Characteristics of the annihilation of positrons in nanosized metal coatings Zr/Nb

New technologies for producing structural materials that are resistant to hydrogen and radiation damage are pressing problems in materials science. Hydrogen damage and radiation degradation are important factors limiting the fatigue life of structural materials. One promising alternative in developing radiation-hydrogen-resistant materials with improved physical and mechanical properties is the application of nanoscale metal coatings (NMC). The current work is devoted to studying positron annihilation in NMC Zr/Nb with different thicknesses of individual layers, Zr and Nb

Characteristics of the annihilation of positrons in nanosized metal coatings Zr/Nb

New technologies for producing structural materials that are resistant to hydrogen and radiation damage are pressing problems in materials science. Hydrogen damage and radiation degradation are important factors limiting the fatigue life of structural materials. One promising alternative in developing radiation-hydrogen-resistant materials with improved physical and mechanical properties is the application of nanoscale metal coatings (NMC). The current work is devoted to studying positron annihilation in NMC Zr/Nb with different thicknesses of individual layers, Zr and Nb

The Computer Code for Calculations of the Positron Distribution in a Layered Stack Systems

In this paper we present experimental and theoretical studies of the implantation profile of positrons emitted from ²²Na radionuclide into layered sample. The measured profile for the nonsymmetrical, around the positron emitter, stack of aluminium and silver foils was measured using the depth scanning of implantation profile technique. For the description of the obtained results two theoretical approaches were applied. The first one was the Monte Carlo simulation using the GEANT4 tool kit. The generated profile does not reproduce accurately the experimental profile. We proposed the multiple scattering model based on the fact that a positron due to backscattering can travel as an energetic particle several times through the whole sample before it annihilates. In this model absorption is also taken into account. The multiple scattering model algorithm was implemented in the LYS-1 program. The calculated profile using the LYS-1 program reproduces the experimental profile with much better accuracy

The Computer Code for Calculations of the Positron Distribution in a Layered Stack Systems

In this paper we present experimental and theoretical studies of the implantation profile of positrons emitted from ²²Na radionuclide into layered sample. The measured profile for the nonsymmetrical, around the positron emitter, stack of aluminium and silver foils was measured using the depth scanning of implantation profile technique. For the description of the obtained results two theoretical approaches were applied. The first one was the Monte Carlo simulation using the GEANT4 tool kit. The generated profile does not reproduce accurately the experimental profile. We proposed the multiple scattering model based on the fact that a positron due to backscattering can travel as an energetic particle several times through the whole sample before it annihilates. In this model absorption is also taken into account. The multiple scattering model algorithm was implemented in the LYS-1 program. The calculated profile using the LYS-1 program reproduces the experimental profile with much better accuracy

Annealing behaviour of plastically deformed stainless steel 1.4307 studied by positron annihilation methods

Isochronal and isothermal annealing of stainless steel 1.4307 samples deformed by compression were investigated using Doppler broadening measurements of the annihilation line. We made an attempt to describe the obtained dependencies in terms of vacancy migration and sinking to the grain boundaries. The model assumed spherical grains with a homogeneous initial distribution of vacancies. The model was capable of following the isochronal annealing data quite accurately. However, the obtained activation energy of vacancy migration equal to 0.44 plus or minus 0.05 eV seemed too low. The isothermal annealing dependency was reproduced less precisely. The reason for this may be the presence of the alfa'-martensite particles in the samples, which can introduce additional defects seen by positrons in the temperature range in which the martensite reversion takes place

Optical and positron annihilation studies of structural defects in LiInSe<inf>2</inf> single crystals

© 2020 Elsevier B.V. Lithium-indium di-selenide (LiInSe2) is a semiconductor material, which has been shown promising for applications in nonlinear optics and neutron detection. LiInSe2 crystals of optical quality, of different (from greenish to red) color were grown. Analysis of the fundamental absorption edge shows allowed direct band-to-band transitions and reveals structural disorder leading to the blurring of the edges of valence and conduction bands. Photoluminescence (PL) intensity is low in LiInSe2 of stoichiometric composition and increases after sample annealing in Se vapors. A narrow line at 408 nm is associated with free excitons. Analysis of PL and PL excitation spectra allows one to associate broad emission bands with point defects as well as with self-trapped excitons. The mean positron lifetime increases after annealing in Se vapor as a result of changes of the dominating defect type. For red crystals only big voids with lifetime of about 1021 ps are observed. Both methods suggest that greenish and red coloring of LiInSe2 are due to Se vacancies and interstitial Se atoms, respectively

Positron annihilation spectroscopy on a beam of positrons the LEPTA facility

The results and possibilities of the samples surfaces research by the Doppler method of positron annihilation spectroscopy (PAS) for a monochromatic beam of positrons at the LEPTA facility are presented in this paper. Method with high-resolution sensitivity to defects like vacancies and dislocations allows scanning of the surface and near-surface sample layers to a depth of several micrometers by the method of Doppler broadening of annihilation lines. The opportunities for the development of a PAS method based on the measurement of the positron lifetime in the sample irradiated by ordered flow of positrons from the injector of accelerator complex LEPTA at JINR are discussed

Slow Positron Beam Studies of the Stainless Steel Surface Exposed to Sandblasting

The paper presents slow positron beam studies of the stainless steel grade 304 AISI samples annealed in the flow $N_2$ atmosphere and sandblasted under different pressure from 1 to 7 bar. Heating of specimens caused formation of an additional layer on the surface which can be identified as oxides. Sandblasting reduces the thickness of the oxide layer and also defects concentration (vacancies as we suppose) decreases in dependence on pressure applied during blasting. Additionally, the atomic concentrations of oxygen have been obtained using nuclear methods (Rutherford backscattering and nuclear reactions) in the near surface layers of the studied samples