The combined effect of gamma and e-beam irradiation on the electrical properties of polyethylene Terephthalate

The combined effects of two kinds of irradiation, being gamma and electron-beam, on the PET electrical conductivity are investigated. Gamma ray produces homogeneous irradiation in the material bulk whereas in e-beam with moderate energy (20keV), energy and primary electrons are deposited near the surface. The study is focused on the comparison between the gamma irradiated films and those successively irradiated using gamma and electron sources. 25 μm-thick films were first irradiated in air at room temperature by means of a
⁶⁰
Co gamma source at different absorbed doses (0.1 to 2MGy); thereafter exposed during 5 min to a 20 keV electron-beam with 1 nA/cm
²
flux. Transient charging current measurements were performed in the DC field range 40-160 MV/m, at ambient temperature (25°C). The results show that the current increases substantially with the gamma dose. For all irradiated samples, the current-voltage characteristics exhibit a power law V
ⁿ
, with n greater than two (3 - 5), which could be related to space charge limited conduction process. The variation of the current with the dose is linear for the gamma irradiated samples and exponential on the combined gamma and electron irradiated ones. It was concluded that the electron irradiation tends to attenuate the previous irradiation effects at low gamma doses, whereas it accentuates it at high doses. The change in current-time characteristics and the variation of the exponent n with dose are also discussed.