Temperature and dose dependence of metal colloid production in alpha-irradiated CaF2

Single crystals of CaF2 were irradiated with 5.8 MeV alpha particles from a 244Cm source. The absorbance spectra were recorded as a function of dose and temperature. At low doses, the absorbance from the colloid band increased with dose to saturation values that changed with temperature. The colloid band exhibited a sharp increase in rate of growth over a narrow temperature range with a peak at 150 degrees C. The intensity of the colloid band after a dose of 1.4 x 1016 a/cm2 is a factor of 7 to 8 higher than the intensity at 100 and 200 degrees C. The temperature (150 degrees C) for the maximum rate of colloid growth in CaF2 under the alpha irradiation conditions (∼ 5 x 108 rad/h) of this study is significantly higher than the peak temperature (60 degrees C) reported for colloid production in CaF2 under electron irradiation at slightly higher dose rates (∼ 109 rad/h). Cryogenic transmission electron microscopy of the irradiated crystals revealed dislocation loops and small dark clusters as the dominant microstructural features