Beta Decay of68–74Niand Level Structure of Neutron-Rich Cu Isotopes

The isotopes ${}^{68–74}\mathrm{Ni}$, of interest both for nuclear physics and astrophysics, have been produced in proton-induced fission of ${}^{238}\mathrm{U}$ and ionized in a laser ion guide coupled to an on-line mass separator. Their $\beta$ decay was studied by means of $\beta$- $\gamma$ and $\gamma$- $\gamma$ spectroscopy. Half-lives have been determined and production cross sections extracted. A partial level scheme is presented for ${}^{73}\mathrm{Cu}$ and additional levels for ${}^{71}\mathrm{Cu}$, providing evidence for a sharply lowered position of the $\pi {1f}_{5/2}$ orbital as occupancy of the $\nu {1g}_{9/2}$ state increases. The latter may have a clear impact on the predicted structure and decay properties of doubly magic ${}^{78}\mathrm{Ni}$.