Effect of gamma-ray irradiation on surface charge behavior of polybutylene naphthalate

Polymer insulating materials are widely used in radioactive environment. Surface charge accumulated on the material has been considered as an important factor for inducing discharge which may cause serious damage to electrical devices. Thus, from the safety point of view, it is necessary to investigate the charge behavior on polymer surface after the irradiation. In this paper, polybutylene naphthalate (PBN) was employed as test sample which was previously irradiated in air up to 100 kGy and then up to 1000 kGy with dosage rate of 10 kGy/h by using a 60Co gamma-source. The experiment was carried out under a negative dc stress between two parallel electrodes. An electrostatic probe was designed to measure the charge density. Obtained results show that with the increase of the total dose of gamma-ray irradiation, the charge density and the storing capacity decrease. The charge accumulation depends upon the density of localized surface states, which is varied by the radiation induced cross-linking and degradation reactions of the molecule structure. The charge decay mainly relies on the recombination of surface charge with ions of opposite sign in surrounding air.