Temperature and Dose Dependence of Metal Colloid Production in Alpha-Irradiated CaF2 Single Crystals

Abstract

AbstractSingle crystals of CaF2 were irradiated with 5.8 MeV alpha particles from a 244Cm source, and the absorbance spectra were recorded as a function of dose and temperature. Absorbance from the metal colloid band increases with dose at all temperatures. The colloid band exhibits a sharp increase in rate of growth over a narrow temperature range with a peak at 150°C. After a dose of 1.4 x 1016 α/cm2 at 150°C, the intensity of the colloid band is a factor of 7 to 8 higher than the intensity produced at 100 and 200°C. The optimum temperature (150°C) for colloid formation in CaF2 under the alpha-irradiation conditions (σ5 x 108 rad/h) of this study is significantly higher than the peak temperature (60°C) reported for colloid production in electron irradiated CaF2 at slightly higher dose rates (σ109 rad/h). Cryogenic transmission electron microscopy of the irradiated crystals reveals dislocation loops and small dark clusters as the dominant microstructural features.