The ${}^{65}\mathrm{Cu}$ nucleus was populated by the ${}^{64}\mathrm{Ni}$(${}^7\mathrm{Li}$,$\alpha 2\mathrm{n}$)${}^{65}\mathrm{Cu}$ reaction and the lifetime of the 9/2${}^{+}$ state at 2.5 MeV was measured by electronic fast-timing technique, providing the value $\tau =$ 37(3) ps. The reduced transition probability $B\left(E3\right)=8.82\left(165\right)$ W.u. is deduced and compared to theoretical predictions in the framework of a particle-vibration (weak) coupling model. The results indicate that the 9/2${}^{+}$ state is a member of the 3${}^{-}\otimes \pi p$3/2 multiplet, built by coupling the octupole 3${}^{-}$ phonon of ${}^{64}\mathrm{Ni}$ to an unpaired proton in the $p_{3/2}$ level, confirming the robustness of core excitations in the medium mass nucleus ${}^{64}\mathrm{Ni}$.

• Received 4 March 2014

DOI:https://doi.org/10.1103/PhysRevC.89.054302