IUPAC-IUGS status report on the half-lives of ²³⁸U, ²³⁵U and ²³⁴U

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• 作者：I.M. Villa^a ; ^b ; ^d ; ^e ; ; M.L. Bonardi^a ; ^c ; ^f ; P. De Biè ; vre^a ; ^c ; ^g ; N.E. Holden^a ; ^c ; ^h ; P.R. Renne^a ; ^b ; ⁱ ; ^j
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2016
• 出版时间：1 January 2016
• 年：2016
• 卷：172
• 期：Complete
• 页码：387-392
• 全文大小：241 K

文摘

The current state of knowledge on the half-lives of the long-lived U radionuclides has been reviewed by the IUPAC-IUGS joint Task Group “Isotopes in Geosciences”. ²³⁸U is assigned a half-life of (4.4683 ± 0.0096) Ga, i.e. a decay constant λ₂₃₈ = (0.155125 ± 0.000333) Ga⁻¹. The coverage factor is k = 2 for this and all other estimates presented here. The ²³⁸U half-life can be used as a reference for the half-lives/decay constants of all other isotopic geochronometers.

A revision of the half-life of ²³⁵U based on intercomparison of natural geological samples is premature. The improved repeatability of mass spectrometric measurements has revealed Type B uncertainties that had been dismissed as subordinate in the past. The combined uncertainty of these as yet incompletely charted and quantified sources of Type B uncertainty may be no smaller than the currently accepted uncertainty of the α counting experiments.

A provisional value for the ²³⁴U half-life can be calculated with the assumption of secular equilibrium in the analyzed natural samples. This assumption has not yet been verified independently and its metrological traceability appears sub-optimum. A Type B evaluation suggests that the ca. 0.17% offset between the N(²³⁴U)/N(²³⁸U) number-ratios of the natural samples used to estimate the ²³⁵U half-life and those of the four samples used to estimate the ²³⁴U half-life should be compounded into the standard measurement uncertainty of the latter. The resulting provisional uncertainty interval (k = 2) for the ²³⁴U half-life is (244.55–247.77) ka, corresponding to λ₂₃₄ = (2.8203–2.8344) Ma⁻¹.