Annihilation of Positrons in Condensed Materials

Abstract

An analysis of the experimental results on the annihilation of positrons in condensed materials is suggested, differing from that recently published by Dixon and Trainor. Considerations are offered which make it seem unlikely that excited states of positronium play a significant role. The long lifetime in molecular materials is explained in terms of the formation of $1s$ triplet positronium, while the short lifetime in these materials is interpreted as having a complex origin. The frequency of three-quantum annihilation, the temperature effect of the long lifetime, the angular correlation of the $\gamma$ rays, and annihilation in superconductors are discussed.