Precise analysis of 234U/238U ratio using UO2+ ion with thermal ionization mass spectrometry for natural samples
Precise analysis of 234U/238U ratio using UO2+ ion with thermal ionization mass spectrometry for natural samples
复制标题
使用 UO2 离子和热电离质谱法精确分析天然样品的 234U/238U 比率
DOI：
10.1016/s0009-2541(01)00270-4
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发表时间：
2001
期刊：
影响因子：
3.9
通讯作者：
E. Nakamura
中科院分区：
文献类型：
--
作者：
T. Yokoyama;A. Makishima;E. Nakamura
我们发展了一种用热电离质谱(TIMS)分析铀同位素的新的、高精度的方法，通过测量极少量(100-10 ng)铀释放的UO2+离子。一种新的电离激活剂，硅酸稀释的磷酸溶液，被发现不仅能有效地产生强而稳定的UO2+离子束，而且还能保持测量过程中的质量分馏小而恒定。铀同位素分析采用动态多次收集的方法，使用三个法拉第杯收集器和一个带有RPQ的离子计数模式的二次电子倍增器(RPQ-SEM)。为了进行精确的同位素分析，在铀同位素采集的同时，精确地测定了法拉第杯的基线和法拉第杯与RPQ-SEM之间的换算系数。对于从天然流纹岩黑岩中提取的铀，234U/238U比值的分析精密度和重复性分别为0.10%~0.38%(2σ平均值)和0.13%~0.31%(2σ)。与以前的研究相比，精密度和重现性都有所提高，因此，我们的方法特别适用于U丰度很低的样品。
We have developed a new, highly precise method for U isotopic analysis using a thermal ionization mass spectrometry (TIMS) by measuring UO2+ions emitted from a very small amount (100–10 ng) of U. A new ionization activator, a silicic acid–diluted phosphoric acid solution, was found to be effective not only for producing a strong and stable UO2+ion beam, but also for keeping the mass fractionation during measurement small and constant. U isotope analysis was carried out by a “dynamic multi collection” method using three Faraday cup collectors and a secondary electron multiplier in ion counting mode with RPQ (RPQ-SEM). For precise isotope analysis, baselines of the Faraday cups and a conversion factor between Faraday cups and the RPQ-SEM were precisely determined simultaneously with U isotope collection. Analytical precision and reproducibility of234U/238U ratio ranged from 0.10% to 0.38% (2σmean) and from 0.13% to 0.31% (2σ), respectively, for 100–10 ng of U extracted from a natural rhyolitic obsidian. The precision and reproducibility were improved compared with previous studies, and thus, our method is especially useful for samples with very low abundance of U.