Search for long lived isomers in the neutron-rich mass 180 region.

Nuclei in the A~ 180 region were populated and investigated in a series of deep-inelastic reactions involving an 11.4 MeV per nucleon 136Xe beam produced by the GSI UNILAC accelerator, impinging on a selection of tantalum, tungsten and rhenium targets. The reaction products were released from both thermal (TIS) and FEBIAD ion sources and subsequently mass-separated using the GSI on-line mass separator. This work concentrates on the observation of gamma rays associated with the decay of the well known Kpi= 37/2--, t1/2 = 51.4 min. isomer in 177Hf. Due to the anomalous half-life characteristics and unexpectedly high yield of this decay, it is interpreted as being fed via the beta-decay of a high-K isomer in 177Lu. By comparing the experimental findings with the results obtained from multi-quasiparticle blocked-BCS-Nilsson calculations (which predict a low-lying state with Kpi = 39/2-- in 177Lu), the proposed decay is suggested to be an energetically favoured Kpi= 39/2-- five-quasiparticle state in 177Lu. A half-life of 7.7+/-3.0 min. is determined for this previously unreported A = 177 beta-decay path, also involving 89-keV and 1003-keV gamma-ray transitions in association with hafnium X-rays. In addition, two previously unreported transitions (2016 and 2114 keV) were assigned to 182Hf as a result of their coincidence with Hf X-rays and the 98 keV 2+ → 0+ decay of that nucleus