Positronium formation between positron and trapped electron studied by positron annihilation lifetime and ESR

Positronium (Ps) formation probability and trapped electron density as functions of Co-60 γ-irradiation dose in poly(methyl methacrylate) and linear poly(ethylene) at 77 K have been measured. A linear relationship between the enhancement of the Ps formation and the density of trapped electrons in both polymers is obtained. This clear correlation strongly supports that the increase in Ps formation with positron annihilation measurement time can be explained as a reaction of free positrons with trapped electrons produced by the previously injected positrons. (author)