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

Abstract

The 235 U(n, f) cross section was measured at n TOF relative to 6 Li(n, t) and 10 B(n, α), with high resolution (L = 183.49(2) m) and in a wide energy range (25 meV-170 keV) with 1.5% systematic uncertainty, making use of a stack of six samples and six silicon detectors placed in the neutron beam. This allowed us to make a direct comparison of the yields of the 235 U(n, f) and of the two reference reactions 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 cross section in the 9-18 keV neutron energy range is indeed overestimated by almost 5% in the recently released evaluated data files ENDF/B-VIII.0 and JEFF3.3, as a consequence of a 7% overestimate in a single GMA node in the IAEA reference file. Furthermore, these new high-resolution data confirm the existence of resonance-like structures in the keV neutron energy region. The results here reported may lead to a reduction of the uncertainty in the 1-100 keV neutron energy region. Finally, from the present data, a value of 249.7 ± 1.4(stat) ± 0.94(syst) b · eV has been extracted for the cross section integral between 7.8 and 11 eV, confirming the value of 247.5±3 b · eV recently established as a standard.

Measurement of the α ratio and (n,γ) cross section of U235Balibrea1, Cembranos2, Cano‐Ott3 et al. 2020Phys. Rev. CSelf Cite4000View full textAdd to dashboardCite

“…4. Recent fission measurements at n_TOF show a similar level of agreement [48]. The fission cross section obtained in this work is also compared with other evaluations in Sec.…”

The gamma and neutron monitor counters for the MICADO project

“…However, even considering the total neutron flux on the detectors, a life longer than hundreds of years is to be foreseen under these conditions. Indeed, as observed in reference [16], similar detectors were exposed to a fast neutron fluence of 3•10 10 /cm 2 without appreciable changes in their characteristics.…”

SiLiF Neutron Counters to Monitor Nuclear Materials in the MICADO Project

“…However, even considering the total neutron flux on the detectors, that is about 11 n/cm 2 /s from the simulation, a life longer than many hundreds of years is to be foreseen under these conditions. Indeed, as observed in reference [ 26 ], similar detectors were exposed to a fast neutron fluence of 3 × 10 10 /cm 2 without appreciable changes in their characteristics.…”