The rotational bands in the nuclei 229Pa and 231Pa

Experimental evidence is presented for the similarity between the rotational spectra built on the 1/2-[530] state in Pa-231, where the 3/2- member of the band forms the ground state, and in Pa-229, where this state lies within 20 keV of the ground state. Our findings are in contrast with earlier work invoking octupole deformations in the ground state to account for the different positions of low-lying Nilsson states in the two isotopes.