Evaluating uncertainties in the calibration of isotopic reference materials and multi-element isotopic tracers (EARTHTIME Tracer Calibration Part II)
Evaluating uncertainties in the calibration of isotopic reference materials and multi-element isotopic tracers (EARTHTIME Tracer Calibration Part II)
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DOI：
10.1016/j.gca.2015.02.040
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发表时间：
2015-09-01
影响因子：
5
通讯作者：
Bowring, Samuel A.
中科院分区：
文献类型：
--
作者：
McLean, Noah M.;Condon, Daniel J.;Bowring, Samuel A.
本文提出了一种评价多元素同位素示踪剂刻度不确定度的统计方法，并应用于精确同位素稀释U-Pb年代学中混合U-Pb（Pb-202-Pb-205-U-233-U-235）示踪剂的同位素组成测定。我们的实验是EARTHTIME计划的一部分，直接将示踪剂校准与质量和纯度的第一原理测量联系起来，这些测量都可追溯到SI单位，从而量化了绝对时间内U-Pb日期的准确性和精确度。校准包括一些常用的铅和铀标准物质的新的更准确和精确的纯度测量，并需要相互关联的同位素组成和不确定性。类似的方法可以用于利用多个同位素标准品用于校准目的的其他同位素系统。我们还详细介绍了三个公开可用的U-Pb重量分析解决方案的相互校准，这可以用来将相同的第一性原理溯源性，以内部U-Pb示踪剂从其他实验室。考虑到示踪剂同位素比值的不确定性相关性，产生了对Pb-206/U-238日期的相对不确定性的示踪剂校准贡献，该贡献仅为示踪剂的U-235/Pb-205比值的相对不确定性的一半，该比值在历史上用于近似与Pb-206/U-238日期相关的示踪剂不确定性贡献。示踪剂不确定性对Pb-206/U-238测年的贡献以这种方式减少到
A statistical approach to evaluating uncertainties in the calibration of multi-element isotopic tracers has been developed and applied to determining the isotopic composition of mixed U-Pb (Pb-202-Pb-205-U-233-U-235) tracers used for accurate isotope dilution U-Pb geochronology. Our experiment, part of the EARTHTIME initiative, directly links the tracer calibration to first-principles measurements of mass and purity that are all traceable to SI units, thereby quantifying the accuracy and precision of U-Pb dates in absolute time. The calibration incorporates new more accurate and precise purity measurements for a number of commonly used Pb and U reference materials, and requires inter-relating their isotopic compositions and uncertainties. Similar methods can be used for other isotope systems that utilize multiple isotopic standards for calibration purposes. We also detail the inter-calibration of three publicly available U-Pb gravimetric solutions, which can be used to bring the same first-principles traceability to in-house U-Pb tracers from other laboratories. Accounting for uncertainty correlations in the tracer isotope ratios yields a tracer calibration contribution to the relative uncertainty of a Pb-206/U-238 date that is only half of the relative uncertainty in the U-235/Pb-205 ratio of the tracer, which was historically used to approximate the tracer related uncertainty contribution to Pb-206/U-238 dates. The tracer uncertainty contribution to Pb-206/U-238 dates has in this way been reduced to