氙同位素β-γ符合谱解谱中气体本底扣除方法改进  

Improvement of subtraction method of gas background in β-γ coincidence spectra analysis

作　　者：张新军[1] 王世联[1] 贾怀茂[1] 李奇[1] 石建芳[1] 樊元庆[1] 赵允刚[1] ZHANG Xinjun;WANG Shilian;JIA Huaimao;LI Qi;SHI Jianfang;FAN Yuanqing;ZHAO Yungang(CTBT Beijing National Data Centre and Beijing Radionuclide Laboratory,Beijing 100085,China)

机构地区：[1]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》2020年第11期7-12,共6页Nuclear Techniques

基　　金：国家自然科学基金(No.11975109)资助。

摘　　要：β-γ符合测量是全面禁止核试验条约(Comprehensive Nuclear-Test-Ban Treaty,CTBT)放射性核素核查惰性气体氙活度检测的一种重要技术手段。为消除“记忆效应”对样品测量的干扰,β-γ符合能谱的解谱算法——符合净计数计算法(Net Count Calculation Method,NCC)系统性扣除由“记忆效应”产生的气体本底计数,但对于残留氙同位素少的气体本底,由于统计涨落,计算得到的气体本底净计数可能出现负值,从而导致氙同位素活度计算错误,甚至出现误识别。针对符合净计数计算法中系统性扣除气体本底存在的问题,提出了扣除气体本底的判断条件并对符合净计数计算法进行了改进,能够将131Xem、133Xem、133Xe和135Xe等4种氙同位素的误识别数目分别减少63%、68%、72%和26%,并提高放射性活度浓度计算的准确性。[Background]Theβ-γcoincidence technique is a key method to measure the radioactivity of radioxenon isotopes for comprehensive nuclear-test-ban treaty(CTBT)radionuclide verification.Theβ-γcoincidence spectrum is usually analyzed by the net count calculation method(NCC)which systematically subtracts gas background from sample spectra regardless of memory effect of the previous sample.Negative net gas background counts are very frequently observed inβ-γcoincidence data from International Monitoring System(IMS)radionuclide stations.Gas background subtraction in such cases can potentially lead to overestimated of the activity concentration and even false positives.[Purpose]This study aims to solve the problem of gas background subtraction in NCC.[Methods]First of all,the judgment condition of gas background subtraction was proposed to avoid negative net gas background counts.Then the memory effect of the previous sample was eliminated by modifying the processing flow in NCC algorithm for analyzingβ-γcoincidence spectrum.Finally,historicalβ-γcoincidence data from IMS radionuclide stations were taken for verification of modified NCC and comparison with original NCC.[Results]Comparing the analysis results of original NCC and modified NCC,the false identification number of 131Xem,133Xem,133Xe and 135Xe is reduced by 63%,68%,72%and 26%,respectively.[Conclusions]The modified NCC algorithm can decrease the positive fault of identification of xenon isotopes and improve the accuracy of calculation of their radioactivity concentration.

关 键 词：放射性氙同位素 β-γ 符合能谱 符合净计数计算法 记忆效应 

分 类 号：TL816.4[核科学技术—核技术及应用]