Investigation of optical transmittance and light response uniformity of 600-mm-long BGO crystals

Optical transmittance and light response uniformity were investigated for 25 mm×25 mm×600 mm BGO crystals, the longest BGO single crystals reported so far. The long BGO crystals exhibit good optical transmittance within the wavelength range concerned and an overall energy resolution of 19.68% for 0.662 MeV γ-rays. The light response uniformity of one long BGO, SIC-BGO-125, was measured in the single-end or dual-end readout mode combined with different reflecting materials. It was suggested that the light response uniformity of the long rectangular BGO is primarily affected by internal absorption, the reflectivity of reflecting materials and the readout mode. The best uniformity of −1.4±0.8% can be achieved when the crystal is measured only from the tail end and wrapped with ESR. Reflecting materials of high reflectivity can significantly improve the light response uniformity, but further improvement is limited by the internal absorption of the crystal.