Neutron total and capture cross-section measurement and resolved resonance analysis of Er

Abstract

The neutron total and capture cross sections of ${}^{nat}$Er were measured at the Accurate Neutron-Nucleus Reaction Measurement Instrument beamline in the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex. For the neutron total cross-section measurements, Li-glass detectors were employed to derive the neutron transmission ratio of three ${}^{nat}$Er transmission samples with thicknesses of 1 mm, 0.175 mm and 0.05 mm. The neutron capture cross-section was determined from measurements of 0.025-mm-thick ${}^{nat}$Er samples with NaI(Tl) and Ge spectrometers in separate experiments, since they offer complementary capabilities. Moreover, the capture cross-section of ¹⁶⁷Er was derived below 1 eV, since it accounted for over 95% of the capture events in ${}^{nat}$Er. For the neutron total cross-section, at the thermal energy, the present results align with the JENDL-5, ENDF/B-VIII.0 and JEFF-3.3 evaluated nuclear data, the past experimental results of Danon et al. and the recommended values of Mughabghab. For the capture cross-section, similar consistencies were found for ${}^{nat}$Er and ¹⁶⁷Er, with the present results agreeing within uncertainties with the JENDL-5, ENDF/B-VIII.0 and JEFF-3.3 recommended values, the work of Danon et al. and the evaluation of Mughabghab. In addition, the resolved resonance region up to 65 eV was analyzed using the REFIT code. The resonance parameters of 20 ¹⁶⁷Er resonances, together with one resonance for each ¹⁶⁴Er and ¹⁶⁶Er were determined in a least-square fit using a combination of both capture data and the transmission data from the thicker 1 mm and 0.175 mm samples. The fitting results were found to be highly consistent in-between the four measured data sets, providing convincing experimental data to improve the current knowledge of the resonance region for the Er isotopes in nuclear data libraries, which diverged from the present experimental results in terms of both resonance energy and resonance kernels for most of the resonances above 20 eV.