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The resonance structure observed in the "Y(n, n)*@Y total cross section measurements in the range of 0.3-1.2 MeV incident energy was investigated using the generalized R-matrix theory of nuclear reactions and the doorway interpretation of intermediate structure. The energies and wavefunctions of the doorway resonances were calculated in a two-particle and 3p-Ih basis of the shell-model. The model space and the parameters of the model calculation chosen were consistent with other shell model calculations in the mass-90 region. Several strong p-wave doorways with Jn = O+, l+, and 2+ were predicted by the model in the energy range studied. This is due to proximity of p-wave giant resonance. The escape widths [' and the spreading widths [l for these states were evaluated using the model wavefunctions and the R-matrix formalism. The calculated energy dependence of the total cross section shows that most of the predicted doorways are in general qualitative agreement with the observed anamolies with similar relative strength. More significantly, the underlyingp-wave gross structure representing a grand average is of very similar shape in both theory and experiment. As expected in the mass-90 region, the s-and d-wave doorways contribute less significantly to the calculated resonance structure. Optimally Simple Comeciion between the Reaction M,atri.v and the Observables.
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