Post-accelerated isomerically purified radioactive beams, available at the CERN On-Line Isotope Mass Separator facility using the resonant ionization laser technique, have been used to study the Coulomb excitation of the $I^{\pi }$ = 3${}^{-}$ state in ${}^{70}$Cu ($Z=29$, $N=41$). While first results using a $I^{\pi }=6^{-}$ beam were reported previously, the present complementary experiment allows us to complete the study of the multiplet of states (3${}^{-}$, 4${}^{-}$, 5${}^{-}$, 6${}^{-}$) arising from the $\pi 2p_{3/2}\nu 1g_{9/2}$ configuration. Besides the known $\gamma$-ray transition deexciting the 4${}^{-}$ state, a ground-state $\gamma$ ray of 511(3) keV was observed for the first time and was unambiguously associated with the 5${}^{-}$ state deexcitation. This observation fixes the energy, spin, and parity of this state, completing the low-energy level scheme of ${}^{70}$Cu. $B\left(E2\right)$ values for all possible $E2$ transitions within the multiplet were determined. A comparison with large-scale shell model calculations using different interactions and valence spaces shows the importance of proton excitation across the $Z=28$ shell gap and the role of the $2d_{5/2}$ neutron orbital.

• Received 12 October 2011

DOI:https://doi.org/10.1103/PhysRevC.84.064323