Positron irradiation effects on polypropylene and polyethylene studied by positron annihilation

Positron irradiation effects on polypropylene (PP) and polyethylene (PE) have been studied using the positron source for positron annihilation (PA) experiments. From the intensities ( I 3) of the long-lived component of ortho-positronium ( o-Ps), it has been shown that the irradiation effect is larger in PP than in PE and that the samples with high crystallinity receive larger effect. The positron irradiation effect was compared with the effect of 60Co γ-rays. The decrease in I 3 in 1 MGy γ-irradiated PP was smaller than that of positron irradiated samples, although the latter dose was estimated to be about two orders of magnitude smaller than the former. By decomposing the o-Ps component further into two components, it has been found that most of the decrease is concerned with the longest-lived component, indicating that it is mainly the Ps formed in the amorphous region that is affected by radiation.