The threshold photodisintegration of ${\mathrm{Pb}}^{208}$ and the thermal-neutron capture by ${\mathrm{Pb}}^{207}$ is considered. It is shown that the magnitude of the thermal capture cross section and the asymmetry of the resonance observed in the ($\gamma ,n$) reaction at 41 ke V above threshold may be explained by extrapolating the giant resonance amplitude and the amplitude of a subthreshold resonance into the appropriate energy domains. It is found that the direct (optical) processes are small compared with the effects of the "resonance tails."

• Received 24 June 1970

DOI:https://doi.org/10.1103/PhysRevC.2.1809