Mass Measurement of 28Si-Enriched Spheres at NMIJ for the Determination of the Avogadro Constant

Abstract

The Avogadro constant, $N_{\mathbf {A}}$ , is the physical constant that connects microscopic and macroscopic quantities, and is indispensable especially in the field of chemistry. In addition, the Avogadro constant is closely related to the fundamental physical constants, namely, the electron relative atomic mass, fine-structure constant, Rydberg constant, and Planck constant. For several decades, the Avogadro constant has been determined using the x-ray crystal density (XRCD) method, which is currently one of the practical methods to redefine the kilogram based on fundamental physical constants. In this paper, we present the results of mass measurements of 28Si-enriched spheres, performed at the National Metrology Institute of Japan (NMIJ) in 2014, for the determination of the Avogadro constant using the XRCD method. The results of repeatability of the cleaning effect on the mass of the spheres and the determination of the physical adsorption of water vapor on the spheres are shown. These results establish the reliability of the mass measurement at NMIJ. In addition, we report the results of the mass measurements of 28Si-enriched sphere AVO28-S5c conducted in 2016 to participate in the Pilot Study organized by the Consultative Committee for Mass and Related Quantities aiming at the redefinition of the kilogram based on the fixed numerical value of the Planck constant.