Development of Compact Coded Aperture Gamma Camera for Radiation Monitoring in Nuclear Facility

초록

Gamma camera is a useful device to monitor various radiation sources in a wide range of areas at nuclear facility. To localize and identify radiation sources in large area, angular resolution and detection efficiency of gamma camera should be high, which can he achieved by employing coded aperture in gamma camera. The purpose of this study was to develop a compact gamma camera consisting of coded aperture, SiPM based detector and dedicated electronics. Coded mask, which consisted of 2 x 2 mosaic of 19 x 19 asymmetric modified uniformly redundant array pattern with 1.5 mm hole size and 15 mm thickness, was designed. To assess the performance of the designed coded aperture, spatial resolution and sensitivity of gamma camera employing the coded aperture were estimated by Monte Carlo simulation using GATE and compared to that of gamma camera with pinhole collimator. SiPM based detector and dedicated electronics were also designed and fabricated. The gamma camera detector block was composed of 3 x 3 matrix of detector modules, each consisting of a 4 x 4 GAGG array coupled to a 4 x 4 SiPM array. The 144 output signals of the detector block were sent to 144:4 multiplexing circuit employing a symmetric charge division network developed in this study and then digitized by custom-made DAQ. To evaluate the intrinsic performance of the developed gamma camera, initial flood image and energy spectrum were acquired. Gamma camera image was successfully reconstructed and its SNR was further improved by subtracting background noise using inask/anti-mask method. Spatial resolution and sensitivity were 7.6 mm/4.9 cps/MBq for coded aperture and 7.3 mm/0.2 cps/MBq for single pinhole collimator. Each crystal pixel was clearly identified in the flood images and average energy resolution was 14.5 +/- 1.7%. Preliminary investigation results indicate that the coded aperture gamma camera developed in this study could accurately localize and identify radiation sources with improved sensitivity.