ON THE MEASUREMENT OF RADIATION-INDUCED ELECTRICAL DEGRADATION IN INSULATING MATERIALS

Permanent increases of the electrical conductivity due to radiation-induced electrical degradation in electrically insulating ceramic materials have been observed by several different research groups, and the degree of degradation has become a major concern for the applicability of electric insulators in fusion reactors. The existence of the effect has, however, recently come into dispute. The present work tries to reproduce the effect with emphasis put on detailed control of the experimental conditions. Previously neglected limitations of the standard electric guarding technique are considered, and a simple equation for estimating the importance of surface leakage currents is derived. Alpha-particle irradiations at elevated temperatures in an electric field and for various dose rates were performed in various ceramic insulators. After subtraction of the radiation-enhanced surface conductances, no permanent conductivity increases have been observed under irradiation conditions where radiation-induced electrical degradation is expected to occur. The significance of this result is discussed.