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    Historical Isotopic Abundances

    Summarized below are standard values of the isotopic abundances of the elements recommended by the CIAAW. These values appear in Column 9 of the Table of Isotopic Composition of the Elements (TICE) and are known as 'representative isotopic abundances'. The representative isotopic abundances and their uncertainties for all elements are consistent with the standard atomic weights and their uncertainties.

    Please enter the name or symbol of the element, isotope, or the year in order to retrieve the relevant historical isotopic abundances.

    An entry is given only when the Commission recommended for the element a revised (or new) value for the isotopic abundance of an element. All values are given here as originally published by the Commission.
    All names and symbols of the elements are given in their present form even though many changes have occured in this regard over the last century.

    SOURCE (TEXT)   Data compiled by Juris Meija from CIAAW Isotopic Composition reports and Atomic Weight reports spanning time period of 1975-2017.
    © CIAAW 2018-2020 (last updated in Jan 2020)
    Excerpt from the 1931 Report of Committee on Atomic Weights


    The CIAAW has provided regular assessments of the standard atomic weights and isotopic compositions of the elements. The first Table of Isotopic Compositions was published by the CIAAW in 1931, based on the work of Francis W. Aston, and it included only seven elements.

    Since then, the CIAAW has evaluated the isotopic compositions of all elements having a tabulated standard atomic weight by examining the most accurate isotopic-abundance measurements in selected samples and by compiling evidence for known variations of the isotopic abundances of the elements in normal materials.