The temperature dependence of the diffusion coefficient and of the trapping rate of positrons in metals

Abstract

The paper explores the consequences of metastable self-trapping of positrons for the temperature variation of positron diffusion coefficients and trapping rates. It is shown that the diffusion coefficient is expected to decrease with increasing temperatures from a value determined by the scattering of positron Bloch waves by acoustic phonons to a much lower one governed by a hopping process. The temperature variation of the rate of trapping by small defects such as vacancies is more complicated since only at high temperatures can we expect it to be limited by the positron diffusion coefficient. At low temperatures the observed magnitude of the rate of trapping at monovacancies can only be understood if the trapping rate is controlled by the rate of capture of positrons that have arrived at the trap.