A Study on Radiation Damage in BGO and PWO-II Crystals

We report in this paper an investigation on radiation damage in 20 cm long BGO crystals produced at SIC as well as 20 cm long PWO-II crystals produced at BTCP for the proposed Panda experiment at GSI. The optical and scintillation properties of BGO and PWO-II crystals, such as transmittance, light output and light response uniformity, were measured before and after γ-ray irradiations at different dose rates. BGO crystals produced recently are compared to crystals used in the L3 experiment at LEP which was produced in early eighties. PWO-II crystals are compared to crystals used in the CMS experiment. Progresses are observed in the radiation hardness for both crystals. Their use for crystal calorimeters in future high energy physics experiments is discussed. To maintain crystal precision, a precision light monitoring system is mandatory to trace variations of crystal transparency in situ for a BGO or PWO crystal calorimeter in radiation environment.