Pre-equilibrium components of the fluctuation cross section

It is shown that the fluctuation cross section for the generalized-exciton or nested-doorway model can be obtained explicitly and exactly in the limit that doorways of successive classes have very different widths, GAMMA/sub n/ >> GAMMA/sub n/+1 and that the doorways of a given class are overlapping, GAMMA/sub n/>D/sub n/. The result is given in terms of experimentally observable quantities, and explicitly separates the compound and precompound contributions. It contains the results of previous, more specialized, models as limiting cases.