Thermal annealing and optical darkening effects in CsI(Tl) crystals

The effects of thermal annealing and optical darkening on Φ2.54×2.54 cm2 CsI(Tl) crystals damaged by exposure to 60Co gamma radiation and on unirradiated crystals have been studied. Thermal annealing can restore radiation-damaged crystals to their unirradiated state and can even improve the scintillation performance of unirradiated crystals. Optical darkening of crystals with an intense UV source leads to the production of a number of bands in the absorption spectra of crystals, which may be removed by isochronal annealing.