Low-energy isoscalar dipole response of heavy nuclei within kinetic model

TL;DR

This paper investigates the low-energy isoscalar dipole response in heavy nuclei using a semiclassical kinetic model, revealing three resonance structures with distinct physical origins and a dominant toroidal mode.

Contribution

It introduces a semiclassical Vlasov kinetic model that accurately separates center-of-mass motion and internal excitations in heavy nuclei, providing new insights into low-energy dipole resonances.

Findings

Identification of three resonance structures up to 15 MeV

Vortex (toroidal) character of two resonances

Lowest resonance linked to single-particle excitations

Abstract

The low-energy isoscalar dipole response of heavy spherical nuclei is studied by using a semiclassical model, based on the solution of the linearized Vlasov kinetic equation for finite Fermi systems. In this translation-invariant model the excitations of the center of mass motion are exactly separated from the internal ones. The low-energy dipole strength function displays three resonance structures in the energy region up to 15 MeV. Calculations of the velocity fields associated with the resonance structures at the centroid energies show a vortex (toroidal) character of two overlying resonances, while the origin of the lowest isoscalar dipole resonance structure is related to the dipole single-particle excitations. Its centroid energy is close to the minimum energy of the dipole single-particle spectrum. The main toroidal resonance gives a qualitative description of the low-energy isoscalar dipole resonance observed in heavy spherical nuclei.