Orateur
Description
Fission dynamics from saddle-to-scission, and even beyond, is a non-equilibrium quantum process and its description within a fully quantum many-body framework has been a formidable problem to find its solution in theoretical physics for more than 8 decades now. Within the Time-Dependent Density Functional Theory (TDDFT) extended to superfluid fermion systems, which is a mathematically equivalent formulation of the Schrödinger many-body equation at the one-body level, many questions can now be addressed. It was recently proven within TDDFT framework that the saddle-to-scission dynamics is strongly dissipative, hence the use of nuclear potential energy surface and corresponding collective moments of inertia becomes illegitimate, and only a small number general properties of the nuclear energy density functional are important (nuclear saturation density, surface tension, symmetry energy and to a less extent its density dependence, spin-orbit interaction, pairing, and single-particle level density at the Fermi level, thus only 7 parameters) in order to quite accurately describe the properties of the fission fragments, without any fitting parameters. Apart from that TDDFT reveal that several other assumptions made in many phenomenological approaches are incorrect.
Within a series of recent studies, we have extracted the fully separated fission fragment intrinsic spins and their relative orbital angular momentum, before the emission of neutrons or statistical gammas, without resorting to any assumptions or simplification. Moreover, we have also extracted the triple probability distributions of the fission fragments intrinsic spins and their relative orbital momentum for several actinides, in both spontaneous and induced fission and studied the dependence of these properties, including the excitation energies of the emerging fission fragments on the initial energy of the fission compound nucleus. We were able to characterize various relative fission fragments modes (twisting and tilting, bending and wriggling) and their correlations between fission fragments. We showed that twisting mode is extremely active, and that the bending mode surprisingly favor and almost anti-parallel fission fragment intrinsic spin orientation, at odds with other predictions from phenomenological models so far. Among the many unexpected surprises reveled by the real-time microscopic study of fission dynamics we have shown that the primordial light fission fragment carries more excitation energy, and as a result is “hotter,’’ and that the primordial light fission fragment carries a larger intrinsic spin before the emission of neutrons and statistical gammas. Estimates of fission fragment spin distributions show an increase of the average spin in both fragments with the energy of the compound, with the heavy fragment spin increasing faster.
