An investigation of radiation-induced ageing in cable insulation via loss measurements at high and low frequencies

Samples of coaxial signal cables, insulated with polyethylene, were irradiated in a ⁶⁰Co gamma source-in ambient air to a dose of 500 kGy. Measurements of dielectric loss at low frequencies were made by means of the Hamon transform of depolarising current and measurements of insertion loss at high frequencies were carried out using a network analyser. Upon comparing the response of the irradiated cables with that of fresh unaged material it was evident that there were differences in behaviour that could be attributed to ageing. The results indicate that the effects of radiation-induced ageing in polymer cable insulation can be monitored in principle by employing nondestructive electrical techniques to measure loss at low and high frequencies