Monte Carlo study to enhance background suppression in TDCR-LSC using BGO anti-coincidence method

Abstract Tritium ( 3 H) decay emits low-energy beta radiation (average 5.7 keV, maximum 18.9 keV), which is challenging to detect. Upon entering biological systems, tritium can cause ionizing radiation damage. Liquid scintillation counting (LSC) is currently the most effective method for measuring tritium in water, and reducing the system's background can lower the detection limit, allowing for the measurement of lower activity concentrations. This study explores the use of a bismuth germanate (BGO) crystals guard detector to reduce background noise in LSC by discriminating background signals, which significantly reduces system noise while having minimal impact on the scintillation light collection efficiency. The results show that incorporating a BGO guard detector with lead and copper shielding reduces the system's background from 3.16 cpm to 0.18 cpm, a reduction of 94.3%, significantly lowering the detection limit. The LSC designed in this study demonstrates a leading level in terms of theoretical background count rate, outperforming commercially available liquid scintillation spectrometers and exhibiting the lowest background count rate. The development of low-background LSC technology provides an effective solution for assessing tritium levels in environmental waters, such as those found in treated wastewater from the Fukushima nuclear power plant. Additionally, this method can be applied to measure other low-energy beta-emitting radionuclides, such as 14 C.