A 2-DIMENSIONAL DETECTOR DECODING STUDY ON BGO ARRAYS WITH QUADRANT SHARING PHOTOMULTIPLIERS

This is a theoretical estimation and experimental study of the positro n camera detector design using quadrant sharing of phototubes and opti cally cross-coupled BGO scintillation crystals. This study estimates t he maximum number of BGO crystals which can be coupled to a photomulti plier and be decoded with this design, based on the number of photoele ctrons generated and the optical efficiency of the crystal-phototube c ombination. From photoelectron statistics, a 10x10 BGO array can be co upled to a single square phototube (Hamamatsu R-2497) and have each cr ystal clearly decoded. Simulation of 1-dimensional and 2-dimensional s tatistical photoelectron distribution verifies the estimations. The si mulation also yields the optimal distribution of light to the decoding phototubes. This theoretically optimal light distribution is used to guide the development of an 8x8 array of 3.2x3.2mm BGO crystals (10mm deep) using Hamamatsu R-2497 phototubes. All 64 crystals in the array can be clearly identified. The reconstructed image resolution is furth er estimated for the 8x8 and 10x10 arrays. These resolution results ar e also compared to discrete detectors which do not use analog decoding . The comparison shows that the analog decoding process degrades the i mage resolution by 7 to 9%.