Silicon spheres for the future realization of the kilogram and the mole

Publication date: Available online 17 January 2019Source: Comptes Rendus PhysiqueAuthor(s): Horst Bettin, Kenichi Fujii, Arnold NicolausAbstractNew definitions of the units for amount of substance – the mole – and for mass – the kilogram – will presumably come into force on the World Metrology Day 2019. In the revised SI, the mole will be defined by a fixed value of the Avogadro constant and the kilogram by a fixed value of the Planck constant. The X-ray-crystal-density (XRCD) method has been used for the determination of these fundamental constants by counting the number of atoms in 28Si-enriched spheres. Thus, silicon spheres will – after the redefinition – be used to realize the definitions of the mole and the kilogram. This is possible by SI-traceable measurements of lattice parameter, isotopic composition, volume, and surface properties, yielding a relative standard uncertainty below 2⋅10−8. Whereas this high accuracy is only reached with isotopically enriched silicon, it is also planned to use natural silicon spheres on a slightly lower level of accuracy. The future definitions will allow also new realization methods using silicon, in particular for small mass values.RésuméDe nouvelles définitions des unités de quantité de matière (la mole) et de masse (le kilogramme) entreront vraisemblablement en vigueur lors de la Journée mondiale de la métrologie de 2019. Dans le Système international révisé, la mole sera définie par une valeur fixe de la...

Source: Comptes Rendus Physique - January 18, 2019 Category: Physics Source Type: research