Measurement of the 235U(n,f) cross section relative to the 6Li(n,t) and 10B(n,alpha) standards from thermal to 170 keV neutron energy range at n_TOF
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Amaducci, S., Cosentino, L., Barbagallo, M., Colonna, N., Mengoni, A., Massimi, C., ... & Audouin, L. (2019). Measurement of the 235U (n, f) cross section relative to the 6Li (n, t) and 10B (n, $\alpha $) standards from thermal to 170 keV neutron energy range at n_TOF. The European Physical Journal A, 55(7), 120.
SponsorshipThis research was partially funded by the European Atomic Energy Community (Euratom) Seventh Framework Programme No. FP7/2007-2011 under Project CHANDA (Grant No. 605203). We also acknowledge the support of the Narodowe Centrum Nauki (NCN), under Grant No. UMO- 2016/22/M/ST2/00183; the Spanish Ministerio de Ciencia e Innovaci`on under grants FPA2014-52823-C2-1-P, FPA2017- 83946-C2-1-P and the program Severo Ochoa (SEV-2014- 0398); the Croatian Science Foundation under the project IP- 2018-01-8570.
The 235U(n,f) cross section was measured in a wide energy range at n_TOF relative to 6Li(n,t) and 10B(n,alpha), with high resolution and in a wide energy range, with a setup based on a stack of six samples and six silicon detectors placed in the neutron beam. This allowed us to make a direct comparison of the reaction yields under the same experimental conditions, and taking into account the forward/backward emission asymmetry. A hint of an anomaly in the 10÷30 keV neutron energy range had been previously observed in other experiments, indicating a cross section systematically lower by several percent relative to major evaluations. The present results indicate that the evaluated cross section in the 9÷18 keV neutron energy range is indeed overestimated, both in the recent updates of ENDF/B-VIII.0 and of the IAEA reference data. Furthermore, these new high-resolution data confirm the existence of resonance-like structures in the keV neutron energy region. The new, high accuracy results here reported may lead to a reduction of the uncertainty in the 1÷100 keV neutron energy region. Finally, the present data provide additional confidence on the recently re-evaluated cross section integral between 7.8 and 11 eV.