Fast rabbit measurements: determination of the neutron flux inside the TRIGA core at critical

This report presents the results of measurements carried out during weeks 28 and 29 of year 2004. They concern the determination of the neutron flux inside the TRIGA core at a critical configuration with a reactor power of 10 Watt. For that purpose, the well-known activation technique was used. A pneumatic fast rabbit device was settled down inside the reactor hall in order to send gold and indium samples into the reactor. Those samples were irradiated with and without cadmium covers. Thermal and epithermal neutron fluxes were extracted from the yields of γ-rays emitted by irradiated samples. Fast neutron flux components were roughly estimated from the activation of the Al shuttle material. An overall quantitative agreement is observed between Au and In results. Due to its higher neutron capture cross-section and to its shorter half-life, In allows performing measurements more rapidly and with higher statistics than Au does. Since neutron fluxes are expected to be lower for subcritical configurations, the use of In samples will be recommended for experiments in subcritical configurations. (A.C.)