Abstract: Coded aperture imaging technology is widely used in nuclear safety, nuclear facility decontamination and decommissioning measurement as well as nuclear medicine due to its advantages of high detection efficiency, high signal-to-noise ratio, good angular resolution, and stable and reliable imaging quality. Aiming at the problems of the fixed imaging field of view and angular resolution of the traditional coded aperture gamma imaging system, a gamma imaging system with variable angular resolution is proposed by changing the distance between the coded collimator and the detector. The imaging system is mainly composed of coded collimator, position sensitive detector (PSD), data acquisition card and image reconstruction system. The coded collimator of the imaging system adopts the Modified Uniformly Redundant Array (MURA) coded method. In order to ensure the detection ability of higher energy rays, the material of the coding collimator adopts tungsten copper alloy with 90% tungsten content. The PSD is composed of LaBr₃(Ce) crystal coupled SiPM array, and the reconstruction algorithm adopts the direct convolution algorithm which is fast and efficient. The test results show that the average energy resolution of the PSD is 4.96% (662 keV). The radiation imaging system can accurately locate Am-241, Cs-137, and Co-60 clearly, and can successfully distinguish the positions of two Cs-137 point sources by changing the distance between the coded collimator and the detector.

Key words: gamma ray detection, MURA coded method, camera of coded aperture, LaBr₃(Ce) detector