Coupling a proton and a neutron to the semidoubly magic nucleusNi68: A study ofCu70via theβdecay ofNi70andCu70

The ${}^{70}\mathrm{Ni}$ nucleus has been produced at the LISOL facility and its $\beta$ decay to ${}^{70}\mathrm{Cu}$ has been observed. In parallel, the ${}^{70}\mathrm{Cu}$ nucleus has been produced at the ISOLDE facility. A new third $\beta$-decaying isomeric state in ${}^{70}\mathrm{Cu}$ has been identified, partly with the aid of the in-source laser spectroscopy method. Its measured half-life is $T_{1∕2}=33\left(2\right)\mathrm{s}$. In addition, two isomeric transitions in ${}^{70}\mathrm{Cu}$ have been observed at energies of 101.1(3) and $141.3\left(3\right)\text{keV}$, and it allowed the relative placement of the three ${}^{70}\mathrm{Cu}$ isomeric states and their tentative spin and parity assignments. The new ${}^{70}\mathrm{Cu}$ isomer was found to be weakly populated in the $\beta$ decay of ${}^{70}\mathrm{Ni}$. It allowed the construction of the ${}^{70}\mathrm{Ni}$ decay scheme. Furthermore, the $\beta$ decay of the three ${}^{70}\mathrm{Cu}$ isomers to ${}^{70}\mathrm{Zn}$ has been measured and their decay schemes are presented. The ${}^{70}\mathrm{Ni}$ $\beta$ decay to the isomeric states in ${}^{70}\mathrm{Cu}$ and their subsequent isomeric decay and $\beta$ decay to ${}^{70}\mathrm{Zn}$ are discussed within the extreme shell-model picture of two valence nucleons outside the semidouble magic ${}_{28}{}^{68}\mathrm{Ni}_{40}$ core and it yields satisfactory results. Large-basis shell-model calculations using ${}_{28}{}^{56}\mathrm{Ni}_{28}$ as the core and a realistic effective interaction support rather well the suggested interpretation.