Strongly damped nuclear collisions: Zero or first sound?

Abstract

The relaxation of the collective quadrupole motion in the initial stage of a central heavy ion collision at beam energies ${E}_{\mathrm{lab}}=5$--20 $A\mathrm{MeV}$ is studied within a microscopic kinetic transport model. The damping rate is shown to be a nonmonotonic function of ${E}_{\mathrm{lab}}$ for a given pair of colliding nuclei. This fact is interpreted as a manifestation of the zero-to-first sound transition in a finite nuclear system.