Fission properties of very heavy nuclei produced in deep-inelastic collisions

Kinematically complete experiments have been performed on the three-body exit channels in the reactions 7.5 MeV/u 238U on 90Zr, 238U and 248Cm to investigate the fission properties of nuclei with a vanishing liquid-drop fission barrier. Thus far, no evidence was found for true instantaneous three-body break-up of the collision system. Instead, a seemingly sequential fission pattern in the sense of unperturbed fission-fragment kinetic energies (as found before for lighter systems) is observed even for the heaviest elements. However, a considerable broadening of the fragment mass distributions as well as angular distributions incompatible with the usual saddle-point concept are also observed in this region. Possible explanations in terms of non-equilibrium processes or a revision of the equilibrium liquid-drop picture near instability are discussed. (author)