Measurement of $^{50}$Cr and $^{53}$Cr neutron capture cross sections for nuclear technology at CERN n_TOF and HiSPANoS

Nuclear energy has been recognized as crucial in terms of decreasing the CO$_2$ emissions due to carbon sources while satisfying the increasing energy demands worldwide. The associated development towards a more efficient and safer nuclear energy requires nuclear data of high quality, serving criticality safety benchmarks to identify and set priorities about those that need to be improved. In this context, because of its significant abundance in stainless steel, chromium plays an important role in some benchmarks focused on structural materials. Indeed, it has been found that current ∼30% discrepancies in the neutron capture cross sections of $^{50}$Cr and $^{53}$Cr have an impact of about 1% on k$_{eff}$ . Such high discrepancy is related to the fact that the old chromium measurements could suffer from neutron-scattering effects, while the most recent one (Guber et al. from 2011) seems to have sample related issues. This was pointed out in the most recent evaluation (INDEN), which proposed an important increase of these cross sections but called for new data to confirm or deny it. For this reason, the Nuclear Energy Agency (NEA) opened an entry in its High Priority Request List (HPRL) to measure the $^{50,53}$Cr (n,$\gamma$) cross sections with an accuracy of 8 to 10% between 1 and 100 keV, with emphasis on the region below 10 keV. This work is dedicated to the measurements carried out as a response to the NEA request. First, a time-of-flight measurement was performed at the n_TOF facility of CERN (Switzerland), in which the capture yield of both isotopes was measured and a new set of resonance parameters has been proposed. In addition, for the first time a neutron activation measurement of $^{50}$Cr was performed at the HiSPANoS facility of CNA (Spain) to determine its MACS at kT = 30 keV. The results from both experiments are in agreement, while the comparison to the evaluations indicates a clear cross section overestimation by 20-40% in the recent INDEN evaluation for both isotopes. When all evaluations are considered, our results are in better agreement with CENDL-3.2, which is the only one not considering the most recent data by Guber et al. (2011). With these findings, the new differential and integral cross sections reported herein should contribute to impulse new evaluation effort and solve the chromium puzzle.