A RING COMPTON SCATTER CAMERA FOR IMAGING MEDIUM-ENERGY GAMMA-RAYS

Characteristics of a new ring Compton scatter camera are described. Th is camera is designed to image medium energy (0.5 to 3 MeV) gamma-ray fields. It consists of two position sensitive detector arrays: a 4x4 p lanar 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 angl e scatter in the first detector. A ring array significantly reduces di rect and small angle scattered events in the second detector. An analy tical model for ring camera systems has been developed to predict angu lar resolution and efficiency, and has been benchmarked against measur ements made with a prototype system consisting of the 4x4 HPGe array a nd an 8 element ring. Predictions are made for a system with 64 crysta ls in the second detector ring.