Energy splitting between the first two quasi-particle states in $^230$Pa in comparison with the isotone $^229$Th

Abstract

Excited states of the odd-odd isotope 230Pa have been identified by means of the one-neutron transfer reaction 231Pa(d_s13_s178594_s19,_s13_s178201_s19t)230Pa at a beam energy of 22 MeV. The ground state of 230Pa is assigned to be a 2- state. A sequence of four rotational states is measured on top of the ground state up to spin values of 6_s13_s178463_s19. The band head of the first excited rotational band has an excitation energy of 48 keV, the corresponding rotational band is observed up to a spin value of 5_s13_s178463_s19. Based on the distribution of the strength among the low-lying states, the Nilsson configuration 1/2[530_s163/2[631 is considered the most probable configuration of the ground state, leaving 1/2[530-5/2[633 for the second excited band. The energy difference between the band heads of these two bands is compared to similar states in other N=139 isotones, especially the directly neighboring odd-mass isotone 229Th. Here the two neutron orbitals 5/2[633 and 3/2[631 cause an extremely low-lying isomeric state.