scholarly journals Slow positron beam at the JINR, Dubna

Nukleonika ◽  
2015 ◽  
Vol 60 (4) ◽  
pp. 725-728 ◽  
Author(s):  
Paweł Horodek ◽  
Andrey G. Kobets ◽  
Igor N. Meshkov ◽  
Alexey A. Sidorin ◽  
Oleg S. Orlov
Keyword(s):  
Diffusion Length ◽  
Nuclear Research ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Low Energy ◽  
Positron Energy ◽  
Slow Positron ◽  
Tungsten Foil ◽  
Sample Chamber ◽  
Variable Energy

Abstract The Low Energy Positron Toroidal Accumulator (LEPTA) at the Joint Institute for Nuclear Research (JINR) proposed for generation of positronium in flight has been adopted for positron annihilation spectroscopy (PAS). The positron injector generates continuous slow positron beam with positron energy range between 50 eV and 35 keV. The radioactive 22Na isotope is used. In distinction to popular tungsten foil, here the solid neon is used as moderator. It allows to obtain the beam intensity of about 105 e+/s width energy spectrum characterized by full width at half maximum (FWHM) of 3.4 eV and a tail to lower energies of about 30 eV. The paper covers the characteristic of variable energy positron beam at the LEPTA facility: parameters, the rule of moderation, scheme of injector, and transportation of positrons into the sample chamber. Recent status of the project and its development in the field of PAS is discussed. As an example, the measurement of the positron diffusion length in pure iron is demonstrated.

scholarly journals Studies of stainless steel exposed to sandblasting

Nukleonika ◽  
2015 ◽  
Vol 60 (4) ◽  
pp. 721-724 ◽  
Author(s):  
Paweł Horodek ◽  
Marat K. Eseev ◽  
Andrey G. Kobets
Keyword(s):  
Stainless Steel ◽  
Diffusion Length ◽  
Applied Pressure ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Time Duration ◽  
Force Microscopy ◽  
Atomic Force ◽  
Positron Lifetimes ◽  
Variable Energy

Abstract The influence of sandblasting on surface and subsurface of stainless steel is investigated using variable energy positron beam (VEP), positron annihilation spectroscopy (PAS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Samples of stainless steel were blasted using 110 μm particles of Al2O3 under different pressure and time duration. In the case of sandblasting for 90 s, the reduction of positron diffusion length depending on the applied pressure was observed. Sandblasting during 30 s leads only to the reduction of positron diffusion length to about 60 nm for all samples. Positron lifetimes close to 170 ps measured using positrons emitted directly from the source point to the presence of vacancies on the dislocation lines. SEM and AFM images show that surface roughness depends rather on pressure of sandblasting than time of exposition.

Slow Positron Beam Probe for the ZnO/Silicone under Proton Irradiation

2008 ◽  
Vol 607 ◽  
pp. 108-110
Author(s):  
Ying Ping Hao ◽  
Hui Min Weng ◽  
Chun Dong Li ◽  
Wei Feng Guo ◽  
Jian Dang Liu ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Crosslink Density ◽  
Proton Irradiation ◽  
Diffusion Length ◽  
Effective Diffusion ◽  
Positron Beam ◽  
Coating System ◽  
Slow Positron ◽  
Silicone Coating ◽  
Variable Energy

The degradation of ZnO/Silicone coating system under 90keV proton irradiation varying from 5×1014cm-2 to 1×1016cm-2, was studied by slow positron annihilation spectrum. Effective diffusion length calculated by Variable energy positron fit (VEPFIT) shows a dramatically break in a dose of 1×1015cm-2. It is ascribed to the increase of crosslink density and decrease of free volume and hole during the proton irradiation. Furthermore, positron has shown a satisfying sensitivity in detecting the nano-scale defect on ZnO/Silicone system.

Design and Construction of a Slow Positron Beam for Solid and Surface Investigations

2012 ◽  
Vol 331 ◽  
pp. 25-40 ◽  
Author(s):  
Wolfgang Anwand ◽  
Gerhard Brauer ◽  
Maik Butterling ◽  
Hans Rainer Kissener ◽  
Andreas Wagner
Keyword(s):  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Vacuum System ◽  
Sample Holder ◽  
Slow Positron ◽  
Financial Costs ◽  
Sample Chamber ◽  
Magnetic Transport ◽  
Short Time ◽  
Design And Construction

On the basis of the design and construction of the slow positron beam SPONSOR at the Helmholtz-Centre Dresden-Rossendorf an example is given how to build-up a simple slow positron beam for solid surface investigations within a short time and without high financial costs. The system uses a 22Na source and consists of three main parts: (1) the source chamber with a thin film tungsten moderator used in transmission, and a pre-accelerator stage, (2) the vacuum system with magnetic transport, a bent tube for energy selection and an accelerator, (3) the sample chamber with a sample holder, Ge detectors and (4) facilities for remote control and data acquisition. These parts are described in detail. The paper is preferentially addressed to beginners in the field of slow positron beam techniques and other readers being generally interested in positron annihilation spectroscopy.

Positron Annihilation Spectroscopy at LEPTA Facility

2012 ◽  
Vol 733 ◽  
pp. 322-325 ◽  
Author(s):  
Aleksey A. Sidorin ◽  
Igor Meshkov ◽  
E. Ahmanova ◽  
M. Eseev ◽  
A. Kobets ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Condensed Matter ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Layered Structures ◽  
Low Energy ◽  
Slow Positron ◽  
Monochromatic Beam

The Low Energy Positron Toroidal Accumulator (LEPTA) at JINR proposed for generation of positronium in flight can be used for positron annihilation spectroscopy (PAS) [1]. The positron injector of the LEPTA facility can generate continuous a slow positron beam with the intensity up to 1∙107s-1 at the energy in the range of a few eV to 100 keV and width of the spectrum 1 – 2 eV. The injector is based on radioactive 22Na isotope. The solid neon is used as a moderator to generate monochromatic beam. The parameters of the positron beam allow scanning the condensed matter in depth up to 10 microns with resolutions less than 10 nanometers and investigating layered structures for microelectronics and properties of a surface.

Defect Formation by Ion Implantation in Cz-Si Studied by a Monoenergetic Positron Beam

1992 ◽  
Vol 262 ◽  
Author(s):  
A. Uedono ◽  
Y. Ujihira ◽  
L. Wei ◽  
Y. Tabuki ◽  
S. Tanigawa ◽  
...  
Keyword(s):  
Oxygen Vacancy ◽  
Ion Implantation ◽  
Defect Formation ◽  
Positron Beam ◽  
Low Energy ◽  
Doppler Broadening ◽  
Positron Energy ◽  
Annealing Experiments ◽  
Incident Positron ◽  
Ion Implanted

ABSTRACTVacancy-type defects in ion implanted Si were studied by a monoenergetic positron beam. The depth-distributions of the defects were obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. The results showed that a size of vacany-clusters introduced by 150-keV P+-ion implantation was found to be smaller than that introduced by 2-MeV P+-ion implantation. This was attributed to an overlap of collision cascades in low-energy (150 keV) ion implanted specimens. From isochronal annealing experiments for 80-keV B+- and 150-keV P+-ion implanted specimens, the defected region was removed by 1200 °C annealing, however, for 2-MeV P+-implanted specimen, two-types of oxygen-vacancy complexes were found to coexist even after 1200 °C annealing.

Isochronal annealing studies on 1.1 MeV Fe ion irradiated RAFM steel using variable energy slow positron beam

2017 ◽  
Author(s):  
Renjith Ramachandran ◽  
C. David ◽  
R. Rajaraman ◽  
S. Abhaya ◽  
B. K. Panigrahi ◽  
...  
Keyword(s):  
Positron Beam ◽  
Isochronal Annealing ◽  
Slow Positron ◽  
Rafm Steel ◽  
Variable Energy

POSITRON INTERACTION IN POLYMERS

2004 ◽  
Vol 19 (23) ◽  
pp. 3951-3959 ◽  
Author(s):  
CORINE BAS ◽  
N. DOMINIQUE ALBÉROLA ◽  
MARIE-FRANCE BARTHE ◽  
JÉRÉMIE De BAERDEMAEKER ◽  
CHARLES DAUWE
Keyword(s):  
Positron Annihilation ◽  
Chemical Structure ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Hole Size ◽  
Doppler Broadening ◽  
Positron Source ◽  
Positron Annihilation Lifetime ◽  
Doppler Broadening Spectra ◽  
Variable Energy

A series of dense copolyimide membranes was characterized using positron annihilation spectroscopy. The positron annihilation lifetime spectroscopy performed on film with a classical positron source gives informations on the positronium fraction formed and also on the hole size within the film. The Doppler broadening spectra (DBS) of the gamma annihilation rays coupled with a variable energy positron beam allow the microstructural analyses as a function of the film depth. Experimental data were also linked to the chemical structure of the polyimides. It was found that the presence of the fluorine atoms strongly affects the positron annihilitation process and especially the DBS responses.

Slow Positron Studies in Polymers

2010 ◽  
Vol 307 ◽  
pp. 85-92
Author(s):  
S.B. Shrivastava ◽  
Aman Deep Acharya ◽  
R. Sharma
Keyword(s):  
Positron Lifetime ◽  
Hole Concentration ◽  
Low Energy ◽  
Positronium Formation ◽  
Positron Energy ◽  
Slow Positron ◽  
Polymeric Surface ◽  
S Parameter ◽  
Free Volume Hole ◽  
Incident Positron

The diffusion trapping model has been applied to slow positron annihilation in He+ irradiated polystyrene and polystyrene – polystyrene bilayers. The S-parameter and the positron lifetime have been calculated as a function of the incident positron energy. The effect of the fluence upon the nature of the S-parameter curve has been discussed. It has been found that a change in fluence affects positronium formation. The transition rate for surface to positronium formation has been found to be dependent upon the fluence and the atomic number of the irradiated ion. The lifetime results show that, at low energy, the o-Ps annihilates mainly at the polymeric surface. The free volume hole concentration is found to decrease at low energy, and becomes constant at higher energies.

Investigations of HAVAR® Alloy Using Positrons

2012 ◽  
Vol 331 ◽  
pp. 95-112 ◽  
Author(s):  
S. May Tal Beck ◽  
Wolfgang Anwand ◽  
Andreas Wagner ◽  
Gerhard Brauer ◽  
A. Beck ◽  
...  
Keyword(s):  
Lattice Structure ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Total Charge ◽  
Slow Positron ◽  
Positron Spectroscopy ◽  
Thin Foils ◽  
Transmission Electron ◽  
Cold Rolled ◽  
Proton Dose

A study of irradiation-induced damage in HAVAR® foils was initiated in order to extract the highest proton dose the foils can sustain. The lattice structure of HAVAR® foils in different metallurgic conditions is presented, as well as visible internal structure, measured by Transmission Electron Microscopy (TEM). Positron Annihilation Spectroscopy (PAS) techniques were used to investigate these foils, and another foil that had been irradiated to the maximal proton dose limit, set by the manufacturer to a total charge of 1 mAh (= 3.6 C). PAS techniques included Doppler broadening (DB) measurement in the SPONSOR beam and lifetime (LT) measurements, both carried at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Both positron spectroscopy methods show clear differences between the investigated foils, with distinguished characteristics for annealed, cold-rolled and irradiated foils. The advantages of using a slow positron beam to study thin foils and defect profiles, over a table-top LT spectrometer, are discussed and demonstrated by the HAVAR® measurements.

The Study of Si, Se and O-Implanted GaAs by Slow Positrons

1992 ◽  
Vol 262 ◽  
Author(s):  
S. Fujii ◽  
S. Shikata ◽  
L. Wei ◽  
S. Tanigaw
Keyword(s):  
Positron Beam ◽  
Annealed Specimen ◽  
Electrical Characteristics ◽  
High Concentration ◽  
Positron Energy ◽  
Vacancy Clusters ◽  
Activation Efficiency ◽  
Before And After ◽  
Parallel Measurement ◽  
Variable Energy

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

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