Studies of radiation tolerance and optical absorption bands of CsI(Tl) crystals

The effects of 60Co γ-irradiation on six Φ2.54×2.54 cm2 CsI(Tl) crystals, grown by the Kyropoulos technique, have been studied. The scintillation light output and radiation-induced optical absorption spectra of these crystals have been measured over a wide range of γ-ray doses. A high-Tl concentration always reduces radiation-tolerance and scintillation light output. A group of six distinct absorption bands in the 350–600 nm region, referred to as the sextet band, and one infrared band peaked at 840 nm were observed in all samples following γ-irradiation. Arguments are made that the 840 nm band and the sextet band induced by γ-irradiation are the FA and L bands, respectively.