Berlin 2001 – scientific programme

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MS: Massenspektrometrie

MS V: HV V

MS V.1: Invited Talk

Friday, April 6, 2001, 15:45–16:15, EB 202

Prompt (n,γ)-measurements for the AVOGADRO project — •Stefan Röttger, Annette Paul, Andreas Zimbal, and Uwe Keyser — Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany

The aim of the AVOGADRO project is to replace the kilogram artifact by a high-purity, perfect single crystal of natural or isotope-enriched silicon. The isotopic composition and the impurities of the silicon crystal must, therefore, be known with highest possible accuracy and precision. The only method to obtain all this information without destruction of the massive samples is prompt (n,γ)-spectrometry. The measurements are performed at a thermal neutron guide of the ILL (Institut Max von Laue Paul Langevin) in Grenoble, France. The spectrometry of γ-radiation emitted by a nucleus promptly after thermal neutron capture allows a highly precise determination of atomic mass differences, as well as the determination of isotope abundances and thus leading to the molar mass. The final aim of the AVOGADRO project is to provide a well specified crystal, which allows a more accurate value of the Avogadro constant to be determined. This constant is one of the key input parameters for the CODATA values of fundamental constants and for a new definition of the unit of mass - the kilogram itself.