Gamma Ray Spectrum from Thermal Neutron Capture on Gadolinium-157

International audienceWe have measured the |$\gamma$|-ray energy spectrum from the thermal neutron capture, |${}^{157}$|Gd|$(n,\gamma)$|⁠, on an enriched |$^{157}$|Gd target (Gd|$_{2}$|O|$_{3}$|⁠) in the energy range from 0.11 MeV up to about 8 MeV. The target was placed inside the germanium spectrometer of the ANNRI detector at J-PARC and exposed to a neutron beam from the Japan Spallation Neutron Source (JSNS). Radioactive sources (⁠|$^{60}$|Co, |$^{137}$|Cs, and |$^{152}$|Eu) and the |$^{35}$|Cl(⁠|$n$|⁠,|$\gamma$|⁠) reaction were used to determine the spectrometer‘s detection efficiency for |$\gamma$| rays at energies from 0.3 to 8.5 MeV. Using a Geant4-based Monte Carlo simulation of the detector and based on our data, we have developed a model to describe the |$\gamma$|-ray spectrum from the thermal |${}^{157}$|Gd(⁠|$n$|⁠,|$\gamma$|⁠) reaction. While we include the strength information of 15 prominent peaks above 5 MeV and associated peaks below 1.6 MeV from our data directly into the model, we rely on the theoretical inputs of nuclear level density and the photon strength function of |${}^{158}$|Gd to describe the continuum |$\gamma$|-ray spectrum from the |${}^{157}$|Gd(⁠|$n$|⁠,|$\gamma$|⁠) reaction. Our model combines these two components. The results of the comparison between the observed |$\gamma$|-ray spectra from the reaction and the model are reported in detail