Transient current pulses in gamma-irradiated polyethylene

A series of experiments has been carried out to investigate transient current pulse activity in low-density polyethylene which has been subjected to 60Co γ radiation to doses between 104 and 106 Gy while immersed in the different gaseous environments of air and nitrogen at essentially ambient temperature and pressure. Following irradiation the test specimens were placed in a heated air enclosure and pulse activity monitored using a multichannel analyser for applied fields in the range 1-60 MV/m and temperatures from 30 to 90oC. Pulse activity was seen to be a function of temperature, field and dose. With any two of these parameters fixed, activity increased with a rise in the value of the third, although there was evidence of some annealing effects above 70oC. The pulse activity was also a function of the environment in which the samples were irradiated, with those done in air showing greater activity compared to the nitrogen samples. This behaviour derives from the greater radiation-induced alteration to the trapping structure via oxidation of samples irradiated in air compared to what will have taken place in nitrogen. It is suggested that the observed transient current pulse activity is the result of field-enhanced thermal detrapping. (author)