Single-proton states in neutron-rich lutetium isotopes relevant to the 180mTa nucleosynthesis puzzle

The 178,180Hf(t,α)177,179Lu reactions have been studied using beams of 17 MeV tritons from the McMaster University tandem Van de Graaff accelerator. The reaction products were analyzed with a magnetic spectrograph. Measured angular distributions, and the population patterns observed for previously known rotational bands in 177Lu, permitted reliable assignments of the 72+[404], 92−[514], 12+[411], and 52+[402] Nilsson orbitals in 179Lu, nuclide for which no information on excited states was available earlier. Assignments for the 72−[523] and 32+[411] proton hole states have been made in both isotopes. As expected from known changes in the hexadecapole deformation, the 92−[514] band-head energy decreases rapidly towards the 72+[404] ground state with increasing neutron number, and in 179Lu is found at only 35±5 keV. This is consistent with the suggestion that the odd proton in the 180Lu ground state is in the 92−[514] orbital. The single-quasiproton energies for 179Lu from this work are useful for estimating the energies of isomeric excited states in 180Lu, that are of interest for 180mTa nucleosynthesis.