LGSO scintillation crystals coupled to new large area APDs compared to LSO and BGO

Recent developments of large area avalanche photodiodes (APDs) and fast scintillators with high light yield offer unique advantages for imaging applications. To test possible scintillator-APD combinations, 3.7/spl times/3.7/spl times/12.0 mm/sup 3/ LGSO, BGO and LSO crystals were coupled to large area, low capacitance, round and rectangular APDs (5 mm diameter, 3/spl times/3 mm/sup 2/ and 5/spl times/5 mm/sup 2/, Hamamatsu, Japan). Light output, energy resolution and time resolution were compared. The light output of BGO was about 86% worse and of LGSO about 30% worse compared to LSO (100%). The energy resolution at 511 keV was 13.8/spl plusmn/0.5% for LSO and 15.1/spl plusmn/0.5% for LGSO (FWHM). For BGO, 16.9/spl plusmn/0.5% (FWHM) was measured at 662 keV. The coincident time resolution of two opposing single detectors was 2.7/spl plusmn/0.2 ns for LSO and 3.9/spl plusmn/0.2 ns for LGSO (FWHM). Chemical treatment of crystals showed an improved energy resolution compared to mechanical polishing of more than 1%, providing reduced cost and less processing time. An energy resolution of 10.7/spl plusmn/0.5% for LSO could be reached after chemical etching. With the new large area APDs, results similar to PMT readout could be achieved. The scintillation characteristic of LGSO makes this material a promising candidate for APD readout, although the performance was inferior to LSO.