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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
A procedure has been developed for determining the number of missing atoms in a silicon crystal. Possible voids are filled with Cu 5Si by indiffusion of copper. After removal of the interstitially dissolved copper, the samples are digested and the copper content is determined by isotope-dilution mass spectrometry. The detection limit of this highly specific and accurate measurement method was developed...
This paper describes an attempt to replace the present definition of the kilogram with the mass of a certain number of carbon atoms. This requires determination of the Avogadro constant, NA, with a relative uncertainty of 1 times 10-8. Silicon crystals are used in this determination. At present, a factor limiting factor is the measurement of the average molar mass of natural Si. Consequently, a worldwide...
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