Optimization of an underwater in-situ LaBr₃:Ce spectrometer with energy self-calibration and efficiency calibration

An underwater in-situ gamma-ray spectrometer based on LaBr₃:Ce was developed and optimized to monitor marine radioactivity. The intrinsic background mainly from ¹³⁸La and ²²⁷Ac of LaBr₃:Ce was well determined by low background measurement and pulse shape discrimination method. A method of self-calibration using three internal contaminant peaks was proposed to eliminate the peak shift during long-term monitoring. With experiments under different temperatures, the method was proved to be helpful for maintaining long-term stability. To monitor the marine radioactivity, the spectrometer's efficiency was calculated via water tank experiment as well as Monte Carlo simulation.