Temperature Dependence ofF-Center Production and Aggregation in NaCl

The temperature dependence of the vacancy production rate and of the $F$-aggregate-center equilibrium ratio has been measured for electron-irradiated NaCl. The onset of the doserate dependence has also been observed. Temperatures obtained from these measurements are compared with the thermal annealing temperature of self-trapped holes and with the temperature at which $F$-aggregate centers form spontaneously in the dark. The maximum vacancy production efficiency occurs near 210 °K; the dose-rate dependence can be observed above 175 °K. These temperatures are significantly below 260 °K at which aggregation occurs. Thus different processes appear to be rate controlling for radiation-defect production on one hand and aggregation on the other. The results support the suggestion that electron-hole recombination at non-defect-producing sites limits defect production at temperatures at which holes are mobile. They also support the idea that aggregate-center formation in the presence or absence of irradiation is determined by motion of $F^{+}$ centers.