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.)

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

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)

PF slow positron source

International Nuclear Information System (INIS)

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

1993-01-01

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

Intense positron beam and its application to surface science

International Nuclear Information System (INIS)

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

1992-01-01

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

Preliminary considerations of an intense slow positron facility based on a 78Kr loop in the high flux isotopes reactor

International Nuclear Information System (INIS)

Hulett, L.D. Jr.; Donohue, D.L.; Peretz, F.J.; Montgomery, B.H.; Hayter, J.B.

1990-01-01

Suggestions have been made to the National Steering Committee for the Advanced Neutron Source (ANS) by Mills that provisions be made to install a high intensity slow positron facility, based on a 78 Kr loop, that would be available to the general community of scientists interested in this field. The flux of thermal neutrons calculated for the ANS is E + 15 sec -1 m -2 , which Mills has estimated will produce 5 mm beam of slow positrons having a current of about 1 E + 12 sec -1 . The intensity of such a beam will be a least 3 orders of magnitude greater than those presently available. The construction of the ANS is not anticipated to be complete until the year 2000. In order to properly plan the design of the ANS, strong considerations are being given to a proof-of-principle experiment, using the presently available High Flux Isotopes Reactor, to test the 78 Kr loop technique. The positron current from the HFIR facility is expected to be about 1 E + 10 sec -1 , which is 2 orders of magnitude greater than any other available. If the experiment succeeds, a very valuable facility will be established, and important formation will be generated on how the ANS should be designed. 3 refs., 1 fig

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.)

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

Design for a high intensity slow positron facility using forward scattered radiation from an electron linear accelerator

International Nuclear Information System (INIS)

Hulett, L.D. Jr.; Lewis, T.A.; Alsmiller, R.G. Jr.; Peelle, R.; Pendyale, S.; Dale, J.M.; Rosseel, T.M.

1986-01-01

A tungsten moderator will be placed behind the target of the Oak Ridge Electron Linear Accelerator (ORELA) to convert gamma radiation to slow positrons. These will be extracted and led through evacuated solenoids to an experiment room. A Penning trap will be used to extend the slow positron pulses to achieve duty factors of 10% or greater. The facility will be used for atomic and molecular physics studies, positron microscopy, and materials research. Operations will be inexpensive and will not interfere with the normal function of ORELA, the measurement of neutron cross sections by flight-time spectrometry

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

Polymeric membrane studied using slow positron beam

International Nuclear Information System (INIS)

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

2008-01-01

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

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)

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

The generation and development of the moderators for slow positron beam

International Nuclear Information System (INIS)

Yu Weizhong; Yuan Jiaping

2001-01-01

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

Concepts for a slow-positron target at the advanced photon source

International Nuclear Information System (INIS)

Lessner, E.; White, M.

1997-01-01

The Advanced Photon Source (APS) linear accelerator beam could be used to produce slow positrons during the hours between the storage ring injection cycles. Initial concepts for the design of a target that is optimized for slow-positron production are discussed, and simulation results are presented. Some possible ways to increase the nominal linac beam power for improved slow-positron production are also discussed

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)

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.

Generation of slow positron beam and beam bunching

International Nuclear Information System (INIS)

Azuma, O.; Satoh, T.; Shitoh, M.; Kaneko, N.; Kawaratani, T.; Hara, O.

1994-01-01

Two items are described in this report. One is about the outline of our slow positron beam system, which has been fabricated as a commercial prototype. The other is about the calculation result of positron beam bunching, which will be an additional function to the system. (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)

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...

Elastic scattering of slow positrons by helium

International Nuclear Information System (INIS)

Amusia, M.Ya.; Cherepkov, N.A.; Chernysheva, L.V.; Shapiro, S.G.

1976-01-01

The s-, p-, d- and f-wave phaseshifts for elastic scattering of slow positrons by He are calculated using a simplified version of the random phase approximation with exchange, with virtual positronium formation effect taken into account. (author)

Design of an efficient pulsing system for a slow-positron beam

Energy Technology Data Exchange (ETDEWEB)

Oshima, Nagayasu; Suzuki, Takenori [National Lab. for High Energy Physics, Tsukuba, Ibaraki (Japan); Kanazawa, Ikuzo; Ito, Yasuo

1996-07-01

In this paper, a new design of a pulsed slow positron system for PALS measurement is reported. By using this new system, it will be possible to obtain a short-pulsed slow-positron beam with high efficiency ({>=}50%) and a relatively low minimum energy ({approx}200 eV). This system is also easy to construct on the laboratory scale. (J.P.N.)

Production of slow-positron beams with an electron linac

International Nuclear Information System (INIS)

Howell, R.H.; Alvarez, R.A.; Stanek, M.

1982-01-01

Intense, pulsed beams of low-energy positrons have been produced by a high-energy beam from an electron linac. The production efficiency for low-energy positrons has been determined for electrons with 60 to 120 MeV energy, low-energy positron beams from a linac can be of much higher intensity than those beams currently derived from radioactive sources

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.

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.)

Current status and future view of generation of slow positrons and applications of available antiparticles

International Nuclear Information System (INIS)

Tomimasu, T.

1988-01-01

The positron is the antielectron and annihilates with an electron from the surrounding medium dominantly into two 511 keV γ-rays. The two annihilation γ-rays are modified by the momentum and energy distributions of the electrons in the annihilation site. The annihilation rates are proportional to the electron density in the site. Therefore, the two annihilation γ-rays and the average lifetime of positrons can provide unique informations on a wide variety of problems in condensed matter physics. Slow positrons with narrow energy spread are more useful, compared with white positrons from radioactive isotopes, to the positron annihilation experiment, the low energy positron diffraction, the positron microscope and so on. This review describes the current status and future view on (1) the applications of the positron annihilation to the condensed matter physics, (2) the generation of slow positrons using electron linacs, (3) the positron beam handling system including the pulse stretcher with a Penning trap and (4) the applications of available antiparticles including monoenergetic positrons, muons, pions and antiprotons to the analysis and evaluation of materials, the energy storage and positronium radiations. (author)

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).

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.

Generation of an intense pulsed positron beam and its applications

International Nuclear Information System (INIS)

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

1994-01-01

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

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.

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

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

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

International Nuclear Information System (INIS)

Suzuki, Takenori

2004-01-01

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

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)

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

International Nuclear Information System (INIS)

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

2011-01-01

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

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.

The correlations of electrochromism and thermochromism of tungsten oxide films studied by slow positron beam

International Nuclear Information System (INIS)

Ma Chuangxin; Zhou Chunlan; Zhang Zhiming; Wang Baoyi; Wei Long

2004-01-01

Electrochromic (EC) and thermochromic (TC) tungsten oxide (WO 3 ) films, deposited by magnetron sputtering and vacuum thermal evaporation, were studied systematically by means of slow positron measurements. The S parameters of colored amorphous WO 3 film and crystalline WO 3 film behaved quite similarly in the processes of thermochromism and electrochromism, little influenced by the different deposition methods. It indicates that the coloration processes under various external conditions are correlated with each other. It also shows that the slow positron beam technique may play a particular role in the study of chromogenic materials. (orig.)

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)

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

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

Defect layer in SiO2-Sic interface proved by a slow positron beam

International Nuclear Information System (INIS)

Maekawa, M.; Kawasuso, A.; Yoshikawa, M.; Miyashita, A.; Suzuki, R.; Ohdaira, T.

2006-01-01

The structure of the SiO 2 -4ph-SiC interface layer produced by dry oxidation has been studied by positron annihilation spectroscopy using slow positron beams. From Doppler broadening measurements, the interface layer was clearly distinguished from the SiO 2 and SiC layers and was observed to be defective. At the interface layer, a single long positron lifetime of 451 ps, which is close to the second lifetime in the SiO 2 layer, was obtained, thus suggesting that the structure of the interface layer resembles an amorphous SiO 2 network. A comparison was made between the obtained electron momentum distribution at the interface layer and the theoretical calculation. It was found that positrons annihilate with oxygen valence electrons. By annealing after the oxidation, the annihilation probability of the positrons with oxygen valence electrons and the number of interface traps decreased in the same temperature range, thus suggesting a correlation between interface traps and positron annihilation sites

Slow positron beam study of hydrogen ion implanted ZnO thin films

Science.gov (United States)

Hu, Yi; Xue, Xudong; Wu, Yichu

2014-08-01

The effects of hydrogen related defect on the microstructure and optical property of ZnO thin films were investigated by slow positron beam, in combination with x-ray diffraction, infrared and photoluminescence spectroscopy. The defects were introduced by 90 keV proton irradiation with doses of 1×1015 and 1×1016 ions cm-2. Zn vacancy and OH bonding (VZn+OH) defect complex were identified in hydrogen implanted ZnO film by positron annihilation and infrared spectroscopy. The formation of these complexes led to lattice disorder in hydrogen implanted ZnO film and suppressed the luminescence process.

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...

Tunable pores in mesoporous silica films studied using a pulsed slow positron beam

International Nuclear Information System (INIS)

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

2007-01-01

Positron annihilation lifetime spectroscopy (PALS) based on a pulsed slow positron beam was applied to study mesoporous silica films, synthesized using amphiphilic PEO-PPO-PEO triblock copolymers as structure-directing agents. The pore size depends on the loading of different templates. Larger pores were formed in silica films templated by copolymers with higher molecular-weights. Using 2-dimensional PALS, open porosity of silica films was also found to be influenced by the molecular-weight as well as the ratio of hydrophobic PPO moiety of the templates

Slow positron beam study of hydrogen ion implanted ZnO thin films

International Nuclear Information System (INIS)

Hu, Yi; Xue, Xudong; Wu, Yichu

2014-01-01

The effects of hydrogen related defect on the microstructure and optical property of ZnO thin films were investigated by slow positron beam, in combination with x-ray diffraction, infrared and photoluminescence spectroscopy. The defects were introduced by 90 keV proton irradiation with doses of 1×10 15 and 1×10 16 ions cm −2 . Zn vacancy and OH bonding (V Zn +OH) defect complex were identified in hydrogen implanted ZnO film by positron annihilation and infrared spectroscopy. The formation of these complexes led to lattice disorder in hydrogen implanted ZnO film and suppressed the luminescence process. - Highlights: • Hydrogen introduced by ion implantation can form hydrogen-related defect complex. • V Zn +OH defect complex is identified by positron annihilation and IR spectroscopy. • Irradiation defects suppress the luminescence process

Proton energy dependence of slow neutron intensity

International Nuclear Information System (INIS)

Teshigawara, Makoto; Harada, Masahide; Watanabe, Noboru; Kai, Tetsuya; Sakata, Hideaki; Ikeda, Yujiro

2001-01-01

The choice of the proton energy is an important issue for the design of an intense-pulsed-spallation source. The optimal proton beam energy is rather unique from a viewpoint of the leakage neutron intensity but no yet clear from the slow-neutron intensity view point. It also depends on an accelerator type. Since it is also important to know the proton energy dependence of slow-neutrons from the moderators in a realistic target-moderator-reflector assembly (TMRA). We studied on the TMRA proposed for Japan Spallation Neutron Source. The slow-neutron intensities from the moderators per unit proton beam power (MW) exhibit the maximum at about 1-2 GeV. At higher proton energies the intensity per MW goes down; at 3 and 50 GeV about 0.91 and 0.47 times as low as that at 1 GeV. The proton energy dependence of slow-neutron intensities was found to be almost the same as that of total neutron yield (leakage neutrons) from the same bare target. It was also found that proton energy dependence was almost the same for the coupled and decoupled moderators, regardless the different moderator type, geometry and coupling scheme. (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.)

Present status of positron factory project

International Nuclear Information System (INIS)

Okada, S.; Sunaga, H.; Kaneko, H.; Tachibana, H.; Yotsumoto, K.; Okamoto, J.

1992-01-01

The Japan Atomic Energy Research Institute, JAERI, has been promoting design studies for the 'Positron Factory', in which linac-based intense monoenergetic positron beams are planned to be applied to advanced materials characterization and new fields of basic research. A tentative goal of the beam intensity is 10 10 s -1 , which is assumed to be realized with an electron linac of 100 kW class with a beam energy around 100 to 150 MeV. We performed a technical survey on the dedicated linac. It confirmed technical feasibility of manufacturing the state-of-the-art machine. We have been carrying out a design study of the target. A new concept of the target design is proposed, which is expected to supply intense slow positron beams simultaneously for multiple beam channels, on the basis of Monte Carlo simulations. (author)

Exploring of defects in He+ implanted Si(100) by slow positron beam

International Nuclear Information System (INIS)

Zhang Tianhao; Weng Huimin; Fan Yangmei; Du Jiangfeng; Zhou Xianyi; Han Rongdian; Zhang Miao; Lin Chenglu

2001-01-01

Si(100) crystal implanted by 5 x 10 16 cm -2 , 140 keV He + was probed by slow positron beam, and defect distribution along depth was obtained from the relation between S parameter and positron incidence energy. The near surface region of implanted sample was only slightly damaged. Small vacancies and vacancy clusters less than 1 nm in diameter were the dominant defects, while the deeper region around the He + projected range was heavily damaged and had dense larger helium micro-bubbles and microvoids. Thermal anneal study at different temperatures showed that low temperature annealing could remove most vacancy-type defects effectively. However, annealing at high temperature enlarged the diameters of micro-bubbles and microvoids

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.

Intense low energy positron beams

International Nuclear Information System (INIS)

Lynn, K.G.; Jacobsen, F.M.

1993-01-01

Intense positron beams are under development or being considered at several laboratories. Already today a few accelerator based high intensity, low brightness e + beams exist producing of the order of 10 8 - 10 9 e + /sec. Several laboratories are aiming at high intensity, high brightness e + beams with intensities greater than 10 9 e + /sec and current densities of the order of 10 13 - 10 14 e + sec - 1 cm -2 . Intense e + beams can be realized in two ways (or in a combination thereof) either through a development of more efficient B + moderators or by increasing the available activity of B + particles. In this review we shall mainly concentrate on the latter approach. In atomic physics the main trust for these developments is to be able to measure differential and high energy cross-sections in e + collisions with atoms and molecules. Within solid state physics high intensity, high brightness e + beams are in demand in areas such as the re-emission e + microscope, two dimensional angular correlation of annihilation radiation, low energy e + diffraction and other fields. Intense e + beams are also important for the development of positronium beams, as well as exotic experiments such as Bose condensation and Ps liquid studies

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.

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...

14th International Workshop on Slow Positron Beam Techniques and Applications

International Nuclear Information System (INIS)

2017-01-01

These proceedings arose from the 14th International Workshop on Slow Positron Beam Techniques (SLOPOS14), which was held at Kunibiki Messe, Matsue, Shimane prefecture, Japan, from the 22nd—27th May 2016. Meetings in the SLOPOS series are held every three years. The SLOPOS workshop series has traditionally been devoted to investigations on the production of positron and positronium beams, their fundamental physics and chemistry, and their applications to materials such as metals, semiconductors and soft matter. During the workshop numerous applications using positron and positronium beams were also presented, clearly demonstrating the usefulness of such beams to the determination of surface structure, defect characterization as well as to fundamental scientific studies. For SLOPOS14 the main subjects of the workshop included the following: • Positron transport and beam technology • Pulsed positron beams and positron traps • Defect profiling in bulk and layered structures • Nano structures, porous materials and thin films • Surface and interface analysis • Positronium formation, emission and beams • Positron and positronium interactions with atoms and molecules • Many positrons and anti-hydrogen • Improvement of experimental techniques 106 delegates from 14 countries participated in the SLOPOS14, including 31 student delegates, which was a most encouraging sign for the future. The scientific program comprised 5 plenary talks, 22 invited talks, 32 contributed talks and 46 posters presented during two poster sessions. Student prizes were awarded for the best presented scientific contributions by 4 students from University of College London, Universität der Bundeswehr München and The University of Tokyo. On a sad note, delegates paid tribute to the contributions of our recently deceased colleagues, Prof. A. Seeger, Prof. R.N. West, Prof. T.C. Griffith, and Prof. Z. Tang. Memorial talks were given and a one minute silence was observed before the

PREFACE 12th International Workshop on Slow Positron Beam Techniques

Science.gov (United States)

Buckman, Stephen; Sullivan, James; White, Ronald

2011-01-01

Preface These proceedings arose from the 12th International Workshop on Slow Positron Beam Techniques (SLOPOS12), which was held on Magnetic Island, North Queensland, Australia, between 1-6th August 2010. Meetings in the SLOPOS series are held (roughly) every three years and have now been held on (almost) all continents, indicating the truly international nature of the field. SLOPOS12 marked the second time that the Workshop had been held in the southern hemisphere, and the first time in Australia. SLOPOS12 attracted 122 delegates from 16 countries. Most encouraging was the attendance of 28 student delegates, and that about half of the overall delegates were early career researchers - a good sign for the future of our field. We also enjoyed the company of more than a dozen partners and families of delegates. In a slight departure from previous SLOPOS meetings, the International Advisory Committee approved a broader scope of scientific topics for inclusion in the program for the 2010 Workshop. This broader scope was intended to capture the applications of positrons in atomic, molecular and biomedical areas and was encapsulated in the byeline for SLOPOS-12: The 12th International Workshop on Slow Positron Beam Techniques for Solids, Surfaces, Atoms and Molecules. The scientific and social program for the meeting ran over 6 days with delegates gathering on Sunday August 1st and departing on August 6th. The scientific program included plenary, invited, contributed and student lectures, the latter being the subject of a student prize. In all there were 53 oral presentations during the week. There were also two poster sessions, with 63 posters exhibited, and a prize was awarded for the best poster by a student delegate. The standard of the student presentations, both oral and posters, was outstanding, so much so that the judging panel recommended an additional number of prizes be awarded. Topics that were the focus of invited presentations and contributed papers at

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

Science.gov (United States)

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

2013-06-01

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

Direct comparison of photoluminescence lifetime and defect densities in ZnO epilayers studied by time-resolved photoluminescence and slow positron annihilation techniques

Energy Technology Data Exchange (ETDEWEB)

Koida, T. [Institute of Applied Physics and Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573 (Japan); NICP, ERATO, Japan Science and Technology Agency (JST), Chiyoda 102-0071 (Japan); Uedono, A. [Institute of Applied Physics and Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573 (Japan); Tsukazaki, A. [Institute for Materials Research, Tohoku University, Sendai 980-8755 (Japan); Sota, T. [Department of Electrical, Engineering and Bioscience, Waseda University, Shinjuku 169-8555 (Japan); Kawasaki, M. [Institute for Materials Research, Tohoku University, Sendai 980-8755 (Japan); Combinatorial Materials Exploration and Technology (COMET), Tsukuba 305-0044 (Japan); Chichibu, S.F. [NICP, ERATO, Japan Science and Technology Agency (JST), Chiyoda 102-0071 (Japan); Photodynamics Research Center, RIKEN, Sendai 980-0868 (Japan)

2004-09-01

The roles of point defects and defect complexes governing nonradiative processes in ZnO epilayers were studied using time-resolved photoluminescence (PL) and slow positron annihilation measurements. The density or size of Zn vacancies (V{sub Zn}) decreased and the nonradiative PL lifetime ({tau}{sub nr}) increased with higher growth temperature for epilayers grown on a ScAlMgO{sub 4} substrate. Accordingly, the steady-state free excitonic PL intensity increased with increase in {tau}{sub nr} at room temperature. The use of a homoepitaxial substrate further decreased the V{sub Zn} concentration. However, no perfect relation between {tau}{sub nr} and the density or size of V{sub Zn} or other positron scattering centers was found. The results indicated that nonradiative recombination processes are governed not solely by single point defects, but by certain defect species introduced by the presence of V{sub Zn} such as vacancy complexes. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Positron emission intensities in the decay of 64Cu, 76Br and 124I

International Nuclear Information System (INIS)

Qaim, S.M.; Bisinger, T.; Hilgers, K.; Nayak, D.; Coenen, H.H.

2007-01-01

The relatively long-lived positron emitters 64 Cu (t 1/2 = 12.7 h), 76 Br (t 1/2 = 16.2 h) and 124 I (t 1/2 = 4.18 d) are finding increasing applications in positron emission tomography (PET). For precise determination of their positron emission intensities, each radionuclide was prepared via a charged particle induced reaction in a ''no-carrier-added'' form and with high radionuclidic purity. It was then subjected to γ-ray and X-ray spectroscopy as well as to anticoincidence beta and γγ-coincidence counting. The positron emission intensities measured were: 64 Cu (17.8 ± 0.4)%, 76 Br (58.2 ± 1.9)% and 124 I (22.0 ± 0.5)%. The intensity of the weak 1346 keV γ-ray emitted in the decay of 64 Cu was determined as (0.54 ± 0.03)%. Some implications of the precisely determined nuclear data are discussed. (orig.)

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

International Nuclear Information System (INIS)

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

2009-01-01

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

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

Recent progress in annihilation related studies by slow positrons

International Nuclear Information System (INIS)

Lynn, K.G.

1989-01-01

The field of slow-positron physics has expanded significantly in the last few years to include particles and atomic physics but has been most extensive in those associated with condensed matter or material science. This can primarily be attributed to the development of more efficient moderators. These moderators have been associated with both laboratory- and facility-based beams. In this paper I will focus only on the material-science aspects however. Positron can and are being used to examine all of the various fields. I feel the contribution in all these areas will be significant. I will primarily discuss those developments that have been developed in the area of interface science; a field that has both scientific and technological importance and has a limited number of nondestructive probes used in studying a buried interface. Interfaces are technologically important for applications such as electrical properties and mechanical properties. Such applications help to motivate the fundamental research of interface properties and dynamics, which is necessary to develop the basic understanding of new types of interfaces. The role of the interface is also important since it limited length of this paper. Results will be presented in interface studies that have occurred in the last year, including some unpublished results obtained at Brookhaven over the past few months. This field is in the early stages and I expect that the full utilization of this relatively new probe can be anticipated in the next few years. 17 refs., 7 figs

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

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 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

Experimental investigation of slow-positron emission from 4H-SiC and 6H-SiC surfaces

International Nuclear Information System (INIS)

Ling, C.C.; Beling, C.D.; Fung, S.; Weng, H.M.

2002-01-01

Slow-positron emission from the surfaces of as-grown n-type 4H-SiC and 6H-SiC (silicon carbide) with a conversion efficiency of ∼10 -4 has been observed. After 30 min of 1000 deg. C annealing in forming gas, the conversion efficiency of the n-type 6H-SiC sample was observed to be enhanced by 75% to 1.9x10 -4 , but it then dropped to ∼10 -5 upon a further 30 min annealing at 1400 deg. C. The positron work function of the n-type 6H-SiC was found to increase by 29% upon 1000 deg. C annealing. For both p-type 4H-SiC and p-type 6H-SiC materials, the conversion efficiency was of the order of ∼10 -5 , some ten times lower than that for the n-type materials. This was attributed to the band bending at the p-type material surface which caused positrons to drift away from the positron emitting surface. (author)

High intensity positron program at LLNL

International Nuclear Information System (INIS)

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

1999-01-01

Lawrence Livermore National Laboratory (LLNL) is the home of the world'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

Physical design of the positron induced auger electron spectrometer

International Nuclear Information System (INIS)

Qin Xiubo; Jiang Xiaopan; Wang Ping; Yu Runsheng; Wang Baoyi; Wei Long

2009-01-01

Positron Annihilation Induced Auger Electron Spectroscopy (PAES) has several advantages over those excited by X-rays, high energy electrons or neutrons, such as excellent surface selectivity, high signal-to-noise ratio, low radiation damage,etc. A physical design of time of flight PAES (TOF-PAES) apparatus based on the Beijing Intense Slow Positron Beam (BIPB) is described in this paper. The positrons and electrons are transported in a 4 x 10 -3 T uniform magnetic field, and the gradient of magnetic field is designed to pluralize the Auger electrons emitted with 2π angle. The Auger electron energy is adjusted by a Faraday cage to optimize the energy resolution,which can be better than 2 eV. (authors)

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

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.)

Evolution of voids in Al+-implanted ZnO probed by a slow positron beam

International Nuclear Information System (INIS)

Chen, Z.Q.; Maekawa, M.; Yamamoto, S.; Kawasuso, A.; Yuan, X.L.; Sekiguchi, T.; Suzuki, R.; Ohdaira, T.

2004-01-01

Undoped ZnO single crystals were implanted with aluminum ions up to a dose of 10 15 Al + /cm 2 . Vacancy defects in the implanted layers were detected using positron lifetime and Doppler broadening measurements with slow positron beams. It shows that vacancy clusters, which are close to the size of V 8 , are generated by implantation. Postimplantation annealing shows that the Doppler broadening S parameter increases in the temperature range from 200 deg. C to 600 deg. C suggesting further agglomeration of vacancy clusters to voids. Detailed analyses of Doppler broadening spectra show formation of positronium after 600 deg. C annealing of the implanted samples with doses higher than 10 14 Al + /cm 2 . Positron lifetime measurements further suggest that the void diameter is about 0.8 nm. The voids disappear and the vacancy concentration reaches the detection limit after annealing at 600-900 deg. C. Hall measurement shows that the implanted Al + ions are fully activated with improved carrier mobility after final annealing. Cathodoluminescence measurements show that the ultraviolet luminescence is much stronger than the unimplanted state. These findings also suggest that the electrical and optical properties of ZnO become much better by Al + implantation and subsequent annealing

Ion-implantation induced defects in ZnO studied by a slow positron beam

International Nuclear Information System (INIS)

Chen, Z.Q.; Maekawa, M.; Kawasuso, A.; Sekiguchi, T.; Suzuki, R.

2004-01-01

Introduction and annealing behavior of defects in Al + -implanted ZnO have been studied using an energy variable slow positron beam. Vacancy clusters are produced after Al + -implantation. With increasing ion dose above 10 14 Al + /cm 2 the implanted layer is amorphized. Heat treatment up to 600 C enhances the creation of large voids that allow the positronium formation. The large voids disappear accompanying the recrystallization process by further heat treatment above 600 C. Afterwards, implanted Al impurities are completely activated to contribute to the n-type conduction. The ZnO crystal quality is also improved after recrystallization. (orig.)

Ion-implantation induced defects in ZnO studied by a slow positron beam

Energy Technology Data Exchange (ETDEWEB)

Chen, Z.Q.; Maekawa, M.; Kawasuso, A. [Japan Atomic Energy Research Institute, Gunma (Japan); Sekiguchi, T. [National Inst. for Materials Science, Tsukuba, Ibaraki (Japan); Suzuki, R. [National Inst. of Advanced Industrial Science and Technology, Tsukuba, Ibaraki (Japan)

2004-07-01

Introduction and annealing behavior of defects in Al{sup +}-implanted ZnO have been studied using an energy variable slow positron beam. Vacancy clusters are produced after Al{sup +}-implantation. With increasing ion dose above 10{sup 14} Al{sup +}/cm{sup 2} the implanted layer is amorphized. Heat treatment up to 600 C enhances the creation of large voids that allow the positronium formation. The large voids disappear accompanying the recrystallization process by further heat treatment above 600 C. Afterwards, implanted Al impurities are completely activated to contribute to the n-type conduction. The ZnO crystal quality is also improved after recrystallization. (orig.)

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

Science.gov (United States)

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

2010-04-01

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

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

International Nuclear Information System (INIS)

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

2010-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2010-04-01

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

Ion-irradiated polymer studied by a slow positron beam

International Nuclear Information System (INIS)

Kobayashi, Yoshinori; Kojima, Isao; Hishita, Shunichi; Suzuki, Takenori.

1995-01-01

Poly (aryl-ether-ether ketone) (PEEK) films were irradiated with 1MeV and 2MeV 0 + ions and the positron annihilation Doppler broadening was measured as a function of the positron energy. The annihilation lines recorded at relatively low positron energies were found to become broader with increasing the irradiation dose, suggesting that positronium (Ps) formation may be inhibited in the damaged regions. A correlation was observed between the Doppler broadening and spin densities determined by electron spin resonance (ESR). (author)

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.

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

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

Science.gov (United States)

Suzuki, Ryoichi; Ohdaira, Toshiyuki

2002-03-01

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

Defect characterization of CdTe thin films using a slow positron beam

International Nuclear Information System (INIS)

Neretina, S.; Grebennikov, D.; Mascher, P.; Hughes, R.A.; Weber, M.; Lynn, K.G.; Simpson, P.J.; Preston, J.S.

2007-01-01

Cadmium Telluride (CdTe) is the most well established II-VI compound largely due to its use as a photonic material. Existing applications, as well as those under consideration, are demanding increasingly stringent control of the material properties. The deposition of high quality thin films is of the utmost importance to such applications. In this regard, we present a report detailing the role of lattice mismatch in determining the film quality. Thin films were deposited on a wide variety of substrate materials using the pulsed laser deposition technique. Common to all substrates was the strong tendency towards the preferential alignment of CdTe's (111) planes parallel to the substrate's surface. X-ray diffraction analysis, however, revealed that the crystalline quality varied dramatically depending upon the substrate used with the best results yielding a single crystal film. This tendency also manifested itself in the surface morphology with higher structural perfection yielding smoother surfaces. Slow positron beam techniques revealed a strong correlation between the defect concentration and the degree of structural perfection. Simulations of the data using the POSTRAP 5 program were used to calculate the defect concentration in relative (atom -1 ) and absolute units and to determine the diffusion lengths of the positrons in the film. All of these characterization techniques point towards lattice mismatch as being the dominant mechanism in determining the quality of CdTe films. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Slow positron beam study of corrosion behavior of AM60B magnesium alloy in NaCl solution

International Nuclear Information System (INIS)

Yang, W.; Zhu, Z.J.; Wang, J.J.; Wu, Y.C.; Zhai, T.; Song, G.-L.

2016-01-01

Highlights: • Positron annihilation is a sensitive tool to characterize the corrosion layer. • The interfacial voids promoted the formation of Mg(OH) 2 corrosion layer. • Mg(OH) 2 precipitated during early corrosion stage provided a temporary protection. - Abstract: The corrosion behavior of super vacuum die-cast AM60B magnesium alloys immersed in a 5 wt% NaCl solution was investigated by slow positron beam technique, XRD, XPS, SEM and potentiodynamic polarization tests. The XRD and XPS results indicated that Mg(OH) 2 was main corrosion product in the salt solution. With prolonging the immersion time, a significant decrease of Doppler-broadened annihilation line-width parameter near the surface after corrosion was observed and interpreted that the pre-existing interfacial voids between oxide film and matrix might promote the formation of Mg(OH) 2 corrosion layer. Polarization tests found that Mg(OH) 2 could provide a temporary protection.

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

CERN Document Server

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

2000-01-01

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

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

CERN Multimedia

CERN. Geneva

2008-01-01

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

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 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.

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

Science.gov (United States)

Lynn, K. G.; Lutz, H.

1980-11-01

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

Bremsstrahlung pair-production of positrons with low neutron background

International Nuclear Information System (INIS)

Lessner, E.

1998-01-01

Minimization of component activation is highly desirable at accelerator-based positron sources. Electrons in the 8- to 14-MeV energy range impinging on a target produce photons energetic enough to create electron-positron pairs; however, few of the photons are energetic enough to produce photoneutrons. Slow positron production by low-energy electrons impinging on a multilayer tungsten target with and without electromagnetic extraction between the layers was studied by simulation. The neutron background from 14-MeV electrons is expected to be significantly lower than that encountered with higher-energy electron beams. Numerical results are presented and some ideas for a low-activation slow-positron source are discussed

Performance of a slow positron beam using a hybrid lens design

International Nuclear Information System (INIS)

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

2006-01-01

The University of Hong Kong positron beam employs conventional magnetic field transport to the target, but has a special hybrid lens design around the positron moderator that allows the beam to be focused to millimeter spot sizes at the target. The good focusing capabilities of the beam are made possible by extracting work-function positrons from the moderator in a magnetic field free region using a conventional Soa lens thus minimizing beam canonical angular momentum. An Einzel lens is used to focus the positrons into the magnetic funnel at the end of transportation magnetic field while at the same time bringing up the beam energy to the intermediate value of 7.5 keV. The beam is E x B filtered at this intermediate energy. The final beam energy is obtained by floating the Soa-Einzel system, E x B filter and flight tube, and accelerating the positrons just before the target. External beam steering saddle coils fine tune the position, and the magnetic field around the target chamber is adjusted so as to keep one of the beam foci always on the target. The system is fully computer controlled. Variable energy-Doppler broadened annihilation radiation (VEDBAR) data for a GaN sample are shown which demonstrate the performance of the positron beam system

Plasma Wakefield Acceleration of an Intense Positron Beam

Energy Technology Data Exchange (ETDEWEB)

Blue, B

2004-04-21

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

Positron emission tomography suggests that the rate of progression of idiopathic parkinsonism is slow

International Nuclear Information System (INIS)

Bhatt, M.H.; Snow, B.J.; Martin, W.R.; Pate, B.D.; Ruth, T.J.; Calne, D.B.

1991-01-01

The authors performed sequential positron emission tomography scans with 6-[18F]fluoro-L-dopa in 9 patients with idiopathic parkinsonism and 7 age-matched normal control subjects to compare changes in the nigrostriatal dopaminergic pathway over time. The mean interval between the scans was 3.3 years for the group with idiopathic parkinsonism and 3.9 years for the control subjects. The scans were analyzed by calculating the ratio of striatal to background radioactivity. Both groups showed statistically significant reductions of striatal uptake over the interval. The rate of decrease was almost identical in each group (p = 0.6). They infer that the usual rate of loss of integrity of the dopaminergic nigrostriatal pathway in patients with idiopathic parkinsonism is slow and the rate of change between the two groups was comparable

Development of a transmission positron microscope

Energy Technology Data Exchange (ETDEWEB)

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

2011-07-21

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

Positron 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)

Nanometer cavities studied by positron annihilation

International Nuclear Information System (INIS)

Mogensen, O.E.

1992-01-01

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

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-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.)

Demonstration of electron clearing effect by means of a clearing electrode in high-intensity positron ring

International Nuclear Information System (INIS)

Suetsugu, Y.; Fukuma, H.; Wang, L.; Pivi, M.; Morishige, A.; Suzuki, Y.; Tsukamoto, M.; Tsuchiya, M.

2009-01-01

In the beam pipe of high-intensity positron/proton storage rings, undesired electron clouds may be first produced by photoelectrons and the ionization of residual gases; then the clouds increase by the secondary electron emission. In this study, a strip-line clearing electrode has been developed to mitigate the electron-cloud effect in high-intensity positron/proton storage rings. The electrode is composed of a thin tungsten layer with a thickness of 0.1 mm formed on a thin alumina ceramic layer with a thickness of 0.2 mm. The narrow alumina gap between the electrode and the beam pipe decreases the beam impedance and also enhances the heat transfer from the electrode to the beam pipe. A test model has been installed in the KEK B-factory (KEKB) positron ring, along with an electron monitor with a retarding grid. The electron density in a field free region decreased by one order of magnitude was observed on the application of ±500 V to the electrode at a beam current of 1.6 A with 1585 bunches. The reduction in the electron density was more drastic in a vertical magnetic field of 0.77 T, that is, the electron density decreased by several orders by applying +500 V to the electrode at the same beam current. This experiment is the first experiment demonstrating the principle of the clearing electrode that is used to mitigate the electron-cloud effect in a positron ring.

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)

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

International Nuclear Information System (INIS)

Shimazu, Akira

2009-01-01

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

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.

Positron beam studies of solids and surfaces: A summary

International Nuclear Information System (INIS)

Coleman, P.G.

2006-01-01

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

Positron beam studies of solids and surfaces: A summary

Science.gov (United States)

Coleman, P. G.

2006-02-01

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

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)

Depth profiling of boron implanted silicon by positron beam

International Nuclear Information System (INIS)

Oevuenc, S.

2004-01-01

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

Trapping and accumulation of positrons from a pulsed beam produced by a linear accelerator for gravitational interaction of antimatter study

International Nuclear Information System (INIS)

Grandemange, Pierre

2013-01-01

The Gravitational Behaviour of Anti-hydrogen at Rest experiment - GBAR - is designed to perform a direct measurement of the weak equivalence principle on antimatter by measuring the acceleration (g-bar) of anti-hydrogen atoms in free fall. Its originality is to produce H-bar + ions and use sympathetic cooling to achieve μK temperature. H-bar + ions are produced by the reactions: p-bar + Ps → H-bar + e - , and H-bar + Ps → H-bar + + e - , where p-bar is an antiproton, Ps stands for positronium (the bound-state of a positron and an electron), H-bar is the anti-hydrogen and H-bar + the anti-ion associated. To produce enough Ps atoms, 2*10 10 positrons must be impinged on a porous SiO 2 target within 100 ns. Such an intense flux requires the accumulation (collection and cooling) of the positrons in a particle trap. This thesis describes the injector being commissioned at CEA Saclay for GBAR. It consists of a Penning-Malmberg trap (moved from RIKEN) fed by a slow positron beam. A 4.3 MeV linear accelerator shooting electrons on a tungsten target produces the pulsed positron beam, which is moderated by a multi-grid tungsten moderator. The slow positron flux is 10 4 e + /pulse, or 2*10 6 e + /s at 200 Hz. This work presents the first ever accumulation of low-energy positrons produced by an accelerator (rather than a radioactive source) and their cooling by a prepared reservoir of 2*10 10 cold electrons. (author) [fr

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...

Measurement of positron reemission from thin single-crystal W(100) films

International Nuclear Information System (INIS)

Chen, D.M.; Lynn, K.G.; Pareja, R.; Nielsen, B.

1985-01-01

Epitaxial thin single-crystal (100) tungsten films 1000, 2500, and 5000 A thick have been fabricated by high-vacuum electron-beam evaporation. These films were subsequently used as thin-film moderators for the study of the positron-transmission-reemission process with a variable-energy (0--80 keV) monoenergetic positron beam in an ultrahigh-vacuum system. The films were shown to be routinely cleanable by heating first in oxygen (10 -6 Torr) and then in vacuum (10 -9 Torr). Transmission and back reemission of slow positrons from these surfaces was observed. The positron work function, phi/sub +/ has been determined to be approx. =3.0 eV ( +- 0.3 eV). The transmission slow positrons were emitted in a narrow cone with a full width at half maximum of approx. =30 0 consistent with the angular distribution of back-reemission positrons. The reemitted yields as a function of incident positron energy were found to be very different between forward reemission and back reemission. The maximum forward-reemission yields were 18% for 1000-A-thick W film and 12% for 2500-A-thick W film at 5 and 10 keV optimum incident positron energies, respectively. These results show that one can use thin single-crystal tungsten films as positron moderators or remoderators

Native defects in ZnO films studied by slow positron beam

International Nuclear Information System (INIS)

Peng Chengxiao; Weng Huimin; Ye Bangjiao; Zhou Xianyi; Han Rongdian; Yang Xiaojie

2005-01-01

Native defects in ZnO films grown by radio frequency (RF) reactive magnetron sputtering under variable oxygen fraction conditions have been investigated by using monoenergetic positrons beam technique. The results show that the same type defects dominate in these ZnO samples grown at oxygen fraction less than 70% in the process chamber; and zinc vacancies are preponderant in the ZnO films fabricated in richer oxygen environment. The concentration of zinc vacancies increases with oxygen partial fraction rising. While oxygen fraction reaches 85%, zinc vacancies that could trap positrons decrease, which suggests that impurities could shield zinc vacancies. A combination between hydrogen atoms and the dangling bonds in the lattice could weaken the trap of positrons under the 50% oxygen fraction condition. The concentration of zinc vacancies varies in different oxygen fraction films, which is in agreement with the conclusion of photoluminescence spectroscopy. (authors)

Study of surface layer assessment of solids by ultra-slow and short-pulsed positron beams

International Nuclear Information System (INIS)

Suzuki, Ryouichi; Ohdaira, Toshiyuki; Mikado, Tomohisa; Yamada, Kawakatsu

2004-01-01

Thin films of insulators with low dielectric constant, as a candidate for next generation LSI (large scale integration), were assessed by two dimensional positron life time and wave height measurements using variable incident energy and also short pulsed positron beams. Linkages and openness of nano-scale voids in the films were evaluated by the measurements. Amorphous SiO 2 films were compared with SiCOH films synthesized by plasma CVD (Chemical Vapor Deposition) by measurements of the correlation between positron lifetime and momentum using short-pulsed positron beams. From the measurements, many hydrocarbons were found on void surface of SiCOH films. Positron lifetime measurement gives information about void sizes, and Doppler broadening due to annihilation γ-rays offers electron momentum distribution, which is a counterpart of positron annihilation. Two γ-rays are emitted on the positron annihilation. Coincident measurements of these two γ-rays provide the correlation spectra between positron lifetime and momentum. An instrument for positron annihilation excitation Auger electron spectroscopy (PAES) was improved, and a time-of-flight (TOF) PAES instrument was developed. Double counting rate and high resolution, compared with a conventional Auger electron spectrometer, were attained in elementary analysis using above TOF-PAES instrument. (Y. Kazumata)

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

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)

Implantation profile of low-energy positrons in solids

International Nuclear Information System (INIS)

Asoka-Kumar, P.; Lynn, K.G.

1990-01-01

A simple form for an implantation profile of monoenergetic, low-energy (1--10 keV) positrons in solids is presented. Materials studied include aluminum, copper, molybdenum, palladium, and gold with atomic number ranging from 13 to 79. A simple set of parameters can describe the currently used Makhov profile in slow positron studies of solids. We provide curves and tables for the parameters that can be used to describe the implantation profiles of positrons in any material with atomic number in between 13 and 79

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

International Nuclear Information System (INIS)

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

1982-01-01

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

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)

Relaxed geometries and dipole moments of positron complexes with diatomic molecules

Energy Technology Data Exchange (ETDEWEB)

Assafrao, Denise; Mohallem, Jose R, E-mail: rachid@fisica.ufmg.b [Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, CP 702, 30123-970, Belo Horizonte, MG (Brazil)

2010-01-01

Relaxed geometries and dipole moments of diatomic molecules interacting with a slow positron are reported as functions of the positron distance to the more electronegative atom. A molecular model for the complex that allows applications to large systems is used. The electron population on the positron is proposed as a weighting function to calculate the average quantities. Results show Self-Consistent-Field quality or better.

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.)

Ion species dependence of the implantation-induced defects in ZnO studied by a slow positron beam

International Nuclear Information System (INIS)

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

2007-01-01

In this work, we implanted B + , O + , Al + , and P + ions into ZnO with energy of 50-380 keV and total doses of 4 x 10 15 cm -2 for each ion. The implantation-induced defects and their thermal recovery were studied using a slow positron beam. Vacancy clusters are produced in all the implanted samples. It is found that the thermal recovery of these vacancies induced by different ions shows much difference. In case of B + and Al + -implantation, the vacancy clusters agglomerate to much larger size and might evolve to microvoids during annealing. However, for O + and P + ions, which are heavier than B + and Al + , the vacancies show a much weaker agglomeration process. The mechanism of such difference is discussed. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Study on quantum beam science by using ultra short electron pulse, FEL, and slow positron beam at ISIR (Institute of Science and Industrial Research), Osaka University

International Nuclear Information System (INIS)

Yoshida, Y.; Tagawa, S.; Okuda, S.; Honda, Y.; Kimura, N.; Yamamoto, T.; Isoyama, G.

1995-01-01

Three projects for quantum beam science, an ultra fast electron pulse, a free electron laser, and a slow positron beam, has been started by using 38 MeV L-band and 150 MeV S-band linacs at ISIR in Osaka University. Both study on the production of three beams and study on quantum material science by using three beams will play an important role in the beam science. (author)

Positron Emission Tomography/Computed Tomography-Guided Intensity-Modulated Radiotherapy for Limited-Stage Small-Cell Lung Cancer

International Nuclear Information System (INIS)

Shirvani, Shervin M.; Komaki, Ritsuko; Heymach, John V.; Fossella, Frank V.; Chang, Joe Y.

2012-01-01

Purpose: Omitting elective nodal irradiation from planning target volumes does not compromise outcomes in patients with non–small-cell lung cancer, but whether the same is true for those with limited-stage small-cell lung cancer (LS-SCLC) is unknown. Therefore, in the present study, we sought to determine the clinical outcomes and the frequency of elective nodal failure in patients with LS-SCLC staged using positron emission tomography/computed tomography and treated with involved-field intensity-modulated radiotherapy. Methods and Materials: Between 2005 and 2008, 60 patients with LS-SCLC at our institution underwent disease staging using positron emission tomography/computed tomography before treatment using an intensity-modulated radiotherapy plan in which elective nodal irradiation was intentionally omitted from the planning target volume (mode and median dose, 45 Gy in 30 fractions; range, 40.5 Gy in 27 fractions to 63.8 Gy in 35 fractions). In most cases, concurrent platinum-based chemotherapy was administered. We retrospectively reviewed the clinical outcomes to determine the overall survival, relapse-free survival, and failure patterns. Elective nodal failure was defined as recurrence in initially uninvolved hilar, mediastinal, or supraclavicular nodes. Survival was assessed using the Kaplan-Meier method. Results: The median age of the study patients at diagnosis was 63 years (range, 39–86). The median follow-up duration was 21 months (range, 4–58) in all patients and 26 months (range, 4–58) in the survivors. The 2-year actuarial overall survival and relapse-free survival rate were 58% and 43%, respectively. Of the 30 patients with recurrence, 23 had metastatic disease and 7 had locoregional failure. We observed only one isolated elective nodal failure. Conclusions: To our knowledge, this is the first study to examine the outcomes in patients with LS-SCLC staged with positron emission tomography/computed tomography and treated with definitive

Positron Emission Tomography/Computed Tomography-Guided Intensity-Modulated Radiotherapy for Limited-Stage Small-Cell Lung Cancer

Energy Technology Data Exchange (ETDEWEB)

Shirvani, Shervin M.; Komaki, Ritsuko [Department of Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX (United States); Heymach, John V.; Fossella, Frank V. [Department of Thoracic/Head and Neck Medical Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX (United States); Chang, Joe Y., E-mail: jychang@mdanderson.org [Department of Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX (United States)

2012-01-01

Purpose: Omitting elective nodal irradiation from planning target volumes does not compromise outcomes in patients with non-small-cell lung cancer, but whether the same is true for those with limited-stage small-cell lung cancer (LS-SCLC) is unknown. Therefore, in the present study, we sought to determine the clinical outcomes and the frequency of elective nodal failure in patients with LS-SCLC staged using positron emission tomography/computed tomography and treated with involved-field intensity-modulated radiotherapy. Methods and Materials: Between 2005 and 2008, 60 patients with LS-SCLC at our institution underwent disease staging using positron emission tomography/computed tomography before treatment using an intensity-modulated radiotherapy plan in which elective nodal irradiation was intentionally omitted from the planning target volume (mode and median dose, 45 Gy in 30 fractions; range, 40.5 Gy in 27 fractions to 63.8 Gy in 35 fractions). In most cases, concurrent platinum-based chemotherapy was administered. We retrospectively reviewed the clinical outcomes to determine the overall survival, relapse-free survival, and failure patterns. Elective nodal failure was defined as recurrence in initially uninvolved hilar, mediastinal, or supraclavicular nodes. Survival was assessed using the Kaplan-Meier method. Results: The median age of the study patients at diagnosis was 63 years (range, 39-86). The median follow-up duration was 21 months (range, 4-58) in all patients and 26 months (range, 4-58) in the survivors. The 2-year actuarial overall survival and relapse-free survival rate were 58% and 43%, respectively. Of the 30 patients with recurrence, 23 had metastatic disease and 7 had locoregional failure. We observed only one isolated elective nodal failure. Conclusions: To our knowledge, this is the first study to examine the outcomes in patients with LS-SCLC staged with positron emission tomography/computed tomography and treated with definitive intensity

Ion species dependence of the implantation-induced defects in ZnO studied by a slow positron beam

Energy Technology Data Exchange (ETDEWEB)

Chen, Z.Q. [Department of Physics, Wuhan University (China); Maekawa, M.; Kawasuso, A.; Naramoto, H. [Advanced Science Research Center, Japan Atomic Energy Agency, Takasaki, Gunma (Japan)

2007-07-01

In this work, we implanted B{sup +}, O{sup +}, Al{sup +}, and P{sup +} ions into ZnO with energy of 50-380 keV and total doses of 4 x 10{sup 15} cm{sup -2} for each ion. The implantation-induced defects and their thermal recovery were studied using a slow positron beam. Vacancy clusters are produced in all the implanted samples. It is found that the thermal recovery of these vacancies induced by different ions shows much difference. In case of B{sup +} and Al{sup +}-implantation, the vacancy clusters agglomerate to much larger size and might evolve to microvoids during annealing. However, for O{sup +} and P{sup +} ions, which are heavier than B{sup +} and Al{sup +}, the vacancies show a much weaker agglomeration process. The mechanism of such difference is discussed. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

CUTANEUS STIMULATION: SLOW-STROKE BACK MASSAGE REDUCES THE INTENSITY OF OSTEOARTRITIS PAIN OF ELDERLY

Directory of Open Access Journals (Sweden)

Mira Triharini

2017-04-01

Full Text Available Introduction: Osteoarthritis disease is the result of both mechanical and biological process which lead come to unstable degradation and synthesis of condrozyte cartilage and extracellular matrix. The risk factor of this instability is aging process. The aging process stimulates osteophytes formation and degradation of cartilage, and emerged pain as primary clinical symptom. One of the non pharmacological ways to cope this pain is by applying cutaneus stimulation through slow-stroke back massage method. The objective of this study was to analyze the effect of applying cutaneus stimulation with slow-stroke back massage method to osteoarthritis’s pain intensity. Method: Pre experimental design with one group pre test-post test approach was used in this study. The subject of this study were elderly above 50 years old living in Panti Werdha Hargo Dedali Surabaya, 15 participants were involved using purpose sampling technique. This study started on January 29th until February 6th, 2010. Data were collected by interview and observation and analyzed by WIlcoxcon Signed Rank Test α = 0.05, p value <α. Result: The Result showed that the message intervention was significantly affect the elder’s level of osteoarthritis pain in Panti Werdha Hargo Dedali Surabaya (p = 0.003. Discussion: It can be concluded that gives stimulation cutaneus: slow-stroke back massage reduce osteoathritis pain intensity. Slow-stroke back massage increase level of endorphin, so that pain reduction and individual pain perception will decrease.

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

Interface properties of 4H-SiC MOS structures studied by a slow positron beam

International Nuclear Information System (INIS)

Maekawa, M.; Kawasuso, A.; Ichimiya, A.; Yoshikawa, M.

2004-01-01

Interfacial defects existing near the SiO 2 /SiC interface are an important issue for fabrication of high performance SiC devices. We investigate a thermally grown SiO 2 /SiC layer of 4H-SiC MOS structure by positron annihilation spectroscopy. The Doppler broadening of annihilation quanta was measured as a function of the incident positron energy and the gate bias. Applying a negative gate bias, significant increases in S-parameters were observed. This indicates the migration of implanted positrons towards the SiO 2 /SiC interface and annihilation at interfacial defects. Ultraviolet (UV) ray irradiation was used to extract the influence of the positron trapping to the interfacial states. S-parameters in the interface region were reduced by UV irradiation. This shows that positron trapping probability decreased because the charge state of interfacial defects changed to positive. From the recovery of S-parameters after 24 hours, the interfacial states discharge slowly and exist in large quantities, because the changes of S-parameter by the UV irradiation are larger than changes induced by bias change. (orig.)

Application of positron annihilation techniques for semiconductor studies

International Nuclear Information System (INIS)

Karwasz, G.P.; Zecca, A.; Brusa, R.S.; Pliszka, D.

2004-01-01

Positron annihilation techniques, being non-destructive, allowing depth profiling down to a few micrometers and detecting open-volume defects (vacancies, dislocations etc.) at single ppm concentrations constitute a valuable and complementary method, compared to other solid-state-physics studies. We give examples of investigation in the field of semiconductors with different techniques, both with and without use of positron low-energy beams. The Doppler broadening of the 511 keV annihilation line method and the slow positron beam were used to study helium-implanted silicon and the surface reduction processes in semiconducting glasses. The positron lifetime technique and coincidence spectra of the Doppler broadening were used for systematic studies of metals and semiconductors. Doppler-coincidence method was then used to identify the kinetics of oxygen precipitates in Czochralski-grown silicon

Chemical effect of Si+ ions on the implantation-induced defects in ZnO studied by a slow positron beam

Science.gov (United States)

Jiang, M.; Wang, D. D.; Chen, Z. Q.; Kimura, S.; Yamashita, Y.; Mori, A.; Uedono, A.

2013-01-01

Undoped ZnO single crystals were implanted with 300 keV Si+ ions to a dose of 6 × 1016 cm-2. A combination of X-ray diffraction (XRD), positron annihilation, Raman scattering, high resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) was used to study the microstructure evolution after implantation and subsequent annealing. A very large increase of Doppler broadening S parameters in Si+-implanted region was detected by using a slow positron beam, indicating that vacancy clusters or microvoids are induced by implantation. The S parameters increase further after annealing up to 700 °C, suggesting agglomeration of these vacancies or microvoids to larger size. Most of these defects are removed after annealing up to 1100 °C. The other measurements such as XRD, Raman scattering, and PL all indicate severe damage and even disordered structure induced by Si+ implantation. The damage and disordered lattice shows recovery after annealing above 700 °C. Amorphous regions are observed by HRTEM measurement, directly testifies that amorphous phase is induced by Si+ implantation in ZnO. Analysis of the S - W correlation and the coincidence Doppler broadening spectra gives direct evidence of SiO2 precipitates in the sample annealed at 700 °C, which strongly supports the chemical effect of Si ions on the amorphization of ZnO lattice.

Positrons trapped in polyethylene: Electric field effect

International Nuclear Information System (INIS)

Bertolaccini, M.; Bisi, A.; Gambarini, G.; Zappa, L.

1978-01-01

The intensity of the iot 2 -component of positrons annihilated in polyethylene is found to increase with increasing electric field, while the formation probability of the positron state responsible for this component remains independent of the field. (orig.) 891 HPOE [de

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.

The study of sub-surface and interface characteristics of semiconductor heterostructures by slow positron implantation spectroscopy

International Nuclear Information System (INIS)

Baker, J.A.; Coleman, P.G.

1989-01-01

Experiments are described in which the controlled implantation of mono-energetic positrons is used to gain information non-destructively on epilayer and interface defects in semiconductor heterostructures. The implantation, and hence annihilation, profile is changed by varying the incident positron energy from 1 to 35 keV. Characteristics of the positron state at the annihilation site are reflected in the width of the measure Doppler-broadened annihilation line. The fractions of positrons annihilating from each state are deduced by solving the steady-state diffusion equation. The application of the technique is illustrated by application to a series of SiO 2 -Si samples. (author)

Frozen-in vacancies in PVD-Cu films with improved high-pressure reflowability studied using a slow positron beam

Energy Technology Data Exchange (ETDEWEB)

Yabuuchi, A; Kubo, D; Mizuno, M; Araki, H [Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Onishi, T [Materials Research Laboratory, Kobe Steel Ltd., 5-5 Takatsukadai 1-chome, Nishi-ku, Kobe, Hyogo 651-2271 (Japan); Shirai, Y [Department of Materials Science and Engineering, Graduate School of Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501 (Japan)], E-mail: atsushi.yabuuchi@mat.eng.osaka-u.ac.jp

2009-05-01

Recently, a new process has been proposed for fabricating a LSI interconnection; filling trenches and via holes with Cu using high-pressure annealing treatment. It is already known that a Cu film produced by physical vapor deposition (PVD) has a lower reflowability compared to a Cu film produced by electrochemical deposition (ECD). Additionally, it has also been recognized that the addition of Sb to the PVD-Cu film improves the reflowability. However, the factors responsible for the reflowability of Cu films have not yet been studied. In this work, we evaluated a PVD pure-Cu film and a PVD Cu-0.5at%Sb film by using a slow positron beam. Addition of Sb led to the introduction of lattice defects in the as-deposited film. These defects that were observed in the PVD-CuSb dilute alloy film were identified as frozen-in vacancies that were produced during deposition.

Frozen-in vacancies in PVD-Cu films with improved high-pressure reflowability studied using a slow positron beam

International Nuclear Information System (INIS)

Yabuuchi, A; Kubo, D; Mizuno, M; Araki, H; Onishi, T; Shirai, Y

2009-01-01

Recently, a new process has been proposed for fabricating a LSI interconnection; filling trenches and via holes with Cu using high-pressure annealing treatment. It is already known that a Cu film produced by physical vapor deposition (PVD) has a lower reflowability compared to a Cu film produced by electrochemical deposition (ECD). Additionally, it has also been recognized that the addition of Sb to the PVD-Cu film improves the reflowability. However, the factors responsible for the reflowability of Cu films have not yet been studied. In this work, we evaluated a PVD pure-Cu film and a PVD Cu-0.5at%Sb film by using a slow positron beam. Addition of Sb led to the introduction of lattice defects in the as-deposited film. These defects that were observed in the PVD-CuSb dilute alloy film were identified as frozen-in vacancies that were produced during deposition.

Studies of Oxidation of the Cu(100) Surface Using Low Energy Positrons

International Nuclear Information System (INIS)

Fazleev, N. G.; Maddox, W. B.; Nadesalingam, M.; Rajeshwar, K.; Weiss, A. H.

2009-01-01

Changes in the surface of an oxidized Cu(100) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the positron annihilation induced Cu M 2,3 VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The intensity then decreases monotonically as the annealing temperature is increased to ∼600 deg. C. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-positron correlations effects. Possible explanation for the observed behavior of the intensity of positron annihilation induced Cu M 2,3 VV Auger peak with changes of the annealing temperature is proposed.

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.

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

International Nuclear Information System (INIS)

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

1995-01-01

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

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

International Nuclear Information System (INIS)

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

2004-01-01

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

Positron cross-field transport due to quasibound states of antihydrogen

International Nuclear Information System (INIS)

Ahat, Y.; Correa, C.E.; Ordonez, C.A.

2007-01-01

Within the past few years, experiments have been reported in which antiprotons produced at the CERN Antiproton Decelerator facility were slowed, trapped in nested Penning traps and made to interact with a positron plasma such that antihydrogen was formed. Classical trajectory simulations of the interactions between the antiprotons and positrons have been reported to indicate that positive-energy, quasibound states of antihydrogen can form at a rate that exceeds the rate of formation of stable Rydberg states. The formation of quasibound states may affect the rate of diffusion of positrons across the magnetic field that confines them in the nested Penning trap. Simulations indicate that a binary interaction associated with the formation and disintegration of a quasibound state can cause a shift of the positron's guiding center that is much larger than the positron cyclotron radius before the interaction. A theory is presented that describes positron cross-magnetic-field diffusion due to quasibound states of antihydrogen

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

The Upgrade of the Neutron Induced Positron Source NEPOMUC

Science.gov (United States)

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

2013-06-01

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

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

Positron implantation studies of YBa2Cu3O7-x

International Nuclear Information System (INIS)

Anwand, W.; Brauer, G.; Coleman, P.G.; Knights, A.P.; Teske, K.; Schuster, G.; Rudolph, K.

1995-01-01

Slow positron implantation spectroscopy has been applied to the study of a set of samples of superconducting YBa 2 Cu 3 O 7-x . The depth-sensitive positron response to oxygen content and preparation history is presented. An outline is given of the experimental method - solid electrolyte coulometry in carrier-gas mode - used to measure oxygen exchange for the same set of samples. (orig.)

Electrostatic solitons in unmagnetized hot electron-positron-ion plasmas

International Nuclear Information System (INIS)

Mahmood, S.; Ur-Rehman, H.

2009-01-01

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

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)

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

International Nuclear Information System (INIS)

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

1975-01-01

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

Manipulation of positron orbits in a dipole magnetic field with fluctuating electric fields

Science.gov (United States)

Saitoh, H.; Horn-Stanja, J.; Nißl, S.; Stenson, E. V.; Hergenhahn, U.; Pedersen, T. Sunn; Singer, M.; Dickmann, M.; Hugenschmidt, C.; Stoneking, M. R.; Danielson, J. R.; Surko, C. M.

2018-01-01

We report the manipulation of positron orbits in a toroidal dipole magnetic field configuration realized with electric fields generated by segmented electrodes. When the toroidal circulation motion of positrons in the dipole field is coupled with time-varying electric fields generated by azimuthally segmented outer electrodes, positrons undergo oscillations of their radial positions. This enables quick manipulation of the spatial profiles of positrons in a dipole field trap by choosing appropriate frequency, amplitude, phase, and gating time of the electric fields. According to numerical orbit analysis, we applied these electric fields to positrons injected from the NEPOMUC slow positron facility into a prototype dipole field trap experiment with a permanent magnet. Measurements with annihilation γ-rays clearly demonstrated the efficient compression effects of positrons into the strong magnetic field region of the dipole field configuration. This positron manipulation technique can be used as one of essential tools for future experiments on the formation of electron-positron plasmas.

Proceedings of the European Meeting on Positron Studies of Defects

International Nuclear Information System (INIS)

1987-01-01

The meeting dealt with both theoretical and experimental aspects of positron studies of defects using conventional and novel positron techniques. The subjects are indicated in the following headings: (1) theory of positrons in imperfect solids, (2) vacancies in metals and alloys, (3) dislocation and deformation effects, (4) amorphous alloys and fine-grained materials, (5) phase transitions, (6) precipitation phenomena, (7) gas impurity-defect interaction and irradiation effects, (8) defects in elemental semiconductors, (9) defects in compound semiconductors, (10) slow positron studies of defects, (11) defects in oxides and halides, (12) defects in molecular solids, and (13) advances in experimental techniques and data treatment. Althogether 141 contributions (invited plenary lectures, short lectures, and posters) are presented as titles with abstracts. Most of them are in INIS scope and are processed individually for the database

Effect of radiation damage on luminescence of erbium-implanted SiO sub 2 /Si studied by slow positron beam

CERN Document Server

Kawasuso, A; Hirata, K; Sekiguchi, T; Kobayashi, Y; Okada, S

2000-01-01

The effect of damage on 1.54 mu m luminescence for 30 keV-Er-implanted SiO sub 2 films has been studied by positron annihilation and cathodoluminescence. It was found that S-parameter in the films decreased after implantation, indicating the suppression of positronium formation. The luminescence appeared with the recovery of the S-parameter after 600 deg. C annealing. The intensity reached a maximum at 900 deg. C annealing whereas the S-parameter did not change significantly. It seems that most damages recover at 600 deg. C and thereafter Er ions transform to an optically active state at 900 deg. C.

Development of positron diffraction and holography at LLNL

International Nuclear Information System (INIS)

Hamza, A.; Asoka-Kumar, P.; Stoeffl, W.; Howell, R.; Miller, D.; Denison, A.

2003-01-01

A low-energy positron diffraction and holography spectrometer is currently being constructed at the Lawrence Livermore National Laboratory (LLNL) to study surfaces and adsorbed structures. This instrument will operate in conjunction with the LLNL intense positron beam produced by the 100 MeV LINAC allowing data to be acquired in minutes rather than days. Positron diffraction possesses certain advantages over electron diffraction which are discussed. Details of the instrument based on that of low-energy electron diffraction are described

Positron-trapping mechanism at dislocations in Zn

DEFF Research Database (Denmark)

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

1987-01-01

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

Positron beams: The journey from fundamental physics to industrial application

International Nuclear Information System (INIS)

Coleman, P.G.

2002-01-01

Monoenergetic beams of positrons developed for fundamental atomic physics experiments have evolved - via basic and applied research in condensed matter physics and chemistry - to a phase in which possibilities for commercial exploitation are becoming apparent. The evolution of positron beam technology, from table-top laboratory-based apparatus with positrons of energies controllable in the 10 0 -10 2 eV energy range and beam intensities of ∼1 s -1 , to systems capable of delivering positrons of energies from 0.02 eV to MeV at intensities as high as 10 8 s -1 , has been both steady and saltatory. The journey from fundamental research to industrial application is a classic example of scientific development; a brief summary of steps on the way is followed by an example in which an attempt is being made to harness the efficacy of positron beams applied to defect spectroscopy of semiconductor structures to create an instrument of value to the ion implantation industry

Slow Antihydrogen

International Nuclear Information System (INIS)

Gabrielse, G.; Speck, A.; Storry, C.H.; Le Sage, D.; Guise, N.; Larochelle, P.C.; Grzonka, D.; Oelert, W.; Schepers, G.; Sefzick, T.; Pittner, H.; Herrmann, M.; Walz, J.; Haensch, T.W.; Comeau, D.; Hessels, E.A.

2004-01-01

Slow antihydrogen is now produced by two different production methods. In Method I, large numbers of H atoms are produced during positron-cooling of antiprotons within a nested Penning trap. In a just-demonstrated Method II, lasers control the production of antihydrogen atoms via charge exchange collisions. Field ionization detection makes it possible to probe the internal structure of the antihydrogen atoms being produced - most recently revealing atoms that are too tightly bound to be well described by the guiding center atom approximation. The speed of antihydrogen atoms has recently been measured for the first time. After the requested overview, the recent developments are surveyed

New Possibilities of Positron-Emission Tomography

Science.gov (United States)

Volobuev, A. N.

2018-01-01

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

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

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

International Nuclear Information System (INIS)

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

2013-01-01

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

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.

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

International Nuclear Information System (INIS)

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

2013-01-01

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

Swift heavy ion irradiation effects in SiC measured by positrons

Energy Technology Data Exchange (ETDEWEB)

Liszkay, L.; Kajcsos, Zs.; Szilagyi, E. [KFKI Research Inst. for Nuclear and Particle Physics, Budapest (Hungary); Havancsak, K. [Dept. for Solid State Physics, Eoetvoes Univ., Budapest (Hungary); Barthe, M.F.; Desgardin, P.; Henry, L. [CNRS Centre d' Etudes et de Recherches par Irradiation, Orleans (France); Battistig, G. [Research Inst. for Technical Physics and Materials Science, Budapest (Hungary); Skuratov, V.A. [Joint Inst. of Nuclear Research, Moscow (Russian Federation). Bogoliubov Lab. of Theoretical Physics

2001-07-01

N-type 6H SiC single crystals irradiated with swift (246 MeV) Kr ions at room temperature (the implantation depth being 21 {mu}m) were investigated by conventional positron lifetime and Doppler-broadening measurements as well as with the application of a slow positron beam. The fluence dependence of the irradiation-induced defects was studied in the 1 x 10{sup 10} - 1 x 10{sup 14} ion cm{sup -2} range. In the fluence and depth range studied, no sign of amorphization (or creation of large voids) was seen in the Kr irradiated crystals. The positron annihilation results were compared with atomic displacement calculations by TRIM. A simple model was used to describe the trapping effect and determine the relationship between the atomic displacement densities and the positron trapping. The 225 ps lifetime of the open-volume defects created suggests that the V{sub Si}-V{sub C} divacancy is the dominant trapping site in the implanted zone. (orig.)

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)

Positron annihilation study of mechanochemical reaction between Zn+Se and Zn+S

International Nuclear Information System (INIS)

Kajcsos, Zs.; Horvath, D.; Tshakarov, C.G.; Gospodinov, G.G.; Vertes, A.

1981-01-01

Positron lifetime spectra were recorded and evaluated in mixtures of Zn+S and Zn+Se powders for various periods. The intensity of the long-lived positron lifetime component is shown to increase with grinding time until an abrupt decrease takes place at a specific grinding time, indicating the onset of the effective chemical reaction. The suitability of positron annihilation for investigating mechanochemical reactions is clearly demonstrated. (author)

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.

Electron-Positron Accumulator (EPA)

CERN Multimedia

Photographic Service

1986-01-01

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

A study of vacancy-type defects in B+-implanted SiO2/Si by a slow positron beam

International Nuclear Information System (INIS)

Uedono, Akira; Tanigawa, Shoichiro; Sugiura, Jun; Ogasawara, Makoto.

1989-01-01

Variable-energy (0∼30 keV) positron beam studies have been carried out on 80 keV B + -implanted SiO 2 (43 nm)/Si specimens. Doppler broadening profiles of the positron annihilation as a function of the incident positron energy were shown to be quite sensitive for the detection of vacancy-type defects introduced by B + -implantation. The average depth of the defected regions was found to shift towards the surface of the specimen with increasing the dose of B + ions. This effect is attributed to the accumulation of vacancy-type defects at the SiO 2 /Si interface. Dominant defect species were identified as vacancy clusters by their annealing stage. (author)

Can positrons be guided by insulating capillaries?

International Nuclear Information System (INIS)

DuBois, R.D.; Toekesi, K.

2011-01-01

Complete text of publication follows. Investigations of guiding of few hundred eV antiparticles by macroscopic insulating capillaries have been described. Using subfemtoamp positron and electron beams, we demonstrated that a portion of the entering beams were transmitted and emerged in the direction of the capillary. We also demonstrated that the transmitted intensities decreased as the capillary tilt angle was increased (see Fig. 1). Both of these are indications of guiding. However, a comparison with transmitted photon data implies that the positron transmission may result from geometric factors associated with our diffuse beams and tapered capillary used in these studies. For electrons, the comparison indicates differences which could imply that even very low intensity beams can be guided. Measurements of the transmitted intensity as a function of charge entering the capillary were inconclusive as no major increases in the transmitted intensity were observed. 2D static simulations imply that our beam intensities, although extremely small with respect to previous guiding experiments, were capable of supplying sufficient charge for guiding to occur. Although not definitive, our study implies that sub-femtoamp beam intensities are sufficient to form charge patches and produce guiding. This may have been observed for electrons with the question remaining open for positrons. That guiding was not clearly seen may have been due to the capillary geometry used or it may indicate that although sufficient charge is being supplied, the surface and bulk resistivities of glass permit this charge to dissipate faster than it is formed. This aspect was not taken into consideration in our simulations but a crude estimate of the discharge rate implies that beam intensities on the order of pA, rather than fA as used here, may be required for guiding to occur in the capillaries used here. Additional studies are required to definitively answer the question as to whether antiparticles

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

Slow positron studies on single crystals of Ag(100), Ag(111) and Cu(111)

International Nuclear Information System (INIS)

Lynn, K.G.

1979-01-01

Monoenergetic positrons were employed to examine positronium formation as a function of sample temperature (300 to 1200 K) and incident energy (0 to 5 keV) on Ag(100), Ag(111) and Cu(111) surfaces with submonolayer contamination. In these metals at the higher temperatures, positronium formation becomes the dominant process. A one-dimensional diffusion model is fit to the data as a function of incident energy. Th positronium fraction is found to be an activated process and is identified as detrapping from a surface state and an estimate of the depth of this trap is extracted. The diffusion length is found to be temperature independent before the onset of vacancy trapping. At the higher temperatures vacancy trapping is observed by the decrease in the positron diffusion length at the higher incident voltages. A vacancy formation energy is extracted from the data and is generally lower than the accepted bulk values. 18 references

N+ ion-implantation-induced defects in ZnO studied with a slow positron beam

International Nuclear Information System (INIS)

Chen, Z Q; Sekiguchi, T; Yuan, X L; Maekawa, M; Kawasuso, A

2004-01-01

Undoped ZnO single crystals were implanted with multiple-energy N + ions ranging from 50 to 380 keV with doses from 10 12 to 10 14 cm -2 . Positron annihilation measurements show that vacancy defects are introduced in the implanted layers. The concentration of the vacancy defects increases with increasing ion dose. The annealing behaviour of the defects can be divided into four stages, which correspond to the formation and recovery of large vacancy clusters and the formation and disappearance of vacancy-impurity complexes, respectively. All the implantation-induced defects are removed by annealing at 1200 deg. C. Cathodoluminescence measurements show that the ion-implantation-induced defects act as nonradiative recombination centres to suppress the ultraviolet (UV) emission. After annealing, these defects disappear gradually and the UV emission reappears, which coincides with positron annihilation measurements. Hall measurements reveal that after N + implantation, the ZnO layer still shows n-type conductivity

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

International Nuclear Information System (INIS)

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

2006-01-01

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

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

Science.gov (United States)

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

2013-06-01

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

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

The Correlation Between Dislocations and Vacancy Defects Using Positron Annihilation Spectroscopy

Science.gov (United States)

Pang, Jinbiao; Li, Hui; Zhou, Kai; Wang, Zhu

2012-07-01

An analysis program for positron annihilation lifetime spectra is only applicable to isolated defects, but is of no use in the presence of defective correlations. Such limitations have long caused problems for positron researchers in their studies of complicated defective systems. In order to solve this problem, we aim to take a semiconductor material, for example, to achieve a credible average lifetime of single crystal silicon under plastic deformation at different temperatures using positron life time spectroscopy. By establishing reasonable positron trapping models with defective correlations and sorting out four lifetime components with multiple parameters, as well as their respective intensities, information is obtained on the positron trapping centers, such as the positron trapping rates of defects, the density of the dislocation lines and correlation between the dislocation lines, and the vacancy defects, by fitting with the average lifetime with the aid of Matlab software. These results give strong grounds for the existence of dislocation-vacancy correlation in plastically deformed silicon, and lay a theoretical foundation for the analysis of positron lifetime spectra when the positron trapping model involves dislocation-related defects.

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)

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.

Time-of-flight positron emission tomography using optical fiber circuit

International Nuclear Information System (INIS)

Yamawaki, Masato; Katsumura, Yousuke; Suzuki, Takenori

2008-01-01

The measurement method and system architecture of a new time-of-flight positron emission tomography (TOF-PET) system are proposed. This system collects scintillation light using optical fibers connected directly to scintillators and measures the position of positron annihilation. Many scintillators are placed cylindrically whereby a pair of scintillators detects a pair of γ-rays generated at the positron annihilation point. Optical fiber circuits, most of which are bundles of optical fibers bound clockwise or counterclockwise around the cylinder of scintillators, collect light signals generated by γ-rays. These light signals are amplified by several photomultiplier tubes and processed using a single digital oscilloscope to determine the TOF of the positron annihilation γ-rays. One of the most important factors in the performance of the TOF-PET system is the TOF resolution. When fiber circuits are used for transmitting light signals, the dispersion of light signals and the decrease in light intensity are the major factors in the deterioration of the TOF resolution. The result of the preliminary experiment leads to the conclusion that the use of optical fibers degrades the intensity of light but does not severely degrade the TOF resolution. (author)

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

International Nuclear Information System (INIS)

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

2009-01-01

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

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)

Positron spectroscopy as an analytical tool in material sciences

International Nuclear Information System (INIS)

Pujari, P.K.

2010-01-01

Full text: Positron annihilation spectroscopy has emerged as a powerful tool in material sciences due to its ability to provide information about the electron momentum distribution and electron density in a given medium. These features help in identifying altered state of electronic rearrangements as one encounters in phase transitions. In addition, positrons prefer regions of lower electron density such as open volume defects i.e. vacancies or vacancy clusters in metals, alloys and semiconductors or free-volumes in molecular solids. Its sensitivity to defects is extremely high e.g. it can detect as small a defect as monovacancy to concentration as low as parts per million(ppm). Innovative nuclear instrumentation has helped in getting chemical specificity at the annihilation site. For example, precipitates, embedded, nanoparticles or element decorated vacancies can now be easily identified. This presentation is structured to introduce the technique and provide a global perspective on area of applications. Specific examples on defect characterization, nanostructure-property correlations in polymers, advantages of elemental specificity by indexing the core electron momentum will be given. In addition, slow positron beam based studies on nanostructured materials as well as particle accelerator based positron spectroscopy for volumetric assay of defects in large engineering samples will be presented

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

a Positron 2D-ACAR Study of the Silicon-Dioxide Interface and the Point Defects in the Semi-Insulating Gallium Arsenide

Science.gov (United States)

Peng, Jianping

The SiO_2-Si system has been the subject of extensive study for several decades. Particular interest has been paid to the interface between Si single crystal and the amorphous SiO_2 which determines the properties and performances of devices. This is significant because of the importance of Si technology in the semiconductor industry. The development of the high-intensity slow positron beam at Brookhaven National Laboratory make it possible to study this system for the first time using the positron two-dimensional angular correlation of annihilation radiation (2D-ACAR) technique. 2D-ACAR is a well established and is a non-destructive microscopic probe for studying the electronic structure of materials, and for doing the depth-resolved measurements. Some unique information was obtained from the measurements performed on the SiO_2-Si system: Positronium (Ps) atoms formation and trapping in microvoids in both oxide and interface regions; and positron annihilation at vacancy-like defects in the interface region which can be attributed to the famous Pb centers. The discovery of the microvoids in the interface region may have some impact on the fabrication of the next generation electronic devices. Using the conventional 2D-ACAR setup with a ^{22}Na as positron source, we also studied the native arsenic (As) vacancy in the semi -insulating gallium-arsenide (SI-GaAs), coupled with in situ infrared light illumination. The defect spectrum was obtained by comparing the spectrum taken without photo -illumination to the spectrum taken with photo-illumination. The photo-illumination excited electrons from valence band to the defect level so that positrons can become localized in the defects. The two experiments may represent a new direction of the application of positron 2D-ACAR technique on the solid state physics and materials sciences.

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

Science.gov (United States)

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

2013-04-01

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

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

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

The annihilation spectrum of relatiVistic electron-positron plasma

International Nuclear Information System (INIS)

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

1980-01-01

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

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

International Nuclear Information System (INIS)

Somoza, Alberto

1998-01-01

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

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

DEFF Research Database (Denmark)

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

1972-01-01

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

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.

N{sup +} ion-implantation-induced defects in ZnO studied with a slow positron beam

Energy Technology Data Exchange (ETDEWEB)

Chen, Z Q [Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan (Japan); Sekiguchi, T [Nanomaterials Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Yuan, X L [Nanomaterials Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Maekawa, M [Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan (Japan); Kawasuso, A [Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan (Japan)

2004-01-21

Undoped ZnO single crystals were implanted with multiple-energy N{sup +} ions ranging from 50 to 380 keV with doses from 10{sup 12} to 10{sup 14} cm{sup -2}. Positron annihilation measurements show that vacancy defects are introduced in the implanted layers. The concentration of the vacancy defects increases with increasing ion dose. The annealing behaviour of the defects can be divided into four stages, which correspond to the formation and recovery of large vacancy clusters and the formation and disappearance of vacancy-impurity complexes, respectively. All the implantation-induced defects are removed by annealing at 1200 deg. C. Cathodoluminescence measurements show that the ion-implantation-induced defects act as nonradiative recombination centres to suppress the ultraviolet (UV) emission. After annealing, these defects disappear gradually and the UV emission reappears, which coincides with positron annihilation measurements. Hall measurements reveal that after N{sup +} implantation, the ZnO layer still shows n-type conductivity.

Positron Annihilation in Solid Charge-Transfer Complexes

DEFF Research Database (Denmark)

Lévay, B.; Jansen, P.

1979-01-01

Positron lifetime and angular correlation measurements have been carried out on 1:1 charge-transfer complexes, on their pure donor and acceptor components and on the 1:1 M mechanical mixtures of these components. Complex formation reduced the intensity of the long-lifetime component of the donor...

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

Application of positron annihilation to the characterization of polymer structure

International Nuclear Information System (INIS)

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

2005-01-01

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

A positron annihilation study of hydrated DNA

DEFF Research Database (Denmark)

Warman, J. M.; Eldrup, Morten Mostgaard

1986-01-01

Positron annihilation measurements are reported for hydrated DNA as a function of water content and as a function of temperature (20 to -180.degree. C) for samples containing 10 and 50% wt of water. The ortho-positronium mean lifetime and its intensity show distinct variations with the degree...

The limits of application of variable-energy slow positron beams for investigating TiN hard coatings prepared by PVD

International Nuclear Information System (INIS)

Marek, T.; Suevegh, K.; Vertes, A.; Szeles, Cs.; Lynn, K.G.

2000-01-01

Samples of TiN hard coatings prepared by physical vapour deposition (PVD) were investigated by means of depth-sensitive positron annihilation spectroscopy. The results indicate that the samples are at the limits of the applicability of this method presumably due to the high defect concentration. Though the samples are thoroughly characterized by other independent methods, they might not be sufficient to explain all aspects of positron-solid interactions in these cases. (author)

Interlaboratory comparison of positron and positronium lifetimes in polymers

DEFF Research Database (Denmark)

Wastlund, C.; Eldrup, Morten Mostgaard; Maurer, F.H.J.

1998-01-01

A comparison of the results of a series of positron annihilation lifetime measurements performed in 12 laboratories is presented. The measurements were conducted on three different polymer samples, all prepared in one laboratory under standard conditions. The objective of the work was to gain...... insight into the variation in derived positron and positronium lifetimes and intensities measured in the different laboratories on identical specimens. Lifetime data were collected at room temperature by each laboratory following their own standard measurement and data evaluation procedures. The polymers...

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.

Positron sources

International Nuclear Information System (INIS)

Chehab, R.

1989-01-01

A tentative survey of positron sources is given. Physical processes on which positron generation is based are indicated and analyzed. Explanation of the general features of electromagnetic interactions and nuclear β + decay makes it possible to predict the yield and emittance for a given optical matching system between the positron source and the accelerator. Some kinds of matching systems commonly used - mainly working with solenoidal fields - are studied and the acceptance volume calculated. Such knowledge is helpful in comparing different matching systems. Since for large machines, a significant distance exists between the positron source and the experimental facility, positron emittance has to be preserved during beam transfer over large distances and methods used for that purpose are indicated. Comparison of existing positron sources leads to extrapolation to sources for future linear colliders

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

Positron sources

International Nuclear Information System (INIS)

Chehab, R.

1994-01-01

A tentative survey of positron sources is given. Physical processes on which positron generation is based are indicated and analyzed. Explanation of the general features of electromagnetic interactions and nuclear β + decay makes it possible to predict the yield and emittance for a given optical matching system between the positron source and the accelerator. Some kinds of matching systems commonly used - mainly working with solenoidal field - are studied and the acceptance volume calculated. Such knowledge is helpful in comparing different matching systems. Since for large machines, a significant distance exists between the positron source and the experimental facility, positron emittance has to be preserved during beam transfer over large distances and methods used for that purpose are indicated. Comparison of existing positron sources leads to extrapolation to sources for future linear colliders. Some new ideas associated with these sources are also presented. (orig.)

Low energy positron beam system for the investigation of 2D and porous materials

International Nuclear Information System (INIS)

Chrysler, M D; Chirayath, V A; Mcdonald, A D; Gladen, R W; Fairchild, A J; Koymen, A R; Weiss, A H

2017-01-01

An advanced variable energy positron beam (∼2 eV to 20 keV) has been designed, tested and utilized for coincidence Doppler broadening (CDB) measurements at the University of Texas at Arlington (UTA). A high efficiency solidified rare gas (Neon) moderator was used for the generation of a slow positron beam. The gamma rays produced as a result of the annihilation of positrons with the sample electrons are measured using a high purity Germanium (HPGe) detector in coincidence with a NaI(Tl) detector. Modifications to the system, currently underway, permits simultaneous measurements utilizing Positron annihilation induced Auger Electron Spectroscopy (PAES) and CDB. The tendency of positrons to become trapped in an image potential well at the surface will allow the new system to be used in measurements of the chemical structure of surfaces, internal or external and interfaces. The system will utilize a time of flight (TOF) technique for electron energy measurements. A 3m flight path from the sample to a micro-channel plate (MCP) in the new system will give it superior energy resolution at higher electron energies as compared to previous TOF systems utilizing shorter flight paths. (paper)

Pierce-type dispersion relation for an intense relativistic electron beam interacting with a slow-wave structure

International Nuclear Information System (INIS)

Chen, C.

1994-01-01

A Pierce-type dispersion relation is derived for the interaction of an intense relativistic electron beam with a cylindrical slow-wave structure of arbitrary corrugation depth. It is shown that near a resonance, the Pierce parameter can be expressed in terms of the vacuum dispersion function and the beam current. The dispersion relation is valid in both the low-current (Compton) regime and the high-current (Raman) regime. The dispersion characteristics of the interaction, such as the linear instability growth rate and bandwidth, are analyzed for both regimes

Slow positron studies of hydrogen activation/passivation on SiO2/Si(100) interfaces

International Nuclear Information System (INIS)

Lynn, K.G.; Asoka-Kumar, P.

1991-01-01

The hydrogen atoms are one of the most common impurity species found in semiconductor systems owing to its large diffusivity, and are easily incorporated either in a controlled process like in ion implantation or in an uncontrolled process like the one at the fabrication stage. Hydrogen can passivate dangling bonds and dislocations in these systems and hence can be used to enhance the electrical properties. In a SiO 2 /Si system, hydrogen can passivate electronic states at the interface and can alter the fixed or mobile charges in the oxide layer. Since hydrogen is present in almost all of the environments of SiO 2 /Si wafer fabrication, the activation energy of hydrogen atoms is of paramount importance to a proper understanding of SiO 2 /Si based devices and has not been measured on the technologically most important Si(100) face. There are no direct, nondestructive methods available to observe hydrogen injection into the oxide layer and subsequent diffusion. This study uses the positrons as a ''sensitive'', nondestructive probe to observe hydrogen interaction in the oxide layer and the interface region. We also describe a new way of characterizing the changes in the density of the interface states under a low-temperature annealing using positrons. 9 refs., 6 figs

Slow positron studies of hydrogen activation/passivation on SiO2/Si(100) interfaces

Science.gov (United States)

Lynn, K. G.; Asoka-Kumar, P.

The hydrogen atoms are one of the most common impurity species found in semiconductor systems owing to its large diffusivity, and are easily incorporated either in a controlled process like in ion implantation or in an uncontrolled process like the one at the fabrication stage. Hydrogen can passivate dangling bonds and dislocations in these systems and hence can be used to enhance the electrical properties. In a SiO2/Si system, hydrogen can passivate electronic states at the interface and can alter the fixed or mobile charges in the oxide layer. Since hydrogen is present in almost all of the environments of SiO2/Si wafer fabrication, the activation energy of hydrogen atoms is of paramount importance to a proper understanding of SiO2/Si based devices and has not been measured on the technologically most important Si(100) face. There are no direct, nondestructive methods available to observe hydrogen injection into the oxide layer and subsequent diffusion. The positrons are used as a 'sensitive', nondestructive probe to observe hydrogen interaction in the oxide layer and the interface region. A new way is described of characterizing the changes in the density of the interface states under a low temperature annealing using positrons.

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2017-01-15

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

Defects in fine-grained and porous materials characterized by positron annihilation

International Nuclear Information System (INIS)

Staab, T.E.M.; Krause-Rehberg, R.; Kieback, B.

2003-01-01

We investigate the annihilation parameters (lifetimes and intensities) for positrons becoming trapped at grain boundaries and at inner surfaces (pores), examining fine-grained nickel powder compacts (effective powder particle size 1 - 10 μm with grains in or even below the micron size). Furthermore, we can monitor grain growth and sintering (volume shrinkage) during successive heat treatment of powder compacts. To reach this aim, we correlate the annihilation parameters with results of a Monte-Carlo simulation and analytical solutions of the positron diffusion. We find that it is possible to determine an effective average powder particle size as well as grain sizes by positron lifetime spectroscopy. (author)

Characterization of ZnO nanostructures: A challenge to positron annihilation spectroscopy and other methods

Energy Technology Data Exchange (ETDEWEB)

Brauer, Gerhard; Anwand, Wolfgang; Grambole, Dieter; Skorupa, Wolfgang [Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden-Rossendorf, Dresden (Germany); Egger, Werner; Sperr, Peter [Institut fuer Angewandte Physik und Messtechnik LRT2, Fakultaet fuer Luft- und Raumfahrttechnik, Werner-Heisenberg-Weg 39, Universitaet der Bundeswehr, Neubiberg (Germany); Beinik, Igor; Wang, Lin; Teichert, Christian [Institut fuer Physik, Montanuniversitaet Leoben (Austria); Kuriplach, Jan; Lang, Jan [Department of Low Temperature Physics, Charles University, Prague (Czech Republic); Zviagin, Sergei; Cizmar, Erik [Institut Hochfeld-Magnetlabor, Forschungszentrum Dresden-Rossendorf, Dresden (Germany); Ling, Chi Chung; Hsu, Yuk Fan; Xi, Yan Yan; Chen, Xinyi; Djurisic, Aleksandra B. [Department of Physics, University of Hong Kong, Hong Kong (China)

2009-11-15

ZnO nanostructures are of special interest for device applications. However, their structural characterization remains an ongoing challenge. This paper reviews recent efforts and latest achievements in this direction. Results comprise PAS in the form of Slow Positron Implantation Spectroscopy (SPIS) and Pulsed Low Energy Positron Lifetime Spectroscopy (PLEPS), Nuclear Reaction Analysis (NRA), Atomic Force Microscopy (AFM), conductive AFM (C-AFM), Nuclear Magnetic Resonance (NMR), Electron Spin Resonance (ESR), Photoluminescence (PL) spectroscopy, and latest theoretical investigations of structure-related and positron properties of selected defects. The fundamental importance of a relationship between fabrication conditions, native defect formation, and resulting optical and electronic properties is demonstrated by getting either inferior (nanorods) or significantly improved (tetrapods) optical properties compared to single crystal samples, depending on the nanostructure fabrication method. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Hypoxia positron emission tomography imaging: combining information on perfusion and tracer retention to improve hypoxia specificity

DEFF Research Database (Denmark)

Busk, Morten; Munk, Ole L; Jakobsen, Steen S

2017-01-01

BACKGROUND: Static positron emission tomography (PET) allows mapping of tumor hypoxia, but low resolution and slow tracer retention/clearance results in poor image contrast and the risk of missing areas where hypoxic cells and necrosis are intermixed. Fully dynamic PET may improve accuracy but scan...

Theoretical aspects of studies of oxide and semiconductor surfaces using low energy positrons

Science.gov (United States)

Fazleev, N. G.; Maddox, W. B.; Weiss, A. H.

2011-01-01

This paper presents the results of a theoretical study of positron surface and bulk states and annihilation characteristics of surface trapped positrons at the oxidized Cu(100) single crystal and at both As- and Ga-rich reconstructed GaAs(100) surfaces. The variations in atomic structure and chemical composition of the topmost layers of the surfaces associated with oxidation and reconstructions and the charge redistribution at the surfaces are found to affect localization and spatial extent of the positron surface-state wave functions. The computed positron binding energy, work function, and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the surfaces. Theoretical positron annihilation probabilities with relevant core electrons computed for the oxidized Cu(100) surface and the As- and Ga-rich reconstructed GaAs(100) surfaces are compared with experimental ones estimated from the positron annihilation induced Auger peak intensities measured from these surfaces.

Photoluminescence and positron annihilation spectroscopic investigation on a H+ irradiated ZnO single crystal

Science.gov (United States)

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

2012-08-01

Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6 MeV H+ ions in a hydrothermally grown ZnO single crystal. Prior to irradiation, the emission from donor bound excitons is at 3.378 eV (10 K). The irradiation creates an intense and narrow emission at 3.368 eV (10 K). The intensity of this peak is nearly four times that of the dominant near band edge peak of the pristine crystal. The characteristic features of the 3.368 eV emission indicate its origin as a ‘hydrogen at oxygen vacancy’ type defect. The positron annihilation lifetime measurement reveals a single component lifetime spectrum for both the unirradiated (164 ± 1 ps) and irradiated crystal (175 ± 1 ps). It reflects the fact that the positron lifetime and intensity of the new irradiation driven defect species are a little higher compared to those in the unirradiated crystal. However, the estimated defect concentration, even considering the high dynamic defect annihilation rate in ZnO, comes out to be ˜4 × 1017 cm-3 (using SRIM software). This is a very high defect concentration compared to the defect sensitivity of positron annihilation spectroscopy. A probable reason is the partial filling of the incorporated vacancies (positron traps), which in ZnO are zinc vacancies. The positron lifetime of ˜175 ps (in irradiated ZnO) is consistent with recent theoretical calculations for partially hydrogen-filled zinc vacancies in ZnO. Passivation of oxygen vacancies by hydrogen is also reflected in the photoluminescence results. A possible reason for such vacancy filling (at both Zn and O sites) due to irradiation has also been discussed.

Photoluminescence and positron annihilation spectroscopic investigation on a H+ irradiated ZnO single crystal

International Nuclear Information System (INIS)

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

2012-01-01

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

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

Science.gov (United States)

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

2012-08-15

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

Nonlinear electromagnetic waves in a degenerate electron-positron plasma

Energy Technology Data Exchange (ETDEWEB)

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

2015-08-15

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

Positron annihilation spectroscopic studies of solvothermally synthesized ZnO nanobipyramids and nanoparticles

Science.gov (United States)

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

2008-02-01

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

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

International Nuclear Information System (INIS)

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

2007-01-01

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

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)

HAWC Observations Strongly Favor Pulsar Interpretations of the Cosmic-Ray Positron Excess

Energy Technology Data Exchange (ETDEWEB)

Hooper, Dan [Fermilab; Cholis, Ilias [Johns Hopkins U.; Linden, Tim [Ohio State U., CCAPP; Fang, Ke [Maryland U.

2017-11-17

Recent measurements of the Geminga and B0656+14 pulsars by the gamma-ray telescope HAWC (along with earlier measurements by Milagro) indicate that these objects generate significant fluxes of very high-energy electrons. In this paper, we use the very high-energy gamma-ray intensity and spectrum of these pulsars to calculate and constrain their expected contributions to the local cosmic-ray positron spectrum. Among models that are capable of reproducing the observed characteristics of the gamma-ray emission, we find that pulsars invariably produce a flux of high-energy positrons that is similar in spectrum and magnitude to the positron fraction measured by PAMELA and AMS-02. In light of this result, we conclude that it is very likely that pulsars provide the dominant contribution to the long perplexing cosmic-ray positron excess.

Radiation from channeled positrons in a hypersonic wave field

International Nuclear Information System (INIS)

Mkrtchyan, A.R.; Gasparyan, R.A.; Gabrielyan, R.G.

1987-01-01

The radiation emitted by channeled positrons in a longitudinal or transverse standing hypersonic wave field is considered. In the case of plane channeling the spectral distribution of the radiation intensity is shown to be of a resonance nature depending on the hypersound frequency

Temperature and time dependence of free volume in bisphenol A polycarbonate studied by positron lifetime spectroscopy

NARCIS (Netherlands)

Kluin, J.E.; Yu, Z.; Vleeshouwers, S.M.; McGervey, J.D.; Jamieson, A.M.; Simha, R.

1992-01-01

New positron lifetime expts. were carried out for Bisphenol-A polycarbonate. The influence of unavoidable pos. charged positron irradn. on the lifetime and intensity of o-positronium (o-Ps) annihilation was studied. Results obtained using a state-of-the-art lifetime spectrometer (count rate 670 cps

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

CERN Document Server

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

2000-01-01

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

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

Science.gov (United States)

Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Weiss, A. H.

2011-06-01

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The PAES intensity then decreases monotonically as the annealing temperature is increased to ˜550 °C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M2,3VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 °C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

International Nuclear Information System (INIS)

Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Weiss, A. H.

2011-01-01

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The PAES intensity then decreases monotonically as the annealing temperature is increased to ∼550 deg. C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M 2,3 VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 deg. C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.

Positron annihilation in superconducting 123 compounds

International Nuclear Information System (INIS)

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

1998-01-01

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

Application of positron annihilation technique to reverse osmosis membrane materials

International Nuclear Information System (INIS)

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

2000-01-01

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

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

Light storage via slow-light four-wave mixing

International Nuclear Information System (INIS)

Fan, Yun-Fei; Wang, Hai-Hua; Wei, Xiao-Gang; Li, Ai-Jun; Kang, Zhi-Hui; Wu, Jin-Hui; Zhang, Han-Zhuang; Xu, Huai-Liang; Gao, Jin-Yue

2012-01-01

We experimentally demonstrate a light storage via slow-light four-wave mixing in a solid-state medium with a four-level double lambda scheme. Using slow light based on electromagnetically induced transparency, we obtain a slowed four-wave mixing signal pulse together with the slowed probe pulse. During the propagation of light pulses, the storage and retrieval of both the slowed four-wave mixing pulse and the slowed probe pulse are studied by manipulating the intensities of the control fields. -- Highlights: ► A light storage via slow-light four-wave mixing is observed in a solid. ► The probe pulse is slowed under electromagnetically induced transparency. ► A slowed four-wave mixing pulse is obtained by slow light. ► The storage of slowed double pulses is studied.

Positron lifetime studies of electron irradiated copper

International Nuclear Information System (INIS)

Hadnagy, T.D.

1976-01-01

Single-crystal copper was irradiated with 4.5-MeV electrons producing simple Frenkel defects as well as a significant concentration of divacancies. Mean positron lifetime characteristics, which are sensitive to the presence of vacancies and multivacancies in copper, was monitored after isochronal anneals between 80 and 800 0 K to determine the relative change of characteristic mean lifetimes and their associated intensities. Also a study of the dependence of the mean positron lifetime on the total electron fluence was made and compared with existing theories relating these lifetimes to vacancy or multivacancy concentrations. Numerical data from curve fitting procedures using a conventional trapping model for defect-induced changes in positron lifetimes indicate that upon irradiation with 4.5-MeV electrons at 80 0 K, about 8 percent of the defects produced are divacancy units. Divacancy units appear to be several times more effective in trapping positrons than are monovacancies. Further, the experimental data suggest that the stage III annealing processes in electron-irradiated copper most probably involve the motion and removal of both monovacancies and divacancies. A conglomerate (multivacancy) unit appears to exist as a stable entity even after annealing procedures are carried out at temperatures slightly above the stage III region. Such a stable unit could serve as a nucleation center for the appearance of voids

Use of specific features of electron and positron interactions with monocrystals for the control of high-energy particle beam parameters

International Nuclear Information System (INIS)

Bochek, G.L.; Vit'ko, V.I.; Grishaev, I.A.; Kovalenko, G.D.; Kulibaba, V.I.; Morokhovskij, V.L.; Shramenko, B.I.

1977-01-01

To study possibilities of using the effect of high energy positron and electron interactions with crystals in practice at the 2 GeV Kharkov lineac the effect of a light particle charge sign on the processes of bremsstrahlung, elastic scattering and revealing ''blocking effect'' in elastic scatterina has been investigated experimentally of 1 GeV electron (positron) beam is directed to a silicon crystal of 185 μkm thickness. Dependence of total bremsstrahlung flow on the angle between the beam direction and crystal axis has shown, that positron bremsstrahlung is minimum (positrons are channelling, but electron bremsstrahlung is maximum, when crystallographic axis direction coincides with particle direction. The process of positron annihilation in flight has been investigated in 300 μkm thick silicon monocrystal. Bremsstrahlung intensity for channeling positrons drops 4.4 times, and intensity of annihilation radiation - 1.6 times as compared to the case, when channeling regime is absent. Experimental data point out the possibility of using monocrystals for control of the parameters of high-energy particle control beams

Time of flight spectra of electrons emitted from graphite after positron annihilation

International Nuclear Information System (INIS)

Gladen, R W; Chirayath, V A; Chrysler, M D; Mcdonald, A D; Fairchild, A J; Shastry, K; Koymen, A R; Weiss, A H

2017-01-01

Low energy (∼2 eV) positrons were deposited onto the surface of highly oriented pyrolytic graphite (HOPG) using a positron beam equipped with a time of flight (TOF) spectrometer. The energy of the electrons emitted as a result of various secondary processes due to positron annihilation was measured using the University of Texas at Arlington’s (UTA) TOF spectrometer. The positron annihilation-induced electron spectra show the presence of a carbon KLL Auger peak at ∼263 eV. The use of a very low energy beam allowed us to observe a new feature not previously seen: a broad peak which reached to a maximum intensity at ∼4 eV and extended up to a maximum energy of ∼15 eV. The low energy nature of the peak was confirmed by the finding that the peak was eliminated when a tube in front of the sample was biased at -15 V. The determination that the electrons in the peak are leaving the surface with energies up to 7 times the incoming positron energy indicates that the electrons under the broad peak were emitted as a result of a positron annihilation related process. (paper)

Temporary acceleration of electrons while inside an intense electromagnetic pulse

Directory of Open Access Journals (Sweden)

Kirk T. McDonald

1999-12-01

Full Text Available A free electron can temporarily gain a very significant amount of energy if it is overrun by an intense electromagnetic wave. In principle, this process would permit large enhancements in the center-of-mass energy of electron-electron, electron-positron, and electron-photon interactions if these take place in the presence of an intense laser beam. Practical considerations severely limit the utility of this concept for contemporary lasers incident on relativistic electrons. A more accessible laboratory phenomenon is electron-positron production via an intense laser beam incident on a gas. Intense electromagnetic pulses of astrophysical origin can lead to very energetic photons via bremsstrahlung of temporarily accelerated electrons.

Positron annihilation studies of icosahedral quasicrystals and their approximants in the Al-Cu-Ru-(Si) alloy systems

International Nuclear Information System (INIS)

Uchiyama, H; Takahashi, T; Arinuma, K; Sato, K; Kanazawa, I; Hamada, E; Suzuki, T; Kirihara, K; Kimura, K

2004-01-01

The positron lifetimes for the icosahedral quasicrystal Al 62.4 Cu 25.4 Ru 12.2 and its cubic approximants (1/ 1-Al 58 Cu 31.5 Ru 10.5 , 1/ 1-Al 68 Cu 7 Ru 17 Si 8 , and 1/0-Al 55 Cu 15 Ru 20 Si 10 ), two-detector coincident Doppler broadening for the icosahedral quasicrystal Al 62.4 Cu 25.4 Ru 12.2 and its 1/ 1-Al 68 Cu 7 Ru 17 Si 8 cubic approximant, and the Doppler broadening obtained by making use of a slow positron beam for the 1/ 1-Al 58 Cu 31.5 Ru 10.5 cubic approximant have been measured. Structurally intrinsic trapping sites giving rise to saturation trapping were detected by lifetime measurements. The chemical environments of the trapping sites in the icosahedral quasicrystal Al 62.4 Cu 25.4 Ru 12.2 and the 1/ 1-Al 68 Cu 7 Ru 17 Si 8 cubic approximant were determined by coincident Doppler broadening techniques to be dominantly surrounded by Al atoms. The positron diffusion length in the 1/ 1-Al 58 Cu 31.5 Ru 10.5 cubic approximant derived from the measured S parameter measured by means of a slow positron beam was ∼ 180 A, which is clearly too short, probably due to the high concentration of trapping sites as described above. The atomic structures of the icosahedral quasicrystal Al 62.4 Cu 25.4 Ru 12.2 and its variety of approximants are discussed and compared to the present proposed model

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

International Nuclear Information System (INIS)

Ma Minyang; Qin Xiubo; Wang Baoyi; Wu Weiming

2013-01-01

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

Positron lifetime and Doppler broadening study of defects created by swift ion irradiation in sapphire

International Nuclear Information System (INIS)

Liszkay, L.; Gordo, P.M.; Lima, A. de; Havancsak, K.; Skuratov, V.A.; Kajcsos, Z.

2004-01-01

Swift ions create a defect profile penetrating deep into a solid compared to the sampling range of typical slow positron beams, which may consequently study a homogeneous zone of defected materials. To investigate the defect population created by energetic ions, we studied α-Al 2 O 3 single crystals irradiated with swift Kr ions by using conventional and pulsed positron beams. Samples irradiated with krypton at 245 MeV energy in a wide fluence range show nearly saturated positron trapping above 5 x 10 10 ions cm -2 fluence, indicating the creation of monovacancies in high concentration. At 1 x 10 14 ions cm -2 irradiation a 500 ps long lifetime component appears, showing the creation of larger voids. This threshold corresponds well to the onset of the overlap of the damage zones after Bi ion irradiation along the ion trajectories observed with microscopic methods. (orig.)

Positron annihilation studies in ZnO nanoparticles

Science.gov (United States)

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

2009-04-01

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

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

Behavior of positronium in polystyrene and its derivatives

International Nuclear Information System (INIS)

Honda, Y.; Watanabe, M.; Tashiro, M.; Terashima, Y.; Miyamoto, K.; Kimura, N.; Tagawa, S.

2003-01-01

The polystyrene, poly(4-bromostyrene) and poly(4-vinylphenol) are investigated using slow positron beam based on electron linac. There was a difference in the intensity of long-lived component of lifetime in o-Ps (τ 3 ). The S-parameter and the intensity of τ 3 were strongly influenced by the presence of the substituents of polystyrene. In thin films, irradiation effect caused by positron beam was observed

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 lifetime studies on thorium oxide powders

International Nuclear Information System (INIS)

Upadhyaya, D.D.; Muraleedharan, R.V.; Sharma, B.D.

1982-01-01

Positron lifetime spectra have been studied for ThO 2 powders, calcined at different temperatures and having different particle sizes. Three lifetime components could be resolved, the longest component being of low intensity. An observed strong dependence on the particle size of the annihilation process and the variation of positronium diffusion constant is explained on the basis of defect density variations in these powders. (author)

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2002-12-01

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

Brilliant positron sources for CLIC and other collider projects

CERN Document Server

Rinolfi, Louis; Dadoun, Olivier; Kamitani, Takuya; Strakhovenko, Vladimir; Variola, Alessandro

2013-01-01

The CLIC (Compact Linear Collider), as future linear collider, requires an intense positron source. A brief history is given up to the present baseline configuration which assumes unpolarized beams. A conventional scheme, with a single tungsten target as source of e-e+ pairs, has been studied several years ago. But, in order to reduce the beam energy deposition on the e+ target converter, a double-target system has been studied and proposed as baseline for CLIC. With this ‘‘hybrid target’’, the positron production scheme is based on the channeling process. A 5 GeV electron beam impinges on a thin crystal tungsten target aligned along its axis, enhancing the photon production by channeling radiation. A large number of photons are sent to a thick amorphous tungsten target, generating large number of e-e+ pairs, while the charged particles are bent away, reducing the deposited energy and the PEDD (Peak Energy Deposition Density). The targets parameters are optimized for the positron production. Polarize...

Using polarized positrons to probe physics beyond the standard model

Science.gov (United States)

Furletova, Yulia; Mantry, Sonny

2018-05-01

A high intensity polarized positron beam, as part of the JLAB 12 GeV program and the proposed electron-ion collider (EIC), can provide a unique opportunity for testing the Standard Model (SM) and probing for new physics. The combination of high luminosity with polarized electrons and positrons incident on protons and deuterons can isolate important effects and distinguish between possible new physics scenarios in a manner that will complement current experimental efforts. A comparison of cross sections between polarized electron and positron beams will allow for an extraction of the poorly known weak neutral current coupling combination 2C3u - C3d and would complement the proposed plan for a precision extraction of the combination 2C2u - Cd at the EIC. Precision measurements of these neutral weak couplings would constrain new physics scenarios including Leptoquarks, R-parity violating supersymmetry, and electron and quark compositeness. The dependence of the charged current cross section on the longitudinal polarization of the positron beam will provide an independent probe to test the chiral structure of the electroweak interactions. A polarized positron can probe charged lepton flavor violation (CLFV) through a search for e+ → τ+ transitions in a manner that is independent and complementary to the proposed e- → τ- search at the EIC. A positron beam incident on an electron in a stationary nuclear target will also allow for a dark-photon (A') search via the annihilation process e+ + e- → A' + γ.

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

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

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

Science.gov (United States)

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

1996-01-01

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

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

BEPC II positron source

International Nuclear Information System (INIS)

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

2006-01-01

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

Positron annihilation spectroscopy study of porous silicon

International Nuclear Information System (INIS)

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

2007-01-01

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

Recent Progress on Laser Produced Positron Research At LLN

Science.gov (United States)

Chen, Hui; Hermann, M.; Kalantar, D.; Kemp, A.; Link, A.; Jiang, S.; Martinez, D.; Park, J.; Remington, B.; Sherlock, M.; Williams, Gj; Beg, F.; Edghill, B.; Fedosejevs, R.; Kerr, S.; D'Humieres, E.; Fiuza, F.; Willingale, L.; Fiksel, G.; Nakai, N.; Arikawa, Y.; Morace, A.; Sentoku, Y.

2017-10-01

We report the recent results on laser-produced relativistic electron-positron plasma jets. This includes: the prepulse and material dependence of pair generation; time dependent positron acceleration and maximum achieved pair density. We will highlight the results from recent experiments on the Omega EP laser testing nanostructured target to increase pair yield. We will also report on a newly commissioned platform using the NIF ARC lasers which was developed for efficient pair creation using 10 ps laser duration at near relativistic laser intensity. This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344, and funded by LDRD (#17-ERD-010).

Polarized positrons in Jefferson lab electron ion collider (JLEIC)

Science.gov (United States)

Lin, Fanglei; Grames, Joe; Guo, Jiquan; Morozov, Vasiliy; Zhang, Yuhong

2018-05-01

The Jefferson Lab Electron Ion Collider (JLEIC) is designed to provide collisions of electron and ion beams with high luminosity and high polarization to reach new frontier in exploration of nuclear structure. The luminosity, exceeding 1033 cm-2s-1 in a broad range of the center-of-mass (CM) energy and maximum luminosity above 1034 cm-2s-1, is achieved by high-rate collisions of short small-emittance low-charge bunches with proper cooling of the ion beam and synchrotron radiation damping of the electron beam. The polarization of light ion species (p, d, 3He) and electron can be easily preserved, manipulated and maintained by taking advantage of the unique figure-8 shape rings. With a growing physics interest, polarized positron-ion collisions are considered to be carried out in the JLEIC to offer an additional probe to study the substructure of nucleons and nuclei. However, the creation of polarized positrons with sufficient intensity is particularly challenging. We propose a dedicated scheme to generate polarized positrons. Rather than trying to accumulate "hot" positrons after conversion, we will accumulate "cold" electrons before conversion. Charge accumulation additionally provides a novel means to convert high repetition rate (>100 MHz) electron beam from the gun to a low repetition rate (<100 MHz) positron beam for broad applications. In this paper, we will address the scheme, provide preliminary estimated parameters and explain the key areas to reach the desired goal.

3D fast reconstruction in positron emission tomography

International Nuclear Information System (INIS)

Egger, M.L.; Scheurer, A. Hermann; Joseph, C.; Morel, C.

1996-01-01

The issue of long reconstruction times in positron emission tomography (PET) has been addressed from several points of view, resulting in an affordable dedicated system capable of handling routine 3D reconstructions in a few minutes per frame : on the hardware side using fast processors and a parallel architecture, and on the software side, using efficient implementation of computationally less intensive algorithms

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

International Nuclear Information System (INIS)

Xie Jialin

1985-01-01

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

Positron emission tomography

International Nuclear Information System (INIS)

Paans, A.M.J.

1981-01-01

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

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

International Nuclear Information System (INIS)

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

2005-01-01

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

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)

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

International Nuclear Information System (INIS)

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

2009-01-01

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

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...

Study of Coulomb effects using the comparison of positrons and electrons elastic scattering on nuclei

International Nuclear Information System (INIS)

Breton, Vincent

1990-01-01

We have studied Coulomb effects in the electron-nucleus interaction by measuring electron and positron elastic scattering. The Coulomb field of the nucleus acts differently on theses particles because of their opposite charges. The experiment took place at the Accelerateur Lineaire de Saclay, with 450 MeV electrons and positrons. We measured the emittance of the positron and electron beams. We compared electron and positron beams having the same energy, the same emittance and the same intensity. This way, we measured positron scattering cross sections with 2 % systematic error. By comparing positron and electron elastic scattering cross sections for momentum transfers between 1 and 2 fm -1 , on a Lead 208 target, we showed that the calculations of Coulomb effects in elastic scattering are in perfect agreement with experimental results. The comparison of positron and electron elastic scattering cross sections on Carbon showed that dispersive effects are smaller than 2 % outside the diffraction minima. These two results demonstrate in a definitive way that electron scattering allows to measure charge densities in the center of nuclei with an accuracy of the order of 1 %. (author) [fr

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.

Slow extraction from the IHEP accelerator by internal target scattering

International Nuclear Information System (INIS)

Maksimov, A.V.

1994-01-01

The existing slow extraction system is not able to satisfy the required quality of the beam time structure in the intensity region 10 10 - 10 11 ppp. Calculations on simulation of slow extraction by internal target scattering are presented. Two regime of slow extraction are analysed: nonresonant and resonant extraction by target scattering. Resonant extraction by target scattering is able to ensure intensity of extracted beam up to 10 11 . The agreement between calculations and experimental data is good enough. The calculation of extraction possibility by thin W-target scattering are also presented. In this case the extraction efficiency is about 85%. 15 refs., 6 figs

Radiation from planar channeled 5-55 GeV/c positrons and electrons

International Nuclear Information System (INIS)

Atkinson, M.; Sharp, P.H.; Giddings, D.; Bussey, P.J.

1982-01-01

The emission of radiation from 5 to 55 GeV/c planar channeled positrons and electrons passing through a 135 μ thick silicon-crystal has been investigated. The intensity of the channeling-radiation is found to be 10 to 30 times the intensity of normal bremsstrahlung. For channeled electrons no structure is found in the spectrum, whereas strong and sharp peaks are found for positrons. This peak structure is extremely sharp at 5 GeV/c and for momenta above 20 GeV/c the structure disappears. For a classical description of channeling, but using an anharmonic potential, certain energies are found for which the maximum energy of the channeling radiation is practically independent of transverse energy. The possibility of making a monoenergetic γ-source in the range of 10-100 MeV is mentioned. (orig.)

Novel time-of-flight spectrometer for the analysis of positron annihilation induced Auger electrons

International Nuclear Information System (INIS)

Hugenschmidt, Christoph; Legl, Stefan

2006-01-01

Positron annihilation induced Auger-electron spectroscopy (PAES) has several advantages over conventional Auger-electron spectroscopy such as extremely high surface sensitivity and outstanding signal-to-noise ratio at the Auger-transition energy. In order to benefit from these prominent features a low-energy positron beam of high intensity is required for surface sensitive PAES studies. In addition, an electron energy analyzer is required, which efficiently detects the Auger electrons with acceptable energy resolution. For this reason a novel time-of-flight (TOF) spectrometer has been developed at the intense positron source NEPOMUC that allows PAES studies within short measurement time. This TOF-PAES setup combines a trochoidal filter and a flight tube in a Faraday cage in order to achieve an improved energy resolution of about 1 eV at high electron energies up to E≅1000 eV. The electron flight time is the time between the annihilation radiation at the sample and when the electron hits a microchannel plate detector at the end of the flight tube

Positron studies of defected metals, metallic surfaces

International Nuclear Information System (INIS)

Bansil, A.

1991-01-01

Specific problems proposed under this project included the treatment of electronic structure and momentum density in various disordered and defected systems. Since 1987, when the new high-temperature superconductors were discovered, the project focused extensively on questions concerning the electronic structure and Fermiology of high-T c superconductors, in particular, (i) momentum density and positron experiments, (ii) angle-resolved photoemission intensities, (iii) effects of disorder and substitutions in the high-T c 's

Low energy positron diffraction from Cu(111): Importance of surface loss processes at large angles of incidence

International Nuclear Information System (INIS)

Lessor, D.L.; Duke, C.B.; Lippel, P.H.; Brandes, G.R.; Canter, K.F.; Horsky, T.N.

1990-10-01

Intensities of positrons specularly diffracted from Cu(111) were measured at the Brandeis positron beam facility and analyzed in the energy range 8eV i = 4eV. At lower energies strong energy dependences occur associated both with multiple elastic scattering phenomena within atomic layers of Cu parallel to the surface and with the thresholds of inelastic channels (e.g., plasmon creation). Use of the free electron calculation of V i shows that energy dependence of inelastic processes is necessary to obtain a satisfactory description of the absolute magnitude of the diffracted intensities below E = 50eV. Detailed comparison of the calculated and observed diffraction intensities reveals the necessity of incorporating surface loss processes explicitly into the model in order to achieve a quantitative description of the measured intensities for E 40 degree. 30 refs., 5 figs., 1 tab

Positron Annihilation Spectroscopy as a Novel Interfacial Probe for Thin Polymeric Films and Nano-Composites

Science.gov (United States)

Awad, Somia; Chen, Hongmin; Maina, Grace; Lee, L. James; Gu, Xiaohong; Jean, Y. C.

2010-03-01

Positron annihilation spectroscopy (PAS) has been developed as a novel probe to characterize the sub-nanometer defect, free volume, profile from the surface, interfaces, and to the bulk in polymeric materials when a variable mono-energy slow positron beam is used. Free-volume hole sizes, fractions, and distributions are measurable as a function of depth at the high precision. PAS has been successfully used to study the interfacial properties of polymeric nanocomposites at different chemical bonding. In nano-scale thin polymeric films, such as in PS/SiO2, and PU/ZnO, significant variations of Tg as a function of depth and of wt% oxide are observed. Variations of Tg are dependent on strong or weak interactions between polymers and nano-scale oxides surfaces.

Modelling low energy electron and positron tracks in biologically relevant media

International Nuclear Information System (INIS)

Blanco, F.; Munoz, A.; Almeida, D.; Ferreira da Silva, F.; Limao-Vieira, P.; Fuss, M.C.; Sanz, A.G.; Garcia, G.

2013-01-01

This colloquium describes an approach to incorporate into radiation damage models the effect of low and intermediate energy (0-100 eV) electrons and positrons, slowing down in biologically relevant materials (water and representative biomolecules). The core of the modelling procedure is a C++ computing programme named 'Low Energy Particle Track Simulation (LEPTS)', which is compatible with available general purpose Monte Carlo packages. Input parameters are carefully selected from theoretical and experimental cross section data and energy loss distribution functions. Data sources used for this purpose are reviewed showing examples of electron and positron cross section and energy loss data for interactions with different media of increasing complexity: atoms, molecules, clusters and condense matter. Finally, we show how such a model can be used to develop an effective dosimetric tool at the molecular level (i.e. nanodosimetry). Recent experimental developments to study the fragmentation induced in biologically material by charge transfer from neutrals and negative ions are also included. (authors)

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.

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

Structural characterization of H plasma-doped ZnO single crystals by positron annihilation spectroscopies

Energy Technology Data Exchange (ETDEWEB)

Anwand, Wolfgang; Brauer, Gerhard; Cowan, Thomas E. [Institut fuer Strahlenphysik, Forschungszentrum Dresden-Rossendorf, P.O. Box 510 119, 01314 Dresden (Germany); Grambole, Dieter; Skorupa, Wolfgang [Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden-Rossendorf, P.O. Box 510 119, 01314 Dresden (Germany); Cizek, Jakub; Kuriplach, Jan; Prochazka, Ivan [Department of Low Temperature Physics, Charles University, V Holesovickach 2, 18000 Prague (Czech Republic); Egger, Werner; Sperr, Peter [Institut fuer Angewandte Physik und Messtechnik, Fakultaet fuer Luft- und Raumfahrttechnik, Universitaet der Bundeswehr, Heisenbergweg 39, 85579 Neubiberg (Germany)

2010-11-15

Nominally undoped, hydrothermally grown ZnO single crystals have been investigated before and after exposure to remote H plasma. Structural characterizations have been made by various positron annihilation spectroscopies (continuous and pulsed slow positron beams, conventional lifetime). The content of bound hydrogen (H-b) before and after the remote H plasma treatment at the polished side of the crystals was determined at depths of 100 and 600 nm, respectively, using nuclear reaction analysis. At a depth of 100 nm, H-b increased from (11.8{+-}2.5) to (48.7{+-}7.6) x 10{sup 19} cm{sup -3} after remote H plasma treatment, whereas at 600 nm no change in H-b was observed. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

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

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

Positron studies in catalysis research

International Nuclear Information System (INIS)

1994-01-01

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

22 Na positron source for annihilation positron spectroscopy

International Nuclear Information System (INIS)

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

2003-01-01

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

Positron effective mass in silicon

International Nuclear Information System (INIS)

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

1995-01-01

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

Positron emission tomography

International Nuclear Information System (INIS)

Iio, Masahiro

1982-01-01

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

Relaxed electric dipole moments of polar molecules interacting with a slow positron: H{sub 2}O and CH{sub 3}X (X=F, Cl, Br)

Energy Technology Data Exchange (ETDEWEB)

Assafrao, Denise; Mohallem, Jose R, E-mail: rachid@fisica.ufmg.b [Laboratorio de Atomos e Moleculas Especiais, Departamento de FIsica, ICEx, Universidade Federal de Minas Gerais, PO Box 702, 30123-970, Belo Horizonte, MG (Brazil)

2010-08-14

The variation in the electric dipole moments of H{sub 2}O, CH{sub 3}F, CH{sub 3}Cl and CH{sub 3}Br as their geometries relax due to interaction with a positron is evaluated. The results are in good agreement with a recently observed empirical dependence of the positron binding energy on molecular properties (Danielson et al 2009 J. Phys. B: At. Mol. Opt. Phys. 42 235203). For binding energies larger than 100 meV relaxation could alter significantly the analysis of the binding, but it is in the prospect of generating effective potentials for positron scattering by molecules that the effect can be more important.

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.

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 annihilation investigation and nuclear reaction analysis of helium and oxygen-implanted zirconia

International Nuclear Information System (INIS)

Grynszpan, R.I.; Saude, S.; Anwand, W.; Brauer, G.

2005-01-01

Since irradiation affects in-service properties of zirconia, we investigated the fluence dependence on production and thermal stability of defects induced by helium and oxygen-ion implantation in single crystals of yttria-fully-stabilized zirconia. In either case, depth profiling by slow positron implantation spectroscopy (SPIS) detects a distribution of vacancy-type defects peaking at 60% of the projected ion range R p . Owing to the saturation of positron-trapping occurring for low fluences, which depends on the ion mass, we could estimate a critical size of clusters ranging from 0.4 to 1.6 nm. The lack of SPIS-evidence of an open-volume excess at R p is explained by the presence of over-pressurized gas bubbles. This assumption is confirmed by Nuclear Reaction Analysis of 3 He concentration profiles, which shows that helium remains partly trapped at R p , even after annealing above 400 o C

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

International Nuclear Information System (INIS)

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

2008-01-01

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

22 Na positron source for annihilation positron spectroscopy

International Nuclear Information System (INIS)

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

2002-01-01

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

Positron 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

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

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

Positron lifetime studies in undoped and Sr doped La2CuO4

International Nuclear Information System (INIS)

Sundar, C.S.; Bharathi, A.; Hariharan, Y.; Vasumathi, D.

1992-01-01

The results of positron lifetime measurements as a function of temperature, in undoped and Sr doped La 2 CuO 4 are presented. A second component of lifetime with a value of 225 ps is seen to develop after 100degC, whose intensity grows sharply in the range of 100degC to 250degC. The mean lifetime increases from 170 ps to 207 ps as the temperature is increased from room temperature to 300degC. Using the results of the theoretical calculations of positron lifetimes at vacancies in La 2 CuO 4 , it is argued that the increase in lifetime with temperature is due to positron trapping at the thermally generated La vacancies. From a two state trapping model analysis, the formation energy is estimated to be 0.39±0.04 eV

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

Analysis of the experimental positron lifetime spectra by neural networks

International Nuclear Information System (INIS)

Avdic, S.; Chakarova, R.; Pazsit, I.

2003-01-01

This paper deals with the analysis of experimental positron lifetime spectra in polymer materials by using various algorithms of neural networks. A method based on the use of artificial neural networks for unfolding the mean lifetime and intensity of the spectral components of simulated positron lifetime spectra was previously suggested and tested on simulated data [Pazsit et al., Applied Surface Science, 149 (1998), 97]. In this work, the applicability of the method to the analysis of experimental positron spectra has been verified in the case of spectra from polymer materials with three components. It has been demonstrated that the backpropagation neural network can determine the spectral parameters with a high accuracy and perform the decomposition of lifetimes which differ by 10% or more. The backpropagation network has not been suitable for the identification of both the parameters and the number of spectral components. Therefore, a separate artificial neural network module has been designed to solve the classification problem. Module types based on self-organizing map and learning vector quantization algorithms have been tested. The learning vector quantization algorithm was found to have better performance and reliability. A complete artificial neural network analysis tool of positron lifetime spectra has been constructed to include a spectra classification module and parameter evaluation modules for spectra with a different number of components. In this way, both flexibility and high resolution can be achieved. (author)

Simulation of QED effects in ultrahigh intensity laser-plasma interaction

International Nuclear Information System (INIS)

Kostyukov, I.; Nerush, E.

2010-01-01

Complete text of publication follows. Due to an impressive progress in laser technology, laser pulses with peak intensity of nearly 2 x 10 22 W/cm 2 are now available in laboratory. When the matter is irradiated by so intense laser pulses high energy density plasma is produced. Besides of fundamental interest such plasma is the efficient source of particles and radiation with extreme parameters that opens bright perspectives in developments of advanced particle accelerators, next generation of radiation sources, laboratory modelling of astrophysics phenomena etc. Even high laser intensity the radiation reaction and QED effects become important. One of the QED effects, which recently attracts much attention, is the electron-positron plasma creation in strong laser field. The plasma can be produced via electromagnetic cascades: the seeded charged particles is accelerated in the field of counter-propagating laser pulses, then they emit energetic photons, the photons by turn decay in the laser field and create electron-positron pairs. The pair particles accelerated in the laser field produce new generation of the photons and pairs. For self-consistent study of the electron-positron plasma dynamics in the laser field we develop 2D code based on particle-in-cell and Monte-Carlo methods. The electron, positron and photon dynamics as well as evolution of the plasma and laser fields are calculated by PIC technique while photon emission and pair production are calculated by Monte-Carlo method. We simulate pair production in the field of counter-propagating linearly polarized laser pulses. It is shown that for the laser intensity above threshold the plasma production becomes so intense that the laser pulse are strongly absorbed in the plasma. The laser intensity threshold and the rate of laser field absorption are calculated. Acknowledgements. This work has been supported by federal target 'The scientific and scientific-pedagogical personnel of innovation in Russia' and by

Bitemporal hypometabolism in Creutzfeldt-Jakob disease measured by positron emission tomography with [18F]-2-fluorodeoxyglucose

International Nuclear Information System (INIS)

Friedland, R.P.; Prusiner, S.B.; Jagust, W.J.; Budinger, T.F.; Davis, R.L.

1984-01-01

It is well established that Creutzfeldt-Jakob disease (CJD) is caused by a slow infectious agent similar to the scrapie prion. However, the pathogenesis of this infection is poorly understood. Positron emission tomography (PET) was performed on a 54-year-old man with autopsy confirmed CJD using [18F]-2-fluorodeoxyglucose (FDG) and the Donner 280-crystal tomograph. Temporal lobe hypometabolism with hemispheric asymmetry was observed. These findings are similar to those previously obtained in PET-FDG studies of patients with clinically defined Alzheimer disease (AD). The similarities in the regional metabolic alterations between CJD and AD provide additional evidence for the possibility that AD may be caused by a slow infectious prion

Investigation of electronic lattice structure by positron annihilation in some insulators

International Nuclear Information System (INIS)

Coussot, Gerard

1970-01-01

The angular distribution of gamma quanta resulting from positron annihilation in single insulator crystals was measured with long slit geometry apparatus for intense positron sources ( 64 Cu ≅ 1 Ci). Two new phenomena were observed in the angular correlation curves. In the f. c. c. MgO, UO 2 , CaF 2 crystals, modulations appeared at angles corresponding to the limit of the first Brillouin zone in relation to the crystallographic direction studied. In SiO 2 , F 2 Mg, F 2 Mn crystals, a narrow peak at 0 mrad and a fine structure superimposed on the broad distribution, were resolved. The fine structure which is correlated with the narrow component is characterized by modulations appearing at angles corresponding to the projection of reciprocal lattice vectors along the crystallographic direction investigated. The narrow peak at p ≅ 0 suggests the formation of a bound state (positron-electron). If this bound state is described by a Bloch wave, the modulations observed correspond to the Fourier components which contribute to every reciprocal lattice vector p = G ('Umklapp' process). This model predicts that the 'Umklapp' process in polycrystals must produce a change in slope which can be experimentally observed. A systematic research of optimal observation conditions shows that the intensity of the narrow component is closely correlated with the purity and the perfection of the crystal where p-Ps is presumably formed as suggested by magnetic experiments. (author) [fr

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.

Simulation of the annihilation emission of galactic positrons; Modelisation de l'emission d'annihilation des positrons Galactiques

Energy Technology Data Exchange (ETDEWEB)

Gillard, W

2008-01-15

Positrons annihilate in the central region of our Galaxy. This has been known since the detection of a strong emission line centered on an energy of 511 keV in the direction of the Galactic center. This gamma-ray line is emitted during the annihilation of positrons with electrons from the interstellar medium. The spectrometer SPI, onboard the INTEGRAL observatory, performed spatial and spectral analyses of the positron annihilation emission. This thesis presents a study of the Galactic positron annihilation emission based on models of the different interactions undergone by positrons in the interstellar medium. The models are relied on our present knowledge of the properties of the interstellar medium in the Galactic bulge, where most of the positrons annihilate, and of the physics of positrons (production, propagation and annihilation processes). In order to obtain constraints on the positrons sources and physical characteristics of the annihilation medium, we compared the results of the models to measurements provided by the SPI spectrometer. (author)

Mining the bulk positron lifetime

International Nuclear Information System (INIS)

Aourag, H.; Guittom, A.

2009-01-01

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

Moisture dependence of positron lifetime in Kevlar-49

Science.gov (United States)

Singh, Jag J.; Holt, William H.; Mock, Willis, Jr.

1984-01-01

Because of filamentary character of Kevlar-49 aramid fibers, there is some concern about the moisture uptake and its effect on plastic composites reinforced with Kevlar-49 fibers. As part of continuing studies of positron lifetime in polymers, we have measured positron lifetime spectra in Kevlar-49 fibers as a function of their moisture content. The long lifetime component intensities are rather low, being only of the order of 2-3 percent. The measured values of long component lifetimes at various moisture levels in the specimens are as follows: 2072 +/- 173 ps (dry); 2013 +/- 193 ps (20.7 percent saturation); 1665 +/- 85 ps (25.7 percent saturation); 1745 +/- 257 ps (32.1 percent saturation); and 1772 +/- 217 ps (100 percent saturation). It is apparent that the long component lifetime at first decreases and then increases as the specimen moisture content increases. These results have been compared with those inferred from Epon-815 and Epon-815/K-49 composite data.

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...

Observation of magnetic resonances in electron clouds in a positron storage ring

International Nuclear Information System (INIS)

Pivi, M.T.F.; Ng, J.S.T.; Cooper, F.; Kharakh, D.; King, F.; Kirby, R.E.; Kuekan, B.; Spencer, C.M.; Raubenheimer, T.O.; Wang, L.F.

2010-01-01

The first experimental observation of magnetic resonances in electron clouds is reported. The resonance was observed as a modulation in cloud intensity for uncoated as well as TiN-coated aluminum surfaces in the positron storage ring of the PEP-II collider at SLAC. Electron clouds frequently arise in accelerators of positively charged particles, and severely impact the machines' performance. The TiN coating was found to be an effective remedy, reducing the cloud intensity by three orders of magnitude.

Few-photon electron-positron pair creation in the collision of a relativistic nucleus and an intense x-ray laser beam

International Nuclear Information System (INIS)

Mueller, C.; Gruen, N.; Voitkiv, A.B.

2004-01-01

We study the nonlinear process of e - e + pair creation by a nucleus which moves at a relativistic energy in the laboratory frame and collides with an intense x-ray laser beam. The collision system under consideration is chosen in such a way that the simultaneous absorption of at least two photons from the laser wave is required in order to exceed the energy threshold of the reaction. We calculate total and differential rates for both free-free and bound-free pair production. In the case of free-free pair creation we demonstrate the effect of the laser polarization on the spectra of the produced particles, and we show that at very high intensities the total rate exhibits features analogous to those well known from above-threshold ionization rates for atoms. In the case of bound-free pair creation a singularity is found in the laboratory frame angular distribution of the produced positron. This singularity represents a distinct characteristic of the bound-free pair production and allows one to separate this process from free-free pair creation even without detecting a bound state of the captured electron. For both types of pair creation we consider the dependences of the total rates on the collision parameters, give the corresponding scaling laws, and discuss the possibility to observe these nonlinear processes in a future experiment

Survey of elemental specificity in positron annihilation peak shapes

Science.gov (United States)

Myler, U.; Simpson, P. J.

1997-12-01

Recently the detailed interpretation of positron-annihilation γ-ray peak shapes has proven to be of interest with respect to their chemical specificity. In this contribution, we show highly resolved spectra for a number of different elements. To this purpose, annihilation spectra with strongly reduced background intensities were recorded in the two detector geometry, using a variable-energy positron beam. Division of the subsequently normalized spectra by a standard spectrum (in our case the spectrum of pure silicon) yields quotient spectra, which display features characteristic of the sample material. First we ascertain that the specific spectrum of an element is conserved in different chemical compounds, demonstrated here by identical oxygen spectra obtained from both SiO2/Si and MgO/Mg. Second, we show highly resolved spectra for a number of different elements (Fe...Zn, Ag, Ir...Au). We show that the characteristic features in these spectra vary in a systematic fashion with the atomic number of the element and can be tentatively identified with particular orbitals. Finally, for 26 different elements we compare the maximum intensity in the quotient spectra with the relative atomic density in the corresponding element. To our knowledge, this is the most comprehensive survey of such data made to date.

Thermal stability of grain boundaries in nanocrystalline Zn studied by positron lifetime spectroscopy

International Nuclear Information System (INIS)

Zhou Kai; Li Hui; Pang Jinbiao; Wang Zhu

2012-01-01

Nanocrystalline Zn prepared by compacting nanoparticles with mean grain size about 55 nm at 15 MPa has been studied by positron lifetime spectroscopy. For the bulk Zn sample, the vacancy defect is annealed out at about 350 °C, but for the nanocrystalline Zn sample, the vacancy cluster in grain boundaries is quite difficult to be annealed out even at very high temperature (410 °C). In the grain boundaries of nanocrystalline Zn, the small free volume defect (not larger than divacancy) is dominant according to the high relative intensity for the short positron lifetime (τ 1 ). The oxide (ZnO) inside the grain boundaries has been found having an effect to hinder the decrease of average positron lifetime (τ av ), which probably indicates that the oxide stabilizes the microstructure of the grain boundaries. This stabilization is very important for the nanocrystalline materials using as radiation resistant materials.

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

Science.gov (United States)

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

2016-02-01

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

MODELING OF REFLECTIVE PROPAGATING SLOW-MODE WAVE IN A FLARING LOOP

Energy Technology Data Exchange (ETDEWEB)

Fang, X.; Yuan, D.; Van Doorsselaere, T.; Keppens, R.; Xia, C. [Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven (Belgium)

2015-11-01

Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in extreme ultraviolet images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by the synthesized Solar Dynamics Observatory/Atmospheric Imaging Assembly 131, 94 Å emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km s{sup −1} in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps of the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation Fe xix line emission, we confirm that these reflected slow mode waves are propagating waves.

EEG, transmission computed tomography, and positron emission tomography with fluorodeoxyglucose 18F. Their use in adults with gliomas

International Nuclear Information System (INIS)

Newmark, M.E.; Theodore, W.H.; Sato, S.; De La Paz, R.; Patronas, N.; Brooks, R.; Jabbari, B.; Di Chiro, G.

1983-01-01

We evaluated the relationship between findings from EEG, transmission computed tomography (CT), and positron emission tomography in 23 adults with gliomas. The cortical metabolic rate was suppressed in patients with and without focal slowing. Focal delta activity was not related to involvement of gray or white matter. Rhythmic delta activity and focal attenuation of background amplitude on EEG, however, were correlated with involvement of the thalamus

FROM SLOW FOOD TO SLOW TOURISM

Directory of Open Access Journals (Sweden)

Bac Dorin Paul

2014-12-01

Full Text Available One of the effects of globalization is the faster pace of our lives. This rhythm can be noticed in all aspects of life: travel, work, shopping, etc. and it has serious negative effects. It has become common knowledge that stress and speed generate serious medical issues. Food and eating habits in the modern world have taken their toll on our health. However, some people took a stand and argued for a new kind of lifestyle. It all started in the field of gastronomy, where a new movement emerged – Slow Food, based on the ideas and philosophy of Carlo Petrini. Slow Food represents an important adversary to the concept of fast food, and is promoting local products, enjoyable meals and healthy food. The philosophy of the Slow Food movement developed in several directions: Cittaslow, slow travel and tourism, slow religion and slow money etc. The present paper will account the evolution of the concept and its development during the most recent years. We will present how the philosophy of slow food was applied in all the other fields it reached and some critical points of view. Also we will focus on the presence of the slow movement in Romania, although it is in a very early stage of development. The main objectives of the present paper are: to present the chronological and ideological evolution of the slow movement; to establish a clear separation of slow travel and slow tourism, as many mistake on for the other; to review the presence of the slow movement in Romania. Regarding the research methodology, information was gathered from relevant academic papers and books and also from interviews and discussions with local entrepreneurs. The research is mostly theoretical and empirical, as slow food and slow tourism are emerging research themes in academic circles.

Early positron emission tomography response-adapted treatment in stage I and II hodgkin lymphoma

DEFF Research Database (Denmark)

André, Marc P.E.; Girinsky, Théodore; Federico, Massimo

2017-01-01

Purpose Patients who receive combined modality treatment for stage I and II Hodgkin lymphoma (HL) have an excellent outcome. Early response evaluation with positron emission tomography (PET) scan may improve selection of patients who need reduced or more intensive treatments. Methods We performed...

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)

Bitemporal hypometabolism in Creutzfeldt-Jakob disease measured by positron emission tomography with (/sup 18/F)-2-fluorodeoxyglucose

Energy Technology Data Exchange (ETDEWEB)

Friedland, R.P.; Prusiner, S.B.; Jagust, W.J.; Budinger, T.F.; Davis, R.L.

1984-10-01

It is well established that Creutzfeldt-Jakob disease (CJD) is caused by a slow infectious agent similar to the scrapie prion. However, the pathogenesis of this infection is poorly understood. Positron emission tomography (PET) was performed on a 54-year-old man with autopsy confirmed CJD using (18F)-2-fluorodeoxyglucose (FDG) and the Donner 280-crystal tomograph. Temporal lobe hypometabolism with hemispheric asymmetry was observed. These findings are similar to those previously obtained in PET-FDG studies of patients with clinically defined Alzheimer disease (AD). The similarities in the regional metabolic alterations between CJD and AD provide additional evidence for the possibility that AD may be caused by a slow infectious prion.

Positron annihilation in a high-temperature superconductor YBa2Cu3O7-δ

International Nuclear Information System (INIS)

Vavryshchuk, Ya.; Levandovski, M.; Rybakov, V.N.; Yutlandov, I.A.

1988-01-01

Positron annihilation as a function of temperature in high-temperature superconductors YBa 2 Cu 3 O 7-δ has been investigated. It is shown that a change in the annihilation capacity at the transition into superconducting state is relatively small. The change of r 1 and r 2 positron lifetimes as well as of the intensity of the component with r 2 -J 2 and Doppler broadening S parameter allows one to assume that transition into superconducting state is accompanied with a certain decrease in electron density and with decreasing number of defects or increasing size of crystalline net

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

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

Study on defect properties of nanocrystalline TiO2 during phase transition by positron annihilation lifetime

Science.gov (United States)

Zheng, F.; Liu, Y.; Liu, Z.; Dai, Y.-Q.; Fang, P.-F.; Wang, S.-J.

2012-08-01

The defect properties of nanocrystalline TiO2 were investigated by positron annihilation lifetime spectroscopy (PALS) and X-ray diffraction (XRD) as a function of annealed temperature that ranged from 300 to 850 °C. Below 500 °C, the measured positron lifetimes of τ1 (200-206 ps) and τ2 (378-402 ps) revealed the existence of mono-vacancy and vacancy-clusters at grain surface and in the micro-void of intergranular region. Between 500 and 750 °C, the phase transition from anatase to rutile was probed by the variations of positron lifetime and XRD pattern. With the increasing temperature from 500 to 850 °C, the positron lifetime τ1, τ2 and its intensity I2 sharply decreased from 200 ps, 378 ps, and 60% to 135 ps, 274 ps, and 33%, respectively. The results clearly indicate that the mono-vacancy or vacancy-clusters at grain surface and micro-voids between the grains were annealed out during the phase transition.

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

International Nuclear Information System (INIS)

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

2003-01-01

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

Positron astronomy with SPI/INTEGRAL

International Nuclear Information System (INIS)

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

2008-01-01

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

Positron implantation profile in kapton

International Nuclear Information System (INIS)

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

1988-01-01

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

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

International Nuclear Information System (INIS)

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

2011-01-01

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

AGS intensity upgrades

International Nuclear Information System (INIS)

Roser, T.

1995-01-01

After the successful completion of the AGS Booster and several upgrades of the AGS, a new intensity record of 6.3 x 10 13 protons per pulse accelerated to 24 GeV was achieved. The high intensity slow-extracted beam program at the AGS typically serves about five production targets and about eight experiments including three rare Kaon decay experiments. Further intensity upgrades are being discussed that could increase the average delivered beam intensity by up to a factor of four

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

Characterization of vacancy-type defects induced by the implantation of Se and Si ions into GaAs by a slow positron beam

International Nuclear Information System (INIS)

Fujii, Satoshi; Shikata, Shinichi; Wei Long; Tanigawa, Shoichiro.

1992-01-01

Variable-energy (0-30keV) positron beam studies have been carried out on 200 keV Se-implanted and 70 keV Si-implanted GaAs specimens before and after annealing for electrical activation. From the measurements of Doppler broadened profiles as a function of incident positron energy, it was found that vacancy clusters with high concentration were introduced in the annealed specimen after Se implantation. From the parallel measurement of electrical characteristics, a higher activation efficiency was found for the higher concentration of vacancy clusters. That fact implies that electrons supplied by the activation of Se also convert the charge state of As vacancies from positive to negative. In contrast, no vacancy clusters were introduced in the Si-implanted GaAs. (author)

A positron annihilation study on the hydration of cement pastes

International Nuclear Information System (INIS)

Consolati, G.; Quasso, F.

2007-01-01

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

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.

The Potential of/for 'Slow': Slow Tourists and Slow Destinations

Directory of Open Access Journals (Sweden)

J. Guiver

2016-05-01

Full Text Available Slow tourism practices are nothing new; in fact, they were once the norm and still are for millions of people whose annual holiday is spent camping, staying in caravans, rented accommodation, with friends and relations or perhaps in a second home, who immerse themselves in their holiday environment, eat local food, drink local wine and walk or cycle around the area. So why a special edition about slow tourism? Like many aspects of life once considered normal (such as organic farming or free-range eggs, the emergence of new practices has highlighted differences and prompted a re-evaluation of once accepted practices and values. In this way, the concept of ‘slow tourism’ has recently appeared as a type of tourism that contrasts with many contemporary mainstream tourism practices. It has also been associated with similar trends already ‘branded’ slow: slow food and cittaslow (slow towns and concepts such as mindfulness, savouring and well-being.

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)

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 lifetime studies of sol-gel transition of carrageenan gels

International Nuclear Information System (INIS)

Wakabayashi, Y.; Ito, K.; Li, H.L.; Ujihara, Y.

1996-01-01

Positron annihilation lifetime measurement was applied to study the sol-gel transition of anionic polysaccharide aqueous solutions in terms of free-volume parameters the size, intensity, and size distribution of free volumes of the gelation of K-form κ-carrageenan solutions as a function of temperature. Slight variations of free volume size and intensity against temperature were observed near 295 K. The correlation of free-volume data with other physical properties vibrational spectra (IR and Raman), conductivity, SAXS, elastic measurement, differential scanning calorimetry were investigated to understand the mechanism of sol-gel transition of carrageenan. (author)

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.)

Vacancy defects in epitaxial La0.7Sr0.3MnO3 thin films probed by a slow positron beam

International Nuclear Information System (INIS)

Jin, S W; Zhou, X Y; Wu, W B; Zhu, C F; Weng, H M; Wang, H Y; Zhang, X F; Ye, B J; Han, R D

2004-01-01

Vacancy defects in epitaxial La 0.7 Sr 0.3 MnO 3 (LSMO) thin films on LaAlO 3 substrates were detected using a variable energy positron beam. The line-shape S parameter of the epitaxial thin films deposited at different oxygen pressures was measured as a function of the implanting positron energy E. Our results show that the S parameter of the films changes non-monotonically with their deposition oxygen pressures. For the films deposited at lower oxygen pressures, the increase in S value in the films is attributed to the increase in oxygen vacancies and/or related defect-V O complexes, and for those deposited at higher oxygen pressures, the larger S parameter of the films is caused by the grain boundaries and/or metallic ion vacancies. The surface morphology of the films was also characterized to analyse the open volume defects in the LSMO films

Nonlinear positron acoustic solitary waves

International Nuclear Information System (INIS)

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

2009-01-01

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

Positron emission tomography. Basic principles

International Nuclear Information System (INIS)

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

2001-01-01

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

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

Science.gov (United States)

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

2017-11-01

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

Positron annihilation 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...

Evaluation of vacancy-type defects in ZnO by the positron annihilation lifetime spectroscopy

International Nuclear Information System (INIS)

Ono, R.; Togimitsu, T.; Sato, W.

2015-01-01

Thermal behavior of vacancy-type defects in polycrystalline ZnO was studied by the positron annihilation lifetime spectroscopy. Two-component analysis of the PALS spectra revealed that the defect-related longer-lifetime component decreases as the annealing temperature is raised, and almost disappears within 15 min when annealed at 1,273 K. We also found that the intensity of this component decreases with increasing density of the annealed ZnO pellets; however, little density dependence was seen in its lifetime. These observations evidently suggest that this component having long lifetime of about 400 ps corresponds to the positrons trapped in grain boundaries in the polycrystalline ZnO. (author)

Depth-dependent positron annihilation in different polymers

Energy Technology Data Exchange (ETDEWEB)

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

2013-09-01

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

Simulation of the annihilation emission of galactic positrons; Modelisation de l'emission d'annihilation des positrons Galactiques

Energy Technology Data Exchange (ETDEWEB)

Gillard, W

2008-01-15

Positrons annihilate in the central region of our Galaxy. This has been known since the detection of a strong emission line centered on an energy of 511 keV in the direction of the Galactic center. This gamma-ray line is emitted during the annihilation of positrons with electrons from the interstellar medium. The spectrometer SPI, onboard the INTEGRAL observatory, performed spatial and spectral analyses of the positron annihilation emission. This thesis presents a study of the Galactic positron annihilation emission based on models of the different interactions undergone by positrons in the interstellar medium. The models are relied on our present knowledge of the properties of the interstellar medium in the Galactic bulge, where most of the positrons annihilate, and of the physics of positrons (production, propagation and annihilation processes). In order to obtain constraints on the positrons sources and physical characteristics of the annihilation medium, we compared the results of the models to measurements provided by the SPI spectrometer. (author)

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)

Photon emission by electrons and positrons traversing thin single crystal

International Nuclear Information System (INIS)

Ol'chak, A.S.

1984-01-01

Radiation emission by planar channeled particles (electrons, positrons) in a thin single crystal of thickness L is considered. It is shown that for L approximately πb/THETAsub(L) (b is the lattice constant, THETA sub(L) the Lindhard angle) besides the main spontaneous channeling maxima there exist auxiliary interference maxima, the positions of all the maxima depending on L. The dependence of the radiation spectral intensity on crystal thickness is discussed

Theoretical calculations of positron lifetimes for metal oxides

International Nuclear Information System (INIS)

Mizuno, Masataka; Araki, Hideki; Shirai, Yasuharu

2004-01-01

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

Production and applications of positron microbeams

International Nuclear Information System (INIS)

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

1989-01-01

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

Detection of tokamak plasma positrons using annihilation photons

Energy Technology Data Exchange (ETDEWEB)

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

2017-05-15

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

Time-dependent behavior of positrons in noble gases

International Nuclear Information System (INIS)

Wadehra, J.M.

1990-01-01

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

Positron annihilation probing for the hydratation rate of cement paste

International Nuclear Information System (INIS)

Myllylae, R.; Karras, M.

1975-01-01

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

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.)

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

International Nuclear Information System (INIS)

Dryzek, Jerzy

2009-01-01

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

Applications of positron depth profiling

Energy Technology Data Exchange (ETDEWEB)

Hakvoort, R A

1993-12-23

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

Applications of positron depth profiling

International Nuclear Information System (INIS)

Hakvoort, R.A.

1993-01-01

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

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.

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.)

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)

Positron lifetime technique with applications in materials science

International Nuclear Information System (INIS)

Vries, J. de.

1987-01-01

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

Results on positron diffusion in Si

International Nuclear Information System (INIS)

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

1984-10-01

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

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

International Nuclear Information System (INIS)

Colgate, S.A.

1983-01-01

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

Theoretical aspects of positrons in imperfect solids

International Nuclear Information System (INIS)

Puska, M.J.

1987-01-01

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

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.)

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

International Nuclear Information System (INIS)

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

1994-01-01

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

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 depth profiling of the structural and electronic structure transformations of hydrogenated Mg-based thin films

Science.gov (United States)

Eijt, S. W. H.; Kind, R.; Singh, S.; Schut, H.; Legerstee, W. J.; Hendrikx, R. W. A.; Svetchnikov, V. L.; Westerwaal, R. J.; Dam, B.

2009-02-01

We report positron depth-profiling studies on the hydrogen sorption behavior and phase evolution of Mg-based thin films. We show that the main changes in the depth profiles resulting from the hydrogenation to the respective metal hydrides are related to a clear broadening in the observed electron momentum densities in both Mg and Mg2Ni films. This shows that positron annihilation methods are capable of monitoring these metal-to-insulator transitions, which form the basis for important applications of these types of films in switchable mirror devices and hydrogen sensors in a depth-sensitive manner. Besides, some of the positrons trap at the boundaries of columnar grains in the otherwise nearly vacancy-free Mg films. The combination of positron annihilation and x-ray diffraction further shows that hydrogen loading at elevated temperatures, in the range of 480-600 K, leads to a clear Pd-Mg alloy formation of the Pd catalyst cap layer. At the highest temperatures, the hydrogenation induces a partial delamination of the ˜5 nm thin capping layer, as sensitively monitored by positron depth profiling of the fraction of ortho-positronium formed at interface with the cap layer. The delamination effectively blocks the hydrogen cycling. In Mg-Si bilayers, we investigated the reactivity upon hydrogen loading and heat treatments near 480 K, which shows that Mg2Si formation is fast relative to MgH2. The combination of positron depth profiling and transmission electron microscopy shows that hydrogenation promotes a complete conversion to Mg2Si for this destabilized metal hydride system, while a partially unreacted, Mg-rich amorphous prelayer remains on top of Mg2Si after a single heat treatment in an inert gas environment. Thin film studies indicate that the difficulty of rehydrogenation of Mg2Si is not primarily the result from slow hydrogen dissociation at surfaces, but is likely hindered by the presence of a barrier for removal of Mg from the readily formed Mg2Si.

Slow potentials in a melody recognition task.

Science.gov (United States)

Verleger, R; Schellberg, D

1990-01-01

In a previous study, slow negative shifts were found in the EEG of subjects listening to well-known melodies. The two experiments reported here were designed to investigate the variables to which these slow potentials are related. In the first experiment, two opposite hypotheses were tested: The slow shifts might express subjects' acquaintance with the melodies or, on the contrary, the effort invested to identify them. To this end, some of the melodies were presented in the rhythms of other melodies to make recognition more difficult. Further, melodies rated as very well-known and as very unknown were analysed separately. However, the slow shifts were not affected by these experimental variations. Therefore in the second experiment, on the one hand the purely physical parameters intensity and duration were varied, but this variation had no impact on the slow shifts either. On the other hand, recognition was made more difficult by monotonously repeating the pitch of the 4th tone for the rest of some melodies. The slow negative shifts were enhanced with these monotonous melodies. This enhancement supports the "effort" hypothesis. Accordingly, the ofter shifts obtained in both experiments might likewise reflect effort. But since the task was not demanding, it is suggested that these constant shifts reflect the effort invested for coping with the entire underarousing situation rather than with the task. Frequently, slow eye movements occurred in the same time range as the slow potentials, resulting in EOG potentials spreading to the EEG recording sites. Yet results did not change substantially when the EEG recordings were corrected for the influence of EOG potentials.

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.

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

Science.gov (United States)

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

2016-03-01

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

Experiments on the thermalization of slow neutrons by liquid hydrogen (1962)

International Nuclear Information System (INIS)

Cribier, D.; Jacrot, B.; Lacaze, A.; Roubeau, P.

1962-01-01

In order to increase the flux of neutrons of long wave-length (λ > 4 A) emerging from a channel in the EL-3, a liquid hydrogen device was introduced into a channel of the reactor (Channel H 1 ). The principle of the device is simple. A volume of liquid hydrogen is introduced as close as possible to the reactor core into a region of intense isotropic flux. This hydrogen slows down the slow neutrons; because of the very small mean free diffusion path of slow in hydrogen, this slowing down is considerable even in a small volume of liquid hydrogen, and the spectrum temperature of neutrons emerging from the volume of liquid hydrogen can therefore be shifted. The intensity gain for neutrons with a wave length λ, is a G (λ) function which, for perfect thermalization and ignoring capture, is expressed by: G (λ) = 225 exp (- 45.3/λ 2 ), assuming a temperature of 300 deg. K for the neutrons before cooling and is 20 deg. K after cooling. For a wave-length of 5 A, the theoretical maximum gain of thus about 37. (authors) [fr

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.

Simulation of the annihilation emission of galactic positrons

International Nuclear Information System (INIS)

Gillard, W.

2008-01-01

Positrons annihilate in the central region of our Galaxy. This has been known since the detection of a strong emission line centered on an energy of 511 keV in the direction of the Galactic center. This gamma-ray line is emitted during the annihilation of positrons with electrons from the interstellar medium. The spectrometer SPI, onboard the INTEGRAL observatory, performed spatial and spectral analyses of the positron annihilation emission. This thesis presents a study of the Galactic positron annihilation emission based on models of the different interactions undergone by positrons in the interstellar medium. The models are relied on our present knowledge of the properties of the interstellar medium in the Galactic bulge, where most of the positrons annihilate, and of the physics of positrons (production, propagation and annihilation processes). In order to obtain constraints on the positrons sources and physical characteristics of the annihilation medium, we compared the results of the models to measurements provided by the SPI spectrometer. (author)

Positron probes for mechanical fatigue detection system

International Nuclear Information System (INIS)

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

1976-01-01

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

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

Positron annihilation in solids: positronium diffusion

International Nuclear Information System (INIS)

Paulin, R.

1969-04-01

The existence of two slow components in life-time spectrum of positron annihilation in silicium, aluminium and alkaline-earth oxides powders is established. These two long mean-lives ≅ 10 -9 s and ≅ 10 -7 s result from annihilation, inside and outside the grains respectively, of ortho-positronium formed in defects present in ionic crystals investigated. Dynamic behaviour of Ps, so revealed, is analyzed in terms of diffusion in excellent agreement with experiment. Diffusion constants of the order of 10 -4 cm 2 sec -1 and mean path before annihilation from 50 to 300 Angstrom are measured. From 100 to 500 K the temperature influence upon diffusion process is effective only in SiO 2 where activation energy is found about 10 -2 eV. The p-Ps zero point energy evaluated by angular correlation gives the order of magnitude for defects dimensions and diffusion mean-time. Finally, o-Ps behaviour in space between grains, where its interaction with atmospheric gases can be only detected, is analysed. (author) [fr

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

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

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

Slowing of a fast electron beam in a plasma in an intense electromagnetic wave

Energy Technology Data Exchange (ETDEWEB)

Karapetyan, R.V.; Fedorov, M.V.

1980-01-01

The slowing of a fast electron beam as it penetrates into a plasma in a strong external electromagnetic field is studied. The effective collision frequency ..nu../sub p/ which is responsible for the slowing is derived in the dipole approximation; many-photon stimulated bremsstrahlung and inverse bremsstrahlung are taken into account. The asymptotic behavior of ..nu../sub p/ in strong wave fields E/sub 0/ is found. The results show that ..nu../sub p/ falls off with increasing E/sub 0/, because of a decrease in the frequency of collisions with plasma ions proportional to E/sub 0//sup -1/.

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

Ultrarelativistic electron and positron radiation in planar channeling

International Nuclear Information System (INIS)

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

1980-01-01

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

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

International Nuclear Information System (INIS)

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

2008-01-01

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

Polymerization of epoxy resins studied by positron annihilation

Energy Technology Data Exchange (ETDEWEB)

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

2001-04-01

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

Slow evaporation method and enhancement in photoluminescence ...

Indian Academy of Sciences (India)

nescence (PL) properties and decay time of phosphors were studied at room temperature. The YPO4 ... Keywords. Slow evaporation method; YPO4 : Eu3+, Bi3+; quenching effect; optical material. 1. ... intensity of Eu3+-doped compounds such as CaMoO4 : Bi3+, .... Figure 4 shows FESEM images of YPO4 : Eu3+ and Bi3+.

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.

Low-temperature positron lifetime and Doppler-broadening measurements for single-crystal nickel oxide containing cation vacancies

International Nuclear Information System (INIS)

Waber, J.T.; Snead, C.L. Jr.; Lynn, K.G.

1985-01-01

Lifetime and Doppler-broadening measurements for positron annihilation in substoichiometric nickelous oxide have been made concomitantly from liquid-helium to room temperature. The concentration of cation vacancies is readily controlled by altering the ambient oxygen pressure while annealing the crystals at 1673 0 K. It was found that neither of the three lifetimes observed or their relative intensities varied significantly with the oxygen pressure, and the bulk rate only increased slightly when the specimen was cooled from room to liquid-helium temperatures. These results are interpreted as indicating that some of the positrons are trapped by the existing cation vacancies and a smaller fraction by vacancy clusters

Studies of positron induced luminescence from polymers

International Nuclear Information System (INIS)

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

1994-01-01

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

Cardiac positron tomography

International Nuclear Information System (INIS)

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

1980-01-01

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

Variable energy positron beam study of Xe-implanted uranium oxide

International Nuclear Information System (INIS)

Djourelov, Nikolay; Marchand, Benoît; Marinov, Hristo; Moncoffre, Nathalie; Pipon, Yves; Nédélec, Patrick; Toulhoat, Nelly; Sillou, Daniel

2013-01-01

Doppler broadening of annihilation gamma-line combined with a slow positron beam was used to measure the momentum density distribution of annihilating pair in a set of sintered UO 2 samples. The influence of surface polishing, of implantation with 800-keV 136 Xe 2+ at fluences of 1 × 10 15 and 1 × 10 16 Xe cm −2 , and of annealing were studied by following the changes of the momentum distribution shape by means of S and W parameters. The program used for this purpose was VEPFIT. At the two fluences in the stoichiometric as-implanted UO 2 , formation of Xe bubbles was not detected. The post-implantation annealing and over-stoichiometry in the as-implanted sample caused Xe precipitation and formation of Xe bubbles.

Positron lifetime experiments in indium selenide

International Nuclear Information System (INIS)

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

1988-01-01

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

Cosmic Ray Positrons from Pulsars

Science.gov (United States)

Harding, Alice K.

2010-01-01

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

Undulator-based production of polarized positrons

Energy Technology Data Exchange (ETDEWEB)

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

2009-05-15

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

Positron lifetime study of neutron-irradiated molybdenum

International Nuclear Information System (INIS)

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

1978-01-01

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

Positron annihilation spectroscopy in materials structure studies

International Nuclear Information System (INIS)

Grafutin, Viktor I; Prokop'ev, Evgenii P

2002-01-01

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

Digital positron annihilation spectrometer

International Nuclear Information System (INIS)

Cheng Bin; Weng Huimin; Han Rongdian; Ye Bangjiao

2010-01-01

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

Positron emission tomography imaging--technical considerations

International Nuclear Information System (INIS)

Muehllehner, G.; Karp, J.S.

1986-01-01

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

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

CERN Multimedia

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

2002-01-01

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

Toward a European Network of Positron Laboratories

Directory of Open Access Journals (Sweden)

Karwasz Grzegorz P.

2015-12-01

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

Present status of the ETL LINAC facility

International Nuclear Information System (INIS)

Suzuki, Ryoichi; Mikado, Tomohisa; Ohgaki, Hideaki

1993-01-01

The ETL LINAC has been operated for the beam injection to the storage rings NIJI-II, III, IV, and TERAS, and for the generation of an intense slow positron beam. The status of the ETL LINAC on the operations, the maintenances, and the improvements is described. (author)

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

Cyclotrons and positron emitting radiopharmaceuticals

International Nuclear Information System (INIS)

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

1984-01-01

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

Positron emission tomography now and in the future

International Nuclear Information System (INIS)

Vaalburg, W.

1987-01-01

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

Positron creation in superheavy quasi-molecules

International Nuclear Information System (INIS)

Mueller, B.

1976-01-01

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

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

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

Science.gov (United States)

Stoneking, Matthew

2017-10-01

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

Positron studies of metal-oxide-semiconductor structures

Science.gov (United States)

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

1993-03-01

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

In-situ positron emission of CO oxidation

NARCIS (Netherlands)

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

1993-01-01

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

Shielding calculation of slow extracted beam facility at KEK proton synchrotron

International Nuclear Information System (INIS)

Hirabayashi, Hiromi; Katoh, Kazuaki

1978-01-01

The KEK proton synchrotron has two external beam lines, i.e. a fast extracted beam line for a bubble chamber and a slow extracted beam line for counter experiments. The maximum total intensity of the slow beam is estimated as 5 x 10 12 protons per sec. For beam losses along the line, shielding calculation was made, and on the basis of these results, adequacy of the current shielding construction plans was discussed. (Mori, K.)

Positron emission tomography

International Nuclear Information System (INIS)

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

1994-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-12-31

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

Cyclotrons and positron emitting radiopharmaceuticals

Energy Technology Data Exchange (ETDEWEB)

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

1984-01-01

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

Positron emission tomography with Positome, 2

International Nuclear Information System (INIS)

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

1979-01-01

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