Prompt (n, γ)-spectrometry for the isotopic analysis of silicon crystals for the Avogadro project

The aim of the Avogadro Project is to replace the kilogram artifact by a high-purity, perfect single crystal of natural silicon. Therefore, the isotopic composition and the impurities of Si single crystals have to be known to the highest possible accuracy. The only method to obtain all of this information without destruction of the massive samples is by prompt (n, γ)-spectrometry. This method involves the analysis of the prompt emitted γ rays according to their energy and intensity after thermal neutron capture. The prompt γ-ray energy ranges up to 12 MeV and is used to identify all nuclides, while the intensity of the prompt γ rays gives the abundances of the isotopes