ATOMIC WEIGHTS OF THE ELEMENTS: REVIEW 2000
(IUPAC Technical Report)
Prepared for publication by J. R. DE LAETER1, J. K. BÖHLKE2,‡, P. DE BIÈVRE3, H. HIDAKA4, H. S. PEISER2, K. J. R. ROSMAN1, AND P. D. P. TAYLOR3 of Applied Physics, Curtin University of Technology, Perth, Australia; 2United States Geological Survey, 431 National Center, Reston, VA 20192, USA; 3Institute for Reference Materials and Measurements, European Commission – JRC B-2440, Geel, Belgium; 4Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan 1Department
of the Commission for the period 2000–2001 was as follows:
Chairman: L. Schultz (Germany); Secretary: R. D. Loss (Australia); Titular Members: J. K. Böhlke (USA); T. Ding (China); M. Ebihara (Japan); G. I. Ramendik (Russia); P. D. P. Taylor (Belgium); Associate Members: M. Berglund (Belgium); C. A. M. Brenninkmeijer (Germany); H. Hidaka (Japan); D. J. Rokop (USA); T. Walczyk (Switzerland); S. Yoneda (Japan); National Representatives: J. R. de Laeter (Australia); P. De Bièvre (Belgium); C. L. do Lago (Brazil); Y. K. Xiao (China/Beijing). ‡Corresponding
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J. R. de LAETER et al.
Atomic weights of the elements: Review 2000
(IUPAC Technical Report)
Abstract: A consistent set of internationally accepted atomic weights has long been an essential aim of the scientific community because of the relevance of these values to science and technology, as well as to trade and commerce subject to ethical, legal, and international standards. The standard atomic weights of the elements are regularly evaluated, recommended, and published in updated tables by the Commission on Atomic Weights and Isotopic Abundances (CAWIA) of the International Union of Pure and Applied Chemistry (IUPAC). These values are invariably associated with carefully evaluated uncertainties. Atomic weights were originally determined by mass ratio measurements coupled with an understanding of chemical stoichiometry, but are now based almost exclusively on knowledge of the isotopic composition (derived from isotope-abundance ratio measurements) and the atomic masses of the isotopes of the elements. Atomic weights and atomic masses are now scaled to a numerical value of exactly 12 for the mass of the carbon isotope of mass number 12. Technological advances in mass spectrometry and nuclear-reaction energies have enabled atomic masses to be determined with a relative uncertainty of better than 1 × 10–7. Isotope abundances for an increasing number of elements can be measured to better than 1 × 10–3. The excellent precision of such measurements led to the discovery that many elements, in different specimens, display significant variations in their isotope-abundance ratios, caused by a variety of natural and industrial physicochemical processes. While such variations increasingly place a constraint on the uncertainties with which some standard atomic weights can be stated, they provide numerous opportunities for investigating a range of important phenomena in physical, chemical, cosmological, biological, and industrial processes. This review reflects the current and increasing interest of science in the measured differences between source-specific and...