A versatile R-matrix module including alternative parametrizations

The evaluation of nuclear reaction data within the resolved resonance regime relies on phenomeno-logical R-matrix analyses. In absence of quantitatively reliable microscopic models phenomenological R-matrix manages to reproduce experiment data at high accuracy especially in the resolved resonance regime with a limited number of parameters while unitarity constraints and sum rules are automatically met. However, due to non-trivial mapping between fitting parameters and observables as well as interference effects, standard R-matrix parameters only loosely correlate with observed resonance structures in cross sections making the fitting process challenging. Elegant alternative parametrizations have been introduced by Brune [1] and recently by Park [2] to enforce the agreement between R-matrix parameters and observed resonance positions, thus simplifying the fitting process. In this contribution the alternative parametrizations are compared as well as the successful implementation of Park’s parametrization into the R-matrix module of GECCCOS [3] is demonstrated on first examples.