Performance Characteristics of BGO-Silicon Avalanche Photodiode Detectors for PET

Spectroscopic and timing characteristics of a gamma-ray detector based on silicon avalanche photodiodes (APD) and bismuth germanate (BGO) scintillators are reported. The APD used in this work is a large area (25 mm2) device of the "reach through" type having a quantum efficiency of 70% at 480 nm. When coupled to a 5×5×3 mm3 BGO crystal, its spectroscopic performance is found to be superior to that of a PMT coupled to the same crystal, owing largely to its higher quantum efficiency. At room temperature, the APD achieves better energy resolution than any other (unity gain) solid state photodetector currently available; at -15 °C, its spectroscopic performance is comnparable to that of large area p-i-n photodiodes at -150 °C. Preliminary measurements show that the timing performance of the new detector allows it to be used for both energy and coincidence discrimination in positron emission tomography (PET). Results obtained with a realistic BGO crystal shape and size for PET are also presented. Limitations and possible improvements are discussed.