Abstract
The mechanism of the distribution of an isobaric analogue resonance over its fine structure peaks is studied in the frame of the shell-model theory of nuclear reactions. A two-channel model is constructed, where the isobaric analogue doorway state is dominated by the entrance proton channel which, in turn, is coupled to the outgoing neutron channel only via complicated shell-model states. The energy averages of the differential elastic scattering, total and reaction cross sections are calculated. It is shown that these averages do not display the same resonance energies and widths, unless the background of the (p, n) cross section reaches its maximum value. This holds in spite of the fact that the diagonal and off-diagonal S-matrix elements have the same poles. The elastic, scattering and total cross sections in the absence of the isobaric analogue resonance are studied from a microscopic point of view and the connection with the phenomenological optical-model treatment is given. The extraction of the spectroscopic factor from the experimental data is discussed. The fluctuations of the differential elastic scattering cross section around its average are investigated. The distribution of the fine structure resonance parameters is derived for overlapping as well as isolated peaks; the results are compared with the experimental data obtained at Duke University for the reaction 40Ar(p, p)40Ar.
Published Version
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