Measurement and resonance analysis of the ¹⁶⁵Ho(n,γ) reaction at the CSNS Back-n facility

Accurate neutron capture cross sections are essential for constraining nuclear reaction models and for applications in reactor technology and astrophysical nucleosynthesis. Among potential reference isotopes, holmium-165 exhibits favorable nuclear characteristics but lacks high-precision experimental data in the resolved resonance region. In this work, the neutron capture yield of ¹⁶⁵Ho was measured using the 4πBaF2 Gamma Total Absorption Facility (GTAF) at the Back-streaming White Neutron Beamline (Back-n) of the China Spallation Neutron Source (CSNS). Resonance parameters in the energy range from 1 to 1.0 keV were extracted through Bayesian R-matrix analyses performed with the code SAMMY. For 18 s-wave resonances below 100 eV, the resonance energy ER, neutron width Γn, and radiative width Γγ were determined. The distribution of mean level spacings follows the Wigner–Dyson form with ⟨D0⟩ = 4.53(3) eV, indicating chaotic compound-nucleus behavior, while the reduced neutron widths obey the Porter–Thomas χ2 distribution with one degree of freedom, consistent with a single entrance channel. The mean radiative width for s-wave resonances was ⟨Γγ⟩ = 88.10(89) meV, and the s-wave neutron strength function was determined to be 104S0 = 2.01(1), in excellent agreement with evaluated values in the Atlas of Neutron Resonances and the ENDF/B-VIII.0 library. These results provide an improved experimental foundation for neutron-capture modeling and for refining nuclear data evaluations involving odd-odd systems.