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

Positron Source from Betatron X-rays Emitted in a Plasma Wiggler

Energy Technology Data Exchange (ETDEWEB)

Johnson, D.K.; Clayton, C.E.; Huang, C.; Joshi, C.; Lu, W.; Marsh, K.A.; Mori, W.B.; Zhou, M.; /UCLA; Barnes, C.D.; Decker, F.J.; Hogan, M.J.; Iverson, R.H.; Krejcik, P.; O' Connell, C.L.; Siemann, R.; Walz, D.R.; /SLAC; Deng, S.; Katsouleas, T.C.; Muggli, P.; Oz, E.; /Southern California U.

2006-04-21

In the E-167 plasma wakefield accelerator (PWFA) experiments in the Final Focus Test Beam (FFTB) at the Stanford Linear Accelerator Center (SLAC), an ultra-short, 28.5 GeV electron beam field ionizes a neutral column of Lithium vapor. In the underdense regime, all plasma electrons are expelled creating an ion column. The beam electrons undergo multiple betatron oscillations leading to a large flux of broadband synchrotron radiation. With a plasma density of 3 x 10{sup 17}cm{sup -3}, the effective focusing gradient is near 9 MT/m with critical photon energies exceeding 50 MeV for on-axis radiation. A positron source is the initial application being explored for these X-rays, as photo-production of positrons eliminates many of the thermal stress and shock wave issues associated with traditional Bremsstrahlung sources. Photo-production of positrons has been well-studied; however, the brightness of plasma X-ray sources provides certain advantages. In this paper, we present results of the simulated radiation spectra for the E-167 experiments, and compute the expected positron yield.

Study of an hybrid positron source using channeling for CLIC

CERN Document Server

Dadoun, O; Chehab, R; Poirier, F; Rinolfi, L; Strakhovenko, V; Variola, A; Vivoli, A

2009-01-01

The CLIC study considers the hybrid source using channeling as the baseline for positron production. The hybrid source uses a few GeV electron beam impinging on a crystal tungsten radiator. With the tungsten crystal oriented on its axis it results an intense, relatively low energy photon beam due mainly to channeling radiation. Those photons are then impinging on an amorphous tungsten target producing positrons by e+e− pair creation. In this note the optimization of the positron yield and the peak energy deposition density in the amorphous target are studied according to the distance between the crystal and the amorphous targets, the primary electron energy and the amorphous target thickness.

Development of a Positron Source for JLab at the IAC

Energy Technology Data Exchange (ETDEWEB)

Forest, Tony [Idaho State Univ., Pocatello, ID (United States)

2013-10-12

We report on the research performed towards the development of a positron sour for Jefferson Lab's (JLab) Continuous Electron Beam Accelerator Facility (CEBAF) in Newport News, VA. The first year of work was used to benchmark the predictions of our current simulation with positron production efficiency measurements at the IAC. The second year used the benchmarked simulation to design a beam line configuration which optimized positron production efficiency while minimizing radioactive waste as well as design and construct a positron converter target. The final year quantified the performance of the positron source. This joint research and development project brought together the experiences of both electron accelerator facilities. Our intention is to use the project as a spring board towards developing a program of accelerator based research and education which will train students to meet the needs of both facilities as well as provide a pool of trained scientists.

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

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

The Baseline Positron Production and Capture Scheme for CLIC

CERN Document Server

Dadoun, Olivier; Lepercq, Pierre; Poirier, Freddy; Variola, Alessandro; Chehab, Robert; Rinolfi, Louis; Vivoli, Alessandro; Strakhovenko, Vladimir; Xu, Chengai

2010-01-01

The CLIC study considers the hybrid source using channeling as the baseline for unpolarised positron production. The hybrid source uses a few GeV electron beam impinging on a tungsten crystal target. With the crystal oriented on its axis it results an intense relatively low energy photon beam. The later is then impinging on an amorphous tungsten target producing positrons by e+e− pair creation. Downstream the amorphous target, a capture section based on an adiabatic matching device followed by a 2 GHz Pre- Injector Linac focuses and accelerates the positron beam up to around 200 MeV

Project of positron source at the U-120 Cyclotron, Bucharest. Status report

International Nuclear Information System (INIS)

Racolta, P.M.; Popa Simil, L.; Voiculescu, Dana; Miron, N.

1999-01-01

To extend the applications with our U-120 Cyclotron we started a project of off-line and on-line positron sources produced at the cyclotron. This machine may be successfully used for producing positron sources with few day half-life for off-line positron studies (eg. 48 V), or a cyclotron on-line intense positron beam (eg. 27 Si) with a variable energy for various materials study experiments, enough to cover a depth range from few micrometers down to tens of nanometers. Until now, using a 48 V positron source we performed experiments for determination of the Doppler broadening of the 511 KeV peak for different materials (copper, lead, indium). This research is carrier out on a cooperation agreement between IFIN-HH Bucharest and LISES-Chisinau. The positron source project is now in its initial stage. This stage consists of the experiments on the off-line version using positron sources produced in the cyclotron (eg. 48 V, 22 Na), to develop experience with detection chains (Doppler broadening and positron annihilation lifetime spectroscopy), to choose proper experiments in order to select moderator materials (W, Mo, Pt, etc.) and to study and design the different versions for the on-line production of positrons with the cyclotron. Slow positrons are valuable tools in atomic physics, materials science and solid state physics research. The controlled energy beam facility can be used to probe defects in metals, to study Fermi surfaces and materials surfaces and interfaces and to obtain detailed information about the electronic structure of materials. The aim of this project is to perform applications in the semiconductor industry, for coating materials, polymers, biomaterials etc. (authors)

Project of positron source at the U-120 cyclotron Bucharest status report

International Nuclear Information System (INIS)

Racolta, P.M.; Simil Popa, L.; Voiculescu, Dana; Miron, N.

2000-01-01

To extend the applications with our U-120 Cyclotron we started a project of off-line positron sources produced at the cyclotron. This machine may be successfully used for producing positron sources with few day half-life for off-line positron studies (e.g. 48 V), or a cyclotron on-line intense positron beam (e.g. 27 Si) with a variable energy for various materials study experiments, enough to cover a depth range from a few micrometers down to tens of nanometers. Until now, using a 48 V positron source we performed experiments for determination of the Doppler broadening of the 511 keV peak for different materials (copper, lead, indium). This research is carried out on a cooperation agreement between IFIN-HH Bucharest and LISES-Chisinau. The positron source project is now in its initial stage. This stage consists of the experiments on the off-line version using positron source produced in the cyclotron (e.g. 48 V, 22 Na), to develop experience with detection chains (Doppler broadening and positron annihilation lifetime spectroscopy) to choose proper experiments in order to select moderator materials (W, Mo, Pt, etc.) and to study and design the different versions for the on-line positron production by cyclotron. Slow positrons are valuable tools in atomic physics, materials science and solid state physics research. The controlled energy beam facility can be used to probe defects in metals, to study Fermi surfaces and materials surfaces and interfaces and to obtained detailed information about electronic structures of materials. The aim of this project is to perform applications in the semiconductor industry, for coating materials, polymers, biomaterials, etc. (authors)

A feasibility study of high intensity positron sources for the S-band and TESLA linear colliders

Energy Technology Data Exchange (ETDEWEB)

Glantz, R.

1997-10-01

Future high energy linear colliders require luminosities above 10{sup 33} cm{sup -2}s{sup -1}. Therefore beam intensities have to be provided up to two orders of magnitude higher than achieved at present. It is comparably simple to reach high electron intensities. Positron intensities in this range, however, are difficult to realize with conventional positron sources. A new method of positron production was proposed in 1979 by V.E. Balakin and A.A. Mikhailichenko. The photons, necessary for pair production, are not generated by bremsstrahlung but by high energy electrons passing through an undulator. Based on this principle, a high intensity, unpolarized and polarized positron source for linear colliders was developed by K.Floettmann. In the present work, the requirements derived by K.Floettmann are used to study the feasibility of both the polarized and the unpolarized positron source. For economical reasons it is advantageous to use the beam after the interaction for positron production. In the main part of the present work a beam line is developed which guarantees a stable operation of the unpolarized wiggler-based positron source for the S-Band and TESLA linear collider. The requirements on the electron beam emittances are much higher for the polarized undulator-based source. For TESLA it is shown, that an operation of the polarized source is possible for design interactions. For a stable operation, taking into account perturbations at the interaction point, further investigations are necessary. For the SBLC, an operation of the polarized source is not possible with the present design.

Positron production using a 1.7 MV pelletron accelerator

Energy Technology Data Exchange (ETDEWEB)

Alcantara, K. F.; Santos, A. C. F. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ 21941-972 (Brazil); Crivelli, P. [Institute for Particle Physics, ETH Zurich (Switzerland)

2013-04-19

We report the foremost phase of a fourth generation positron source, being constructed at the Federal University of Rio de Janeiro. Positron yields are reported by making use of the {sup 19}F(p,{alpha}e{sup +}e{sup -}){sup 16}O reaction, where the fluorine target is in the form of a CaF{sub 2} pellet. Positron production has been observed by detecting 511 keV annihilation gamma rays emerging from the irradiated CaF{sub 2} target.

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.

Feasibility studies of a polarized positron source based on the Bremsstrahlung of polarized electrons

International Nuclear Information System (INIS)

Dumas, J.

2011-09-01

The nuclear and high-energy physics communities have shown a growing interest in the availability of high current, highly-polarized positron beams. A sufficiently energetic polarized photon or lepton incident on a target may generate, via Bremsstrahlung and pair creation within a solid target foil, electron-positron pairs that should carry some fraction of the initial polarization. Recent advances in high current (> 1 mA) spin polarized electron sources at Jefferson Lab offer the perspective of creating polarized positrons from a low energy electron beam. This thesis discusses polarization transfer from electrons to positrons in the perspective of the design optimization of a polarized positron source. The PEPPo experiment, aiming at a measurement of the positron polarization from a low energy (< 10 MeV) highly spin polarized electron beam is discussed. A successful demonstration of this technique would provide an alternative scheme for the production of low energy polarized positrons and useful information for the optimization of the design of polarized positron sources in the sub-GeV energy range. (author)

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.)

Production And Characterization Of Tungsten-Based Positron Moderators

International Nuclear Information System (INIS)

Lucio, O. G. de; Morales, J. G.; Cruz-Manjarrez, H.

2011-01-01

Experiments of interest in Atomic Physics require production of well-defined low-energy positron beams through a moderation process of high-energy positrons, which can be produced by either the use of a radioactive source or by accelerator based pair production process. Tungsten is one of the most commonly used moderator materials because of its reasonable efficiency, high work function and relatively low cost. In this work we present different methods to produce tungsten-based candidate moderators in a variety of shapes. We also present results from characterizing these candidate moderators by ion beam analysis and microscopy techniques.

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.

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

Design of an intense positron source for linear colliders

International Nuclear Information System (INIS)

Ida, H.; Yamada, K.; Funahashi, Y.

1994-01-01

The Japan Linear Collider (JLC) requires an intense positron source of 8x10 11 particles per rf-pulse. A computer simulation reveals the possibility of such an intense positron source using 'conventional' technology. In order to relax the limitation of the incident electron energy density due to thermal stress in the converter target, the incident beam radius is enlarged within the range so as not to reduce the positron capture efficiency. A pre-damping ring and beam transport system to the pre-damping ring, which have a large transverse acceptance, play important roles for a high capture efficiency. A prototype positron source has been designed and installed at downstream of 1.54 GeV S-band linac in Accelerator Test Facility (ATF) in order to carry out experiments to develop the essential technology for JLC. The simulated results will be tested in experiments with the prototype positron source. (author)

EPOS-An intense positron beam project at the ELBE radiation source in Rossendorf

International Nuclear Information System (INIS)

Krause-Rehberg, R.; Sachert, S.; Brauer, G.; Rogov, A.; Noack, K.

2006-01-01

EPOS, the acronym of ELBE Positron Source, describes a running project to build an intense pulsed beam of mono-energetic positrons (0.2-40 keV) for materials research. Positrons will be created via pair production at a tungsten target using the pulsed 40 MeV electron beam of the superconducting linac electron linac with high brilliance and low emittance (ELBE) at Forschungszentrum Rossendorf (near Dresden, Germany). The chosen design of the system under construction is described and results of calculations simulating the interaction of the electron beam with the target are presented, and positron beam formation and transportation is also discussed

Internal positron source production with a cyclotron and vacancy study in silicon

Energy Technology Data Exchange (ETDEWEB)

Kawasuso, Atsuo; Masuno, Shin-ichi; Okada, Sohei [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan). Takasaki Radiation Chemistry Research Establishment; Hasegawa, Masayuki; Suezawa, Masashi

1997-03-01

In order to detect thermal vacancies in Si, in situ positron annihilation measurement has been performed using an internal source method. An increase (decrease) in S-parameter (W-parameter) was observed above 1200degC. It was explained in terms of the formation of thermal vacancies. (author)

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.)

Model-independent requirements to the source of positrons in the galactic centre

International Nuclear Information System (INIS)

Aharonyan, F.A.

1986-01-01

The main requirements, following from the observational data in a wide range of electromagnetic waves, to positron source in the galactic centre are formulated. The most probable mechanism providing an efficiency of positron production of 10% is the pair production at photon-photon collisions. This mechanism can be realized a) in a thermal e + e - pair-dominated weak-relativistic plasma and b) at the development of a nonthermal electromagnetic cascade initiated by relativistic particles in the field of X-rays. Gamma-astronomical observations in the region of E γ ≥ 10 11 eV can be crucial in the choice of the model

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

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.

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.)

Beam Collimation Studies for the ILC Positron Source

Energy Technology Data Exchange (ETDEWEB)

Drozhdin, A.; /Fermilab; Nosochkov, Y.; Zhou, F.; /SLAC

2008-06-26

Results of the collimation studies for the ILC positron source beam line are presented. The calculations of primary positron beam loss are done using the ELEGANT code. The secondary positron and electron beam loss, the synchrotron radiation along the beam line and the bremsstrahlung radiation in the collimators are simulated using the STRUCT code. The first part of the collimation system, located right after the positron source target (0.125 GeV), is used for protection of the RF Linac sections from heating and radiation. The second part of the system is used for final collimation before the beam injection into the Damping Ring at 5 GeV. The calculated power loss in the collimation region is within 100 W/m, with the loss in the collimators of 0.2-5 kW. The beam transfer efficiency from the target to the Damping Ring is 13.5%.

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.

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...

Ion implanted Na22 source for positron lifetime measurements

International Nuclear Information System (INIS)

Fluss, M.J.; Smedeskjaer, L.C.

1979-04-01

A new positron source-sample fabrication technique, intended for high temperature positron annihilation measurements, was developed. The method makes use of a mass separator to implant pure Na 22 into the sample surface. The application of this technique to Cu is described. A brief discussion of the origin of the source component is given, and different possibilities of correcting for it are pointed out. 3 references

Proceedings of the workshop on new kinds of positron sources for linear colliders

International Nuclear Information System (INIS)

Clendenin, J.; Nixon, R.

1997-06-01

It has been very clear from the beginning of studies for future linear colliders that the conventional positron source approach, as exemplified by the SLC source, is pushing uncomfortably close to the material limits of the conversion target. Nonetheless, since this type of positron source is better understood and relatively inexpensive to build, it has been incorporated into the initial design studies for the JLC/NLC. New ideas for positron sources for linear colliders have been regularly reported in the literature and at accelerator conferences for at least a decade, and indeed the recirculation scheme associated with the VLEPP design is nearly two decades old. Nearly all the new types of positron sources discussed in this workshop come under the heading of crystals (or channeling), undulators, and Compton. Storage ring and nuclear reactor sources were not discussed. The positron source designs that were discussed have varying degrees of maturity, but except for the case of crystal sources, where proof of principle experiments have been undertaken, experimental results are missing. It is hoped that these presentations, and especially the recommendations of the working groups, will prove useful to the various linear collider groups in deciding if and when new experimental programs for positron sources should be undertaken

Orbiting transmission source for positron tomography

International Nuclear Information System (INIS)

Huesman, R.H.; Derenzo, S.E.; Cahoon, J.L.; Geyer, A.B.; Moses, W.W.; Uber, D.C.; Vuletich, T.; Budinger, T.F.

1988-01-01

Accidental suppression and effective data rates have been measured for the orbiting transmission source as implemented in the Donner 600-Crystal Positron Tomograph. A mechanical description of the orbiting source and a description of the electronics used to discard scattered and accidental events is included. Since accidental coincidences were the rate-limiting factor in transmission data acquisition, the new method allows us to acquire sufficient transmission data in a shorter time with a more active transmission source

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)

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.

Investigations on a hybrid positron source with a granular converter

Energy Technology Data Exchange (ETDEWEB)

Artru, X. [Institut de Physique Nucleaire de Lyon, Universite Lyon 1, CNRS/IN2P3, Villeurbanne (France); Chaikovska, I. [Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris-Sud, Bat. 200, 91898 Orsay (France); Chehab, R., E-mail: chehab@lal.in2p3.fr [Institut de Physique Nucleaire de Lyon, Universite Lyon 1, CNRS/IN2P3, Villeurbanne (France); Chevallier, M. [Institut de Physique Nucleaire de Lyon, Universite Lyon 1, CNRS/IN2P3, Villeurbanne (France); Dadoun, O. [Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris-Sud, Bat. 200, 91898 Orsay (France); Furukawa, K. [Accelerator Laboratory (KEK), Oho, Tsukuba, Ibaraki 305-0801 (Japan); Guler, H. [Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris-Sud, Bat. 200, 91898 Orsay (France); Kamitani, T.; Miyahara, F.; Satoh, M. [Accelerator Laboratory (KEK), Oho, Tsukuba, Ibaraki 305-0801 (Japan); Sievers, P. [CERN, Geneva (Switzerland); Suwada, T.; Umemori, K. [Accelerator Laboratory (KEK), Oho, Tsukuba, Ibaraki 305-0801 (Japan); Variola, A. [Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris-Sud, Bat. 200, 91898 Orsay (France)

2015-07-15

Promising results obtained with crystal targets for positron production led to the elaboration of a hybrid source made of an axially oriented tungsten crystal, as a radiator, and an amorphous tungsten converter. If the converter is granular, made of small spheres, the heat dissipation is greatly enhanced and the thermal shocks reduced, allowing the consideration of such device for the future linear colliders. A positron source of this kind is investigated. Previous simulations have shown very promising results for the yield as for the energy deposition and the PEDD (Peak Energy Deposition Density). Here, we present detailed simulations made in this granular converter with emphasis on the energy deposition density, which is a critical parameter as learned from the breakdown of the SLC target. A test on the KEKB linac is foreseen; it will allow a determination of the energy deposited and the PEDD in the converter through temperature measurements. Four granular converters, made of W spheres of mm radius have been built at LAL-Orsay; they will be installed at KEK and compared to compact converters. A description of the experimental layout at KEK is provided. Applications to future linear colliders as CLIC and ILC are considered.

Positron energy distributions from a hybrid positron source based on channeling radiation

International Nuclear Information System (INIS)

Azadegan, B.; Mahdipour, A.; Dabagov, S.B.; Wagner, W.

2013-01-01

A hybrid positron source which is based on the generation of channeling radiation by relativistic electrons channeled along different crystallographic planes and axes of a tungsten single crystal and subsequent conversion of radiation into e + e − -pairs in an amorphous tungsten target is described. The photon spectra of channeling radiation are calculated using the Doyle–Turner approximation for the continuum potentials and classical equations of motion for channeled particles to obtain their trajectories, velocities and accelerations. The spectral-angular distributions of channeling radiation are found applying classical electrodynamics. Finally, the conversion of radiation into e + e − -pairs and the energy distributions of positrons are simulated using the GEANT4 package

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.

Study on efficiency of multi-wire tungsten moderator for slow positron source on SPring-8 hard synchrotron radiation

International Nuclear Information System (INIS)

Plokhoi, Vladimir; Kandiev, Yadgar; Samarin, Sergey; Malyshkin, Gennady; Baidin, Grigory; Litvinenko, Igor; Nikitin, Valery

1999-01-01

The paper provides results of numeric simulations of in-target positron production process, processes of moderation, thermalization, diffusion, and reemission of positrons in high efficiency multi-wire moderator made of tungsten monocrystalline wire with regular wire spacing. The paper looks into dynamics of slow positrons in the moderator's vacuum gaps taking into account of external fields. The possibility for using multi-wire moderator with non-regular structure - multi-layer w ire felt m oderator is discussed. According to maximal estimate the multi-wire moderators can reach very high efficiency of fast-slow positron transformation ∼ 10 -2 . Using such moderator the intensity of slow positron source on hard synchrotron radiation of Spring-8 can reach the level of ∼10 11 e + /s. (author)

Positron annihilation lifetime spectroscopy source correction determination: A simulation study

Energy Technology Data Exchange (ETDEWEB)

Kanda, Gurmeet S.; Keeble, David J., E-mail: d.j.keeble@dundee.ac.uk

2016-02-01

Positron annihilation lifetime spectroscopy (PALS) can provide sensitive detection and identification of vacancy-related point defects in materials. These measurements are normally performed using a positron source supported, and enclosed by, a thin foil. Annihilation events from this source arrangement must be quantified and are normally subtracted from the spectrum before analysis of the material lifetime components proceeds. Here simulated PALS spectra reproducing source correction evaluation experiments have been systematically fitted and analysed using the packages PALSfit and MELT. Simulations were performed assuming a single lifetime material, and for a material with two lifetime components. Source correction terms representing a directly deposited source and various foil supported sources were added. It is shown that in principle these source terms can be extracted from suitably designed experiments, but that fitting a number of independent, nominally identical, spectra is recommended.

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.)

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

A low-neutron background slow-positron source

International Nuclear Information System (INIS)

White, M. M.

1998-01-01

The addition of a thermionic rf gun [1] and a photocathode rf gun will allow the Advanced Photon Source (APS) linear accelerator (linac) [2] [3] to become a free-electron laser (FEL) driver [4]. As the FEL project progresses, the existing high-charge DC thermionic gun will no longer be critical to APS operation and could be used to generate high-energy or low-energy electrons to drive a slow-positron source. We investigated possibilities to create a useful low-energy source that could operate semi-independently and would have a low neutron background

Pulsars as the sources of high energy cosmic ray positrons

International Nuclear Information System (INIS)

Hooper, Dan; Blasi, Pasquale; Serpico, Pasquale Dario

2009-01-01

Recent results from the PAMELA satellite indicate the presence of a large flux of positrons (relative to electrons) in the cosmic ray spectrum between approximately 10 and 100 GeV. As annihilating dark matter particles in many models are predicted to contribute to the cosmic ray positron spectrum in this energy range, a great deal of interest has resulted from this observation. Here, we consider pulsars (rapidly spinning, magnetized neutron stars) as an alternative source of this signal. After calculating the contribution to the cosmic ray positron and electron spectra from pulsars, we find that the spectrum observed by PAMELA could plausibly originate from such sources. In particular, a significant contribution is expected from the sum of all mature pulsars throughout the Milky Way, as well as from the most nearby mature pulsars (such as Geminga and B0656+14). The signal from nearby pulsars is expected to generate a small but significant dipole anisotropy in the cosmic ray electron spectrum, potentially providing a method by which the Fermi gamma-ray space telescope would be capable of discriminating between the pulsar and dark matter origins of the observed high energy positrons

Construction of the spin-polarized slow positron beam with the RI source

Energy Technology Data Exchange (ETDEWEB)

Nakajyo, Terunobu; Tashiro, Mutsumi; Kanazawa, Ikuzo [Tokyo Gakugei Univ., Koganei (Japan); Komori, Fumio; Murata, Yoshimasa; Ito, Yasuo

1997-03-01

The electrostatic slow-positron beam is constructed by using {sup 22}Na source. We design the electrostatic lens, the system of the detector, and the Wien filter for the experiment`s system of the spin-polarized slow positron beam. The reemitted spin-polarized slow-positron spectroscopy is proposed for studying magnetic thin films and magnetic multilayers. We calculated the depolarized positron fractions in the Fe thin film Fe(10nm)/Cu(substrate) and the multilayers Cu(1nm)/Fe(10nm)/Cu(substrate). (author)

Research of the internal electron-positron pair production

International Nuclear Information System (INIS)

Fenyes, Tibor

1985-01-01

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

Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth

OpenAIRE

Abeysekara, A. U.; Albert, A.; Alfaro, R.; Alvarez, C.; Álvarez, J. D.; Arceo, R.; Arteaga-Velázquez, J. C.; Rojas, D. Avila; Solares, H. A. Ayala; Barber, A. S.; Bautista-Elivar, N.; Becerril, A.; Belmont-Moreno, E.; BenZvi, S. Y.; Berley, D.

2017-01-01

The unexpectedly high flux of cosmic ray positrons detected at Earth may originate from nearby astrophysical sources, dark matter, or unknown processes of cosmic-ray secondary production. We report the detection, using the HighAltitude Water Cherenkov Observatory (HAWC), of extended tera-electron volt gamma-ray emission coincident with the locations of two nearby middle-aged pulsars (Geminga and PSR B0656+14). The HAWC observations demonstrate that these pulsars are indeed local sources of ac...

Hybrid scheme of positron source at SPARC-LAB LNF facility

Energy Technology Data Exchange (ETDEWEB)

Abdrashitov, S.V., E-mail: abdsv@tpu.ru [National Research Tomsk Polytechnic University, Lenin Ave 30, 634050 Tomsk (Russian Federation); National Research Tomsk State University, Lenin Ave 36, 634050 Tomsk (Russian Federation); Bogdanov, O.V. [National Research Tomsk Polytechnic University, Lenin Ave 30, 634050 Tomsk (Russian Federation); Dabagov, S.B. [INFN Laboratori Nazionali di Frascati, Via E. Fermi 40, I-00044 Frascati, RM (Italy); RAS PN Lebedev Physical Institute, Leninskiy Prospekt 53, 119991 Moscow (Russian Federation); NRNU MEPhI, Kashirskoe Highway 31, 115409 Moscow (Russian Federation); Pivovarov, Yu.L.; Tukhfatullin, T.A. [National Research Tomsk Polytechnic University, Lenin Ave 30, 634050 Tomsk (Russian Federation)

2015-07-15

The hybrid scheme of the positron source for SPARC-LAB LNF facility (Frascati, Italy) is proposed. The comparison of the positron yield in a thin amorphous W converter of 0.1 mm thickness produced by bremsstrahlung, by axial 〈1 0 0〉 and planar (1 1 0) channeling radiations in a W crystal is performed for the positron energy range of 1 ÷ 3 MeV. It is shown that the radiation from 200 MeV electrons (parameters of SPARC-LAB LNF Frascati) in a 10 μm W crystal can produce positrons in the radiator of 0.1 mm thickness with the rate of 10–10{sup 2} s{sup −1} at planar channeling, of 10{sup 2}–10{sup 3} s{sup −1} at bremsstrahlung and of 10{sup 3}–10{sup 4} s{sup −1} at axial channeling.

Characterization of a transmission positron/positronium converter for antihydrogen production

Science.gov (United States)

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

2017-09-01

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

Design and Characterization of a Three-Dimensional Positron Annihilation Spectroscopy System Using a Low-Energy Positron Beam

Science.gov (United States)

2012-03-22

Technique Applied to Measure Oxygen -Atom Defects in 6H Silicon Carbide”. 2010. [31] Y. C. Jean , P. E. Mallon and D. M. Schrader. Principles and Applications...that result in β+ emission, by photon interactions with nuclei and subsequent pair production, or by β+ decays from radioactive isotopes made by...reactions for creating positrons [7], some of which are used to to create radioactive isotopes that β+ decay. Regardless of the positron source, positrons

Comment on AMS02 results support the secondary origin of cosmic ray positrons

OpenAIRE

Dado, Shlomo; Dar, Arnon

2015-01-01

We present a simple calculation of the flux of secondary positrons produced in the ISM that is based only on priors. Our calculated ISM flux agrees very well with that calculated with the elaborate GALPROP code. It confirms that secondary production of positrons in the ISM by the primary cosmic rays cannot explain the observed sub-TeV flux of CR positrons. Moreover, we show that once energy loss of positrons in source and in the ISM are included, secondary production inside the CR sources plu...

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

Production of an electron-positron plasma in a pulsar magnetosphere

International Nuclear Information System (INIS)

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

1985-01-01

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

Study of a positron source generated by photons from ultrarelativistic channeled particles

International Nuclear Information System (INIS)

Chehab, R.; Couchot, F.; Nyaiesh, A.R.; Richard, F.; Artru, X.

1989-03-01

Radiation by channeled electrons in Germanium and Silicon crystals along the axis is studied as a very promising photon source of small angular divergence for positron generation in amorphous targets. Radiation rates for different crystal lengths - from some tenths of mm to 10 mm - and two electron incident energies, 5 and 20 GeV, are considered and a comparison between the two crystals is presented. Thermic behaviour of the crystal under incidence of bunches of 10 10 electrons is also examined. The corresponding positron yields for tungsten amorphous converters - of 0.5 and 1 X o thickness - are calculated considering the case of a Germanium photon generator. Assuming a large acceptance optical matching system as the adiabatic device of the SLC, accepted positrons are evaluated and positron yields larger than 1 e + /e - are obtained

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)

Electron-positron pair production in Coulomb collisions at ultrarelativistic energies

International Nuclear Information System (INIS)

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

1993-01-01

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

Positron Production in Multiphoton Light-by-Light Scattering

Energy Technology Data Exchange (ETDEWEB)

Koffas, Thomas

2003-07-28

We present the results of an experimental study on e{sup +}e{sup -} pair production during the collision of a low emittance 46.6 GeV electron beam with terawatt laser pulses from a Nd:glass laser at 527 nm wavelength and with linear polarization. The experiment was conducted at the Final Focus Test Beam facility in the Stanford Linear Accelerator Center. Results with a 49.1 GeV electron beam are also included. A signal of 106 {+-} 14 positrons for the 46.6 GeV electron beam case and of 22 {+-} 10 positrons for the 49.1 GcV case above background, has been detected. We interpret the positrons as the products of a two-step process during which laser photons are backscattered to high energy gamma photons that absorb in their turn several laser photons in order to produce a e{sup +}e{sup -} pair. The data compare well with the existing theoretical models. This is the first observation in the laboratory of inelastic Light-by-Light scattering with only real photons. Alternatively, the data are interpreted as a manifestation of the spontaneous breakdown of the vacuum under the influence of an intense external alternating electric field.

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.

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

CERN Document Server

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

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

Studies of Positron Generation from Ultraintense Laser-Matter Interactions

Science.gov (United States)

Williams, Gerald Jackson

Laser-produced pair jets possess unique characteristics that offer great potential for their use in laboratory-astrophysics experiments to study energetic phenomenon such as relativistic shock accelerations. High-flux, high-energy positron sources may also be used to study relativistic pair plasmas and useful as novel diagnostic tools for high energy density conditions. Copious amounts of positrons are produced with MeV energies from directly irradiating targets with ultraintense lasers where relativistic electrons, accelerated by the laser field, drive positron-electron pair production. Alternatively, laser wakefield accelerated electrons can produce pairs by the same mechanisms inside a secondary converter target. This dissertation describes a series of novel experiments that investigate the characteristics and scaling of pair production from ultraintense lasers, which are designed to establish a robust platform for laboratory-based relativistic pair plasmas. Results include a simple power-law scaling to estimate the effective positron yield for elemental targets for any Maxwellian electron source, typical of direct laser-target interactions. To facilitate these measurements, a solenoid electromagnetic coil was constructed to focus emitted particles, increasing the effective collection angle of the detector and enabling the investigation of pair production from thin targets and low-Z materials. Laser wakefield electron sources were also explored as a compact, high repetition rate platform for the production of high energy pairs with potential applications to the creation of charge-neutral relativistic pair plasmas. Plasma accelerators can produce low-divergence electron beams with energies approaching a GeV at Hz frequencies. It was found that, even for high-energy positrons, energy loss and scattering mechanisms in the target create a fundamental limit to the divergence and energy spectrum of the emitted positrons. The potential future application of laser

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)

Influence of the nuclear autocorrelation function on the positron production in heavy-ion collisions

International Nuclear Information System (INIS)

Tomoda, T.; Weidenmueller, H.A.

1983-01-01

The influence of a nuclear reaction on atomic positron production in heavy-ion collisions is investigated. Using statistical concepts, we describe the nuclear S matrix for a heavy-ion induced reaction as a statistically fluctuating function of energy. The positron production rate is then dependent on the autocorrelation function of this S matrix, and on the ratio of the ''direct'' versus the ''fluctuating'' part of the nuclear cross section. Numerical calculations show that in this way, current experimental results on positron production in heavy-ion collisions can be reproduced in a semiquantitative fashion

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

International Nuclear Information System (INIS)

Rubinstein, J.E.

1976-01-01

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

The Intense Slow Positron Source concept: A theoretical perspective on a proposed INEL Facility

International Nuclear Information System (INIS)

Makowitz, H.; Abrashoff, J.D.; Landman, W.H.; Albano, R.K.; Tajima, T.

1992-01-01

An analysis has been performed of the INEL Intense Slow Positron Source (ISPS) concept. The results of the theoretical study are encouraging. A full-scale device with a monoenergetic 5 KeV positron beam of ≥10 12 e + /s on a ≤0.03-cmdiameter target appears feasible and can be obtained within the existing infrastructure of INEL reactor facilities. A 30.0-cm-diameter, large area source dish, moderated at first with thin crystalline W films and later by solid Ne, is proposed as the initial device in order to explore problems with a facility scale system. A demonstration scale beam at ≥10 10 slow e + /s is proposed using a 58 Co source plated on a 6-cm-diameter source dish insert, placed in a 30- cm adapter

Measurement of the positron polarization at an helical undulator based positron source for the international linear collider ILC. The E-166 experiment at SLAC

Energy Technology Data Exchange (ETDEWEB)

Karim, Laihem

2008-06-05

A helical undulator based polarized positron source is forseen at a future International Linear Collider (ILC). The E-166 experiment has tested this scheme using a one meter long, short-period, pulsed helical undulator installed in the Final Focus Test Beam (FFTB) at SLAC. A low-emittance 46.6 GeV electron beam passing through this undulator generated circularly polarized photons with energies up to about 8 MeV. The generated photons of several MeV with circular polarization are then converted in a relatively thin target to generate longitudinally polarized positrons. Measurements of the positron polarization have been performed at 5 different energies of the positrons. In addition electron polarization has been determined for one energy point. For a comparison of the measured asymmetries with the expectations detailed simulations were necessary. This required upgrading GEANT4 to include the dominant polarization dependent interactions of electrons, positrons and photons in matter. The measured polarization of the positrons agrees with the expectations and is for the energy point with the highest polarization at 6MeV about 80%. (orig.)

Production of new particles in electron-positron annihilation

International Nuclear Information System (INIS)

Gilman, F.J.

1977-02-01

A number of areas are reviewed where there is important progress in the production of new particles in electron--positron annihilation, but of a more detailed quantitative nature. Charmonium states, charmed mesons, and evidence for a charged heavy lepton are covered. 50 references

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)

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.)

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

International Nuclear Information System (INIS)

Smirnov, A.I.

1977-01-01

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

Minicyclotron-based technology for the production of positron-emitting labelled radiopharmaceuticals

International Nuclear Information System (INIS)

Barrio, J.R.; Bida, G.; Satyamurthy, N.; Padgett, H.C.; MacDonald, N.S.; Phelps, M.E.

1983-01-01

The use of short-lived positron emitters such as carbon 11, fluorine 18, nitrogen 13, and oxygen 15, together with positron-emission tomography (PET) for probing the dynamics of physiological and biochemical processes in the normal and diseased states in man is presently an active area of research. One of the pivotal elements for the continued growth and success of PET is the routine delivery of the desired positron emitting labelled compounds. To date, the cyclotron remains the accelerator of choice for production of medically useful radionuclides. The development of the technology to bring the use of cyclotrons to a clinical setting is discussed

Minicyclotron-based technology for the production of positron-emitting labelled radiopharmaceuticals

Energy Technology Data Exchange (ETDEWEB)

Barrio, J.R.; Bida, G.; Satyamurthy, N.; Padgett, H.C.; MacDonald, N.S.; Phelps, M.E.

1983-01-01

The use of short-lived positron emitters such as carbon 11, fluorine 18, nitrogen 13, and oxygen 15, together with positron-emission tomography (PET) for probing the dynamics of physiological and biochemical processes in the normal and diseased states in man is presently an active area of research. One of the pivotal elements for the continued growth and success of PET is the routine delivery of the desired positron emitting labelled compounds. To date, the cyclotron remains the accelerator of choice for production of medically useful radionuclides. The development of the technology to bring the use of cyclotrons to a clinical setting is discussed. (ACR)

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.)

New positron annihilation spectroscopy techniques for thick materials

International Nuclear Information System (INIS)

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

2003-01-01

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

Possible Contribution to Electron and Positron Fluxes from Pulsars and their Nebulae

CERN Document Server

Della Torre, S.; Rancoita, P.G.; Rozza, D.; Treves, A.

2014-01-01

The AMS-02 experiment confirms the excess of positrons in cosmic rays (CRs) for energy above 10 GeV with respect to the secondary production of positrons in the interstellar medium. This is interpreted as evidence of the existence of a primary source of these particles. Possible candidates are dark matter or astrophysical sources. In this work we discuss the possible contribution due to pulsars and their nebulae. Our key assumption is that the primary spectrum of electrons and positrons at the source is the same of the well known photon spectrum observed from gamma-rays telescopes. Using a diffusion model in the Galaxy we propagate the source spectra up to the Solar System. We compare our results with the recent experiments and with the LIS model

Slow positron beam production by a 14 MeV C.W. electron accelerator

Science.gov (United States)

Begemann, M.; Gräff, G.; Herminghaus, H.; Kalinowsky, H.; Ley, R.

1982-10-01

A 14 MeV c.w. electron accelerator is used for pair production in a tungsten target of 0.7 radiation lengths thickness. A small fraction of the positrons is thermalized and diffuses out of the surface ofsurface of a well annealed tungsten foil coated with MgO which is positioned immediately behind the target. The slow positrons are extracted from the target region and magnetically guided over a distance of 10 m onto a channelplate multiplier at the end of an S-shaped solenoid. The positrons are identified by their annihilation radiation using two NaI-detectors. The intensity of the slow positrons is proportional to the accelerator electron beam current. The maximum intensity of 2.2 × 10 5 slow positrons per second reaching thedetector at an accelerator current of 15 μA was limited by the power deposited in the uncooled target. The energy of the positrons is concentrated in a small region at about 1 eV and clearly demonstrates the emission of thermal positrons.

Slow positron beam production by a 14 MeV c.w. electron accelerator

International Nuclear Information System (INIS)

Begemann, M.; Graeff, G.; Herminghaus, H.; Kalinowsky, H.; Ley, R.

1982-01-01

A 14 MeV c.w. electron accelerator is used for pair production in a tungsten target of 0.7 radiation lengths thickness. A small fraction of the positrons is thermalized and diffuses out of the surface of a well annealed tungsten foil coated with MgO which is positioned immediately behind the target. The slow positrons are extracted from the target region and magnetically guided over a distance of 10 m onto a channelplate multiplier at the end of an S-shaped solenoid. The positrons are identified by their annihilation radiation using two Nal-detectors. The intensity of the slow positrons is proportional to the accelerator electron beam current. The maximum intensity of 2.2 x 10 5 slow positrons per second reaching the detector at an accelerator current of 15 μA was limited by the power deposited in the uncooled target. The energy of the positrons is concentrated in a small region at about 1 eV and clearly demonstrates the emission of thermal positrons. (orig.)

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.)

Undulator-Based Production of Polarized Positrons, A Proposal for the 50-GeV Beam in the FFTB

Energy Technology Data Exchange (ETDEWEB)

Alexander, G

2004-03-25

The full exploitation of the physics potential of future linear colliders such as the JLC, NLC, and TESLA will require the development of polarized positron beams. In the proposed scheme of Balakin and Mikhailichenko [1] a helical undulator is employed to generate photons of several MeV with circular polarization which are then converted in a relatively thin target to generate longitudinally polarized positrons. This experiment, E-166, proposes to test this scheme to determine whether such a technique can produce polarized positron beams of sufficient quality for use in future linear colliders. The experiment will install a meter-long, short-period, pulsed helical undulator in the Final Focus Test Beam (FFTB) at SLAC. A low-emittance 50-GeV electron beam passing through this undulator will generate circularly polarized photons with energies up to 10 MeV. These polarized photons are then converted to polarized positrons via pair production in thin targets. Titanium and tungsten targets, which are both candidates for use in linear colliders, will be tested. The experiment will measure the flux and polarization of the undulator photons, and the spectrum and polarization of the positrons produced in the conversion target, and compare the measurement results to simulations. Thus the proposed experiment directly tests for the first time the validity of the simulation programs used for the physics of polarized pair production in finite matter, in particular the effects of multiple scattering on polarization. Successful comparison of the experimental results to the simulations will lead to greater confidence in the proposed designs of polarized positrons sources for the next generation of linear colliders. This experiment requests six-weeks of time in the FFTB beam line: three weeks for installation and setup and three weeks of beam for data taking. A 50-GeV beam with about twice the SLC emittance at a repetition rate of 30 Hz is required.

Undulator-Based Production of Polarized Positrons, A Proposal for the 50-GeV Beam in the FFTB

Energy Technology Data Exchange (ETDEWEB)

G. Alexander; P. Anthony; V. Bharadwaj; Yu.K. Batygin; T. Behnke; S. Berridge; G.R. Bower; W. Bugg; R. Carr; E. Chudakov; J.E. Clendenin; F.J. Decker; Yu. Efremenko; T. Fieguth; K. Flottmann; M. Fukuda; V. Gharibyan; T. Handler; T. Hirose; R.H. Iverson; Yu. Kamyshkov; H. Kolanoski; T. Lohse; Chang-guo Lu; K.T. McDonald; N. Meyners; R. Michaels; A.A. Mikhailichenko; K. Monig; G. Moortgat-Pick; M. Olson; T. Omori; D. Onoprienko; N. Pavel; R. Pitthan; M. Purohit; L. Rinolfi; K.P. Schuler; J.C. Sheppard; S. Spanier; A. Stahl; Z.M. Szalata; J. Turner; D. Walz; A. Weidemann; J. Weisend

2003-06-01

The full exploitation of the physics potential of future linear colliders such as the JLC, NLC, and TESLA will require the development of polarized positron beams. In the proposed scheme of Balakin and Mikhailichenko [1] a helical undulator is employed to generate photons of several MeV with circular polarization which are then converted in a relatively thin target to generate longitudinally polarized positrons. This experiment, E-166, proposes to test this scheme to determine whether such a technique can produce polarized positron beams of sufficient quality for use in future linear colliders. The experiment will install a meter-long, short-period, pulsed helical undulator in the Final Focus Test Beam (FFTB) at SLAC. A low-emittance 50-GeV electron beam passing through this undulator will generate circularly polarized photons with energies up to 10 MeV. These polarized photons are then converted to polarized positrons via pair production in thin targets. Titanium and tungsten targets, which are both candidates for use in linear colliders, will be tested. The experiment will measure the flux and polarization of the undulator photons, and the spectrum and polarization of the positrons produced in the conversion target, and compare the measurement results to simulations. Thus the proposed experiment directly tests for the first time the validity of the simulation programs used for the physics of polarized pair production in finite matter, in particular the effects of multiple scattering on polarization. Successful comparison of the experimental results to the simulations will lead to greater confidence in the proposed designs of polarized positrons sources for the next generation of linear colliders. This experiment requests six-weeks of time in the FFTB beam line: three weeks for installation and setup and three weeks of beam for data taking. A 50-GeV beam with about twice the SLC emittance at a repetition rate of 30 Hz is required.

Application of the 4 pigammaMethod to the Absolute Standardization of Radioactive Sources of Positron Emitters

International Nuclear Information System (INIS)

Peyres Medina, V.; Garcia-Torano Martinez, E.; Roteta Ibarra, M.

2006-01-01

We discuss the application of the method known as 4 p i g amma c ounting t o the standardization of positron emitters. Monte Carlo simulations are used to calculate the detection efficiency of positrons emitted by the nuclides 22Na and 18F. Two experimental setups are used, both based on a NaI(Tl) well detector. The results of the standardizations are in good agreement with those obtained by other methods. It is shown that the 4 p i g amma m ethod can be successfully used for the absolute standardization of sources of positron emitters. (Author) 23 refs

Physical models and primary design of reactor based slow positron source at CMRR

Science.gov (United States)

Wang, Guanbo; Li, Rundong; Qian, Dazhi; Yang, Xin

2018-07-01

Slow positron facilities are widely used in material science. A high intensity slow positron source is now at the design stage based on the China Mianyang Research Reactor (CMRR). This paper describes the physical models and our primary design. We use different computer programs or mathematical formula to simulate different physical process, and validate them by proper experiments. Considering the feasibility, we propose a primary design, containing a cadmium shield, a honeycomb arranged W tubes assembly, electrical lenses, and a solenoid. It is planned to be vertically inserted in the Si-doping channel. And the beam intensity is expected to be 5 ×109

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

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.

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.

Search for positron anisotropies in cosmic rays with AMS

Energy Technology Data Exchange (ETDEWEB)

Machate, Fabian [1. Physikalisches Institut B, RWTH Aachen University (Germany)

2016-07-01

The Alpha Magnetic Spectrometer (AMS-02) on the International Space Station has observed a significant excess of cosmic ray positrons over the background expected from secondary production at energies above 10 GeV. Nearby pulsars and annihilating dark matter particles as a primary source of electrons and positrons have been discussed as an explanation. A possible way of distinguishing between pulsar and dark matter origin is the measurement of dipole anisotropies in the positron flux or the positron to electron ratio. Any anisotropy will be reduced by diffusion in galactic magnetic fields to below the percent level. AMS-02 is the leading space-based experiment for cosmic ray detection and well suited for this search. A new analysis procedure for anisotropies using an event sample with large acceptance is presented. It relies on the ability of the Transition Radiation Detector (TRD) to separate positrons from the proton background.

Production and Applications of Long-Lived Positron-Emitting Radionuclides

Science.gov (United States)

Graves, Stephen A.

Positron emission tomography (PET) is a medical imaging modality capable of determining the in vivo spatial distribution of a biologically relevant molecule which has been labeled with a positron-emitting isotope. The use of molecules such as monoclonal antibodies and nanoparticles for therapeutic and diagnostic applications has expanded preclinically in recent years. As these larger molecules tend to have longer circulation times and slow clearance kinetics, positron-emitting isotopes with half-lives longer than conventional medical radioisotopes are required for PET applications. This dissertation details methods for the production of 51Mn (t1/2: 45.4 min), 52gMn (t1/2: 5.59 d), 64Cu (t1/2: 12.7 h), 76Br (t1/2: 16.2 h), 89Zr (t1/2: 3.27 d), and 194Au (t1/2: 38.0 h) on low-energy medical cyclotrons, including targetry considerations, radiochemical separation methods, and analysis of resulting purity. Pursuant to the production of these isotopes, several instrumentation developments have been made including implementation of an automatic nuclide identification library for gamma spectroscopy; development of methods for dead time correction and background estimation in auto-gamma counting; and the creation of a new linearly-filled Derenzo-type PET phantom. Measurement of the radioactive half-lives of 51Mn and 52gMn are presented in addition to their use in a variety of preclinical molecular imaging applications, including immunoPET, stem cell tracking, functional beta-cell mass determination, and probing the impact of isoflurane on acute pancreatic function. An analytic model of effective specific activity is formed and tested against preliminary trace metal analysis results. Measurements of excitation functions for the large-scale production of medically relevant isotopes, including 52gMn, at the Los Alamos National Laboratory Isotope Production Facility (100 MeV p+) are presented. The results described herein have enabled and informed a variety of novel

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

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.)

A self-consistent model of cosmic-ray fluxes and positron excess: roles of nearby pulsars and a sub-dominant source population

Energy Technology Data Exchange (ETDEWEB)

Joshi, Jagdish C.; Razzaque, Soebur, E-mail: jjagdish@uj.ac.za, E-mail: srazzaque@uj.ac.za [Department of Physics, University of Johannesburg, P. O. Box 524, Auckland Park 2006 (South Africa)

2017-09-01

The cosmic-ray positron flux calculated using the cosmic-ray nuclei interactions in our Galaxy cannot explain observed data above 10 GeV. An excess in the measured positron flux is therefore open to interpretation. Nearby pulsars, located within sub-kiloparsec range of the Solar system, are often invoked as plausible sources contributing to the excess. We show that an additional, sub-dominant population of sources together with the contributions from a few nearby pulsars can explain the latest positron excess data from the Alpha Magnetic Spectrometer (AMS). We simultaneously model, using the DRAGON code, propagation of cosmic-ray proton, Helium, electron and positron and fit their respective flux data. Our fit to the Boron to Carbon ratio data gives a diffusion spectral index of 0.45, which is close to the Kraichnan turbulent spectrum.

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)

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

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)

Calibration of an advanced photon source linac beam position monitor used for positron position measurement of a beam containing both positrons and electrons

International Nuclear Information System (INIS)

Sereno, Nicholas S.

1998-01-01

The Advanced Photon Source (APS) linac beam position monitors can be used to monitor the position of a beam containing both positrons and electrons. To accomplish this task, both the signal at the bunching frequency of 2856 MHz and the signal at 2x2856 MHz are acquired and processed for each stripline. The positron beam position is obtained by forming a linear combination of both 2856 and 5712 MHz signals for each stripline and then performing the standard difference over sum computation. The required linear combination of the 2856 and 5712 MHz signals depends on the electrical calibration of each stripline/cable combination. In this paper, the calibration constants for both 2856 MHz and 5712 MHz signals for each stripline are determined using a pure beam of electrons. The calibration constants are obtained by measuring the 2856 and 5712 MHz stripline signals at various electron beam currents and positions. Finally, the calibration constants measured using electrons are used to determine positron beam position for the mixed beam case

Construction and use of an intense positron source at new linac facilities in Germany. Conceptual report

International Nuclear Information System (INIS)

Brauer, G.

2000-07-01

In this conceptual report the idea to establish an European positron source for applied research (''EPOS'') based on new LINAC facilities in Germany (ELBE/Rossendorf or TTF-DESY/Hamburg) is considered. The report contains not only the outline of obvious applications in atomic physics, materials science and surface physics, but also several new methodical developments which are only possible with an intense positron beam. This opportunity will also allow the use and further development of imaging techniques being of special interest for industrial applications. (orig.)

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.)

Notes on the rf system for the SLC positron source

Energy Technology Data Exchange (ETDEWEB)

Hoag, H.

1984-10-17

The proposed arrangement of accelerator structures, waveguide feeds and klystrons is shown. A 50 MW klystron at 20-3C will provide power for the high-field capture section immediately following the target. About 1 meter downstream of this section there will be a standard girder of four 3.05-meter SLAC constant gradient accelerator sections. These will be powered by a klystron at station 20-3D. Current thinking is that this will also be a 50 MW tube, but 35 MW might well be sufficient. Both stations will be SLEDded. The length of the rectangular waveguide feed to the capture section will be approximately 132 ft, and the attenuation will be about 0.97 db. The corresponding numbers for the feed to the standard girder are 153 ft and 1.07 db. In CN-268 dated 6/22/84: Positron Source: First 50 Nanoseconds, K. Moffeit shows that good positron acceptance requires very high accelerating fields (on the order of 70 MV/m) in the first meter following the target. Various ways of approaching this gradient in a 1-meter section have been examined.

Positron production in superheavy collisional systems - a sensitive probe for new atomic as well as nuclear physical phenomena

International Nuclear Information System (INIS)

Tsertos, H.

1985-04-01

In the present thesis a systematic study of the integral and spectral properties of the positron production in the collisional systems U+Pd, Pb+Th, U+Th and U+U for incident energies near the Coulomb threshold (5.9 MeV/u) was performed. Additionally for the system U+U the incident energy was varied between 5.7 MeV/u and 6.2 MeV/u with a constant step width of about 0.1 MeV/u. It could uniquely be shown that the positron production in the lighter system U+Pd can be solely explained by the nuclear production process while in the other three collisional systems both the dynamical and the nuclear positron production are experimentally verificable. The energy-integrated positron production in dependence both on the combined nuclear charge number of the collisional energy and on the impact parameter respectively the incident energy show the expected slope of a scattering process determined by the dynamics of the heavy ion collision which can be well described by the theoretical calculation. From this in the transition from the subcritical system Pb+Th to the supercritical systems U+Th and U+U no significant deviation can be observed, and so no statement about spontaneous positron emission in the supercritical system is possible. (orig./HSI) [de

Production of 68Ge, 64Cu, 86Y, 89Zr, 73Se, 77Br and 124I positron emitting radionuclides through future laser-accelerated proton beams at ELI-Beamlines for innovative PET diagnostics

OpenAIRE

Italiano, Antonio; Amato, Ernesto; Minutoli, Fabio; Margarone, Daniele; Baldari, Sergio

2016-01-01

The development of innovative production pathways for high-Z positron emitters is of great interest to enlarge the applicability of PET diagnostics, especially in view of the continuous development of new radiopharmaceuticals. We evaluated the theoretical yields of 64Cu, 86Y, 89Zr, 73Se, 77Br and 124I PET isotopes, plus the 68Ge isotope, parent of the 68Ga positron emitter, in the hypothesis of production through laser-accelerated proton sources expected at the ELI-Beamlines facility. By mean...

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.

COSMIC-RAY POSITRONS FROM MILLISECOND PULSARS

Energy Technology Data Exchange (ETDEWEB)

Venter, C.; Kopp, A.; Büsching, I. [Centre for Space Research, North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom 2520 (South Africa); Harding, A. K. [Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Gonthier, P. L. [Hope College, Department of Physics, Holland, MI (United States)

2015-07-10

Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 GeV. Fermi has also uncovered many new MSPs, impacting Galactic stellar population models. We investigate the contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters.

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

Gamma-induced Positron Spectroscopy (GiPS) at a superconducting electron linear accelerator

International Nuclear Information System (INIS)

Butterling, Maik; Anwand, Wolfgang; Cowan, Thomas E.; Hartmann, Andreas; Jungmann, Marco; Krause-Rehberg, Reinhard; Krille, Arnold; Wagner, Andreas

2011-01-01

A new and unique setup for Positron Annihilation Spectroscopy has been established and optimized at the superconducting linear electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (Germany). The intense, pulsed (26 MHz) photon source (bremsstrahlung with energies up to 16 MeV) is used to generate positrons by means of pair production throughout the entire sample volume. Due to the very short gamma bunches (< 5 ps temporal length), the facility for Gamma-induced Positron Spectroscopy (GiPS) is suitable for positron lifetime spectroscopy using the accelerator's radiofrequency as time reference. Positron lifetime and Doppler broadening Spectroscopy are employed by a coincident measurement (Age-Momentum Correlation) of the time-of-arrival and energy of the annihilation photons which in turn significantly reduces the background of scattered photons resulting in spectra with high signal to background ratios. Simulations of the setup using the GEANT4 framework have been performed to yield optimum positron generation rates for various sample materials and improved background conditions.

Gamma-induced Positron Spectroscopy (GiPS) at a superconducting electron linear accelerator

Energy Technology Data Exchange (ETDEWEB)

Butterling, Maik, E-mail: maik.butterling@googlemail.com [Martin-Luther University, Dept. of Physics, 06099 Halle (Germany); Institute of Radiation Physics, Helmholtz-Zentrum, Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany); Anwand, Wolfgang; Cowan, Thomas E.; Hartmann, Andreas [Institute of Radiation Physics, Helmholtz-Zentrum, Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany); Jungmann, Marco; Krause-Rehberg, Reinhard [Martin-Luther University, Dept. of Physics, 06099 Halle (Germany); Krille, Arnold; Wagner, Andreas [Institute of Radiation Physics, Helmholtz-Zentrum, Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany)

2011-11-15

A new and unique setup for Positron Annihilation Spectroscopy has been established and optimized at the superconducting linear electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (Germany). The intense, pulsed (26 MHz) photon source (bremsstrahlung with energies up to 16 MeV) is used to generate positrons by means of pair production throughout the entire sample volume. Due to the very short gamma bunches (< 5 ps temporal length), the facility for Gamma-induced Positron Spectroscopy (GiPS) is suitable for positron lifetime spectroscopy using the accelerator's radiofrequency as time reference. Positron lifetime and Doppler broadening Spectroscopy are employed by a coincident measurement (Age-Momentum Correlation) of the time-of-arrival and energy of the annihilation photons which in turn significantly reduces the background of scattered photons resulting in spectra with high signal to background ratios. Simulations of the setup using the GEANT4 framework have been performed to yield optimum positron generation rates for various sample materials and improved background conditions.

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

International Nuclear Information System (INIS)

Golge, S.; Vlahovic, B.; Wojtsekhowski, B.

2014-01-01

We present a conceptual design for a novel continuous wave electron-linac based high-intensity high-brightness slow-positron production source with a projected intensity on the order of 10 10  e + /s. Reaching this intensity in our design relies on the transport of positrons (T + below 600 keV) from the electron-positron pair production converter target to a low-radiation and low-temperature area for moderation in a high-efficiency cryogenic rare gas moderator, solid Ne. This design progressed through Monte Carlo optimizations of: electron/positron beam energies and converter target thickness, transport of the e + beam from the converter to the moderator, extraction of the e + beam from the magnetic channel, a synchronized raster system, and moderator efficiency calculations. For the extraction of e + from the magnetic channel, a magnetic field terminator plug prototype has been built and experimental results on the effectiveness of the prototype are presented. The dissipation of the heat away from the converter target and radiation protection measures are also discussed.

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

Energy Technology Data Exchange (ETDEWEB)

Golge, S., E-mail: serkan.golge@nasa.gov; Vlahovic, B. [North Carolina Central University, Durham, North Carolina 27707 (United States); Wojtsekhowski, B. [Jefferson Laboratory, 12000 Jefferson Ave., Newport News, Virginia 23606 (United States)

2014-06-21

We present a conceptual design for a novel continuous wave electron-linac based high-intensity high-brightness slow-positron production source with a projected intensity on the order of 10{sup 10 }e{sup +}/s. Reaching this intensity in our design relies on the transport of positrons (T{sub +} below 600 keV) from the electron-positron pair production converter target to a low-radiation and low-temperature area for moderation in a high-efficiency cryogenic rare gas moderator, solid Ne. This design progressed through Monte Carlo optimizations of: electron/positron beam energies and converter target thickness, transport of the e{sup +} beam from the converter to the moderator, extraction of the e{sup +} beam from the magnetic channel, a synchronized raster system, and moderator efficiency calculations. For the extraction of e{sup +} from the magnetic channel, a magnetic field terminator plug prototype has been built and experimental results on the effectiveness of the prototype are presented. The dissipation of the heat away from the converter target and radiation protection measures are also discussed.

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)

Origin and annihilation physics of positrons in the Galaxy

International Nuclear Information System (INIS)

Alexis, Anthony

2014-01-01

A gamma radiation at 511 keV is observed since the early 1970's toward the Galactic bulge region. This emission is the signature of a large number of electron-positron annihilations, the positron being the electron's antiparticle. Unfortunately, the origin of the positrons responsible for this emission is still a mystery. Many positron-source candidates have been suggested but none of them can account for the galactic annihilation emission. The spatial distribution of this emission is indeed very atypical. Since 2002, the SPI spectrometer onboard the INTEGRAL space laboratory revealed an emission strongly concentrated toward the galactic bulge and a weaker emission from the galactic disk. This morphology is unusual because it does not correspond to any of the known galactic astrophysical-object or interstellar-matter distributions. The assumption that positrons annihilate close to their sources (i.e. the spatial distribution of the annihilation emission reflects the spatial distribution of the sources) has consequently been called into question. Recent studies suggest that positrons could propagate far away from their sources before annihilating. This physical aspect could be the key point to solve the riddle of the galactic positron origin. This thesis is devoted to the modelling of the propagation and annihilation of positrons in the Galaxy, in order to compare simulated spatial models of the annihilation emission with recent measurements provided by SPI/INTEGRAL. This method allows to put constraints on the origin of galactic positrons. We therefore developed a propagation Monte-Carlo code of positrons within the Galaxy in which we implemented all the theoretical and observational knowledge about positron physics (sources, transport modes, energy losses, annihilation modes) and the interstellar medium of our Galaxy (interstellar gas distributions, galactic magnetic fields, structures of the gaseous phases). Due to uncertainties in several physical parameters

Study of radiation damage in ODS steels by positron annihilation spectroscopy

International Nuclear Information System (INIS)

Bartošová, I; Bouhaddane, A; Slugeň, V; Dománková, M; Wall, D; Selim, F A

2016-01-01

Microstructure of various oxide-dispersion-strengthened (ODS) steels with 15% chromium content was studied in term of vacancy defects presence and their accumulation after defined irradiation treatment, respectively. Studied materials originated from Kyoto University and studied via IAEA collaborative project. Samples were characterized “as received” by positron annihilation lifetime spectroscopy and their microstructure was examined by transmission electron microscopy as well. Samples were afterwards irradiated in Washington State University Nuclear Radiation Center via a strong gamma source (6TBq). Damage induced by gamma irradiation was evaluated by positron lifetime measurements in emphasis on defect accumulation in the materials. We have demonstrated strong defect production induced by gamma irradiation which results from positron measurement data. (paper)

Generation and application of slow positrons based on a electron LINAC

International Nuclear Information System (INIS)

Kurihara, Toshikazu

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 58 Co, 64 Cu, 11 C, 13 N, 15 O and 18 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 annihilation excitation and positron reemission microscope are developed. (S.Y.)

Proposal for an intense slow positron beam facility at PSI

International Nuclear Information System (INIS)

Waeber, W.B.; Taqqu, D.; Zimmermann, U.; Solt, G.

1990-05-01

In the domain of condensed matter physics and materials sciences monoenergetic slow positrons in the form of highest intensity beams are demonstrated to be extreamly useful and considered to be highly needed. This conclusion has been reached and the scientific relevance of the positron probe has been highlighted at an international workshop in November 1989 at PSI, where the state of the art and the international situation on slow positron beams, the fields of application of intense beams and the technical possibilities at PSI for installing intense positron sources have been evaluated. The participants agreed that a high intensity beam as a large-scale user facility at PSI would serve fundamental and applied research. The analysis of responses given by numerous members of a widespread positron community has revealed a large research potential in the domain of solid-state physics, atomic physics and surface, thin-film and defect physics, for example. The excellent feature of slow positron beams to be a suitable probe also for lattice defects near surfaces or interfaces has attracted the interest not only of science but also of industry.In this report we propose the installation of an intense slow positron beam facility at PSI including various beam lines of different qualities and based on the Cyclotron production of β + emitting source material and on a highest efficiency moderation scheme which exceeds standard moderation efficiencies by two orders of magnitude. In its proposed form, the project is estimated to be realizable in the nineties and costs will amount to between 15 and 20 MSFr. (author) 10 figs., 6 tabs., 78 refs

Electron-positron pair production in inhomogeneous electromagnetic fields

International Nuclear Information System (INIS)

Kohlfürst, C.

2015-01-01

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

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...

Developments on positron scattering experiments including beam production and detection

International Nuclear Information System (INIS)

Selim, F.A.; Golovchenko, J.A.

2001-01-01

Positron scattering and channeling experiments require high quality (low emittance) beams. A new electrostatic optics system for extracting positrons from a moderator is presented. The system features improved efficiency of focusing and beam transport of moderated positrons emitted with angular spreads up to ± 30 , with good phase space characteristics. The presented optics also provides a high degree of freedom in controlling exit beam trajectories. The system has been installed in the LLNL Pelletron accelerator and showed great enhancement on the beam quality. On the detection side, image plates were used to measure the angular distributions of positrons transmitted through the gold crystals. The measurements demonstrate the advantages of image plates as quantitative position sensitive detectors for positrons. (orig.)

Laser generation of proton beams for the production of short-lived positron emitting radioisotopes

International Nuclear Information System (INIS)

Spencer, I.; Ledingham, K.W.D.; Singhal, R.P.; McCanny, T.; McKenna, P.; Clark, E.L.; Krushelnick, K.; Zepf, M.; Beg, F.N.; Tatarakis, M.; Dangor, A.E.; Norreys, P.A.; Clarke, R.J.; Allott, R.M.; Ross, I.N.

2001-01-01

Protons of energies up to 37 MeV have been generated when ultra-intense lasers (up to 10 20 W cm -2 ) interact with hydrogen containing solid targets. These protons can be used to induce nuclear reactions in secondary targets to produce β + -emitting nuclei of relevance to the nuclear medicine community, namely 11 C and 13 N via (p, n) and (p,α) reactions. Activities of the order of 200 kBq have been measured from a single laser pulse interacting with a thin solid target. The possibility of using ultra-intense lasers to produce commercial amounts of short-lived positron emitting sources for positron emission tomography (PET) is discussed

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

International Nuclear Information System (INIS)

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

1997-01-01

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

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

Production of positron annihilation radiation by cosmic-rays near sea level

CERN Document Server

Puzovic, J M

2002-01-01

Production of positron annihilation radiation by cosmic-rays in Al, Fe, Sn and Pb is measured by means of a triggered HPGe detector. The equipment is located in Belgrade, at an absolute height of 125 m a.s.l. The production rate per unit mass is found to be proportional to the square of the atomic number of the material divided by its mass number, with the proportionality constant equal to 8.1(3)x10 sup - sup 6 s sup - sup 1 g sup - sup 1.

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

International Nuclear Information System (INIS)

Katuya, Mituaki

1987-01-01

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

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.

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.

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.

Effective source size, radial, angular and energy spread of therapeutic 11C positron emitter beams produced by 12C fragmentation

Science.gov (United States)

Lazzeroni, Marta; Brahme, Anders

2014-02-01

The use of positron emitter light ion beams in combination with PET (Positron Emission Tomography) and PET-CT (Computed Tomography) imaging could significantly improve treatment verification and dose delivery imaging during radiation therapy. The present study is dedicated to the analysis of the beam quality in terms of the effective source size, as well as radial, angular and energy spread of the 11C ion beam produced by projectile fragmentation of a primary point monodirectional and monoenergetic 12C ion beam in a dedicated range shifter of different materials. This study was performed combining analytical methods describing the transport of particles in matter and the Monte Carlo code SHIELD-HIT+. A high brilliance and production yield of 11C fragments with a small effective source size and emittance is best achieved with a decelerator made of two media: a first liquid hydrogen section of about 20 cm followed by a hydrogen rich section of variable length. The calculated intensity of the produced 11C ion beam ranges from about 5% to 8% of the primary 12C beam intensity depending on the exit energy and the acceptance of the beam transport system. The angular spread is lower than 1 degree for all the materials studied, but the brilliance of the beam is the highest with the proposed mixed decelerator.

External tandem target system for efficient production of short-lived positron emitting radionuclides

International Nuclear Information System (INIS)

Koh, K.; Dwyer, J.; Finn, R.; Sheh, Y.; Sinnreich, J.; Wooten, T.

1983-01-01

Recent developments in radiopharmaceutical chemistry allow the incorporation of short-lived, positron-emitting radionuclides into a variety of compounds which when used with a positron emission tomograph provide a means of monitoring physiological disorders by a standard technique. To effectively meet the increased ''in-house'' clinical demands while maintaining a production schedule, a tandem target was designed and has been installed for the simultaneous ''on-line'' preparation of oxygen-15 labelled compounds such as CO 2 15 , H 2 O 15 ; and nitrogen-13 labelled compounds such as 13 NH 3 , 13 N 2 O, and 13 N 2 . The processing time required for the synthesis of the nitrogen-13 products as compared to the essentially instantaneous formation of oxygen-15 labelled compounds has provided the necessary time delay for clinical utilization. The characterisitcs of this external tandem target system as well as the automation for the dual processing are presented

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

Sources for charged particles; Les sources de particules chargees

Energy Technology Data Exchange (ETDEWEB)

Arianer, J.

1997-09-01

This document is a basic course on charged particle sources for post-graduate students and thematic schools on large facilities and accelerator physics. A simple but precise description of the creation and the emission of charged particles is presented. This course relies on every year upgraded reference documents. Following relevant topics are considered: electronic emission processes, technological and practical considerations on electron guns, positron sources, production of neutral atoms, ionization, plasma and discharge, different types of positive and negative ion sources, polarized particle sources, materials for the construction of ion sources, low energy beam production and transport. (N.T.).

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

Study of tungsten based positron moderators

International Nuclear Information System (INIS)

Lucio, O.G. de; Pérez, M.; Mendoza, U.; Morales, J.G.; Cruz, J.C.; DuBois, R.D.

2015-01-01

Positrons and how they interact with matter has a growing interest in many fields. Most of their uses require the production of slow positron beams with a well-defined energy, but since these particles are usually generated by means of a radioactive source, they are fast and with a broad distribution of energies. For this reason it is necessary to moderate them to lower energies via inelastic collisions. Then, they can be accelerated to the desired energies. This requires the use of a moderator. Tungsten is one of the most commonly used moderator materials because of its reasonable efficiency and relatively low cost. In this work we present different methods of producing transmission tungsten-based moderators, with particular interest in a combination of tungsten thin foils and grids. We also show results about the characterization of these moderators by ion beam analysis and microscopy techniques along with their relative moderation efficiencies

Study of tungsten based positron moderators

Energy Technology Data Exchange (ETDEWEB)

Lucio, O.G. de; Pérez, M.; Mendoza, U.; Morales, J.G.; Cruz, J.C. [Instituto de Física, Universidad Nacional Autónoma de México, Apartado Postal 20-364, 01000 México DF (Mexico); DuBois, R.D. [Missouri University of Science and Technology, Rolla, MO 65409 (United States)

2015-07-01

Positrons and how they interact with matter has a growing interest in many fields. Most of their uses require the production of slow positron beams with a well-defined energy, but since these particles are usually generated by means of a radioactive source, they are fast and with a broad distribution of energies. For this reason it is necessary to moderate them to lower energies via inelastic collisions. Then, they can be accelerated to the desired energies. This requires the use of a moderator. Tungsten is one of the most commonly used moderator materials because of its reasonable efficiency and relatively low cost. In this work we present different methods of producing transmission tungsten-based moderators, with particular interest in a combination of tungsten thin foils and grids. We also show results about the characterization of these moderators by ion beam analysis and microscopy techniques along with their relative moderation efficiencies.

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.

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)

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

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.

Development of a Slow Positron Facility at Hebrew University of Jerusalem

Science.gov (United States)

Kelleher, Aidan

2013-03-01

Positron annihilation spectroscopy provides both depth of penetration to study bulk defects in materials as well as nano-scale resolution. This measurement range is achieved by slowing positrons from a radioactive source, typically 22Na, by sending them through a moderator, typically W or solid Ne. The nearly thermal positrons are then accelerated to the desired energy by means of an electrostatic potential. The SPOT project at The Hebrew University of Jerusalem proposes to increase the luminosity of the beam by applying the best practices currently in us, as well as using a short-lived source of positrons, 18F. Simulations based on our current designs indicate this project will be able to deliver positrons in the energy range of 50-50000eV with an energy resolution of 1eV is possible. We will present the unique technical challenges of using this source of positrons, how we plan to overcome them, the results of simulations, and facility construction progress.

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

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)

Electron-positron pair production in ultrastrong laser fields

Directory of Open Access Journals (Sweden)

Bai Song Xie

2017-09-01

Full Text Available Electron–positron pair production due to the decay of vacuum in ultrastrong laser fields is an interesting topic which is revived recently because of the rapid development of current laser technology. The theoretical and numerical research progress of this challenging topic is reviewed. Many new findings are presented by different approaches such as the worldline instantons, the S-matrix theory, the kinetic method by solving the quantum Vlasov equation or/and the real-time Dirac–Heisenberg–Wigner formalism, the computational quantum field theory by solving the Dirac equation and so on. In particular, the effects of electric field polarizations on pair production are unveiled with different patterns of created momentum spectra. The effects of polarizations on the number density of created particles and the nonperturbative signatures of multiphoton process are also presented. The competitive interplay between the multiphoton process and nonperturbation process plays a key role in these new findings. These newly discovered phenomena are valuable to deepen the understanding of pair production in complex fields and even have an implication to the study of strong-field ionization. More recent studies on the pair production in complex fields as well as beyond laser fields are briefly presented in the view point of perspective future.

Description of the intense, low energy, monoenergetic positron beam at Brookhaven

International Nuclear Information System (INIS)

Lynn, K.G.; Mills, A.P. Jr.; Roellig, L.O.; Weber, M.

1985-01-01

An intense (4 x 10 7 s -1 ), low energy (approx. =1.0 eV), monoenergetic (ΔE approx. = 75 MeV) beam of positrons has been built at the Brookhaven National Laboratory. This flux is more than 10 times greater than any existing beam from radioactive sources. Plans are underway to increase further the flux by more than an order of magnitude. The intense low energy positron beam is made by utilizing the High Flux Beam Reactor at Brookhaven to produce the isotope 64 Cu with an activity of 40 curies of positrons. Source moderation techniques are utilized to produce the low energy positron beam from the high energy positrons emitted from 64 Cu. 31 refs., 7 figs

Positron annihilation lifetime spectroscopy study of Kapton thin foils

Science.gov (United States)

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

2016-01-01

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

Development of accelerator-based γ-ray-induced positron annihilation spectroscopy technique

International Nuclear Information System (INIS)

Selim, F.A.; Wells, D.P.; Harmon, J. F.; Williams, J.

2005-01-01

Accelerator-based γ-ray-induced positron annihilation spectroscopy performs positron annihilation spectroscopy by utilizing MeV bremsstrahlung radiation generated from an accelerator (We have named the technique 'accelerator-based γ-ray-induced PAS', even though 'bremsstrahlung' is more correct here than 'γ rays'. The reason for that is to make the name of the technique more general, since PAS may be performed by utilizing MeV γ rays emitted from nuclei through the use of accelerators as described later in this article and as in the case of positron lifetime spectroscopy [F.A. Selim, D.P. Wells, and J.F. Harmon, Rev. Sci. Instrum. 76, 033905 (2005)].) instead of using positrons from radioactive sources or positron beams. MeV γ rays create positrons inside the materials by pair production. The induced positrons annihilate with the material electrons emitting a 511-keV annihilation radiation. Doppler broadening spectroscopy of the 511-keV radiation provides information about open-volume defects and plastic deformation in solids. The high penetration of MeV γ rays allows probing of defects at high depths in thick materials up to several centimeters, which is not possible with most of the current nondestructive techniques. In this article, a detailed description of the technique will be presented, including its benefits and limitations relative to the other nondestructive methods. Its application on the investigation of plastic deformation in thick steel alloys will be shown

Conceptual design of a slow positron source based on a magnetic trap

CERN Document Server

Volosov, V I; Mezentsev, N A

2001-01-01

A unique 10.3 T superconducting wiggler was designed and manufactured at BINP SB RAS. The installation of this wiggler in the SPring-8 storage ring provides a possibility to generate a high-intensity beam of photons (SR) with energy above 1 MeV (Ando et al., J. Synchrotron Radiat. 5 (1998) 360). Conversion of photons to positrons on high-Z material (tungsten) targets creates an integrated positron flux more than 10 sup 1 sup 3 particles per second. The energy spectrum of the positrons has a maximum at 0.5 MeV and the half-width about 1 MeV (Plokhoi et al., Jpn. J. Appl. Phys. 38 (1999) 604). The traditional methods of positron moderation have the efficiency epsilon=N sub s /N sub f of 10 sup - sup 4 (metallic moderators) to 10 sup - sup 2 (solid rare gas moderators) (Mills and Gullikson, Appl. Phys. Lett. 49 (1986) 1121). The high flux of primary positrons restricts the choice to a tungsten moderator that has epsilon approx 10 sup - sup 4 only (Schultz, Nuc. Instr. and Meth. B 30 (1988) 94). The aim of our pr...

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

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.)

A combined matrix isolation spectroscopy and cryosolid positron moderation apparatus

Energy Technology Data Exchange (ETDEWEB)

Molek, Christopher D.; Michael Lindsay, C.; Fajardo, Mario E. [Air Force Research Laboratory, Munitions Directorate, Ordnance Division, Energetic Materials Branch, AFRL/RWME, 2306 Perimeter Road, Eglin AFB, Florida 32542-5910 (United States)

2013-03-15

We describe the design, construction, and operation of a novel apparatus for investigating efficiency improvements in thin-film cryogenic solid positron moderators. We report results from solid neon, argon, krypton, and xenon positron moderators which illustrate the capabilities and limitations of our apparatus. We integrate a matrix isolation spectroscopy diagnostic within a reflection-geometry positron moderation system. We report the optical thickness, impurity content, and impurity trapping site structures within our moderators determined from infrared absorption spectra. We use a retarding potential analyzer to modulate the flow of slow positrons, and report positron currents vs. retarding potential for the different moderators. We identify vacuum ultraviolet emissions from irradiated Ne moderators as the source of spurious signals in our channel electron multiplier slow positron detection channel. Our design is also unusual in that it employs a sealed radioactive Na-22 positron source which can be translated relative to, and isolated from, the cryogenic moderator deposition substrate. This allows us to separate the influences on moderator efficiency of surface contamination by residual gases from those of accumulated radiation damage.

Electron-cooled accumulation of $4 × 10^9$ positrons for production and storage of antihydrogen atoms

CERN Document Server

Fitzakerley, DW; Hessels, E A; Skinner, T D G; Storry, C H; Weel, M; Gabrielse, G; Hamley, C D; Jones, N; Marable, K; Tardiff, E; Grzonka, D; Oelert, W; Zielinski, M

2016-01-01

Four billion positrons (e+) are accumulated in a Penning–Ioffe trap apparatus at 1.2 K and <6 × 10−17 Torr. This is the largest number of positrons ever held in a Penning trap. The e+ are cooled by collisions with trapped electrons (e−) in this first demonstration of using e− for efficient loading of e+ into a Penning trap. The combined low temperature and vacuum pressure provide an environment suitable for antihydrogen ($\\bar{{\\rm{H}}}$) production, and long antimatter storage times, sufficient for high-precision tests of antimatter gravity and of CPT.

Mechanical design and development of a high power target system for the SLC Positron Source

International Nuclear Information System (INIS)

Reuter, E.; Mansour, D.; Porter, T.; Sax, W.; Szumillo, A.

1991-12-01

In order to bring the SLC Positron Source luminosity up to design specifications, the previous (stationary) positron target had to be replaced with a version which could reliably dissipate the higher power levels and cyclic pulsed thermal stresses of the high intensity 33GeV electron beam. In addition to this basic requirement, the new target system had to meet SLAC's specifications for Ultra High Vacuum, be remotely controllable, ''radiation hard,'' and designed in such a way that it could be removed and replaced quickly and easily with minimum personnel exposure to radiation. It was also desirable to integrate the target and collection components into a compact, easily manufacturable, and easily maintainable module. This paper briefly summarize the mechanical design and development of the new modular target system, its associated controls and software, alignment, and the quick removal system. Operational experience gained with the new system over the first running cycle is also summarized

Sources for charged particles

International Nuclear Information System (INIS)

Arianer, J.

1997-01-01

This document is a basic course on charged particle sources for post-graduate students and thematic schools on large facilities and accelerator physics. A simple but precise description of the creation and the emission of charged particles is presented. This course relies on every year upgraded reference documents. Following relevant topics are considered: electronic emission processes, technological and practical considerations on electron guns, positron sources, production of neutral atoms, ionization, plasma and discharge, different types of positive and negative ion sources, polarized particle sources, materials for the construction of ion sources, low energy beam production and transport. (N.T.)

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...

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

CERN Document Server

Gail, M; Scheid, W

2003-01-01

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

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

Application of the 4 {sup {pi}{sup {gamma}}} Method to the Absolute Standardization of Radioactive Sources of Positron Emitters; Aplicacion del Metodo 4 {sup {pi}{sup {gamma}}} a la Medida Absoluta de la Actividad de Fuentes Radiactivas Emisoras de Positrones

Energy Technology Data Exchange (ETDEWEB)

Peyres Medina, V.; Garcia-Torano Martinez, E.; Roteta Ibarra, M.

2006-07-01

We discuss the application of the method known as 4 {sup {pi}{sup {gamma}}} counting to the standardization of positron emitters. Monte Carlo simulations are used to calculate the detection efficiency of positrons emitted by the nuclides 22Na and 18F. Two experimental setups are used, both based on a NaI(Tl) well detector. The results of the standardizations are in good agreement with those obtained by other methods. It is shown that the 4 {sup {pi}{sup {gamma}}} method can be successfully used for the absolute standardization of sources of positron emitters. (Author) 23 refs.

Production of 68Ge, 64Cu, 86Y, 89Zr, 73Se, 77Br and 124I positron emitting radionuclides through future laser-accelerated proton beams at ELI-Beamlines for innovative PET diagnostics

Directory of Open Access Journals (Sweden)

Antonio Italiano

2016-05-01

Full Text Available The development of innovative production pathways for high-Z positron emitters is of great interest to enlarge the applicability of PET diagnostics, especially in view of the continuous development of new radiopharmaceuticals. We evaluated the theoretical yields of 64Cu, 86Y, 89Zr, 73Se, 77Br and 124I PET isotopes, plus the 68Ge isotope, parent of the 68Ga positron emitter, in the hypothesis of production through laser-accelerated proton sources expected at the ELI-Beamlines facility. By means of the TALYS software we simulated the nuclear reactions leading to the above radionuclides, hypothesizing three possible scenarios of broad proton spectra, with maximum energies of about 9, 40 and 100 MeV. The production yields of the studied radionuclides, within the expected fluences, appear to be suitable for pre-clinical applications.

Effects of displacement damage and helium production rates on the nucleation and growth of helium bubbles - Positron annihilation spectroscopy aspects

Science.gov (United States)

Krsjak, Vladimir; Degmova, Jarmila; Sojak, Stanislav; Slugen, Vladimir

2018-02-01

Fe-12 wt% Cr model alloy samples were implanted by 250 keV He2+ ions to three different fluencies (3 × 1017, 9 × 1017 and 1.5 × 1018 cm-2) at T steel samples [1] irradiated in the frame of a two-years irradiation program of the Swiss Spallation Neutron Source. Bi-modal defect distribution represented by two defect components in positron lifetime spectrum reveals two distinct helium bubbles growth mechanisms. While at the lower helium production rate of the spallation environment, the bubbles grow primarily by migration and coalescence, at the high production rates of helium in the implanted samples, the results indicate this growth is driven by Ostwald ripening mechanism. A competitive growth process via emission of interstitial atoms (clusters) is discussed in terms of low-temperature He implantations.

Study of the production and confinement of positron beams. An application to the Linear Accelerator of Orsay

International Nuclear Information System (INIS)

Chehab, Robert.

1975-04-01

This study on the production and confinement of positron beams is divided into three parts. In the first one, an analytical approximation of lateral, angular and energy distribution is given. This survey is based on the late tables of Messel et Crawford (1970) and is in good agreement with SLAC and FRASCATI estimations and measurements. Positron beam focusing is investigated in the second part: ''quarter wave'' and adiabatically tapered solenoids as well as pediodic multiplets are considered. More specially, positron injector focussing for DCI collision rings is described. In the last part of this work, a comparison between ''quarter wave'' and adiabatically tapered solenoids is presented. Larger total acceptance of the latter is pointed out in the range of medium and higher energy (>=1 GeV) accelerators [fr

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

International Nuclear Information System (INIS)

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

2006-01-01

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

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

International Nuclear Information System (INIS)

Sizun, P.

2007-04-01

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

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

International Nuclear Information System (INIS)

Bjoernsson, G.

1990-01-01

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

Source theory analysis of electron--positron annihilation experiments

International Nuclear Information System (INIS)

Schwinger, J.

1975-01-01

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

Production and application of pulsed slow-positron beam using an electron LINAC

Energy Technology Data Exchange (ETDEWEB)

Yamazaki, Tetsuo; Suzuki, Ryoichi; Ohdaira, Toshiyuki; Mikado, Tomohisa [Electrotechnical Lab., Tsukuba, Ibaraki (Japan); Kobayashi, Yoshinori

1997-03-01

Slow-positron beam is quite useful for non-destructive material research. At the Electrotechnical Laboratory (ETL), an intense slow positron beam line by exploiting an electron linac has been constructed in order to carry out various experiments on material analysis. The beam line can generates pulsed positron beams of variable energy and of variable pulse period. Many experiments have been carried out so far with the beam line. In this paper, various capability of the intense pulsed positron beam is presented, based on the experience at the ETL, and the prospect for the future is discussed. (author)

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)

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

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

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)

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)

Irradiation damage of alkali halide crystals during positron bombardment

International Nuclear Information System (INIS)

Arefiev, K.P.; Arefiev, V.P.; Vorobiev, S.A.

1978-01-01

The bleaching effect of positron irradiation of KCl and KBr single crystals previously coloured with electrons or protons was investigated. Positrons injection in the coloured alkali halide samples reduced the F-centres concentration considerably. For KCl crystals thicker than the positrons range the appearance of additional bands in the absorption spectra is noticeable. The experimental data show that the bleaching phenomenon should be observed merely throughout the positron exposure both for irradiated and non-irradiated regions of the sample. Irradiation effects, due to positron source, on the peak counting rate of (γ-γ) angular correlation in KCl crystals under applied magnetic field were also investigated. The growth of peak counting rate shows the increase of positronium-like states formation near defects of cation sublattice. (author)

Production of slow positron beam with small diameter using electron linac in Osaka University

Energy Technology Data Exchange (ETDEWEB)

Honda, Yoshihide; Sawada, Junichi; Yamada, Masaki; Maekawa, Masaki; Okuda, Shuichi; Yoshida, Yoichi; Isoyama, Goro; Tagawa, Seiichi [Osaka Univ., Ibaraki (Japan). Inst. of Scientific and Industrial Research; Yamamoto, Takayoshi

1997-03-01

A slow positron facility using an electron linac was designed and constructed. The specifications were mainly decided by numerical calculations. The slow positrons are transported along magnetic field line. The cross sectional size of slow positron beam is 1-2cm and the maximum conversion rate from electron to positron is about 1.5 x 10{sup -6}. This value is about 1/4 of ideal case in our system. Extraction of slow positron beam from magnetic field region was made and preliminary brightness enhancement experiment was also performed. (author)

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

Prospects for the creation of positron-electron plasmas in a non-neutral stellarator

International Nuclear Information System (INIS)

Pedersen, T Sunn; Boozer, A H; Dorland, W; Kremer, J P; Schmitt, R

2003-01-01

The prospects of creating positron-electron plasmas confined in a stellarator are discussed. A pure electron plasma would be created before the positrons are introduced, to facilitate efficient injection and a long confinement time of the positrons. Gyrokinetic simulations are presented suggesting that a positron-electron plasma may be stable to low-frequency microturbulence if operated well below the Brillouin limit, and transport may be neoclassical. If this is the case, significant positron-electron plasma densities can be reached with positron sources that exist today

Observation of exclusive electron-positron production in hadron-hadron collisions.

Science.gov (United States)

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

2007-03-16

We present the first observation of exclusive e(+)e(-) production in hadron-hadron collisions, using pp[over] collision data at (square root) s = 1.96 TeV taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb(-1). We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E(T) > 5 GeV and pseudorapidity |eta| p + e(+)e(-) + p[over] through two-photon exchange. The measured cross section is 1.6(-0.3)(+0.5)(stat) +/- 0.3(syst) pb. This agrees with the theoretical prediction of 1.71+/-0.01 pb.

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...

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)

Radiopharmaceuticals in positron emission tomography: Radioisotope productions and radiolabelling procedures at the Austin and Repatriation Medical Centre

International Nuclear Information System (INIS)

Tochon-Danguy, H.J.; Sachinidis, J.I.; Chan, J.G.; Cook, M.

1997-01-01

Positron Emission Tomography (PET) is a technique that utilizes positron-emitting radiopharmaceuticals to map the physiology, biochemistry and pharmacology of the human body. Positron-emitting radioisotopes produced in a medical cyclotron are incorporated into compounds that are biologically active in the body. A scanner measures radioactivity emitted from a patient's body and provides cross-sectional images of the distribution of these radiolabelled compounds in the body. It is the purpose of this paper to review the variety of PET radiopharmaceuticals currently produced at the Austin and Repatriation Medical Centre in Melbourne. Radioisotope production, radiolabelling of molecules and quality control of radiopharmaceuticals will be discussed. A few examples of their clinical applications will be shown as well. During the last five years we achieved a reliable routine production of various radiopharmaceuticals labelled with the four most important positron-emitters: oxygen-15 (t, 1/2 =2min), nitrogen-13 (t 1/2 = 10 min), carbon-11 (t 1/2 =20 min) and fluorine-18 (t 1/2 = 110 min). These radiopharmaceuticals include [ 15 O]oxygen, [ 15 O]carbon monoxide, [ 15 O]carbon dioxide, [ 15 O]water, [ 13 N]ammonia, [ 11 C]flumazenil, [ 11 C]SCH23390, [ 18 F]fluoromisonidazole and [ 18 F]fluoro-deoxy-glucose ([ 18 F]FDG). In addition, since the half life of [ 18 F] is almost two hours, regional distribution can be done, and the Austin and Repatriation Medical Centre is currently supplying [ 18 F]FDG in routine to other hospitals. Future new radiopharmaceuticals development include a [ 18 F]thymidine analog to measure cell proliferation and a [ 11 C]pyrroloisoquinoline to visualize serotonergic neuron abnormalities. (authors)

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

International Nuclear Information System (INIS)

Gregory, R.B.

1991-01-01

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

Performance characterisation and optimisation of the HIPOS positron generator setup

Energy Technology Data Exchange (ETDEWEB)

Tucek, K., E-mail: kamil.tucek@ec.europa.eu [European Commission, Joint Research Centre, Institute for Energy and Transport, P.O. Box 2, NL-1755 ZG Petten (Netherlands); Zeman, A.; Daquino, G.; Debarberis, L. [European Commission, Joint Research Centre, Institute for Energy and Transport, P.O. Box 2, NL-1755 ZG Petten (Netherlands); Hogenbirk, A. [Nuclear Research and Consultancy Group (NRG), P.O. Box 25, NL-1755 ZG Petten (Netherlands)

2012-01-01

As part of an Exploratory Research Project at the Institute for Energy and Transport (Joint Research Centre of the European Commission), a feasibility assessment was performed for the construction and placement of a high-intensity positron facility (HIPOS) in a beam tube, HB9, at the High flux reactor (HFR) in Petten. This paper reports on the results of Monte Carlo simulations to optimise the concept of the HIPOS positron generator and to determine the performance characteristics of the chosen generator design. In the first step, a detailed model of the HFR reactor core, reflector, instrumentation and HB9 beam tube was prepared, and coupled neutron and photon transport calculations were carried out with the MCNP4C3 code to establish neutron and photon source terms on boundary surfaces of the HB9 beam tube. These sources were subsequently used with the MCNPX code to optimise the positron generator concept and geometry. The results showed that the positron beam can reach an integral intensity of 10{sup 13} e{sup +}/s before the moderation stage, easily meeting the specified target and confirming the hypothesis that very high positron yields can be obtained by using combined neutron and gamma radiation sources from a high flux reactor. Full details of the research work are reported in this study.

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.

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

Positron-annihilation-radiation transmission gauge

International Nuclear Information System (INIS)

Padawer, G.M.

1984-01-01

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

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 production in a hot accretion plasma around a massive black hole

International Nuclear Information System (INIS)

Takahara, Fumio; Kusunose, Masaaki.

1985-01-01

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

A novel source of MeV positron bunches driven by energetic protons for PAS application

Energy Technology Data Exchange (ETDEWEB)

Tan, Zongquan, E-mail: tqq1123@mail.ustc.edu.cn [State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Xu, Wenzhen; Liu, Yanfen; Xiao, Ran; Kong, Wei [State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Ye, Bangjiao, E-mail: bjye@ustc.edu.cn [State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2014-11-01

This paper proposes a novel methodology of MeV positrons generation for PAS application. Feasibility of this proposal analyzed by G4Beamline and Transport have shown reasonable success. Using 2 Hz, 1.6 GeV, 100 ns and 1.5 μC/bunch proton bunches for bombarding a graphite target, about 100 ns e{sup +} bunches are generated. Quasi-monochromatic positrons in the range of 1–10 MeV included in these bunches have a flux of >10{sup 7}/s, peak brightness of 10{sup 14}/s. A magnetic-confinement beamline is utilized to transport the positrons and a “Fast Beam Chopper” is unprecedentedly extended to chop those relativistic bunches. The positron beam can be finally characterized by the energy range of 1–10 MeV and bunch width from one hundred ps up to 1 ns. Such ultrashort bunches can be useful in tomography-type positron annihilation spectroscopy (PAS) as well as other applications.

A novel source of MeV positron bunches driven by energetic protons for PAS application

Science.gov (United States)

Tan, Zongquan; Xu, Wenzhen; Liu, Yanfen; Xiao, Ran; Kong, Wei; Ye, Bangjiao

2014-11-01

This paper proposes a novel methodology of MeV positrons generation for PAS application. Feasibility of this proposal analyzed by G4Beamline and Transport have shown reasonable success. Using 2 Hz, 1.6 GeV, 100 ns and 1.5 μC/bunch proton bunches for bombarding a graphite target, about 100 ns e+ bunches are generated. Quasi-monochromatic positrons in the range of 1-10 MeV included in these bunches have a flux of >107/s, peak brightness of 1014/s. A magnetic-confinement beamline is utilized to transport the positrons and a "Fast Beam Chopper" is unprecedentedly extended to chop those relativistic bunches. The positron beam can be finally characterized by the energy range of 1-10 MeV and bunch width from one hundred ps up to 1 ns. Such ultrashort bunches can be useful in tomography-type positron annihilation spectroscopy (PAS) as well as other applications.

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.)

Positron kinetics in an idealized PET environment

Science.gov (United States)

Robson, R. E.; Brunger, M. J.; Buckman, S. J.; Garcia, G.; Petrović, Z. Lj.; White, R. D.

2015-08-01

The kinetic theory of non-relativistic positrons in an idealized positron emission tomography PET environment is developed by solving the Boltzmann equation, allowing for coherent and incoherent elastic, inelastic, ionizing and annihilating collisions through positronium formation. An analytic expression is obtained for the positronium formation rate, as a function of distance from a spherical source, in terms of the solutions of the general kinetic eigenvalue problem. Numerical estimates of the positron range - a fundamental limitation on the accuracy of PET, are given for positrons in a model of liquid water, a surrogate for human tissue. Comparisons are made with the ‘gas-phase’ assumption used in current models in which coherent scattering is suppressed. Our results show that this assumption leads to an error of the order of a factor of approximately 2, emphasizing the need to accurately account for the structure of the medium in PET simulations.

Selection of the optimum magnet design for the International Linear Collider positron source helical undulator

Directory of Open Access Journals (Sweden)

D. J. Scott

2007-03-01

Full Text Available A comparison of possible undulator designs for the International Linear Collider positron source has resulted in a superconducting bifilar wire design being selected. After a comprehensive paper study and fabrication of the two preeminent designs, the superconducting undulator was chosen instead of the permanent magnet alternative. This was because of its superior performance in terms of magnetic field strength and quality, operational flexibility, risk of radiation damage, ease in achieving the required vacuum, and cost. The superconducting undulator design will now be developed into a complete system design for the full 200 m long magnet that is required.

Ultrashort megaelectronvolt positron beam generation based on laser-accelerated electrons

Science.gov (United States)

Xu, Tongjun; Shen, Baifei; Xu, Jiancai; Li, Shun; Yu, Yong; Li, Jinfeng; Lu, Xiaoming; Wang, Cheng; Wang, Xinliang; Liang, Xiaoyan; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan

2016-03-01

Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with high charge; thus, a charge-neutralized MeV positron beam with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron-positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8 × 1021 s-1, thus allows specific studies of fast kinetics in millimeter-thick materials with a high time resolution and exhibits potential for applications in positron annihilation spectroscopy.

Positron emission tomography in a national research centre

International Nuclear Information System (INIS)

Weinreich, R.

1989-01-01

The example of the Paul Scherrer Institute shows that positron emission tomography can be implanted successfully as spin-off into an appropriate environment. The adaption to the existing irradiation facilities of the technique of production of the short-lived positron emitters is complex. However, the basic necessities of a tomography programme can be covered. Moreover, the relatively high energy of the institute's injector cyclotron allows additional production of rare-used longer-lived positron emitters. The scanner exceeded the guaranteed specifications. With respect to the somewhat lower availability of beam time compared to a usual baby cyclotron, the research programme must not be very patient-intense. A strong participation of the pharmaceutical industry has directed research priorities into the pharmacological area. (orig.) [de

Radiopharmaceuticals in positron emission tomography: Radioisotope productions and radiolabelling procedures at the Austin and Repatriation Medical Centre

Energy Technology Data Exchange (ETDEWEB)

Tochon-Danguy, H.J.; Sachinidis, J.I.; Chan, J.G.; Cook, M. [Austin and Repatriation Medical Centre, Melbourne, VIC (Australia). Centre for Positron Emission Tomography

1997-10-01

Positron Emission Tomography (PET) is a technique that utilizes positron-emitting radiopharmaceuticals to map the physiology, biochemistry and pharmacology of the human body. Positron-emitting radioisotopes produced in a medical cyclotron are incorporated into compounds that are biologically active in the body. A scanner measures radioactivity emitted from a patient`s body and provides cross-sectional images of the distribution of these radiolabelled compounds in the body. It is the purpose of this paper to review the variety of PET radiopharmaceuticals currently produced at the Austin and Repatriation Medical Centre in Melbourne. Radioisotope production, radiolabelling of molecules and quality control of radiopharmaceuticals will be discussed. A few examples of their clinical applications will be shown as well. During the last five years we achieved a reliable routine production of various radiopharmaceuticals labelled with the four most important positron-emitters: oxygen-15 (t,{sub 1/2}=2min), nitrogen-13 (t{sub 1/2}= 10 min), carbon-11 (t{sub 1/2}=20 min) and fluorine-18 (t{sub 1/2}= 110 min). These radiopharmaceuticals include [{sup 15}O]oxygen, [{sup 15}O]carbon monoxide, [{sup 15}O]carbon dioxide, [{sup 15}O]water, [{sup 13}N]ammonia, [{sup 11}C]flumazenil, [{sup 11}C]SCH23390, [{sup 18}F]fluoromisonidazole and [{sup 18}F]fluoro-deoxy-glucose ([{sup 18}F]FDG). In addition, since the half life of [{sup 18}F] is almost two hours, regional distribution can be done, and the Austin and Repatriation Medical Centre is currently supplying [{sup 18}F]FDG in routine to other hospitals. Future new radiopharmaceuticals development include a [{sup 18}F]thymidine analog to measure cell proliferation and a [{sup 11}C]pyrroloisoquinoline to visualize serotonergic neuron abnormalities. (authors) 23 refs., 2 tabs.

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

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.

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

CERN Document Server

Del Duca, Vittorio

2016-01-01

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

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.

An adiabatic matching device for the Orsay linear positron accelerator

International Nuclear Information System (INIS)

Chehab, R.; Le Meur, G.; Mouton, B.; Renard, M.

1983-03-01

An adiabatically tapered solenoidal magnetic field is used to match positron beam source emittance to accelerating section acceptance. Such a matching system improves the accepted energy band which has been accurately computed and compared with analytical determination. The tapered field is provided by stacked pancakes and solenoids of various radii; total lens length is about 0.75m. The adiabatic matching system took place of a quarter wave transformer system and has been in operation for two years. Positron conversion ratio is 3.3% for a 1 GeV incident beam and presents a factor of nearly two of improvement for the positron yield. Energy bandwidth of positron beam has also been increased by a factor of nearly 2.5; the output positron beam energy is of 1.2 GeV

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

Science.gov (United States)

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

2014-04-01

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

Correction of head movements in positron emission tomography using point source tracking system: a simulation study.

Science.gov (United States)

Nazarparvar, Babak; Shamsaei, Mojtaba; Rajabi, Hossein

2012-01-01

The motion of the head during brain positron emission tomography (PET) acquisitions has been identified as a source of artifact in the reconstructed image. In this study, a method is described to develop an image-based motion correction technique for correcting the post-acquisition data without using external optical motion-tracking system such as POLARIS. In this technique, GATE has been used to simulate PET brain scan using point sources mounted around the head to accurately monitor the position of the head during the time frames. The measurement of head motion in each frame showed a transformation in the image frame matrix, resulting in a fully corrected data set. Using different kinds of phantoms and motions, the accuracy of the correction method is tested and its applicability to experimental studies is demonstrated as well.

Improved Slow-Positron Yield using a Single Crystal Tungsten Moderator

DEFF Research Database (Denmark)

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

1983-01-01

A well-annealed W(110) single crystal was used as a fast-to-slow positron moderator. The measured moderator efficiency at room temperature using a58Co positron source in the backscattering geometry isɛ =(3.2±0.4)×10−3, roughly a factor of three better thanɛ for the best previously reported Cu(111......)+S moderator. We find a stable positron moderation efficiency over a period of several weeks when maintained at pressures around 10−9 Torr and an energy spreadΔE = 0.7 eV of the emitted slow positrons. An initial attempt was made to fabricate a hybrid Cu on W(110) moderator, which yieldedɛ of about 1...

Application of positron emitters to studies on plants

Energy Technology Data Exchange (ETDEWEB)

Ishioka, N S; Matsuoka, H [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan). Takasaki Radiation Chemistry Research Establishment; Sekine, T [and others

1998-10-01

A newly developed positron emitting tracer imaging system enables us to study dynamically the physiological function of plants, although this system covers, at present, a limited area in a plant. Production of the positron emitters {sup 11}C, {sup 13}N, {sup 18}F and {sup 48}V for this application, using an AVF cyclotron, is described. (author)

Synthesis of the radiopharmaceuticals for positron emission tomography

International Nuclear Information System (INIS)

Biricova, V.; Kuruc, J.

2007-01-01

In this paper is shown a short overview of the biogenic positron radiopharmaceuticals production and a brief summary of some PET preparation synthesis. At the end the overview of some forward-looking positron radionuclides, which can be used for a preparation of the PET radiopharmaceuticals is said. A short review of diagnostic use of PET radiopharmaceuticals is presented (authors)

Topics in electron-positron interactions

International Nuclear Information System (INIS)

Soeding, P.

1983-01-01

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

Millimeter positron focusing using a hybrid lens design

International Nuclear Information System (INIS)

Cheung, C.K.; Kwan, P.Y.; Shan, Y.Y.; Naik, P.S.; Weng, H.M.; Beling, C.D.; Fung, S.

2004-01-01

The study of metal-semiconductor and metal-oxide-semiconductor systems with low energy positrons is made considerably easier if structures of millimeter dimension can be studied. For this reason the production of a positron beam of sub-millimeter dimension has been a long-term goal of the positron research group at the university of Hong Kong. The hybrid lens system employed consists of a standard Soa extraction lens in a magnetic field free region followed by a gridded Einzel lens that focuses positrons into a 100G magnetic funnel at an energy of 10keV for transportation to the target. Here we report on the present progress, by showing the capability of obtaining millimeter diameter focusing at a preliminary 7.5 kV beam energy. (orig.)

Anomalous positron emission in heavy ion-collisions

International Nuclear Information System (INIS)

Kienle, P.

1986-09-01

In section two we shortly present the experimental methods and first results on positron lines. Section three deals with the dependence of the positron line production on the charge of the collision system, bombarding energy and scattering angle. The results of the first e + -e - -coincidence studies are reviewed in section 4. In the last paragraph we make some remarks on future developments of the experimental methods. (orig./HSI)

3D numerical thermal stress analysis of the high power target for the SLC Positron Source

International Nuclear Information System (INIS)

Reuter, E.M.; Hodgson, J.A.

1991-05-01

The volumetrically nonuniform power deposition of the incident 33 GeV electron beam in the SLC Positron Source Target is hypothesized to be the most likely cause target failure. The resultant pulsed temperature distributions are known to generate complicated stress fields with no known closed-form analytical solution. 3D finite element analyses of these temperature distributions and associated thermal stress fields in the new High Power Target are described here. Operational guidelines based on the results of these analyses combined with assumptions made about the fatigue characteristics of the exotic target material are proposed. 6 refs., 4 figs

Overview of the advanced photon source (APS)

International Nuclear Information System (INIS)

White, M.M.

1994-01-01

The Advanced Photon Source (APS) is a state-of-the-art synchrotron light source facility dedicated to the production of extremely brilliant x-ray beams for research. Its super-intense x-ray beams will be used in many areas of research including industrial research, biological and medical research, defense-related research, and basic research. The APS x-ray beams will allow scientists to study smaller samples, more complex systems, faster reactions and processes, and gather data at a greater level of detail than has been possible to date. Creation of these beams begins with electron production by an electron gun with a thermionic cathode. The electrons are accelerated to 200 MeV by a linear accelerator (linac) and then impinge on a tungsten target, resulting in electron-positron pair production. The positrons are accelerated to 450 MeV in the remainder of the linac, then accumulated, damped, and transferred to a synchrotron that increases their energy to 7 GeV. The 7-GeV positrons are injected into a storage ring, where they pass through special magnets that cause them to emit x-rays of the desired quality. Construction at ANL is nearly complete at this time, and the APS will begin operating for users in 1996. The accelerator and experimental facilities are described in this paper, and a brief overview of some of the experimental programs is given

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.

Analysis of defects near the surface and the interface of semiconductors by monoenergetic positron beam

International Nuclear Information System (INIS)

Uedono, Akira; Tanigawa, Shoichiro

1989-01-01

A monoenergetic low-speed positron beam line is constructed and a study is made on defects near the surface and the interface of semiconductors by using the beam line. Sodium-22 is used as beam source. Ion implantation, though being an essential technique for semiconductor integrated circuit production, can introduce lattice defects, affecting the yield and reliability of the resultant semiconductor devices. Some observations are made on the dependence of the Doppler broadening on the depth, and the ΔS-E relationship in P + -ion implanted SiO 2 (43nm)-Si. These observations demonstrate that monoenergetic positron beam is useful to detect hole-type defects resulting from ion implantation over a very wide range of defect density. Another study is made for the detection of defects near an interface. Positrons are expected to drift when left in an electric field with a gradient. Observations made here show that positrons can be concentrated at any desired interface by introducing an electric field intensity gradient in the oxide. This process also serves for accurate measurement of the electronic structure at the interface, and the effect of ion implantation and radiations on the interface. (N.K.)

Bremsstrahlung Based Positron Annihilation Spectroscopy for Material Defect Analysis

International Nuclear Information System (INIS)

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

2003-01-01

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

First image from a combined positron emission tomography and field-cycled MRI system.

Science.gov (United States)

Bindseil, Geron A; Gilbert, Kyle M; Scholl, Timothy J; Handler, William B; Chronik, Blaine A

2011-07-01

Combining positron emission tomography and MRI modalities typically requires using either conventional MRI with a MR-compatible positron emission tomography system or a modified MR system with conventional positron emission tomography. A feature of field-cycled MRI is that all magnetic fields can be turned off rapidly, enabling the use of conventional positron emission tomography detectors based on photomultiplier tubes. In this demonstration, two photomultiplier tube-based positron emission tomography detectors were integrated with a field-cycled MRI system (0.3 T/4 MHz) by placing them into a 9-cm axial gap. A positron emission tomography-MRI phantom consisting of a triangular arrangement of positron-emitting point sources embedded in an onion was imaged in a repeating interleaved sequence of ∼1 sec MRI then 1 sec positron emission tomography. The first multimodality images from the combined positron emission tomography and field-cycled MRI system show no additional artifacts due to interaction between the systems and demonstrate the potential of this approach to combining positron emission tomography and MRI. Copyright © 2010 Wiley-Liss, Inc.

Positron annihilation spectroscopy in condensed matter

International Nuclear Information System (INIS)

Brauer, G.

1982-09-01

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

First on-line positron experiments en route to pair-plasma creation

Energy Technology Data Exchange (ETDEWEB)

Stanja, Juliane; Hergenhahn, Uwe; Stenson, Eve V. [Max-Planck-Institut fuer Plasmaphysik (Germany); Niemann, Holger; Sunn Pedersen, Thomas [Max-Planck-Institut fuer Plasmaphysik (Germany); Ernst-Moritz-Arndt Universitaet Greifswald (Germany); Saitoh, Haruhiko [Max-Planck-Institut fuer Plasmaphysik (Germany); The University of Tokyo (Japan); Stoneking, Matthew R. [Lawrence University (United States); Hugenschmidt, Christoph; Piochacz, Christian [Technische Universitaet Muenchen (Germany); Schweikhard, Lutz [Ernst-Moritz-Arndt Universitaet Greifswald (Germany)

2016-07-01

Electron-positron plasmas are predicted to show a fundamentally different behavior from traditional ion-electron plasmas, because of the equal masses of the two species. Using up to 10{sup 9} positrons per second provided by the NEPOMUC (Neutron-Induced Positron Source Munich) facility, the APEX/PAX team aims to create the first such plasma confined in a toroidal magnetic trap. Positron beam parameters as well as efficient injection and confinement schemes for both species in toroidal geometries are fundamental to the project. In this contribution we present results from first on-line positron experiments. Besides characterizing the NEPOMUC beam we conducted positron injection experiments into a dipole magnetic field configuration. Using static electric fields, a 5-eV positron beam was transported across magnetic field lines into the confinement region. With this method, up to 38% of the incoming particles reach the confinement region and make at least a 180 revolution around the magnet. Under dedicated experimental conditions confinement on the order of 1 ms was realized.

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-12-19

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

A positron beam for the linear collider scheme of a B-meson factory

International Nuclear Information System (INIS)

Chehab, R.

1988-02-01

An approach for a conventional positron source intended to a BantiB linear collider scheme is here given. Optical matching devices between the source and the accelerator are considered and some comparisons are made regarding the maximum acceptance and the positron beam qualities. Focusing in the preaccelerator and in the main linac are also considered. Heating and radiation problems which may introduce severe limitations are only partly examined

Progress of the intense positron beam project EPOS

International Nuclear Information System (INIS)

Krause-Rehberg, R.; Brauer, G.; Jungmann, M.; Krille, A.; Rogov, A.; Noack, K.

2008-01-01

EPOS (the ELBE POsitron Source) is a running project to build an intense, bunched positron beam for materials research. It makes use of the bunched electron beam of the ELBE radiation source (Electron Linac with high Brilliance and low Emittance) at the Research Centre Dresden-Rossendorf (40 MeV, 1 mA). ELBE has unique timing properties, the bunch length is <5 ps and the repetition time is 77 ns. In contrast to other Linacs made for Free Electron Lasers (e.g., TTF at DESY, Hamburg), ELBE can be operated in full cw-mode, i.e., with an uninterrupted sequence of bunches. The article continues an earlier publication. It concentrates on details of the timing system and describes issues of radiation protection

Construction of a pulsed MeV positron beam line

Energy Technology Data Exchange (ETDEWEB)

Masuno, Shin-ichi; Okada, Sohei; Kawasuso, Atsuo [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan). Takasaki Radiation Chemistry Research Establishment

1997-03-01

To develop a fast (1 MeV) and short pulsed (100 ps) positron beam which enables defect behavior analysis of bulk states of materials even at high temperatures where a usual positron source would melt, we have been performing design study and construction of the beam line in a three-year program since 1994. This report describes the components, design study results and experimental results of the completed parts until now. (author)

Antiparticle sources for antihydrogen production and trapping

DEFF Research Database (Denmark)

Charlton, M.; Bruun Andresen, Gorm; Ashkezari, M. D.

2011-01-01

Sources of positrons and antiprotons that are currently used for the formation of antihydrogen with low kinetic energies are reviewed, mostly in the context of the ALPHA collaboration and its predecessor ATHENA. The experiments were undertaken at the Antiproton Decelerator facility, which...... is located at CERN. Operations performed on the clouds of antiparticles to facilitate their mixing to produce antihydrogen are described. These include accumulation, cooling and manipulation. The formation of antihydrogen and some of the characteristics of the anti-atoms that are created are discussed....... Prospects for trapping antihydrogen in a magnetic minimum trap, as envisaged by the ALPHA collaboration, are reviewed....

Antiparticle sources for antihydrogen production and trapping

Energy Technology Data Exchange (ETDEWEB)

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

2011-12-01

Sources of positrons and antiprotons that are currently used for the formation of antihydrogen with low kinetic energies are reviewed, mostly in the context of the ALPHA collaboration and its predecessor ATHENA. The experiments were undertaken at the Antiproton Decelerator facility, which is located at CERN. Operations performed on the clouds of antiparticles to facilitate their mixing to produce antihydrogen are described. These include accumulation, cooling and manipulation. The formation of antihydrogen and some of the characteristics of the anti-atoms that are created are discussed. Prospects for trapping antihydrogen in a magnetic minimum trap, as envisaged by the ALPHA collaboration, are reviewed.

Positron emission tomography

International Nuclear Information System (INIS)

Marchenkov, N.S.

2000-01-01

The foundations of the positron emission tomography (PET), widely used for the medical diagnostics, are considered. The brief description of the cyclotron for production of radionuclides, applied in the PET, the target devices for manufacturing the position emitters, the moduli for the radiopharmaceuticals synthesis (RPS) for the PET is presented. The necessity and concept of complete automation of the RPS for the PET are discussed [ru

Fission-product source terms

International Nuclear Information System (INIS)

Lorenz, R.A.

1981-01-01

This presentation consists of a review of fission-product source terms for light water reactor (LWR) fuel. A source term is the quantity of fission products released under specified conditions that can be used to calculate the consequences of the release. The source term usually defines release from breached fuel-rod cladding but could also describe release from the primary coolant system, the reactor containment shell, or the site boundary. The source term would be different for each locality, and the chemical and physical forms of the fission products could also differ

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

Science.gov (United States)

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

2016-10-01

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

Electron-positron plasma generation in a pulsar magnetosphere

International Nuclear Information System (INIS)

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

1985-01-01

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

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

The production of collimated beams of o-Ps atoms using charge exchange in positron-gas collisions

International Nuclear Information System (INIS)

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

1987-01-01

Using positron-gas collisions in a short scattering cell it is demonstrated that, at certain impact energies, approximately 4% of the scattered positrons can be detected as o-Ps atoms collimated in a 6 0 cone about the incident positron direction. (author)

Design of a superconducting accelerator for positron annihilation spectroscopy

International Nuclear Information System (INIS)

Oshima, Nagayasu; Kuroda, Ryunosuke; Suzuki, Ryoichi; Kinomura, Atsushi; Ohdaira, Toshiyuki; Hayashizaki, Noriyosu; Hattori, Toshiyuki

2008-01-01

A design of a superconducting accelerator for a positron beam with energy of ∼1 MeV for positron annihilation spectroscopy is proposed. The total system can be extremely small with an application of superconducting technology. Both a miniaturization and easy maintenance of the accelerator can be achieved by usage of a small liquidless refrigerator for cooling of a superconducting RF cavity. Moreover, operation duty cycle of the superconducting cavity is ∼100%. The required RF power to drive the system is only ∼10 W, therefore a large-size klystron is not necessary. The designed system including a slow positron source is small (∼2 m 3 ) enough to be used in a general laboratory. (author)

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 range in tissue-equivalent materials: experimental microPET studies

Science.gov (United States)

Alva-Sánchez, H.; Quintana-Bautista, C.; Martínez-Dávalos, A.; Ávila-Rodríguez, M. A.; Rodríguez-Villafuerte, M.

2016-09-01

In this work an experimental investigation was carried out to study the effect that positron range has over positron emission tomography (PET) scans through measurements of the line spread function (LSF) in tissue-equivalent materials. Line-sources consisted of thin capillary tubes filled with 18F, 13N or 68Ga water-solution inserted along the axis of symmetry of cylindrical phantoms constructed with the tissue-equivalent materials: lung (inhale and exhale), adipose tissue, solid water, trabecular and cortical bone. PET scans were performed with a commercial small-animal PET scanner and image reconstruction was carried out with filtered-backprojection. Line-source distributions were analyzed using radial profiles taken on axial slices from which the spatial resolution was determined through the full-width at half-maximum, tenth-maximum, twentieth-maximum and fiftieth-maximum. A double-Gaussian model of the LSFs was used to fit experimental data which can be incorporated into iterative reconstruction methods. In addition, the maximum activity concentration in the line-sources was determined from reconstructed images and compared to the known values for each case. The experimental data indicates that positron range in different materials has a strong effect on both spatial resolution and activity concentration quantification in PET scans. Consequently, extra care should be taken when computing standard-uptake values in PET scans, in particular when the radiopharmaceutical is taken up by different tissues in the body, and more even so with high-energy positron emitters.

Development of positron sensor for multi-modal endoscopy

Energy Technology Data Exchange (ETDEWEB)

Shimazoe, Kenji, E-mail: shimazoe@it-club.jp [Department of Bioengineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Takahashi, Hiroyuki [Department of Nuclear Engineering and Management, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Fujita, Kaoru [Japan Atomic Energy Agency, 4-29 Tokaimura, 319-1184 Ibaraki (Japan); Mori, Hiroshi; Momose, Toshimitsu [Department of Bioengineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2011-08-21

Endoscopy is an important inspection device to detect cancers in the human body, but there exists the case of cancer that is hard to detect with only an optical device. Double inspection with optical and radio images is preferable for high accuracy diagnosis, and real time radio imaging is also promising for real time surgery with an endoscope. We have simulated, designed and fabricated a Si-based positron imaging probe for more accurate cancer detection in multi-modality endoscope systems. The fabricated Si-based detector with 2 mm diameter and 1 mm thickness was tested with gamma and positron sources, and also tested to detect cancers in a tumor bearing mouse. The direct positron imaging could have an advantage over gamma imaging in its high sensitivity and resolution.

Electron-positron pair production in relativistic ion-atom collisions

International Nuclear Information System (INIS)

Eichler, Joerg

2005-01-01

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

Rf power sources

International Nuclear Information System (INIS)

Allen, M.A.

1988-05-01

This paper covers RF power sources for accelerator applications. The approach has been with particular customers in mind. These customers are high energy physicists who use accelerators as experimental tools in the study of the nucleus of the atom, and synchrotron light sources derived from electron or positron storage rings. This paper is confined to electron-positron linear accelerators since the RF sources have always defined what is possible to achieve with these accelerators. 11 refs., 13 figs

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)

Intense positron beams and possible experiments

International Nuclear Information System (INIS)

Lynn, K.G.; Frieze, W.E.

1983-07-01

In this paper, we survey some of the ideas that have been proposed regarding the production of intense beams of low energy positrons. Various facilities to produce beams of this type are already under design or construction and other methods beyond those in use have been previously discussed. Moreover, a variety of potential experiments utilizing intense positron beams have been suggested. It is to be hoped that this paper can serve as a useful summary of some of the current ideas, as well as a stimulation for new ideas to be forthcoming at the workshop. 31 references

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 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

Annihilation of unthermalized positrons in a silicon single crystal at 770K

International Nuclear Information System (INIS)

Zaitsev, Yu.E.; Mungir, L.; Ue'pe, L.R.

1984-01-01

A model is considered for the annihilation of nonrelativistic positrons from quantized states in lattice channels. Annihilation gamma rays of energy over 511 keV have been observed when the positrons from an Na 22 source strike a silicon single crystal at 77 0 K. The experimental results agree well with the proposed model

Generation of monoenergetic positrons

International Nuclear Information System (INIS)

Hulett, L.D. Jr.; Dale, J.M.; Miller, P.D. Jr.; Moak, C.D.; Pendyala, S.; Triftshaeuser, W.; Howell, R.H.; Alvarez, R.A.

1983-01-01

Many experiments have been performed in the generation and application of monoenergetic positron beams using annealed tungsten moderators and fast sources of 58 Co, 22 Na, 11 C, and LINAC bremstrahlung. This paper will compare the degrees of success from our various approaches. Moderators made from both single crystal and polycrystal tungsten have been tried. Efforts to grow thin films of tungsten to be used as transmission moderators and brightness enhancement devices are in progress

Towards high-resolution positron emission tomography for small volumes

International Nuclear Information System (INIS)

McKee, B.T.A.

1982-01-01

Some arguments are made regarding the medical usefulness of high spatial resolution in positron imaging, even if limited to small imaged volumes. Then the intrinsic limitations to spatial resolution in positron imaging are discussed. The project to build a small-volume, high resolution animal research prototype (SHARP) positron imaging system is described. The components of the system, particularly the detectors, are presented and brief mention is made of data acquisition and image reconstruction methods. Finally, some preliminary imaging results are presented; a pair of isolated point sources and 18 F in the bones of a rabbit. Although the detector system is not fully completed, these first results indicate that the goals of high sensitivity and high resolution (4 mm) have been realized. (Auth.)

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

Positron emission tomography/computed tomography scanning for ...

African Journals Online (AJOL)

Background: Although the site of nosocomial sepsis in the critically ill ventilated patient is usually identifiable, it may remain occult, despite numerous investigations. The rapid results and precise anatomical location of the septic source using positron emission tomography (PET) scanning, in combination with computed ...

Systematic studies of positron production in heavy-ion collisions near the Coulomb barrier

International Nuclear Information System (INIS)

Tsertos, H.; Berdermann, E.; Bosch, F.; Kienle, P.; Koenig, W.; Kozhuharov, C.; Clemente, M.; Huchler, S.

1991-04-01

We present the results obtained from systematic studies of positron creation for a series of heavy-collision systems, with united charge Z u = Z 1 + Z 2 ranging from Z u = 164 (Pb+Pb) to Z u = 184 (U+U) at bombarding energies close to the Coulomb barrier, using the Orange-β-spectrometer at GSI. For each collision system studied, the dominating continuous distributions due to quasi-atomic and nuclear positron emission are determined accurately. This is essential in obtaining the characteristics of the still unexplained monoenergetic positron lines which appear in the energy range between 200 keV and 400 keV. Our results are compared with coupled-channels calculations for quasi-atomic positron creation. The latter describe quite well the global features of the measured spectra, but overestimate systematically their absolute values. From the comparison, a common normalization factor of f = 0.76 ± 0.04 can be established for the calculated spectra. In particular, the dependence on Z u of the measured emission probabilities was found to follow a power law; ∝ Z u 19.5±1 , in fair agreement with the theoretical predictions. (orig.)

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

International Nuclear Information System (INIS)

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

1996-05-01

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

Monte Carlo simulation study of the positron contribution to displacements per atom production in YBCO superconductors

International Nuclear Information System (INIS)

Pinera, I.; Cruz, C.M.; Abreu, Y.; Leyva, A.

2008-01-01

The contribution from positrons to the displacements per atom (dpa) distribution induced by the gamma irradiation on YBCO superconducting slabs is presented. The procedure implemented previously by the authors was adapted to take into account the contribution from positrons to dpa induced by the gamma radiation. The results show that, when positrons are considered in the atom displacement process, the total dpa almost doubles at 10 MeV of incident gamma radiation. At that energy positrons contribute 7% more to the total dpa than electrons, although electrons maintain having the highest contribution up to about 8 MeV.

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

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

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

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

International Nuclear Information System (INIS)

Wiktor, Julia

2015-01-01

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

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

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

International Nuclear Information System (INIS)

Klein, S.R.

1988-01-01

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

Characterization of lacunar defects by positrons annihilation

International Nuclear Information System (INIS)

Barthe, M.F.; Corbel, C.; Blondiaux, G.

2003-01-01

Among the nondestructive methods for the study of matter, the positrons annihilation method allows to sound the electronic structure of materials by measuring the annihilation characteristics. These characteristics depend on the electronic density as seen by the positon, and on the electron momentums distribution which annihilate with the positon. The positon is sensible to the coulombian potential variations inside a material and sounds preferentially the regions away from nuclei which represent potential wells. The lacunar-type defects (lack of nuclei) represent deep potential wells which can trap the positon up to temperatures close to the melting. This article describes the principles of this method and its application to the characterization of lacunar defects: 1 - positrons: matter probes (annihilation of electron-positon pairs, annihilation characteristics, positrons sources); 2 - positrons interactions in solids (implantation profiles, annihilation states, diffusion and trapping, positon lifetime spectrum: evolution with the concentration of defects); 3 - measurement of annihilation characteristics with two gamma photons (lifetime spectroscopy with the β + 22 Na isotope, spectroscopy of Doppler enlargement of the annihilation line); 4 - determination of the free volume of defects inside or at the surface of materials (annihilation signature in lacunar defects, lacuna, lacunar clusters and cavities, acceptors nature in semiconductors: ionic or lacunar, interface defects, precipitates in alloys); 5 - conclusions. (J.S.)

Application of positron annihilation techniques in non-destructive testing

International Nuclear Information System (INIS)

Zeng Hui; Chen Zhiqiang; Jiang Jing; Xue Xudong; Wu Yichu; Liang Jianping; Liu Xiangbing; Wang Rongshan

2014-01-01

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

On the Possibility of Accelerating Positron on an Electron Wake at SABER

International Nuclear Information System (INIS)

Ischebeck, R.; Joshi, C.; Katsouleas, T.C.; Muggli, P.; Wang, X.

2008-01-01

A new approach for positron acceleration in non-linear plasma wakefields driven by electron beams is presented. Positrons can be produced by colliding an electron beam with a thin foil target embedded in the plasma. Integration of positron production and acceleration in one stage is realized by a single relativistic, intense electron beam. Simulations with the parameters of the proposed SABER facility [1] at SLAC suggest that this concept could be tested there

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

International Nuclear Information System (INIS)

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

2003-01-01

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

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...

An attenuation measurement technique for rotating planar detector positron tomographs

International Nuclear Information System (INIS)

McNeil, P.A.; Julyan, P.J.; Parker, D.J.

1997-01-01

This paper presents a new attenuation measurement technique suitable for rotating planar detector positron tomographs. Transmission measurements are made using two unshielded positron-emitting line sources, one attached to the front face of each detector. Many of the scattered and accidental coincidences are rejected by including only those coincidences that form a vector passing within a predetermined distance of either line source. Some scattered and accidental coincidences are still included, which reduces the measured linear attenuation; in principle their contribution can be accurately estimated and subtracted, but in practice, when limited statistics are available (as is the case with the multi-wire Birmingham positron camera), this background subtraction unacceptably increases the noise. Instead an attenuation image having the correct features can be reconstructed from the measured projections. For objects containing only a few discrete linear attenuation coefficients, segmentation of this attenuation image reduces noise and allows the correct linear attenuation coefficients to be restored by renormalization. Reprojection through the segmented image may then provide quantitatively correct attenuation correction factors of sufficient statistical quality to correct for attenuation in PET emission images. (author)

Reliability of eye lens dosimetry in workers of a positron emission tomography radiopharmaceutical production facility

International Nuclear Information System (INIS)

Silva, Teógenes A. da; Guimarães, Margarete C.; Meireles, Leonardo S.; Teles, Luciana L.D.; Lacerda, Marco Aurélio S.

2016-01-01

A new regulatory statement was issued concerning the eye lens radiation protection of persons in planned exposures. A debate was raised on the adequacy of the dosimetric quantity and on its method of measurement. The aim of this work was to establish the individual monitoring procedure with the EYE-D™ holder and a MCP-N LiF:Mg,Cu,P thermoluminescent chip detector for measuring the personal dose equivalent H_p(3) in workers of a Positron Emission Tomography Radiopharmaceutical Production Facility. - Highlights: • New regulatory statement was issued concerning eye lens radiation protection. • The calibration procedure of dosimeters for measuring H_p(3) was studied on a slab and cylindrical phantoms. • H_p(3) measurements in workers in a radiopharmaceutical production facility were done.

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.

The influence of antioxidant on positron annihilation in polypropylene

International Nuclear Information System (INIS)

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

2003-01-01

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

Positron emission tomography of the lung

International Nuclear Information System (INIS)

Wollmer, P.

1984-01-01

Positron emission tomography enables the distribution of positron emitting isotopes to be imaged in a transverse plane through the body and the regional concentration of the isotope to be measured quantitatively. This thesis reports some applications of positron emission tomography to studies of pulmonary pathophysiology. Measurements in lung phantoms showed that regional lung density could be measured from a transmission tomogram obtained with an external source of positron emitting isotope. The regional, fractional blood volume was measured after labelling the blood with carbon-11-monoxide. Regional extravascular lung density (lung tissue and interstitial water per unit thoracic volume) was obtained by subtracting fractional blood volume from lung density. Measurements in normal subjects revealed large regional variations in lung density and fractional blood volume in the supine posture. Extravascular lung density showed a more uniform distribution. The technique has been used to study patients with chronic interstitial pulmonary oedema, pulmonary sarcoidosis and fibrosis, pulmonary arterial hypertension and patients with intracardiac, left-to-right shunt. Tomographic measurements of pulmonary tissue concentration of radionuclides are difficult, since corrections for the blood content and the inflation of the lung must be applied. A simultaneous measurement of lung density and fractional blood volume allows such corrections to be made and the extravascular tracer concentration to be calculated. This has been applied to measurements of the tissue penetration of carbon-11-labelled erythromycin in patients with lobar pneumonia. (author)

Influence of defects on positron transmission and annihilation in the lithium fluoride crystal

International Nuclear Information System (INIS)

Varisov, A.Z.; Kozlov, V.G.

1984-01-01

The positron implantation profile and the angular distribution of annihilation γ quanta were determined for a lithium fluoride crystal under β + and γ irradiation ( 22 Na source). The positron absorption coefficient of the irradiated crystal was α = 76.2 +- 1.5 cm -1 . The angular distribution had a strong narrow component. After thermal bleaching of the crystal, α = 91.9 +- 1.5 cm -1 , the narrow component made a smaller contribution to the angular distribution, and its half-width increased. The positron mobility was found to be μ = 18 +- 8 cm 2 x V -1 x sec -1 . It is suggested that defects influence in two ways the fate of positrons in the lithium fluoride crystal: free positrons may be trapped by some defects (cationic vacancies) or annihilated in collisions with others (F centers). The defect concentration is estimated

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)

Precision measurement of positron polarization in 68Ga decay based on the use of a new positron polarimeter

International Nuclear Information System (INIS)

Gerber, G.; Newman, D.; Rich, A.; Sweetman, E.

1977-01-01

We report a new measurement of positron polarization (P) in 68 Ga decay. Using a new polarimeter the asymmetry (A) in the decay of positronium in a magnetic field was measured to 5%. When combined with a calculation of the positron depolarization on stopping in MgO powder the overall uncertainty in P is 11%. The most precise prior determination of P was to 12% accuracy. An eventual precision of 1% in A and 0.1% in comparisons of asymmetries from different sources is anticipated. In addition to the 68 Ga work we point out the possible use of the polarimeter in a number of new measurements including a determination of e + polarization in μ + and nuclear decay and in a g - 2 experiment

Positron-annihilation studies of cyclic fatigue damage in metals and aging in polymers

International Nuclear Information System (INIS)

Panigrahi, N.

1987-01-01

Positron-lifetime measurements were performed on fatigued nickel samples. Both ex-situ type of source ( 22 Na source deposited on a nickel foil in a sandwich geometry) and in-situ source ( 58 Co) (produced by proton irradiation of the nickel sample through the reaction 61 Ni(p,α) 58 Co) were used. Specimens were both flexurally and axially fatigued. Spectra were analyzed by resolving into three and four exponentials. In contrast to other studies, positrons are found to be sensitive to defects formed during the cyclic fatiguing. These data were analyzed in terms of various trapping models. The results could be explained by assuming the detrapping of positrons from defect sites. In both types of fatigued specimens the lifetimes of the defect clusters decreased with increasing intensities, showing either the proliferation of smaller clusters or the formation of the new relaxed microstructures. Advantage of using in-situ source for the study of fatigue cycling is stressed. Quenching experiments were performed on polystyrene and polyvinyl acetate samples. In the former the long lifetime (tau 3 ) increased with aging, while the intensity decreased. These indicate that the cavities in the polymers getting bigger while becoming fewer in number

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

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.)

Positron-electron pairs produced in heavy-ion collisions

International Nuclear Information System (INIS)

Ahmad, I.; Austin, Sam. M.; Back, B. B.; Betts, R. R.; Calaprice, F. P.; Chan, K. C.; Chishti, A.; Conner, C. M.; Dunford, R. W.; Fox, J. D.

1999-01-01

The production of positron-electron pairs in collisions of 238 U+ 232 Th at 5.95 MeV/nucleon, and of 238 U+ 181 Ta at 5.95, 6.1, and 6.3 MeV/nucleon, has been studied with the APEX spectrometer at Argonne National Laboratory. Several analyses have been performed to search for sharp structures in sum-energy spectra for positron-electron pairs. Such features have been reported in previous experiments. No statistically convincing evidence for such behavior is observed in the present data. (c) 1999 The American Physical Society

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 production in heavy-ion collisions. II. Application of the formalism to the case of the U+U collision

International Nuclear Information System (INIS)

Tomoda, T.

1982-01-01

The method developed in the preceding paper is applied to the calculation of the spectra of positrons produced in the U + U collision. Matrix elements of the radial derivative operator between adiabatic basis states are calculated in the monopole approximation, with the finite nuclear size taken into account. These matrix elements are then modified for the supercritical case with the use of the analytical method presented in paper I of this series. The coupled differential equations for the occupation amplitudes of the basis states are solved and the positron spectra are obtained for the U + U collision. It is shown that the decomposition of the production probability into a spontaneous and an induced part depends on the definition of the resonance state and cannot be given unambiguously. The results are compared with those obtained by Reinhardt et al

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

Status and Perspectives for a Slow Positron Beam Facility at the HH-NIPNE Bucharest

Science.gov (United States)

Straticiuc, Mihai; Craciun, Liviu Stefan; Constantinescu, Olimpiu; Ghita, Ionica Alina; Ionescu, Cristina; Racolta, Petru Mihai; Vasilescu, Angela; Braic, Viorel; Zoita, Catalin; Kiss, Adrian; Bojin, Dionezie

2009-03-01

The development of a positron annihilation spectroscopy laboratory at the HH-NIPNE Bucharest-to be used for material studies and applications was started in the last 10 years. In the framework of a national research project extended over the last 3 years, was designed a low energy positron accelerator, as a high-vacuum dedicated beam line with two options: a 25 mCi 22NaCl source and in line with the NIPNE-cyclotron or a new intense compact cyclotron. The construction of the beam line was planned as a sequence of modules: source- moderator system; magnetical filter for fast positrons in order to select the positrons energies in the range 0.8-1 keV; a modular system for focusing, transport and acceleration of monoenergetic positrons in the energy range 0.8-50 keV and a CDBS analysis chamber. The moderator proposed-is tungsten as a foil of about 3 μm prepared at the Optoelectronics Institute were put into a thermal treatment vacuum chamber and bombarded with electrons from a 100 W electron gun After the treatment, they were tested for changes of elemental composition of the surface and structure at the Polytechnic University. The structure tests were performed on a DRON 3 M diffractometer, with a Co tube (λKα = 1.7903 A)-the angular regions studied were around 34° (1 0 0) and 69° (2 0 0). In the present time, the trajectories of the positron are going to be simulated with dedicated software (an ion and electron optics simulator). For the coincidence measurements (CDBS) set-up we used a home-made 22NaCl source, by separation without carrier from a metallic Mg target irradiated with 12 MeV protons and separated by columnar cation exchange. A home- made biparametric system for CDBS measurements will be reported, also.

Status and Perspectives for a Slow Positron Beam Facility at the HH—NIPNE Bucharest

Science.gov (United States)

Constantin, Florin; Craciun, Liviu Stefan; Constantinescu, Olimpiu; Ghita, Ionica Alina; Ionescu, Cristina; Racolta, Petru Mihai; Straticiuc, Mihai; Vasilescu, Angela; Braic, Viorel; Zoita, Catalin; Kiss, Adrian; Bojin, Dionezie

2009-03-01

The development of a positron annihilation spectroscopy laboratory at the HH-NIPNE Bucharest-to be used for material studies and applications was started in the last 10 years. In the framework of a national research project extended over the last 3 years, was designed a low energy positron accelerator, as a high-vacuum dedicated beam line with two options: a 25 mCi 22NaCl source and in line with the NIPNE-cyclotron or a new intense compact cyclotron. The construction of the beam line was planned as a sequence of modules: source- moderator system; magnetical filter for fast positrons in order to select the positrons energies in the range 0.8-1 keV; a modular system for focusing, transport and acceleration of monoenergetic positrons in the energy range 0.8-50 keV and a CDBS analysis chamber. The moderator proposed—is tungsten as a foil of about 3 μm prepared at the Optoelectronics Institute were put into a thermal treatment vacuum chamber and bombarded with electrons from a 100 W electron gun After the treatment, they were tested for changes of elemental composition of the surface and structure at the Polytechnic University. The structure tests were performed on a DRON 3 M diffractometer, with a Co tube (λKα = 1.7903 A)—the angular regions studied were around 34° (1 0 0) and 69° (2 0 0). In the present time, the trajectories of the positron are going to be simulated with dedicated software (an ion and electron optics simulator). For the coincidence measurements (CDBS) set-up we used a home-made 22NaCl source, by separation without carrier from a metallic Mg target irradiated with 12 MeV protons and separated by columnar cation exchange. A home- made biparametric system for CDBS measurements will be reported, also.

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.

A high intensity positron beam at the Brookhaven reactor

International Nuclear Information System (INIS)

Weber, M.; Lynn, K.G.; Roellig, L.O.; Mills, A.P. Jr.; Moodenbaugh, A.R.

1987-01-01

We describe a high intensity, low energy positron beam utilizing high specific activity /sup 64/Cu sources (870 Ci/g) produced in a reactor with high thermal neutron flux. Fast-to-slow moderation can be performed in a self moderation mode or with a transmission moderator. Slow positron rates up to 1.6 x 10/sup 8/ e/sup +//s with a half life of 12.8 h are calculated. Up to 1.0 x 10/sup 8/ e/sup +//s have been observed. New developments including a Ne moderator and an on-line isotope separation process are discussed. 21 refs., 9 figs

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

Electron-positron annihilation physics

International Nuclear Information System (INIS)

Foster, B.

1990-01-01

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

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.)

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

International Nuclear Information System (INIS)

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

1995-01-01

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

76 FR 6143 - Draft Guidance on Positron Emission Tomography Drug Applications-Content and Format for New Drug...

Science.gov (United States)

2011-02-03

...; formerly Docket No. 00D-0892] Draft Guidance on Positron Emission Tomography Drug Applications--Content and... Applications for Certain Positron Emission Tomography Drug Products; Availability,'' issued on March 10, 2000... and ANDAs.'' The draft guidance is intended to assist manufacturers of certain positron emission...

Overview and status of the advanced photon source at Argonne National Laboratory

International Nuclear Information System (INIS)

White, M.

1994-01-01

The Advanced Photon Source (APS) is a state-of-the-art synchrotron light source facility dedicated to the production of extremely brilliant X-ray beams for research. Its super-intense X-ray beams will be used for many areas of research including industrial research, biological and medical research, defense-related research, and basic research. The APS X-ray beams will allow scientists to study smaller samples, more complex systems, faster reactions and processes, and gather data at a greater level of detail than has been possible to date. Creation of these beams begins with electron production by an electron with a thermionic cathode. The electrons are accelerated to 200 MeV by a linear accelerator (linac) and then impinge on a tungsten target. resulting in electron-positron pair production. The positrons are accelerated to 450 MeV in the remainder of the linac, then accumulated, damped, and transferred to a synchrotron which increases their energy to 7-GeV. The 7-GeV positrons are injected into a storage ring, where they pass through special magnets and emit X-rays of the desired quality. The APS is under construction at ANL at this time, and will begin operating for users in 1996. The accelerator and experimental facilities are described in this paper, and an overview of some of the experimental programs is given

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.

A new crystal whole-body scanner for positron emitters

International Nuclear Information System (INIS)

Ostertag, H.; Kuebler, W.; Kubesch, R.; Lorenz, W.J.; Woerner, P.

1980-01-01

A multicrystal whole body scanner for positron emitters has been constructed. The annihilation quanta are measured in two opposing detector banks. Each detector bank consists of 64 NaI crystals of 1.5'' diameter x 3'' length. Directly opposing single detectors are in coincidence. The patient moves linearly between the stationary transverse detector banks. The scanning area of the system is 64 x 192 cm 2 . The spatial resolution is 2 cm at a sampling distance of 1 cm. The sensitivity is 6400 counts/s for a pure positron flood source with 1 μCi/cm 2 . The system is controlled by a microcomputer (DEC LSI-11). The scintigrams are shown on a display. Absolute activities can be calculated by mathematical comparison of consecutive emission and transmission scans. The design of the positron scanner and its capacibilities are described. Experimental and initial clinical results are presented. (author)

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.)

Iterative image reconstruction for positron emission tomography based on a detector response function estimated from point source measurements

International Nuclear Information System (INIS)

Tohme, Michel S; Qi Jinyi

2009-01-01

The accuracy of the system model in an iterative reconstruction algorithm greatly affects the quality of reconstructed positron emission tomography (PET) images. For efficient computation in reconstruction, the system model in PET can be factored into a product of a geometric projection matrix and sinogram blurring matrix, where the former is often computed based on analytical calculation, and the latter is estimated using Monte Carlo simulations. Direct measurement of a sinogram blurring matrix is difficult in practice because of the requirement of a collimated source. In this work, we propose a method to estimate the 2D blurring kernels from uncollimated point source measurements. Since the resulting sinogram blurring matrix stems from actual measurements, it can take into account the physical effects in the photon detection process that are difficult or impossible to model in a Monte Carlo (MC) simulation, and hence provide a more accurate system model. Another advantage of the proposed method over MC simulation is that it can easily be applied to data that have undergone a transformation to reduce the data size (e.g., Fourier rebinning). Point source measurements were acquired with high count statistics in a relatively fine grid inside the microPET II scanner using a high-precision 2D motion stage. A monotonically convergent iterative algorithm has been derived to estimate the detector blurring matrix from the point source measurements. The algorithm takes advantage of the rotational symmetry of the PET scanner and explicitly models the detector block structure. The resulting sinogram blurring matrix is incorporated into a maximum a posteriori (MAP) image reconstruction algorithm. The proposed method has been validated using a 3 x 3 line phantom, an ultra-micro resolution phantom and a 22 Na point source superimposed on a warm background. The results of the proposed method show improvements in both resolution and contrast ratio when compared with the MAP

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.

Positron production in heavy ion collisions: Current status of the problem - II

International Nuclear Information System (INIS)

Ahmad, I.; Back, B.B.; Betts, R.R.; Dunford, R.W.; Last, J.; Kutschera, W.; Rhein, M.D.; Schiffer, J.P.; Wilt, P.; Wuosmaa, A.H.

1994-01-01

Narrow peaks have been observed at GSI Darmstadt in the energy spectra of positrons and sum-energy spectra of positron-electron pairs, produced in collisions of very heavy ions. To date, there is no satisfactory explanation of the origin of these lines although many differing models have been proposed. In this contribution, the authors describe the features of a new experiment aimed at the study of the line phenomenon and present the results of their first experiments. The specific goals of their experiment are to clarify the experimental situation regarding the lines through high-resolution, high-statistics data and, by direct measurement of the vector momenta of the peak pairs, to determine their kinematics

Development and applications of the positron microscope

International Nuclear Information System (INIS)

1991-01-01

Progress on the positron microscope during the past year has been steady, and we currently project that initial microscope images can be collected during mid to late summer of 1992. Work during the year has mainly been divided among four areas of effort: hardware construction; power supply and control system development; radioactive source fabrication; and planning of initial experimental projects. Details of progress in these areas will be given below. An initial optical design of the microscope was completed during 1990, but during the past year, significant improvements have been made to this design, and several limiting cases of microscope performance have been evaluated. The results of these evaluations have been extremely encouraging, giving us strong indications that the optical performance of the microscope will be better than originally anticipated. In particular, we should be able to explore ultimate performance capabilities of positron microscopy using our currently planned optical system, with improvements only in the image detector system, and the positron-source/moderator configuration. We should be able to study imaging reemission microscopy with resolutions approaching 10 Angstrom and be able to produce beam spots for rastered microscope work with diameters below the 1000 Angstrom diffusion limit. Because of these exciting new possibilities, we have decided to upgrade several microscope subsystems to levels consistent with ultimate performance earlier in our construction schedule than we had previously intended. In particular, alignment facilities in the optical system, vibration isolation, and power supply and control system flexibility have all been upgraded in their design over the past year

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

Users' guide to the positron camera DDP516 computer system

International Nuclear Information System (INIS)

Bracher, B.H.

1979-08-01

This publication is a guide to the operation, use and software for a DDP516 computer system provided by the Data Handling Group primarily for the development of a Positron Camera. The various sections of the publication fall roughly into three parts. (1) Sections forming the Operators Guide cover the basic operation of the machine, system utilities and back-up procedures. Copies of these sections are kept in a 'Nyrex' folder with the computer. (2) Sections referring to the software written particularly for Positron Camera Data Collection describe the system in outline and lead to details of file formats and program source files. (3) The remainder of the guide, describes General-Purpose Software. Much of this has been written over some years by various members of the Data Handling Group, and is available for use in other applications besides the positron camera. (UK)

High-field penning-malmberg trap: confinement properties and use in positron accumulation

Energy Technology Data Exchange (ETDEWEB)

Hartley, J.H.

1997-09-01

This dissertation reports on the development of the 60 kG cryogenic positron trap at Lawrence Livermore National Laboratory, and compares the trap`s confinement properties with other nonneutral plasma devices. The device is designed for the accumulation of up to 2{times}10{sup 9} positrons from a linear-accelerator source. This positron plasma could then be used in Bhabha scattering experiments. Initial efforts at time-of-flight accumulation of positrons from the accelerator show rapid ({approximately}100 ms) deconfinement, inconsistent with the long electron lifetimes. Several possible deconfinement mechanisms have been explored, including annihilation on residual gas, injection heating, rf noise from the accelerator, magnet field curvature, and stray fields. Detailed studies of electron confinement demonstrate that the empirical scaling law used to design the trap cannot be extrapolated into the parameter regime of this device. Several possible methods for overcoming these limitations are presented.

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

Performance and limitations of positron emission tomography (PET) scanners for imaging very low activity sources.

Science.gov (United States)

Freedenberg, Melissa I; Badawi, Ramsey D; Tarantal, Alice F; Cherry, Simon R

2014-02-01

Emerging applications for positron emission tomography (PET) may require the ability to image very low activity source distributions in the body. The performance of clinical PET scanners in the regime where activity in the field of view is source in the NEMA scatter phantom), the BGO-based scanner significantly outperformed the LSO-based scanner. This was largely due to the effect of background counts emanating from naturally occurring but radioactive (176)Lu within the LSO detector material, which dominates the observed counting rate at the lowest activities. Increasing the lower energy threshold from 350 keV to 425 keV in an attempt to reduce this background did not significantly improve the measured NECR performance. The measured singles rate due to (176)Lu emissions within the scanner energy window was also found to be dependent on temperature, and to be affected by the operation of the CT component, making approaches to correct or compensate for the background more challenging. We conclude that for PET studies in a very low activity range, BGO-based scanners are likely to have better performance because of the lack of significant background. Copyright © 2013 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

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

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

International Nuclear Information System (INIS)

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

1981-01-01

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

Positrons annihilation and the Galactic center

International Nuclear Information System (INIS)

Wallyn, Pierre

1992-01-01

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

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

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

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.

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

International Nuclear Information System (INIS)

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

1994-01-01

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

Specific GMP guidelines for radiopharmaceutical products

International Nuclear Information System (INIS)

2000-01-01

These guidelines are intended to complement those provided in ''Good manufacturing practices for pharmaceutical products'', as well as the GMP for sterile pharmaceutical products. The regulatory procedures necessary to control radiopharmaceutical products are in large part determined by the sources of products and methods of manufacture. Manufacturing procedures within the scope of these guidelines include: preparation of radiopharmaceuticals in hospital radiopharmacies, preparation of radiopharmaceuticals in centralized radiopharmacies, production of radiopharmaceuticals in nuclear centres, institutes or industrial manufacturers, preparation and production of radiopharmaceuticals in Positron Emission Tomography (PET) centres

Surface negative ion production in ion sources

International Nuclear Information System (INIS)

Belchenko, Y.

1993-01-01

Negative ion sources and the mechanisms for negative ion production are reviewed. Several classes of sources with surface origin of negative ions are examined in detail: surface-plasma sources where ion production occurs on the electrode in contact with the plasma, and ''pure surface'' sources where ion production occurs due to conversion or desorption processes. Negative ion production by backscattering, impact desorption, and electron- and photo-stimulated desorption are discussed. The experimental efficiencies of intense surface negative ion production realized on electrodes contacted with hydrogen-cesium or pure hydrogen gas-discharge plasma are compared. Recent modifications of surface-plasma sources developed for accelerator and fusion applications are reviewed in detail

Modeling and prototyping of a flux concentrator for positron capture

International Nuclear Information System (INIS)

Liu, W.; Gai, W.; Wang, H.; Wong, T.

2008-01-01

An adiabatic matching device (AMD) generates a tapered high-strength magnetic field to capture positrons emitted from a positron target to a downstream accelerating structure. The AMD is a key component of a positron source and represents a technical challenge. The International Linear Collider collaboration is proposing to employ a pulsed, normal-conducting, flux-concentrator to generate a 5 Tesla initial magnetic field. The flux-concentrator structure itself and the interactions between the flux-concentrator and the external power supply circuits give rise to a nontrivial system. In this paper, we present a recently developed equivalent circuit model for a flux concentrator, along with the characteristics of a prototype fabricated for validating the model. Using the model, we can obtain the transient response of the pulsed magnetic field and the field profile. Calculations based on the model and the results of measurements made on the prototype are in good agreement.

Undulator-Based Production of Polarized Photons

International Nuclear Information System (INIS)

McDonald, Kirk

2008-01-01

'Project Title: Undulator-Based Production of Polarized Photons' DOE Contract Number: FG02-04ER41355 Principal Investigator: Prof. Kirk McDonald Period of Performance: 09/10/2004 thru 08/31/2006 This award was to fund Princeton's activity on SLAC experiment E166, 'Undulator-Based Production of Polarized Positrons' which was performed at SLAC during June and September 2005. Princeton U. fabricated a magnetic spectrometer for this experiment, and participated in the commissioning, operation, and analysis of the experiment, for which Prof. McDonald was a co-spokesperson. The experiment demonstrated that an intense positron beam with 80% longitudinal polarization could be generated by conversion of MeVenergy circularly polarized photons in a thin target, which photons were generated by passage of high-energy electrons through a helical undulator. This technique has since been adopted as the baseline for the polarized positron source of the proposed International Linear Collider. Results of the experiment have been published in Physical Review Letters, vol 100, p 210801 (2008) (see attached .pdf file), and a longer paper is in preparation.

Advantages of axially aligned crystals used in positron production at future linear colliders

Directory of Open Access Journals (Sweden)

X. Artru

2003-09-01

Full Text Available The characteristics of the electron-photon showers initiated by 2 to 10 GeV electrons aligned along the ⟨111⟩ axis of tungsten crystals are compared with those for the amorphous tungsten. In this energy range, as known, the positron yield at the optimal target thicknesses is larger in a crystal case only by several percent. However, the amount of the energy deposition in a crystal turns out to be considerably (by 20%–50% lower than in an amorphous target providing the same positron yield, while the peak energy-deposition density is approximately of the same magnitude in both cases.

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.)

A method for skin hand exposure by positrons during handling of 18F-FDG radiopharmaceutical

International Nuclear Information System (INIS)

Fueloep, M.; Hudzietzova, J.; Foltinova, L.

2014-01-01

By handling with radiopharmaceutical local irradiation of skin on hands of nearly 20% workers in nuclear medicine is likely to reach more than the legal dose limit for the skin. During syringe preparation and administration of positron radiopharmaceutical 18 F-FDG to patients there are operations that can lead to hand irradiation by positrons. At present, there is insufficient data available about the positron exposure of the hands, which would serve as a basis for the optimization of procedures, including the preparation and administration of positron radiopharmaceuticals. This deficiency impedes the improvement of protective shielding of relevant tools against positrons and the availability of more accurate specifications of the distribution of local exposure of the skin of hands. Presented method of positron dose evaluation is based on pair of TLDs MCP-7 and MCP-Ns with different detection sensitivity to positrons and photons. Detection sensitivities of TLD MCP-Ns and MCP-7 were calculated by Monte Carlo code MCNPX 2.7 in units of skin dose equivalent Hp(0,07).Experimentally has been verified decreasing of skin dose by about factor 5 if positron source 18 F-FDG in syringe, or infusion tube is shielded by a simple additional local shielding from 1 mm polyethylene foil. (authors)

Single-shot positron annihilation lifetime spectroscopy with LYSO scintillators

Science.gov (United States)

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

2016-08-01

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

Single-shot positron annihilation lifetime spectroscopy with LYSO scintillators

Energy Technology Data Exchange (ETDEWEB)

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

2016-08-21

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

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...

Positron emitters for in vivo plant research

International Nuclear Information System (INIS)

Fares, Y.; Goeschl, J.D.; Emran, A.M.; Drew, M.C.; McKinney, C.E.; Musser, R.L.; Strain, B.R.; Jaeger, C.H.

1993-01-01

Adopting a systems approach in analysis of the behavior of a biological system is a prime importance because all factors are considered simultaneously. Feedback is an important phenomenon occurring in dynamic biological systems, enabling appropriate regulatory and control functions to be maintained. In plants, the question whether photosynthesis or translocation controls carbon partitioning and hence productivity is of great agronomic importance, because many efforts are directed at selecting plant varieties with high rates of photosynthesis via genetic engineering and/or selective breeding. By use of short-lived positron emitting isotopes, such as C-11 and N-13, coupled with time-dependent and steady-state compartmental kinetic models, such dynamic biophysical plant problems are being unravelled. Questions such as: (i) source-sink complexities, (ii) experimental tests of the Munich-Horwitz theory of phloem transport (iii) uptake, transport and kinetics of nitrate and ammonium ions, and (iv) effects of ecological factors on growth rates were answered

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

The Intense Slow Positron Beam Facility at the NC State University PULSTAR Reactor

International Nuclear Information System (INIS)

Hawari, Ayman I.; Moxom, Jeremy; Hathaway, Alfred G.; Brown, Benjamin; Gidley, David W.; Vallery, Richard; Xu, Jun

2009-01-01

An intense slow positron beam is in its early stages of operation at the 1-MW open-pool PULSTAR research reactor at North Carolina State University. The positron beam line is installed in a beam port that has a 30-cmx30-cm cross sectional view of the core. The positrons are created in a tungsten converter/moderator by pair-production using gamma rays produced in the reactor core and by neutron capture reactions in cadmium cladding surrounding the tungsten. Upon moderation, slow (∼3 eV) positrons that are emitted from the moderator are electrostatically extracted, focused and magnetically guided until they exit the reactor biological shield with 1-keV energy, approximately 3-cm beam diameter and an intensity exceeding 6x10 8 positrons per second. A magnetic beam switch and transport system has been installed and tested that directs the beam into one of two spectrometers. The spectrometers are designed to implement state-of-the-art PALS and DBS techniques to perform positron and positronium annihilation studies of nanophases in matter.

Automatically controlled correlation spectrometer with a bounded positron beam

International Nuclear Information System (INIS)

Grone, R.

1991-01-01

The spectrometer consists of a frame which carries a fixed arm with collimating slits and a pair of scintillator units positioned against each other, and a movable arm which moves in the horizontal plane and also holds collimating slits and two scintillator units positioned against each other. In the centre of the frame is a shielding cover with a chamber housing a slidable positron source. The end of the cover is fitted with a replaceable diaphragm against which a sample holder is positioned. The chamber with a bounded positron beam can be employed to measure a sample at preselected sites and thus gain information concerning various parts of the sample surface and its inhomogeneity. (M.D.). 3 figs

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.

Dynamics of positron beam from a convertor target while beam additional accelerating in a travelling wave electron linac

International Nuclear Information System (INIS)

Dzhilavyan, L.Z.; Karev, A.I.

1981-01-01

The results of experimental and theoretical investigations of the dynamics of a positron beam produced in a tantalum converter of the 6 mm thickness in the process of beam reacceleration in an electron linac (ELA) are presented. The mean finite positron currents and their dependences on the accelerating electric field are measured. The energy spectra of accelerated positrons are given. A good agreement between the calculated and experimental data is shown. As a result of investigations some peculiarities of positron production on the ELA intersection targets, which are defined by both the initial positron beam parameters from the converter and the dynamics of positron reacceleration in the ELA [ru

Tungsten mesh as positron transmission moderator in a monoenergetic positron beam

International Nuclear Information System (INIS)

Weng, H.M.; Ling, C.C.; Beling, C.D.; Fung, S.; Cheung, C.K.; Kwan, P.Y.; Hui, I.P.

2004-01-01

The slow positron yield has been measured for various tungsten (W) moderator samples from a 22 Na radioactive source. Multi-folded W mesh, W(1 0 0) single crystal foil and W polycrystalline foil samples have been investigated. It is found that the fast to slow conversion efficiency of the W mesh moderator depends on: (1) the annealing pretreatments, (2) the chemical etching duration and (3) the number of the folding layers. With the raw W mesh material having a wire diameter of 20 μm and transmission efficiency of 92.5%, an optimal efficiency of 1.2 x 10 -3 was achieved with 5 min etching duration and a folding number of 12 layers

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)

Recoil effects in multiphoton electron-positron pair creation

International Nuclear Information System (INIS)

Krajewska, K.; Kaminski, J. Z.

2010-01-01

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

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 range in PET imaging: non-conventional isotopes

International Nuclear Information System (INIS)

Jødal, L; Le Loirec, C; Champion, C

2014-01-01

In addition to conventional short-lived radionuclides, longer-lived isotopes are becoming increasingly important to positron emission tomography (PET). The longer half-life both allows for circumvention of the in-house production of radionuclides, and expands the spectrum of physiological processes amenable to PET imaging, including processes with prohibitively slow kinetics for investigation with short-lived radiotracers. However, many of these radionuclides emit ‘high-energy’ positrons and gamma rays which affect the spatial resolution and quantitative accuracy of PET images. The objective of the present work is to investigate the positron range distribution for some of these long-lived isotopes. Based on existing Monte Carlo simulations of positron interactions in water, the probability distribution of the line of response displacement have been empirically described by means of analytic displacement functions. Relevant distributions have been derived for the isotopes 22 Na, 52 Mn, 89 Zr, 45 Ti, 51 Mn, 94m Tc, 52m Mn, 38 K, 64 Cu, 86 Y, 124 I, and 120 I. It was found that the distribution functions previously found for a series of conventional isotopes (Jødal et al 2012 Phys. Med. Bio. 57 3931–43), were also applicable to these non-conventional isotopes, except that for 120 I, 124 I, 89 Zr, 52 Mn, and 64 Cu, parameters in the formulae were less well predicted by mean positron energy alone. Both conventional and non-conventional range distributions can be described by relatively simple analytic expressions. The results will be applicable to image-reconstruction software to improve the resolution. (paper)

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

Application of positron annihilation spectroscopy for investigation of reactor steels

International Nuclear Information System (INIS)

Sojak, S.; Slugen, V.; Petriska, M.; Stacho, M.; Veternikova, J.; Sabelova, V.; Egger, W.; Ravelli, L.

2013-01-01

Our work is focused on the study of radiation damage simulated by ion implantations and thermal treatment evaluation of RAFM steels in the form of binary Fe-Cr model alloys. In order to study the microstructure recovery after ion irradiation, we applied an approach for restoration of initial physical and mechanical characteristics of structural materials in the form of thermal annealing, with the goal to decrease the size and amount of accumulated defects. The experimental analysis of material damage at microstructural level was performed by the pulsed low energy positron system (PLEPS) [1] at the high intensity positron source NEPOMUC at the Munich research reactor FRM-II. (authors)

Quantum mechanical theory of positron production in heavy ion collisions with nuclear contact

International Nuclear Information System (INIS)

Heinz, U.

1986-01-01

The interplay between atomic and nuclear interactions in heavy ion collisions with nuclear contact is studied. The general theoretical description is outlined and analyzed in a number of different limits (semiclassical approximation, DWBA, fully quantal description). The two most important physical mechanisms for generating atomic-nuclear interference, i.e., energy conservation and the introduction of additional phase shifts by nuclear reactions, are extracted. The resulting typical coupling matrix elements are analyzed for their relative importance in atomic and nuclear excitations. The description of nuclear influence on atomic excitations in terms of a classical time delay caused by nuclear reactions is reviewed, and its relationship to the underlying quantal character of the nuclear reaction is discussed. The theory is applied to spontaneous positron emission in supercritical heavy-ion collisions (Z/sub tot/ ≥ 173). It is shown that nuclear contact can lead to line structures in the positron energy spectra if the probability distribution for nuclear delay times caused by the contact has contributions for T ≥ 10 -19 sec. We explicitly evaluate a model where a pocket in the internuclear potential near the touching configuration leads to formation of nuclear molecules, and predict a resonance-like excitation function for the positron peak. 25 refs., 7 figs

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)

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

Energy Technology Data Exchange (ETDEWEB)

Sizun, P

2007-04-15

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

Development and applications of time-bunched and velocity-selected positron beams

DEFF Research Database (Denmark)

Merrison, J.P.; Charlton, M.; Aggerholm, P.

2003-01-01

the buncher was used to compress positron pulses produced from an electron accelerator-based beam. Computer simulations of particle trajectories in the buncher have been performed resulting in a detailed evaluation of the factors that govern and limit the time resolution of the instrument. A sector magnet...... for propagation of the applied voltage pulse along the electrode system and to facilitate operation at frequencies up to 100 kHz. A parabolic potential distribution for time focusing was used. Tests with a dc positron beam produced from a radioactive source are described, together with measurements in which...

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)

What can we learn from a sharply falling positron fraction?

Directory of Open Access Journals (Sweden)

Delahaye Timur

2015-01-01

Full Text Available Recent results from the AMS-02 data have confirmed that the cosmic ray positron fraction increases with energy between 10 and 200 GeV. This quantity should not exceed 50%, and it is hence expected that it will either converge towards 50% or fall. We study the possibility that future data may show the positron fraction dropping down abruptly to the level expected with only secondary production, and forecast the implications of such a feature in term of possible injection mechanisms that include both Dark Matter and pulsars.

Interpretation of recent positron-electron measurements between 20 and 800 MeV

International Nuclear Information System (INIS)

Pellerin, C.J.; Hartman, R.C.

1975-01-01

The recent positron and negatron spectra measured by Hartman and Pellerin (see pages 402-407) are discussed with regard to the problem of solar modulation. At energies above 180 MeV, the spherically symmetric Fokker-Planck equation with a diffusion coefficient proportional to particle rigidity provides reasonable fits to both the positron and total electron data. At energies below 180 MeV the data are consistent with a continuation of the same diffusion coefficient and local source of negatrons, or a change in the diffusion coefficient to a constant value. (orig.) [de

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)

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

Energy Technology Data Exchange (ETDEWEB)

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

2009-11-15

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

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

The Chandra Source Catalog: Source Properties and Data Products

Science.gov (United States)

Rots, Arnold; Evans, Ian N.; Glotfelty, Kenny J.; Primini, Francis A.; Zografou, Panagoula; Anderson, Craig S.; Bonaventura, Nina R.; Chen, Judy C.; Davis, John E.; Doe, Stephen M.; Evans, Janet D.; Fabbiano, Giuseppina; Galle, Elizabeth C.; Gibbs, Danny G., II; Grier, John D.; Hain, Roger; Hall, Diane M.; Harbo, Peter N.; He, Xiang Qun (Helen); Houck, John C.; Karovska, Margarita; Kashyap, Vinay L.; Lauer, Jennifer; McCollough, Michael L.; McDowell, Jonathan C.; Miller, Joseph B.; Mitschang, Arik W.; Morgan, Douglas L.; Mossman, Amy E.; Nichols, Joy S.; Nowak, Michael A.; Plummer, David A.; Refsdal, Brian L.; Siemiginowska, Aneta L.; Sundheim, Beth A.; Tibbetts, Michael S.; van Stone, David W.; Winkelman, Sherry L.

2009-09-01

The Chandra Source Catalog (CSC) is breaking new ground in several areas. There are two aspects that are of particular interest to the users: its evolution and its contents. The CSC will be a living catalog that becomes richer, bigger, and better in time while still remembering its state at each point in time. This means that users will be able to take full advantage of new additions to the catalog, while retaining the ability to back-track and return to what was extracted in the past. The CSC sheds the limitations of flat-table catalogs. Its sources will be characterized by a large number of properties, as usual, but each source will also be associated with its own specific data products, allowing users to perform mini custom analysis on the sources. Source properties fall in the spatial (position, extent), photometric (fluxes, count rates), spectral (hardness ratios, standard spectral fits), and temporal (variability probabilities) domains, and are all accompanied by error estimates. Data products cover the same coordinate space and include event lists, images, spectra, and light curves. In addition, the catalog contains data products covering complete observations: event lists, background images, exposure maps, etc. This work is supported by NASA contract NAS8-03060 (CXC).

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.)

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

Polarized γ source based on Compton backscattering in a laser cavity

Directory of Open Access Journals (Sweden)

V. Yakimenko

2006-09-01

Full Text Available We propose a novel gamma source suitable for generating a polarized positron beam for the next generation of electron-positron colliders, such as the International Linear Collider (ILC, and the Compact Linear Collider (CLIC. This 30-MeV polarized gamma source is based on Compton scattering inside a picosecond CO_{2} laser cavity generated from electron bunches produced by a 4-GeV linac. We identified and experimentally verified the optimum conditions for obtaining at least one gamma photon per electron. After multiplication at several consecutive interaction points, the circularly polarized gamma rays are stopped on a target, thereby creating copious numbers of polarized positrons. We address the practicality of having an intracavity Compton-polarized positron source as the injector for these new colliders.

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

Design and commissioning of the photon monitors and optical transport lines for the advanced photon source positron accumulator ring

International Nuclear Information System (INIS)

Berg, W.; Yang, B.; Lumpkin, A.; Jones, J.

1996-01-01

Two photon monitors have been designed and installed in the positron accumulator ring (PAR) of the Advanced Photon Source. The photon monitors characterize the beam's transverse profile, bunch length, emittance, and energy spread in a nonintrusive manner. An optical transport line delivers synchrotron light from the PAR out of a high radiation environment. Both charge-coupled device and fast-gated, intensified cameras are used to measure the transverse beam profile (0.11 - 1 mm for damped beam) with a resolution of 0.06 mm. A streak camera (θ τ =I ps) is used to measure the bunch length which is in the range of 0.3-1 ns. The design of the various transport components and commissioning results of the photon monitors will be discussed

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...

Single-quantum annihilation of positrons with shell-bound atomic electrons

International Nuclear Information System (INIS)

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

1991-01-01

The single-quantum annihilation of positrons has been studied experimentally with a positron beam and a thin lead target, at energies 1 MeV and higher. Spectral peaks corresponding to the K, L, and M shells have been resolved and observed distinctly for the first time. The shell ratios L/K and M/K have been determined. An analysis of the L peak has yielded the (LII+LIII)/L ratio. The first measurements of the directional distributions of the annihilation quanta of the three individual electron shells are also reported. The results are in agreement with theory. They also point out the potential for applying the phenomena to the development of a tunable, highly directional gamma-ray source

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.

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)

Positron annihilation study of Pd contacts on impurity-doped GaN

International Nuclear Information System (INIS)

Lee, Jong-Lam; Kim, Jong Kyu; Weber, Marc H.; Lynn, Kelvin G.

2001-01-01

Pd contacts on both n-type and p-type GaN were studied using positron annihilation spectroscopy, and the results were used to interpret the role of Ga vacancies on the band bending below the contacts. The concentration of Ga vacancy in Si-doped GaN was higher than that in the Mg-doped one. In Si-doped GaN, implanted positrons were annihilated at the nearer surface region and the interface of Pd/n-type GaN was detected by positrons clearly shifted toward the surface of Pd. This suggests that Ga vacancies could act as an interface state, pinning the Fermi level at the interface of Pd with GaN, leading to the production of a negative electric field below the interface. [copyright] 2001 American Institute of Physics

High energy resolution and first time-dependent positron annihilation induced Auger electron spectroscopty

International Nuclear Information System (INIS)

Mayer, Jakob

2010-01-01

It was the aim of this thesis to improve the existing positron annihilation induced Auger spectrometer at the highly intense positron source NEPOMUC (NEutron induced POsitron source MUniCh) in several ways: Firstly, the measurement time for a single spectrum should be reduced from typically 12 h to roughly 1 h or even less. Secondly, the energy resolution, which amounted to ΔE/E∼10%, should be increased by at least one order of magnitude in order to make high resolution positron annihilation induced Auger spectroscopy (PAES)-measurements of Auger transitions possible and thus deliver more information about the nature of the Auger process. In order to achieve these objectives, the PAES spectrometer was equipped with a new electron energy analyzer. For its ideal operation all other components of the Auger analysis chamber had to be adapted. Particularly the sample manipulation and the positron beam guidance had to be renewed. Simulations with SIMION registered ensured the optimal positron lens parameters. After the adjustment of the new analyzer and its components, first measurements illustrated the improved performance of the PAES setup: Firstly, the measurement time for short overview measurements was reduced from 3 h to 420 s. The measurement time for more detailed Auger spectra was shortened from 12 h to 80 min. Secondly, even with the reduced measurement time, the signal to noise ratio was also enhanced by one order of magnitude. Finally, the energy resolution was improved to ΔE/E 2,3 VV-transition with PAES. Thus, within this thesis two objectives were achieved: Firstly, the PAES spectrometer was renewed and improved by at least one order of magnitude with respect to the signal to noise ratio, the measurement time and the energy resolution. Secondly, several measurements have been carried out, demonstrating the high performance of the spectrometer. Amongst them are first dynamic PAES measurements and a high resolution measurement of the CuM 2,3 VV

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.

An asymmetric distribution of positrons in the Galactic disk revealed by γ-rays

International Nuclear Information System (INIS)

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

2008-01-01

Gamma-ray line radiation at 511 keV is the signature of electron positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk (∼ 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies ≥20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the positrons. Although it had long been suspected that electron-positron pair plasmas may exist in X-ray binaries, it was not evident that many of the positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511 keV line. For these models, our result implies that up to a few times 10 41 positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter. (authors)

An asymmetric distribution of positrons in the Galactic disk revealed by {gamma}-rays

Energy Technology Data Exchange (ETDEWEB)

Weidenspointner, G; Skinner, G; Jean, P; Knoedlseder, J; Von Ballmoos, P; Bignami, G [UPS, CNRS, Ctr Etud Spatiale Rayonnements, Toulouse 4, (France); Weidenspointner, G; Diehl, R; Strong, A [Max Planck Inst Extraterr Phys, D-85741 Garching, (Germany); Weidenspointner, G [MPI Halbleiterlab, D-81739 Munich, (Germany); Skinner, G [NASA, CRESST, Greenbelt, MD 20771 (United States); Skinner, G [NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 (United States); Skinner, G [Univ Maryland, Dept Astron, College Pk, MD 20742 (United States); Cordier, B; Schanne, S [CEA Saclay, DSM, DAPNIA, SAp, F-91191 Gif Sur Yvette, (France); Winkler, Ch [ESA, ESTEC, SCI SA, NL-2201 AZ Noordwijk, (Netherlands); Bignami, G [IUSS, I-27100 Pavia, (Italy)

2008-07-01

Gamma-ray line radiation at 511 keV is the signature of electron positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk ({approx} 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies {>=}20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the positrons. Although it had long been suspected that electron-positron pair plasmas may exist in X-ray binaries, it was not evident that many of the positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511 keV line. For these models, our result implies that up to a few times 10{sup 41} positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter. (authors)

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)

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...

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.)

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)

Positron induced scattering cross sections for hydrocarbons relevant to plasma

Science.gov (United States)

Singh, Suvam; Antony, Bobby

2018-05-01

This article explores positron scattering cross sections by simple hydrocarbons such as ethane, ethene, ethyne, propane, and propyne. Chemical erosion processes occurring on the surface due to plasma-wall interactions are an abundant source of hydrocarbon molecules which contaminate the hydrogenic plasma. These hydrocarbons play an important role in the edge plasma region of Tokamak and ITER. In addition to this, they are also one of the major components in the planetary atmospheres and astrophysical mediums. The present work focuses on calculation of different positron impact interactions with simple hydrocarbons in terms of the total cross section (Qtot), elastic cross section (Qel), direct ionization cross section (Qion), positronium formation cross section (Qps), and total ionization cross section (Qtion). Knowing that the positron-plasma study is one of the trending fields, the calculated data have diverse plasma and astrophysical modeling applications. A comprehensive study of Qtot has been provided where the inelastic cross sections have been reported for the first time. Comparisons are made with those available from the literature, and a good agreement is obtained with the measurements.

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

Electron irradiation-induced defects in ZnO studied by positron annihilation

International Nuclear Information System (INIS)

Chen, Z.Q.; Maekawa, M.; Kawasuso, A.; Sakai, S.; Naramoto, H.

2006-01-01

ZnO crystals were subjected to 3 MeV electron irradiation up to a high dose of 5.5x10 18 cm -2 . The production and recovery of vacancy defects were studied by positron annihilation spectroscopy. The increase of positron lifetime and Doppler broadening S parameter after irradiation indicates introduction of V Zn related defects. Most of these vacancies are annealed at temperatures below 200 o C. However, after annealing at around 400 o C, secondary defects are produced. All the vacancy defects are annealed out at around 700 o C

A study on 2% PdO/Al2O3 by means of free positron annihilation technique in the solid surface layer

International Nuclear Information System (INIS)

Shi Zikang; Huang Cunping

1992-01-01

The relationship between heat treatment and space structure of the PdO layer in 2% PdO/Al 2 O 3 was studied by the positrons from 2 2N a radiative source, and grain size was calculated by the positron annihilation parameters, demonstrating that the free positron annihilation technique for the solid surface layer can be applied can be applied to catalyst research

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

Science.gov (United States)

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

2018-01-01

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

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.

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)

Properties of the electron cloud in a high-energy positron and electron storage ring

International Nuclear Information System (INIS)

Harkay, K.C.; Rosenberg, R.A.

2003-01-01

Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in a positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.

Positron Annihilation in Thunderstorms Observed by ILDAS.

Science.gov (United States)

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

2017-12-01

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

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

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)

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)

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.

Experimental and computational study of the injection of antiprotons into a positron plasma for antihydrogen production

International Nuclear Information System (INIS)

Amole, C.; Capra, A.; Menary, S.; Ashkezari, M. D.; Hayden, M. E.; Baquero-Ruiz, M.; Little, A.; So, C.; Zhmoginov, A.; Bertsche, W.; Butler, E.; Cesar, C. L.; Silveira, D. M.; Charlton, M.; Deller, A.; Eriksson, S.; Isaac, C. A.; Madsen, N.; Napoli, S. C.; Shields, C. R.

2013-01-01

One of the goals of synthesizing and trapping antihydrogen is to study the validity of charge–parity–time symmetry through precision spectroscopy on the anti-atoms, but the trapping yield achieved in recent experiments must be significantly improved before this can be realized. Antihydrogen atoms are commonly produced by mixing antiprotons and positrons stored in a nested Penning-Malmberg trap, which was achieved in ALPHA by an autoresonant excitation of the antiprotons, injecting them into the positron plasma. In this work, a hybrid numerical model is developed to simulate antiproton and positron dynamics during the mixing process. The simulation is benchmarked against other numerical and analytic models, as well as experimental measurements. The autoresonant injection scheme and an alternative scheme are compared numerically over a range of plasma parameters which can be reached in current and upcoming antihydrogen experiments, and the latter scheme is seen to offer significant improvement in trapping yield as the number of available antiprotons increases.

Experimental and computational study of the injection of antiprotons into a positron plasma for antihydrogen production

Energy Technology Data Exchange (ETDEWEB)

Amole, C.; Capra, A.; Menary, S. [Department of Physics and Astronomy, York University, Toronto, M3J 1P3 Ontario (Canada); Ashkezari, M. D.; Hayden, M. E. [Department of Physics, Simon Fraser University, Burnaby, V5A 1S6 British Columbia (Canada); Baquero-Ruiz, M.; Little, A.; So, C.; Zhmoginov, A. [Department of Physics, University of California, Berkeley, California 94720 (United States); Bertsche, W. [Department of Physics, College of Science, Swansea University, SA2 8PP Swansea (United Kingdom); School of Physics and Astronomy, University of Manchester, M13 9PL Manchester (United Kingdom); Daresbury Laboratory, Cockcroft Institute, WA4 4AD Warrington (United Kingdom); Butler, E. [Physics Department, CERN, CH-1211 Geneva 23 (Switzerland); Cesar, C. L.; Silveira, D. M. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941 (Brazil); Charlton, M.; Deller, A.; Eriksson, S.; Isaac, C. A.; Madsen, N.; Napoli, S. C.; Shields, C. R. [Department of Physics, College of Science, Swansea University, SA2 8PP Swansea (United Kingdom); Collaboration: ALPHA Collaboration; and others

2013-04-15

One of the goals of synthesizing and trapping antihydrogen is to study the validity of charge-parity-time symmetry through precision spectroscopy on the anti-atoms, but the trapping yield achieved in recent experiments must be significantly improved before this can be realized. Antihydrogen atoms are commonly produced by mixing antiprotons and positrons stored in a nested Penning-Malmberg trap, which was achieved in ALPHA by an autoresonant excitation of the antiprotons, injecting them into the positron plasma. In this work, a hybrid numerical model is developed to simulate antiproton and positron dynamics during the mixing process. The simulation is benchmarked against other numerical and analytic models, as well as experimental measurements. The autoresonant injection scheme and an alternative scheme are compared numerically over a range of plasma parameters which can be reached in current and upcoming antihydrogen experiments, and the latter scheme is seen to offer significant improvement in trapping yield as the number of available antiprotons increases.

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

Science.gov (United States)

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

2005-01-01

small- scale magnetic field structure is appropriate to the generation of "jitter" radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation has different properties than synchrotron radiation calculated assuming a uniform magnetic field. The jitter radiation resulting from small-scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

Initial results from the Donner 600 crystal positron tomograph

International Nuclear Information System (INIS)

Derenzo, S.E.; Huesman, R.H.; Cahoon, J.L.; Geyer, A.; Uber, D.; Vuletich, T.; Budinger, T.F.

1986-10-01

We describe a positron tomograph using a single ring of 600 close-packed 3 mm wide bismuth germanate (BGO) crystals coupled to 14 mm phototubes. The phototube preamplifier circuit derives a timing pulse from the first photoelectron, and sends it to address and coincidence circuits only if the integrated pulse height is within a pre-set window. The timing delays and pulse height windows for all 600 detectors and the coincidence timing windows are computer adjustable. An orbiting positron source is used for transmission measurements and a look-up table is used to reject scattered and random coincidences that do not pass through the source. Data can be acquired using a stationary mode for 1.57 mm lateral sampling or the two-position clam sampling mode for 0.79 mm lateral sampling. High maximum data rates are provided by 45 parallel coincidence circuits and 4 parallel histogram memory units. With two-position sampling and 1.57 mm bins, the reconstructed point spread function (PSF) of a 0.35 mm diam 22 Na wire source at the center of the tomograph is circular with 2.9 mm full-width at half-maximum (fwhm) and the PSF at a distance of 8 cm from the center is elliptical with a radial fwhm of 4.0 mm and tangential fwhm of 3.0 mm. 12 refs., 6 figs., 3 tabs

Initial results from the Donner 600 crystal positron tomograph

International Nuclear Information System (INIS)

Derenzo, S.E.; Huesman, R.H.; Cahoon, J.L.; Geyer, A.; Uber, D.; Vuletich, T.; Budinger, T.F.

1987-01-01

The authors describe a positron tomography using a single ring of 600 close-packed 3 mm wide bismuth germanate (BGO) crystals coupled to 14 mm phototubes. The phototube preamplifier circuit derives a timing pulse from the first photoelectron, and sends it to address and coincidence circuits only if the integrated pulse height is within a pre-set window. The timing delays and pulse height windows for all 600 detectors and the coincidence timing windows are computer adjustable. An orbiting positron source is used for transmission measurements and look-up table is used to reject scattered and random coincidences that do not pass through the source. Data can be acquired using a stationary mode for 1.57 mm lateral sampling or the two-position clam sampling mode for 0.79 mm lateral sampling. High maximum data rates are provided by 45 parallel coincidence circuits and 4 parallel histogram memory units. With two-position sampling and 1.57 mm bins, the reconstructed point spread function (PSF) of a 0.35 mm diam /sup 22/Na wire source at the center of the tomograph is circular with 2.9 mm full-width at half-maximum (fwhm) and the PSF at a distance of 8 cm from the center is elliptical with a radial fwhm of 4.0 mm and tangential fwhm of 3.0 mm

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.

Pumping Electron-Positron Pairs from a Well Potential.

Science.gov (United States)

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

2016-04-29

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

21 CFR 212.71 - What actions must I take if a batch of PET drug product does not conform to specifications?

Science.gov (United States)

2010-04-01

... PRACTICE FOR POSITRON EMISSION TOMOGRAPHY DRUGS (Eff. 12-12-2011) Finished Drug Product Controls and..., operations, records, complaints, and any other relevant sources of information concerning the nonconforming...

Head-on collision between positron acoustic waves in homogeneous and inhomogeneous plasmas

Science.gov (United States)

Alam, M. S.; Hafez, M. G.; Talukder, M. R.; Ali, M. Hossain

2018-05-01

The head-on collision between positron acoustic solitary waves (PASWs) as well as the production of rogue waves (RWs) in homogeneous and PASWs in inhomogeneous unmagnetized plasma systems are investigated deriving the nonlinear evolution equations. The plasmas are composed of immobile positive ions, mobile cold and hot positrons, and hot electrons, where the hot positrons and hot electrons are assumed to follow the Kappa distributions. The evolution equations are derived using the appropriate coordinate transformation and the reductive perturbation technique. The effects of concentrations, kappa parameters of hot electrons and positrons, and temperature ratios on the characteristics of PASWs and RWs are examined. It is found that the kappa parameters and temperature ratios significantly modify phase shifts after head-on collisions and RWs in homogeneous as well as PASWs in inhomogeneous plasmas. The amplitudes of the PASWs in inhomogeneous plasmas are diminished with increasing kappa parameters, concentration and temperature ratios. Further, the amplitudes of RWs are reduced with increasing charged particles concentration, while it enhances with increasing kappa- and temperature parameters. Besides, the compressive and rarefactive solitons are produced at critical densities from KdV equation for hot and cold positrons, while the compressive solitons are only produced from mKdV equation for both in homogeneous and inhomogeneous plasmas.

Positron annihilation spectroscopy in defects of semiconductors

International Nuclear Information System (INIS)

Fujinami, Masanori

2002-01-01

Interaction of positron and defects, application to research of defects of semiconductor and defects on the surface of semiconductor are explained. Cz (Czochralski)-Si single crystal with 10 18 cm -3 impurity oxygen was introduced defects by electron irradiation and the positron lifetime was measured at 90K after annealing. The defect size and recovery temperature were determined by the lifetime measurement. The distribution of defects in the depth direction is shown by S-E curve. The chemical state analysis is possible by CBS (Coincidence Doppler Broadening) spectra. The application to silicon-implanted (100 keV, 2x10 15 cm -2 ) silicon and oxygen-implanted (180 keV, 2x10 15 cm -2 ) silicon are stated. On the oxygen-implanted silicon, the main product was V2 after implantation, V 6 O 2 at 600degC and V 10 O 6 at 800degC. (S.Y.)

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

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

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

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

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...

Flash lamp annealing of tungsten surfaces marks a new way to optimized slow positron yields

Science.gov (United States)

Anwand, W.; Johnson, J. M.; Butterling, M.; Wagner, A.; Skorupa, W.; Brauer, G.

2013-06-01

Tungsten in the form of a mono-crystalline foil with an optimum thickness of about 2 μm is often used as a positron moderator in mono-energetic positron beams with 22Na positron sources. The efficiency of such a moderator strongly depends on its prior heat treatment, i.e. an annealing procedure with considerable difficulty at temperatures of about 2000 °C under vacuum conditions. Flash lamp annealing (FLA) has been tested as new method to quickly anneal W foils in order to produce easy manageable, low-cost moderators with a high efficiency. With FLA, just the surface of a W foil is heated above the melting point (3422°C) within 1 to 3 ms, i.e. without melting the whole foil volume. In this way, a surface cleaning is reached connected with a considerable increase in the positron diffusion length. Conventional polycrystalline W foils of 9 μm ± 25% thickness, heat treated by FLA, were characterized and tested as positron moderators. First promising tests result in a moderator efficiency of ~3*10-4 and clearly demonstrate that FLA is also applicable to tungsten meshes.

Electron irradiation-induced defects in ZnO studied by positron annihilation

Energy Technology Data Exchange (ETDEWEB)

Chen, Z.Q. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan)]. E-mail: zhiquanchen@hotmail.com; Maekawa, M. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Kawasuso, A. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Sakai, S. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Naramoto, H. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan)

2006-04-01

ZnO crystals were subjected to 3 MeV electron irradiation up to a high dose of 5.5x10{sup 18} cm{sup -2}. The production and recovery of vacancy defects were studied by positron annihilation spectroscopy. The increase of positron lifetime and Doppler broadening S parameter after irradiation indicates introduction of V {sub Zn} related defects. Most of these vacancies are annealed at temperatures below 200 {sup o}C. However, after annealing at around 400 {sup o}C, secondary defects are produced. All the vacancy defects are annealed out at around 700 {sup o}C.

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

Quality control procedures in positron tomography

International Nuclear Information System (INIS)

Spinks, T.; Jones, T.; Heather, J.; Gilardi, M.

1989-01-01

The derivation of physiological parameters in positron tomography relies on accurate calibration of the tomograph. Normally, the calibration relates image pixel count density to the count rate from an external blood counter per unit activity concentration in each device. The quality control of the latter is simple and relies on detector stability assessed by measurement of a standard source of similar geometry to a blood sample. The quality control of the tomographic data depends on (i) detector stability, (ii) uniformity of calibration and normalisation sources and (iii) reproducibility of the attenuation correction procedure. A quality control procedure has been developed for an 8 detector ring (15 transaxial plane) tomograph in which detector response is assessed by acquiring data from retractable transmission ring sources. These are scanned daily and a print out of detector efficiencies is produced as well as changes from a given data. This provides the raw data from which decisions on recalibration or renormalisation are made. (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

Bruno Touschek: From Betatrons to Electron-Positron Colliders

Science.gov (United States)

Bernardini, Carlo; Pancheri, Giulia; Pellegrini, Claudio

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

The Advanced Photon Source list of parameters

International Nuclear Information System (INIS)

Bizek, H.M.

1996-07-01

The Advanced Photon Source (APS) is a third-generation synchrotron radiation source that stores positrons in a storage ring. The choice of positrons as accelerating particles was motivated by the usual reason: to eliminate the degradation of the beam caused by trapping of positively charged dust particles or ions. The third-generation synchrotron radiation sources are designed to have low beam emittance and many straight sections for insertion devices. The parameter list is comprised of three basic systems: the injection system, the storage ring system, and the experimental facilities system. The components of the injection system are listed according to the causal flow of positrons. Below we briefly list the individual components of the injection system, with the names of people responsible for managing these machines in parentheses: the linac system; electron linac-target-positron linac (Marion White); low energy transport line from linac to the PAR (Michael Borland); positron accumulator ring or PAR (Michael Borland); low energy transport line from PAR to injector synchrotron (Michael Borland); injector synchrotron (Stephen Milton); high energy transport line from injector synchrotron to storage ring (Stephen Milton). The storage ring system, managed by Glenn Decker, uses the Chasman-Green lattice. The APS storage ring, 1104 m in circumference, has 40 periodic sectors. Six are used to house hardware and 34 serve as insertion devices. Another 34 beamlines emit radiation from bending magnets. The experimental facilities system's parameters include parameters for both an undulator and a wiggler

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