Superdeformation, hyperdeformation and clustering in the actinide region

Excited states in the second minimum of ²⁴⁰Pu were populated by the ²³⁸U(α,2n) reaction at E_α=25 MeV. Conversion electrons from electromagnetic transitions preceding the fission of the 3.7 ns ^240fPu shape isomer have been measured. In a combined analysis of e^- and high resolution γ-ray spectroscopy data previously established octupole bands could be studied in more detail. In order to study higher lying states in the second and third minimum the ²³⁹Pu(d,pf)²⁴⁰Pu, and the ²³³U(d,pf)²³⁴U reactions have been studied with high energy resolution. The observed fission resonances were described as members of rotational bands with rotational parameters characteristic to super- and hyperdeformed nuclear shapes. The level density of the most strongly excited states has been compared to the prediction of the back-shifted Fermi-gas formula and the energy of the ground state in third minimum has been estimated for the first time in ²³⁴U. The fission fragment mass distribution of the hyperdeformed states in ²³⁶U has also been measured. The width of the mass distribution, coincident with the hyperdeformed bands, is significantly smaller than the ones obtained in coincidence with background regions below and above the resonances, which suggests a pear-shaped di-nuclear configuration of ²³⁶U in the third well of the potential barrier.