Factors which define the α/γ ratio in CsI:Tl crystals

Dependences of light yield and α/γ ratio on the Tl concentration have been studied within a wide range of shaping times. It is shown that the α/γ ratio essentially depends on the Tl concentration. Proper combination of the Tl concentration and optimum shaping time in electronics allows to obtain detectors with rather high light output for γ-rays, α-particles and α/γ ratio values. It has been shown that both the light yield at α-excitation and the α/γ-ratio depend on the time of crystal storage after polishing. On the basis of the idea of the formation of deformation-induced point defects in a thin surface-adjacent layer, the causes of the temporary increasing in light yield for α-particle are explained. An explanation is given of the results obtained by Gwin and Murray concerning the fact that the α/γ ratio is practically independent on Tl concentration.