Effect of Simultaneous Optical Bleaching and Gamma Radiation on the Room-Temperature Colorability of KCl

The effect of simultaneous gamma irradiation and optical bleaching on $F$-center production in high-purity KCl at room temperature has been investigated. It is found that for high gamma-ray intensities (∼4×${10}^3$R/min) simultaneous irradiation and bleaching decreases the net $F$-center production rate compared with that characteristic of the same samples irradiated in the dark. This suppression of $F$ centers is associated with the later stage of coloration and is a function of bleaching intensity and dose rate. When a sample is given the same total dose and amount of bleaching sequentially, there is a small net decrease in the $F$-center concentration. However, this decrease is much less than the amount of suppression observed in crystals irradiated in light. The effect of simultaneous bleaching and irradiation on the late-stage coloration suggests that the charge state of the radiation-produced vacancies, e.g., whether $F$ centers or $\alpha$ centers are formed, is very important in the coloration process. In the case of low dose rates (∼92 R/min) the $F$-center growth curves in dark-irradiated crystals consist of essentially only early-stage centers, whereas in samples simultaneously bleached and irradiated (light-irradiated), $F$-center production was completely suppressed.