Study of the Enhancement of X-Ray Coloration of NaCl by Divalent Impurities

Abstract

The growth of F centers and the change of d. c. conductivity by X-irradiation were measured around room temperature in NaCl grown in chlorine atmosphere both pure and doped with Ca⁺⁺, Cd⁺⁺, Sr⁺⁺, and Mn⁺⁺. The enhancement of coloration by divalent impurities at room temperature was found to be proportional to the square root of the concentration of each impurity. It was also found that the ionic conductivity in doped NaCl was decreased by X-irradiation in such a way that the decrease in the concentration of the positive ion vacancies was nearly equal to the increase in the F center concentration. From these results it was concluded that the isolated positive ion vacancies are the source of the F centers at the early stage of coloration. The temperature dependence of the formation rate of F centers in doped NaCl was measured and the activation energy 0.08±0.01 ev was obtained.