Measurement of the neutron induced fission of 245Cm in the resolved resonance region and its resonance analysis

In order to improve the prediction of heavy actinide concentration in reactor fuel elements and to study the reduction of the long-term nuclear waste radiotoxicity by using transmutation, cross sections for neutron induced reactions are highly required by nuclear industry for many minor actinides. In this context, a new measurement of the Cm-245(n,f) cross section has been performed at the GELINA neutron facility of the Institute for Reference Materials and Measurements (IRMM) in Gee], Belgium. This measurement was motivated by the fact that in the thermal region a strong dispersion between measurements is observed and in the resolved resonance region, only a few old measurements exist with in some cases a poor energy resolution. The energy of the neutrons is determined applying the time of flight method using a flight path length of about 9 m. In the present work, the incident neutron energy covers the resolved and unresolved resonance regions up to a few keV. A highly enriched Cm-245 sample (98.48%) was mounted back-to-back with a B-10 sample in the centre of a vacuum chamber together with two surface barrier detectors positioned outside the neutron beam. One detector measured the B-10(n,alpha)Li-7 reaction products for the neutron flux determination, while the second one registered the Cm-245(n,f) fragments. In this way, the neutron flux can be determined simultaneously with the fission fragments. A control measurement has been performed replacing the Cm-245 sample with a U-235 sample in order to check that the well-known U-235(n,f) cross section can be reproduced. In comparison with previous Cm-245 fission cross section measurements, our results show a nice improvement of the energy resolution, in particular below 20 eV. A new set of resonance parameters is determined using the evaluation code CONRAD which was recently developed by CEA-Cadarache.