Shigeki Mizushima

Counting the atoms in a 28Si crystal for a new kilogram definition

This paper concerns an international research project aimed at determining the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The counting procedure was based on the measurement of the molar volume and the volume of an atom in two 1 kg crystal spheres. The novelty was the use of isotope dilution mass spectrometry as a new and very accurate method for the determination of the molar mass of enriched silicon. Because of an unexpected metallic contamination of the sphere surfaces, the relative measurement uncertainty, 3 × 10−8 NA, is larger by a factor 1.5 than that targeted. The measured value of the Avogadro constant, NA = 6.022 140 82(18) × 1023 mol−1, is the most accurate input datum for the kilogram redefinition and differs by 16 × 10−8 NA from the CODATA 2006 adjusted value. This value is midway between the NIST and NPL watt-balance values.

Improved measurement results for the Avogadro constant using a 28Si-enriched crystal

New results are reported from an ongoing international research effort to accurately determine the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The surfaces of two 28Si-enriched spheres were decontaminated and reworked in order to produce an outer surface without metal contamination and improved sphericity. New measurements were then made on these two reconditioned spheres using improved methods and apparatuses. When combined with other recently refined parameter measurements, the Avogadro constant derived from these new results has a value of

Present Status of the a Vogadro Constant Determination from Silicon Crystals with Natural Isotopic Composition

N_A = 6.022 140 76(12) \times 10^{23}

Results of the Sixth International Comparison of Absolute Gravimeters, ICAG-2001

mol

State-of-the-art mass determination of 28Si spheres for the Avogadro project

^{-1}

Evaluation of the molar volume of silicon crystals for a determination of the Avogadro constant

. The X-ray crystal density method has thus achieved the target relative standard uncertainty of

Mass comparison of the 1 kg silicon sphere AVO#3 traceable to the International Prototype K

2.0 \times 10^{-8}

Density Determination of Silicon Spheres Using an Interferometer With Optical Frequency Tuning

necessary for the realization of the definition of the new kilogram.

CCM.G-K2 key comparison

The determination of the Avogadro constant from two selected silicon crystals is described. The density, molar mass, and lattice spacing of the two crystals were measured at NMU, PTB, IRMM, IMGC, and NIST. When all the data are combined, it leads to the Avogadro constant of 6.022 1353 (21) times 1023 mol-1 with a relative combined standard uncertainty of 3.4 times 10-7

Realization of the kilogram based on the Planck constant at NMIJ

Like all the previous International Comparisons of Absolute Gravimeters (ICAGs) the sixth, ICAG-2001, was held at the Bureau International des Poids et Mesures (BIPM). Major improvements in the 2001 campaign were a new measurement strategy using the absolute gravimeters to measure the ties of the gravity network, new sites constructed at the BIPM, improved relative measurements of the ties and gravity gradients, and combined adjustment of the absolute and relative data, realized using new software with a novel data weighting and rejection scheme. The g-values at four sites of the BIPM were measured with an uncertainty of 6 μGal. Good agreement was obtained between the results of the absolute and relative measurements of the ties of the gravity network. The final mean gvalue obtained at the reference site A was 7 μGal less than that obtained in the previous comparison, ICAG-97.