Radiation effects in CsI(Tl) crystals from a controlled growth process

Colorations induced by Co-60 γ-irradiation have been studied in six 2.54 cm thick CsI(Tl) samples cut from three crystal boules grown in an experiment on the control of impurities. The growth of a “sextet” structure of bands on the high-energy side of the F-band was observed in all the samples as doses of γ-rays were increased. It is speculated that the sextet bands may be related to the excited states of the F centre. It is found that high concentrations of thallium in CsI(Tl) always reduce tolerance to radiation.