从理论角度降低低本底α、β测量仪净计数率探测下限研究  

Study on reducing the low detection limit of net count rate by low backgroundα,βmeasurement instrument from theoretical point of view

作　　者：金涛[1] 孙宇[1] 张志鹏[1] 吴耀 宋纪高 李俊杰 罗远攀 裴敏 曾波 JIN Tao;SUN Yu;ZHANG Zhipeng;WU Yao;SONG Jigao;LI Junjie;LUO Yuanpan;PEI Min;ZENG Bo(Nuclear Power Institute of China,Sichuan Provincial Engineering Laboratory of Nuclear Facility Decommissioning and Radwaste Management,Sichuan Chengdu 610065)

机构地区：[1]中国核动力研究设计院四川省退役治理工程实验室,成都610005

出　　处：《辐射防护》2020年第6期550-555,共6页Radiation Protection

摘　　要：本文从不等式角度推导了低本底α、β测量仪测量过程中净计数率探测下限的公式,并计算两种典型探测下限公式对应的犯第二类错误的实际概率值。在不做近似的情况下,一定时间发生原子核衰变的数目服从二项分布。当净计数率的平均值为探测下限这个值时,净计数率的随机数低于判断限的概率就是犯第二类错误的实际概率值。结合初始时刻的放射性原子核数目、整个测量时间发生了衰变的放射性原子核数、放射性原子核发生衰变的概率,可以计算犯第二类错误(产生误判)的实际概率值。通过计算,发现大多数情况下犯第二类错误的实际最大概率比标称概率值低1到2个量级。因此在保证犯第二类错误的实际概率值趋近并小于标称值的情况下,通过引入修正系数对探测下限进行了修正。通过计算发现,当kα=1.645,kβ=1.645时,通过引入修正系数可以使探测下限至少降低22%。In this paper,the formula of the low detection limit of the net count rate in radioactive measurement is derived from the point of non-equality,the actually probability of making type II errors corresponding to the two typical low detection limit is calculated.In the absence of an approximation,the number of radionuclides that have decayed follow a binomial distribution.When the average of the net count rate is the low detection limit of the net count rate,the probability that the random value of the net count rate is less than the decision threshold is the probability value of making type II errors.Combining the number of radioactive nuclei at initial moment,the number of radioactive nuclei in the whole measurement time that has decayed and the probability of radioactive nuclides decay,the actual probability value of making type II errors can be calculated.It is found that the maximum practical probability value of the type II errors is 1 to 2 orders of magnitude less than the nominal value in most case.Therefore,the low detection limit can be modified,and an appropriate correction coefficient can be given,so that the actual probability value of making type II errors is close to and slightly less than the nominal value.Through calculation,it is found that the correction coefficient given by kα=1.645 and kβ=1.645 can reduce low detection limit by 22 percent.

关 键 词：净计数率 探测下限 修正系数 

分 类 号：TL817[核科学技术—核技术及应用]