Collective properties of the low-lying levels in the odd-$A$ ${}^{67–73}\mathrm{Cu}$ were investigated by Coulomb excitation with radioactive beams. The beams were produced at ISOLDE and postaccelerated by REX-ISOLDE up to $2.99\mathrm{MeV}/\mathrm{u}$. In ${}^{67,69}\mathrm{Cu}$, low-lying $1/2^{-}$, $5/2^{-}$, and $7/2^{-}$ states were populated. In ${}^{71,73}\mathrm{Cu}$, besides the known transitions deexciting the single-particle-like $5/2^{-}$ and core-coupled $7/2^{-}$ levels, $\gamma$ rays of 454 and 135 keV, respectively, were observed for the first time. Based on a reanalysis of $\beta$-decay work and comparison with the systematics, a spin $1/2^{-}$ is suggested for these excited states. Three $B(E2)$ values were determined in each of the four isotopes. The results indicate a significant change in the structure of the odd-$A$ Cu isotopes beyond $N=40$ where single-particle-like and collective levels are suggested to coexist at very low excitation energies.

• Received 3 December 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.112502