Positron annihilation characteristics in high energy electron-irradiated polyethylene and polypropylene

Positron annihilation lifetime spectra and Doppler broadening were used to investigate high energy (12 MeV) electron-irradiated polyethylene and polypropylene. With the increasing of the electron dose less than 160kGy, the short lifetime component of positrons for PP became longer, while the intensity of the medium lifetime component decreased. When the irradiation dose reached 320 kGy, the lifetime components in the irradiated-PP were similar to those in virgin samples. However, the intensity of the longest lifetime component was nearly unchanged with the increasing of the irradiation dose. In the irradiated-PE both intensity of the longer lifetime component and shape parameter of Doppler broadening decreased quite a bit at the beginning but remained constant after 80 kGy electron irradiation. The mechanisms of different effects of high energy electron irradiation on the two polymers are discussed