The half-lives of 20 neutron-rich nuclei with $Z=27–30$ have been measured at the RIBF, including five new half-lives of ${}^{76}\mathrm{Co}(21.7_{-4.9}^{+6.5}\mathrm{ms})$, ${}^{77}\mathrm{Co}(13.0_{-4.3}^{+7.2}\mathrm{ms})$, ${}^{79}\mathrm{Ni}({43.0}_{-7.5}^{+8.6}\mathrm{ms})$, ${}^{80}\mathrm{Ni}(23.9_{-17.2}^{+26.0}\mathrm{ms})$, and ${}^{81}\mathrm{Cu}(73.2\pm 6.8\mathrm{ms})$. In addition, the half-lives of ${}^{73–75}\mathrm{Co}$, ${}^{74–78}\mathrm{Ni}$, ${}^{78–80}\mathrm{Cu}$, and ${}^{80–82}\mathrm{Zn}$ were determined with higher precision than previous works. Based on these new results, a systematic study of the $\beta$-decay half-lives has been carried out, which suggests a sizable magicity for both the proton number $Z=28$ and the neutron number $N=50$ in ${}^{78}\mathrm{Ni}$.

• Received 28 March 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.032505