Some effects of temperature on positron annihilation characteristics in metals

Abstract

Measurements of positron lifetime changes from 100K to the onset of trapping at vacancies in Al, Cu, Ag and Au are presented. The extracted temperature coefficients of positron lifetimes increase with temperature so that they become greater than theoretical predictions based on expansion of a static lattice. In addition, a simple representation of a one-dimensional momentum distribution is used to establish a relationship between changes in positron annihilation rates with temperature and the corresponding changes in shape parameters of the momentum distributions observed in angular correlation or Doppler broadening measurements, permitting a comparison of theoretical predictions of the temperature dependence of annihilation rates with various experimental determinations of the temperature coefficients of the momentum shape parameters.