A 2-dimensional detector decoding study on BGO arrays with quadrant sharing photomultipliers

This is a theoretical estimation and experimental study of the positron camera detector design using quadrant sharing of phototubes and optically cross-coupled BGO scintillation crystals. This study estimates the maximum number of BGO crystals which can be coupled to a photomultiplier and be decoded with this design, based on the number of photoelectrons generated and the optical efficiency of the crystal-phototube combination. From photoelectron statistics, a 10×10 BGO array can be coupled to a single square phototube (Hamamatsu R-2497) and have each crystal clearly decoded. Simulation of 1-dimensional and 2-dimensional statistical photoelectron distribution verifies the estimations. The simulation also yields the optimal distribution of light to the decoding phototubes. This theoretically optimal light distribution is used to guide the development of an 8×8 array of 3.2×3.2 mm BGO crystals (10 mm deep) using Hamamatsu R-2497 phototubes. All 64 crystals in the array can be clearly identified. The reconstructed image resolution is further estimated for the 8×8 and 10×10 arrays. These resolution results are also compared to discrete detectors which do not use analog decoding. The comparison shows that the analog decoding process degrades the image resolution by 7 to 9%