Département de Physique Nucléaire

A complete description of the fission process still represents a challenge, despite the recent progress based on time-dependent Hartree-Fock models. Statistical models provide a tool to describe fission probabilities at excitation energies around the fission barrier. This approach is justified because, under such conditions, statistical times dominate over the typical time scales for the coupling between intrinsic and collective degrees of freedom (~10^-21s). At high excitation energies, pre- and post-scission particle emission and fission probabilities indicate that simple statistical approaches are not valid and models, describing the dynamics of the process, are required. These models are based on transport equations, e.g. Fokker-Planck or Langevin [1], where the main ingredients are the potential landscape and the dissipation and inertia tensors. The dissipation parameter is particularly interesting because it quantifies the magnitude of the coupling between collective and intrinsic degrees of freedom in fission.

In this talk, I will summarize the main experimental advance in the investigation of fission during last decade at GSI, describing the SOFIA experiment and the results obtained for proton-induced fission reactions on ²⁰⁸Pb at high excitation energies where dissipative effects should manifest in a clear way. The SOFIA setup, together with the inverse-kinematics technique, are used for the first time to measure in coincidence the mass and atomic number of the two fission fragments with good resolution [2], defining new experimental observables sensitive to the dynamics of the fission process. These observables are used to investigate the temperature and deformation dependences of the dissipation parameter [3,4]. Finally, I will present the future perspectives to investigate the fission dynamics at FAIR using quasi-free (p,2p) reactions.

[1] Y. Abe et al., Phys. Rep. 275, 49 (1996)

[2] J.L. Rodriguez-Sanchez et al., Phys. Rev. C 91, 064616 (2015)

[3] J.L. Rodriguez-Sanchez et al., Phys. Rev. C 92, 044612 (2015)

[4] J.L. Rodriguez-Sanchez et al., Phys. Rev. C 94, 061601(R) (2016)