On collective dynamics in low-energy nucleus-nucleus collisions: nuclear elastoplasticity

Collective nuclear dynamics at velocities small compared to the Fermi velocity is briefly reviewed. For finite collective velocities where the adiabatic approximation is no longer valid, a qualitatively new feature of collective nuclear motion is predicted: elastoplasticity. For finite Fermi systems this dynamical behavior results from a coherent coupling between collective and intrinsic degrees of freedom and subsequent equilibration by residual two-body collisions. Within a non-markovian transport-theoretical approach, the elastic response is described by scaling of the diabatic single-particle wave functions according to the collective deformation, while two-body dissipation is accounted for by a relaxation equation. This dissipative diabatic dynamics ascribes elastoplasticity to unclei and establishes a link between time-dependent Hartree-Fock and Markovian transport theories. Isoscalar giant quadrupole vibrations of nuclei and mass diffusion in nucleus-nucleus collisions are considered as well-established examples for the elastic and plastic limits, respectively, of elastoplasticity. The transition region may be explored in central nucleus-nucleus collisions. Observable effects from the approach phase, like the hindrance of fusion reactions and the diabatic emission of nucleons are discussed. Further signatures of nuclear elastoplasticity are pointed out