TIMS测定铀矿石样品中^234U/^238U、^230Th/^232Th、^228Ra/^226Ra的方法研究

研究了TIMS测定铀矿石样品中234U/238U、230Th/232Th、228Ra/226Ra的方法。建立了铀矿石密闭混酸一次溶样的方法和采用阴离子、阳离子和Sr特效树脂逐级离子交换分离纯化U、Th和Ra的流程,满足了TIMS测量要求。测定结果表明：100～1000 ng的天然铀中234U/238U,其测量精密度从静态多接收的2.34%提高到动态多接收的0.47%;对230Th与232Th丰度接近、质量为1μg左右的钍,采用三带点样技术和法拉第多接收技术测定230Th/232Th,其内精度平均值为0.0048%,外精度为0.028%;采用单带加钽发射剂,ETP跳峰测定50～100 fg镭-228稀释剂中的228Ra/226Ra,其内精度小于0.10%,外精度小于0.20%。比较TIMS和HR-ICP-MS、α能谱法测定234U/238U、230Th/232Th、228Ra/226Ra结果,三者结果相吻合。TIMS测量法样品用量少、快速、准确、精密度高,是U、Th、Ra同位素比值测定方法的又一补充。

Methods for the determination of 234U/230 U, 230Th/232 Th and 228Ra/226Ra in uranium ores by TIMS

A method has been established to determine 234U/238U,230Th/232Th and 228Ra/226Ra isotope values in uranium ores by TIMS.The samples were decomposed by mixed acids in airproof vessels.U,Th and Ra were gradually purified by anion,cation and Sr-Spec exchange chromatography columns.The isotope values of 234U/238U（about 100～1000 ng U）were subsequently measured by TIMS.The RSD values of 234U/238U were increased from 2.34% by the multistatic analysis mode to 0.47% by the multidynamic analysis mode.With the methods of trip-filament loading and multistatic Faraday measurements,the RSD values of 230Th/232Th were within 0.10%.The precision for 228Ra/226Ra concentration range of 50～100 fg was within 0.2%.It is a rapid and precise method for analysis of 234U/238U,230Th/232Th and 228Ra/226Ra isotope values.The analysis results show a good consistency with HR-ICP-MS.This method can be considered as an important complementarity for the isotopic determination of U,Th and Ra.