Electron beam and gamma irradiation effects on conducting polystyrene studied by positron annihilation technique

Abstract

The effects of electron beam and gamma irradiation on microscopic structure of a conducting polystyrene (polystyrene + 15% carbon black) have been studied using positron annihilation lifetime spectroscopy. X-ray diffraction profiles for non-irradiated and irradiated conducting polystyrene are performed to investigate the structural nature of the samples. The samples were irradiated at room temperature with doses ranging from 30 up to 1500 kGy . The observed lifetime spectra were resolved into three components and the ortho-positronium ( o-Ps) lifetime component was associated with the pick-off annihilation of positronium trapped by the free volume. After gamma irradiation no detectable changes are observed in the o-Ps lifetime. In contrast, the intensity of the o-Ps component, I 3, decreases with the dose, up to about 540 kGy , followed by a much smooth decrease up to 1200 kGy then it levels off up to 1500 kGy . Meanwhile, after electron irradiation, the intensity of the o-Ps lifetime component as the dose increases exhibits two different regions may be identified as a rapid drop, followed by a smooth increase, then, it levels off and remains constant. The back increase in the electron curve seems to be absent in the case of gamma irradiation. These results are discussed on the basis of the free volume model.