Current pulse activity in irradiated low-density polyethylene

Transient pulses or spikes of current under direct applied fields have been observed in LDPE (low-density polyethylene) following gamma irradiation in ambient air and nitrogen and reactor irradiation in air to doses between 10⁴ and 10⁶ Gy. This pulse activity is a function of field strength, dose, and temperature, and it is also evidently a function of the environment in which the irradiations were carried out and the type of radiation. While the production of gas and/or microvoids within the material may make a contribution to such pulse activity, it is suggested that the dominant mechanism is a field-assisted thermal detrapping process. The greater pulse activity observed with test specimens gamma-irradiated in air compared to those irradiated in nitrogen is associated with the greater abundance of trapping centers in the air samples. These derive from changes in the polymer structure due to the oxidation which took place during irradiation. A similar argument is suggested to hold for reactor versus gamma irradiations in air