Papers by Keyword: Positron Annihilation Spectroscopy

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Authors: Maik Butterling, Frank Bergner, Cornelia Heintze, Wolfgang Anwand, Andreas Ulbricht
Abstract: The aim of this work was to investigate the effect of Cr on the microstructure of neutron-irradiated Fe-Cr alloys. Neutron irradiation-induced damage at its early stage was simulated by ion implantation. Positron Annihilation Spectroscopy was applied to identify irradiation-induced defects depending on the Cr-content in Fe-Cr alloys. Different irradiation scenarios were used to investigate the influences of irradiation step by step.
Authors: Hong Min Chen, J. David van Horn, Yan Ching Jean
Abstract: Positron annihilation spectroscopy (PAS) is a novel method that can provide molecular-level information about complex biological and macromolecular structure in a manner which is different, but complementary, to conventional medical and biochemical research methodology. Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening energy spectroscopy (DBES), coupled with a slow positron beam have been extensively applied to the life science research recently. These techniques provide new information about the atomic and molecular level free-volume and void sizes, and their distributions 0.1 nm to a few nm, molecular bonding, structures at depth-layers, and phase transitions. This paper is to review recent research on positron annihilation spectroscopy applied to the area of life science and also focus on current bioscience-related work in the positron group at the University of MissouriKansas City (UMKC).
Authors: F. Baier, M.A. Müller, W. Sprengel, B. Grushko, Roland Sterzel, Wolf Assmus, Hans Eckhardt Schaefer
Authors: Ivan Procházka, Jakub Čížek, Jan Valenta, Vladimír Havránek, Petr Hruška, Michal Novotný, Ján Lančok
Abstract: In the present work, defects created by implantation of hydrothermally grown ZnO single crystals of high quality with H+ ions were investigated by positron annihilation lifetime (LT) spectroscopy combined with measurements of optical transmittance (OT) and photoluminescence (PL). First, zinc vacancies attached with one hydrogen impurity (VZn – 1H) atom were identified in the virgin ZnO single crystal. The ZnO single crystals were then bombarded by H+ ions with the energy of 2.5 MeV to the fluence of 1016 cm-2. It was found that VZn – VO divacancies were introduced into ZnO by H+-implantation. Effects of H+-implantation on the optical activity of defects in ZnO lattice are characterised in the light of the present OT and PL data.
Authors: Ehsan. A.H. Gomaa, M. Mohsen, A.S. Taha, M.M. Mostafa
Abstract: The variations during isochronal annealing of cold-rolled commercial pure Al (1050) and Al-Mn (3004) has been investigated between room temperature (RT) and 823 K. The annealing stages have been identified as recovery, partial recrystallization, complete recrystallization and grain growth using positron annihilation lifetime (PAL) spectroscopy, Doppler broadening of annihilation radiation (DBAR) spectroscopy and Vickers microhardness (Hv) measurements. The retardation of complete recovery in Al-Mn alloys is due to the presence of vacancy-Mn complexes. A positive correlation has been found between positron annihilation parameters (τav & Snor) and mechanical properties (Hv) for the two alloys under investigation.
Authors: Paweł Horodek, Jerzy Dryzek
Abstract: We present experimental results of measurements of the Doppler broadening of annihilation line and positron annihilation lifetimes in martensitic stainless steel 1.4031 (EN) samples exposed to the dry sliding under different loads. In particular, we tested the subsurface zone under the worn surfaces. As a main result, we obtained information about the defect profiles in this zone and the total extent of the damage region induced by the dry sliding.
Authors: Marek Pietrow, J. Wawryszczuk
Abstract: A systematic study of o-Ps intensity quenching by different wavelength of SWIR light was performed for a set of n-alkanes which form different crystal structures. The maximal wavelength able to quench was determined for two temperatures. The results for odd- and even-numbered alkanes were compared from this point of view. A systematic decrease in the maximal wavelength with shortening the carbon chain was found. Two kinds of traps were observed in the alkanes with chain length exceeding 30 carbon atoms, one kind only in the shorter ones. It was found that in a binary mixture of alkanes the traps are shallower than in the neat ones.
Authors: Pushkar N. Patil, Kathi Sudarshan, Pradeep K. Pujari, Dhanadeep Dutta
Abstract: The Poly N-Isopropyl acrylamide (PNIPA) gels were prepared in different synthesis media by crosslinking with acrylate monomers with varying chain length. The microstructural characterization in terms of the free volume fractions and distributions were studied using positron annihilation lifetime spectroscopy (PALS). The equilibrium swelling of the PNIPA in distilled water was measured. An attempt has been made to understand the correlations between microscopic free volumes and the equilibrium swelling of the gels. The free volume fraction of the gels prepared in Dimethyl formamide (DMF) was directly correlated with swelling while it varied inversely with chain length of the crosslinker. The microstructure of the gels was found to be very sensitive to the solvent/medium used for polymerization. Our studies show that the swelling property is influenced by the free volumes, chain relaxation as well as the chemical nature of the cross linkers.
Authors: M. Abdel-Rahman, Yahia A. Lotfy, M.A. Abdel-Rahman, Emad A. Badawi
Abstract: Positron Annihilation Spectroscopy (PAS) is a powerful and versatile tool for the study of the microscopic structure of materials. Doppler Broadening Positron Annihilation Technique (DBPAT) is the fastest technique used among positron annihilation techniques. The dose effect in Al-6.5at. % Cu alloy was investigated by means of DBPAT. An abrupt change in both the S and W line-shape parameter values occurred at 70 kGy of irradiation. The S- and W-Parameters of the trapped positrons at 70 kGy of γ−irradiation dose are about 48 % and 14 % respectively. The S- versus W-parameter reveals a linear relationship indicating the presence of only one type of defect. The S- and W-parameters have been used in the determination of the positron trapping rate and the grain size of the AlCu6.5 alloy.
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