Temperature Dependence of Positron Vacancy Trapping

Abstract

A critical discussion is given of the several conflicting models that have been proposed for the temperature dependence of positron trapping by vacancies in metals. It is found that models utilizing the concept of a velocity independent trapping radius do not give a consistent description. If the trapping potential is not too strong the model most appropriate to the problem is one proposed by Hodges in which plane wave perturbation theory and the golden rule is used. When particle–hole pairs take up the excess energy and when the trap is deep compared to kBT this gives a trapping rate per unit vacancy concentration which is essentially independent of temperature. The condition on the strength of the potential is found to be well satisfied assuming a hydrogenic wave function for the trapped state with a Bohr radius determined from the energy of the state. Even if the trapping potential should be too strong for the golden rule to be completely valid no important temperature dependence of the trapping rate is expected.