Development of activation foils method for the IFMIF neutron flux characterization

Abstract

This work proposes to use the activation foil method for the neutron spectrum determination in the IFMIF facility. Suitable elements were selected to this end with dosimetry reactions having thresholds and effective cross sections covering the whole IFMIF energy range up to 55 MeV. The available evaluated nuclear data libraries and experimental data were carefully screened to select appropriate dosimetry cross sections with uncertainties as low as possible. For the determination of the neutron spectra from the induced γ-activities the unfolding code SAND-II was applied after having it modified for the use of the selected dosimetry cross sections above 20 MeV. This approach was tested by measuring the white neutron spectrum at the cyclotron of Nuclear Physics Institute (Řež), where neutrons up to 35 MeV energy were generated by a 37 MeV proton beam impinging on a heavy water target. The paper concludes with recommendations for the procedure for determining the neutron energy differential flux in the IFMIF test cell with respect to the size of the dosimetry foils, the irradiation time and the expected induced activities.