Doorway States and Intermediate Structure Phenomena

Abstract
The phenomenon of the distribution of a doorway state over many complicated compound nuclear states, i. e. the formation and properties of a so-called micro-giant resonance, are investigated analytically and numerically by means of a simple model. The distribution of the poles in the complex plane and the distribution of the residues of the S-matrix are obtained numerically and used to calculate the average cross-section. It is shown that the LANE-THOMAS-WIGNER theory applies, except for a possible correction to the shape of the resonance occuring in the cross-section averaged over the energy. This shape need not be describable by a LORENTzian. Estimates of the “spreading width” W and the “total width” W0 are given for particular cases. It is noteworthy that the relationship W0=W+Γ need not be correct even as an order-of-magnitude estimate, where Γ is the decay width of the doorway state.

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