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Alternative Geometries for Improved Light Output of Inorganic Scintillating Crystals

It is important to optimize the crystal-photodetector coupling for gamma detection since it improves the light extraction and is directly linked to the achieved time resolution. In this paper we present our work on altering the geometry of the crystal coupling face to enhance the light output. Simulations compare the light output of alternative geometries of the crystal extraction face with respect to that of the regular cuboid geometry. We machined two different crystal shapes from 2 × 2 × 15 mm3 LSO crystals and measured the light output for different wrapping and coupling conditions. We also measured the coincidence time resolution (CTR) of the shaped crystals to compare the effect of timing on shaped crystals with respect to the reference samples. Simulations predicted an increase of up to 35% in light transfer efficiency for certain geometries of the exit face with respect to that of a regular cuboid geometry. Experimental measurements performed on shaped LSO crystals (2 × 2 × 15 mm3) show that an increase in light output of up to 40% and a systematic improvement in CTR of at least 5% is possible for one of the tested geometries. This opens new windows for preparing crystals used in TOF-PET scanners and high energy physics experiments.