M-Zentrenbildung in r�ntgenbestrahlten KCl-Kristallen

Abstract

The production of F- and M-centres in KCl by X-irradiation has been studied at temperatures between −20 °C and 50 °C. The optical absorption measurements could be conducted without interrupting the X-irradiation. The results can be summarized as follows: 1. In Harshaw KCl crystals the number of F-centres created by the so-called fast coloration process was proportional to the height of the absorption band at 204 mμ prior to the irradiation. 2. The F-centres formed by the fast process did not contribute to the formation of M-centres. 3. In crystals with a strong absorption band at 204 mμ unstable M-centres were observed, which decayed rapidly after the cessation of the X-irradiation. Their concentration was found to be independent of the F-centre concentration. 4. At temperatures below 0 °C the relation between the concentration of the stable M-centres and the F-centre concentration could not any longer be represented by [M]=k12·[F1]·[F2]+k22·[F2]2, F1 and F2 referring to the F-centres created respectively by the fast and the slow coloration process. Except at very low F2-centre concentrations however the relationship [M]=k0+k2·[F2]2 represented the experimental data at all temperatures between −20 °C and 50 °C. At constant temperaturek2 varied withL, the X-ray energy absorbed per unit time and unit volume, according to 1/k2=a+bL+cL2. The temperature dependence ofa−1b−1 andc−1 could be approximated by Boltzmann factors. The corresponding activation energies wereEa=0.12 eV,Eb=0.53 eV,Ec=0.97 eV.