Dynamic behavior of surface charge on gamma-ray irradiated polybutylene naphthalate

Polymer insulating materials used in radioactive environment can be degraded by discharge which is induced by surface charge accumulation. Hence the stability of the electrical insulation is dependent upon the dynamic behavior of surface charge that may be changed by irradiation. In this paper, polybutylene naphthalate was employed as test sample to investigate the effects of gamma-ray irradiation on the charge behavior. The samples were previously irradiated in air up to 100 kGy and then up to 1000 kGy with dose rate of 10 kGy/h using a 60Co gamma-source. The experiment was carried out under a negative dc stress between two aluminum plate electrodes. An electrostatic probe was designed to measure the charge density. Obtained results show that with the increase of the total dose of the irradiation, both the capacity of surface charge and the rate of charge decay decrease. It is proposed that the charging behavior depends upon the density of localized surface states that is reduced by the radiation induced cross-linking reactions. The decay is caused by the recombination of surface charge with ions of the opposite sign in air.