Mobility of Positrons in Gamma-Irradiated Polypropylene and Polyethylene

Positron mobilities in polypropylene (PP) and polyethylene (PE) were determined by observing the Doppler shift of the positron annihilation gamma-line as a function of an external electric field up to 50 kVcm^-1. The measurements were carried out for pristine and gamma-irradiated samples with different crystallinities. The determined mobilities for low density and high density PE, 32 �} 2 cm²V^-1s^-1 and 36 �} 3 cm²V^-1s^-1, respectively, were in agreement with most of the literature values. The results for the irradiated samples revealed that the positron mobilities in PP and PE are dramatically decreased by gamma-irradiation.