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

Abstract

Lifetimes of excited states in Tc-107, Rh-109, Rh-111, and Rh-113 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 U-238 beam impinging on a Be-9 target. Fission fragments were identified event-by-event in the ray-tracing spectrometer VAMOS++ and correlated with prompt gamma rays observed around the target position with the EXOGAM Ge detector array. Several lifetimes were obtained for states in the positiveparity 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 Tc-107 and suggest a gradual increase of triaxial deformation with atomic number Z, reaching almost maximum triaxiality for the neutron-rich Rh nuclei.