carbon 12 既問題

Let review the long history on the atomic weights scale. Since there is word limit, I only copy the extraction of "The Atomic Weights Scale" section from teh article "Atomic Weights and the International Committee —A Historical Review"

In April 1957 at the bar in the Hotel Krasnapolski in Amsterdam, Nier suggested to Mattauch that the 12C = 12 mass scale be adopted because of carbon's use as a secondary standard in mass spectrometry63. Also, 12C = 12 implied acceptable relative changes in the atomic weight scale, i.e., 42 parts-per-million (ppm) compared to 275 ppm for the 16O = 16 scale (which would not acceptable to chemists). Enthusiastically, Mattauch made a worldwide effort in the late 1950s to publicize the 12C = 12 scale and obtain the physicist's approval, while Wichers obtained the chemist's approval. (Mattauch was so anxious to tell the world of Nier's suggestion of the 12C mass scale as the resolution of the atomic weight dispute between chemists and physicists that he rushed off to the IUPAC General Assembly in Paris without his passport. After phoning Nier at the Max Planck Institute in Mainz, Mattauch had to spend the night at Trier on the German-French border, while he waited until Nier retrieved his passport from the Institute before he could continue on to the Commission meeting and unveil the solution64). Following the approval of the International Union of Pure and Applied Physics (IUPAP) General Assembly at Ottawa, Canada in 1960 and the IUPAC General Assembly at Montreal, Canada in 1961, the atomic weights were officially given on the 12C = 12 scale for the first time in the 1961 report65. Mattauch and his colleagues66 combined data on direct nuclidic mass measurements with data on measured binding energies and beta decay energies derived from the masses to produce a consistent least squares fit of all nuclidic masses. This mass data was combined with the isotopic compositions to provide atomic weight values used in that 1961 Atomic Weight report.