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    Uranium Isotope Materials

    With new and improved instrumentation allowing for much smaller sample sizes, δ(238/235U) variations of the order of 1 ‰ have been observed in naturally occurring terrestrial materials. This variation could be a result of uranium oxidation–reduction reactions and/or due to a nuclear field shift which would cause preferential separation of some uranium isotopomers.

    δ(238/235U) Values of Reference Materials

    Name Material δSRM950A(238/235U)
    NIST SRM 950-Auranium oxide 0 ‰ *
    NBL CRM C112-Asolution+0.02(5) ‰
    NBL CRM 129-Auranium oxide-1.2 ‰
    IRMM 184solution-1.15 ‰
    REIMEP-18a-0.18(6) ‰
    seawater-0.41(2) ‰
    Name Material δSRM950A(238/235U)

    Footnotes      Back to Top
    * Exact value defining the δ(238/235U) SRM950A scale.
    Values in parenthesis are expanded (k = 2) uncertainties applicable to the last digits. The values listed in this table are compilation and are not necessarily CIAAW recommendations.


    W.A. Brand et al
    Assessment of international reference materials for isotope-ratio analysis Pure and Applied Chemistry 86, 425-467 (2014)

    CIAAW recommends the standard value for the isotope ratio, N(238U)/N(235U) = 137.8(1), in naturally occurring terrestrial materials.