Thermoluminescence Response of Heavily Irradiated Calcic Bentonite

Bentonite has been suggested as a material for an engineering barrier in high level radioactive waste repositories. Its performance under irradiation (eg. radiation-induced damage in its crystalline lattice) is very important in safety assessments. The results presented were obtained in a thermoluminescence and electron spin resonance study of several bentonite samples in order to gain knowledge about defect formation. The samples were irradiated at fixed temperature of 95 deg. C and at doses of up to 920 kGy. In this experiment an industrial irradiator that consists of several sources of 60Co with an activity close to 300,000 Ci allowed us to reach dose rates higher than 20 kGy.h-1. The results indicate that the behaviour depends on the granulometrical fraction (clay fraction or coarse fraction), which in turn reflects differences in the mineralogical composition of the material. The coarse fraction had a higher concentration in defects (over one order of magnitude) than the clay fraction. In addition, as expected the concentration of radiation-induced defects increased with increasing dose. (author)