In the present research, mixed crystals KCl 1-x Br x (x = 0.1, 0.3, 0.5, 0.7 & 0.9) were grown by Czochralski method. Then some analysis such as chemical etching, XRD, and absorbing spectrum were established on the irradiated crystals by γ-ray. The results of this research show that configuration of defects in mixed crystals in contrast with pure crystals is different. Somehow that type and percentage of cumulative composition cause to changing in lattice parameter and lattice defect density in alkali halide crystals and finally change optical properties of crystal.