Speaker: Joachim A. Maruhn (University of Frankfurt)

Skyrme Hartree-Fock Applied to Nuclear Molecules and Heavy-Ion Collisions

In this work we have investigated a new method for looking at the existence of nuclear molecules.  Based on a newly developed Hartree-Fock code a static Hartree-Fock solution is sought on a three-dimensional grid based on an initialization with cluster wave functions placed in any geometric arrangement.  After initialization the static iterations will lead either to the ground state of the compound system, if the fragments are placed too close together, or to a highly deformed state, if initialization is sufficiently close to such a configuration.  The third alternative is that the fragments will drift further apart, if they are spaced too distantly.  We find that the method appears to be very robust, in the sense that the convergence to a highly deformed state happens for a large number of the initial spacings. Varying the initial configuration systematically, therefore, seems to allow a good judgment on the existence of such exotic states. Employing the Skyrme force SkI3 and in some cases also Sly6, the method was applied to a number of systems and led to highly deformed and possibly molecular states while making the existence of configurations such as a triangle of alpha particles for 12C unlikely.

The time-dependent version of the code was used to reexamine the TDHF description of heavy-ion reactions, which was developped in the late 1970s.  Many qualitative features of such reactions could be understood, but also the energy loss and the fusion cross-section for light and medium-heavy reaction partners was described semi-quantitatively. The advance in computer technologies now makes it possible to do such calculations without many of the restrictions that were practically necessary 30 years ago. The new code that can deal with time-dependent Hartree-Fock in a three-dimensional spatial grid without imposing any symmetries.  It also allows the use of any modern Skyrme force. The first application was devoted to collisions between light deformed nuclei.  The results drastically demonstrate that the initial relative orientation of such nuclei has great importance for what happens in the collision.  As a second initial application we examined collisions near the Coulomb barrier for medium-heavy and heavy systems.  The energy was buried systematically until a reaction set in.  It is shown that the dynamic behavior drastically differs between, for example, a collision of 16O and 48Ca or one between 48Ca and 208Pb:in the former case they reaction is characterized by a very rapid strong surface dynamics, while in the latter one a neck is formed and then the surface appears to remain practically stationary.