A Global Fitting Method with the R-Matrix code RAC

This report introduces the evaluation method RAC-CERNGEPLIS and the results obtained for the project "R-matrix Codes for harged-particle Induced Reactions in the Resolved Resonance Region" that is coordinated by the Nuclear Data Section. In fact, this method has been used before in the evaluation of the compound systems n+6Li and n+10B, for the IAEA Neutron Standards (2006 and 2017 release). The main characteristics of the RAC code are that i) the eliminated channel width is included in the R-matrix algorithm and ii) the Generalized-Least Square method is used in the fitting procedure. In this report we discuss different approaches to R-Matrix fitting that are used in nuclear data evaluation. Practice shows that the RAC-CERNGEPLIS method is a reasonable, useful and powerful tool for evaluation of nuclear data.