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This paper describes the progress of a joint research project aimed at developing and demonstrating the technologies, based both on the watt balance experiment and the counting of 28Si atoms, necessary to realize the kilogram on the basis of an agreed conventional value of the Planck constant.
The European Metrology Research Programme (EMRP) funds research to address the discrepancy between the values of the Planck and Avogadro constants measured via the watt balance experiments and by the counting of 28Si atoms. The strategy will be to strain the procedures, models, and apparatuses up to their limit by repeating the measurements with accuracies stricter than those achievable by today's...
Future measurements of the silicon lattice-parameter by combined X-ray and optical interferometry require displacement measurements having 10−9 relative accuracy. Experimental and numerical investigations are under way to bring into light the limiting factors, excluding or identifying and eliminating them.
The uncertainty of the Si molar mass measurement is theoretically investigated by means of a two-isotope model, with particular emphasis to the role of this measurement in the determination of the Avogadro constant. This model allows an explicit calibration formula to be given and propagation of error analysis to be made. It also shows that calibration cannot correct for non-linearity.
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