New measurement of ${}^{50}$Cr and ${}^{53}$Cr (n,$\gamma$) cross sections at n_TOF: a call for chromium nuclear data revision

Abstract

${}^{50}$Cr and ${}^{53}$Cr are very relevant in criticality safety benchmarks related to nuclear reactors. The discrepancies of up to 30% between the neutron capture cross section evaluations have an important effect on the $k_{eff}$ and $k_{\infty }$ in criticality benchmarks particularly sensitive to chromium. In this work, the ${}^{50,53}$Cr(n,$\gamma$) cross sections are to be determined between 1 and 100 keV with an 8-10% accuracy following the requirements of the NEA High Priority Request List (HPRL) to solve the current discrepancies. We have measured these reactions by the time-of-flight technique at the EAR1 experimental area of the n_TOF facility, using an array of four C${}_6$D${}_6$ detectors with very low neutron sensitivity. The highly-enriched samples used are significantly thinner than in previous measurements, thus minimizing the multiple-scattering effects. We have produced, and analysed with the R-matrix analysis code SAMMY, capture yields featuring 33 resonances of ${}^{50}$Cr and 51 of ${}^{53}$Cr with an accuracy between 5% and 9%, hence fulfilling the requirements made by the NEA. The differential and integral cross sections have been compared to previous data and evaluations. The new measured ${}^{50,53}$Cr(n,$\gamma$) cross sections provide a valuable input for upcoming evaluations, which are deemed necessary given that the results presented herein do not support the increase in both cross sections proposed in the recent INDEN evaluation.

References in corpus (5)

• GEANT4 simulation of the neutron background of the C${}_6$D${}_6$ set-up for capture studies at n_TOF
• Design of the third-generation lead-based neutron spallation target for the neutron time-of-flight facility at CERN
• Design development and implementation of an irradiation station at the neutron time-of-flight facility at CERN
• HPRL -- International cooperation to identify and monitor priority nuclear data needs for nuclear applications
• Newly Evaluated Neutron Reaction Data on Chromium Isotopes