Annihilation of Positrons in Condensed Materials

Abstract

Approximately \textonehalf{} percent fewer positrons are found to annihilate with emission of two photons in amorphous solids and benzene than do so in metals. Fused quartz shows the same effect when compared with crystalline quartz. Assuming, with Bell and Graham, that this defect is due to triplet positronium in the amorphous materials, the mean life of triplet positronium against three-photon annihilation in the various materials is found to be approximately that observed in gases. Addition of a free radical to the benzene partially quenches the difference between pure benzene and metals. High-purity crystalline germanium is found to be similar to crystalline quartz.