Abstract
The new definition of the kilogram based on the Planck constant was implemented in May 2019. The National Metrology Institute of Japan (NMIJ) will realize the new kilogram by the X-ray crystal density method using a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup> Si-enriched sphere. An international comparison of the realizations of the new kilogram by national metrology institutes was organized. As a participant in the comparison, the NMIJ realized the kilogram by the volume measurement and surface characterization of a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup> Si-enriched sphere. Details of the measurement results and the uncertainty evaluation of the realization are described. The comparison of the realization results with previous realization results in 2016 is also provided.
Highlights
I N MAY 2019, the International System of Units (SI) was essentially revised
The surface was characterized with the X-ray photoelectron spectroscopy (XPS) system from November to December 2019 and the ellipsometer in January 2020
Before the volume measurement using the interferometer, the sphere was cleaned by the same procedure as that used by National Metrology Institute of Japan (NMIJ) in the international comparison of the diameter measurement of a 1 kg Si sphere in the International Avogadro Coordination (IAC) project [15] and for the pilot study of the realization of the kilogram [4]
Summary
I N MAY 2019, the International System of Units (SI) was essentially revised. Presently, all SI units are defined in terms of the seven defining constants [1]. It is, in principle, possible for each national metrology institute to realize the kilogram independently. To ensure consistency among the realizations by national metrology institutes, an international comparison of the realizations based on the new definition, CCM.M-K8.2019, was organized by the Consultative Committee for Mass and Related Quantities. This comparison is an essential step toward the dissemination of the kilogram based on the individual realizations by each national metrology institute [2], [3]. The National Metrology Institute of Japan (NMIJ) will realize the new kilogram by using the X-ray crystal den-.
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