Determination of the Avogadro Constant: A Contribution to the New Definition of Mass

  1. French College of Metrology
  1. I. Busch1,
  2. S. Valkiers2 and
  3. P. Becker1

Published Online: 3 FEB 2010

DOI: 10.1002/9780470611371.ch12

Transverse Disciplines in Metrology

Transverse Disciplines in Metrology

How to Cite

French College of Metrology (2009) Determination of the Avogadro Constant: A Contribution to the New Definition of Mass, in Transverse Disciplines in Metrology, ISTE, London, UK. doi: 10.1002/9780470611371.ch12

Author Information

  1. 1

    Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany

  2. 2

    Institute for Reference Materials and Measurements, Retieseweg, B-2440 Geel, Belgium

Publication History

  1. Published Online: 3 FEB 2010
  2. Published Print: 1 JAN 2009

ISBN Information

Print ISBN: 9781848210486

Online ISBN: 9780470611371



  • molar mass;
  • isotope enrichment;
  • hydrocarbons;
  • polycrystalline silicon;
  • atomic volume


An improved attempt of several national metrology institutes to replace the present definition of the kilogram with the mass of a certain number of 12C atoms is described. This requires the determination of the Avogadro constant, NA, via the silicon route with a relative uncertainty better than 2ṁ10-8. Previously, the limiting factor is the measurement of the average molar mass. Consequently, a world-wide collaboration has been set up, to produce, approximately, 5 kg of 28Si single-crystal with an enrichment factor greater than 99.985% to be used for an improved determination of NA. The first successful tests of all technological steps (enrichment of SiF4, purification and synthesis of silane, deposition of polycrystalline 28Si, single crystal growth) for the production of high-purity 28Si are reported.