Organic-scintillator compton gamma ray telescope

Abstract

Apparatus and methods for imaging sources of gamma rays with a large area, comparatively low-cost Compton telescope (20). The Compton telescope (20) uses multiple layers (24) of low-cost organic solid plastic or liquid scintillator, arranged in large arrays of identical scintillator pixels (28). Photodiodes, avalanche photodiodes (30), or solid-state photomultipliers are used to read out the fluorescent pulses from scintillator pixels (28). Multiple scintillator pixels (28) are multiplexed into a few fast digitizers (80) and a few fast FPGA programmable digital microprocessors (78). Selection rule methods are presented for processing multiple near-simultaneous gamma ray collisions within the Compton telescope (28) to identify trackable events that yield gamma ray image data of interest. A calibration method achieves improved energy resolution along with (x,y) position information in pixels (28) made of organic scintillator materials with multiple photodetectors (30). Synchronization trigger signals are used from a pulsed neutron source (58) to maximize the signal-to-background ratio for prompt gamma neutron activation analysis (PGNAA) of objects at greater than 2 meters range, where such trigger signals are based on the estimated range to PGNAA sources and neutron time-of-flight.

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