One-body dissipation and the super-viscidity of nuclei

This is a study of a type of fluid dynamics dominated by a ''one-body'' dissipation mechanism expected to be relevant for an assembly of particles whose mean free paths are comparable to or larger than the size of the system. Two simple dissipation formulas are derived, one relevant for the process of nuclear fission and the other for nuclear collisions. The resulting predictions, free of adjustable parameters, are compared quantitatively with measured fission-fragment kinetic energies and qualitatively with nucleus--nucleus collision data. The one-body dissipation concept is also tested against classical and quantal computer studies of particles in a deforming potential well. This brings out special effects associated with the symmetries of the well and points to a macroscopic dynamics of nuclear deformations which, except for super-fluidity at very low temperatures, consists of a smooth background dominated by one-body dissipation (''super-viscidity'' of nuclei), on which are superposed modifications due to symmetries and quantization