Role of Doorway States in Neutron Capture inNb93Resonance

A comparison between the $\gamma$-ray spectra following the capture of $l=0\mathrm{}$ and $l=1\mathrm{}$ neutrons in niobium shows characteristic differences which are not expected with a purely statistical model of compound nucleus decay. The data suggest that the strong $E1\mathrm{}$ $\gamma$ rays are due to particle-hole annihilations across the $Z=50\mathrm{}$ proton shell, and demonstrate the influence of two-particle, one-hole "doorway" states in the neutron capture process.