Radiation damage in NaCl. II. The early stage of<i>F</i>-center aggregation

Abstract

We study the early stage of aggregation of F centers into colloids in pure NaCl under irradiation. The crystals have been electron irradiated with a dose rate of 2 Mrad/h up to doses of 1500 Mrad and measured by optical-absorption spectroscopy. The major bands, the F, M, and the colloid band, are analyzed qualitatively as well as quantitatively. We have observed a relationship between the concentrations of the F and the M centers, which changes from quadratic to linear. The colloid band appears to peak at two distinct wavelengths, indicating that two types of colloids are formed during the nucleation stage. The defect concentrations are determined as a function of the dose and the irradiation temperature and are discussed in terms of models which describe the kinetics of defect formation.