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.