Partial γ-ray production cross sections and the total radiative thermal-neutron capture cross section for the Re185(n,γ)Re186 reaction were measured using the Prompt Gamma Activation Analysis facility at the Budapest Research Reactor with an enriched Re185 target. The Re186 cross sections were standardized using well-known Cl35(n,γ)Cl36 cross sections from irradiation of a stoichiometric natReCl3 target. The resulting cross sections for transitions feeding the Re186 ground state from low-lying levels below a cutoff energy of Ec=746keV were combined with a modeled probability of ground-state feeding from levels above Ec to arrive at a total cross section of σ0=111(6)b for radiative thermal-neutron capture on Re185. A comparison of modeled discrete-level populations with measured transition intensities led to proposed revisions for seven tentative spin-parity assignments in the adopted level scheme for Re186. Additionally, 102 primary γ rays were measured, including 50 previously unknown. A neutron-separation energy of Sn=6179.59(5)keV was determined from a global least-squares fit of the measured γ-ray energies to the known Re186 decay scheme. The total capture cross section and separation energy results are comparable to earlier measurements of these values.

The neutron-capture reaction is fundamental for identifying and analyzing the γ-ray spectrum from an unknown assembly because it provides unambiguous information on the neutron-absorbing isotopes. Nondestructive-assay applications may exploit this phenomenon passively, for example, in the presence of spontaneous-fission neutrons, or actively where an external neutron source is used as a probe. There are known gaps in the Evaluated Nuclear Data File libraries corresponding to neutron-capture γ-ray data that otherwise limit transport-modeling applications. In this work, we describe how new thermal neutron-capture data are being used to improve information in the neutron-data libraries for isotopes relevant to nonproliferation applications. We address this problem by providing new experimentally-deduced partial and total neutron-capture reaction cross sections and then evaluate these data by comparison with statistical-model calculations.