Formation ofFCenters in KCl by X Rays

Measurements have been made of the growth of the $F$ band in undeformed, deformed, and heat-treated KCl crystals at room temperature using 140-kvp x-ray irradiation. The growth curves were analyzed in terms of the initial concentration of negative-ion vacancies in the lattice before irradiation, rate of formation of new vacancies, rate of electron capture by the initial and by the new vacancies, and bleaching constants. These parameters were studied as a function of the intensity of irradiation. It appears that the new vacancies are generated at a rate proportional to the square of the intensity of irradiation and inversely proportional to the dislocation density. Deformation increases the concentration of initial vacancies near dislocations, while heat treatment increases the concentration of initial vacancies dispersed in the volume of the crystal. Since neither the jog mechanism nor the Varley mechanism can account for the observations, a new model is proposed which accounts for all the observed phenomena.