Prompt (n, /spl gamma/)-spectrometry for the isotopical analysis of silicon crystals for the Avogadro-project

The aim of the Avogadro-project is to replace the kilogram artefact by a high purity, perfect single crystal of natural silicon. Therefore, the isotopical compositon and the impurities of the single crystals have to be known with highest possible accuracy. The only method to achieve all this information without destruction of the massive samples is the prompt (n, /spl gamma/)-spectrometry. This method involves the analysis of the prompt emitted /spl gamma/-rays according to their energy and intensity after thermal neutron capture. The prompt /spl gamma/-energy ranges up to 12 MeV and is used to identify all the impurities, while the intensity of the prompt /spl gamma/-rays results in the abundances of the isotopes.