Some Spectroscopic Properties of Fine Structures Observed near thePa231(n,f) Fission Threshold

The ${}_{}{}^{231}{}_{}{}^{}\mathrm{Pa}$ neutron-induced fission cross section from 140 to 400 keV was resolved into finer structures. For some of the fractionated vibrational resonances in this energy region, the assignment of spectroscopic parameters may support evidence for an asymmetrically deformed third minimum in the ${}_{}{}^{232}{}_{}{}^{}\mathrm{Pa}$ fission barrier. Also, for the first time, narrow fission resonances are observed above 1.3 eV exhibiting an average fission width ${〈{\Gamma }_f〉}_{\mathrm{ob}\mathrm{}\mathrm{s}}=8\mathrm{}$ μeV.