Hyperdeformed sub-barrier fission resonances observed inU232

Abstract

The fission probability of $^{232}\mathrm{U}$ has been measured using the $^{231}\mathrm{Pa}$($^{3}\mathrm{He}$,df) reaction with an energy resolution of 11 keV in the excitation energy region of ${E}^{*}=4.0\text{\ensuremath{-}}6.4$ 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 ($\ensuremath{\hbar}{}^{2}/2\ensuremath{\Theta}=1.96\ifmmode\pm\else\textpm\fi{}0.11$ 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 $^{232}\mathrm{U}$ have been determined by analyzing the overall features of the fission probability. A deep third minimum with an excitation energy of ${E}_{\mathrm{III}}=3.2(2)$ MeV and rather low inner barrier height of ${E}_{A}=4.0(3)$ MeV could be established.