COMPARISON OF SILICON DENSITY STANDARDS AT NRLM AND IMGC

IMGC and NRLM have developed density standards in the form of single-c rystal silicon spheres within their projects for the determination of the Avogadro constant. The results of the first intercomparison 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 de nsity of the NRLM sphere was measured by hydrostatic comparison to the IMGC silicon standard. Additional diameter measurements were also mad e. The overall results have shown an excellent agreement: within 0.16 ppm in density, 0.1 ppm in mass, 0.06 ppm in volume, and 0.04 ppm in d iameter measurements.