Comparison of silicon density standards at NRLM and IMGC

The Istituto di Metrologia 'G Colonnetti' in Torino, Italy, (IMGC) and the National Research Laboratory of Metrology in Japan (NRLM) have developed density standards in the form of single-crystal silicon spheres within their projects for the determination of the Avogadro constant. The results of the first comparison on two such artifacts are presented. The mass and volume of the IMGC sphere were measured at NRLM with an absolute method, whereas , at IMGC, the density of the NRLM sphere was measured by hydrostatic comparison to the IMGC silicon standard. Additional diameter measurements were also made. The overall results show excellent agreement: within 0.16 ppm in density, 0.1 ppm in mass, 0.06 ppm in volume, and 0.04 ppm in diameter measurements.<
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