On the effect of vacancy migration upon the annihilation of a trapped positron in metals

The effect of vacancy migration on positron annihilation has been considered. It was found that for most metals, in which positrons are deeply trapped at vacancies, it does not have a significant effect. For the alkali metals, however, vacancy migration can lead to positron detrapping. This process is fast relative to positron trapping by a vacancy. Nevertheless, in these cases ordinary thermal detrapping of positrons is found to be even more important. It is pointed out that by going to low temperatures and introducing a sufficiently high nonequilibrium vacancy concentration one might be able to observe trapping of positrons by vacancies in the alkali metals. Finally the effect of positron localization on the lattice relaxation around a vacancy has been estimated.