Nuclear structure of Lu178

The Hf179(t,α)178Lu reaction has been studied using beams of 17 MeV tritons from the McMaster University tandem Van de Graaff accelerator. Reaction products were analyzed with a magnetic spectrograph, and the resolution achieved for the alpha spectra was ∼20 keV (FWHM). Two-quasiparticle states in Lu178 involving the 9/2+[624] target neutron coupled with the 7/2+[404], 9/2-[514], and 1/2+[411] proton orbitals were identified. The difference in ground-state (t,α) Q values for Hf178 and Hf179 components of the target, combined with the known masses of Lu177, Hf178, and Hf179, yields an improved value of -50 351±5 keV for the mass excess of Lu178. This result, combined with the two-quasiparticle assignments from the present work, has resolved the long-standing puzzle concerning the character and excitation energy of the well-known 23 min high-spin beta-decaying isomer in Lu178.