Dynamics of fission and heavy ion reactions

We discuss recent advances in a unified macroscopic-microscopic description of large-amplitude collective nuclear motion such as occurs in fission and heavy ion reactions. With the goal of finding observable quantities that depend upon the magnitude and mechanism of nuclear dissipation, we consider one-body dissipation and two-body viscosity within the framework of a generalized Fokker-Planck equation for the time-dependence of the distribution function in phase space of collective coordinates and momenta. Proceedings in two separate directions, we first solve the generalized Hamilton equations of motion for the first moments of the distribution function with a new shape parametrization and other technical innovations. This yields the mean translational fissioin-fragment kinetic energy and mass of a third fragment that sometimes forms between the two end fragments, as well as the energy required for fusion in symmetric heavy ion reactions and the mass transfer and capture cross section in asymmetric heavy-ion reactions. In a second direction, we specialize to an inverted-oscillator fission barrier and use Kramers' stationary solution to calculate the mean time from the saddle point to scission for a heavy-ion-induced fission reaction for which experimental information is becoming available. (orig.)