Dynamical evolution of super-heavy systems studied using the x-ray fluorescence technique

Proceeding of INPC 2016 conference; International audience; The dynamical evolution of super-heavy systems on their potential landscape and the possibleexistence of a potential pocket allowing compound nucleus formation can be efficientlyprobed with the X-ray fluorescence process. The latter gives rise to characteristic X-rays,powerful tools to achieve atomic number (Z) identification of the emitting atoms.Furthermore, it provides us with a sensitive clock for nuclear fission (as well as for any otherprocess where a Z modification of the atoms occurs), provided the fission time distributionpresents sizeable components with lifetimes of the same order of magnitude as the lifetimes ofthe electronic vacancies responsible for the atomic fluorescence.The X-ray fluorescence technique has thus been applied in order to get evidence forcompound nucleus formation from long lifetime components in the fission time distributions.Three systems have been studied with projectile energies around 6 MeV/nucleon: 238U + 64Ni,238U + 76Ge and 48Ti + 238U. The first two systems were studied at Ganil using reversekinematics that permitted fission fragment Z identification by ΔE-E technique. For the lastsystem, studied at the Australian National University in direct kinematics, fission fragmentmasses were determined from their relative flight times, whereas their atomic numbers weresimultaneously determined from X-ray fluorescence. For the 3 systems, the fission timedistributions have been probed and, for the last one, the initial N/Z of the fission fragments (Nbeing the number of neutrons) has been determined as a function of the energy dissipation andmass asymmetry.