Gamma-ray induced radiation damage in large size BGO crystals for the superb calorimeter

Calorimeters for high-energy physics experiments at are often made of inorganic crystal scintillators, exploiting their high stopping power and Light Yield (LY). Among these experiments are the last generation of detectors working at e⁺e^- colliders with center-of-mass energy equal to the Y(4S) resonance (B-factories). In view of the realization of the SuperB project [1], with a new B-factory with 1036 cm^-2s^-1 luminosity, the BaBar electromagnetic calorimeter will be the starting point to build the SuperB calorimeter. The higher expected event rate and machine background call for scintillating crystals different from the presently used CsI(TI), which would have a decay time τ too long to cope with the expected event and background rates. In addition, the higher expected machine background will imply higher radiation doses delivered to the detector components, in particular in the End-Cap regions close to the beam pipe, where the expected radiation dose due to low-energy photons will be around 0.5 rad/h. The optimal solution would be a scintillator with shorter decay time to avoid event pileup, comparable LY and radiation-hard, together with an affordable cost to replace the 820 crystals in the End-Cap.