Generalization of the SPRT Method for the Modeling of the Neutron Cross Sections in the Unresolved Resonance Range

For the modeling of the neutron cross sections, three energy ranges can be distinguished. The resolved resonance range can be interpreted in terms of single-level, multilevel, Reich-Moore, or R-matrix parameters. The unresolved resonance range (URR) is described with the average R-matrix and Hauser-Feshbach formalisms. For the high energies ("continuum"), optical model parameters are used in association with statistical and preequilibrium models. One of the main challenges of such a work is to study the consistency of the average parameters obtained by these different calculations. With the ESTIMA and SPRT methods, we provide a set of parameters for partial s-waves and p-waves (strength functions S_l and effective potential scattering radius R'). However, accurate analysis of the URR domain needs more information than parameters R' and S_l associated with orbital moments l = 0 and l = 1. Using links between the average R-matrix formalism and the optical model calculations, we propose a generalization of the SPRT method for l > 1 and a new description of the URR domain in terms of S_l and R_lJ.