Hyperdeformed sub-barrier fission resonances observed in 232U

The fission probability of U-232 has been measured using the Pa-231(He-3,df) reaction with an energy resolution of 11 keV in the excitation energy region of E-*=4.0-6.4 MeV. A number of sub-barrier fission resonances have been observed for the first time in the excitation energy range below E-*=4.8 MeV and interpreted as rotational bands with a rotational parameter characteristic to a hyperdeformed nuclear shape (h(2)/2 Theta=1.96 +/- 0.11 keV). The angular distribution of the associated fission fragments was measured to deduce the K value of the rotational bands. The fission barrier parameters of U-232 have been determined by analyzing the overall features of the fission probability. A deep third minimum with an excitation energy of E-III=3.2(2) MeV and rather low inner barrier height of E-A=4.0(3) MeV could be established.