Overview of recent theory advances in fission yields

The theory of fission dynamics is currently experiencing a multitude of significant advances.  The present talk gives an overview of the most recent ones, with a view towards the calculation of fission fragment yields.

Among the microscopic approaches, the time-dependent density functional approach with pairing has now become sufficiently tractable to allow extensive dynamical calculations to be carried out and a variety of important quantities have been extracted, including the resulting fragment mass distributions as well as the excitations and kinetic energies of the fragments.  Spontaneous fission has also been addressed in various ways.  Moreover, it has become possible to use microscopic calculations to test some of the key assumptions made in the transport treatments; in particular, it was found that the dissipation is indeed very strong, lending support to the idealization of overdamped shape evolution.

Important advances have been made in the transport treatment of nuclear shape dynamics by invoking more microscopic information.  In particular, the use of microscopically calculated shape-dependent level densities to guide the stochastic evolution has established a consistent framework for treating the dependence on energy and angular-momentum because the gradual disappearance of shell and pairing effects are automatically included.  Notably, the large pairing correlations in the fission barrier region may cause the resulting fragment yields to exhibit a non-monotonic energy dependence.  Furthermore, use of the microscopic level densities of the individual nascent fragments as a basis for distributing the available excitation energy at scission leads to a reasonably good reproduction of the fragment mass dependence of the neutron multiplicity.