Lifetimes of excited states in triaxially deformed ¹⁰⁷Tc and ^109,111,113Rh

Lifetimes of excited states in ¹⁰⁷Tc, ¹⁰⁹Rh, ¹¹¹Rh, and ¹¹³Rh were measured at GANIL using the Recoil-Distance Doppler Shift method. The neutron-rich nuclei were produced in fission reactions in inverse kinematics with a ²³⁸U beam impinging on a ⁹Be target. Fission fragments were identified event-by-event in the ray-tracing spectrometer VAMOS++ and correlated with prompt γ rays observed around the target position with the EXOGAM Ge detector array. Several lifetimes were obtained for states in the positive-parity yrast bands in the four nuclei and compared to triaxial particle-rotor calculations. The results clarify the configuration for the strongest positive-parity band in ¹⁰⁷Tc and suggest a gradual increase of triaxial deformation with atomic number Z, reaching almost maximum triaxiality for the neutron-rich Rh nuclei. (orig.)