Triple-Humped Fission Barrier and Clusterization in the Actinide Region

The fission probability of ²³⁶U has been measured as a function of the excitation energy with high energy resolution. Rotational band structures have been observed, with moments of inertia corresponding to hyperdeformed nuclear shapes. From the level density of the rotational bands the excitation energy of the ground state in the third minimum was determined. The excitation energy of the lowest hyperdeformed transmission gave an upper limit for the height of the inner fission barrier. The predicted effects of the clusterization in hyperdeformed states have been studied by measuring the mass and total kinetic energy distribution of the fission fragments in case of ²³²Th.