Positron annihilation in irradiated and unirradiated polyethylenes

Abstract

Abstract Positron lifetimes were measured for four kinds of polyethylene samples and were resolved into four components. The temperature dependence of the two longlived components was examined in detail. In agreement with other results, the longest lived component could be reasonably assigned to ortho ‐positronium located in amorphous regions. This component was shown to be sensitive to the defects in high‐density polyethylene introducted in the course of its production. Both the intensity and the lifetime of the second longest lived component were structure insensitive, i.e., they did not change even on passing through the melting point. This component has been tentatively assigned to a positronium compound state. The effect of gamma‐ray irradiation was also examined. Although the intensity ( I 4 ) of the longest lived component was reduced by the irradiation, correlation between I 4 and the free radical concentration was poor, and the reduction in I 4 caused by the irradiation is considered to be due to structure change and not to chemical reasons.