βdecay of66Co,68Co,and70Co

The neutron-rich nuclei, ${}^{66}\mathrm{Co},$ ${}^{68}\mathrm{Co},$ and ${}^{70}\mathrm{Co}$ were produced using a laser-ionization isotope-separation on-line method. The resulting $\beta$-delayed $\gamma$ decay was studied. The half-life of ${}^{66}\mathrm{Co}$ is measured to be 0.18(1) s. Two $\beta$-decaying states are identified in ${}^{68}\mathrm{Co}$ with half-lives of 0.23(3) and 1.6(3) s. In addition, two $\beta$-decaying states are observed in ${}^{70}\mathrm{Co}$ with half-lives of 0.12(3) and 0.50(18) s. From the $\beta$ decay of these states in ${}^{66,68,70}\mathrm{Co},$ many new excited levels are established in ${}^{66}\mathrm{Ni},$ ${}^{68}\mathrm{Ni},$ and ${}^{70}\mathrm{Ni}.$ These results are compared to the valence mirror nuclei in the $N=50\mathrm{}$ region as well as with shell-model calculations. It can be concluded that collective excitations appear to play an increasingly important role with increasing occupation of the $\nu g_{9/2}$ orbital.