Radiation Equilibrium ofFandMCenters in KCl

Abstract

A study of F- and M-center coloration by electronirradiatirg single crystals of KCl is made as a function of radiation intensity, electron energy, and crystal preparation. The quadratic relation between M-center and Fcenter concentration in any particular sample, previously observed for both x-ray and gamma irradiation, is verified for electrons if a constant current is used throughout the irradiation. However, the ratio of M-center concentration to the square of the F-center concentration is dependent upon electron current and sample preparation. Moreover, if a specimen is irradiated at one radiation intensity for a long period and then the intensity is changed for a short time, the relative M- and F-center concentrations are characteristic of the last irradiation intensity. It is concluded from this result that a dynamic equilibrium exists between F centers and M centers during irradiation. Interpretation of the results is proposed in terms of four simultaneous processes producing and destroying F centers and M centers, respectively. The processes for destruction of F certers and creation of M certers are thought to involve a mobile imperfection created by the irradiation. Means by which small concentrations of impurities can affect some of these processes to change the F-M equilibrium and F-centermore » coloring curves are discussed. (auth)« less