ULTRASONIC ATTENUATION IN GAMMA IRRADIATED VITREOUS SILICA

Abstract- Longitudinal ultrasonic attenuation measurements in four types of gamma irradiated vitreous silicas have been carried out for frequencies be-tween 30 and 90 MHz over the temperature range from 1 to 300 K. The mag-nitude and temperature dependence of the low- and high-temperature ultra-sonic relaxations characteristic of glasses were found to be independent of the degree of room temperature gamma irradiation to a dose of 10 MRads. The results indicate that the low activation energy dielectric center created by gamma rays in impure silicas is not acoustically active. I- INTRODUCTTION On the basis of production processes fused silica is commercially available in four types. Table I lists some of the reasonably well defined characteristics of the different silica glasses /1,2 / which make them useful for comparative studies of their properties. Dielectric measurements in fused silicas /2,3 / have established that the magnitude of the low frequency dielectric losses is sensitive to metallic and polar impurities. Type I and to some extent Type I1 fused silicas show a 240