A number of reaction theories are tested and compared by their application to a simple model of $s$-wave scattering from a two-state nucleus. These theories include the extended $R$-matrix theory of Garside and Tobocman, the $L$-operator formalism of Lane and Robson, and variations of the Brown-de Dominicis theory. We find that the Hüfner-Lemmer version of the Brown-de Dominicis theory gives the best results in the few-level approximation.

• Received 28 September 1970

DOI:https://doi.org/10.1103/PhysRevC.3.1010