Realization of the New Kilogram Using 28Si-Enriched Spheres and Dissemination of Mass Standards at NMIJ

Abstract

The new definition of the kilogram was implemented on May 20, 2019. The kilogram is presently defined by a fixed value of the Planck constant. On the basis of the new definition, the kilogram will be realized at the National Metrology Institute of Japan by the X-ray crystal density method using 28Si-enriched spheres. For the realization, the volume of 28Si-enriched spheres is measured by optical interferometry. The sphere surface characterization by X-ray photoelectron spectroscopy and ellipsometry is also performed. The relative standard uncertainty of the realization is estimated to be 2.4 × 10−8. Details of the realization and future dissemination of mass standards in Japan based on the 28Si-enriched spheres are described.