The Precise Determination of Loschmidt’s Number (Avogadro Constant) as a Step towards a Redefinition of the SI Unit of Mass

  • Peter Becker


The paper summarises the activities of several national metrological institutes in replacing the kilogram artefact by the mass of a certain number of silicon atoms. Defining the unit of mass by such an atomic procedure requires a very accurate determination of the Avogadro constant, N A, with a relative uncertainty of better than 5 × 10−8. At present the most limiting factors are the purity of the silicon material, the measurement of isotopic abundances and the content of impurities and vacancies varying from sample to sample, and the realization of exact density standards. Recently, several improvements in molar mass and density determination have been made, so a further reduction of the relative uncertainty, approaching 10−7, may be expected in the near future. Beyond this point, new experimental methods are needed.


Relative Uncertainty Silicon Isotope Avogadro Constant Silicon Lattice Regular Lattice Site 
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Copyright information

© Springer Science+Business Media New York 1997

Authors and Affiliations

  • Peter Becker
    • 1
  1. 1.Physikalisch-Technische BundesanstaltBraunschweigGermany

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