Interplay of compressional and vortical nuclear currents in overtones of the isoscalar giant dipole resonance

Within a semiclassical nuclear Fermi-fluid dynamic approach, the properties of the isoscalar giant dipole resonance (ISGDR) and the structure of various electromagnetic characteristics associated with the most important states building this resonance are investigated. The apparent puzzling outcome of microscopic predictions that the ISGDR distribution is split into two main broad structures is confirmed within the presented macroscopic approach by the occurrence of a 'low-lying' and a 'high-lying' state, as the first two overtones of the same resonance. Macroscopicaly, they are pictured as a combination of compressional and vortical nuclear flows. The second part of the paper analyzes the electromagnetic structure of the ISGDR relevant to reactions with inelasticly scattered electrons and the relation between the vorticity and the toroidal dipole moment. The relative strengths of the compressional and vortical collective currents are evaluated by means of electron-scattering sum rules