Intensity Dependence of X-Ray-Induced Strain and Coloration in KCl at Room Temperature

Abstract

The rate of generation of $F$ centers and the induced external strain rate of Harshaw KCl crystals irradiated at room temperature with 46-kVp x rays have been investigated as a function of the incident radiation power density. The influence of linear plastic deformation on these two rates has also been studied. The $F$-center concentration was determined by standard optical techniques, and the radiation-induced strain was measured by using a capacitance-type, temperature-compensated dilatometer with a sensitivity of approximately 1 Å. It was found that the rate of slow-stage $F$-center generation varied as the 1.4 power of the incident intensity, in substantial agreement with the results reported by Mitchell, Wiegand, and Smoluchowski, and that the strain rate varied linearly with the intensity. A further set of experiments in which the ratio of the slow-stage $F$-center generation rate to the strain rate was investigated directly yielded the observation that this ratio varied as the approximately 0.7 power of the intensity. These three intensity dependences are consistent within experimental error. The discrepancy between the intensity dependences of the rates of coloration and vacancy generation is explained on the basis of a significant self-bleaching of radiation-induced color centers as reported by Schultz. The deformation experiments yielded the observation that, for the crystals used, deformation had a negligible effect on the coloration rate. From this observation and from a comparison of the observed strain rate with that predicted by the various mechanisms for defect generation by ionizing radiation which have been proposed in the literature it is suggested that the predominant mechanism, at least for the crystals used in this study, is most likely one of the bulk multiple ionization mechanisms initiated by an inner shell ionization followed by an Auger transition.