Low-energy dipole excitations in neon isotopes and N=16 isotones within the quasiparticle random phase approximation and the Gogny force

TL;DR

This paper investigates low-energy dipole excitations in neon isotopes and N=16 isotones using a consistent QRPA approach with the Gogny D1S force, revealing their microscopic structure and isospin nature.

Contribution

It provides a detailed microscopic analysis of low-lying dipole states in neon isotopes and N=16 isotones using a fully consistent QRPA with Gogny D1S, highlighting the role of specific neutron orbits.

Findings

N=16 isotones show similar excitation behavior

Occupation of 2s_1/2 neutron orbit influences transition densities

Some excitations exhibit collective and isoscalar characteristics

Abstract

Low-energy dipole excitations in neon isotopes and N=16 isotones are calculated with a fully consistent axially-symmetric-deformed quasiparticle random phase approximation (QRPA) approach based on Hartree-Fock-Bogolyubov (HFB) states. The same Gogny D1S effective force has been used both in HFB and QRPA calculations. The microscopical structure of these low-lying resonances, as well as the behavior of proton and neutron transition densities, are investigated in order to determine the isoscalar or isovector nature of the excitations. It is found that the N=16 isotones 24O, 26Ne, 28Mg, and 30Si are characterized by a similar behavior. The occupation of the 2s_1/2 neutron orbit turns out to be crucial, leading to nontrivial transition densities and to small but finite collectivity. Some low-lying dipole excitations of 28Ne and 30Ne, characterized by transitions involving the neutron 1d_3/2 state, present a more collective behavior and isoscalar transition densities. A collective proton low-lying excitation is identified in the 18Ne nucleus.