Abstract
New high-K isomers have been populated in Ta and W by bombarding thick targets with pulsed 238U beams at 1600 MeV. The new inelastically excited multi-quasiparticle states include Kpi = 21/2- and 29/2- 3-quasiparticle isomers in 181Ta and Kpi = 7- and (16+) isomers in 186W. The Kpi = (16+) state in 186w has t1/2≥3 ms and extends the 4-quasiparticle isomer systematics beyond the limit accessible with fusion-evaporation reactions, using stable beams and targets, for the first time. In addition, a t1/2≥1 ms 3-quasiparticle isomeric state feeding a strongly coupled rotational band has been populated in Ta by nucleon transfer. The excitation energies of the intrinsic states are compared to predictions of blocked BCS calculations. A different study of high-K states used a radioactive 14C beam at 67 MeV to investigate the high-spin structure of Os. New rotational bands built on multi-quasiparticle states with Kpi = 5-, 7-, 9-, 10+ and 15+ are observed. The first crossing of the ground-state band at I = 14 h, is interpreted as involving a high-K t-band structure and explained using a two-band mixing model. The structure at higher angular momentum is dominated by intrinsic states, that exhibit a dramatic loss of isomerism. Potential-energy-surface calculations, with Lipkin-Nogami pairing, show these configurations to be triaxial, accounting for the breakdown in K conservation. The relation between the K projection and the total angular momentum is investigated for these non-axial states.