Effect of gamma-ray irradiation on lateral charge motion on surface of laminated polymer insulating materials

Polymer insulating materials installed in electronic and electrical devices have been used in space equipment and nuclear power station where the materials are exposed to high energetic radioactive rays. The molecular structure can be changed by radiation induced chemical reactions that possibly lead to the variation of characteristics of surface charge dynamics, which in turn influences the safe use of the devices. From the viewpoint of safety, it is essential to have a firm understanding of radiation effect on the surface charge behavior. This paper presents study aimed at clarifying gamma-ray irradiation effect on lateral charge decay on surface of epoxy resin. The samples were 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 in advance of the test. Surface charge was introduced by corona charging and the decay behavior was examined with an electrostatic voltmeter. Isothermal surface potential decay was also performed to verify the lateral charge motion. Obtained results show that the lateral motion of charge is encouraged by the irradiation. It is suggested that the lateral charge decay is dependent upon the characteristics of localized surface states that are altered by the degradation reaction occurred within surface layer of ER.