Au197(n,γ)Au198Reaction Mechanism

The variation in intensity of 24 $\gamma$ rays emitted in neutron capture near the 4.9-eV resonance in gold was measured as a function of neutron energy. Significant interference was observed in the partial capture cross sections, which was consistent with interference between local resonances provided that a bound level was postulated which contributes 3.5 b to the thermal-capture cross section. With this assumption, no directreaction mechanism is required in the capture process. Capture $\gamma$-ray spectra were also observed in the various resonances for neutron energies $\gamma$ rays were observed in thermalneutron capture, while additional new $\gamma$ rays were observed in resonance capture. The choice of relative signs of the partial-width amplitudes of the 4.9- and 60-eV resonances required to fit the data is inconsistent with the usual assumption of normally distributed width amplitudes.