Abstract
Using the Experimental Storage Ring (ESR) coupled to the FRagment Separator (FRS) and SIS-UNILAC accelerators, it has been possible to observe new isomers in neutron-rich isotopes with proton numbers 72 ≤ Z ≤ 77. With the ESR set-up in Schottky Mass Spectrometry (SMS) mode, observation of ‘well' cooled ions with lifetimes greater than 1 s is possible. Masses of the observed ion can be measured with a precision down to ~10 keV. Projectile fragmentation of a 197Au beam on a 9Be target was used to create the nuclei of interest. The measured isomers ranged in energy from ~ 100 keV to ~3.5 MeV with half-lifes ranging from ~1 s to greater than 5 mins. Long-lived four-quasiparticle isomers populated in 184Hf and 186Hf confirm long-standing predictions of a region favouring the formation of high-energy long-lived isomers. Evidence for low-lying isomers in 188Ta and 192Re support the prediction of a region of shape transition from 7-soft prolate ground states to ‘well deformed’ oblate excited states.