^(41)Arβ-γ符合探测器的Geant4模拟研究  

Geant4 simulation study of β-γcoincidence detector for ^(41)Ar measurement

作　　者：冯亚洁 张瑞芹 牛亚洲 李奇[2] 佟立丽[1] 王世联[2] 赵允刚[2] 樊元庆[2] 张新军[2] FENG Yajie;ZHANG Ruiqin;NIU Yazhou;LI Qi;TONG Lili;WANG Shilian;ZHAO Yungang;FAN Yuanqing;ZHANG Xinjun(School of Mechanical Engineering,Shanghai Jiao Tong University,Shanghai 200240,China;CTBT Beijing National Data Centre and Beijing Radionuclide Laboratory,Beijing 100085,China)

机构地区：[1]上海交通大学机械与动力工程学院,上海200240 [2]禁核试北京国家数据中心和北京放射性核素实验室,北京100085

出　　处：《核技术》2025年第2期116-123,共8页Nuclear Techniques

基　　金：国家自然科学基金(No.D11975109)资助。

摘　　要：^(41)Ar是反应堆和加速器运行释放到环境中的主要放射性核素之一,测量其活度浓度对于确保公众健康具有重要意义。由于β-γ符合法能显著降低本底,提高探测灵敏度,为此设计了由BC404和CsI(Tl)组成的β-γ符合闪烁体探测器,用于进行^(41)Ar高灵敏度测量,并建立了以最小可探测活度浓度(Minimum Detectable Concentration,MDC)为优化目标的探测器结构优化方法。首先,运用Geant4对β射线穿过BC404和铝膜沉积到CsI(Tl)中的穿透率进行模拟计算,选择BC404厚度为3 mm,此时穿透率为0.78%;其次,对不同的气体腔尺寸进行模拟,分析计算β射线探测效率、γ射线全能峰效率,以及气体腔体积和取样时间对MDC的综合影响,完成探测器的结构优化;最后,分析了本底计数率和测量时间对MDC的影响。当测量时间为200 min、冷却处理时间为30 min、本底计数率为5×10^(-3) s^(-1)时,优化后的探测器对^(41)Ar的MDC估算值为1.7 Bq·m^(-3)。[Background]^(41)Ar is one of the main radionuclides released into the environment by the operation of reactors and accelerators.The measurement of ^(41)Ar activity concentration is of great significance for ensuring public health.In the field of radioactive gas measurement,the β-γcoincidence method is widely used because it can significantly reduce the background and improve the sensitivity of the detector.However,there is currently little research onβ-γcoincidence detectors for ^(41)Ar measurements in literature.[Purpose]This study aims to optimize theβ-γcoincidence detector composed of plastic scintillator(PS)and CsI(Tl)scintillator to realize high sensitivity measurement of ^(41)Ar.[Methods]An optimization method of detector structure based on minimum detectable concentration(MDC)was proposed.The optimization process of the detector was realized based on Geant4 simulation.Firstly,the penetration percentage ofβ-rays depositing energy into CsI(Tl)through different thicknesses of BC404 and 0.5 mm aluminum film was simulated.Secondly,the variation of full-energy peak efficiency of 1293.6 keVγ-ray in CsI(Tl)scintillator with different thicknesses of CsI(Tl)was simulated.Thirdly,simulating with different gas chamber volume,the comprehensive effects ofβ-rays detection efficiency,γ-ray full-energy peak efficiency,gas chamber volume and sampling time on MDC were analyzed with the assumption that the sampling time of argon was proportional to the volume of the detector's gas chamber.Finally,the influence of measurement time on MDC under different background counting rates was analyzed.[Results]Simulation results show that the penetration percentage ofβ-rays emitted from the decay of ^(41)Ar is about 0.78%when the thickness of BC404 is 3 mm.Theγ-ray full-energy peak efficiency increases with the increase of CsI(Tl)scintillator thickness.With the argon sampling rate of 600 mL·h^(-1),the optimal detector size parameters that minimize MDC are completely determined.When the background count rate is 1×10^(-3)~1

关 键 词：GEANT4 ^(41)Ar β-γ符合 闪烁体 最小可探测活度浓度 

分 类 号：TL812.1[核科学技术—核技术及应用]