The Avogadro constant: determining the number of atoms in a single-crystal28Si sphere

The Avogadro constant, the number of entities in an amount of substance of one mole, links the atomic and the macroscopic properties of matter. Since the molar Planck constant—the product of the Planck constant and the Avogadro constant—is very well known via the measurement of the Rydberg constant,...

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Bibliographic Details
Published in:Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences physical, and engineering sciences, 2011-10, Vol.369 (1953), p.3925-3935
Main Authors: Becker, Peter, Bettin, Horst
Format: Article
Language:English
Subjects:
Atoms
Average linear density
Crystals
Interferometers
Isotopes
Mass
Metrology
Planck constant
Review
Silicon
Teeth
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Summary:The Avogadro constant, the number of entities in an amount of substance of one mole, links the atomic and the macroscopic properties of matter. Since the molar Planck constant—the product of the Planck constant and the Avogadro constant—is very well known via the measurement of the Rydberg constant, the Avogadro constant is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a new definition of the kilogram in terms of a fundamental constant. Here, we describe a new and unique approach to determine the Avogadro constant from the number of atoms in 1 kg single-crystal spheres that are highly enriched with the 28 Si isotope. This approach has enabled us to apply isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, N A = 6.022 140 82(18) × 10 23 mol -1 , is now the most accurate input datum for a new definition of the kilogram.
ISSN:1364-503X