Gamma-ray Irradiation Inhibiting Surface Charge Accumulation on Polyethylene

Polymer insulating materials installed in electrical and electronic devices are widely used in spacecraft and nuclear power stations where the polymers are exposed to energetic radioactive rays. The chemical structure can be changed by radiation induced reactions that possibly gives rise to the alteration of characteristics of surface charge, which can enhance the local electrical field and cause surface discharge that damages the insulation. For the safe use of the material, it´s necessary to gain a good understanding of radiation effect on surface charge accumulation. In this paper, polyethylene was employed as test sample which was previously irradiated in air up to 100 kGy and then up to 1000 kGy with dose rate of 10 kGy / h by using a ⁶⁰Co gamma-source. The sample surface was corona charged by applying a series of dc stresses on needle electrode that was set 6 mm above the surface. An electrostatic probe was designed to measure the surface charge density immediately after the charging process. Obtained results show the dependence of surface charge distribution upon the radiation dose varying as a function of the polarity of charging particles. It is suggested that surface charge accumulation depends upon the behavior of localized surface states, which is altered by radiation-induced degradation and cross-linking reactions of the chemical structure.