Title: Counting the Atoms in a 28Si Crystal for a New Kilogram Definition
Authors: ANDREAS B.AZUMA Y.BARTL G.BECKER P.BETTIN H.BORYS M.BUSCH I.FUCHS P.FUJII K.FUJIMOTO H.Kessler, Jr. ErnestKRUMREY M.KUETGENS U.KURAMOTO N.MANA G.MASSA E.MIZUSHIMA S.NICOLAUS A.PICARD A.PRAMANN A.RIENITZ O.SCHIEL DVALKIERS StafWASEDA A.ZAKEL S.
Citation: METROLOGIA vol. 48 no. 2 p. S1-S13
Publisher: IOP PUBLISHING LTD
Publication Year: 2011
JRC N°: JRC65156
ISSN: 0026-1394
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC65156
DOI: 10.1088/0026-1394/48/2/S01
Type: Articles in Journals
Abstract: This paper concerns an international research project aimed at determining the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The counting procedure was based on the measurement of the molar volume and the volume of an atom in two 1 kg crystal spheres. The novelty was the use of isotope dilution mass spectrometry as a new and very accurate method for the determination of the molar mass of enriched silicon. Because of an unexpected metallic contamination of the sphere surfaces, the relative measurement uncertainty, 3 × 10-8 NA, is larger by a factor 1.5 than that targeted. The measured value of the Avogadro constant, NA = 6.022 140 82(18) × 1023 mol-1, is the most accurate input datum for the kilogram redefinition and differs by 16 × 10-8 NA from the CODATA 2006 adjusted value. This value is midway between the NIST and NPL watt-balance values.
JRC Institute:Institute for Reference Materials and Measurements

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