Prototype Solid State Photomultiplier Based Intra-Operative Beta Camera

We have developed a working prototype of a beta camera based on solid state photomultipliers (SSPMs), to demonstrate proof of concept. The SSPM, essentially an array of avalanche photodiodes operating in Geiger mode, produces a gain equal to or better than that of a photomultiplier tube, while operating at low bias voltage. The beta camera consists of a sheet of red-emitting plastic scintillator coupled to a 4 times 4 array of SSPMs. The signals are multiplexed through a 4-channel readout board and digitized by a custom data acquisition program; the image is constructed via simple Anger logic. We have obtained a positron energy spectrum and initial images from the camera, as well as linearity data and spatial resolution measurements.