Regularization of scattering calculations at R-matrix poles

Physical quantities of scattering expressed in terms of the R-matrix are not well defined at R-matrix poles. It is shown that these unphysical singularities can be removed and the regularized expressions are obtained. The method is straightforwardly applicable to various scattering theory quantities such as the reactance matrix, the Green function, the cumulative reaction probability and the density of resonance states. (author)