Radiation damage mechanisms in CsI(Tl) studied by ion beam induced luminescence

Ion beam induced luminescence (IBIL) has been used to study the kinetics of defect production under ion beam irradiation in CsI(Tl) crystals with different Tl+ concentrations (250, 560, 3250 and 6500 ppm). The crystals have been irradiated with H+ and 4He+ at 1.8 MeV. Both the scintillator spectra after irradiation and the intensity decrease at different wavelengths as a function of the fluence have been measured. The emission bands shift to higher wavelengths after irradiation, and the light decrease has been interpolated following a saturation model for the point defect concentration. Crystals with low Tl+ concentrations present the UV emission peak of pure CsI at 300 nm whose intensity during H+ irradiation and reaches a maximum under He+ irradiation. At low Tl+ concentrations the damage rate depends on the ion stopping power, while at higher concentrations it depends on the activator concentration. The results can be interpreted by assuming that the defects affecting the light emission are point defects nearby Tl+ ions.