Toroidal collective motions in atomic nuclei

The thesis treats one of the types of collective motion. Using the multipole parametrization for the charge and current, introduced by Dubovik and Cheshkov, the toroidal multipoles are extracted from the expansion of the transverse part of the current density. This new class of electromagnetic multipoles is associated with poloidal flows from a macroscopic point of view. 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. Next we study the spin-dependent collective excitations with toroidal electromagnetic structure by means of the Generalized Goldhaber-Teller model with emphasis on the 1- spin-flip mode and its excitation in spherical nuclei by inelastic electron scattering. In the second part of the thesis 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 multiple we use the back scattering 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. (author) 21 figs., 1 tab., 181 refs