Effect of Plastic Deformation on the Colorability of "Pure" and "Doped" KCl Crystals

The effect of plastic deformation on the room-temperature production of $F$ centers and $M$ centers by ${\mathrm{Co}}^{60}$ gamma rays in KCl: pure, KCl: Ca, KCl: Pb, and KCl: Sr crystals was investigated. It was found that the deformation-induced enhancement of the colorability was very sensitive to impurity type and concentration, and that there was little enhancement of the $F$-center concentration in the "pure" samples. The blue coloration which has been observed previously to occur at dislocation boundaries in specimens that have been deformed, irradiated, and then bleached was present in the KCl: Ca crystals but not the KCl: Pb samples. This suggests that the coloration along these boundaries is not due only to vacancy clusters produced through deformation but also depends upon certain impurities.