Simulation of background reduction and Compton suppression in a low-background HPGe spectrometer at a surface laboratory

• Published in: Chinese physics C Vol. 39; no. 8; pp. 66 - 72
• Main Author: 牛顺利 蔡啸 吴振忠 刘义 谢宇广 俞伯祥 王志刚 方建 孙希磊 孙丽君 刘颖彪 高龙 张烜 赵航 周莉 吕军光 胡涛
• Format: Journal Article
• Language: English
• Published: Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Sciences and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing 01.08.2015
• Subjects: anti-compton ratio; Background radiation; BGO (crystal); BGO晶体; Copper; Detectors; gamma background; Gamma rays; Geant4 simulation; Germanium; HPGe; HPGeγ谱仪; Simulation; Spectrometers; 仿真结果; 地面; 实验室; 康普顿抑制; 探测器模拟; 环境背景
• ISSN: 1674-1137; 0254-3052
• DOI: 10.1088/1674-1137/39/8/086002

High-purity germanium （HPGe） detectors are well suited to analyse the radioactivity of samples. In order to reduce the environmental background for an ultra-low background HPGe spectrometer, low-activity lead and oxygen free copper are installed outside the probe to shield from gamma radiation, with an outer plastic scintillator to veto cosmic rays, and an anti-Compton detector to improve the peak-to-Compton ratio. Using Geant4 tools and taking into account a detailed description of the detector, we optimize the sizes of these detectors to reach the design requirements. A set of experimental data from an existing HPGe spectrometer was used to compare with the simulation. For the future low-background HPGe detector simulation, considering different thicknesses of BGO crystals and anti-coincidence efficiency, the simulation results show that the optimal BGO thickness is 5.5 cm, and the peak-to-Compton ratio of 40K is raised to 1000 when the anti-coincidence efficiency is 0.85. In the background simulation, 15 cm oxygen-free copper plus 10 cm lead can reduce the environmental gamma rays to 0.0024 cps/100 cm3 Ge （50 keV-2.8 MeV）, which is about 10-5 of the environmental background.