Effect of Impurities on the Hardening and Coloration of KCl Irradiated at Room Temperature

Abstract

Measurements of flow stress and F‐band coloration have been made at room temperature on a number of ``pure'' and impurity‐doped KCl crystals as a function of gamma and electron irradiation. As has been observed, the flow stress increase, for late‐stage coloration, is proportional to the square root of the F‐band absorption. However, it is found that the early‐stage coloration does not contribute to the radiation hardening. These results suggest that the late‐stage production mechanism for F centers involves interstitial formation and clustering, whereas no stable interstitials are formed during early‐stage coloration. Moreover, even though it is known that certain impurities enhance early‐stage coloration, it is found that the concentration of early‐stage F centers is only a small percentage of the total impurity concentration. This suggests that only isolated positive‐ion vacancies are involved in the F‐center production mechanism for this stage.