The isotopic composition of natural uranium samples—Measurements using the new n(²³³U)/n(²³⁶U) double spike IRMM-3636

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• 作者：S. Richter ; A. Alonso-Munoz ; R. Eykens ; U. Jacobsson ; H. Kuehn ; A. Verbruggen ; Y. Aregbe ; R. Wellum ; E. Keegan
• 关键词：Isotope reference materials ; Isotope mass spectrometry ; Natural uranium ; Double spike
• 刊名：International Journal of Mass Spectrometry
• 出版年：2008
• 出版时间：1 January 2008
• 年：2008
• 卷：269
• 期：1-2
• 页码：145-148
• 全文大小：230 K

文摘

The new double spike isotope reference material IRMM-3636 was prepared gravimetrically using highly enriched ²³³U and ²³⁶U isotopic material. The n(²³³U)/n(²³⁶U) ratio was adjusted to about 1:1 and certified with an extended relative uncertainty of 0.016 % (coverage factor k = 2). By mixing the n(²³³U)/n(²³⁶U) double spike with a sample and applying internal mass fractionation correction, the n(²³⁵U)/n(²³⁸U) ratio of a given sample can be determined with the highest possible precision and accuracy. Due to the low relative abundance of ²³⁴U for the IRMM-3636 double spike (<0.00037 % ) measurements for n(²³⁴U)/n(²³⁶U) of samples close to natural isotopic composition (n(²³⁴U)/n(²³⁶U) 5.4 × 10⁻⁵) are also possible with a rather small correction and without significant increase in the uncertainty.

The IRMM-3636 double spike was applied for measurements of natural uranium ore samples. The results for n(²³⁵U)/n(²³⁸U) ratios were compared to earlier data obtained using UF₆ gas sources mass spectrometry and to the most recent IUPAC recommended value, published in 2003. The results show that the historically used “consensus value” of 1/137.88 (earlier IUPAC value) cannot be considered representative for natural uranium samples.