Positron annihilation in metals

Abstract

Positron annihilation in copper, silver and indium has been studied by means of the Doppler broadening method.High resolution germanium detectors have been used to observe the changes in the annihilation line profiles due to the trapping of positrons by metallic defects.

Positron trapping by thermally generated vacancies have been investigated. The smaller temperature effects which occur in addition to the dominant vacancy trapping effect have been discussed and taken into account in deducing mono-vacancy formation energies. The plausible hypothesis of metastable seIf-trapping of positrons has also been discussed. The best values of the mono-vacancy formation energies are estimated to be 1.26 eV for copper and 0.95 eV for silver. For indium a precise value could not be deduced from the data.

From the analysis of the line shapes, the probabilities of positron annihilation with core and conduction electrons at different temperatures have been calculated.

The results of the measurements on plastically deformed copper indicate that the specific trapping rate of positrons by dislocations is constant in the range 77-293 K. On extending the range of measurements down to 4.2 K, a significant decline in the specific trapping rate has been observed.

Alsco included is a chapter on the annihilation of positrons in liquid helium-3 and helium-4. Analysis of the line shapes as well as the deconvolution of the spectra indicate no significant difference in the amount of Positronium formation in liquid helium-3 and helium-4.