The penetration of electrons in alkali halide single crystals and the effect of nonuniform irradiation on colour centre growth curves

Growth curves of F centres in KCl, KBr, KI and NaCl single crystals up to saturation are measured at room temperature by irradiation with 5-45 keV electrons. The optical density at saturation was found to be proportional to E n , with E the energy of incident electrons and n a parameter equal to between 1.35 and 1.69 according to the material. The F-centre formation efficiency at the beginning of the late stage of coloration was found to be independent of electron energy. A hypothesis about the behaviour of the absorption coefficient alpha is made, by means of which it is shown that the electron range T obeys the same relationship T varies as E n . For alpha as a function of time, two approximating functions are given.