Progress in Positron Annihilation

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Authors: Dawid Giebel, Jerzy Kansy
Abstract: LT 10 is a new version of LT program designed to analysis of Positron Annihilation Lifetime Spectra (PALS). The new program is equipped with a new user interface and other features unavailable in its previous versions. It has been created again in a modern programming language and is now compatible with the latest operating systems.
Authors: G. Kontrym-Sznajd, M. Samsel-Czekała, S. Kaprzyk
Abstract: We demonstrate what kind of information about the electronic structure one can get from plane projections of electron densities. As an example we use one dimensional (1D) angular correlation of annihilation radiation (ACAR) and Compton scattering spectra for Cd “measured” only for two crystal orientations. Spectra are interpreted in terms of reconstructed 2D densities both in the reduced and extended zone schemes.
Authors: M. Biasini, G. Kontrym-Sznajd
Abstract: Reconstruction techniques, belonging to two different categories (series expansion and transform methods), are compared with regard to their applicability to line projections of a model density. It is demonstrated that in the case of this model the algebraic technique gives much better results than the filtered back projection (FBP) algorithm. However, it could not be a case for real data where a region of densities to be considered is very large comparing to the modelled one. In this connection we propose a new way of dealing with two-dimensional (2D) angular correlation of annihilation radiation (ACAR) data. Such a treatment, proposed for all reconstruction techniques, allows to improve reconstructed densities and filters the experimental noise.
Authors: M. Pylak, Ludwik Dobrzyński, G. Kontrym-Sznajd
Abstract: Novel application of Maximum Entropy method to the reconstruction of electron momentum density distribution from line projections is presented. Our new algorithm is applied to two dimensional angular correlation of annihilation radiation data in Gd. Reconstructed densities are in very good agreement with corresponding densities reconstructed by Cormack’s method.
Authors: Andrzej Karbowski, Janusz D. Fidelus, Grzegorz P. Karwasz
Abstract: We report preliminary performance tests of an ORTEC PLS lifetime system based on plastic scintillators and analog electronic system. A variety of samples was measured, from metals (Cu, stainless steel), across semiconductors (Cz-grown silicon, ZnSe) to nanostructured ceramics (ZrO2). All results obtained are compatible with literature reports and indicate the lifetime resolution of the whole system as 180 ps.

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