Lifetime measurements in ${}^{63}$Co and ${}^{65}$Co

Abstract

Lifetimes of the $9/2_1^{-}$ and $3/2_1^{-}$ states in ${}^{63}$Co and the $9/2_1^{-}$ state in ${}^{65}$Co were measured using the recoil distance Doppler shift and the differential decay curve methods. The nuclei were populated by multi-nucleon transfer reactions in inverse kinematics. Gamma 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 $3/2_1^{-}$ and $9/2_1^{-}$ states to the $7/2^{-}$ ground state could be extracted in ${}^{63}$Co as well as an upper limit for the $9/2_1^{-}\to 7/2_1^{-}$ $B$(E2) value in ${}^{65}$Co. The experimental results were compared to large-scale shell-model calculations in the $pf$ and $pf{g}_{9/2}$ model spaces, allowing to draw conclusions on the single-particle or collective nature of the various states.

8 pages, 8 figures, 1 table, accepted for publication in Physical Review C