Study on the relationship between water-to-detection crystal distance and detection efficiency in underwater γ spectrum measurement

The quantitative relationship between the water to detection crystal distance and the detector efficiency must be determined in the design of the shell dimension of the underwater gamma spectrometer. In this study, a 3-inch LaBr₃ crystal and hollow water sphere model was established based on the underwater γ spectrum measurement conditions. The γ-ray counting rate that reached the surface of the detector crystal and γ ray full-energy peak counting rate were calculated respectively through mathematical calculation and Monte Carlo sampling calculation. The results show that the detection efficiency of the specific γ ray full-energy peak emitted from the water is constant while the distance between the detection crystal and the water is changing. The conclusion provides a basis for the design of the shell structure of the underwater gamma spectrometer. (authors)