Hyperdeformed sub-barrier fission resonances observed in 232U

The fission probability of 232U has been measured using the 231Pa(3He,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/2π)2/2Θ=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 232U have been determined by analyzing the overall features of the fission probability. A deep third minimum with an excitation energy of EIII=3.2(2) MeV and rather low inner barrier height of EA=4.0(3) MeV could be established.