Generalization of the SPRT method: application to ²⁴²Pu cross sections in the Unresolved Resonance Range

Abstract
The modelling of the neutron cross sections consists in their interpretation in three different energy ranges: the first one is the Resolved Resonance Range (RRR) at low energy, the second is the Unresolved Resonance Range (URR), and the third one concerns the high energies. For this, we generally use the Reich-Moore approximation of the R-Matrix formalism, the average R-Matrix formalism and optical model calculations. 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 and p waves (strength functions, effective potential scattering radius, mean-level spacing and reduced neutron width). But, in order to analyse accurately the URR domain, we need more information than the parameters associated to the orbital moments L = 0 and L = 1. This work describes the link between the average R-Matrix formalism and the optical model, especially concerning the transmission coefficients, total and shape elastic cross sections. Based on these two models, we propose a generalization of the SPRT method for L > 1, and we obtain a new set of parameters for the URR domain in terms of S_LJ and .