ABSOLUTE VOLUME MEASRUMENET OF SILICON SPHERES AT NMIJ

Naoki Kuramoto, Kenichi Fujii

Abstract

The method and devices for absolute volume measurements of 1 kg silicon spheres are described. An interferometer equipped with a direct optical frequency tuning system is used to measure the sphere volume, in which the optical frequency of a diode laser can be tuned continuously over a frequency range of 19 GHz. Accurate frequency changes in the laser produced by this system are used to measure the sphere diameters by phase-shifting interferometry. A total of seventy diameters, which are distributed near-uniformly over the surface of the sphere, are measured in vacuum. The volume of the sphere is determined by fitting the diameters to a series of spherical harmonics. The mass of the sphere is compared with that of the national prototype of the kilogram through a secondary 1 kg standard. The relative combined standard uncertainty in the density determined by direct measurements of the mass and volume is presently estimated to be 7.3·10^-8. Recent results on the volume determination for three 1 kg silicon spheres are shown.

Keywords

volume standard, density standard, silicon sphere, Avogadro constant

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PWC-2006-TC3-032u.pdf

DOI

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IMEKO TC

TC3 - Measurement of Force, Mass, Torque, and Gravity

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