Nature of isoscalar dipole resonances in heavy nuclei

TL;DR

This paper investigates the nature of isoscalar dipole resonances in heavy spherical nuclei, revealing vortex behavior at low energies and compression at high energies through kinetic model calculations.

Contribution

It provides a detailed analysis of the velocity fields in isoscalar dipole resonances, highlighting the vortex and compression characters and their evolution with excitation energy.

Findings

Low-energy resonance exhibits vortex character.

High-energy resonance shows compression character.

Velocity field shifts inside the nucleus with energy variation.

Abstract

Isoscalar dipole nuclear response reveals the low- and high-energy resonances. The nature of isoscalar dipole resonances in heavy spherical nuclei is studied by using the translation-invariant kinetic model of small oscillations of finite Fermi systems. Calculations of the velocity field at the centroid energy show a pure vortex character of the low-energy isoscalar dipole resonance in spherical nuclei and confirm the anisotropic compression character of the high-energy one. The evolution of the velocity field in dependence on the excitation energy of the nucleus within the resonance width is studied. It is found that the low-energy isoscalar dipole resonance retains a vortex character while with increasing energy this collective excitation also involves compression. The high-energy resonance keeps the compression character with a change in the excitation energy within the resonance width but the compression-expansion region of the velocity field related to this resonance shifts inside the nucleus.