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

Excited states of the odd-odd isotope Pa-230 have been identified by means of the one-neutron transfer reaction Pa-231((d) over right arrow ,t)Pa-230 at a beam energy of 22 MeV. The ground state of Pa-230 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 6h. The band head of the first excited rotational band has an excitation energy of 48 key, the corresponding rotational band is observed up to a spin value of 5h. 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 Th-229. Here the two neutron orbitals 5/2[633](n) and 3/2[631](n) cause an extremely low-lying isomeric state. (C) 2012 Elsevier B.V. All rights reserved