Indirect determination of neutron capture cross sections on spherical and near-spherical nuclei using the surrogate method

Abstract

The ${}^{92}$Mo($n,\ensuremath{\gamma}$) cross section was obtained using both the absolute surrogate approach and surrogate ratio method (SRM), relative to the ${}^{94}$Mo($n,\ensuremath{\gamma}$) cross section, in an equivalent neutron energy range of 80 to 890 keV. Excited ${}^{93}$Mo and ${}^{95}$Mo nuclei were populated using the ${}^{92}$Mo($d,p$) and ${}^{94}$Mo($d,p$) reactions, respectively. Both discrete and statistical tagging approaches were employed to identify the $\ensuremath{\gamma}$-decay channel and were examined in terms of their sensitivity to the initial angular momentum population distribution. The absolute surrogate ${}^{92}$Mo($n,\ensuremath{\gamma}$) cross sections disagree with evaluated neutron capture cross section data by as much as a factor of 4, whereas the results obtained using the SRM trend more favorably with the evaluated result. Experimental results suggest that discrete and statistical tagging approaches may sample different contributions of the $\ensuremath{\gamma}$ cascade for near-spherical nuclei. This work uses the surrogate method in the determination of neutron capture cross sections on spherical and quasispherical nuclei in the mass-90 region and provides a possible pathway to extend the SRM to a broader mass range.