Intermediate structures in the $s$- and $d$-wave elastic and inelastic neutron scattering cross sections of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ are explained on the basis of a doorway state model. A particle-vibrator coupling model is used to calculate the cross sections from which resonance energies and widths of the doorway states are extracted. No adjustable parameters are used in the calculations. Doorway state resonances in both the ${1/2}^{+}$ elastic scattering channel and the ${3/2}^{+}$ elastic and inelastic scattering channels can be accounted for by a ($d_{\frac{5}{2}}\otimes 2^{+}$) doorway state configuration in which a single quasibound $d_{\frac{5}{2}}$ neutron in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ is coupled to the first $2^{+}$ state of the ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ target. The agreement obtained between the calculations and the observed intermediate structure widths as well as the summed compound nucleus fine structure widths is good. Doorway state resonances in the $p$-wave neutron channels which result from ($d_{\frac{5}{2}}\otimes 3^{-}$) configurations are also calculated.

[NUCLEAR REACTIONS ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}+n$; calculated doorway state structure in $\sigma \mathrm{}\left(E\right)\mathrm{} E_n=0-2.2\mathrm{}$ MeV; coupled channels for $s$-,$p$-, $d$-wave neutrons.]

• Received 4 October 1976

DOI:https://doi.org/10.1103/PhysRevC.16.153