Design of a novel gamma camera with large field of view for ¹⁶N diagnosis in the primary loop of nuclear reactor

The assessment of the concentration and distribution of N-l6, derived from O-16 in the cooling water exposed to neutron irradiation, is essential for ensuring radiation safety during nuclear reactor operation. The imaging method allows for the visualization of the intensity distribution of these N-l6 by capturing gamma-rays emitted during their decay process. However, the existing gamma camera is exclusively compatible with gamma-rays below 2 MeV. In this paper, a novel gamma camera featuring a thick double-conical penumbra aperture, a pixelated Lu1.8Y0.2SiO5:Ce scintillator array, and a position-sensitive photomultiplier tube is proposed to address this limitation. This innovative design offers a large field of view (FOV) and is suitable for high energy extended gamma source imaging. The optimization of key parameters of the camera was conducted, and a FOV of 60 degrees and an angular resolution of up to 4.57 degrees were achieved. Imaging simulations, including a simplified model of the primary loop of the pressurized-water reactor by GEANT4 code and image reconstruction using the expectation maximum algorithm, demonstrated that the proposed gamma camera could obtain a satisfactory spatial resolution for diagnosing the distribution of N-16 in the primary loop of a nuclear reactor.