Comprehensive Formalism for Nuclear-Reaction Problems. II. Applications—Giant Resonances and Doorway States

Abstract

The formal theory of nuclear reactions introduced in a preceding paper is applied to several phenomena of current interest. Particular attention is given to the derivation of a single-level form for the transition amplitude, the interpretation of this form being dependent on the physical situation involved. Under certain conditions the single-level form is appropriate for the deseription of an isolated resonance; under other conditions it corresponds to a giant resonance. The width of the giant resonance is discussed in detail, in particular the possibility of observing the so-called "spreading" width. The theory is used to describe "doorway" states and their connection with giant resonances. Some clarification of the relationship between earlier alternative approaches to this problem is obtained. The occurrence of statistical fluctuations near a giant resonance is considered and leads to the suggestion that fine structure and gross structure are intimately connected, the actual connection being simple in some cases. Several of these results are illustrated by considering the phenomena of isobaric analog resonances within the framework of the present formalism.