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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 28Si-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 28Si-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. [ABSTRACT FROM AUTHOR]

The kilogram based on the Plank constant will be realized at the National Metrology Institute of Japan (NMIJ) by using the X-ray crystal density method. In this study, for the realization, the volume of a 28Si-enriched sphere, named AVO28-S5c, was measured. The volume was determined from diameter measurements taken in many directions using an optical interferometer. The apparent volume of the sphere, which does not consider the influence of the surface layers on the volume measurement, was determined with a relative standard uncertainty of $1.8\times 10^{-8}$. The reproducibility of the kilogram realization is important for the reliable dissemination of the kilogram at the NMIJ. Therefore, the volume determined in this study was compared with that determined in 2016. These volumes were shown to agree with the uncertainty. This article provides details on the measurements, improvements of the interferometer, data analysis, and uncertainty evaluation. [ABSTRACT FROM AUTHOR]

For a determination of the Avogadro constant by the X-ray crystal density method, the volume of a Si sphere manufactured from a Si crystal isotopically enriched in 28Si, named Si28-23Pr11, was measured at the National Metrology Institute of Japan (NMIJ). The volume was determined on the basis of diameter measurement in 2175 directions by an optical interferometer. The surface layers on the sphere were characterized by X-ray photoelectron spectroscopy and spectroscopic ellipsometry. Taking into account the effect of the surface layers on the diameter measurement, the volume of the Si core excluding the surface layers was determined with a relative uncertainty of $2.0\times 10^{\mathbf {-8}}$. The results were used to determine the Avogadro constant in 2017 by the International Avogadro Coordination project, which was used as an input datum to determine the CODATA 2017 adjusted value of the Planck constant $h$. This $h$ value will be used in the new definition of the kilogram. This paper provides details of the measurement apparatus and the uncertainty analysis of the Si core volume measurement. In addition, an approach to reduce the uncertainty in the Si core volume determination is proposed for the accurate realization of the kilogram based on the new definition at NMIJ. Details of the approach are also provided. [ABSTRACT FROM AUTHOR]

We report an uncertainty evaluation of an 171Yb optical lattice clock with a total fractional uncertainty of $3.6\times 10^{-16}$ , which is mainly limited by the lattice-induced light shift and the blackbody radiation shift. Our evaluation of the lattice-induced light shift, the density shift, and the second-order Zeeman shift is based on an interleaved measurement where we measure the frequency shift using the alternating stabilization of a clock laser to the 6s2 1S0–6s6p 3P0 clock transition with two different experimental parameters. In the present evaluation, the uncertainties of two sensitivity coefficients for the lattice-induced hyperpolarizability shift $d$ incorporated in a widely used light shift model by RIKEN and the second-order Zeeman shift $a_{Z}$ are improved compared with the uncertainties of previous coefficients. The hyperpolarizability coefficient $d$ is determined by investigating the trap potential depth and the light shifts at the lattice frequencies near the two-photon transitions 6s6p3P0–6s8p3P0, 6s8p3P2, and 6s5f3F2. The obtained values are $d=-1.1(4)\,\,{\mu }$ Hz and $a_{Z}=-6.6(3)$ Hz/mT2. These improved coefficients should reduce the total systematic uncertainties of Yb lattice clocks at other institutes. [ABSTRACT FROM AUTHOR]

In the determination of the Avogadro constant using the X-ray crystal density method with a 28Si-enriched crystal prepared by the International Avogadro Coordination (IAC) project, the volume measurement and surface analysis of 28Si spheres play a crucial role. For accurate volume determination, an optical interferometer has been improved taking account of the geometrical shape of the optical components. Furthermore, a new spectroscopic ellipsometer with a sphere rotation system has been developed for accurate surface analysis. The optical interferometer and the ellipsometer have been used for the volume determination and surface analysis of the 28Si spheres repolished by the IAC, respectively. On the basis of the preliminary uncertainty estimation, the relative standard uncertainty of the apparent volume measurement has been reduced from 4.4 \times 10^-8 to 2.7 \times 10^-8 by the improvement of the interferometer. The number of ellipsometric measurement points on the sphere surface has been increased from 20 to 7782 by the installation of the new ellipsometer, yielding more reliable information on the sphere surface. Details of the improvements and the preliminary results of the measurements of the 28Si spheres are given. [ABSTRACT FROM PUBLISHER]