When the energy resolution of a reaction is considerably large compared to the width and spacing of compound nuclear states, but small compared to optical model shape resonances, one observes the well-known intermediate structure resonances. In the case of compound nuclear processes, a dynamical account of intermediate structure resonances exists, where one assumes the existence of a doorway state through which the incident (or the final) state couples to the compound nuclear states. In the case of compound nuclear reactions the incident and the final states are, in general, different and so are the doorway states which lead the incident and the final states to compound nuclear states, the former doorway states being the usual entrance doorway states and the latter the exit doorway states. A new dynamical formalism is developed using a recently proposed nested doorway model, which explains how intermediate structure resonances arise because of these two types of doorway states. In this model the system develops through a series of doorway hallway states before entering the true compound nuclear state. The first stage of the doorway hallway states is the usual entrance doorway and the last stage is the exit doorway. Finally, we present experimental evidence of the occurrence of intermediate structure resonances due to isolated exit doorway states.

• Received 16 September 1985

DOI:https://doi.org/10.1103/PhysRevC.33.471