Fully microscopic scission-point model to predict fission fragment observables

Jean-François Lemaitre (Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, Belgium)

Nuclear fission is known to be of fundamental importance in many applications, for example for energy production applications, such as nuclear power reactors or nuclear waste recycling. In astrophysics, nuclear fission plays a significant role during the rapid neutron-capture process (r-process) of stellar nucleosynthesis by recycling the matter during the neutron irradiation occurring in a neutron star merger ejecta [1,2]

The description the nuclear fission is a theoretical challenge because the many-body problem has to be solved with an interaction between nucleons that is known in a phenomenologically way only. In addition of these static considerations there are dynamical effects which leads to the splitting of the nucleus. There are four major aspects that need to be described during the fission process, namely i) the fissioning nucleus formation, ii) the fission barrier penetration and transmission, iii) the fission fragment formation, and iv) the fission fragment de-excitation. Fissioning nucleus can be formed by neutron (neutron-induced fission), gamma capture (photofission), or beta decay (beta-delayed fission). The fission barrier can be crossed by tunnel
effect like in spontaneous fission or be crossed over if the nucleus is sufficiently excited like in neutron/gamma-induced fission. When the barrier is crossed, nucleus can be splitted in many ways with different probabilities, called the fission yields. Finally fission fragments de-excite mainly by neutron and gamma evaporation.

I will present the scission-point model, called SPY [3,4], developed to estimate yields and kinetic energies of the fission fragments, which corresponds to the third step of the fission process. To improve the description of the fissioning system at the scission point, microscopic state densities, proton and neutron distributions as well as potential energy surfaces of each fragments are now considered within the mean-field approach. I will show that these new developments have a significant impact on the predictions of fission yields and fragment
excitation energies. Implications for the r-process nucleosynthesis will be discussed.

[1] S. Goriely et al, Phys. Rev. Lett 111, 242502 (2013)
[2] S. Goriely, Eur. Phys. J. A 51, (2015)
[3] J.-F. Lemaı̂tre et al, Phys. Rev. C 92, 034617 (2015)
[4] J.-F. Lemaı̂tre et al, Phys. Rev. C, to be published (2019)

Practical information:

11h00 GANIL seminar room (105)
Coffee will be served 15mn before