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Determination of the Avogadro Constant by Counting the Atoms in a Si28 Crystal

B. Andreas et al.
Phys. Rev. Lett. 106, 030801 – Published 18 January 2011
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Abstract

The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by counting the atoms in 1 kg single-crystal spheres, which are highly enriched with the Si28 isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, NA=6.02214078(18)×1023mol1, is the most accurate input datum for a new definition of the kilogram.

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  • Received 12 October 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.030801

© 2011 The American Physical Society

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Chemistry class

Published 18 January 2011

Precision x-ray measurements hone in on a more accurate value of Avogadro’s constant.

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Vol. 106, Iss. 3 — 21 January 2011

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