Precise analysis of the 228Ra/226Ra isotope ratio for short-lived U-series disequilibria in natural samples by total evaporation thermal ionization mass spectrometry (TE-TIMS)
Precise analysis of the 228Ra/226Ra isotope ratio for short-lived U-series disequilibria in natural samples by total evaporation thermal ionization mass spectrometry (TE-TIMS)
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DOI：
10.1039/b400829d
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发表时间：
2004-06
影响因子：
3.4
通讯作者：
T. Yokoyama;E. Nakamura
中科院分区：
文献类型：
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作者：
T. Yokoyama;E. Nakamura
我们报告了一种新的分析技术，精确和准确的测定228 Ra/226 Ra的比例全蒸发热电离质谱（TE-TIMS）。还描述了采用新的串联柱技术的改进的色谱分离方法，其能够实现高收率和高纯度的Ra。对Ra标准溶液（228 Ra/226 Ra = 1.1）进行重复分析，得到的228 Ra/226 Ra的分析重现性范围为0.2%-0.9%（2σ），Ra为170 - 2 fg。重现性强控制的计数统计的226 Ra+和228 Ra+离子束强度收集的离子计数检测器，这意味着在运行中的精度Ra同位素分析的方法可以使用计数统计法进行评估。硅酸盐岩石样品中226 Ra丰度的测定采用同位素稀释TE-TIMS进行检验，JR-2（226 Ra = 3700 fg g−1）和JB-2（226 Ra = 81 fg g −1）的重现性分别为0.3%（2σ）和0.6%（2σ）;这些测量的重现性比以前公布的常规TIMS程序好2-3倍。天然样品中~（226）Ra/~（228）Ra比值的测量不确定度为± 1%（2σ）。我们的方法的准确性得到了证实，通过测量（226 Ra/230 Th）和（228 Ra/232 Th）的JR-2，一个足够老（1 Ma）的样品在230 Th-226 Ra和232 Th-228 Ra放射性平衡的比率。我们的方法对于Ra丰度非常低的样品特别有效。
We report a new analytical technique for precise and accurate determination of the 228Ra/226Ra ratio by total evaporation thermal ionization mass spectrometry (TE-TIMS). An improved chromatographic separation method employing a new tandem column technique that enables high yield and high purity of Ra is also described. Repeated analysis of Ra standard solution (228Ra/226Ra = 1.1) yielded an analytical reproducibility for 228Ra/226Ra ranging from 0.2% to 0.9% (2σ) for 170 to 2 fg of Ra. Reproducibility was strongly controlled by counting statistics of 226Ra+ and 228Ra+ ion beam intensities collected by an ion counting detector, implying that in-run precision for Ra isotope analysis of our method can be evaluated using a counting statistics law. Determination of 226Ra abundances in silicate rock samples were examined by isotope dilution TE-TIMS, and reproducibility was 0.3% (2σ) for JR-2 (226Ra = 3700 fg g−1) and 0.6% (2σ) for JB-2 (226Ra = 81 fg g−1); the reproducibility of these measurements are 2–3 times better than previously published conventional TIMS procedures. The 226Ra/228Ra ratio in natural samples can be also measured with an analytical uncertainty of ∼1% (2σ). The accuracy of our method was confirmed by measuring (226Ra/230Th) and (228Ra/232Th) ratios for JR-2, a sample old enough (1 Ma) to be in 230Th–226Ra and 232Th–228Ra radioactive equilibria. Our method is especially effective for samples with a very low abundance of Ra.