中文摘要：

本文介绍了测量海水中224Ra和223Ra比活度的国际通用仪器镭延迟符合计数器（Ra De CC）,该仪器具有效率高、灵敏度高、背景值低、方便携带和适合海上现场测量等优点。结合本实验室3 a使用经验和工作数据,对仪器测量误差、探测效率、本底值和探测限等做出系统的阐述和讨论。结果表明,Ra De CC对224Ra和223Ra的探测效率分别在0.47～0.59和0.45～0.57之间,探测限分别为0.04 dpm和0.01 dpm,对224Ra和223Ra测量的相对标准偏差一般在5%和15%左右,但是,当224Ra比活度低于5 dpm/100 L时,变异系数将升高至10%～30%;当223Ra低于0.3 dpm/100 L时,变异系数将高达20%～80%。

英文摘要：

A method for determination of224 Ra and223Ra in seawater using a radium delayed coincidence counter（ RaDe CC） is presented in this study. After pre-concentrating224 Ra and223Ra from seawaters by adsorbing onto a column of Mn O2 coated fiber,samples are measured for224 Ra and223Ra by discrimination of decays of their daughters,220Rn-216 Po and219Rn-215 Po,respectively. The Ra De CC system provides a highly effective,sensitive,and simple way to determine224 Ra and223Ra. It is characterized by low background,and designed conveniently for field operation. Based on three years experience in measurement and data of224 Ra and223Ra by Ra De CC,we discuss systematic uncertainties,efficiencies,background values,critical and detective limits. The results show that the system efficiencies of224 Ra and223Ra are in the ranges of 0. 47 ～ 0. 59 and 0. 45 ～ 0. 57. The detective limits are 0. 04 dpm for224 Ra and 0. 01 dpm for223Ra,with a precision of 5% for224 Ra activity and 15% for223 Ra in routine analyses. However,the uncertainties of low activities samples will increase to 10% ～ 30% for lower than 5 dpm /100 L of224Ra and 20% ～ 80% for lower than 0. 3 dpm /100 L of223Ra.