MULTI-QUASI-PARTICLE STATES IN THE MASS-180 REGION

Nuclei in the mass-180 region have many high-Omega(2) single-particle levels close to the Fermi energy and are, therefore, prime candidates for high-K isomers. Since both neutron and proton level densities are rather low, one should expect blocking and particle-number fluctuations to be rather important. We have performed good-particle-number calculations and have shown that the simpler blocked BCS theory gives a good approximation to the multi-quasiparticle spectra if the pairing strength is chosen appropriately. This has allowed us to perform a systematic theoretical study of this mass region. Residual spin-spin interactions are shown to be essential in reproducing the energies and even the correct order of known states. Good agreement has been found for Hf-175, Hf-176 and Ta-177, where extensive data already exist. Predictions for new high-K states near the yrast line are made for these nuclei and for W-178.