Low-energy radiative-capture reactions within two-cluster coupled-channel description

TL;DR

This paper develops a gauge-independent formalism for low-energy radiative-capture reactions within a two-cluster potential model, using the MCAS approach to accurately describe scattering states and applying it to the 3He(alpha,gamma)7Be reaction.

Contribution

It introduces a generalized Siegert theorem-based operator for photon emission in a two-cluster system, incorporating multichannel scattering and Coulomb effects.

Findings

The formalism accurately reproduces the energy dependence of the 3He(alpha,gamma)7Be cross section.

Calculated S factors slightly overestimate experimental data but show good overall agreement.

The approach provides a gauge-independent, microscopic-consistent method for low-energy radiative capture calculations.

Abstract

The formalism that describes radiative-capture reactions at low energies within an extended two-cluster potential model is presented. Construction of the operator of single-photon emission is based on a generalisation of the Siegert theorem with which the amplitude of the electromagnetic process is constructed in an explicitly gauge-independent way. While the starting point for this construction is a microscopic (single-nucleon) current model, the resulting operator of low-energy photon emission by a two-cluster system is expressed in terms of macroscopic quantities for the clusters and does not depend directly on their intrinsic coordinates and momenta. The multichannel algebraic scattering (MCAS) approach has been used to construct the initial- and final-state wave functions. We present a general expression for the scattering wave function obtained from the MCAS T matrix taking into account inelastic channels and Coulomb distortion. The developed formalism has been tested on the 3He(alpha,gamma)7Be reaction cross section at astrophysical energies. The energy dependence of the evaluated cross section and S factor agrees well with that extracted from measurement though the calculated quantities slightly overestimate data.