Single-particle states and parity doublets in odd- Z Ac 221 and Pa 225 from α -decay spectroscopy

Low-lying states in the odd-Z isotopes Ac13289221 and Pa13491225 have been studied using α-particle and αγ-coincidence spectroscopy in the Pa225→Ac221→Fr217 decay chain. Ground-state spin and parity assignments of Iπ = 5/2- are proposed for both Ac221 and Pa225, with the odd proton occupying the ω = 5/2 orbital of the quadrupole-octupole deformed shell model in both nuclei. In Ac221, excited states in the bands based on the ω = 5/2 and ω = 3/2 orbitals have been identified, including proposed parity-doublet states. The results suggest that reflection-asymmetric deformation of the ground state persists in the odd-A members of the isotope chains down to N = 132 for Ac and N = 134 for Pa, before reaching the transitional region at N = 130.