Fully microscopic scission-point model to predict fission fragment observables

We present an upgraded version of the SPY model, called SPY2 for version 2 of the scission point yield, toestimate mainly the yields and the kinetic energy distributions of fission fragments: The theoretical frameworkis similar to our previous version, i.e. a statistical scission point model, but this version is based on fullymicroscopic nuclear ingredients describing the fragments properties at the scission point. These include the staticproperties of some 7000 nuclei at 120 axial quadrupole deformations, such as binding energies, proton densities,single-particle level schemes, and states densities, coherently calculated within the constrained Hartree-Fock-Bogoliubov model on the basis of the Skyrme BSk27 interaction. The use of microscopic ingredients has beenextended to the proton density distribution and the nuclear states densities. Considering realistic proton densitiesof fragments allows us to improve the definition of the scission point as well as the prediction of the kineticenergy distribution and to link the kinetic energy to the diffuseness of the fragments’ proton density. Newmicroscopic nuclear states densities improve the general coherence of the model, in particular regarding theinclusion of the odd-even pairing effect. In this updated SPY2 version, the calculation of the fission yieldsand kinetic energy distributions is significantly improved and found to be in relatively good agreement withexperiments, at least qualitatively. A detailed study is performed for three well known fissioning systems, namely,thermal neutron induced fission of 235U and 239Pu and spontaneous fission of 252Cf. A systematic analysis of thefission mode as well as mean fragments deformation and total kinetic energies has been performed for some2000 fissioning nuclei with 78<Z