![]() ![]() Additionally, the Commission reviewed the recommendations to change the standard atomic weights of Yb (2015), Ar (2017), Ir (2017), Hf (2019), and Pb (2021) based on the review of published data on the isotopic composition of these elements, as well as the standard atomic weights of 14 other elements (2017, 2021) based on the Atomic Mass Evaluation 20 under the auspices of the International Union of Pure and Applied Physics (Al, Au, Co, F, Ho, Mn, Nb, Pa, Pr, Rh, Sc, Tb, Tm, Y). ![]() The recommendations included modifying the definition of normal materials and changing the expression of uncertainty of standard atomic weights and isotopic composition values. At these meetings, the Commission reviewed recommendations of its Subcommittees (Subcommittee on Natural Assessment of Fundamental Understanding of Isotopes, Subcommittee on Isotopic Abundance Measurements, and Subcommittee on Stable Isotope Reference Material Assessment). The Commission met in Tulln (Austria) from 3 to 4 August 2015, Groningen (The Netherlands) from 16 to 18 September 2017, in Berlin (Germany) from 3 to 4 July 2019 and in a virtual meeting 27 to 28 July 2021 under the chairmanship of Juris Meija. ![]() The Commission on Isotopic Abundances and Atomic Weights (CIAAW, hereafter called the Commission) convenes biennially to evaluate recent developments in isotope measurement science and deliberate on related matters. ![]()
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