Long-lived isomers in neutron-rich Z=72-76 nuclides

A study of neutron-rich isotopes in the A = 185 region of the nuclear chart has uncovered long-lived (>1 s) isomers in several isotopes of hafnium, tantalum, tungsten, rhenium, and osmium. The region was accessed via the use of projectile fragmentation with the UNILAC-SIS accelerators at GSI. Fragmentation products of Au-197 were passed through the fragment separator (FRS) and injected into the experimental storage ring (ESR), where single-ion identifications could be made. Evidence is presented for isomers in Hf-183,Hf-184,Hf-186, Ta-186,Ta-187, W-186, Re-190,Re-192,Re-194, and Os-195 with excitation energies in the range of 0.1-3.0 MeV. The lightest of these nuclides have well deformed prolate shapes, while the heaviest are transitional and susceptible to shape changes. Their properties are interpreted with the help of multi-quasiparticle and potential-energy-surface calculations.