The effect of gamma-irradiation on positronium formation in polyethylene

The effect of gamma -irradiation on positronium (Ps) formation, especially the decrement of Ps formation at room temperature, was studied in linear po ly(ethylene). We found that chemical changes, such as oxidation, cross-link ing, or radicals created by gamma -irradiation of similar to 50 kGy do not affect Ps formation very much. The decrement of Ps formation was probably c aused by a temporary change of physical structure by irradiation that disap pears by anneals in the temperature range from room temperature to 120 degr eesC, gradually. (C) 2001 Elsevier Science Ltd. All rights reserved.