Some Properties of Defects Produced by Ionizing Radiation in KCl between 80 and 300°K

A number of experimental techniques have been combined to study radiation-induced defects that are complementary to $F$ centers. One series of experiments, in which the resistance to dislocation motion due to interstitial centers was monitored by means of flow-stress changes, indicated that the centers produced by irradiation at 80°K and warming in the dark to room temperature were less effective barriers than were those produced by irradiation above 150°K. In a second series of experiments, measurement of vacancy-center bleaching rates indicated that defects produced by 80°K irradiation and warming to room temperature were much more easily bleached out than were those created by irradiation above 150°K. These results appeared to be correlated with changes in the ultraviolet absorption spectra where, for liquid-nitrogen irradiation and warming, the main absorption band appeared near 228 nm, whereas, for irradiation above 150°K, the main absorption appeared near 190 and 215 nm. The peak of the latter band moved to shorter wavelengths for higher irradiation temperatures. The results may be explained by assuming that interstitial clusters, together with vacancy centers, are produced by ionizing radiation, and that the clusters are of different sizes, depending upon irradiation temperature. There is also some evidence that trace impurities of concentration in the points per million (ppm) range influence the clustering process.