Effect of X-Ray Intensity on the Production of Color Centers in NaCl and KCl

Abstract

The results of a study of the effect of irradiation intensity on the coloration of NaCl and KCl are reported. Three observations stand out: (1) The equilibrium established between F and complex certers shifts to favor F centers with increasing intensity of irradiation. Cycling of the irradiation intensity between low and high values complex centers. (2) The density of F centers produced by uv irradiation of a crystal following optical bleaching of a prior x irradiation, increases with the intensity of the prior x irradiation. The density of uv-produced F centers could also be shifted in a reversible manner on cycling the intensity of x irradiation. (3) The intensity dependence of the F- center growth curves is present only at irradiation temperatures above 200 deg K. It is proposed that the intensity dependence of the F-center coloration arises from the establishment of a balance between two competing processes. It is proposed that the primary effect of x-ray photons is to disperse single vacancies in the crystal. Competing with this dispersal is the tendency of the anion vacancies to reaggregate by the diffusion of mobile vacancy units. (auth)