Neutron-induced fission cross sections measurements at n_TOF

The neutron-induced fission cross sections of 233 U, 234 U, 235 U, 238 U, 232 Th, 237 Np, 209 Bi, nat Pb have been measured at the n TOF facility at CERN over 9 orders of magnitude in neutron energy using 235 Ua s a reference. Parallel Plate Avalanche Counters were used to detect both fission fragments in coincidence, thus efficiently discriminating fissions from other reactions. Data benefit from the remarkable energy resolution of the n TOF facility. They are found in overall good agreement with databases and previous measurements, but some clear discrepancies can be put in evidence. These data are the first full coverage of the high-energy region (up to 1GeV). 1 Motivations Although the neutron-induced fission from some actinides like 235 U and 238 U has been extensively measured in the thermal and epithermal region up to a few MeV due to their key role in nuclear power, many nuclei that are important for the fuel cy- cle or for future reactors such as thorium-based reactors are not so well known. Furthermore, at higher energies, measurements are less numerous and beyond a few MeV they become scarce at best. The design of fast reactors requires precise knowledge of the nuclei behavior in the MeV region, and the design of Accelerator Driven System (ADS) extends such requirements to a few tens of MeV due to the very hard neutron spectra created by the ADS spallation source. In order to design such spallation sources, precise information about their constitutive material (lead and bismuth) are also required. In a more fundamental point of view, it is well know that in the few tens of MeV energy region, fission reactions are not necessarily isotropic; but measurements of these phenom- enons are very scarce and concern only a very few nuclei. Also, the transition from the compound nucleus regime toward the spallation regime has never been properly measured with neutrons, and the modeling of nuclear reactions could greatly benefit from the comparison of such neutron-induced reactions with the more well-known proton-induced reactions.