Measurement of the (236)U(n, f) Cross Section at n_TOF

A precise knowledge of the (236)U neutron-induced fission cross-section is required for the development of accelerator-driven systems and reactors based on the Th-U cycle. The evaluated data presently stored in the nuclear data libraries rely on outdated experimental measurements and show large discrepancies in the energy region between 1 keV and 100 keV. More recent measurements made at LANSCE and GELINA yielded results which are in disagreement with the literature for the resonance region and below 10 eV. In order to improve the present knowledge of the (236)U(n, f) cross-section, a new measurement was performed at the neutron Time-Of-Flight facility n\_TOF at CERN. A Fast Ionization Chamber was used, in which four samples of (236)U and two of (235)U were mounted. The (236)U(n, f) cross-section was determined relative to the standard (235)U(n, f) reaction. The contribution from the (235)U contamination in the samples was subtracted, together with the alpha-particle background. Finally, the data were corrected for dead-time and detection efficiency. The n\_TOF results on the (236)U(n, f) cross-section are reported in the neutron energy region from 200 meV to 2 MeV. The present high-resolution data point to several shortcomings in the current evaluated databases in the sub-threshold region. High accuracy cross-sections, important for applications to fast nuclear reactors as well as for fundamental Nuclear Physics, are also reported here.