Lifetime measurements in 63Co and 65Co

Lifetimes of the 9/21- and 3/21- states in 63Co and the 9/21- state in 65Co were measured using the recoil distance Doppler shift and the differential decay curve methods. The nuclei were populated by multinucleon transfer reactions in inverse kinematics. γ rays were measured with the EXOGAM Ge array and the recoiling fragments were fully identified using the large-acceptance VAMOS spectrometer. The E2 transition probabilities from the 3/21- and 9/21- states to the 7/2- ground state could be extracted in 63Co as well as an upper limit for the 9/21-→7/21- B(E2) value in 65Co. The experimental results were compared to large-scale shell-model calculations in the pf and pfg9/2 model spaces, allowing us to draw conclusions on the single-particle or collective nature of the various states.