Low-lying dipole resonance in neutron-rich Ne isotopes

TL;DR

This paper investigates the microscopic structure of low-lying isovector dipole excitations in neutron-rich Ne isotopes using deformed QRPA calculations, revealing specific resonance energies, transition contributions, and deformation effects.

Contribution

It provides a detailed microscopic analysis of low-lying dipole modes in neutron-rich Ne isotopes, highlighting the structure and origin of these excitations with deformation considerations.

Findings

Low-lying resonance in 26Ne at ~8.5 MeV exhausts about 6% of the dipole sum rule.

Resonance involves specific neutron transitions, notably 2s1/2 to 2p3/2 and 2p1/2.

Deformation causes splitting and overlap of resonances in 30Ne.

Abstract

Microscopic structure of the low-lying isovector dipole excitation mode in neutron-rich $^{26,28,30}$Ne is investigated by performing deformed quasiparticle-random-phase-approximation (QRPA) calculations. The particle-hole residual interaction is derived from a Skyrme force through a Landau-Migdal approximation. We have obtained the low-lying resonance in $^{26}$Ne at around 8.5 MeV. It is found that the isovector dipole strength at $E_{x}<10$ MeV exhausts about 6.0% of the classical Thomas-Reiche-Kuhn dipole sum rule. This excitation mode is composed of several QRPA eigenmodes, one is generated by a $\nu(2s^{-1}_{1/2} 2p_{3/2})$ transition dominantly, and the other mostly by a $\nu(2s^{-1}_{1/2} 2p_{1/2})$ transition. The neutron excitations take place outside of the nuclear surface reflecting the spatially extended structure of the $2s_{1/2}$ wave function. In $^{30}$Ne, the deformation splitting of the giant resonance is large, and the low-lying resonance is overlapping with the giant resonance.