DOSE-EFFECT IN GAMMA-IRRADIATED POLYETHYLENE STUDIED BY THE POSITRON-ANNIHILATION LIFETIME TECHNIQUE

Commercial high density polyethylene samples have been irradiated by g amma rays with doses ranging from 10 to 200 KGy. Positron annihilation lifetime measurements have been performed to study the effect of gamm a radiation on the structure of polyethylene. The lifetime, tau3, asso ciated with the pick-off process, in which the positron in o-Ps annihi lates with an electron from the surrounding material, and its intensit y, I3, are measured as a function of gamma dose. It can be concluded t hat the effect of gamma irradiation on polyethylene results in intensi ve formation of new bonds or cross-linking from 10 to around 100 KGy. Saturation of I3 from 100 to 200 KGy may indicate the achievement of s tructural stability.