Positron Annihilation in Materials under Ionizing Radiation

Abstract
Positron-annihilation lifetime spectra in tritiated water and ice are described, and the effect of irradiation products on positron-annihilation rates in a medium is estimated. In a liquid medium the interference mainly comes from stable products accumulated during irradiation and in a solid medium from free radicals frozen in the lattice. It is also indicated that care must be taken in preparing samples for positron-annihilation experiments to avoid excessive radiation damage to the medium by the positron source.