Towards a Universal Kilogram: 

CMS/ITRI Participates in CCM.M-K8.2024 InterComparison

News from Members - CMS/ITRI

The ²⁸Si-enriched sphere Si28kg03a 

To make contribution for the redefinition of the kilogram with the Planck constant, CMS/ITRI participated in CCM.M-K8.2024—the third CCM key comparison of kilogram realizations based on the fixed numerical value of the Planck constant.

The objectives of this comparison were to assess the level of agreement among two different realization methods of the kilogram—the Kibble balances, and the X-ray crystal density (XRCD) method—and to provide data for calculating the third “consensus value” of the kilogram. The consensus value serves as the basis for an internationally coordinated dissemination of the kilogram and is updated after each new key comparison. Its use will continue until satisfactory agreement between realization experiments has been achieved. Another objective was to assess the reproducibility of these realization methods by comparing the 2024 results with those from the first/second key comparisons, CCM.M-K8.2019 & 2021.

Ten institutes participated in the comparison: the BIPM, LNE (France), METAS (Switzerland), NIM (China), NIST (USA), NRC (Canada) and UME (Turkey) used Kibble balances, and the CMS/ITRI (Chinese Taipei), NMIJ/AIST (Japan), and PTB (Germany) used the XRCD method as the basis for their mass determinations.

The system CMS/ITRI established consisting of a 28Si-enriched sphere and a combined X-ray fluorescence (XRF)/X-ray photoelectron spectroscopy (XPS) surface-analysis system. The mass of the Si-sphere was determined to be 1000.078400(36) g, with a relative standard uncertainty of 3.6 × 10−8. In parallel, the sphere’s mass was also measured via dissemination from platinum-iridium kilogram prototype No. 78, traceable to the Planck constant. This gravimetric approach yielded a mass of 1000.078433(36) g. The masses determined by the two different approaches are consistent within their standard uncertainties, affirming the reliability of the kilogram realization by the XRCD method at CMS/ITRI.

Dr. Yu-Hsin Wu

YH.Wu@itri.org.tw