A ring Compton scatter camera for imaging medium energy gamma rays

The characteristics of a new ring Compton scatter camera are described. This camera is designed to image medium energy (0.5 to 3 MeV) gamma-ray fields. It consists of two positron sensitive detector arrays, i.e. a 4*4 planar array of high purity germanium (HPGe) crystals and a ring array of up to 64 NaI(Tl) crystals. Past evaluations of Compton cameras have employed a planar second detector, which is subjected to a large flux of gamma rays that either pass directly through or undergo small angle scatter in the first detector. A ring array significantly reduces direct and small angle scattered events in the second detector. An analytical model for ring camera systems is developed to predict angular resolution and efficiency, and is benchmarked against measurements made with a prototype system consisting of the 4*4 HPGe array and an eight-element ring. Predictions are made for a system with 64 crystals in the second detector ring.<
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