A study on radiation hardness of BGO crystals

We report an investigation on the radiation hardness of 20 cm long BGO crystals produced at Shanghai Institute of Ceramics. Their optical and scintillation properties, such as transmittance and emission spectra, light output and response uniformity, were measured before, during and after γ-ray irradiations at 2, 8, 30 and 5,444 rad/h. BGO crystals produced in 2004 and 2011 are compared to a sample grown in early eighties for the L3 experiment at LEP. Significantly better radiation harness is observed in the sample grown in 2011 in transmittance, light output and radiation hardness. Their use for crystal calorimeters in future high energy physics experiments is discussed. To maintain crystal resolution, a precision light monitoring system is mandatory to trace variations of crystal transparency in situ for a BGO crystal calorimeter in a radiation environment. The origin of radiation damage in BGO is also discussed.