J. Balibrea-Correa, E. Mendoza, E. Griesmayer, E. Jericha, H. Leeb, C. Weiß, -. n_TOF Collaboration et al.:
"Measurement of the α ratio and (n,γ) cross section of 235U from 0.2 to 200 eV at n_TOF";
Physical Review C, 102 (2020), 044615; S. 1 - 18.

Kurzfassung englisch:
We measured the neutron capture-to-fission cross-section ratio (α ratio) and the capture cross section of 235U between 0.2 and 200 eV at the n_TOF facility at CERN. The simultaneous measurement of neutron-induced capture and fission rates was performed by means of the n_TOF BaF2 Total Absorption Calorimeter (TAC), used for detection of γ rays, in combination with a set of micromegas detectors used as fission tagging detectors. The energy dependence of the capture cross section was obtained with help of the 6Li(n,t) standard reaction determining the n_TOF neutron fluence; the well-known integral of the 235U(n,f) cross section between 7.8 and 11 eV was then used for its absolute normalization. The α ratio, obtained with slightly higher statistical fluctuations, was determined directly, without need for any reference cross section. To perform the analysis of this measurement we developed a new methodology to correct the experimentally observed effect that the probabilities of detecting a fission reaction in the TAC and the micromegas detectors are not independent. The results of this work have been used in a new evaluation of 235U performed within the scope of the Collaborative International Evaluated Library Organisation (CIELO) Project, and are consistent with the ENDF/B-VIII.0 and JEFF-3.3 capture cross sections below 4 eV and above 100 eV. However, the measured capture cross section is on average 10% larger between 4 and 100 eV.

Neutron physics; Radiative capture; Radioactive waste; Reactor fuels & coolants; Resonance reactions; Theory, design & simulation of reactors; A >= 220

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