allow for the reconstruction of both capsule shell radius and areal density between 0.002 and 2 g/cm2. The energy-downshifted positron spectrum and angular scattering of the source particles are sufficient to constrain the conditions of the capsule between preshot and stagnation. We evaluate the effects of magnetic fields near the capsule surface using analytic estimates where it is shown that this diagnostic can tolerate line integrated field strengths of 100 T mm.

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.

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

Positron emitter labeled enzyme inhibitors

International Nuclear Information System (INIS)

Fowler, J.S.; MacGregor, R.R.; Wolf, A.P.; Langstrom, B.

1990-01-01

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

Instrumentation for positron emission tomography

International Nuclear Information System (INIS)

Budinger, T.F.; Derenzo, S.E.; Huesman, R.H.

1984-01-01

Positron emission tomography with a spatial resolution of 2 mm full width at half maximum for quantitation in regions of interest 4 mm in diameter will become possible with the development of detectors that achieve ultrahigh resolution. Improved resolution will be possible using solid-state photodetectors for crystal identification or photomultiplier tubes with many small electron multipliers. Temporal resolution of 2 seconds and gating of cyclic events can be accomplished if statistical requirements are met. The major physical considerations in achieving high-resolution positron emission tomography are the degradation in resolution resulting from positron range, emission angle, parallax error, detector sampling density, the sensitivity of various detector materials and packing schemes, and the tradeoff between temporal resolution and statistical accuracy. The accuracy of data required for physiological models depends primarily on the fidelity of spatial sampling independent of statistical constraints

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)

A new slow positron beam facility using a compact cyclotron

International Nuclear Information System (INIS)

Hirose, Masafumi

1998-01-01

In 1993, Sumitomo Heavy Industries became the first in the world to successfully produce a slow positron beam using a compact cyclotron. Slow positron beam production using an accelerator had mainly consisted of using an electron linear accelerator (LINAC). However, the newly developed system that uses a compact cyclotron enabled cost reduction, downsizing of equipment, production of a DC slow positron beam, a polarized slow positron beam, and other benefits. After that, a genuine slow positron beam facility was developed with the construction of compact cyclotron No.2, and beam production in the new facility has already been started. The features of this new slow positron beam facility are explained below. 1) It is the world's first compact slow positron beam facility using a compact cyclotron. 2) It is the only genuine slow positron beam facility in the world which incorporates the production and use of a slow positron beam in the design stage of the cyclotron. To use a slow positron beam for non-destructive detection of lattice defects in semiconductor material, it is necessary to convert the beam into ultra-short pulses of several hundreds of pico-seconds. Sumitomo Heavy Industries has devised a new short-pulsing method (i.e. an induction bunching method) that enables the conversion of a slow positron beam into short pulses with an optimum pulsing electric field change, and succeeded in converting a slow positron beam into short pulses using this method for the first time in the world. Non-destructive detection of lattice defects in semiconductor material using this equipment has already been started, and some information about the depth distribution, size, density, etc. of lattice defects has already been obtained. (J.P.N.)

Plasma Wakefield Acceleration of an Intense Positron Beam

Energy Technology Data Exchange (ETDEWEB)

Blue, B

2004-04-21

The Plasma Wakefield Accelerator (PWFA) is an advanced accelerator concept which possess a high acceleration gradient and a long interaction length for accelerating both electrons and positrons. Although electron beam-plasma interactions have been extensively studied in connection with the PWFA, very little work has been done with respect to positron beam-plasma interactions. This dissertation addresses three issues relating to a positron beam driven plasma wakefield accelerator. These issues are (a) the suitability of employing a positron drive bunch to excite a wake; (b) the transverse stability of the drive bunch; and (c) the acceleration of positrons by the plasma wake that is driven by a positron bunch. These three issues are explored first through computer simulations and then through experiments. First, a theory is developed on the impulse response of plasma to a short drive beam which is valid for small perturbations to the plasma density. This is followed up with several particle-in-cell (PIC) simulations which study the experimental parameter (bunch length, charge, radius, and plasma density) range. Next, the experimental setup is described with an emphasis on the equipment used to measure the longitudinal energy variations of the positron beam. Then, the transverse dynamics of a positron beam in a plasma are described. Special attention is given to the way focusing, defocusing, and a tilted beam would appear to be energy variations as viewed on our diagnostics. Finally, the energy dynamics imparted on a 730 {micro}m long, 40 {micro}m radius, 28.5 GeV positron beam with 1.2 x 10{sup 10} particles in a 1.4 meter long 0-2 x 10{sup 14} e{sup -}/cm{sup 3} plasma is described. First the energy loss was measured as a function of plasma density and the measurements are compared to theory. Then, an energy gain of 79 {+-} 15 MeV is shown. This is the first demonstration of energy gain of a positron beam in a plasma and it is in good agreement with the predictions

High efficiency cyclotron trap assisted positron moderator

OpenAIRE

Gerchow, L.; Cooke, D. A.; Braccini, S.; Döbeli, M.; Kirch, K.; Köster, U.; Müller, A.; Van Der Meulen, N. P.; Vermeulen, C.; Rubbia, A.; Crivelli, P.

2017-01-01

We report the realisation of a cyclotron trap assisted positron tungsten moderator for the conversion of positrons with a broad keV- few MeV energy spectrum to a mono-energetic eV beam with an efficiency of 1.8(2)% defined as the ratio of the slow positrons divided by the $\\beta^+$ activity of the radioactive source. This is an improvement of almost two orders of magnitude compared to the state of the art of tungsten moderators. The simulation validated with this measurement suggests that usi...

Positron emission tomography. Positronemisionstomografi

Energy Technology Data Exchange (ETDEWEB)

Bolwig, T G; Haunsoe, S; Dahlgaard Hove, J; Hesse, B; Hoejgard, L; Jensen, M; Paulson, O B; Hastrup Svendsen, J; Soelvsten Soerensen, S

1994-10-01

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

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

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

International Nuclear Information System (INIS)

Harzmann, Sophie

2014-01-01

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

Application of position-sensitive detectors to positron imaging

International Nuclear Information System (INIS)

Yamashita, Takaji; Uchida, Hiroshi; Watanabe, Mitsuo; Omura, Tomohide

1994-01-01

Positron imaging including positron emission tomography (PET) is expected to be a promising tool for basic and clinical research, because it makes possible the study of regional chemistry within multiple organs of the body in living human beings and experimental animals. New schemes of high resolution block detectors have been developed to improve the performance of positron imaging systems, which employ small segments of bismuth germanate (BGO) arrays and position-sensitive photomultiplier tubes (PS-PMT). The coincidence detector resolution of less than 2.0 mm in full width at half maximum was achieved with the detectors, which is very close to the theoretical resolution limit in positron imaging. (author)

The Upgrade of the Neutron Induced Positron Source NEPOMUC

Science.gov (United States)

Hugenschmidt, C.; Ceeh, H.; Gigl, T.; Lippert, F.; Piochacz, C.; Pikart, P.; Reiner, M.; Weber, J.; Zimnik, S.

2013-06-01

In summer 2012, the new NEutron induced POsitron Source MUniCh (NEPOMUC) was installed and put into operation at the research reactor FRM II. At NEPOMUC upgrade 80% 113Cd enriched Cd is used as neutron-gamma converter in order to ensure an operation time of 25 years. A structure of Pt foils inside the beam tube generates positrons by pair production. Moderated positrons leaving the Pt front foil are electrically extracted and magnetically guided to the outside of the reactor pool. The whole design, including Pt-foils, the electric lenses and the magnetic fields, has been improved in order to enhance both the intensity and the brightness of the positron beam. After adjusting the potentials and the magnetic guide and compensation fields an intensity of about 3·109 moderated positrons per second is expected. During the first start-up, the measured temperatures of about 90°C ensure a reliable operation of the positron source. Within this contribution the features and the status of NEPOMUC upgrade are elucidated. In addition, an overview of recent positron beam experiments and current developments at the spectrometers is given.

Depth profiling of boron implanted silicon by positron beam

International Nuclear Information System (INIS)

Oevuenc, S.

2004-01-01

Positron depth profiling analyses of low energy implants of silicon aim to observe tbe structure and density of the vacancies generating by implantation and the effect of annealing. This work present the results to several set of data starting S and W parameters. Boron implanted Silicon samples with different implantation energies,20,22,24,and 26 keV are analyzed by Slow positron beam (0-40 keV and 10 5 e + /s )(Variable Energy Positron) at the Positron Centre Delf-HOLLAND

Handbook of theoretical atomic physics data for photon absorption, electron scattering, and vacancies decay

CERN Document Server

Amusia, Miron Ya; Yarzhemsky, Victor

2012-01-01

The aim of this book is to present highly accurate and extensive theoretical Atomic data and to give a survey of selected calculational methods for atomic physics, used to obtain these data. The book presents the results of calculations of cross sections and probabilities of a broad variety of atomic processes with participation of photons and electrons, namely on photoabsorption, electron scattering and accompanying effects. Included are data for photoabsorption and electron scattering cross-sections and probabilities of vacancy decay formed for a large number of atoms and ions. Attention is also given to photoionization and vacancy decay in endohedrals and to positron-atom scattering. The book is richly illustrated. The methods used are one-electron Hartree-Fock and the technique of Feynman diagrams that permits to include many-electron correlations. This is done in the frames of the Random Phase approximation with exchange and the many-body perturbation theory. Newly obtained and previously collected atomi...

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...

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

International Nuclear Information System (INIS)

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

2006-01-01

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

Lattice Location of Radioactive Probes in Semiconductors and Metals by Electron and Positron Channelling

CERN Multimedia

2002-01-01

The channelling effect of decay-electrons and positrons is used for the localization of radioactive impurities implanted into single crystals. Because of the low implantation doses and the variety of different isotopes available at ISOLDE, this technique is especially suited for applications in semiconducting materials. \\\\ \\\\ Channelling measurements in Si, GaAs and GaP implanted with In-, Cd- and Xe-isotopes have demonstrated that impurity lattice sites can be studied directly after implantation without any annealing. The electron-channelling technique can be ideally combined with hyperfine interaction techniques like Moessbauer s This was shown for the formation of In-vacancy complexes in ion-implanted Ni. \\\\ \\\\ We intend to continue the lattice location measurements in semiconductors implanted with various radioactive impurities of Cd, In, Sn, Sb and Te.

Positron annihilation spectroscopic studies of 6H silicon carbide

International Nuclear Information System (INIS)

Hu, Y.F.; Lam, C.H.; Ling, C.C.; Fung, S.; Beling, C.D.; Weng, H.M.

2001-01-01

Positron lifetime measurements have been performed on p-type and n-type 6H-SiC with temperatures varying from 10 K to 290 K. The V C V Si divacancy is observed in both types of 6H-SiC where the V Si related defect is only found in the n-type material. Positron trapping into a defect with lifetime value close to the bulk was found to compete with positron trapping into V Si or V C V Si at temperatures lower than 80 K. The positron diffusion length of the 1400 C annealed n-type 6H-SiC has also been measured at different temperatures with the use of a positron beam. Positron diffusion was found to be limited by acoustic phonon scattering at T=150-300 K. However, at T=50-150 K, D + follows T 2.12±0.02 and the details of the physical process is not yet known. (orig.)

The effects of low-energy scattering on positron implantation

Energy Technology Data Exchange (ETDEWEB)

Ritley, K.A. (Dept. of Physics and Materials Research Laboratory, Univ. of Illinois, Urbana, IL (United States)); Lynn, K.G.; Ghosh, V.; Welch, D.O. (Brookhaven National Lab., Upton, NY (United States))

1992-01-01

Existing Monte Carlo models are capable of simulating the behavior of positrons incident at keV energies, then following the energy loss process to arbitrary final kinetic energies of from 20 eV to 100 eV. This work describes a Monte Carlo simulation of the final stages of positron thermalization in Al, from 25 eV to thermal energies, via the mechanisms of conduction-electron and longitudinal acoustic phonon scattering. The latter stages of thermalization can have important effects on the stopping profiles and mean depth. A novel way to obtain information about positron energy loss by considering the time-evolution of a point-concentration (delta-function distribution) of positrons is described. The effects of a positive positron work function are examined for the first time in the context of a positron Monte Carlo calculation. Finally, some issues relating to the agreement of Monte Carlo calculations with experimental data are discussed. 6 figs., 16 refs.

The effects of low-energy scattering on positron implantation

Energy Technology Data Exchange (ETDEWEB)

Ritley, K.A. [Dept. of Physics and Materials Research Laboratory, Univ. of Illinois, Urbana, IL (United States); Lynn, K.G.; Ghosh, V.; Welch, D.O. [Brookhaven National Lab., Upton, NY (United States)

1992-12-31

Existing Monte Carlo models are capable of simulating the behavior of positrons incident at keV energies, then following the energy loss process to arbitrary final kinetic energies of from 20 eV to 100 eV. This work describes a Monte Carlo simulation of the final stages of positron thermalization in Al, from 25 eV to thermal energies, via the mechanisms of conduction-electron and longitudinal acoustic phonon scattering. The latter stages of thermalization can have important effects on the stopping profiles and mean depth. A novel way to obtain information about positron energy loss by considering the time-evolution of a point-concentration (delta-function distribution) of positrons is described. The effects of a positive positron work function are examined for the first time in the context of a positron Monte Carlo calculation. Finally, some issues relating to the agreement of Monte Carlo calculations with experimental data are discussed. 6 figs., 16 refs.

Temperature dependence of positron trapping by vacancies, loops and voids in molybdenum

International Nuclear Information System (INIS)

Bentzon, M.D.; Linderoth, S.; Petersen, K.

1985-01-01

The temperature dependence of positron trapping by defects in molybdenum has been studied. By resolving positron lifetime spectra into three components, it has been possible to distinguish the temperature dependence of positron trapping into loops and voids. The results show that the positron trapping rate into voids depends linearly on temperature. The temperature dependence of positron trapping by loops can be interpreted as positrons being trapped by jogs, directly or via the dislocation line. The temperature dependence of positrons trapped by loops is argued mainly to be due to the trapping at the dislocation line, and not to detrapping. The observed temperature dependence of positron annihilation parameters in an electron irradiated sample (below stage III), is explained by competitive positron trapping in interstitial loops at low temperatures

Temperature dependence of the fraction of re-emitted positrons, the positron work function, and the positronium fraction for Cu(III)+S

International Nuclear Information System (INIS)

Schultz, P.J.; Lynn, K.G.

1982-01-01

A beam of 1 keV positrons incident on a Cu(111)+S surface has been used to study the dependence on temperature of the positron work function (phi/sub +/), the yield of re-emitted positrons (Y) and of the positronium (Ps) fraction. A positive dependence of the slow-positron yield on temperature is found which is attributed in part to a reduction in the magnitude of phi/sub +/ (approx. 25%) at 50 K relative to its value at 300 K. A similar, though weaker, positive dependence on temperature was seen for the Ps fraction down to 40 K. We present a suggestion for the apparent lack of reflection

Positron-trapping mechanism at dislocations in Zn

DEFF Research Database (Denmark)

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

1987-01-01

the average lifetime and the intensity of the long component decrease with increasing temperature. The experimental results are very well described in terms of a generalized trapping model where it is assumed that positrons become trapped in deep traps (jogs) via shallow traps (dislocation lines......). The temperature dependence of the positron-lifetime spectra below 120 K is attributed to the temperature dependence of the trapping rate to the dislocation line. The experimental results have demonstrated that detrapping processes from the dislocation line take place above 120 K. The positron binding energy...

In-situ positron emission of CO oxidation

OpenAIRE

Vonkeman, K.A.; Jonkers, G.; Wal, van der, S.W.A.; Santen, van, R.A.

1993-01-01

Using a Neuro ECAT positron tomog., the Positron Emission computed Tomog. (PET) was utilized to image the catalytic oxidn. of CO by using CO and CO2, labeled with short lived positron emitting nuclides. Studies were performed over highly dispersed CeO2/g-Al2O3 supported Pt and Rh catalysts. With a math. model of the reaction kinetics, based on the elementary steps of the catalytic reaction and partially on literature surface science data, the effect of CeO2 promotion and the presence of NO we...

Positron emission tomography studies of brain receptors

International Nuclear Information System (INIS)

Maziere, B.; Maziere, M.

1991-01-01

Probing the regional distribution and affinity of receptors in the brain, in vivo, in human and non human primates has become possible with the use of selective ligands labelled with positron emitting radionuclides and positron emission tomography (PET). After describing the techniques used in positron emission tomography to characterize a ligand receptor binding and discussing the choice of the label and the limitations and complexities of the in vivo approach, the results obtained in the PET studies of various neurotransmission systems: dopaminergic, opiate, benzodiazepine, serotonin and cholinergic systems are reviewed

Positron-emitting raionuclides: present and future status

International Nuclear Information System (INIS)

Lambrecht, R.M.

1979-01-01

A tabulation of 157 positron-emitting radionuclides that have the physical characteristics deemed appropriate for radiopharmaceutical use in conjunction with positron emission tomography is provided. The most promising radionuclides are within the production capabilities of a variable-energy cyclotron accelerating protons to about 40 MeV and deuterons, helium-3, and helium-4 to compatable energies. To data only 27 positron-emitting radionuclides have been subjected to radiopharmaceutical consideration, whereas only 11 C, 13 N, 15 O, 18 F, 38 K, and 68 Ga have proved to be especially promising. 2 tables

Axial positrons emission tomography: from mouse to human brain imaging

International Nuclear Information System (INIS)

Brard, Emmanuel

2013-01-01

Positrons emission tomography is a nuclear imaging technics using nuclear decays. It is used both in clinical and preclinical studies. The later requires the use of small animals such as the mouse. The objective is to obtain the best signal with the best spatial resolution. Yet, a weight ratio between humans and mice indicates the need of a sub-millimeter resolution. A conventional scanner is based on detection modules surrounding the object to image and arranged perpendicularly. This implies a strong relationship between efficiency and spatial resolution. This work focuses on the axial geometry in which detection modules are arranged parallel to the object. This limits the relationship between the figures of merit, leading to both high spatial resolution and efficiency. The simulations of prototypes showed great perspectives in term of sub-millimeter resolution with efficiencies of 15 or 40% according to the scanner's axial extension. These results indicate great perspectives for both clinical and preclinical imaging. (author)

Positron reemission microscopy

International Nuclear Information System (INIS)

Brandes, G.F.; Canter, K.F.; Mills, A.P. Jr.

1991-01-01

The positron reemission microscope (PRM), originally proposed by Hulett, Dale and Pendyala, operates on principles fundamentally different from those utilized in existing microscopes and offers sensitivity and contrast not available in conventional microscopes

Probing Positron Gravitation at HERA

International Nuclear Information System (INIS)

Gharibyan, Vahagn

2015-07-01

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

Probing Positron Gravitation at HERA

Energy Technology Data Exchange (ETDEWEB)

Gharibyan, Vahagn

2015-07-15

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

Multi-pair states in electron–positron pair creation

Directory of Open Access Journals (Sweden)

Anton Wöllert

2016-09-01

Full Text Available Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron–positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a description of the fermionic quantum field state, from which all observables of the multiple electron–positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron–positron pair creation in-depth, including multi-pair statistics as well as momentum distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are affected by the polarization of the counterpropagating laser fields, which induce the creation of electron–positron pairs.

Multi-pair states in electron–positron pair creation

Energy Technology Data Exchange (ETDEWEB)

Wöllert, Anton, E-mail: woellert@mpi-hd.mpg.de; Bauke, Heiko, E-mail: heiko.bauke@mpi-hd.mpg.de; Keitel, Christoph H.

2016-09-10

Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron–positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a description of the fermionic quantum field state, from which all observables of the multiple electron–positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron–positron pair creation in-depth, including multi-pair statistics as well as momentum distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are affected by the polarization of the counterpropagating laser fields, which induce the creation of electron–positron pairs.

Multi-pair states in electron–positron pair creation

International Nuclear Information System (INIS)

Wöllert, Anton; Bauke, Heiko; Keitel, Christoph H.

2016-01-01

Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron–positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a description of the fermionic quantum field state, from which all observables of the multiple electron–positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron–positron pair creation in-depth, including multi-pair statistics as well as momentum distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are affected by the polarization of the counterpropagating laser fields, which induce the creation of electron–positron pairs.

Organic synthesis with short-lived positron-emitting radioisotopes

International Nuclear Information System (INIS)

Pike, V.W.

1988-01-01

Chemistry with short-lived positron-emitting radioisotopes of the non-metals, principally 11 C, 13 N and 18 F, has burgeoned over the last decade. This has been almost entirely because of the emergence of positron emission tomography (PET) as a powerful non-invasive technique for investigating pathophysiology in living man. PET is essentially an external technique for the rapid serial reconstruction of the spatial distribution of any positron-emitting radioisotope that has been administered in vivo. Such a distribution is primarily governed by the chemical form in which the positron-emitting radioisotope is incorporated, and importantly for clinical research, is often perturbed by physical, biological or clinical factors. Judicious choice of the chemical form enables specific biological information to be obtained. For example, the labelling of glucose with a positron-emitting radioisotope could be expected to provide a radiopharmaceutical for the study of glucose utilisation in both health and disease. (author)

Positron trapping at defects in copper oxide superconductors

International Nuclear Information System (INIS)

McMullen, T.; Jena, P.; Khanna, S.N.; Li, Y.; Jensen, K.O.

1991-01-01

Positron states and lifetimes at defects in the copper oxide superconductors La 2-x Sr x CuO 4 , YBa 2 Cu 3 O 7-x , and Bi 2 Sr 2 CaCu 2 O 8+x are calculated with use of the superposed-atom model. In the Bi 2 Sr 2 CaCu 2 O 8+x compound, we find that the smaller metal-ion vacancies appear to only bind positrons weakly, while missing oxygens do not trap positrons. In contrast, metal-ion vacancies in La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 7-x bind positrons by ∼1 eV, and oxygen-related defects appear to be the weak-binding sites in these materials. The sites that bind positrons only weakly, by energies ∼k BT , are of particular interest in view of the complex temperature dependences of the annihilation characteristics that are observed in these materials

Positrons trapped in polyethylene: Electric field effect

International Nuclear Information System (INIS)