Shape coexistence and isomeric states in neutron-rich 112Tc and 113Tc

Isomeric states in 112Tc and 113Tc, with half-lives of 150 (17) ns and 500 (100) ns respectively, have been observed following the relativistic fission of 238U. The fission fragments have been separated in a fragment separator and identified by means of energy loss and time-of-flight techniques. In both nuclei, the ground-state configuration is calculated to have an oblate shape and the isomerism is proposed to arise due to transitions from a triaxial excited state to a low-lying oblate state.