Toroidal Collective Motions in the Atomic Nucleus

The work deals with one of the topics of collective motion. In the frame of Nuclear Fluid Dynamics, a model which portrays the nuclear matter as a quantum elastic body, the torus-like motions and their associated energies are computed using the thirteen moment approximation. Such excitations correspond to the Hill vortex known from classical Hydrodynamics. There are also calculated the nonvanishing contributions of transverse electric form factors and differential cross sections in the electroexcitation of these collective modes, which are purely toroidal. The spin-dependent collective excitations, with toroidal electromagnetic structure, are studied by means of the Generalized Goldhaber-Teller model, with emphasize on the 1− spin-flip mode and its excitation in spherical nuclei by inelastic electron scattering. We discuss the importance of toroidal contributions in the inclusive electron scattering (e, e′) and exclusive coincidence electron scattering (e, e′γ). In order to extract the toroidal multipole, we use the backscattering angles in the first mentioned reaction, and the separation of the longitudinal/transverse interference in the second case. The introduction of a quantity which accounts for the deviations from the Siegert theorem, shows the importance of toroidal quadrupole transitions at high-momentum transfer. Another important result concerns the dependence of the intensity of toroidal effects on the nuclear vorticity.