Positron annihilation measurements

The apparent and partial molar volumes of aggregated sodium octyl, decyl, dodecyl, and tetradecyl sulfate molecules have been studied in detail by Vass et al. [144] from densities measured by a vibrating capillary densitometer in normal and 99.85% heavy water at 25°C and by Vass [130] from density, small-angle scattering, and positron annihilation measurements. 

The most direct evidence of a correlation between Ga vacancies and YL is based on positron annihilation measurements [5], These experiments provide a direct probe of vacancies in the sample. It was found that the concentration of Vc correlates with the intensity of the YL, providing direct evidence for the involvement of the Vg acceptor levels in the YL. 

Studies on other high-temperature superconductors Positron annihilation measurements across Tc, coupled with the calculations of PDD have been carried out in a variety of hole-doped superconductors that include YBa2Cu40g [48], Bi-Sr-Ca-Cu-0 [49], and Tl-Ba-Ca-Cu-0 [50, 51] systems. We will not labor with the details here, except to state that a variety of temperature dependencies are seen and these can be rationalized when the results are analysed in terms of positron density distribution and the electron-positron overlap function [39]. These calculations show that the positron s sensitivity to the superconducting transition arises primarily from the ability to probe the Cu-O network in the Cu-0 layer. The different temperature dependencies of lifetime, i.e., both the increase and decrease, can be understood in terms of a model of local electron transfer from the planar oxygen atom to the apical oxygen atom, after taking into account the correct positron density distribution within the unit cell of the cuprate superconductor. 

Yu, Z., Yahsi, U., McGervey, J.D., Jamieson, A.M., Simha, R. (1994) Molecular weight-dependence of free volume in polystyrene studied by positron annihilation measurements . J. Poly. Sci. B. 32,2637. 

Nevertheless, positron annihilation measurements on polycrystalline samples, either pure or doped with boron, show that at room temperature Ni-rich alloys contain no detectable vacancies, but stoichiometric and... 

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