The Effect of Gamma Irradiation on Space Charge Behaviour and Dielectric Spectroscopy of Low-density Polyethylene

The influence of gamma irradiation on low-density polyethylene (LDPE) has been studied through space charge measurement and dielectric spectroscopy. Commercial LDPE film with a thickness of 100μm was irradiated with γ-rays at a dose rate of approximately 10kGy/h to different doses up to 100kGy in an atmosphere of air, vacuum and nitrogen respectively. Space charge profiles vary depending on irradiation environments and radiation dose. The space charge profile of a sample after irradiation at 100kGy in air is more complicated than those irradiated in vacuum and nitrogen at same dose. More importantly, the space charge decay rate for the irradiated samples is slower than that of the virgin sample, indicating that the irradiation had changed the material by the generation of deep traps for space charge. Irradiation in air also produced changes in the dielectric spectrum in the frequency range between 10-3Hz and 106Hz where the imaginary part of the permittivity was found to be about one order of magnitude higher than that of the virgin sample (~10-4). This was attributed to oxidation as samples with the same (or lower) radiation dose in vacuum or nitrogen showed no pronounced difference to that of virgin samples.