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

Commercial high-density polyethylene (HDPE) samples were irradiated by gamma-rays with doses ranging from 10 to 200 kGy. Positron annihilati on lifetime measurements were performed to study the effect of gamma-r adiation on the structure of polyethylene. The lifetime tau3, associat ed with the pick-off process, in which the positron in o-Ps annihilate s an electron from the surrounding material, and its intensity I3 are measured as a function of gamma-dose. It can be concluded that the eff ect of gamma-irradiation on polyethylene results in intensive formatio n of new bonds or crosslinking at doses ranging from 10 to 100 kGy. Sa turation of I3 for the irradiated HDPE at doses ranging from 100 to 20 0 kGy may indicate the achievement of a structural stability.