Some Spectroscopic Properties of Fine Structures Observed near the 231Pa(n,f) Fission Threshold

The ²³¹Pa 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 ²³²Pa fission barrier. Also, for the first time, narrow fission resonances are observed above 1.3 eV exhibiting an average fission width <Γ_f>_{ob s}=8 μeV.