Photoexcitation of 209Bi and natHg using neutron-capture γ-rays from cobalt

Using neutron-capture γ-rays from cobalt, the ²⁰⁹Bi(γ,γ') and ^natHg(γ,γ') reactions were studied using a 53 cm³ Ge(Li) detector and the reactor facility at the Rhode Island Nuclear Science Center. Resonant scattering was observed at 4.924±0.005 MeV for ^natHg. Resonant scattering was observed at 5.609±0.005 MeV in ²⁰⁹Bi, with an effective cross section of 348±70 mb. The ratio of intensity scattered at 150° to that scattered at 100° was found to be 1.18±0.12 for ²⁰⁹Bi. This is consistent with a dipole transition to a $\text{9}\text{2}$ state but does not eliminate other transitions and spin assignments. No significant inelastic structure was found in the spectra from either sample. The improved energy specification in the present experiments has led to different energy assignments for the resonant states and hence, different incident intensities are producing the observed scattering. These differences lead to higher effective cross sections than those previously reported. Minimum ground state level widths for ²⁰⁹Bi and ^natHg were estimated to be 0.032 eV and 0.43 eV respectively. The need for high-resolution survey data to re-establish systematics is suggested.