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

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

Energy Technology Data Exchange (ETDEWEB)

Mayer, Jakob

2010-04-03

It was the aim of this thesis to improve the existing positron annihilation induced Auger spectrometer at the highly intense positron source NEPOMUC (NEutron induced POsitron source MUniCh) in several ways: Firstly, the measurement time for a single spectrum should be reduced from typically 12 h to roughly 1 h or even less. Secondly, the energy resolution, which amounted to {delta}E/E{approx}10%, should be increased by at least one order of magnitude in order to make high resolution positron annihilation induced Auger spectroscopy (PAES)-measurements of Auger transitions possible and thus deliver more information about the nature of the Auger process. In order to achieve these objectives, the PAES spectrometer was equipped with a new electron energy analyzer. For its ideal operation all other components of the Auger analysis chamber had to be adapted. Particularly the sample manipulation and the positron beam guidance had to be renewed. Simulations with SIMION {sup registered} ensured the optimal positron lens parameters. After the adjustment of the new analyzer and its components, first measurements illustrated the improved performance of the PAES setup: Firstly, the measurement time for short overview measurements was reduced from 3 h to 420 s. The measurement time for more detailed Auger spectra was shortened from 12 h to 80 min. Secondly, even with the reduced measurement time, the signal to noise ratio was also enhanced by one order of magnitude. Finally, the energy resolution was improved to {delta}E/E < 1. The exceptional surface sensitivity and elemental selectivity of PAES was demonstrated in measurements of Pd and Fe, both coated with Cu layers of varying thickness. PAES showed that with 0.96 monolayer of Cu on Fe, more than 55% of the detected Auger electrons stem from Cu. In the case of the Cu coated Pd sample 0.96 monolayer of Cu resulted in a Cu Auger fraction of more than 30% with PAES and less than 5% with electron induced Auger spectroscopy

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

Automation of variable low-energy positron beam experiments

CERN Document Server

Jayapandian, J; Amarendra, G; Venugopal-Rao, G; Purniah, B; Viswanathan, B

2000-01-01

By exploiting the special BIOS interrupt (INT 1CH) of PC in conjunction with a compatible high-voltage controller card and menu-driven control program, we report here the automation of variable low-energy positron beam experiments. The beam experiment consists of monitoring the Doppler broadening lineshape parameters corresponding to the annihilation 511 keV gamma-ray at various positron beam implantation energies. The variation and monitoring of the sample high voltage, which determines positron beam energy, is carried out using a controller add-on card coupled to a 0-30 kV high-voltage unit. The design features of this controller card are discussed. This controller card is housed in a PC, which also houses a multichannel analyser (MCA) card. The MCA stores the Doppler energy spectrum of the annihilation gamma-ray. The interactive control program, written in Turbo C, carries out the assigned tasks. The design features of the automation and results are presented.

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

Opportunities and challenges of a low-energy positron source in the LERF

Science.gov (United States)

Benson, Stephen; Wojtsekhowski, Bogdan; Vlahovic, Branislav; Golge, Serkan

2018-05-01

Though there are many applications of low energy positrons, many experiments are source limited. Using the LERF accelerator at the Thomas Jefferson National Accelerator Facility, it is possible to build a high brightness source of very low-energy positrons. The accelerator requirements are well within the capabilities of the installed hardware. The accelerator can produce 120 kW of beam with a beam energy of up to 170 MeV. For these experiments, we only need run at up to 120 MeV. The gamma-to-positron converter must be able to absorb 20% of the beam power that the linac delivers. At this low an energy the converter, though challenging, is possible. The transport of the low energy positrons from the production target to the next stage, where the energy is reduced even further, must have a very large acceptance to be able to efficiently transport the flux of positrons from the positron production target to the moderator. We propose to accomplish such a transport by means of a guiding solenoidal field with a novel endcap design. In this presentation, we will present the proposed schemes necessary to realize such a high brightness positron source.

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.

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

International Nuclear Information System (INIS)

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

2003-01-01

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

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

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

Low-energy positron interactions with atoms and molecules

International Nuclear Information System (INIS)

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

2005-01-01

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

Use of a high density lead glass tubing projection chamber in positron emission tomography and in high energy physics

International Nuclear Information System (INIS)

Conti, M.; Guerra, A.D.; Habel, R.; Mulera, T.; Perez-Mendez, V.; Schwartz, G.

1985-10-01

We describe the principle of operation of a high density Projection Chamber, in which the converter/radiator and drift field shaping structures are combined in the form of high density (5 to 6 g/cm 3 ) lead glass tubing. The main applications of this type of detector to Medical Physics (Positron Emission Tomography) and High Energy Physics (Electromagnetic Calorimetry) are discussed

The effects of low-energy scattering on positron implantation

Energy Technology Data Exchange (ETDEWEB)

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

1992-01-01

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

The effects of low-energy scattering on positron implantation

Energy Technology Data Exchange (ETDEWEB)

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

1992-12-31

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

Hard photon emission from high energy electrons and positrons in single crystals

International Nuclear Information System (INIS)

Bajer, V.N.; Katkov, V.M.; Strakhovenko, V.M.

1991-01-01

A radiation of electrons and positrons in single crystals in coherent bremsstrahlung (CBS) region has been considered for the case when CBS has the most hard spectrum. Under this condition a particle moves near a crystalline plane (in fcc(d) crystal for axis (001) this is the plane (110)) and influence of the continuous plane potential should be taken into account. This potential gives additional contribution in soft part of the spectrum and affects on hard photon emission. Observation of this phenomena at high energy is discussed. 14 refs.; 5 figs.; 1 tab

Analysis of experimental positron-molecule binding energies

International Nuclear Information System (INIS)

Danielson, J R; Surko, C M; Young, J A

2010-01-01

Experiments show that positron annihilation on molecules frequently occurs via capture into vibrational Feshbach resonances. In these cases, the downshifts in the annihilation spectra from the vibrational mode spectra provide measures of the positron-molecule binding energies. An analysis of these binding energy data is presented in terms of the molecular dipole polarizability, the permanent dipole moment, and the number of π bonds in aromatic molecules. The results of this analysis are in reasonably good agreement with other information about positron-molecule bound states. Predictions for other targets and promising candidate molecules for further investigation are discussed.

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.)

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

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.)

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

Science.gov (United States)

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

2018-05-01

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

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)

New parameter-free polarization potentials in low-energy positron collisions

Science.gov (United States)

Jain, Ashok

1990-01-01

The polarization potential plays a decisive role in shaping up the cross sections in low energy positron collisions with atoms and molecules. However, its inclusion without involving any adjustable parameter, is still a challenge. Various other techniques employed so far for positron collisions are summarized, and a new, nonadjustable and very simple form of the polarization potential for positron-atom (molecule) collisions below the threshold of positronium formation is discussed. This new recently proposed potential is based on the correlation energy of a single positron in a homogeneous electron gas. The correlation energy was calculated by solving the Schrodinger equation of the positron-electron system and fitted to an analytical form in various ranges of the density parameter. In the outside region, the correlation energy is joined smoothly with the correct asymptotic form. This new positron correlation polarization (PCOP) potential was tested on several atomic and molecular targets such as the Ar, CO, and CH4. The results on the total and differential cross sections on these targets are shown along with the experimental data where available.

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)

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

Variable-energy positron-beam studies of Ni implanted with He

International Nuclear Information System (INIS)

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

1986-01-01

Variable-energy positron-beam studies have been made on well-annealed polycrystalline Ni samples implanted with 30-, 90-, and 180-keV 4 He ions. The positron-annihilation characteristics were measured with a solid-state Ge detector at a number of different incident-positron energies and after isochronal annealing at various temperatures. The Doppler broadening of the annihilation photons was found to be strongly influenced by the 4 He implantations. The data indicate that trapping of the positrons occurred predominantly at small He bubbles. The variation of the broadening with incident-positron energy was sensitive to the depth distribution of the traps. A diffusion model assuming a square concentration-defect profile was developed and analytically fitted to the parametrized momentum data. These fitted results were compared to Monte Carlo range calculations for 4 He in Ni, and fairly good agreement was found. This investigation demonstrates the capabilities of positron annihilation for nondestructive depth profiling in ion-implanted systems. In addition, it establishes parallels between the trapping behavior of positrons and that reported elsewhere for hydrogen, thereby augmenting the present level of understanding of the technologically important trapping of hydrogen by the bubbles

The practicality of high magnification imaging by positron emission

International Nuclear Information System (INIS)

Hulett, L.D. Jr.; Pendyala, S.

1988-01-01

The positron emission microscope has the capability of contrasting areas having high concentrations of monatomic vacancies and other defects. Since the positrons traveling through the specimen will have energies of the same magnitude as that of valence electrons, image contrast will be sensitive to the chemistry of the specimen. In the near future resolutions of 10 nm or lower will be achieved. Whether or not optical aberrations will permit one atom resolution is not clear. For one atom resolution to be obtained positron emission fluxes must be brightness enhanced to 10 11 sec/sup/minus/1/cm/sup/minus/2/ or greater. 5 refs., 1 fig

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

International Nuclear Information System (INIS)

Jain, A.

1990-01-01

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

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

DEFF Research Database (Denmark)

Mogensen, O. E.

1986-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-11-01

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

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

International Nuclear Information System (INIS)

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

2014-01-01

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

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

Elastic positron-cadmium scattering at low energies

International Nuclear Information System (INIS)

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

2010-01-01

The elastic and annihilation cross sections for positron-cadmium scattering are reported up to the positronium-formation threshold (at 2.2 eV). The low-energy phase shifts for the elastic scattering of positrons from cadmium were derived from the bound and pseudostate energies of a very large basis configuration-interaction calculation of the e + -Cd system. The s-wave binding energy is estimated to be 126±42 meV, with a scattering length of A scat =(14.2±2.1)a 0 , while the threshold annihilation parameter, Z eff , was 93.9±26.5. The p-wave phase shift exhibits a weak shape resonance that results in a peak Z eff of 91±17 at a collision energy of about 490±50 meV.

KEK-IMSS Slow Positron Facility

Energy Technology Data Exchange (ETDEWEB)

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

2011-12-01

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

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

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

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

International Nuclear Information System (INIS)

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

2012-01-01

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

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

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

International Nuclear Information System (INIS)

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

2011-01-01

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

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...

Observation of defects associated with the Cu/W(110) interface as studied with variable-energy positrons

International Nuclear Information System (INIS)

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

1983-01-01

Positron emission from a W(110) single crystal has been studied as a function of copper coverage utilizing a variable-energy positron beam in conjunction with low-energy electron diffraction and Auger-electron spectroscopy. Evidence is presented that indicates that sig- p nificant positron localization occurs at defects associated with the Cu/W(110) interface, which can be removed by high-temperature annealing. Our data also reveal new information about the islanding of copper on tungsten, providing a reliable means of identifying and quantifying the relative two-dimensional coverage of the surface by these islands

CO ionization and fragmentation by low-energy positrons.

Science.gov (United States)

Schrader, D. M.; Moxom, J.

2000-06-01

Using the positron beam associated with the electron LINAC ORELA at Oak Ridge National Laboratory, ion yields from carbon monoxide colliding with positrons of low energy are observed as functions of positron beam energy from threshold to 100 eV. Observed appearence potentials are compared with those for electron bombardment, and are interpreted with the aid of potential energy curves for CO, CO^+, and CO^2+. The latter are calculated in the present work at the FORS/MCSCF level using the code GAMESS.^(a) Present results are compared with those of Bluhme, et al.^(b) Progress on our work with the targets N2 and O2 will be discussed and with present results for CO. It is significant that CO and N2 are very similar, but that CO gives a richer mass spectrum because the atomic cations are experimentally distinguishable from the molecular dication. ^(a) M. W. Schmidt, et al., J. Comput. Chem. 14, 1347 (1993). ^(b) H. Bluhme, et al., J. Phys. B 32, 5825 (1999).

Low-energy positron and electron scattering from nitrogen dioxide

International Nuclear Information System (INIS)

Chiari, Luca; Brunger, M J; Zecca, Antonio; García, Gustavo; Blanco, Francisco

2013-01-01

Total cross section (TCS) measurements for positron scattering from nitrogen dioxide (NO 2 ) are presented in the energy range 0.2–40 eV. The TCS, the elastic integral and differential cross sections, and the integral cross section accounting of all the inelastic processes (including positronium formation) have also been computed using the independent atom model with screening corrected additivity rule (IAM-SCAR) for incident energies from 1 to 1000 eV. A qualitative level of agreement is found between the present TCS experiment and theory at the common energies. As no previous measurements or calculations for positron–NO 2  scattering exist in the literature, we also computed the TCS for electron collisions with NO 2  employing the IAM-SCAR method. A comparison of those results to the present positron cross sections and the earlier electron-impact data and calculations is provided. To investigate the role that chemical substitution plays in positron scattering phenomena, we also compare the present positron–NO 2  data with the TCSs measured at the University of Trento for positron scattering from N 2 O and CO 2 . (paper)

Development and application of high energy imaging technology

International Nuclear Information System (INIS)

Chen Shengzu

1999-01-01

High Energy Positron Imaging (HEPI) is a new technology. The idea of positron imaging can be traced back to early 1950's. HEPI imaging is formed by positron emitter radionuclide produced by cyclotron, such as 15 O, 13 N, 11 C and 18 F, which are most abundant elements in human body. Clinical applications of HEPI have been witnessed rapidly in recent years. HEPI imaging can be obtained by both PET and SPECT, namely high energy collimation imaging, Mdecular Coincidence Detection (MCD) and positron emission tomography

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.

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

Energy Technology Data Exchange (ETDEWEB)

Duan, Zhe, E-mail: zhe.duan@ihep.ac.cn [Key Laboratory of Particle Acceleration Physics and Technology, Institute of High Energy Physics, Chinese Academy of Sciences, 100049 Beijing (China); University of Chinese Academy of Sciences, 100049 Beijing (China); Bai, Mei [Forschungszentrum Jülich GmbH, 52428 Jülich (Germany); Barber, Desmond P. [Deutsches Elektronen-Synchrotron, DESY, 22607 Hamburg (Germany); Qin, Qing [Key Laboratory of Particle Acceleration Physics and Technology, Institute of High Energy Physics, Chinese Academy of Sciences, 100049 Beijing (China)

2015-09-01

With the recently emerging global interest in building a next generation of circular electron–positron colliders to study the properties of the Higgs boson, and other important topics in particle physics at ultra-high beam energies, it is also important to pursue the possibility of implementing polarized beams at this energy scale. It is therefore necessary to set up simulation tools to evaluate the beam polarization at these ultra-high beam energies. In this paper, a Monte-Carlo simulation of the equilibrium beam polarization based on the Polymorphic Tracking Code (PTC) (Schmidt et al., 2002 [1]) is described. The simulations are for a model storage ring with parameters similar to those of proposed circular colliders in this energy range, and they are compared with the suggestion (Derbenev et al., 1979 [2]) that there are different regimes for the spin dynamics underlying the polarization of a beam in the presence of synchrotron radiation at ultra-high beam energies. In particular, it has been suggested that the so-called “correlated” crossing of spin resonances during synchrotron oscillations at current energies evolves into “uncorrelated” crossing of spin resonances at ultra-high energies.

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

International Nuclear Information System (INIS)

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

2015-04-01

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

Determination of interfacial states in solid heterostructures using a variable-energy positron beam

Science.gov (United States)

Asoka kumar, Palakkal P. V.; Lynn, Kelvin G.

1993-01-01

A method and means is provided for characterizing interfacial electron states in solid heterostructures using a variable energy positron beam to probe the solid heterostructure. The method includes the steps of directing a positron beam having a selected energy level at a point on the solid heterostructure so that the positron beam penetrates into the solid heterostructure and causes positrons to collide with the electrons at an interface of the solid heterostructure. The number and energy of gamma rays emitted from the solid heterostructure as a result of the annihilation of positrons with electrons at the interface are detected. The data is quantified as a function of the Doppler broadening of the photopeak about the 511 keV line created by the annihilation of the positrons and electrons at the interface, preferably, as an S-parameter function; and a normalized S-parameter function of the data is obtained. The function of data obtained is compared with a corresponding function of the Doppler broadening of the annihilation photopeak about 511 keV for a positron beam having a second energy level directed at the same material making up a portion of the solid heterostructure. The comparison of these functions facilitates characterization of the interfacial states of electrons in the solid heterostructure at points corresponding to the penetration of positrons having the particular energy levels into the interface of the solid heterostructure. Accordingly, the invention provides a variable-energy non-destructive probe of solid heterostructures, such as SiO.sub.2 /Si, MOS or other semiconductor devices.

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)

Electron-positron annihilation at high luminosity colliding beams

International Nuclear Information System (INIS)

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

1977-01-01

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

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.)

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)

Very high energy colliders

International Nuclear Information System (INIS)

Richter, B.

1986-03-01

The luminosity and energy requirements are considered for both proton colliders and electron-positron colliders. Some of the basic design equations for high energy linear electron colliders are summarized, as well as design constraints. A few examples are given of parameters for very high energy machines. 4 refs., 6 figs

High-resolution tomography of positron emitters with clustered pinhole SPECT

Energy Technology Data Exchange (ETDEWEB)

Goorden, Marlies C; Beekman, Freek J [Section of Radiation Detection and Medical Imaging, Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands)], E-mail: m.c.goorden@tudelft.nl

2010-03-07

State-of-the-art small-animal single photon emission computed tomography (SPECT) enables sub-half-mm resolution imaging of radio-labelled molecules. Due to severe photon penetration through pinhole edges, current multi-pinhole SPECT is not suitable for high-resolution imaging of photons with high energies, such as the annihilation photons emitted by positron emitting tracers (511 keV). To deal with this edge penetration, we introduce here clustered multi-pinhole SPECT (CMP): each pinhole in a cluster has a narrow opening angle to reduce photon penetration. Using simulations, CMP is compared with (i) a collimator with traditional pinholes that is currently used for sub-half-mm imaging of SPECT isotopes (U-SPECT-II), and (ii), like (i) but with collimator thickness adapted to image high-energy photons (traditional multi-pinhole SPECT, TMP). At 511 keV, U-SPECT-II is able to resolve the 0.9 mm rods of an iteratively reconstructed Jaszczak-like capillary hot rod phantom, and while TMP only leads to small improvements, CMP can resolve rods as small as 0.7 mm. Using a digital tumour phantom, we show that CMP resolves many details not assessable with standard USPECT-II and TMP collimators. Furthermore, CMP makes it possible to visualize uptake of positron emitting tracers in sub-compartments of a digital mouse striatal brain phantom. This may open up unique possibilities for analysing processes such as those underlying the function of neurotransmitter systems. Additional potential of CMP may include (i) the imaging of other high-energy single-photon emitters (e.g. I-131) and (ii) localized imaging of positron emitting tracers simultaneously with single photon emitters, with an even better resolution than coincidence PET.

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.

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

International Nuclear Information System (INIS)

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

2013-01-01

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

A novel design for a variable energy positron lifetime spectrometer

International Nuclear Information System (INIS)

Chen, D.; Zhang, J.D.; Cheng, C.C.; Beling, C.D.; Fung, S.

2008-01-01

We present computer simulations of a new design of a variable energy positron lifetime beam that uses for a start signal the secondary electron emission from a 25-nm thick carbon foil (C-foil) located in front of the sample. A needle of ∼30 μm diameter is positioned on-axis right behind the foil, creating a radial electric field that deflects the secondary electrons radially outward so as to miss the sample and to hit the micro-channel plate (MCP) detector placed down beam. The MCP signal provides the start signal for the positron lifetime spectrometer. A grid can be further introduced between the sample holder and the MCP to yield a cleaner signal by preventing the positrons with large transmitted scattering angle from hitting the MCP. The cylindrical symmetry of this design reduces the experimental complexity and offers good timing resolution. We show that the design is robust against the transmitted energy and angle of the secondary electrons and positrons

Observations of discrete energy loss effects in spectra of positrons reflected from solid surfaces

International Nuclear Information System (INIS)

Dale, J.M.; Hulett, L.D.; Pendyala, S.

1980-01-01

Surfaces of tungsten and silicon have been bombarded with monoenergetic beams of positrons and electrons. Spectra of reflected particles show energy loss tails with discrete peaks at kinetic energies about 15 eV lower than that of the elastic peaks. In the higher energy loss range for tungsten, positron spectra show fine structure that is not apparent in the electron spectra. This suggests that the positrons are losing energy through mechanisms different from that of the electrons

Positron annihilation studies on high temperature superconductors

International Nuclear Information System (INIS)

Sundar, C.S.; Bharathi, A.

1991-01-01

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

Neutron dosimetry at a high-energy electron-positron collider

Science.gov (United States)

Bedogni, Roberto

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

High energy electron positron physics

International Nuclear Information System (INIS)

Ali, A.; Soding, P.

1987-01-01

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

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)

Spectra of electrons emitted as a result of the sticking and annihilation of low energy positrons to the surfaces of graphene and highly oriented pyrolytic graphite (HOPG)

Science.gov (United States)

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

Positron annihilation induced Auger electron spectroscopy (PAES) was used to study the positron induced low energy electron spectra from HOPG and a sample composed of 6-8 layers of graphene grown on polycrystalline copper. A low energy (~2eV) beam of positrons was used to implant positrons into a surface localized state on the graphene and HOPG samples. Measurements of the energy spectra of the positron induced electrons obtained using a TOF spectrometer indicate the presence of an annihilation induced KLL C Auger peak (at ~263 eV) along with a narrow low energy secondary peak due to an Auger mediated positron sticking (AMPS) process. A broad spectral feature was also observed below ~15 eV which we believe may be due to a VVV C Auger transition not previously observed. The energy dependence of the integrated intensity of the AMPS peak was measured for a series of incident positron kinetic energies ranging from ~1.5 eV up to 11 eV from which the binding energy of the surface localized positron state on graphene and HOPG was estimated. The implication of our results regarding the applicability of AMPS and PAES to the study of graphene surfaces and interfaces will be discussed. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

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.

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

Stress evaluation at the ILC positron source

Energy Technology Data Exchange (ETDEWEB)

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

2016-07-01

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

Study of CT-based positron range correction in high resolution 3D PET imaging

Energy Technology Data Exchange (ETDEWEB)

Cal-Gonzalez, J., E-mail: jacobo@nuclear.fis.ucm.es [Grupo de Fisica Nuclear, Dpto. Fisica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid (Spain); Herraiz, J.L. [Grupo de Fisica Nuclear, Dpto. Fisica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid (Spain); Espana, S. [Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA (United States); Vicente, E. [Grupo de Fisica Nuclear, Dpto. Fisica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid (Spain); Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Cientificas (CSIC), Madrid (Spain); Herranz, E. [Grupo de Fisica Nuclear, Dpto. Fisica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid (Spain); Desco, M. [Unidad de Medicina y Cirugia Experimental, Hospital General Universitario Gregorio Maranon, Madrid (Spain); Vaquero, J.J. [Dpto. de Bioingenieria e Ingenieria Espacial, Universidad Carlos III, Madrid (Spain); Udias, J.M. [Grupo de Fisica Nuclear, Dpto. Fisica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid (Spain)

2011-08-21

Positron range limits the spatial resolution of PET images and has a different effect for different isotopes and positron propagation materials. Therefore it is important to consider it during image reconstruction, in order to obtain optimal image quality. Positron range distributions for most common isotopes used in PET in different materials were computed using the Monte Carlo simulations with PeneloPET. The range profiles were introduced into the 3D OSEM image reconstruction software FIRST and employed to blur the image either in the forward projection or in the forward and backward projection. The blurring introduced takes into account the different materials in which the positron propagates. Information on these materials may be obtained, for instance, from a segmentation of a CT image. The results of introducing positron blurring in both forward and backward projection operations was compared to using it only during forward projection. Further, the effect of different shapes of positron range profile in the quality of the reconstructed images with positron range correction was studied. For high positron energy isotopes, the reconstructed images show significant improvement in spatial resolution when positron range is taken into account during reconstruction, compared to reconstructions without positron range modeling.

Study of CT-based positron range correction in high resolution 3D PET imaging

International Nuclear Information System (INIS)

Cal-Gonzalez, J.; Herraiz, J.L.; Espana, S.; Vicente, E.; Herranz, E.; Desco, M.; Vaquero, J.J.; Udias, J.M.

2011-01-01

Positron range limits the spatial resolution of PET images and has a different effect for different isotopes and positron propagation materials. Therefore it is important to consider it during image reconstruction, in order to obtain optimal image quality. Positron range distributions for most common isotopes used in PET in different materials were computed using the Monte Carlo simulations with PeneloPET. The range profiles were introduced into the 3D OSEM image reconstruction software FIRST and employed to blur the image either in the forward projection or in the forward and backward projection. The blurring introduced takes into account the different materials in which the positron propagates. Information on these materials may be obtained, for instance, from a segmentation of a CT image. The results of introducing positron blurring in both forward and backward projection operations was compared to using it only during forward projection. Further, the effect of different shapes of positron range profile in the quality of the reconstructed images with positron range correction was studied. For high positron energy isotopes, the reconstructed images show significant improvement in spatial resolution when positron range is taken into account during reconstruction, compared to reconstructions without positron range modeling.

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

Energy Technology Data Exchange (ETDEWEB)

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

1996-02-20

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

Simulation of ionization effects for high-density positron drivers in future plasma wakefield experiments

International Nuclear Information System (INIS)

Bruhwiler, D.L.; Dimitrov, D.A.; Cary, J.R.; Esarey, E.; Leemans, W.P.

2003-01-01

The plasma wakefield accelerator (PWFA) concept has been proposed as a potential energy doubler for present or future electron-positron colliders. Recent particle-in-cell (PIC) simulations have shown that the self-fields of the required electron beam driver can tunnel ionize neutral Li, leading to plasma wake dynamics differing significantly from that of a preionized plasma. It has also been shown, for the case of a preionized plasma, that the plasma wake of a positron driver differs strongly from that of an electron driver. We will present new PIC simulations, using the OOPIC code, showing the effects of tunneling ionization on the plasma wake generated by high-density positron drivers. The results will be compared to previous work on electron drivers with tunneling ionization and positron drivers without ionization. Parameters relevant to the energy doubler and the upcoming E-164x experiment at the Stanford Linear Accelerator Center will be considered

Positron impact ionization of atomic hydrogen at low energies

Indian Academy of Sciences (India)

The study of low energy ionization of atomic hydrogen has undergone a rapid ... Three distinct theories for describing low energy ionization can now .... clear evidence that the backward peak for ΘЅѕ = 180° is due to positron-nucleus scat-.

Positron annihilation in Si and Si-related materials in thermal equilibrium at high temperature

International Nuclear Information System (INIS)

Uedono, A.; Muramatsu, M.; Ubukata, T.; Tanino, H.; Shiraishi, T.; Tanigawa, S.; Takasu, S.

2001-01-01

Annihilation characteristics of positrons in the carbon/Si structure in thermal equilibrium at high temperature were studied using a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured as a function of incident positron energy in the temperature range between 298 K and 1473 K. Above 1173 K, the value of S corresponding to the annihilation of positrons near the carbon/Si interface started to increase, which was attributed to the carbonization of Si and the introduction of open-space defects due to the diffusion of Si atoms toward the carbon layer. The behavior of Ps in a thermally grown SiO 2 film was also studied at 298-1523 K. (orig.)

An improved theoretical value for Zsub(eff) for low-energy positron-hydrogen-molecule scattering

International Nuclear Information System (INIS)

Armour, E.A.G.; Baker, D.J.

1986-01-01

The value of Zsub(eff), the effective number of electrons per molecule available to the positron for annihilation, is calculated for low-energy positron-hydrogen-molecule scattering using a scattering wavefunction containing terms in which the positron-electron distance is included linearly as a factor. The results at very low energy are much closer to the experimental value than any that have been obtained previously. (author)

Simulation of a Positron Source for CEBAF

International Nuclear Information System (INIS)

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

2007-01-01

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

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)

Optical model theory of elastic electron- and positron-atom scattering at intermediate energies

International Nuclear Information System (INIS)

Joachain, C.J.

1977-01-01

It is stated that the basic idea of the optical model theory is to enable analysis of the elastic scattering of a particle from a complex target by replacing the complicated interactions between the beam and the target by an optical potential, or pseudopotential, in which the incident particle moves. Once the optical potential is determined the original many-body elastic scattering problem reduces to a one-body situation. The resulting optical potential is, however, a very complicated operator, and the formal expressions obtained from first principles for the optical potential can only be evaluated approximately in a few simple cases, such as high energy elastic hadron-nucleus scattering, for the the optical potential can be expressed in terms of two-body hadron-nucleon amplitudes, and the non-relativistic elastic scattering of fast charged particles by atoms. The elastic scattering of an electron or positron by a neutral atom at intermediate energies is here considered. Exchange effects between the projectile and the atomic electrons are considered; also absorption and polarisation effects. Applications of the full-wave optical model have so far only been made to the elastic scattering of fast electrons and positrons by atomic H, He, Ne, and Ar. Agreements of the optical model results with absolute measurements of differential cross sections for electron scattering are very good, an agreement that improves as the energy increases, but deteriorates quickly as the incident energy becomes lower than 50 eV for atomic H or 100 eV for He. For more complex atoms the optical model calculations also appear very encouraging. With regard to positron-atom elastic scattering the optical model results for positron-He scattering differ markedly at small angles from the corresponding electron-He values. It would be interesting to have experimental angular distributions of positron-atom elastic scattering in order to check predictions of the optical model theory. (U.K.)

Polarization Study for NLC Positron Source Using EGS4

Energy Technology Data Exchange (ETDEWEB)

Liu, James C

2000-09-20

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

Positron annihilation in germanium in thermal equilibrium at high temperature

Energy Technology Data Exchange (ETDEWEB)

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

1996-09-01

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

Calculation of positron binding energies using the generalized any particle propagator theory

International Nuclear Information System (INIS)

Romero, Jonathan; Charry, Jorge A.; Flores-Moreno, Roberto; Varella, Márcio T. do N.; Reyes, Andrés

2014-01-01

We recently extended the electron propagator theory to any type of quantum species based in the framework of the Any-Particle Molecular Orbital (APMO) approach [J. Romero, E. Posada, R. Flores-Moreno, and A. Reyes, J. Chem. Phys. 137, 074105 (2012)]. The generalized any particle molecular orbital propagator theory (APMO/PT) was implemented in its quasiparticle second order version in the LOWDIN code and was applied to calculate nuclear quantum effects in electron binding energies and proton binding energies in molecular systems [M. Díaz-Tinoco, J. Romero, J. V. Ortiz, A. Reyes, and R. Flores-Moreno, J. Chem. Phys. 138, 194108 (2013)]. In this work, we present the derivation of third order quasiparticle APMO/PT methods and we apply them to calculate positron binding energies (PBEs) of atoms and molecules. We calculated the PBEs of anions and some diatomic molecules using the second order, third order, and renormalized third order quasiparticle APMO/PT approaches and compared our results with those previously calculated employing configuration interaction (CI), explicitly correlated and quantum Montecarlo methodologies. We found that renormalized APMO/PT methods can achieve accuracies of ∼0.35 eV for anionic systems, compared to Full-CI results, and provide a quantitative description of positron binding to anionic and highly polar species. Third order APMO/PT approaches display considerable potential to study positron binding to large molecules because of the fifth power scaling with respect to the number of basis sets. In this regard, we present additional PBE calculations of some small polar organic molecules, amino acids and DNA nucleobases. We complement our numerical assessment with formal and numerical analyses of the treatment of electron-positron correlation within the quasiparticle propagator approach

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

International Nuclear Information System (INIS)

Dumas, J.

2011-09-01

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

Positron annihilation studies on high temperature superconductors

International Nuclear Information System (INIS)

Sundar, C.S.; Bharathi, A.

1996-01-01

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

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

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)

Monte Carlo simulation of positron induced secondary electrons in thin carbon foils

International Nuclear Information System (INIS)

Cai, L H; Yang, B; Ling, C C; Beling, C D; Fung, S

2011-01-01

Emission of secondary electrons induced by the passage of low energy positrons through thin carbon foils was studied by the Monte Carlo method. The positron and electron elastic cross sections were calculated by partial wave analysis. The inelastic positron-valence-electron was described by the energy loss function obtained from dielectric theory. The positron-core-electron interaction was modelled by the Gryzinski's excitation function. Positron transport inside the carbon foil was simulated in detail. Secondary electrons created by positrons and high energy secondary electrons through inelastic interactions were tracked through the foil. The positron transmission coefficient and secondary electron yielded in forward and backward geometry are calculated and dependences on positron energy and carbon foil thickness are discussed.

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)

Low-energy positron beams - origins, developments and applications

International Nuclear Information System (INIS)

Beling, C.D.; Charlton, M.

1987-01-01

Over the last 15 years there have been rapid advances in the technology associated with low-energy positron beams. The origins of these advances, and some of the major developments, are discussed. Some applications from the diverse fields of surface physics, atomic scattering and positronium studies are highlighted. (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)

Positron scattering by atomic hydrogen at intermediate energies

International Nuclear Information System (INIS)

Higgins, K.; Burke, P.G.; Walters, H.R.J.

1990-01-01

Results of an accurate calculation based upon the intermediate energy R-matrix theory are reported for elastic scattering of positrons by atomic hydrogen. T-matrix elements for both low and intermediate energy scattering are evaluated for the S e , P o , D e and F o partial wave symmetries. The low-energy elastic phaseshifts are found to be in good agreement with previous accurate variational calculations. Using an optical potential approach to include the effect of the higher partial waves, elastic and total cross sections are presented for energies ranging from near threshold to 3.7 Rydbergs. (author)

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)

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)

Preliminary studies on a variable energy positron annihilation lifetime spectroscopy system

International Nuclear Information System (INIS)

Kwan, P.Y.; Cheung, C.K.; Beling, C.D.; Fung, S.

2006-01-01

There are many advantages in being able to perform positron annihilation lifetime spectroscopy (PALS) using a variable energy positron beam, the most obvious being the easy identification of different defect types at different depths. The difficulty in conducting variable energy (VE) PALS studies lies in the fact that a 'start' signal is required to signal the entry of the positron into the target. Two methods have been used to overcome this problem, namely the bunching technique, which employs radio frequency (RF) cavities and choppers, and secondly the use of secondary electrons emitted from the target. The latter technique is in terms of experimental complexity much simpler, but has in the past suffered from poor time resolution (typically ∼500 ps). In this work, we present a series of computer simulations of a design based on the secondary electron emission from thin C-foils in transmission mode which shows that significant improvements in time resolution can be made with resolutions ∼200 ps being in principle possible

Positron and electron energy bands in several ionic crystals using restricted Hartree-Fock method

Science.gov (United States)

Kunz, A. B.; Waber, J. T.

1981-08-01

Using a restricted Hartree-Fock formalism and suitably localized and symmetrized wave functions, both the positron and electron energy bands were calculated for NaF, MgO and NiO. The lowest positron state at Γ 1 lies above the vacuum level and negative work functions are predicted. Positron annihilation rates were calculated and found to be in good agreement with measured lifetimes.

A calculation of Zsub(eff) for low-energy positron-hydrogen-molecule scattering

International Nuclear Information System (INIS)

Armour, E.A.G.; Baker, D.J.

1985-01-01

The value of Zsub(eff), the effective number of electrons per molecule available to the positron for annihilation, is calculated for low-energy positron-hydrogen-molecule scattering using the scattering wavefunctions obtained in recent detailed ab initio calculations. The results are higher than those obtained in previous calculations but much lower than the experimental value. (author)

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.

Studies of Positron Generation from Ultraintense Laser-Matter Interactions

Science.gov (United States)

Williams, Gerald Jackson

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

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

Towards high-resolution positron emission tomography for small volumes

International Nuclear Information System (INIS)

McKee, B.T.A.

1982-01-01

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

Low energy scattering of positrons by H{sub 2}O

Energy Technology Data Exchange (ETDEWEB)

Arretche, F., E-mail: fsc1sem@fsc.ufsc.b [Departamento de Fisica, Universidade do Estado de Santa Catarina, 89223-100, Joinville, Santa Catarina (Brazil); Tenfen, W.; Mazon, K.T.; Michelin, S.E. [Departamento de Fisica, Universidade Federal de Santa Catarina, 88040-900, Florianopolis, Santa Catarina (Brazil); Lima, M.A.P. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, Unicamp, 13083-970, Campinas, Sao Paulo (Brazil); Lee, M.-T. [Departamento de Quimica, Universidade Federal de Sao Carlos, 13565-905, Sao Carlos, Sao Paulo (Brazil); Machado, L.E. [Departamento de Fisica, Universidade Federal de Sao Carlos, 13565-905, Sao Carlos, Sao Paulo (Brazil); Fujimoto, M.M. [Departamento de Fisica, Universidade Federal do Parana, 13565-905, Curitiba, Parana (Brazil); Pessoa, O.A. [Departamento de Fisica, Universidade do Estado de Santa Catarina, 89111-100, Sao Bento do Sul, Santa Catarina (Brazil)

2010-01-15

We present a theoretical investigation on elastic positron-H{sub 2}O collisions. More specifically, differential and integral cross sections in the 0-10 eV energy range are reported. The calculations were performed using two theoretical approaches, namely, the Schwinger multichannel method and the method of continued fractions. The positron-molecule interaction dynamics is described by using a potential composed of static and correlation-polarization contributions. Comparison of our calculated results with the recent experimental of Zecca et al. [J. Phys. B 39 (2006) 1597] and theoretical results is encouraging.

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.

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

Study of high-k gate dielectrics by means of positron annihilation

International Nuclear Information System (INIS)

Uedono, A.; Naito, T.; Otsuka, T.; Ito, K.; Shiraishi, K.; Yamabe, K.; Miyazaki, S.; Watanabe, H.; Umezawa, N.; Hamid, A.; Chikyow, T.; Ohdaira, T.; Suzuki, R.; Ishibashi, S.; Inumiya, S.; Kamiyama, S.; Akasaka, Y.; Nara, Y.; Yamada, K.

2007-01-01

High-dielectric constant (high-k) gate materials, such as HfSiO x and HfAlO x , fabricated by atomic-layer-deposition techniques were characterized using monoenergetic positron beams. Measurements of the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positrons indicated that positrons annihilated from the trapped state by open volumes that exist intrinsically in amorphous structures of the films. The size distributions of the open volumes and the local atomic configurations around such volumes can be discussed using positron annihilation parameters, and they were found to correlate with the electrical properties of the films. We confirmed that the positron annihilation is useful technique to characterize the matrix structure of amorphous high-k materials, and can be used to determine process parameters for the fabrication of high-k gate dielectrics. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Characteristics of the positron annihilation process in the matter

International Nuclear Information System (INIS)

Dryzek, J.

2000-01-01

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

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.

Acceleration of a trailing positron bunch in a plasma wakefield accelerator

International Nuclear Information System (INIS)

Doche, A.; Beekman, C.; Corde, S.

2017-01-01

High gradients of energy gain and high energy efficiency are necessary parameters for compact, cost-efficient and high-energy particle colliders. Plasma Wakefield Accelerators (PWFA) offer both, making them attractive candidates for next-generation colliders. Here in these devices, a charge-density plasma wave is excited by an ultra-relativistic bunch of charged particles (the drive bunch). The energy in the wave can be extracted by a second bunch (the trailing bunch), as this bunch propagates in the wake of the drive bunch. While a trailing electron bunch was accelerated in a plasma with more than a gigaelectronvolt of energy gain, accelerating a trailing positron bunch in a plasma is much more challenging as the plasma response can be asymmetric for positrons and electrons. We report the demonstration of the energy gain by a distinct trailing positron bunch in a plasma wakefield accelerator, spanning nonlinear to quasi-linear regimes, and unveil the beam loading process underlying the accelerator energy efficiency. A positron bunch is used to drive the plasma wake in the experiment, though the quasi-linear wake structure could as easily be formed by an electron bunch or a laser driver. Finally, the results thus mark the first acceleration of a distinct positron bunch in plasma-based particle accelerators.

Probing the formation of silicon nano-crystals (Si-ncs) using variable energy positron annihilation spectroscopy

Science.gov (United States)

Knights, A. P.; Bradley, J. D. B.; Hulko, O.; Stevanovic, D. V.; Edwards, C. J.; Kallis, A.; Coleman, P. G.; Crowe, I. F.; Halsall, M. P.; Gwilliam, R. M.

2011-01-01

We describe preliminary results from studies of the formation of silicon nano-crystals (Si-ncs) embedded in stoichiometric, thermally grown SiO2 using Variable Energy Positron Annihilation Spectroscopy (VEPAS). We show that the VEPAS technique is able to monitor the introduction of structural damage. In SiO2 through the high dose Si+ ion implantation required to introduce excess silicon as a precursor to Si-nc formation. VEPAS is also able to characterize the rate of the removal of this damage with high temperature annealing, showing strong correlation with photoluminescence. Finally, VEPAS is shown to be able to selectively probe the interface between Si-ncs and the host oxide. Introduction of hydrogen at these interfaces suppresses the trapping of positrons at the interfaces.

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)

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)

Multi-gigaelectronvolt acceleration of positrons in a self-loaded plasma wakefield

Energy Technology Data Exchange (ETDEWEB)

Corde, Sebastien [SLAC National Accelerator Lab., Menlo Park, CA (United States); Adli, E. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Univ. of Oslo, Oslo (Norway); Allen, J. M. [SLAC National Accelerator Lab., Menlo Park, CA (United States); An, W. [Univ. of California, Los Angeles, CA (United States); Clarke, C. I. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Delahaye, J. P. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Frederico, J. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Gessner, S. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Green, S. Z. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Hogan, M. J. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Joshi, C. [Univ. of California, Los Angeles, CA (United States); Lipkowitz, N. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Litos, M. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Lu, W. [Tsinghua Univ., Beijing (China); Marsh, K. A. [Univ. of California, Los Angeles, CA (United States); Mori, W. B. [Univ. of California, Los Angeles, CA (United States); Schmeltz, M. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Vafaei-Najafabadi, N. [Univ. of California, Los Angeles, CA (United States); Walz, D. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Yakimenko, V. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Yocky, G. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Clayton, C. E. [Univ. of California, Los Angeles, CA (United States)

2015-08-26

New accelerator concepts must be developed to make future particle colliders more compact and affordable. The Plasma Wakefield Accelerator (PWFA) is one such concept, where the electric field of a plasma wake excited by a charged-particle bunch is used to accelerate a trailing bunch of particles. To apply plasma acceleration to particle colliders, it is imperative that both the electrons and their antimatter counterpart, the positrons, are efficiently accelerated at high fields using plasmas1. While substantial progress has recently been reported on high-field, high-efficiency acceleration of electrons in a PWFA powered by an electron bunch 2, such an electron-driven wake is unsuitable for the acceleration and focusing of a positron bunch. Here we demonstrate a new regime of PWFA where particles in the front of a single positron bunch transfer their energy to a substantial number of those in the rear of the same bunch by exciting a wakefield in the plasma. In the process, the accelerating field is altered – self-loaded – so that about a billion positrons gain five gigaelectronvolts (GeV) of energy with a narrow energy spread in a distance of just 1.3 meters. They extract about 30% of the wake’s energy and form a spectrally distinct bunch with as low as a 1.8% r.m.s. energy spread. This demonstrated ability of positron-driven plasma wakes to efficiently accelerate a significant number of positrons with a small energy spread may overcome the long-standing challenge of positron acceleration in plasma-based accelerators.

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)

A method for measuring the energy spectrum of coincidence events in positron emission tomography.

Science.gov (United States)

Goertzen, Andrew L; Stout, David B; Thompson, Christopher J

2010-01-21

Positron emission tomography (PET) system energy response is typically characterized in singles detection mode, yet there are situations in which the energy spectrum of coincidence events might be different than the spectrum measured in singles mode. Examples include imaging with isotopes that emit a prompt gamma in coincidence with a positron emission, imaging with low activity in a LSO/LYSO-based cameras, in which the intrinsic activity is significant, and in high scatter situations where the two 511 keV photons have different scattering probabilities (i.e. off-center line source). The ability to accurately measure the energy spectrum of coincidence events could be used for validating simulation models, optimizing energy discriminator levels and examining scatter models and corrections. For many PET systems operating in coincidence mode, the only method available for estimating the energy spectrum is to step the lower and upper level discriminators (LLD and ULD). Simple measurement techniques such as using a narrow sliding energy window or stepping only the LLD will not yield a spectrum of coincidence events that is accurate for cases where there are different energy components contributing to the spectrum. In this work we propose a new method of measuring the energy spectrum of coincidence events in PET based on a linear combination of two sets of coincident count measurements: one made by stepping the LLD and one made by stepping the ULD. The method was tested using both Monte Carlo simulations of a Siemens microPET R4 camera and measured data acquired on a Siemens Inveon PET camera. The results show that our energy spectrum calculation method accurately measures the coincident energy spectra for cases including the beta/gamma spectrum of the (176)Lu intrinsic activity present in the LSO scintillator crystals, a (68)Ge source and an (124)I source (in which there are prompt gamma-rays emitted together with the positron).

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).

Thermal and optical excitation of trapped electrons in high-density polyethylene (HDPE) studied through positron annihilation

International Nuclear Information System (INIS)

Nahid, F.; Zhang, J.D.; Yu, T.F.; Ling, C.C.; Fung, S.; Beling, C.D.

2011-01-01

Positronium (Ps) formation in high-density polyethylene (HDPE) has been studied below the glass transition temperature. The formation probability increases with positron irradiation time due to an increasing number of inter-track trapped electrons becoming available for positron capture. The temperature variation of the saturated Ps level is discussed in different models. The quenching of trapped electrons by light has been studied and the optical de-trapping cross-section for different photon energies has been estimated over the visible region.

Detailed calculations on low-energy positron-hydrogen-molecule and helium-antihydrogen scattering

Energy Technology Data Exchange (ETDEWEB)

Armour, E A G; Cooper, J N; Gregory, M R; Todd, A C [School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Jonsell, S [Department of Physics, University of Swansea, Swansea SA2 8PP (United Kingdom); Plummer, M, E-mail: edward.armour@nottingham.ac.u [Computational Science and Engineering, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom)

2010-01-01

In this paper, we consider two scattering processes: low-energy positron-hydrogen-molecule and helium-antihydrogen scattering. In the positron-hydrogen-molecule scattering calculations, we use the Kohn variational method to calculate Z{sub eff}, the number of target electrons available to the positron for annihilation. In the helium-antihydrogen scattering calculations, we use the Rayleigh-Ritz variational method to calculate a wave function for the leptons as a function of the distance between the helium and the antihydrogen. This is used, together with the associated nuclear wave function and the wave function for {alpha} p-bar + Ps{sup -}, to calculate the cross section for the rearrangement reaction He + H-bar {yields} {alpha} p-bar + Ps{sup -}, using the T-matrix and a form of the distorted wave approximation. For both processes, positron-electron correlation is taken into account accurately using Hylleraas-type functions.

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.

Positron annihilation measurements in high-energy alpha-irradiated n-type gallium arsenide

Energy Technology Data Exchange (ETDEWEB)

Pan, Sandip; Mandal, Arunava; SenGupta, Asmita [Visva-Bharati, Department of Physics, Santiniketan, West Bengal (India); Roychowdhury, Anirban [UGC-DAE Consortium for Scientific Research, Kolkata Centre, Kolkata, West Bengal (India)

2015-07-15

Positron annihilation lifetime spectroscopy and Doppler broadening annihilation line-shape measurements have been carried out in 40-MeV alpha-irradiated n-type GaAs. After irradiation, the sample has been subjected to an isochronal annealing over temperature region of 25-800 C with an annealing time of 30 min at each set temperature. After each annealing, the positron measurements are taken at room temperature. Formation of radiation-induced defects and their recovery with annealing temperature are investigated. The lifetime spectra of the irradiated sample have been fitted with two lifetimes. The average positron lifetime τ{sub avg} = 244 ps at room temperature after irradiation indicates the presence of defects, and the value of τ{sub 2} (262 ps) at room temperature suggests that the probable defects are mono-vacancies. Two distinct annealing stages in τ{sub avg} at 400-600 C and at 650-800 C are observed. The variations in line-shape parameter (S) and defect-specific parameter (R) during annealing in the temperature region 25-800 C resemble the behaviour of τ{sub avg} indicating the migration of vacancies, formation of vacancy clusters and the disappearance of defects between 400 and 800 C. (orig.)

Evaluation of Monte Carlo tools for high energy atmospheric physics

Directory of Open Access Journals (Sweden)

C. Rutjes

2016-11-01

Full Text Available The emerging field of high energy atmospheric physics (HEAP includes terrestrial gamma-ray flashes, electron–positron beams and gamma-ray glows from thunderstorms. Similar emissions of high energy particles occur in pulsed high voltage discharges. Understanding these phenomena requires appropriate models for the interaction of electrons, positrons and photons of up to 40 MeV energy with atmospheric air. In this paper, we benchmark the performance of the Monte Carlo codes Geant4, EGS5 and FLUKA developed in other fields of physics and of the custom-made codes GRRR and MC-PEPTITA against each other within the parameter regime relevant for high energy atmospheric physics. We focus on basic tests, namely on the evolution of monoenergetic and directed beams of electrons, positrons and photons with kinetic energies between 100 keV and 40 MeV through homogeneous air in the absence of electric and magnetic fields, using a low energy cutoff of 50 keV. We discuss important differences between the results of the different codes and provide plausible explanations. We also test the computational performance of the codes. The Supplement contains all results, providing a first benchmark for present and future custom-made codes that are more flexible in including electrodynamic interactions.

Calculations for very low energy scattering of positrons by molecular hydrogen

Energy Technology Data Exchange (ETDEWEB)

Cooper, J.N. [School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD (United Kingdom)], E-mail: james.cooper@maths.nottingham.ac.uk; Armour, E.A.G. [School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2008-02-15

We give a progress report on ongoing calculations of phase shifts for very low energy elastic scattering of positrons by molecular hydrogen, using the generalised Kohn variational method. Further, provisional calculations of Z{sub eff} for molecular hydrogen at low energies are presented and discussed. The preliminary nature of the work is emphasised throughout.

A unified treatment of high energy interactions

International Nuclear Information System (INIS)

Drescher, H.J.; Werner, K.; Ostapchenko, S.; Centre National de la Recherche Scientifique, 44 - Nantes

1999-01-01

It is well known that high energy interactions as different as electron-positron annihilation, deep inelastic lepton-nucleon scattering, proton-proton interactions, and nucleus-nucleus collisions have many features in common. Based upon this observation, a model for all these interactions is constructed which relies on the fundamental hypothesis that the behavior of high energy interactions is universal. (author)

Positron-containing systems and positron diagnostics

International Nuclear Information System (INIS)

1978-01-01

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

Polarized positron sources for the future linear colliders

International Nuclear Information System (INIS)

Chaikovska, I.

2012-01-01

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

ARRONAX, a high-energy and high-intensity cyclotron for nuclear medicine

International Nuclear Information System (INIS)

Haddad, Ferid; Guertin, Arnaud; Michel, Nathalie; Ferrer, Ludovic; Carlier, Thomas; Barbet, Jacques; Chatal, Jean-Francois

2008-01-01

This study was aimed at establishing a list of radionuclides of interest for nuclear medicine that can be produced in a high-intensity and high-energy cyclotron. We have considered both therapeutic and positron emission tomography radionuclides that can be produced using a high-energy and a high-intensity cyclotron such as ARRONAX, which will be operating in Nantes (France) by the end of 2008. Novel radionuclides or radionuclides of current limited availability have been selected according to the following criteria: emission of positrons, low-energy beta or alpha particles, stable or short half-life daughters, half-life between 3 h and 10 days or generator-produced, favourable dosimetry, production from stable isotopes with reasonable cross sections. Three radionuclides appear well suited to targeted radionuclide therapy using beta ( 67 Cu, 47 Sc) or alpha ( 211 At) particles. Positron emitters allowing dosimetry studies prior to radionuclide therapy ( 64 Cu, 124 I, 44 Sc), or that can be generator-produced ( 82 Rb, 68 Ga) or providing the opportunity of a new imaging modality ( 44 Sc) are considered to have a great interest at short term whereas 86 Y, 52 Fe, 55 Co, 76 Br or 89 Zr are considered to have a potential interest at middle term. Several radionuclides not currently used in routine nuclear medicine or not available in sufficient amount for clinical research have been selected for future production. High-energy, high-intensity cyclotrons are necessary to produce some of the selected radionuclides and make possible future clinical developments in nuclear medicine. Associated with appropriate carriers, these radionuclides will respond to a maximum of unmet clinical needs. (orig.) 5

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

Evaluation of Monte Carlo tools for high energy atmospheric physics

NARCIS (Netherlands)

C. Rutjes (Casper); D. Sarria (David); A.B. Skeltved (Alexander Broberg); A. Luque (Alejandro); G. Diniz (Gabriel); N. Østgaard (Nikolai); U. M. Ebert (Ute)

2016-01-01

textabstractThe emerging field of high energy atmospheric physics (HEAP) includes terrestrial gamma-ray flashes, electron-positron beams and gamma-ray glows from thunderstorms. Similar emissions of high energy particles occur in pulsed high voltage discharges. Understanding these phenomena requires

Evaluation of monte carlo tools for high energy atmospheric physics

NARCIS (Netherlands)

Rutjes, Casper; Sarria, David; Skeltved, Alexander Broberg; Luque, Alejandro; Diniz, Gabriel; Østgaard, Nikolai; Ebert, Ute

2016-01-01

The emerging field of high energy atmospheric physics (HEAP) includes terrestrial gamma-ray flashes, electron-positron beams and gamma-ray glows from thunderstorms. Similar emissions of high energy particles occur in pulsed high voltage discharges. Understanding these phenomena requires appropriate

Topics in electron-positron interactions

International Nuclear Information System (INIS)

Soeding, P.

1983-01-01

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

Modeling and Simulation of Longitudinal Dynamics for Low Energy Ring-High Energy Ring at the Positron-Electron Project

International Nuclear Information System (INIS)

Rivetta, Claudio; Mastorides, T.; Fox, J.D.; Teytelman, D.; Van Winkle, D.

2007-01-01

A time domain dynamic modeling and simulation tool for beam-cavity interactions in the Low Energy Ring (LER) and High Energy Ring (HER) at the Positron-Electron Project (PEP-II) is presented. Dynamic simulation results for PEP-II are compared to measurements of the actual machine. The motivation for this tool is to explore the stability margins and performance limits of PEP-II radio-frequency (RF) systems at future higher currents and upgraded RF configurations. It also serves as a test bed for new control algorithms and can define the ultimate limits of the low-level RF (LLRF) architecture. The time domain program captures the dynamic behavior of the beam-cavity-LLRF interaction based on a reduced model. The ring current is represented by macrobunches. Multiple RF stations in the ring are represented via one or two macrocavities. Each macrocavity captures the overall behavior of all the 2 or 4 cavity RF stations. Station models include nonlinear elements in the klystron and signal processing. This enables modeling the principal longitudinal impedance control loops interacting via the longitudinal beam model. The dynamics of the simulation model are validated by comparing the measured growth rates for the LER with simulation results. The simulated behavior of the LER at increased operation currents is presented via low-mode instability growth rates. Different control strategies are compared and the effects of both the imperfections in the LLRF signal processing and the nonlinear drivers and klystrons are explored

Development of slow positron beam lines and applications

Science.gov (United States)

Mondal, Nagendra Nath

2018-05-01

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

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

International Nuclear Information System (INIS)

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

1996-05-01

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

Probing Positron Gravitation at HERA

International Nuclear Information System (INIS)

Gharibyan, Vahagn

2015-07-01

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

Probing Positron Gravitation at HERA

Energy Technology Data Exchange (ETDEWEB)

Gharibyan, Vahagn

2015-07-15

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

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

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)

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

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)

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

Electron-positron pair creation in heavy ion collisions

International Nuclear Information System (INIS)

Kienle, P.

1987-08-01

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

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.

Elementary particle physics and high energy phenomena

International Nuclear Information System (INIS)

Barker, A.R.; Cumalat, J.P.; de Alwis, S.P.; DeGrand, T.A.; Ford, W.T.; Mahanthappa, K.T.; Nauenberg, U.; Rankin, P.; Smith, J.G.

1992-06-01

This report discusses the following research in high energy physics: the properties of the z neutral boson with the SLD detector; the research and development program for the SDC muon detector; the fixed-target k-decay experiments; the Rocky Mountain Consortium for HEP; high energy photoproduction of states containing heavy quarks; and electron-positron physics with the CLEO II and Mark II detectors. (LSP)

Elementary particle physics and high energy phenomena

Energy Technology Data Exchange (ETDEWEB)

Barker, A.R.; Cumalat, J.P.; de Alwis, S.P.; DeGrand, T.A.; Ford, W.T.; Mahanthappa, K.T.; Nauenberg, U.; Rankin, P.; Smith, J.G.

1992-06-01

This report discusses the following research in high energy physics: the properties of the z neutral boson with the SLD detector; the research and development program for the SDC muon detector; the fixed-target k-decay experiments; the Rocky Mountain Consortium for HEP; high energy photoproduction of states containing heavy quarks; and electron-positron physics with the CLEO II and Mark II detectors. (LSP).

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 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

The properties of helium atoms and positrons as impurities in metals

International Nuclear Information System (INIS)

Pendry, J.B.

1980-01-01

Topics covered include: (A) atoms in simple metals: (1) the highly repulsive e - /He interaction and its consequences for binding energies in simple metals; (2) binding energy calculations for jellium and their implications for validity of pair-potential He/M interactions; and (3) the need for experimental data on high negative binding energy systems: (B) low energy positrons in simple metals: (1) behaviour of the positron especially its range (< 100A); (2) consequences for experiments on voids; and (3) possibility for non-destructive depth profiling of defect concentration. (author)

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

Positron annihilation in the high-T/sub c/ superconductors

International Nuclear Information System (INIS)

Chakraborty, B.

1989-01-01

A model for positron annihilation in the high-T/sub c/ oxides is constructed based on the strongly correlated nature of the electrons in these systems. It is shown that the change in positron lifetime as a function of temperature in superconducting, nearly defect-free YBa 2 Cu 3 O 7 and La/sub 1.85/Sr/sub 0.15/CuO 4 can be understood on the basis of this model assuming that real hole-pair formation takes place in the superfluid state. The observed positron-lifetime changes in YBa 2 Cu 3 O/sub 7-//sub x/ as a function of x is also found to be consistent with this model

Production And Characterization Of Tungsten-Based Positron Moderators

International Nuclear Information System (INIS)

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

2011-01-01

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

Clinical application of in vivo treatment delivery verification based on PET/CT imaging of positron activity induced at high energy photon therapy

Science.gov (United States)

Janek Strååt, Sara; Andreassen, Björn; Jonsson, Cathrine; Noz, Marilyn E.; Maguire, Gerald Q., Jr.; Näfstadius, Peder; Näslund, Ingemar; Schoenahl, Frederic; Brahme, Anders

2013-08-01

The purpose of this study was to investigate in vivo verification of radiation treatment with high energy photon beams using PET/CT to image the induced positron activity. The measurements of the positron activation induced in a preoperative rectal cancer patient and a prostate cancer patient following 50 MV photon treatments are presented. A total dose of 5 and 8 Gy, respectively, were delivered to the tumors. Imaging was performed with a 64-slice PET/CT scanner for 30 min, starting 7 min after the end of the treatment. The CT volume from the PET/CT and the treatment planning CT were coregistered by matching anatomical reference points in the patient. The treatment delivery was imaged in vivo based on the distribution of the induced positron emitters produced by photonuclear reactions in tissue mapped on to the associated dose distribution of the treatment plan. The results showed that spatial distribution of induced activity in both patients agreed well with the delivered beam portals of the treatment plans in the entrance subcutaneous fat regions but less so in blood and oxygen rich soft tissues. For the preoperative rectal cancer patient however, a 2 ± (0.5) cm misalignment was observed in the cranial-caudal direction of the patient between the induced activity distribution and treatment plan, indicating a beam patient setup error. No misalignment of this kind was seen in the prostate cancer patient. However, due to a fast patient setup error in the PET/CT scanner a slight mis-position of the patient in the PET/CT was observed in all three planes, resulting in a deformed activity distribution compared to the treatment plan. The present study indicates that the induced positron emitters by high energy photon beams can be measured quite accurately using PET imaging of subcutaneous fat to allow portal verification of the delivered treatment beams. Measurement of the induced activity in the patient 7 min after receiving 5 Gy involved count rates which were about

Generation and application of slow positrons based on a electron LINAC

International Nuclear Information System (INIS)

Kurihara, Toshikazu

2002-01-01

History of slow positron in Institute of Materials Structure Science High Energy Accelerator Research Organization is explained. The principle of generation and application of intense positron beam is mentioned. Two sources of intense positron are radioactive decay of radioactive isotopes emitting positron and electron-positron pair creation. The radioactive decay method uses 58 Co, 64 Cu, 11 C, 13 N, 15 O and 18 F. The electron-positron pair creation method uses nuclear reactor or electron linear accelerator (LINAC). The positron experimental facility in this organization consists of electron LINAC, slow positron beam source, positron transport and experimental station. The outline of this facility is started. The intense slow positron beam is applied to research positronium work function, electron structure of surface. New method such as combination of positron lifetime measurement and slow positron beam or Auger electron spectroscopy by positron annihilation excitation and positron reemission microscope are developed. (S.Y.)

High-temperature equilibrium vacancy formation in ceramic materials studied by positron annihilation

International Nuclear Information System (INIS)

Forster, M.; Claudy, W.; Hermes, H.; Major, J.; Schaefer, H.E.; Koch, M.; Maier, K.; Stoll, H.

1992-01-01

Positron lifetime measurements were used in order to study thermal vacancy formation in NiO, YBa 2 Cu 3 O 7-δ , α-Al 2 O 3 , MgO and 6H-SiC at high temperatures. In NiO two increases of the positron trapping rate at 450K and 1200K (po 2 =10 5 Pa) are attributed to the change of charge of neutral extrinsic Ni-vacancies (c ≅ 10 -4 ) into a negative charge state and to the nonstochiometric formation of charged Ni-vacancies at high temperatures. In YBa 2 Cu 3 O 7-δ the oxygen loss or uptake at T > 680K with an activation enthalpy of 1.03eV can be studied by the variation of the positron lifetime with temperature and oxygen partial pressure. In α-Al 2 O 3 the positrons are annihilated from the delocalized free state between 1000K and 2250K and no positron trapping of thermally formed vacancies was detected which may be understood in terms of the theoretically predicted low concentrations of thermal vacancies. In MgO and 6H-SiC positron lifetime measurements were performed up to temperatures of about 2000K

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

International Nuclear Information System (INIS)

Avignone, F.T. III.

1981-01-01

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

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...

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

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

High resolution and high speed positron emission tomography data acquisition

International Nuclear Information System (INIS)

Burgiss, S.G.; Byars, L.G.; Jones, W.F.; Casey, M.E.

1986-01-01

High resolution positron emission tomography (PET) requires many detectors. Thus, data collection systems for PET must have high data rates, wide data paths, and large memories to histogram the events. This design uses the VMEbus to cost effectively provide these features. It provides for several modes of operation including real time sorting, list mode data storage, and replay of stored list mode data

Positron diffusion in zinc-blende-type semiconductors

International Nuclear Information System (INIS)

Singh, R.P.; Singh, M.

1992-01-01

A theory of positron diffusion in the presence of positron scattering with acoustic, piezoelectric-acoustic, and optical phonons in zinc-blende-type semiconductors is developed. The velocity-velocity correlation function is used to calculate the diffusion coefficient and the Green's function is used to calculate the correlation function. In this formulation the relaxation time automatically appears through the imaginary part of the self-energy. The effect of screening is included within the Thomas-Fermi approximation. The theory is used to calculate the energy relaxation time and diffusion length of positrons in GaAs. It is shown that the transverse and longitudinal phonons contribute almost the same amount towards the relaxation time in the piezoelectric-acoustic-phonon scattering of positrons. It is also found that the contribution of piezoelectric-acoustic-phonon scattering is about 10% to that of acoustic-phonon scattering at low temperatures. We obtained a fairly good agreement between our theory and experimental results available to us. It is found that optical-phonon scattering plays an important role in getting good agreement between theory and experiment at high temperatures

Channeling crystals for positron production

International Nuclear Information System (INIS)

Decker, F.J.

1991-05-01

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

Generation and application of slow positrons based on a electron LINAC

CERN Document Server

Kurihara, T

2002-01-01

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

Interface detection in poly-ethylene terephthalate-metal laminates using variable energy positron annihilation

International Nuclear Information System (INIS)

Escobar Galindo, R.; Schut, H.; Veen, A. van; Rastogi, R.; Vellinga, W.P.; Meijer, H.E.H.

2005-01-01

Thin coatings of poly-ethylene terephthalate (PET) on metal ('laminates') have been studied with a variable energy positron annihilation technique. A correlation between PET crystallinity and the positron annihilation parameter S related to the free volume in the polymer is found. It is shown that buried interfaces in these systems may be detected provided the S parameter of the polymer coating is lower than that of the substrate and higher than that of the surface. Also it is found that large positron diffusion lengths in the substrate favour interface detection. Further, changes in S parameter of PET-metal laminates were measured during uniaxial deformation and shown to be in qualitative accordance with a very simple model description that accounts for changes in free volume in PET during plastic deformation as well as the area fraction of cracks occurring in the PET

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

A new high rate positron lifetime measurement system

International Nuclear Information System (INIS)

Bedwell, M.O.; Paulus, T.J.

1979-01-01

Positron lifetime measuring system, a technique to perform non-destructive studies on the internal structure of materials, has many components common to those used for nuclear time spectroscopy systems. In each case, a timing coincidence curve is measured for the energy range of interest, and this is accomplished in a typical timing coincidence system. The paper first describes the conventional timing coincidence system, then a new fast timing system is introduced. Comparing to the conventional fast/slow timing system, the fast timing technique offers reduced complexity, lower system cost, and improved high data rate capability. Experimental results show that the FWHM timing resolution ranges from 190 ps for a 1.1 : 1 dynamic range to 337 ps for a 100 : 1 dynamic range of signals with 60 Co. As for the timing resolution as a function of energy, the FWHM resolution for each channel ranges from 124 ps at 1 MeV to 400 ps at 100 keV. Since the excellent timing performance is maintained even at very high input rate, the experimenters can use much more active sources to increase the true coincidence rate and reduce data accumulation time. This method has the added advantage of minimizing long term drift effects since the experiments can be conducted in less time. (Wakatsuki, Y.)

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...

Improving depth resolutions in positron beam spectroscopy by concurrent ion-beam sputtering

Science.gov (United States)

John, Marco; Dalla, Ayham; Ibrahim, Alaa M.; Anwand, Wolfgang; Wagner, Andreas; Böttger, Roman; Krause-Rehberg, Reinhard

2018-05-01

The depth resolution of mono-energetic positron annihilation spectroscopy using a positron beam is shown to improve by concurrently removing the sample surface layer during positron beam spectroscopy. During ion-beam sputtering with argon ions, Doppler-broadening spectroscopy is performed with energies ranging from 3 keV to 5 keV allowing for high-resolution defect studies just below the sputtered surface. With this technique, significantly improved depth resolutions could be obtained even at larger depths when compared to standard positron beam experiments which suffer from extended positron implantation profiles at higher positron energies. Our results show that it is possible to investigate layered structures with a thickness of about 4 microns with significantly improved depth resolution. We demonstrated that a purposely generated ion-beam induced defect profile in a silicon sample could be resolved employing the new technique. A depth resolution of less than 100 nm could be reached.

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

Studies of defects in the near-surface region and at interfaces using low energy positron beams

International Nuclear Information System (INIS)

Asoka-Kumar, P.

1995-01-01

Positron Annihilation Spectroscopy (PAS) is a powerful probe to study open-volume defects in solids. Its success is due to the propensity of positrons to seek out low-density regions of a solid, such as vacancies and voids, and the emissions of gamma rays from their annihilations that carry information about the local electronic environment. The development of low-energy positron beams allows probing of defects to depths of few microns, and can successfully characterize defects in the near-surface and interface regions of several technologically important systems. This review focuses on recent studies conducted on semiconductor-based systems

Studies of defects in the near-surface region and at interfaces using low energy positron beams

International Nuclear Information System (INIS)

Asoka-Kumar, P.

1997-01-01

Positron annihilation spectroscopy (PAS) is a powerful probe to study open-volume defects in solids. Its success is due to the propensity of positrons to seek out low-density regions of a solid, such as vacancies and voids, and the emissions of gamma rays from their annihilations that carry information about the local electronic environment. The development of low-energy positron beams allows probing of defects to depths of few microns, and can successfully characterize defects in the near-surface and interface regions of several technologically important systems. This review focuses on recent studies conducted on semiconductor-based systems. (author)

Electron-positron pair creation in heavy ion collisions

International Nuclear Information System (INIS)

Kienle, P.

1987-01-01

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

Elementary particle physics and high energy phenomena

International Nuclear Information System (INIS)

Barker, A.R.; Cumalat, J.P.; De Alwis, S.P.; DeGrand, T.A.; Ford, W.T.; Mahanthappa, K.T.; Nauenberg, U.; Rankin, P.; Smith, J.G.

1992-06-01

Experimental and theoretical high-energy physics programs at the University of Colorado are reported. Areas of concentration include the following: study of the properties of the Z 0 with the SLD detector; fixed-target K-decay experiments; the R ampersand D program for the muon system: the SDC detector; high-energy photoproduction of states containing heavy quarks; electron--positron physics with the CLEO II detector at CESR; lattice QCD; and spin models and dynamically triangulated random surfaces. 24 figs., 2 tabs., 117 refs

Contribution from individual nearby sources to the spectrum of high-energy cosmic-ray electrons

International Nuclear Information System (INIS)

Sedrati, R.; Attallah, R.

2014-01-01

In the last few years, very important data on high-energy cosmic-ray electrons and positrons from high-precision space-born and ground-based experiments have attracted a great deal of interest. These particles represent a unique probe for studying local comic-ray accelerators because they lose energy very rapidly. These energy losses reduce the lifetime so drastically that high-energy cosmic-ray electrons can attain the Earth only from rather local astrophysical sources. This work aims at calculating, by means of Monte Carlo simulation, the contribution from some known nearby astrophysical sources to the cosmic-ray electron/positron spectra at high energy (≥10GeV). The background to the electron energy spectrum from distant sources is determined with the help of the GALPROP code. The obtained numerical results are compared with a set of experimental data

Contribution from individual nearby sources to the spectrum of high-energy cosmic-ray electrons

Energy Technology Data Exchange (ETDEWEB)

Sedrati, R., E-mail: rafik.sedrati@univ-annaba.org; Attallah, R.

2014-04-01

In the last few years, very important data on high-energy cosmic-ray electrons and positrons from high-precision space-born and ground-based experiments have attracted a great deal of interest. These particles represent a unique probe for studying local comic-ray accelerators because they lose energy very rapidly. These energy losses reduce the lifetime so drastically that high-energy cosmic-ray electrons can attain the Earth only from rather local astrophysical sources. This work aims at calculating, by means of Monte Carlo simulation, the contribution from some known nearby astrophysical sources to the cosmic-ray electron/positron spectra at high energy (≥10GeV). The background to the electron energy spectrum from distant sources is determined with the help of the GALPROP code. The obtained numerical results are compared with a set of experimental data.

Elementary particles and high energy phenomena: Progress report

International Nuclear Information System (INIS)

Cumalat, J.P.

1988-01-01

This paper reviews the research being done at the University of Colorado in High Energy Physics. Topics discussed in this paper are: Charmed Photoproduction; Hadronic Production of Charm Particles; Photoproduction of States Containing Heavy Quarks; Electron-Positron Physics with the MAC Detector at PEP; Electron-Positron Physics with the Upgraded Mark II Detector at SLC; The SLD Detector at SLC; Nonperturbative Studies of QCD; Hadron Phenomenology - Application to Experiment; Perturbative QCD and Weak Matrix Elements; Quarkonium Physics; Supersymmetry, Supergravity, and Superstrings; and Experimental Gravity. 50 refs., 13 figs

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

Science.gov (United States)

2009-12-19

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

Positron camera with high-density avalanche chambers

International Nuclear Information System (INIS)

Manfrass, D.; Enghardt, W.; Fromm, W.D.; Wohlfarth, D.; Hennig, K.

1988-01-01

The results of an extensive investigation of the properties of high-density avalanche chambers (HIDAC) are presented. This study has been performed in order to optimize the layout of HIDAC detectors, since they are intended to be applied as position sensitive detectors for annihilation radiation in a positron emission tomograph being under construction. (author)

Scattering of thermal photons by a 46 GeV positron beam at LEP

International Nuclear Information System (INIS)

Bini, C.; De Zorzi, G.; Diambrini-Palazzi, G.; Di Cosimo, G.; Di Domenico, A.; Gauzzi, P.; Zanello, D.

1991-01-01

The scattering of thermal photons present in the vacuum pipe of LEP against the high energy positron beam has been detected. The spectrum of the back-scattered photons is presented for a positron beam energy of 46.1 GeV. Measurements have been performed in the interaction region 1 with the LEP-5 experiment calorimeter. (orig.)

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

CERN Document Server

Volosov, V I; Mezentsev, N A

2001-01-01

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

Positron 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.

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.

Evaluation of Timepix silicon detector for the detection of 18F positrons

Science.gov (United States)

Wang, Q.; Tous, J.; Liu, Z.; Ziegler, S.; Shi, K.

2014-05-01

Timepix is an evolving energy and position sensitive pixel detector. It consists of a silicon detector (sensitive layer 300 μm thick) bump-bonded to the Timepix readout chip developed by the Medipix2 collaboration. This study aims to test the feasibility of using the acquired energy and position signals from Timepix for positron imaging. The signals of the commonly used fluorine-18 PET (positron emission tomography) tracer [18F]FDG were measured using Timepix operated both in single particle counting (Medipix) and in time over threshold (TOT) modes. The spatial resolution (SR) was measured using the absorber edge method (AEM) and was calculated from the over-sampled line spread function. The track of a positron in the Timepix detector was characterized as a cluster and the energy weighted centroid of each cluster was considered as readout for the position of the positron incidence. The measurement results were compared with theoretical predictions using Monte-Carlo simulations. In addition, imaging of a tissue slice of a mouse heart was analysed with reference to standard phosphor plate imaging. Our results show that the SR was improved from 177.1±4.1 μm (centroid without energy weighting) to 155.5±3.1 μm μm (centroid with energy weighting). About 12% enhancement of SR was achieved with energy information in TOT mode. The sensitivity of Timepix was 0.35 cps/Bq based on the measurements. The measuring background and the ratio between detected positrons and gamma rays were also evaluated and were found to be consistent with theoretical predictions. A small enhancement of image quality was also achieved by applying energy information to the data of the measured tissue sample. Our results show that the inclusion of energy information could slightly enhance the positron measurement compared to without energy information and the Timepix provides a high SR and sensitivity for positron detection. Thus, Timepix is a potentially effective tool for 2D positron imaging.

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.

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

Positron and nanoindentation study of helium implanted high chromium ODS steels

Science.gov (United States)

Veternikova, Jana Simeg; Fides, Martin; Degmova, Jarmila; Sojak, Stanislav; Petriska, Martin; Slugen, Vladimir

2017-12-01

Three oxide dispersion strengthened (ODS) steels with different chromium content (MA 956, MA 957 and ODM 751) were studied as candidate materials for new nuclear reactors in term of their radiation stability. The radiation damage was experimentally simulated by helium ion implantation with energy of ions up to 500 keV. The study was focused on surface and sub-surface structural change due to the ion implantation observed by mostly non-destructive techniques: positron annihilation lifetime spectroscopy and nanoindentation. The applied techniques demonstrated the best radiation stability of the steel ODM 751. Blistering effect occurred due to high implantation dose (mostly in MA 956) was studied in details.

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.

The metabolism of the human brain studied with positron emission tomography

International Nuclear Information System (INIS)

Greitz, T.; Ingvar, D.H.; Widen, L.

1985-01-01

This volume presents coverage of the use of positron emission tomography (PET) to study the human brain. The contributors assess new developments in high-resolution positron emission tomography, cyclotrons, radiochemistry, and tracer kinetic models, and explore the use of PET in brain energy metabolism, blood flow, and protein synthesis measurements, receptor analysis, and pH determinations, In addition, they discuss the relevance and applications of positron emission tomography from the perspectives of physiology, neurology, and psychiatry

Proposal for a slow positron facility at Jefferson National Laboratory

Science.gov (United States)

Mills, Allen P.

2018-05-01

One goal of the JPos-17 International Workshop on Physics with Positrons was to ascertain whether it would be a good idea to expand the mission of the Thomas Jefferson National Accelerator Facility (JLab) to include science with low energy (i.e. "slow") spin polarized positrons. It is probably true that experimentation with slow positrons would potentially have wide-ranging benefits comparable to those obtained with neutron and x-ray scattering, but it is certain that the full range of these benefits will never be fully available without an infrastructure comparable to that of existing neutron and x-ray facilities. The role for Jefferson Laboratory would therefore be to provide and maintain (1) a dedicated set of machines for making and manipulating high intensity, high brightness beams of polarized slow positrons; (2) a suite of unique and easily used instruments of wide utility that will make efficient use of the positrons; and (3) a group of on-site positron scientists to provide scientific leadership, instrument development, and user support. In this note some examples will be given of the science that might make a serious investment in a positron facility worthwhile. At the same time, the lessons learned from various proposed and successful positron facilities will be presented for consideration.

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

Theoretical aspects of positrons in imperfect solids

International Nuclear Information System (INIS)

Puska, M.J.

1987-01-01

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

Positron 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...

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

CERN Document Server

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Lutters, G.; Meinhard, H.; Minguet-Rodriguez, J.; Mirabito, L.; Misiejuk, A.; Neugebauer, E.; Ngac, A.; Prange, G.; Rivera, F.; Saraiva, P.; Schafer, U.; Sieler, U.; Smolik, L.; Stephan, F.; Trier, H.; Apollonio, M.; Borean, C.; Bosisio, L.; Della Marina, R.; Giannini, G.; Gobbo, B.; Musolino, G.; Pitis, L.; He, H.; Kim, H.; Putz, J.; Rothberg, J.; Armstrong, S.R.; Bellantoni, L.; Berkelman, K.; Cinabro, D.; Conway, J.S.; Cranmer, K.; Elmer, P.; Feng, Z.; Ferguson, D.P.S.; Gao, Y.; Gonzalez, S.; Grahl, J.; Harton, J.L.; Hayes, O.J.; Hu, H.; Jin, S.; Johnson, R.P.; Kile, J.; McNamara, P.A., III; Nielsen, J.; Orejudos, W.; Pan, Y.B.; Saadi, Y.; Scott, I.J.; Sharma, V.; Walsh, A.M.; Walsh, J.; Wear, J.; von Wimmersperg-Toeller, J.H.; Wiedenmann, W.; Wu, J.; Wu, S.L.; Wu, X.; Yamartino, J.M.; Zobernig, G.; Dissertori, G.; Abdallah, J.; Abreu, P.; Adam, W.; Adzic, P.; Albrecht, T.; Alemany-Fernandez, R.; Allmendinger, T.; Allport, P.P.; Amaldi, U.; Amapane, N.; Amato, S.; Anashkin, E.; Andreazza, A.; 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Orava, R.; Osterberg, K.; Ouraou, A.; Oyanguren, A.; Paganoni, M.; Paiano, S.; Palacios, J.P.; Palka, H.; Papadopoulou, Th. D.; Pape, L.; Parkes, C.; Parodi, F.; Parzefall, U.; Passeri, A.; Passon, O.; Perepelitsa, V.; Perrotta, A.; Petrolini, A.; Piedra, J.; Pieri, L.; Pierre, F.; Pimenta, M.; Podobnik, T.; Poireau, V.; Pol, M.E.; Polok, G.; Poropat, P.; Pozdniakov, V.; Pukhaeva, N.; Pullia, A.; Radojicic, D.; Rames, J.; Ramler, L.; Read, A.; Rebecchi, P.; Rehn, J.; Reid, D.; Reinhardt, R.; Renton, P.; Richard, F.; Ridky, J.; Ripp-Baudot, I.; Rivero, M.; Rodriguez, D.; Romero, A.; Ronchese, P.; Rosenberg, E.; Roudeau, P.; Rovelli, T.; Ruhlmann-Kleider, V.; Ryabtchikov, D.; Sadovsky, A.; Salmi, L.; Salt, J.; Sander, C.; Savoy-Navarro, A.; Schwickerath, U.; Segar, A.; Sekulin, R.; Siebel, M.; Simard, L.; Sisakian, A.; Smadja, G.; Smirnova, O.; Sokolov, A.; Sopczak, A.; Sosnowski, R.; Spassov, T.; Stanitzki, M.; Stocchi, A.; Strauss, J.; Stugu, B.; Szczekowski, M.; Szeptycka, M.; Szumlak, T.; Tabarelli, T.; Taffard, A.C.; Tegenfeldt, F.; Terranova, F.; Thomas, J.; Timmermans, J.; Tkatchev, L.; Tobin, M.; Todorovova, S.; 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Berbeco, R.; Berdugo, J.; Berges, P.; Bertucci, B.; Betev, B.L.; Biasini, M.; Biglietti, M.; Biland, A.; Blaising, J.J.; Blyth, S.C.; Bobbink, G.J.; Bohm, A.; Boldizsar, L.; Borgia, B.; Bottai, S.; Bourilkov, D.; Bourquin, M.; Braccini, S.; Branson, J.G.; Brochu, F.; Burger, J.D.; Burger, W.J.; Cai, X.D.; Capell, M.; Cara Romeo, G.; Carlino, G.; Cartacci, A.; Casaus, J.; Cavallari, F.; Cavallo, N.; Cecchi, C.; Cerrada, M.; Chamizo, M.; Chang, Y.H.; Chemarin, M.; Chen, A.; Chen, G.; Chen, G.M.; Chen, H.F.; Chen, H.S.; Chiefari, G.; Cifarelli, L.; Cindolo, F.; Clare, I.; Clare, R.; Coignet, G.; Colino, N.; Costantini, S.; de la Cruz, B.; Cucciarelli, S.; De Asmundis, R.; D'eglon, P.; Debreczeni, J.; Degre, A.; Dehmelt, K.; Deiters, K.; della Volpe, D.; Delmeire, E.; Denes, P.; DeNotaristefani, F.; De Salvo, A.; Diemoz, M.; Dierckxsens, M.; Dionisi, C.; Dittmar, M.; Doria, A.; Dova, M.T.; Duchesneau, D.; Duda, M.; Echenard, B.; Eline, A.; El Hage, A.; El Mamouni, H.; Engler, A.; Eppling, F.J.; Extermann, P.; Falagan, M.A.; Falciano, S.; Favara, A.; Fay, J.; Fedin, O.; Felcini, M.; Ferguson, T.; Fesefeldt, H.; Fiandrini, E.; Field, J.H.; Filthaut, F.; Fisher, P.H.; Fisher, W.; Forconi, G.; Freudenreich, K.; Furetta, C.; Galaktionov, Yu.; Ganguli, S.N.; Garcia-Abia, P.; Gataullin, M.; Gentile, S.; Giagu, S.; Gong, Z.F.; Grenier, G.; Grimm, O.; Gruenewald, M.W.; Gupta, V.K.; Gurtu, A.; Gutay, L.J.; Haas, D.; Hatzifotiadou, D.; Hebbeker, T.; Herve, A.; Hirschfelder, J.; Hofer, H.; Hohlmann, M.; Holzner, G.; Hou, S.R.; Jin, B.N.; Jindal, P.; Jones, L.W.; de Jong, P.; Josa-Mutuberria, I.; Kaur, M.; Kienzle-Focacci, M.N.; Kim, J.K.; Kirkby, J.; Kittel, W.; Klimentov, A.; Konig, A.C.; Kopal, M.; Koutsenko, V.; Kraber, M.; Kraemer, R.W.; Kruger, A.; Kunin, A.; Ladron de Guevara, P.; Laktineh, I.; Landi, G.; Lebeau, M.; Lebedev, A.; Lebrun, P.; Lecomte, P.; Lecoq, P.; Le Coultre, P.; Le Goff, J.M.; Leiste, R.; Levtchenko, M.; Levtchenko, P.; Li, C.; Likhoded, S.; Lin, C.H.; Lin, W.T.; Linde, F.L.; Lista, L.; Liu, Z.A.; Lohmann, W.; Longo, E.; Lu, Y.S.; Luci, C.; Luminari, L.; Lustermann, W.; Ma, W.G.; Malgeri, L.; Malinin, A.; Mana, C.; Mans, J.; Martin, J.P.; Marzano, F.; Mazumdar, K.; McNeil, R.R.; Mele, S.; Merola, L.; Meschini, M.; Metzger, W.J.; Mihul, A.; Milcent, H.; Mirabelli, G.; Mnich, J.; Mohanty, G.B.; Muanza, G.S.; Muijs, A.J.M.; Musy, M.; Nagy, S.; Natale, S.; Napolitano, M.; Nessi-Tedaldi, F.; Newman, H.; Nisati, A.; Novak, T.; Nowak, H.; Ofierzynski, R.; Organtini, G.; Palomares, C.; Paolucci, P.; Paramatti, R.; Passaleva, G.; Patricelli, S.; Paul, T.; Pauluzzi, M.; Paus, C.; Pauss, F.; Pedace, M.; Pensotti, S.; Perret-Gallix, D.; Piccolo, D.; Pierella, F.; Pieri, M.; Pioppi, M.; Pirou'e, P.A.; Pistolesi, E.; Plyaskin, V.; Pohl, M.; Pojidaev, V.; Pothier, J.; Prokofiev, D.; Rahal-Callot, G.; Rahaman, M.A.; Raics, P.; Raja, N.; Ramelli, R.; Rancoita, P.G.; Ranieri, R.; Raspereza, A.; Razis, P.; Rembeczki, S.; Ren, D.; Rescigno, M.; Reucroft, S.; Riemann, S.; Riles, K.; Roe, B.P.; Romero, L.; Rosca, A.; Rosemann, C.; Rosenbleck, C.; Rosier-Lees, S.; Roth, S.; Rubio, J.A.; Ruggiero, G.; Rykaczewski, H.; Sakharov, A.; Saremi, S.; Sarkar, S.; Salicio, J.; Sanchez, E.; Schafer, C.; Schegelsky, V.; Schopper, H.; Schotanus, D.J.; Sciacca, C.; Servoli, L.; Shevchenko, S.; Shivarov, N.; Shoutko, V.; Shumilov, E.; Shvorob, A.; Son, D.; Souga, C.; Spillantini, P.; Steuer, M.; Stickland, D.P.; Stoyanov, B.; Straessner, A.; Sudhakar, K.; Sultanov, G.; Sun, L.Z.; Sushkov, S.; Suter, H.; Swain, J.D.; Szillasi, Z.; Tang, X.W.; Tarjan, P.; Tauscher, L.; Taylor, L.; Tellili, B.; Teyssier, D.; Timmermans, C.; Ting, S.C.C.; Ting, S.M.; Tonwar, S.C.; Toth, J.; Tully, C.; Ulbricht, J.; Valente, E.; Van de Walle, R.T.; Vasquez, R.; Vesztergombi, G.; Vetlitsky, I.; Viertel, G.; Vivargent, M.; Vlachos, S.; Vodopianov, I.; Vogel, H.; Vogt, H.; Vorobiev, I.; Vorobyov, A.A.; Wadhwa, M.; Wang, Q.; Wang, X.L.; Wang, Z.M.; Weber, M.; Wynhoff, S.; Xia, L.; Xu, Z.Z.; Yamamoto, J.; Yang, B.Z.; Yang, C.G.; Yang, H.J.; Yang, M.; Yeh, S.C.; Zalite, An.; Zalite, Yu.; Zhang, Z.P.; Zhao, J.; Zhu, G.Y.; Zhu, R.Y.; Zhuang, H.L.; Zichichi, A.; Zimmermann, B.; Zoller, M.; Abbiendi, G.; Ackerstaff, K.; Ainsley, C.; Akesson, P.F.; Alexander, G.; Allison, J.; Altekamp, N.; Ametewee, K.; Anagnostou, G.; Anderson, K.J.; Anderson, S.; Arcelli, S.; Asai, S.; Ashby, S.F.; Axen, D.; Azuelos, G.; Ball, A.H.; Bailey, I.; Barberio, E.; Barillari, T.; Barlow, R.J.; Bartoldus, R.; Batley, R.J.; Baumann, S.; Bechtle, P.; Bechtluft, J.; Beeston, C.; Behnke, T.; Bell, K.W.; Bell, P.J.; Bella, G.; Bellerive, A.; Benelli, G.; Bentvelsen, S.; Berlich, P.; Bethke, S.; Biebel, O.; Boeriu, O.; Blobel, V.; Bloodworth, I.J.; Bloomer, J.E.; Bobinski, M.; Bock, P.; Bonacorsi, D.; Bosch, H.M.; Boutemeur, M.; Bouwens, B.T.; Braibant, S.; Bright-Thomas, P.; Brigliadori, L.; Brown, R.M.; Burckhart, H.J.; Burgard, C.; Burgin, R.; Cammin, J.; Campana, S.; Capiluppi, P.; Carnegie, R.K.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, D.G.; Chrisman, D.; Ciocca, C.; Clarke, P.E.L.; Clay, E.; Cohen, I.; Conboy, J.E.; Cooke, O.C.; Couchman, J.; Couyoumtzelis, C.; Coxe, R.L.; Csilling, A.; Cuffiani, M.; Dado, S.; Dallapiccola, C.; Dallavalle, M.; Dallison, S.; de Jong, S.; De Roeck, A.; Dervan, P.; De Wolf, E.A.; del Pozo, L.A.; Desch, K.; Dienes, B.; Dixit, M.S.; do Couto e Silva, E.; Donkers, M.; Doucet, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Edwards, J.E.G.; Estabrooks, P.G.; Etzion, E.; Evans, H.G.; Evans, M.; Fabbri, F.; Fanti, M.; Fath, P.; Feld, L.; Ferrari, P.; Fiedler, F.; Fierro, M.; Fischer, H.M.; Fleck, I.; Folman, R.; Fong, D.G.; Ford, M.; Foucher, M.; Frey, A.; Furtjes, A.; Futyan, D.I.; Gagnon, P.; Gary, J.W.; Gascon, J.; Gascon-Shotkin, S.M.; Gaycken, G.; Geddes, N.I.; Geich-Gimbel, C.; Geralis, T.; Giacomelli, G.; Giacomelli, P.; Giacomelli, R.; Gibson, V.; Gibson, W.R.; Gingrich, D.M.; Giunta, M.; Glenzinski, D.; Goldberg, J.; Goodrick, M.J.; Gorn, W.; Graham, K.; Grandi, C.; Gross, E.; Grunhaus, J.; Gruwe, M.; Gunther, P.O.; Gupta, A.; Hajdu, C.; Hamann, M.; Hanson, G.G.; Hansroul, M.; Hapke, M.; Harder, K.; Harel, A.; Hargrove, C.K.; Harin-Dirac, M.; Hart, P.A.; Hartmann, C.; Hauke, A.; Hauschild, M.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Hensel, C.; Herndon, M.; Herten, G.; Heuer, R.D.; Hildreth, M.D.; Hill, J.C.; Hillier, S.J.; Hilse, T.; Hobson, P.R.; Hocker, A.; Hoffman, K.; Homer, R.J.; Honma, A.K.; Horvath, D.; Hossain, K.R.; Howard, R.; Hughes-Jones, R.E.; Huntemeyer, P.; Hutchcroft, D.E.; Igo-Kemenes, P.; Imrie, D.C.; Ingram, M.R.; Ishii, K.; Jacob, F.R.; Jawahery, A.; Jeffreys, P.W.; Jeremie, H.; Jimack, M.; Joly, A.; Jones, C.R.; Jones, G.; Jones, M.; Jones, R.W.L.; Jost, U.; Jovanovic, P.; Junk, T.R.; Kanaya, N.; Kanzaki, J.; Karapetian, G.; Karlen, D.; Kartvelishvili, V.; Kawagoe, K.; Kawamoto, T.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kim, D.H.; King, B.J.; Kirk, J.; Klein, K.; Klier, A.; Kluth, S.; Kobayashi, T.; Kobel, M.; Koetke, D.S.; Kokott, T.P.; Kolrep, M.; Komamiya, S.; Kowalewski, R.V.; Kramer, T.; Krasznahorkay, A., Jr.; Kress, T.; Krieger, P.; von Krogh, J.; Kuhl, T.; Kupper, M.; Kyberd, P.; Lafferty, G.D.; Lahmann, R.; Lai, W.P.; Landsman, H.; Lanske, D.; Lauber, J.; Lautenschlager, S.R.; Lawson, I.; Layter, J.G.; Lazic, D.; Lee, A.M.; Lefebvre, E.; Leins, A.; Lellouch, D.; Letts, J.; Levinson, L.; Lewis, C.; Liebisch, R.; Lillich, J.; List, B.; List, J.; Littlewood, C.; Lloyd, A.W.; Lloyd, S.L.; Loebinger, F.K.; Long, G.D.; Losty, M.J.; Lu, J.; Ludwig, A.; Ludwig, J.; Macchiolo, A.; Macpherson, A.; Mader, W.; Mannelli, M.; Marcellini, S.; Marchant, T.E.; Markus, C.; Martin, A.J.; Martin, J.P.; Martinez, G.; Mashimo, T.; Matthews, W.; Mattig, P.; McDonald, W.J.; McKenna, J.; Mckigney, E.A.; McMahon, T.J.; McNab, A.I.; McPherson, R.A.; Mendez-Lorenzo, P.; Meijers, F.; Menges, W.; Menke, S.; Merritt, F.S.; Mes, H.; Meyer, N.; Meyer, J.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Mir, R.; Mohr, W.; Montanari, A.; Mori, T.; Morii, M.; Muller, U.; Mutter, A.; Nagai, K.; Nakamura, I.; Nanjo, H.; Neal, H.A.; Nellen, B.; Nijjhar, B.; Nisius, R.; O'Neale, S.W.; Oakham, F.G.; Odorici, F.; Ogren, H.O.; Oh, A.; Okpara, A.; Oldershaw, N.J.; Omori, T.; Oreglia, M.J.; Orito, S.; Pahl, C.; Palinkas, J.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Patt, J.; Pearce, M.J.; Petzold, S.; Pfeifenschneider, P.; Pilcher, J.E.; Pinfold, J.; Plane, D.E.; Poffenberger, P.; Polok, J.; Poli, B.; Pooth, O.; Posthaus, A.; Przybycien, M.; Przysiezniak, H.; Quadt, A.; Rabbertz, K.; Rees, D.L.; Rembser, C.; Renkel, P.; Rick, H.; Rigby, D.; Robertson, S.; Robins, S.A.; Rodning, N.; Roney, J.M.; Rooke, A.; Ros, E.; Rosati, S.; Roscoe, K.; Rossi, A.M.; Rosvick, M.; Routenburg, P.; Rozen, Y.; Runge, K.; Runolfsson, O.; Ruppel, U.; Rust, D.R.; Rylko, R.; Sachs, K.; Saeki, T.; Sahr, O.; Sarkisyan, E.K.G.; Sasaki, M.; Sbarra, C.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schenk, P.; Schieck, J.; Schmitt, S.; Schorner-Sadenius, T.; Schroder, M.; Schultz-Coulon, H.C.; Schulz, M.; Schumacher, M.; Schutz, P.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Shepherd-Themistocleous, C.H.; Sherwood, P.; Siroli, G.P.; Sittler, A.; Skillman, A.; Skuja, A.; Smith, A.M.; Smith, T.J.; Snow, G.A.; Sobie, R.; Soldner-Rembold, S.; Spagnolo, S.; Spano, F.; Springer, R.W.; Sproston, M.; Stahl, A.; Steiert, M.; Stephens, K.; Steuerer, J.; Stockhausen, B.; Stoll, K.; Strom, D.; Strohmer, R.; Strumia, F.; Stumpf, L.; Surrow, B.; Szymanski, P.; Tafirout, R.; Talbot, S.D.; Tanaka, S.; Taras, P.; Tarem, S.; Taylor, R.J.; Tasevsky, M.; Teuscher, R.; Thiergen, M.; Thomas, J.; Thomson, M.A.; von Torne, E.; Torrence, E.; Towers, S.; Toya, D.; Trefzger, T.; Trigger, I.; Trocsanyi, Z.; Tsukamoto, T.; Tsur, E.; Turcot, A.S.; Turner-Watson, M.F.; Ueda, I.; Ujvari, B.; Utzat, P.; Vachon, B.; Van Kooten, R.; Vannerem, P.; Vertesi, R.; Verzocchi, M.; Vikas, P.; Vincter, M.; Vokurka, E.H.; Vollmer, C.F.; Voss, H.; Vossebeld, J.; Wackerle, F.; Wagner, A.; Waller, D.; Ward, C.P.; Ward, D.R.; Ward, J.J.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wetterling, D.; White, J.S.; Wilkens, B.; Wilson, G.W.; Wilson, J.A.; Wolf, G.; Wotton, S.; Wyatt, T.R.; Yamashita, S.; Yekutieli, G.; Zacek, V.; Zer-Zion, D.; Zivkovic, L.

2013-01-01

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

New detector developments for high resolution positron emission tomography

International Nuclear Information System (INIS)

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

1998-01-01

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

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...

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

Observation of diffraction effects in positron channeling

International Nuclear Information System (INIS)

Palathingal, J.C.; Peng, J.P.; Lynn, K.G.; Wu, X.Y.; Schultz, P.J.

1994-01-01

An experimental investigation of positron channeling was made with a high-angular resolution apparatus, employing positrons of kinetic energy 1 MeV, derived from the Brookhaven National Laboratory Dynamitron. The pattern of transmission through a Si (100) single crystal of thickness 0.245 μm was investigated for a number of major planes. The authors have observed for the first time, in excellent detail, the fine structure of the channeling pattern expected to arise from the particle diffraction effects, theoretically explainable in terms of the quantum-mechanical many-beam calculations

Probing the CuO planes with positrons in high Tc cuprates: theoretical predictions

International Nuclear Information System (INIS)

Barbiellini, B.; Jarlborg, T.; Massidda, S.; Peter, M.

1995-01-01

Positron annihilation spectroscopy is a useful tool to investigate the Fermi surface in high T c superconductors. To study the physics of the copper-oxygen subsystem that forms the Cu-O layers, it is important to provide theoretical predictions, on materials where there is a large overlap between the positron and the interesting Cu-O planes. We have performed first-principle electronic structure calculations obtained using the linear muffin-tin orbital and the full-potential linearized augmented plane wave methods. The positron charge distributions and their sensitivity to different potentials are calculated. Secondly, we have computed the annihilation rates and the electron-positron momentum density in order to give predictions of the Fermi surface signals. (orig.)

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

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

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)

Vacancy-type defects and their annealing processes in ion-implanted Si studied by a variable-energy positron beam

International Nuclear Information System (INIS)

Uedono, A.; Wei, L.; Tanigawa, S.; Sugiura, J.; Ogasawara, M.

1992-01-01

Vacancy-type defects in B + -, P + - and Si + -ion implanted SiO 2 (43 nm)/Si(100) and Si(100) were studied by a variable-energy positron beam. Depth distributions of vacancy-type defects were obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. For 200-keV P + -implanted specimen with a dose of 5 x 10 13 P/cm 2 , the damaged layers induced by ion-implantation were found to extend far beyond the stopping range of P-atoms. For 80-keV B + -implanted SiO 2 (43 nm)/Si(100) specimens with different ion-currents, an increase of the ion-current introduced a homogeneous amorphous layer in the subsurface region. Dominant defect species in B + - and P + -implanted specimen were identified as vacancy clusters from their annealing behavior. (author)

A question of balance: Kinetic balance for electrons and positrons

International Nuclear Information System (INIS)

Dyall, Kenneth G.

2012-01-01

Graphical abstract: Kinetic balance for both electrons and positrons is achieved by applying the correct relation for positive and negative energy states separately and then using the electron and positron eigensolutions from the separate diagonalizations of the Hamiltonian as a dual basis. Highlights: ► Kinetic balance for electrons and positrons is achieved in a dual atomic basis. ► Dual atomic balance alleviates, but does not eliminate, energy prolapse. ► Positron affinities converge quicker with basis set size with dual atomic balance. - Abstract: The kinetic balance criterion used in current relativistic basis set codes is satisfied by the electron solutions of the Dirac equation, but not the positron solutions. A proposal for applying kinetic balance to both sets of solutions is presented. The method is applied along with “normal” kinetic balance to one-electron systems, to investigate its possible relation to prolapse, and to the positron affinity of F − , to investigate the kinetic energy deficiency for positron solutions. The new method reduces but does not eliminate prolapse for energy-optimized basis sets, and provides faster and smoother convergence with basis set size for the positron affinity.

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)

Modelling the line shape of very low energy peaks of positron beam induced secondary electrons measured using a time of flight spectrometer

International Nuclear Information System (INIS)

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

2017-01-01

In this paper, we present results of numerical modelling of the University of Texas at Arlington’s time of flight positron annihilation induced Auger electron spectrometer (UTA TOF-PAES) using SIMION® 8.1 Ion and Electron Optics Simulator. The time of flight (TOF) spectrometer measures the energy of electrons emitted from the surface of a sample as a result of the interaction of low energy positrons with the sample surface. We have used SIMION® 8.1 to calculate the times of flight spectra of electrons leaving the sample surface with energies and angles dispersed according to distribution functions chosen to model the positron induced electron emission process and have thus obtained an estimate of the true electron energy distribution. The simulated TOF distribution was convolved with a Gaussian timing resolution function and compared to the experimental distribution. The broadening observed in the simulated TOF spectra was found to be consistent with that observed in the experimental secondary electron spectra of Cu generated as a result of positrons incident with energy 1.5 eV to 901 eV, when a timing resolution of 2.3 ns was assumed. (paper)

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

Harvard University High Energy Physics

International Nuclear Information System (INIS)

1993-01-01

The mainly experimental research program in high energy physics at Harvard is summarized in a descriptive fashion according to the following outline: Proton endash antiproton colliding beam program at Fermilab -- CDF (forward/backward electromagnetic calorimeters -- FEM, central muon extension -- CMX, gas calorimetry and electronics development, front-end electronics upgrades, software development, physics analysis, timetable), electron -- positron collisions in the upsilon region -- CLEO (the hardware projects including CLEO II barrel TOF system and silicon drift detector R ampersand D, physics analysis), search for ν μ to ν τ oscillations with the NOMAD experiment at CERN, the solenoidal detector collaboration at the SSC, muon scattering at FNAL -- E665, the L3 experiment, and phenomenological analysis of high-energy bar pp cross sections. 149 refs

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

Millimeter positron focusing using a hybrid lens design

International Nuclear Information System (INIS)

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

2004-01-01

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

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.)

Status of positron beams for dark photons experiments

Directory of Open Access Journals (Sweden)

Valente Paolo

2017-01-01

Full Text Available High energy positron beams are an important tool for fixed-target experiments searching for new particles produced in the annihilation on atomic electrons of a target. The status of existing or planned infrastructures is reviewed.

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

Binding matter with antimatter: the covalent positron bond.

Science.gov (United States)

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

2018-05-16

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

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

Science.gov (United States)

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

2016-02-01

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

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

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-emitting raionuclides: present and future status

International Nuclear Information System (INIS)

Lambrecht, R.M.

1979-01-01

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

Electron-positron pair production in Coulomb collisions at ultrarelativistic energies

International Nuclear Information System (INIS)

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

1993-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

Karim, Laihem

2008-06-05

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

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

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)

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

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

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)

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.

High-Energy Compton Scattering Light Sources

CERN Document Server

Hartemann, Fred V; Barty, C; Crane, John; Gibson, David J; Hartouni, E P; Tremaine, Aaron M

2005-01-01

No monochromatic, high-brightness, tunable light sources currently exist above 100 keV. Important applications that would benefit from such new hard x-ray sources include: nuclear resonance fluorescence spectroscopy, time-resolved positron annihilation spectroscopy, and MeV flash radiography. The peak brightness of Compton scattering light sources is derived for head-on collisions and found to scale with the electron beam brightness and the drive laser pulse energy. This gamma 2

Theory of e+e/sup /minus// collisions at very high energy

International Nuclear Information System (INIS)

Peskin, M.E.

1988-04-01

In these lectures, the array of new phenomena are reviewed which might be discovered in electron-positron reactions conducted at energies well above the Z/degree/. Before beginning a discussion of what new phenomena we might find, or how we might uncover them, the question is addressed of why such a program of research is important. The question of what we should be looking for, and what discoveries will be the most illuminating, as we search for the next layer of fundamental physics is argued. With this background, we can then discuss in some considerable detail the contributions that the study of electron-positron collisions at high energy can make in this search

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.

Positron production in heavy ion-atom collisions

International Nuclear Information System (INIS)

Kienle, P.

1985-08-01

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

University of Colorado high energy physics progress report for 1990--1991

International Nuclear Information System (INIS)

Baranko, G.; Cumalat, J.; de Alwis, S.P.; DeGrand, T.; Ford, W.T.; Mahanthappa, K.T.; Nauenberg, U.; Rankin, P.; Smith, J.G.

1991-06-01

This report discusses: High energy photoproduction of states containing heavy quarks; electron-positron physics with the Mark II detector at SLC; the study of the properties of the Z 0 with the SLD detector; electron-positron physics with the CLEO II detector at CESR; central tracking for the SDC detector; the R ampersand D program of the muon group in the SDC detector; mostly lattice QCD; spin models and dynamically triangulated random surfaces; string theory and quantum gravity; and reanalysis of a measurement of fifth force

Convergent close-coupling calculations of low-energy positron-atomic-hydrogen scattering

International Nuclear Information System (INIS)

Bray, I.; Stelbovics, A.T.

1993-07-01

The convergent close coupling approach developed by the authors is applied to positron scattering from atomic hydrogen below the first excitation threshold. In this approach the multi-channel expansion one-electron states are obtained by diagonalizing the target Hamiltonian in a large Laguerre basis. It is demonstrated that this expansion of the scattering wave function is sufficient to reproduce the very accurate low-energy variational results, provided target states with l≤ 15 are included in the expansions. 10 refs., 1 tab

Low-energy P-wave phaseshifts for positron-hydrogen elastic scattering using an adiabatic approximation

International Nuclear Information System (INIS)

Armour, E.A.G.; Beker, C.A.; Farina, J.E.G.

1981-01-01

P-wave phaseshifts for positron-hydrogen elastic scattering are calculated using a new adiabatic approximation in which the length of the radius vector from the proton to the positron is fixed but its direction is allowed to vary. This adiabatic approximation makes possible the full inclusion in the calculation of virtual states in which angular momentum is transferred to the target H atom. The results obtained agree qualitatively with the highly accurate results of Bhatia and co-workers (Phys. Rev.; A9:219 (1974)) and are much closer to them than the results obtained using the usual adiabatic approximation in which the radius vector from the proton to the positron is fixed. (author)

Positron radiography of ignition-relevant ICF capsules

Science.gov (United States)

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

2017-12-01

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

Positron annihilation study of the high-Tc (Bi, Pb)2Sr2Ca2Cu3Ox superconductor

International Nuclear Information System (INIS)

Lim, H.J.; Byrne, J.G.

1997-01-01

Positron lifetime spectroscopy (PLS) and positron Doppler-broadening spectroscopy (PDBS) were applied to the high-T c lead-doped Bi 2 Sr 2 Ca 2 Cu 3 O x (BPSCCO 2223) superconductor as a function of temperature. Neither positron lifetimes nor Doppler parameters (S, W, and S/W) showed significant change through T c . This may result from having the highest positron density in the open BiO 2 double layers and no significant positron density in the superconducting CuO 2 layers where positrons, if mainly present, are known to be sensitive to the transition in other high-T c superconductors. Doppler parameters showed that the probability of positron annihilations with core electrons in the lattice slightly increased and that the probability of positron annihilations with conduction electrons slightly decreased as temperature decreased from ambient temperature to 20 K. The lifetime associated with positron annihilations in the perfect lattice of the sample (τ 1 ) was 209 ps and, due to the annihilations at internal surfaces or voids in the sample (τ 2 ) was about 540 ps, independent of temperature. Finally, the mean lifetime for BSCCO 2223 was about 307 ps. (orig.)

An adiabatic matching device for the Orsay linear positron accelerator

International Nuclear Information System (INIS)

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

1983-03-01

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

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.

Differential flux measurement of atmospheric pion, muon, electron and positron energy spectra at balloon altitudes

Energy Technology Data Exchange (ETDEWEB)

Grimani, C.; Brunetti, M.T.; Codino, A. [Perugia Univ. (Italy)]|[INFN, Perugia (Italy); Papini, P.; Massimo Brancaccio, F.; Finetti, N. [Florence Univ. (Italy)]|[INFN, Florence (Italy); Stephens, S.A. [Tata Institute of Fundamental Researc, Bombay (International Commission on Radiation Units and Measurements); Basini, G.; Bongiorno, F. [INFN, Laboratori Nazionali di Frascati, Rome (Italy); Golden, R.L. [New Mexico State Univ. Las Cruces, NM (United States). Particle Astrophysics Lab.

1995-09-01

The fluxes of atmospheric electrons, positrons, positive and negative muons and negative pions have been determined using the NMSU Wizard-MASS2 balloons-borne instrument. The instrument was launched from Fort Sumner, New Mexico, (geomagnetic cut-off about 4.5 GV/c) on september 23, 1991. The flight lasted 9.8 hours and remained above 100.000 ft. Muons and negative pions were observed and their momenta were determined. Since these particles are not a part of the primary component, the measurement of their fluxes provides information regarding production and propagation of secondary particles in the atmosphere. Similarly, observations of electrons and positrons well below the geomagnetic cut-off provides insight into electromagnetic cascade processes in the upper atmosphere. In addition, the determination of the energy spectra of rare particles such as positrons can be used for background subtraction for cosmic ray experiments gathering data below a few g/cm{sup 2} of overlying atmosphere.

Antiproton and positron signal enhancement in dark matter mini-spikes scenarios

International Nuclear Information System (INIS)

Brun, Pierre; Bertone, Gianfranco; Lavalle, Julien; Salati, Pierre; Taillet, Richard

2007-04-01

The annihilation of dark matter (DM) in the Galaxy could produce specific imprints on the spectra of antimatter species in Galactic cosmic rays, which could be detected by upcoming experiments such as PAMELA and AMS02. Recent studies show that the presence of substructures can enhance the annihilation signal by a 'boost factor' that not only depends on energy, but that is intrinsically a statistical property of the distribution of DM substructures inside the Milky Way. We investigate a scenario in which substructures consist of ∼100 'mini-spikes' around intermediate-mass black holes. Focusing on primary positrons and antiprotons, we find large boost factors, up to a few thousand, that exhibit a large variance at high energy in the case of positrons and at low energy in the case of antiprotons. As a consequence, an estimate of the DM particle mass based on the observed cut-off in the positron spectrum could lead to a substantial underestimate of its actual value. (authors)

Positron Beam Characteristics at NEPOMUC Upgrade

Science.gov (United States)

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

2014-04-01

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

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.

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)

Elementary particle physics and high energy phenomena. Progress report for FY92

Energy Technology Data Exchange (ETDEWEB)

Barker, A.R.; Cumalat, J.P.; de Alwis, S.P.; DeGrand, T.A.; Ford, W.T.; Mahanthappa, K.T.; Nauenberg, U.; Rankin, P.; Smith, J.G.

1992-06-01

This report discusses the following research in high energy physics: the properties of the z neutral boson with the SLD detector; the research and development program for the SDC muon detector; the fixed-target k-decay experiments; the Rocky Mountain Consortium for HEP; high energy photoproduction of states containing heavy quarks; and electron-positron physics with the CLEO II and Mark II detectors. (LSP).

Variable low energy positron beams for depth resolved defect spectroscopy in thin film structures

International Nuclear Information System (INIS)

Amarendra, G.; Viswanathan, B.; Venugopal Rao, G.; Parimala, J.; Purniah, B.

1997-01-01

The design, development and commissioning details of an ultra high vacuum compatible, magnetically-guided and compact variable low energy positron beam facility are reported. Information pertaining to the nature, concentration and spatial distribution of defects present at various depths in the near-surface layers of a material can be obtained using this technique. Some of the experimental results obtained using this facility, in terms of surface-sensitive positronium fraction measurements on Cu surfaces as well as defect-sensitive Doppler broadening measurements on semiconductor interfaces and ion irradiated silicon are presented. These results essentially provide an illustration of the research capability of the technique for the study of sub-surface regions and thin film interfaces. (author)

Positron interactions with water–total elastic, total inelastic, and elastic differential cross section measurements

International Nuclear Information System (INIS)

Tattersall, Wade; Chiari, Luca; Machacek, J. R.; Anderson, Emma; Sullivan, James P.; White, Ron D.; Brunger, M. J.; Buckman, Stephen J.; Garcia, Gustavo; Blanco, Francisco

2014-01-01

Utilising a high-resolution, trap-based positron beam, we have measured both elastic and inelastic scattering of positrons from water vapour. The measurements comprise differential elastic, total elastic, and total inelastic (not including positronium formation) absolute cross sections. The energy range investigated is from 1 eV to 60 eV. Comparison with theory is made with both R-Matrix and distorted wave calculations, and with our own application of the Independent Atom Model for positron interactions

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.

Application of a generalisation of the Kohn variational method to the calculation of cross sections for low-energy positron-hydrogen-molecule scattering

International Nuclear Information System (INIS)

Armour, E.A.G.

1984-01-01

The phaseshift corresponding to the lowest partial wave and the associated approximation to the total cross section are calculated for low-energy positron-hydrogen-molecule scattering using a generalisation of the Kohn variational method. The trial wavefunction is expressed in terms of confocal elliptical coordinates. Except at incident positron energies below about 2 eV, reasonable agreement with experiment is obtained below the positronium formation threshold at 8.63 eV. (author)

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.

Bruno Touschek: From Betatrons to Electron-Positron Colliders

Science.gov (United States)

Bernardini, Carlo; Pancheri, Giulia; Pellegrini, Claudio

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

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 Studies of High-Tc Superconductors

Science.gov (United States)

Peter, M.; Manuel, A. A.

1989-01-01

First we present the principles involved in the study of the two-photon momentum distribution: The method requires deconvolution of the positron wavefunction and the estimation of matrix elements effects. Single crystal samples must be of sufficient quality to avoid positron trapping (tested by positron lifetime measurements). In ordinary metals (alkalis, transition- and rare earth metals and compounds) two-photon momentum distribution studies have given results in close agreement with relevant band structure calculations. Discrepancies have been successfully described as enhancement effects due to correlations. In the superconducting oxides, measurements are more difficult because there are fewer conduction electrons and more trapping. Correlation effects of a different nature are expected to be important and might render the band picture inappropriate. Two-photon momentum distribution measurements have now been made by several groups, but have been interpreted in different ways. We relate the current state of affairs, and our present interpretation, to the latest available results.

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.

High-T/sub c/ superconductor YBa2Cu3O/sub 7-//sub δ/ studied by positron annihilation

International Nuclear Information System (INIS)

Wang, S.J.; Naidu, S.V.; Sharma, S.C.; De, D.K.; Jeong, D.Y.; Black, T.D.; Krichene, S.; Reynolds, J.R.; Owens, J.M.

1988-01-01

We have measured the positron lifetime and the Doppler broadening spectra in the high-temperature superconductor YBa 2 Cu 3 O/sub 7-//sub δ/ as a function of temperature between 77 and 295 K. Positron-lifetime and Doppler-broadening data show new features in the superconducting phase. These results are interpreted in terms of positron localization in lattice distortions and positron surface states

Electron-positron colliders: looking at future physics

Energy Technology Data Exchange (ETDEWEB)

Anon.

1991-12-15

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

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

International Nuclear Information System (INIS)

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

1994-01-01

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

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

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)

High Statistics Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5-500 GeV with the Alpha Magnetic Spectrometer on the International Space Station

Science.gov (United States)

Accardo, L.; Aguilar, M.; Aisa, D.; Alvino, A.; Ambrosi, G.; Andeen, K.; Arruda, L.; Attig, N.; Azzarello, P.; Bachlechner, A.; Barao, F.; Barrau, A.; Barrin, L.; Bartoloni, A.; Basara, L.; Battarbee, M.; Battiston, R.; Bazo, J.; Becker, U.; Behlmann, M.; Beischer, B.; Berdugo, J.; Bertucci, B.; Bigongiari, G.; Bindi, V.; Bizzaglia, S.; Bizzarri, M.; Boella, G.; de Boer, W.; Bollweg, K.; Bonnivard, V.; Borgia, B.; Borsini, S.; Boschini, M. J.; Bourquin, M.; Burger, J.; Cadoux, F.; Cai, X. D.; Capell, M.; Caroff, S.; Casaus, J.; Cascioli, V.; Castellini, G.; Cernuda, I.; Cervelli, F.; Chae, M. J.; Chang, Y. H.; Chen, A. I.; Chen, H.; Cheng, G. M.; Chen, H. S.; Cheng, L.; Chikanian, A.; Chou, H. Y.; Choumilov, E.; Choutko, V.; Chung, C. H.; Clark, C.; Clavero, R.; Coignet, G.; Consolandi, C.; Contin, A.; Corti, C.; Coste, B.; Cui, Z.; Dai, M.; Delgado, C.; Della Torre, S.; Demirköz, M. B.; Derome, L.; Di Falco, S.; Di Masso, L.; Dimiccoli, F.; Díaz, C.; von Doetinchem, P.; Du, W. J.; Duranti, M.; D'Urso, D.; Eline, A.; Eppling, F. J.; Eronen, T.; Fan, Y. Y.; Farnesini, L.; Feng, J.; Fiandrini, E.; Fiasson, A.; Finch, E.; Fisher, P.; Galaktionov, Y.; Gallucci, G.; García, B.; García-López, R.; Gast, H.; Gebauer, I.; Gervasi, M.; Ghelfi, A.; Gillard, W.; Giovacchini, F.; Goglov, P.; Gong, J.; Goy, C.; Grabski, V.; Grandi, D.; Graziani, M.; Guandalini, C.; Guerri, I.; Guo, K. H.; Habiby, M.; Haino, S.; Han, K. C.; He, Z. H.; Heil, M.; Hoffman, J.; Hsieh, T. H.; Huang, Z. C.; Huh, C.; Incagli, M.; Ionica, M.; Jang, W. Y.; Jinchi, H.; Kanishev, K.; Kim, G. N.; Kim, K. S.; Kirn, Th.; Kossakowski, R.; Kounina, O.; Kounine, A.; Koutsenko, V.; Krafczyk, M. S.; Kunz, S.; La Vacca, G.; Laudi, E.; Laurenti, G.; Lazzizzera, I.; Lebedev, A.; Lee, H. T.; Lee, S. C.; Leluc, C.; Li, H. L.; Li, J. Q.; Li, Q.; Li, Q.; Li, T. X.; Li, W.; Li, Y.; Li, Z. H.; Li, Z. Y.; Lim, S.; Lin, C. H.; Lipari, P.; Lippert, T.; Liu, D.; Liu, H.; Lomtadze, T.; Lu, M. J.; Lu, Y. S.; Luebelsmeyer, K.; Luo, F.; Luo, J. Z.; Lv, S. S.; Majka, R.; Malinin, A.; Mañá, C.; Marín, J.; Martin, T.; Martínez, G.; Masi, N.; Maurin, D.; Menchaca-Rocha, A.; Meng, Q.; Mo, D. C.; Morescalchi, L.; Mott, P.; Müller, M.; Ni, J. Q.; Nikonov, N.; Nozzoli, F.; Nunes, P.; Obermeier, A.; Oliva, A.; Orcinha, M.; Palmonari, F.; Palomares, C.; Paniccia, M.; Papi, A.; Pedreschi, E.; Pensotti, S.; Pereira, R.; Pilo, F.; Piluso, A.; Pizzolotto, C.; Plyaskin, V.; Pohl, M.; Poireau, V.; Postaci, E.; Putze, A.; Quadrani, L.; Qi, X. M.; Rancoita, P. G.; Rapin, D.; Ricol, J. S.; Rodríguez, I.; Rosier-Lees, S.; Rozhkov, A.; Rozza, D.; Sagdeev, R.; Sandweiss, J.; Saouter, P.; Sbarra, C.; Schael, S.; Schmidt, S. M.; Schuckardt, D.; von Dratzig, A. Schulz; Schwering, G.; Scolieri, G.; Seo, E. S.; Shan, B. S.; Shan, Y. H.; Shi, J. Y.; Shi, X. Y.; Shi, Y. M.; Siedenburg, T.; Son, D.; Spada, F.; Spinella, F.; Sun, W.; Sun, W. H.; Tacconi, M.; Tang, C. P.; Tang, X. W.; Tang, Z. C.; Tao, L.; Tescaro, D.; Ting, Samuel C. C.; Ting, S. M.; Tomassetti, N.; Torsti, J.; Türkoǧlu, C.; Urban, T.; Vagelli, V.; Valente, E.; Vannini, C.; Valtonen, E.; Vaurynovich, S.; Vecchi, M.; Velasco, M.; Vialle, J. P.; Wang, L. Q.; Wang, Q. L.; Wang, R. S.; Wang, X.; Wang, Z. X.; Weng, Z. L.; Whitman, K.; Wienkenhöver, J.; Wu, H.; Xia, X.; Xie, M.; Xie, S.; Xiong, R. Q.; Xin, G. M.; Xu, N. S.; Xu, W.; Yan, Q.; Yang, J.; Yang, M.; Ye, Q. H.; Yi, H.; Yu, Y. J.; Yu, Z. Q.; Zeissler, S.; Zhang, J. H.; Zhang, M. T.; Zhang, X. B.; Zhang, Z.; Zheng, Z. M.; Zhuang, H. L.; Zhukov, V.; Zichichi, A.; Zimmermann, N.; Zuccon, P.; Zurbach, C.; AMS Collaboration

2014-09-01

A precision measurement by AMS of the positron fraction in primary cosmic rays in the energy range from 0.5 to 500 GeV based on 10.9 million positron and electron events is presented. This measurement extends the energy range of our previous observation and increases its precision. The new results show, for the first time, that above ∼200 GeV the positron fraction no longer exhibits an increase with energy.

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

International Nuclear Information System (INIS)

Smirnov, A.I.

1977-01-01

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

Next generation of electron-positron colliding beam machines

International Nuclear Information System (INIS)

Richter, B.

1979-03-01

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

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)

Positron transport: The plasma-gas interface

International Nuclear Information System (INIS)

Marler, J. P.; Petrovic, Z. Lj.; Bankovic, A.; Dujko, S.; Suvakov, M.; Malovic, G.; Buckman, S. J.

2009-01-01

Motivated by an increasing number of applications, new techniques in the analysis of electron transport have been developed over the past 30 years or so, but similar methods had yet to be applied to positrons. Recently, an in-depth look at positron transport in pure argon gas has been performed using a recently established comprehensive set of cross sections and well-established Monte Carlo simulations. The key novelty as compared to electron transport is the effect of positronium formation which changes the number of particles and has a strong energy dependence. This coupled with spatial separation by energy of the positron swarm leads to counterintuitive behavior of some of the transport coefficients. Finally new results in how the presence of an applied magnetic field affects the transport coefficients are presented.

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.

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

Science.gov (United States)

Tomaschitz, Roman

2016-06-01

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

Calculation of positron characteristics for elements of the periodic table

International Nuclear Information System (INIS)

Campillo Robles, J M; Ogando, E; Plazaola, F

2011-01-01

Positron characteristics have been calculated in bulk and monovacancies for most of the elements of the periodic table. Self-consistent and non-self-consistent schemes have been used for the calculation of the electronic structure in the solid, and different parametrizations for the positron enhancement factor and correlation energy. As it is known, positron lifetimes in bulk show a periodic behaviour with atomic number. These calculations also confirm that monovacancy lifetimes follow the same behaviour. The results obtained have been compared with selected experimental lifetime data, which confirms the calculated theoretical trends. Positron binding energies to a monovacancy have been calculated also for most of the elements of the periodic table. The binding energy shows a periodic behaviour with atomic number too.

Electron-positron annihilation physics

International Nuclear Information System (INIS)

Foster, B.

1990-01-01

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

Characterization of a transmission positron/positronium converter for antihydrogen production

Science.gov (United States)

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

2017-09-01

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

Electron-positron colliders: looking at future physics

International Nuclear Information System (INIS)

Anon.

1991-01-01

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

Molecular model for annihilation rates in positron complexes

Energy Technology Data Exchange (ETDEWEB)

Assafrao, Denise [Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, P.O. Box 702, 30123-970 Belo Horizonte, MG (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom); Walters, H.R. James [Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom); Mohallem, Jose R. [Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, P.O. Box 702, 30123-970 Belo Horizonte, MG (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom)], E-mail: rachid@fisica.ufmg.br

2008-02-15

The molecular approach for positron interaction with atoms is developed further. Potential energy curves for positron motion are obtained. Two procedures accounting for the nonadiabatic effective positron mass are introduced for calculating annihilation rate constants. The first one takes the bound-state energy eigenvalue as an input parameter. The second is a self-contained and self-consistent procedure. The methods are tested with quite different states of the small complexes HPs, e{sup +}He (electronic triplet) and e{sup +}Be (electronic singlet and triplet). For states yielding the positronium cluster, the annihilation rates are quite stable, irrespective of the accuracy in binding energies. For the e{sup +}Be states, annihilation rates are larger and more consistent with qualitative predictions than previously reported ones.

Molecular model for annihilation rates in positron complexes

International Nuclear Information System (INIS)

Assafrao, Denise; Walters, H.R. James; Mohallem, Jose R.

2008-01-01

The molecular approach for positron interaction with atoms is developed further. Potential energy curves for positron motion are obtained. Two procedures accounting for the nonadiabatic effective positron mass are introduced for calculating annihilation rate constants. The first one takes the bound-state energy eigenvalue as an input parameter. The second is a self-contained and self-consistent procedure. The methods are tested with quite different states of the small complexes HPs, e + He (electronic triplet) and e + Be (electronic singlet and triplet). For states yielding the positronium cluster, the annihilation rates are quite stable, irrespective of the accuracy in binding energies. For the e + Be states, annihilation rates are larger and more consistent with qualitative predictions than previously reported ones

Probing the structure of matter with Stanford's new $78 million high-energy accelerator

International Nuclear Information System (INIS)

Nolan, G.

1981-01-01

The US high-energy physics program recently gained a powerful new experimental tool with the completion of the Positron Electron Project (PEP). PEP is a colliding beam storage ring two kilometres in circumference. Collisions are obtained in the PEP ring by injecting electrons and positrons from SLAC's existing linear accelerator so that they circulate in opposite directions. At 6 points in the ring the beams will collide. PEP will enable collisions to be produced at up to 36 GeV

Positron deep-level transient spectroscopy in semi-insulating-GaAs using the positron velocity transient method

International Nuclear Information System (INIS)

Tsia, M.; Fung, S.; Beling, C.D.

2001-01-01

Recently a new semiconductor defect spectroscopy, namely positron deep level transient spectroscopy (PDLTS) has been proposed that combines the energy selectivity of deep level transient spectroscopy with the structural sensitivity of positron annihilation spectroscopy. This paper focuses on one variant of PDLTS, namely positron velocity PDLTS, which has no sensitivity towards vacancy defects but nevertheless is useful in studying deep levels in semi-insulators. In the present study the electric field within the depletion region of semi-insulating GaAs is monitored through the measurement of the small Doppler shift in the annihilation radiation that comes from this region as a result of positron drift. The drift is the result of an increasing electric field produced by space charge building up from ionizing deep level defects. Doppler shift transients are measured between 50-300 K. The EL2 level emission transients are clearly seen at temperatures around 300 K that yield E C -0.78±0.08eV for the energy of EL2. The EL2 electron capture rate is found to have an activation energy of 0.61±0.08eV which most probably arises from freeze out of conduction electrons. We find the surprising result that emission and capture transients can be seen at temperatures below 200 K. Possible reasons for these transients are discussed. (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)

Low energy elastic scattering of positrons by CO: An application of continued fractions and Schwinger variational iterative methods

Energy Technology Data Exchange (ETDEWEB)

Arretche, F. [Departamento de Fisica, Universidade Federal de Santa Catarina, 88040-900, Florianopolis, Santa Catarina (Brazil)], E-mail: farretche@hotmail.com; Mazon, K.T.; Michelin, S.E. [Departamento de Fisica, Universidade Federal de Santa Catarina, 88040-900, Florianopolis, Santa Catarina (Brazil); Fujimoto, M.M. [Departamento de Fisica, Universidade Federal do Parana, 81531-990, Curitiba, Parana (Brazil); Iga, I.; Lee, M.-T. [Departamento de Quimica, Universidade Federal de Sao Carlos, 13565-905, Sao Paulo (Brazil)

2008-02-15

Iterative Schwinger variational methods and the method of continued fractions, widely used for electron-molecule scattering, are applied for the first time to investigate positron-molecule interactions. Specifically, integral and differential cross sections for elastic positron scattering by CO in the (0.5-20) eV energy range are calculated and reported. In our calculation, a static plus correlation-polarization potential is used to represent the collisional dynamics. Our calculated results are in general agreement with the theoretical and experimental data available in the literature.

Positron annihilation studies of high dose Sb implanted silicon

International Nuclear Information System (INIS)

Schut, H.; Eijt, S.W.H.; Beling, C.D.; Ho, K.; Takamura, Y.

2005-01-01

The formation and evolution of vacancies and precipitates created by implantation of 60 keV, 2 x 10 16 cm -2 Sb + in pre-amorphized (0 0 1) Cz-Si is studied using the Doppler broadening (DB) and two-dimensional angular correlation of annihilation radiation (2D-ACAR) positron beam techniques. After implantation, samples were laser annealed (LTA) and subsequently thermal annealed at temperatures ranging from 400 to 1000 deg. C. Implantation-induced vacancy-type defects were detected up to a depth of 280 nm. After LTA, positron annihilation related to both Sb and remaining defects is observed in the first 100 nm below the surface. The deeper region only shows positron trapping at vacancy-type defects with strong reduced concentration. Complete removal is obtained after 600 deg. C anneal. At this temperature, the positron data for the upper region reveals trapping at Sb and Si sites only. With increasing annealing time (at 600 deg. C) or increasing temperature (up to 1000 deg. C) positron annihilation at Sb-sites associated with neighboring vacancies becomes apparent. Results are correlated with the observed Sb electrical deactivation above 600 deg. C, the shift from small Sb aggregates to precipitates and out-diffusion of Sb from the implantation region at higher temperatures

Positron scattering from vinyl acetate

International Nuclear Information System (INIS)

Chiari, L; Brunger, M J; Zecca, A; Blanco, F; García, G

2014-01-01

Using a Beer–Lambert attenuation approach, we report measured total cross sections (TCSs) for positron scattering from vinyl acetate (C 4 H 6 O 2 ) in the incident positron energy range 0.15–50 eV. In addition, we also report an independent atom model with screening corrected additivity rule computation results for the TCSs, differential and integral elastic cross sections, the positronium formation cross section and inelastic integral cross sections. The energy range of these calculations is 1–1000 eV. While there is a reasonable qualitative correspondence between measurement and calculation for the TCSs, in terms of the energy dependence of those cross sections, the theory was found to be a factor of ∼2 larger in magnitude at the lower energies, even after the measured data were corrected for the forward angle scattering effect. (paper)

Detectors for high resolution dynamic positron emission tomography

International Nuclear Information System (INIS)

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

1985-01-01

Tomography is the technique of producing a photographic image of an opaque specimen by transmitting a beam of x-rays or gamma rays through the specimen onto an adjacent photographic film. The image results from variations in thickness, density, and chemical composition, of the specimen. This technique is used to study the metabolism of the human brain. This article examines the design of equipment used for high resolution dynamic positron emission tomography. 27 references, 5 figures, 3 tables

High Statistics Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–500 GeV with the Alpha Magnetic Spectrometer on the International Space Station

CERN Document Server

Accardo, L; Aisa, D; Alpat, B; Alvino, A; Ambrosi, G; Andeen, K; Arruda, L; Attig, N; Azzarello, P; Bachlechner, A; Barao, F; Barrau, A; Barrin, L; Bartoloni, A; Basara, L; Battarbee, M; Battiston, R; Bazo, J; Becker, U; Behlmann, M; Beischer, B; Berdugo, J; Bertucci, B; Bigongiari, G; Bindi, V; Bizzaglia, S; Bizzarri, M; Boella, G; de Boer, W; Bollweg, K; Bonnivard, V; Borgia, B; Borsini, S; Boschini, M J; Bourquin, M; Burger, J; Cadoux, F; Cai, X D; Capell, M; Caroff, S; Carosi, G; Casaus, J; Cascioli, V; Castellini, G; Cernuda, I; Cerreta, D; Cervelli, F; Chae, M J; Chang, Y H; Chen, A I; Chen, H; Cheng, G M; Chen, H S; Cheng, L; Chikanian, A; Chou, H Y; Choumilov, E; Choutko, V; Chung, C H; Cindolo, F; Clark, C; Clavero, R; Coignet, G; Consolandi, C; Contin, A; Corti, C; Coste, B; Cui, Z; Dai, M; Delgado, C; Della Torre, S; Demirköz, M B; Derome, L; Di Falco, S; Di Masso, L; Dimiccoli, F; Díaz, C; von Doetinchem, P; Du, W J; Duranti, M; D’Urso, D; Eline, A; Eppling, F J; Eronen, T; Fan, Y Y; Farnesini, L; Feng, J; Fiandrini, E; Fiasson, A; Finch, E; Fisher, P; Galaktionov, Y; Gallucci, G; García, B; García-López, R; Gast, H; Gebauer, I; Gervasi, M; Ghelfi, A; Gillard, W; Giovacchini, F; Goglov, P; Gong, J; Goy, C; Grabski, V; Grandi, D; Graziani, M; Guandalini, C; Guerri, I; Guo, K H; Haas, D; Habiby, M; Haino, S; Han, K C; He, Z H; Heil, M; Henning, R; Hoffman, J; Hsieh, T H; Huang, Z C; Huh, C; Incagli, M; Ionica, M; Jang, W Y; Jinchi, H; Kanishev, K; Kim, G N; Kim, K S; Kirn, Th; Kossakowski, R; Kounina, O; Kounine, A; Koutsenko, V; Krafczyk, M S; Kunz, S; La Vacca, G; Laudi, E; Laurenti, G; Lazzizzera, I; Lebedev, A; Lee, H T; Lee, S C; Leluc, C; Levi, G; Li, H L; Li, J Q; Li, Q; Li, Q; Li, T X; Li, W; Li, Y; Li, Z H; Li, Z Y; Lim, S; Lin, C H; Lipari, P; Lippert, T; Liu, D; Liu, H; Lolli, M; Lomtadze, T; Lu, M J; Lu, Y S; Luebelsmeyer, K; Luo, F; Luo, J Z; Lv, S S; Majka, R; Malinin, A; Mañá, C; Marín, J; Martin, T; Martínez, G; Masi, N; Massera, F; Maurin, D; Menchaca-Rocha, A; Meng, Q; Mo, D C; Monreal, B; Morescalchi, L; Mott, P; Müller, M; Ni, J Q; Nikonov, N; Nozzoli, F; Nunes, P; Obermeier, A; Oliva, A; Orcinha, M; Palmonari, F; Palomares, C; Paniccia, M; Papi, A; Pauluzzi, M; Pedreschi, E; Pensotti, S; Pereira, R; Pilastrini, R; Pilo, F; Piluso, A; Pizzolotto, C; Plyaskin, V; Pohl, M; Poireau, V; Postaci, E; Putze, A; Quadrani, L; Qi, X M; Rancoita, P G; Rapin, D; Ricol, J S; Rodríguez, I; Rosier-Lees, S; Rossi, L; Rozhkov, A; Rozza, D; Rybka, G; Sagdeev, R; Sandweiss, J; Saouter, P; Sbarra, C; Schael, S; Schmidt, S M; Schuckardt, D; Schulz von Dratzig, A; Schwering, G; Scolieri, G; Seo, E S; Shan, B S; Shan, Y H; Shi, J Y; Shi, X Y; Shi, Y M; Siedenburg, T; Son, D; Spada, F; Spinella, F; Sun, W; Sun, W H; Tacconi, M; Tang, C P; Tang, X W; Tang, Z C; Tao, L; Tescaro, D; Ting, Samuel C C; Ting, S M; Tomassetti, N; Torsti, J; Türkoğlu, C; Urban, T; Vagelli, V; Valente, E; Vannini, C; Valtonen, E; Vaurynovich, S; Vecchi, M; Velasco, M; Vialle, J P; Vitale, V; Volpini, G; Wang, L Q; Wang, Q L; Wang, R S; Wang, X; Wang, Z X; Weng, Z L; Whitman, K; Wienkenhöver, J; Wu, H; Wu, K Y; Xia, X; Xie, M; Xie, S; Xiong, R Q; Xin, G M; Xu, N S; Xu, W; Yan, Q; Yang, J; Yang, M; Ye, Q H; Yi, H; Yu, Y J; Yu, Z Q; Zeissler, S; Zhang, J H; Zhang, M T; Zhang, X B; Zhang, Z; Zheng, Z M; Zhou, F; Zhuang, H L; Zhukov, V; Zichichi, A; Zimmermann, N; Zuccon, P; Zurbach, C

2014-01-01

A precision measurement by AMS of the positron fraction in primary cosmic rays in the energy range from 0.5 to 500 GeV based on 10.9 million positron and electron events is presented. This measurement extends the energy range of our previous observation and increases its precision. The new results show, for the first time, that above ∼200  GeV the positron fraction no longer exhibits an increase with energy.

Properties of a large NaI(Tl) spectrometer for the energy measurement of high-energy gamma rays on the Gamma Ray Observatory

International Nuclear Information System (INIS)

Hughes, E.B.; Finman, L.C.; Hofstadter, R.; Lepetich, J.E.; Lin, Y.C.; Mattox, J.R.; Nolan, P.L.; Parks, R.; Walker, A.H.

1986-01-01

A large NaI(T1) spectrometer is expected to play a crucial role in the measurement of the energy spectra from an all-sky survey of high-energy celestial gamma rays on the Gamma Ray Observatory. The crystal size and requirements of space flight have resulted in a novel crystal-packaging and optics combination. The structure of this spectrometer and the operating characteristics determined in a test program using high energy positrons are described

GaN thin films on SiC substrates studied using variable energy positron annihilation spectroscopy

International Nuclear Information System (INIS)

Hu, Y.F.; Shan, Y.Y.; Beling, C.D.; Fung, S.; Xie, M.H.; Cheung, S.H.; Tu, J.; Tong, D.S.Y.

2001-01-01

A variety of GaN epilayers, grown on 6H-SiC substrates using different growth conditions, have been studied using variable energy positron annihilation spectroscopy. In the S-E plots, a peak structure in the S-parameter is seen which is related to the GaN/substrate heterojunction. The position of the peak is found to be much closer to the sample surface than expected from simple mean implantation depth arguments. This anomaly is attributed to the fact that there is a rectifying potential step that prevents diffusing positrons in the GaN from entering the SiC substrate. This effect has been successfully mimicked by inserting an artificial electric field into the thin interfacial region in the VEPFIT analysis. (orig.)

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)

Concerning the trapping of positrons in ionic solids

International Nuclear Information System (INIS)

Kunz, A.B.; Waber, J.T.

1982-01-01

The total energy of several ionic crystals which contain lattice defects plus a positron were studied in the Hartree-Fock limit. Large uncontracted basis sets of GTO's were used to ensure binding if it would occur. Specifically, the attraction of a positron to a cation vacancy was sought for alkali halides as well as for nickel oxide. While the binding energy to nickel oxide was 8.1 eV, there was very little tendency for the positron to be trapped in the alkali halides. The trapping at a Vsub(k) site was also investigated using similar restricted HF approximation with large sets of GTO's. This defect in LiF was shown to be stable by 0.73 eV, by itself but was unable to bind a positron. These two results are not compatible with qPs being localized in such crystals. (Auth.)

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)

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

International Nuclear Information System (INIS)

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

1993-01-01

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

Positron annihilation lifetime spectroscopy study of Kapton thin foils

Science.gov (United States)

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

2016-01-01

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

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

International Nuclear Information System (INIS)

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

1982-01-01

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

Subnanopore filling during water vapor adsorption on microporous silica thin films as seen by low-energy positron annihilation

Science.gov (United States)

Ito, Kenji; Yoshimoto, Shigeru; O'Rourke, Brian E.; Oshima, Nagayasu; Kumagai, Kazuhiro

2018-02-01

Positron annihilation lifetime spectroscopy (PALS) using a low-energy positron microbeam extracted into air was applied to elucidating molecular-level pore structures formed in silicon-oxide-backboned microporous thin films under controlled humidity conditions; as a result, a direct observation of the interstitial spaces in the micropores filled with water molecules was achieved. It was demonstrated that PALS using a microbeam extracted into air in combination with water vapor adsorption is a powerful tool for the in-situ elucidation of both open and closed subnanoscaled pores of functional thin materials under practical conditions.

Isochronous 180 degree turns for the SLC positron system

International Nuclear Information System (INIS)

Helm, R.H.; Clendenin, J.E.; Ecklund, S.D.; Kulikov, A.V.; Pitthan, R.

1991-05-01

The design of the compact, achromatic, second order isochronous 180 degrees turn for the SLC positron transport system will be described. Design criteria require an energy range of 200±20 MeV, energy acceptance of ±5%, transverse admittance of 25π mm-mr, and minimal lengthening of the 3 to 4 mm (rms) positron bunch. The devices had to fit within a maximum height or width of about 10 ft. Optics specifications and theoretical performance are presented and compared to experimental results based on streak camera measurements of bunch length immediately after the first isochronous turn (200 MeV) and positron beam energy spread after S-band acceleration to 1.15 GeV. 5 refs., 7 figs

A coupled channel study on a binding mechanism of positronic alkali atoms

International Nuclear Information System (INIS)

Kubota, Yoshihiro; Kino, Yasushi

2008-01-01

In order to investigate the binding mechanism of weakly bound states of positronic alkali atoms, we calculate the energies and wavefunctions using the Gaussian expansion method (GEM) where a positronium (Ps)-alkali ion channel and a positron-alkali atom channel are explicitly introduced. The energies of the bound states are updated using a model potential that reproduces well the observed energy levels of alkali atoms. The binding mechanism of the positronic alkali atom is analyzed by the wavefunctions obtained. The structure of the positronic alkali atom has been regarded as a Ps cluster orbiting the alkali ion, which is described by the Ps-alkali ion channel. We point out that the fraction having the positron-alkali atom configuration is small but plays an indispensable role for the weakly bound system

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.

Systematics in positron annihilation lifetime analysis of high Tc superconducting transitions

International Nuclear Information System (INIS)

Howell, R.H.; Radousky, H.B.; Wachs, A.L.; Fluss, M.J.; Turchi, P.E.A.; Jean, Y.C.; Sunder, C.S.; Chu, C.W.; Peng, J.L.; Folkerts, T.J.; Shelton, R.N.; Hinks, D.G.

1989-01-01

Values of the positron lifetime have previously been observed to change with temperature below T c in high T c superconducting oxides. The authors report new measurements on Ba .6 K .4 Bio 3 and Nd 1.85 Ce .15 CuO 4

Potential energy curves for the interaction of a low-energy positron with matter: The case He+e{sup +}

Energy Technology Data Exchange (ETDEWEB)

Mohallem, Jose R. [Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, P.O. Box 702, 30123-970 Belo Horizonte, MG (Brazil)]. E-mail: rachid@fisica.ufmg.br; Rolim, Flavia [Departamento de Quimica, Universidade de Coimbra, FCT, 3004-535 Coimbra (Portugal)

2007-02-15

In this introductory exploration of the title theme, we treat a positron as a light nucleus and work within the quasi-molecule approximation to obtain, for the first time, adiabatic potential energy curves for its scattering by the He atom. We then show that different elastic and inelastic processes that contribute to the total scattering cross section can be rationalized in molecular terms as dissociation and non-adiabatic couplings. Particularly, some new insights on positronium yielding are presented.

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

Report of the 1985 High Energy Physics Advisory Panel Study of the US High Energy Physics Program, 1985-1995

International Nuclear Information System (INIS)

1985-09-01

The present study was motivated by the desire to examine the US High Energy Physics Program in depth, to reassess the Superconducting Super Collider (SSC) goal in light of recent scientific and technical developments, and to understand how this project would affect and interact with the US high energy program in the period before it becomes operational. It is recommended that the SSC research and development be given highest priority in the US High Energy Physics Program so that the project can proceed to an early construction start and rapid completion. A limited number of programs are identified as ''forefront programs'' - those which enter a new experimental regime in such a way as to have clear promise for new fundamental discoveries - and it is recommended that these proceed with priority. Research opportunities available during the next ten years are explored, including proton-antiproton colliders, electron-proton collider, electron-positron colliders, fixed-target experiments, and non-accelerator experiments

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.

Positrons as imaging agents and probes in nanotechnology

International Nuclear Information System (INIS)

Smith, Suzanne V

2009-01-01

Positron emission tomography (PET) tracks a positron emitting radiopharmaceutical injected into the body and generates a 3-dimensional image of its location. Introduced in the early 70s, it has now developed into a powerful medical diagnostic tool for routine clinical use as well as in drug development. Unrivalled as a highly sensitive, specific and non-invasive imaging tool, PET unfortunately lacks the resolution of Computer Tomography (CT) and Magnetic Resonance Imaging (MRI). As the resolution of PET depends significantly on the energy of the positron incorporated in the radiopharmaceutical and its interaction with its surrounding tissue, there is growing interest in expanding our understanding of how positrons interact at the atomic and molecular level. A better understanding of these interactions will contribute to improving the resolution of PET and assist in the design of better imaging agents. Positrons are also used in Positron Annihilation Lifetime Spectroscopy (PALS) to determine electron density and or presence and incidence of micro- and mesopores (0.1 to 10 nm) in materials. The control of porosity in engineered materials is crucial for applications such as controlled release or air and water resistant films. Equally important to the design of nano and microtechnologies, is our understanding of the microenvironments within these pores and on surfaces. Hence as radiopharmaceuticals are designed to track disease, nuclear probes (radioactive molecules) are synthesized to investigate the chemical properties within these pores. This article will give a brief overview of the present role of positrons in imaging as well as explore its potential to contribute in the engineering of new materials to the marketplace.

Recoil effects in multiphoton electron-positron pair creation

International Nuclear Information System (INIS)

Krajewska, K.; Kaminski, J. Z.

2010-01-01

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

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...

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)

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 annihilation studies of the electronic structure and fermiology of high-Tc superconductors

International Nuclear Information System (INIS)

Smedskjaer, L.C.; Bansil, A.

1993-01-01

We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of high-Tc superconductors, with focus on the YBa 2 Cu 3 O 7 system where most of the experimental and theoretical work has to date been concentrated. Detailed comparisons between the measured 2D-ACAR positron spectra and the corresponding band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture. (orig.)

Elementary particle physics and high energy phenomena. Progress report for FY93

Energy Technology Data Exchange (ETDEWEB)

Barker, A.R.; Cumalat, J.P.; De Alwis, S.P.; DeGrand, T.A.; Ford, W.T.; Mahanthappa, K.T.; Nauenberg, U.; Rankin, P.; Smith, J.G.

1992-06-01

Experimental and theoretical high-energy physics programs at the University of Colorado are reported. Areas of concentration include the following: study of the properties of the Z{sup 0} with the SLD detector; fixed-target K-decay experiments; the R&D program for the muon system: the SDC detector; high-energy photoproduction of states containing heavy quarks; electron--positron physics with the CLEO II detector at CESR; lattice QCD; and spin models and dynamically triangulated random surfaces. 24 figs., 2 tabs., 117 refs.

Calculation of positron annihilation in high Tc copper oxides

International Nuclear Information System (INIS)

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

1992-01-01

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

Study of SiO2-Si and metal-oxide-semiconductor structures using positrons

Science.gov (United States)

Leung, T. C.; Asoka-Kumar, P.; Nielsen, B.; Lynn, K. G.

1993-01-01

Studies of SiO2-Si and metal-oxide-semiconductor (MOS) structures using positrons are summarized and a concise picture of the present understanding of positrons in these systems is provided. Positron annihilation line-shape S data are presented as a function of the positron incident energy, gate voltage, and annealing, and are described with a diffusion-annihilation equation for positrons. The data are compared with electrical measurements. Distinct annihilation characteristics were observed at the SiO2-Si interface and have been studied as a function of bias voltage and annealing conditions. The shift of the centroid (peak) of γ-ray energy distributions in the depletion region of the MOS structures was studied as a function of positron energy and gate voltage, and the shifts are explained by the corresponding variations in the strength of the electric field and thickness of the depletion layer. The potential role of the positron annihilation technique as a noncontact, nondestructive, and depth-sensitive characterization tool for the technologically important, deeply buried interface is shown.

Study of SiO2-Si and metal-oxide-semiconductor structures using positrons

International Nuclear Information System (INIS)

Leung, T.C.; Asoka-Kumar, P.; Nielsen, B.; Lynn, K.G.

1993-01-01

Studies of SiO 2 -Si and metal-oxide-semiconductor (MOS) structures using positrons are summarized and a concise picture of the present understanding of positrons in these systems is provided. Positron annihilation line-shape S data are presented as a function of the positron incident energy, gate voltage, and annealing, and are described with a diffusion-annihilation equation for positrons. The data are compared with electrical measurements. Distinct annihilation characteristics were observed at the SiO 2 -Si interface and have been studied as a function of bias voltage and annealing conditions. The shift of the centroid (peak) of γ-ray energy distributions in the depletion region of the MOS structures was studied as a function of positron energy and gate voltage, and the shifts are explained by the corresponding variations in the strength of the electric field and thickness of the depletion layer. The potential role of the positron annihilation technique as a noncontact, nondestructive, and depth-sensitive characterization tool for the technologically important, deeply buried interface is shown

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 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.

Beta spectra. II-Positron spectra

International Nuclear Information System (INIS)

Grau, A.; Garcia-Torano, E.

1981-01-01

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

The penetration, diffusion and energy deposition of high-energy photon in layered media

International Nuclear Information System (INIS)

Zhengming, Luo; Chengjun, Gou; Laub, Wolfram

2002-01-01

This paper presents a new theory for calculating the transport of high-energy photons and their secondary charged particles. We call this new algorithm characteristic line method, which is completely analytic. Using this new method we can not only accurately calculate the transport behavior of energetic photons, but also precisely describes the transport behavior and energy deposition of secondary electrons, photoelectrons, Compton recoil electrons and positron-electron pairs. Its calculation efficiency is much higher than the Monte Carlo method's. The theory can be directly applied to layered media situation and obtain a pencil-beam-modeled solution. Therefore, it may be applied to clinical applications for radiation therapy

Positron annihilation study on Y-Ba-Cu-O high Tc superconductors

International Nuclear Information System (INIS)

Balogh, A.G.; Liszkay, L.; Molnar, B.; Puff, W.

1987-08-01

First positron annihilation measurements are reported on high T c superconductor YBa 2 Cu 3 O 7-x . The lifetime and Doppler broadening spectra show a slight but significant change about 240K suggesting a deviation from the normal structure far above 90K where the resistance falls to zero. (author)

Electron and Positron Stopping Powers of Materials

Science.gov (United States)

SRD 7 NIST Electron and Positron Stopping Powers of Materials (PC database for purchase)   The EPSTAR database provides rapid calculations of stopping powers (collisional, radiative, and total), CSDA ranges, radiation yields and density effect corrections for incident electrons or positrons with kinetic energies from 1 keV to 10 GeV, and for any chemically defined target material.

Development of new radiation sources using high energy electrons and their applications

International Nuclear Information System (INIS)

Tomimasu, Takio

1992-01-01

Present and future of compact electron storage rings used for lithography, free electron laser (FEL) and angiography are reviewed and discussed. Recent development of the compact rings with insertion devices capable of storing 1-A beam enable these prospective applications and generations of strong backward compton scattered γ-rays and any kind of elliptically polarizing photons. The high-energy, high current and small-energy spread beam acceleration using conventional type electron linacs is also discussed for the generations of UV-FEL and slow positrons. (author)

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

International Nuclear Information System (INIS)

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

2007-01-01

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

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.)

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-06-24

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

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

International Nuclear Information System (INIS)

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

2014-01-01

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

Metal/oxide/semiconductor interface investigated by monoenergetic positrons

Science.gov (United States)

Uedono, A.; Tanigawa, S.; Ohji, Y.

1988-10-01

Variable-energy positron-beam studies have been carried out for the first time on a metal/oxide/semiconductor (MOS) structure of polycrystalline Si/SiO 2/Si-substrate. We were successful in collecting injected positrons at the SiO 2/Si interface by the application of an electric field between the MOS electrodes.

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

Science.gov (United States)

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

2012-06-01

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

Ultra high energy electrons powered by pulsar rotation.

Science.gov (United States)

Mahajan, Swadesh; Machabeli, George; Osmanov, Zaza; Chkheidze, Nino

2013-01-01

A new mechanism of particle acceleration, driven by the rotational slow down of the Crab pulsar, is explored. The rotation, through the time dependent centrifugal force, can efficiently excite unstable Langmuir waves in the electron-positron (hereafter e(±)) plasma of the star magnetosphere. These waves, then, Landau damp on electrons accelerating them in the process. The net transfer of energy is optimal when the wave growth and the Landau damping times are comparable and are both very short compared to the star rotation time. We show, by detailed calculations, that these are precisely the conditions for the parameters of the Crab pulsar. This highly efficient route for energy transfer allows the electrons in the primary beam to be catapulted to multiple TeV (~ 100 TeV) and even PeV energy domain. It is expected that the proposed mechanism may, unravel the puzzle of the origin of ultra high energy cosmic ray electrons.

Study of tungsten based positron moderators

International Nuclear Information System (INIS)

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

2015-01-01

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

Study of tungsten based positron moderators

Energy Technology Data Exchange (ETDEWEB)

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

2015-07-01

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

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

DEFF Research Database (Denmark)

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

2012-01-01

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

The inclusion of π functions in the treatment of low-energy positron-hydrogen-molecule scattering by a generalisation of the Kohn method

International Nuclear Information System (INIS)

Armour, E.A.G.

1985-01-01

In the application of a generalisation of the Kohn method to low-energy positron-hydrogen-molecule scattering, up to 31 short-range correlation functions, made up of one-particle functions of σ symmetry, were included in the trial function. In the calculation described in this paper, the flexibility of the trial function is greatly improved by the inclusion of up to 64-short-range correlation functions of which 32 contain products of one-particle functions of π symmetry. The behaviour of the phaseshift values with increasing incident energy is qualitatively similar to the behaviour of the corresponding S-wave phaseshifts in low-energy positron-helium scattering. Comparison with experiment indicates that the results reproduce qualitatively the experimental trend at very low energies but higher partial waves must make a significant contribution to the total cross section above about 0.1 eV. (author)

The study on a new superconductor (oxide Ba-Y-Cu) with high critical temperature Tc by positron annihilation

International Nuclear Information System (INIS)

Zhang Caigu; Yu Zhuxing; Wang Zhu; Huang Zhe; Zhou Jun

1987-01-01

The study on a new superconductor oxide Ba-Y-Cu with high critical temperature Tc is described. The experimental results show that positron lifetime reducing reflects variable curve of resistance with temperature. A peak of positron lifetime is appeared at critical temperature

Electron Linacs for High Energy Physics

International Nuclear Information System (INIS)

Wilson, Perry B.

2011-01-01

The purpose of this article is to introduce some of the basic physical principles underlying the operation of electron linear accelerators (electron linacs). Electron linacs have applications ranging from linacs with an energy of a few MeV, such that the electrons are approximately relativistic, to future electron-positron linear colliders having a collision energy in the several-TeV energy range. For the most part, only the main accelerating linac is treated in this article.

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

Measurement of high-Q2 neutral current cross-sections with longitudinally polarised positrons with the ZEUS detector

International Nuclear Information System (INIS)

Stewart, Trevor P.

2012-07-01

The cross sections for neutral current (NC) deep inelastic scattering (DIS) in e + p collisions with a longitudinally polarised positron beam are measured at high momentum transfer squared (Q 2 >185 GeV 2 ) at the ZEUS detector at HERA. The HERA accelerator provides e ± p collisions at a centre-of-mass energy of 318 GeV, which allows the weak contribution to the NC process to be studied at high Q 2 . The measurements are based on a data sample with an integrated luminosity of 135.5 pb -1 collected with the ZEUS detector in 2006 and 2007. The single differential NC cross sections dσ/dQ 2 , dσ/dx and dσ/dy and the reduced cross section σ are measured. The structure function xF 3 is determined by combining the e + p NC reduced cross sections with the previously measured e - p measurements. The interference structure function xF 3 γZ is extracted at Q 2 =1500 GeV 2 . The cross-section asymmetry between the positive and negative polarisation of the positron beam is measured and the parity violation effects of the electroweak interaction are observed. The predictions of the Standard Model of particle physics agree well with the measurements. (orig.)

Can positron 2D-ACAR resolve the electronic structure of high-Tc superconductors

International Nuclear Information System (INIS)

Chan, L.P.; Lynn, K.G.; Harshman, D.R.

1992-01-01

In this paper, the authors examine the ability of the positron Two-Dimensional Angular Correlation Annihilation Radiation (2D-ACAR) technique to resolve the electronic structures of high-T c cuprate superconductors. Following a short description of the technique, discussions of the theoretical assumptions, data analysis and experimental considerations, in relation to the high-T c superconductors, are given. The authors briefly review recent 2D-ACAR experiments on YBa 2 Cu 3 O 7-x , Bi 2 Sr 2 CaCuO 8+δ and La 2-x Sr x CuO 4 . The 2D-ACAR technique is useful in resolving the band crossings associated with the layers of the superconductors that are preferentially sampled by the positrons. Together with other Fermi surface measurements (namely angle-resolved photoemission), 2D-ACAR can resolve some of the electronic structures of high-T c cuprate superconductors

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.)

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)

ANTICOOL: Simulating positron cooling and annihilation in atomic gases

Science.gov (United States)

Green, D. G.

2018-03-01

The Fortran program ANTICOOL, developed to simulate positron cooling and annihilation in atomic gases for positron energies below the positronium-formation threshold, is presented. Given positron-atom elastic scattering phase shifts, normalised annihilation rates Zeff, and γ spectra as a function of momentum k, ANTICOOL enables the calculation of the positron momentum distribution f(k , t) as a function of time t, the time-varying normalised annihilation rate Z¯eff(t) , the lifetime spectrum and time-varying annihilation γ spectra. The capability and functionality of the program is demonstrated via a tutorial-style example for positron cooling and annihilation in room temperature helium gas, using accurate scattering and annihilation cross sections and γ spectra calculated using many-body theory as input.

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.

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)

Electron-positron collision physics: 1 MeV to 2 TeV

International Nuclear Information System (INIS)

Perl, M.L.

1988-07-01

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

Coincidence summing corrections for positron emitters in germanium gamma spectrometry

International Nuclear Information System (INIS)

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

1990-01-01

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

Anomalous positron emission in heavy ion-collisions

International Nuclear Information System (INIS)

Kienle, P.

1986-09-01

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

Beam Commissioning of the PEP-II High Energy Ring

International Nuclear Information System (INIS)

Wienands, U.; Anderson, S.; Assmann, R.; Bharadwaj, V.; Cai, Y.; Clendenin, J.; Corredoura, P.; Decker, F.J.; Donald, M.; Ecklund, S.; Emma, P.; Erickson, R.; Fox, J.; Fieguth, T.; Fisher, A.; Heifets, S.; Hill, A.; Himel, T.; Iverson, R.; Johnson, R.; Judkins, J.; Krejcik, P.; Kulikov, A.; Lee, M.; Mattison, T.; Minty, M.; Nosochkov, Y.; Phinney, N.; Placidi, M.; Prabhakar, S.; Ross, M.; Smith, S.; Schwarz, H.; Stanek, M.; Teytelman, D.; Traller, R.; Turner, J.; Zimmermann, F.; Barry, W.; Chattopadhyay, S.; Corlett, J.; Decking, W.; Furman, M.; Nishimura, H.; Portmann, G.; Rimmer, R.; Zholents, A.; Zisman, M.; Kozanecki, W.; Hofmann, A.; Zotter, B.; Steier, C.; Bialowons, W.; Lomperski, M.; Lumpkin, A.; Reichel, I.; Safranek, J.; Smith, V.; Tighe, R.; Sullivan, M.; Byrd, J.; Li, D.

1998-01-01

The PEP-II High Energy Ring (HER), a 9 GeV electron storage ring, has been in commissioning since spring 1997. Initial beam commissioning activities focused on systems checkout and commissioning and on determining the behavior of the machine systems at high beam currents. This phase culminated with the accumulation of 0.75 A of stored beam-sufficient to achieve design luminosity--in January 1998 after 3.5 months of beam time. Collisions with the 3 GeV positron beam of the Low Energy Ring (LER) were achieved in Summer of 1998. At high beam currents, collective instabilities have been seen. Since then, commissioning activities for the HER have shifted in focus towards characterization of the machine and a rigorous program to understand the machine and the beam dynamics is presently underway

Muon, positron and antiproton interactions with atoms and molecules

Energy Technology Data Exchange (ETDEWEB)

Armour, Edward A G, E-mail: edward.armour@nottingham.ac.u [School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2010-04-01

In this paper, a description is given of some interesting processes involving the interaction of a muon, a positron, or an antiproton with atoms and molecules. The process involving a muon is the resonant formation of the muonic molecular ion, dt{mu}, in the muon catalyzed fusion cycle. In the case of a positron, the process considered is positron annihilation in low-energy positron scattering by the hydrogen molecule. The antiproton is considered as the nucleus of an antihydrogen atom interacting with simple atoms. Attention is given to antiproton annihilation through the strong interaction. An outline is given of proposed tests of fundamental physics to be carried out using antihydrogen.

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-10-15

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

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

Science.gov (United States)

Krsjak, Vladimir; Dai, Yong

2015-10-01

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

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

International Nuclear Information System (INIS)

1975-03-01

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

Status report of the Cornell High Energy Synchrotron Radiation Source (CHESS)

International Nuclear Information System (INIS)

Batterman, B.W.

1980-01-01

The Wilson Laboratory at Cornell University has done pioneering work on the development of high energy synchrotrons. In the last decade the 12 GeV Wilson Synchrotron was the most energetic electron synchrotron in the world. In 1975 plans were formulated at the Wilson Laboratory to build a new electron-positron storage ring to cover the range from 4-8 GeV. The storage ring was to be constructed in the same tunnel as the present synchrotron and to use the latter as an injector for the ring. A novel injection feature was to be incorporated, namely, vernier phase compression. In this scheme, positron coalesence is to be performed by compressing a 30-60 bunch positron beam by tranferring individual bunches from the storage ring to the synchrotron and stacking back into the storage ring. This procedure takes advantage of the slight circumferential difference between the storage ring and the synchrotron. Positron beams of 10 mA have been achieved in CESR at the present time. The first colliding beam studies were performed in an October 1979 two-week running period at which time CHESS, the synchrotron radiation source associated with CESR, also had its first extended experience with synchrotron light. (orig.)

Performance evaluation of BGO block detectors used in positron emission tomography and a coincidence system

International Nuclear Information System (INIS)

Kim, J. H.; Choi, Y.; Lim, K. C.; Lee, M. Y.; Woo, S. K.; Lee, K. H.; Kim, S. E.; Choi, Y. S.; Kim, B. T.

1999-01-01

We investigated the basic performances of the BGO block detectors, which is used in the GE Advance positron emission tomography. The block detector is composed of 36 small BGO crystals coupled to two 2-channel photomultiplier tubes. In this study, we measured the crystal map and the intrinsic energy resolution of the detector. The coincidence signals between the detectors were also obtained using F-18. The intrinsic energy resolution of the block detector was 69% FWHM at 140 keV and 33% FWHM at 511 keV. High quality crystal map and the coincidence signals between the detectors were successfully obtained. The timing resolution of the detectors are being measured. The results of this study demonstrate the feasibility of developing high performance positron emission tomography

Positron Annihilation Studies of the Electronic Structure of Selected High-Temperature Cuprate and Organic Superconductors.

Science.gov (United States)

Chan, Lie Ping

The understanding of the electronic structure of the high-T_{c} superconductors could be important for a full theoretical description of the mechanism behind superconductivity in these materials. In this thesis, we present our measurements of the positron -electron momentum distributions of the cuprate superconductors Bi_2Sr_2CaCu _2O_8, Tl _2Ba_2Ca _2Cu_3O_ {10}, and the organic superconductor kappa-(BEDT)_2Cu(NCS) _2. We use the positron Two-dimensional Angular Correlation of Annihilation Radiation technique to make the measurements on single crystals and compare our high-statistics data with band structure calculations to determine the existence and nature of the respective Fermi surfaces. The spectra from unannealed Bi _2Sr_2CaCu _2O_8 exhibit effects of the superlattice modulation in the BiO_2 layers, and a theoretical understanding of the modulation effects on the electronic band structure is required to interpret these spectra. Since the present theory does not consider the modulation, we have developed a technique to remove the modulation effects from our spectra, and the resultant data when compared with the positron -electron momentum distribution calculation, yield features consistent with the predicted CuO_2 and BiO_2 Fermi surfaces. In the data from unannealed Tl_2Ba _2Ca_2Cu_3 O_{10}, we only observe indications of the TlO Fermi surfaces, and attribute the absence of the predicted CuO_2 Fermi surfaces to the poor sample quality. In the absence of positron-electron momentum calculations for kappa-(BEDT)_2Cu(NCS) _2, we compare our data to electronic band structure calculations, and observed features suggestive of the predicted Fermi surface contributions from the BEDT cation layers. A complete positron-electron calculation for kappa-(BEDT)_2 Cu(NCS)_2 is required to understand the positron wavefunction effects in this material.

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

Use of a YAP:Ce matrix coupled to a position-sensitive photomultiplier for high resolution positron emission tomography

International Nuclear Information System (INIS)

Del Guerra, A.; Zavattini, G.; Notaristefani, F. de; Giganti, M.; Piffanelli, A.; Pani, R.; Turra, A.

1996-01-01

A new scintillation detector system has been designed for application in high resolution Positron Emission Tomography (PET). The detector is a bundle of small YAlO 3 :Ce (YAP) crystals closely packed (0.2 x 0.2 x 3.0 cm 3 ), coupled to a position sensitive photomultiplier tube (PSPMT). The preliminary results obtained for spatial resolution, time resolution, energy resolution and efficiency of two such detectors working in coincidence are presented. These are 1.2 mm for the FWHM spatial resolution, 2.0 ns for the FWHM time resolution and 20% for the FWHM energy resolution at 511 keV. The measured efficiency is (44 ± 3)% with a 150 keV threshold and (20 ± 2)% with a 300 keV threshold

Hydrogen interaction with oxidized Si(111) probed with positrons

International Nuclear Information System (INIS)

Lynn, K.G.; Nielsen, B.; Welch, D.O.

1989-01-01

A variable-energy positron beam was utilized to study the interface action of hydrogen with Si(111) covered by an ultrahigh-vacuum thermally grown oxide of 2-3 nm thickness. It was observed that positrons implanted at shallow depth (< 100 nm) after diffusion are trapped either at the interface between the oxide and the Si or in the oxide. The positron-annihilation characteristics of these trapped positrons are found to be very sensitive to hydrogen exposure. The momentum distribution of the annihilating positron-electron pair, as observed in the Doppler broadening of the annihilation line, broadens considerably after exposure to hydrogen. The effect recovers after annealing at ≅ 1100 K, suggesting a hydrogen binding at the interface of ∼ 3 ± 0.3 eV. (author). 18 refs., 3 figs

Positron range in PET imaging: non-conventional isotopes

International Nuclear Information System (INIS)

Jødal, L; Le Loirec, C; Champion, C

2014-01-01

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

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

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

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

International Nuclear Information System (INIS)

Lalanne, D.

1970-01-01

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

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.)

Study on a high resolution positron emission tomography scanner for brain study

International Nuclear Information System (INIS)

Nohara, N.; Tomitani, T.; Yamamoto, M.; Murayama, H.; Tanaka, E.

1990-01-01

The spatial resolution of positron emission tomography (PET) scanners is usually limited by the finite size of crystals such as bismuth germanate (BGO). To attain high resolution as well as high sensitivity, it is essential to use a large number of small BGO crystals arranged in close-packing on circular rings. In developing high resolution PET scanners, however, there are two physical factors limiting the spatial resolution. One is the finite range of positrons before annihilation and the other the deviation from 180 degrees of annihilation photons. The effect of the factors on the spatial resolution has been evaluated for positron-emitting sources as a function of detector ring radius. A high resolution PET scanner has been developed for brain study, aiming to have spatial resolutions as high as less than 4-mm FWHM in tomographic plane and less than 6-mm FWHM in axial direction at the detector ring center. For the goal of the high resolutions a multi-segment type of photomultiplier tubes has been specially designed and developed, which allows one tube to be directly coupled by four BGO crystals. The scanner consists of five detector rings of 47-cm in diameter, using all 1200 BGO crystals each measuring 5 mm x 12 mm x 30 mm. The scanner provides simultaneous 9 images by combination of in-plane and cross-plane, offering a 24-cm dia. x7.4-cm field-of-view. Physical performance of the scanner was investigated. At the ring center, the spatial resolution in the tomographic plane was measured to be 3.5-mm FWHM. The axial resolution was measured to be 5.7-mm FWHM for in-plane and 5.3-mm FWHM for cross-plane. Sensitivity for a 20-cm dia. uniform source was measured to be 9.5 kcps/μCi/ml for in-plane and 15.3 kcps/μCi/ml for cross-plane. (J.P.N.)

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.

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

Applications of positron annihilation spectroscopy to polymeric and biological systems

International Nuclear Information System (INIS)

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

2007-01-01

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

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

submitter Projects for ultra-high-energy circular colliders at CERN

CERN Document Server

Bogomyagkov, A V; Levichev, E B; Piminov, P A; Sinyatkin, S V; Shatilov, D N; Benedict, M; Oide, K; Zimmermann, F

2016-01-01

Within the Future Circular Collider (FCC) design study launched at CERN in 2014, it is envisaged to construct hadron (FCC-hh) and lepton (FCC-ee) ultra-high-energy machines aimed to replace the LHC upon the conclusion of its research program. The Budker Institute of Nuclear Physics is actively involved in the development of the FCC-ee electron–positron collider. The Crab Waist (CR) scheme of the collision region that has been proposed by INP and will be implemented at FCC-ee is expected to provide high luminosity over a broad energy range. The status and development of the FCC project are described, and its parameters and limitations are discussed for the lepton collider in particular.

Positron annihilation and Wheeler complexes in semiconductors

International Nuclear Information System (INIS)

Prokop'ev, E.P.

1995-01-01

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

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...

Positron trapping at defects in copper oxide superconductors

International Nuclear Information System (INIS)

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

1991-01-01

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

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

Science.gov (United States)

Lazzeroni, Marta; Brahme, Anders

2014-02-01

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

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

International Nuclear Information System (INIS)

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

1991-01-01

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

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...

A high energy photon detector system in compact form

International Nuclear Information System (INIS)

Kato, Sadayuki; Sugano, Katsuhito; Yoshioka, Masakazu.

1975-01-01

The development of a high energy photon detector system in compact form for use in experiments of high energy physics is described, and the results of its characteristics calibrated using converted electron beams and a pair spectrometer are reported. This system consists of a total absorption lead glass Cerenkov counter, twenty hodoscope arrays for the vertical and the horizontal directions respectively, a lead plate for the conversion of γ-rays into electron-positron pairs, veto counters, photon hardener, and lead blocks for shieldings and collimation. The spatial resolution of the hodoscope is 15 mm for each direction, covering 301 x 301 mm 2 area. The energy resolution of the total absorption lead glass Cerenkov counter, whose volume is 30 x 30 x 30 cm 3 , is typically 18 % (FWHM) for the incident electron energy of 500 MeV, and it can be expressed with a relation of ΔE/E = 3.94 Esup(-1/2). (E in MeV). (auth.)

The effect of annealing unimplanted and krypton implanted uranium dioxide using positrons

International Nuclear Information System (INIS)

Evans, H.E.; Rice-Evans, P.; Smith, D.L.; Smith, C.; Evans, J.H.

1992-01-01

Previous studies examining the response of variable energy positrons to metals implanted with krypton ions have been extended to UO 2 . The behaviour of two Kr-implanted samples (one implanted at 300 K, the other at 870 K) during annealing up to 1350 K has been followed, together with an unimplanted, as-polished sample. There are several features of interest in the results although in these initial studies the interpretation is not always clear. Defect recovery and krypton effects can be identified but at high temperatures some suggestion of a sensitivity of positrons to stoichiometry is present

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

Science.gov (United States)

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

2014-05-01

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

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

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)

Electron-positron interactions

International Nuclear Information System (INIS)

Wiik, B.; Wolf, G.

1979-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

Anon.

1993-09-15

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

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

International Nuclear Information System (INIS)

Anon.

1993-01-01

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

Implementation of Cascade Gamma and Positron Range Corrections for I-124 Small Animal PET

Science.gov (United States)

Harzmann, S.; Braun, F.; Zakhnini, A.; Weber, W. A.; Pietrzyk, U.; Mix, M.

2014-02-01

Small animal Positron Emission Tomography (PET) should provide accurate quantification of regional radiotracer concentrations and high spatial resolution. This is challenging for non-pure positron emitters with high positron endpoint energies, such as I-124: On the one hand the cascade gammas emitted from this isotope can produce coincidence events with the 511 keV annihilation photons leading to quantification errors. On the other hand the long range of the high energy positron degrades spatial resolution. This paper presents the implementation of a comprehensive correction technique for both of these effects. The established corrections include a modified sinogram-based tail-fitting approach to correct for scatter, random and cascade gamma coincidences and a compensation for resolution degradation effects during the image reconstruction. Resolution losses were compensated for by an iterative algorithm which incorporates a convolution kernel derived from line source measurements for the microPET Focus 120 system. The entire processing chain for these corrections was implemented, whereas previous work has only addressed parts of this process. Monte Carlo simulations with GATE and measurements of mice with the microPET Focus 120 show that the proposed method reduces absolute quantification errors on average to 2.6% compared to 15.6% for the ordinary Maximum Likelihood Expectation Maximization algorithm. Furthermore resolution was improved in the order of 11-29% depending on the number of convolution iterations. In summary, a comprehensive, fast and robust algorithm for the correction of small animal PET studies with I-124 was developed which improves quantitative accuracy and spatial resolution.

Characterization of point defects in CdTe by positron annihilation spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Elsharkawy, M. R. M. [Carnegie Laboratory of Physics, SUPA, School of Science and Engineering, University of Dundee, Dundee DD1 4HN (United Kingdom); Physics Department, Faculty of Science, Minia University, P.O. Box 61519, Minia (Egypt); Kanda, G. S.; Keeble, D. J., E-mail: d.j.keeble@dundee.ac.uk [Carnegie Laboratory of Physics, SUPA, School of Science and Engineering, University of Dundee, Dundee DD1 4HN (United Kingdom); Abdel-Hady, E. E. [Physics Department, Faculty of Science, Minia University, P.O. Box 61519, Minia (Egypt)

2016-06-13

Positron lifetime measurements on CdTe 0.15% Zn-doped by weight are presented, trapping to monovacancy defects is observed. At low temperatures, localization at shallow binding energy positron traps dominates. To aid defect identification density functional theory, calculated positron lifetimes and momentum distributions are obtained using relaxed geometry configurations of the monovacancy defects and the Te antisite. These calculations provide evidence that combined positron lifetime and coincidence Doppler spectroscopy measurements have the capability to identify neutral or negative charge states of the monovacancies, the Te antisite, A-centers, and divacancy defects in CdTe.

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.

Measurements of the cosmic-ray electron and positron spectrum and anisotropies with the Fermi LAT

Science.gov (United States)

Loparco, F.; Fermi LAT Collaboration

2017-12-01

The Large Area Telescope (LAT) onboard the Fermi satellite is a pair-conversion telescope for high-energy gamma rays of astrophysical origin. Although it was designed to be a high-sensitivity gamma-ray telescope, the LAT has proved to be an excellent electron/positron detector. It has been operating in low Earth orbit since June 2008 and has collected more than 16 million cosmic-ray electron and positron (CRE) events in its first seven years of operation. The huge data sample collected by the LAT enables a precise measurement of the CRE energy spectrum up to the TeV region. A search for anisotropies in the arrival directions of CREs was also performed. The upper limits on the dipole anisotropy probe the presence of nearby young and middle-aged CRE sources.

Search for new physics in final states with a high energy electron and large missing transverse energy

CERN Document Server

AUTHOR|(INSPIRE)INSPIRE-00345099

The most successful and comprehensive theory describing the microcosm is the Standard Model of particle physics (SM). It comprises all known elementary particles and describes in high precision the basic processes of three of the four fundamental interactions. But still, not all experimental observations and theoretical challenges are covered. Many models exist that take the SM as a good approximation of natural phenomena in already discovered energy regions, but extend it in various ways. The Large Hadron Collider (LHC) provides the opportunity to look into these high energy regions using proton-proton collisions at significantly higher center-of-mass energies than previous experiments. This dissertation searches for physics beyond the SM especially in final states with one highly energetic electron (respectively positron) and large missing transverse energy. With the data set recorded in 2012 by the ATLAS detector, a large multi-purpose detector making use of the LHC, the spectrum of the related combined ...

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

International Nuclear Information System (INIS)

Rees, J.R.

1974-01-01

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

High resolution positron Q-value measurements and nuclear structure studies far from the stability line. Progress report, July 1, 1979-June 30, 1980

International Nuclear Information System (INIS)

Avignone, F.T. III.

1980-01-01

This document represents a progress report and renewal proposal for the contract DEAS 09 79 ER10434 between the USDOE and USC. During the time from 1 July 1979 to 1 March 1980, the large 35% intrinsic Ge detector was purchased and tested, and the new hyperpure Ge detector for positron end-point-energy measurements was designed and fabricated by ORTEC. It was delivered just prior to January 1, 1980. Measurements using this special equipment began in January 1980. During this period, a new effort in the measurement of short nuclear lifetimes was completed, and nuclear structure measurements of 206 Rn nd 208 Rn were completed. The results of these efforts are described in the text. A search for the Post Doctoral Research Associate was started last summer and the position will be filled on or about 1 March 1980. The first experiments to measure positron end-point-energies were proposed to the ORIC scheduling committee, and measurements will begin in March 1980. Theoretical efforts describe accurately the interference of annihilation radiation with positron end-point-energy measurements were begun

Scintillators for positron emission tomography

International Nuclear Information System (INIS)

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

1995-09-01

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

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.

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

A High-Performance VME-Based Acquisition System for Positron Emission Mammography

International Nuclear Information System (INIS)

Abbott, D.J.; Weisenberger, A.; Majewski, S.; Kieper, D.; Kross, B.; Popov, V.; Wojcik, R.; Raylman, R.R.

2001-01-01

A prototype for a practical and economical breast imaging system for cancer detection is currently under development at Jefferson Lab. The latest advances in bright, fast, crystal scintillators, compact position-sensitive photomultipliers (PSPMT), and high-performance digitizing and readout electronics are being used to develop a compact imager based on Positron Emission Tomography (PET). To facilitate the performance demands of the detector as well as the high number of readout channels, the data acquisition system is built around an intelligent, self-contained, VME form-factor