Photonuclear cross sections for Au197: An update on the gold standard

Cross sections for the Au197(γ,n) reaction are broadly used in nuclear physics as a standard for normalizing photonuclear reaction cross-section data at photon beam energies above approximately 8 MeV. In this paper, we report cross-section measurements for the Au197(γ,n)196Aug+m1 reaction at beam energies from 13 to 31 MeV. Our measurements provide the first cross-section data for this reaction at beam energies above 20 MeV, enabling the use of this reaction as a cross-section standard up to 30 MeV. Also, this work provides first cross-section measurements for the Au197(γ,n)Aum2196 reaction. In addition, we measured cross-section data for the Au197(γ,3n)Au194 reaction, which can be used as a cross-section standard above about 25 MeV. These measurements were performed using a new target activation method that is based on the angle-energy correlation of the laser Compton-scattered photon beams at the High Intensity Gamma-ray Source (HIγS). The technique enables measuring photonuclear reaction cross-sections at several discrete beam energies concurrently via a single irradiation on a stack of different targets. Measurements were carried out by irradiating a stack of concentric-ring targets consisting of Au, TiO2, Zn, Os, and Au (in order of the γ-ray beam direction). Our data for the Au197(γ,n)Aug+m1196 reaction in the energy range of 13 to 20 MeV are in good agreement with existing ones measured using monoenergetic γ-ray beams, but differ from data acquired using a bremsstrahlung γ-ray beam. Also, above 18 MeV, our data for the Au197(γ,n)Aug+m1196 and Au197(γ,n)Aum2196 reactions differ significantly from the most recent TENDL and JENDL evaluations, suggesting a need to update these data libraries. The TENDL evaluation and existing data are consistent with our data for the Au197(γ,3n) reaction, but differ significantly from the JENDL evaluation above 26 MeV.