SOME TEMPERATURE EFFECTS ON POSITRON ANNIHILATION IN METALS

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Abstract
Angular correlation of gamma rays from two-quantum positron annihilation has been investigated in seven metals: zinc, cadmium, indium, lead, tin, aluminum, and bismuth, over a range of temperatures from –150 °C up to their melting points. The distributions for lead, tin, aluminum, and bismuth show no more than the small variation with temperature expected because of the change in lattice volume. Zinc, cadmium, and indium display a large increase in the proportion of annihilations occurring with the valence electrons at higher temperatures. This observation and evidence of increased thermal scattering correspond to features reported for the solid–liquid transition. Consequently, it is suggested that these three metals exhibit some of the disorder properties of their liquid state as they are heated above room temperature. In addition to the continuous temperature dependence observed for these metals we find evidence of a small discontinuous change in the distribution for zinc. This occurs at a temperature midway between previously reported anomalies in the properties of zinc.