Giant Resonances: A Comparison between TDHF and Fluid Dynamics in Small Amplitude Vibrations of Spherical Nuclei

Small amplitude vibrations of spherical nuclei are considered in microscopic (RPA) and fluid-dynamical description. Assuming the concentration of transition strength into one collective state, the microscopic result can be brought into close analogy to constrained fluid-dynamical motion. The decisive difference occurs in the contribution of the microscopic kinetic energy to the collective potential energy. It is shown that extension of fluid dynamics to include dynamical distortions of the local Fermi surface is sufficient to reproduce the microscopic results. Numerical examples are given for L = 0 and L = 2 isoscalar modes for a Skyrme-type nucleon-nucleon force.