Impact of the phonon coupling on the dipole strength and radiative neutron capture

TL;DR

This paper investigates how phonon coupling influences the dipole strength and neutron capture cross sections in Sn isotopes, highlighting the importance of self-consistent microscopic models for astrophysical applications.

Contribution

It introduces a self-consistent microscopic approach including quasiparticle-phonon coupling, improving the description of pygmy-dipole resonance and neutron capture cross sections.

Findings

Phonon coupling significantly enhances the pygmy-dipole resonance.

Self-consistent calculations show increased cross sections for neutron-rich nuclei.

Comparison indicates phonon effects can triple the predicted neutron capture rates.

Abstract

The E1 strength functions and radiative capture cross sections for several compound Sn isotopes, including unstable 132S n and 150S n, have been calculated using the self-consistent microscopic theory. In addition to the standard RPA or QRPA approaches, the method includes the quasiparticle-phonon coupling and the single-particle continuum. The results obtained show that the phonon contribution is very noticeable for the pygmy-dipole resonance, which, as it is known, is important for a description of the radiative neutron capture. The phonon contribution to the pygmy-dipole resonance and to the radiative neutron capture cross sections is increased with the (N-Z) difference growth. For example, in the (0-10) MeV interval the full theory gives 17% of EWSR for 150S n and 2.8% for 124S n, whereas within the continuum QRPA approach we have 5.1% and 1.7%, respectively. These facts indicate an important role of the self-consistent calculations that are of astrophysical interest for neutron-rich nuclei. The comparison with the phenomenological Generalized Lorentzian approach by Kopecky-Uhl has shown that the (Q)RPA approach gives a significant increase in the cross section by a factor of 2 for 132S n and a factor of 10 for 150S n and inclusion of the phonon coupling increases the cross sections for these nuclei even more, by a factor of 2-3.