An R-matrix package for coupled-channel problems in nuclear physics

TL;DR

This paper introduces an R-matrix Fortran package designed for solving coupled-channel problems in nuclear physics, featuring efficient calculations, handling of open and closed channels, and support for non-local and long-range potentials.

Contribution

The paper presents a novel Fortran package utilizing Lagrange functions for efficient and stable solutions to coupled-channel nuclear physics problems, including non-local and long-range potentials.

Findings

Provides collision matrices and wave functions for nuclear reactions.

Handles open and closed channels simultaneously without numerical instability.

Includes propagation techniques for long-range potentials.

Abstract

We present an $R$-matrix Fortran package to solve coupled-channel problems in nuclear physics. The basis functions are chosen as Lagrange functions, which permits simple calculations of the matrix elements. The main input are the coupling potentials at some nucleus-nucleus distances, specified by the program. The program provides the collision matrix and, optionally, the associated wave function. The present method deals with open and closed channels simultaneously, without numerical instability associated with closed channels. It can also solve coupled-channel problems for non-local potentials. Long-range potentials can be treated with propagation techniques, which significantly speed up the calculations. We first present an overview of the $R$-matrix theory, and of the Lagrange-mesh method. A description of the package and its installation on a UNIX machine is then provided. Finally, five typical examples are discussed.