Design and Development of a 3D Position-Sensitive Detector for 4π View Gamma Imager Based on Dual-Ended Readout Technique

Gamma imager capable of monitoring, detection and localization of radioactive sources is of critical importance for nuclear safety and homeland security with the increasing use of radioactive sources in applications of nuclear technology. A 4π view gamma imager based on gamma ray occlusion technique is under development in our lab. The key component of the gamma imager is a 3D position-sensitive detector, which enables 4π field of view of the imager. In this work, we propose a 3D positionsensitive detector design for the 4π view gamma imager based on dual-ended readout (DER) technique. The detector was composed of a GAGG block coupled to an SiPM array at both crystal ends. DOI calibration was conducted with a collimated fan beam 18F source and DOI resolution was evaluated. Energy calibration was performed for each 3D position region of the detector by incorporating 3D position information to correct for the energy response inconsistency at different 3D position regions inside the detector. Various radioisotopes including 99mTc, 131I, 137Cs and 22Na were tested. An exponential factor was applied to compensate for energy response non-linearity due to SiPM saturation effect at higher gamma energy. The measured average DOI resolution was 1.96 ± 0.21 mm for all the four DER detector modules, indicating excellent 3D positioning accuracy of the detector design. With the proposed energy calibration approach, characteristic photopeaks of each radioisotope can be clearly identified at the correct energy position on the measured energy spectra. The achieved energy resolution was 9.76% at 662 keV, demonstrating good energy performance of the detector design, which could benefit radioisotope identification capability of the gamma imager. To conclude, the proposed 3D position-sensitive detector design based on DER technique features good 3D positioning and energy performance and is feasible for the 4π view gamma imager.