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

Excited states of the odd-odd isotope 230Pa have been identified by means of the one-neutron transfer reaction 231Pa(d→, t)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 6ℏ. 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 5ℏ. Based on the distribution of the strength among the low-lying states, the Nilsson configuration 1/2[530]p+3/2[631]n is considered the most probable configuration of the ground state, leaving 1/2[530]p−5/2[633]n 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]n and 3/2[631]n cause an extremely low-lying isomeric state.