Realization of the new kilogram by the XRCD method using 28Si-enriched spheres

Abstract

The new definition of the kilogram was implemented on May 20, 2019. The kilogram is presently defined by 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 is also characterized by X-ray photoelectron spectroscopy and ellipsometry. The relative standard uncertainty of the realization is estimated to be 2.1 × 10−8. This corresponds to the realization of the new kilogram with a standard uncertainty of 21 μg for 1 kg. Details of the realization and future dissemination of mass standards in Japan based on the 28Si-enriched spheres are described.

Keywords

• Kilogram
• Planck constant
• New SI
• Mass standards