The yrast $J^{\pi }=8^{+}$ states in neutron-rich ${}^{70,72,74,76}\mathrm{Ni}$ nuclei are predicted to be isomeric. The present paper describes two GANIL experiments. In the first of them a search was made for the $8^{+}$ isomeric states in ${}^{72,74}\mathrm{Ni}$ nuclei via fragmentation of ${}^{76}\mathrm{Ge}$ using the ion $\gamma$-decay correlation technique. Although these states were not observed, limits for their lifetimes were determined. In the second experiment the decay spectroscopy of ${}^{70,72}\mathrm{Co}$ nuclei was performed using fragmentation of a ${}^{86}{\mathrm{Kr}}^{36+}$ beam and the new LISE2000 spectrometer. The $\beta$ delayed $\gamma$ rays from the decay of ${}^{70,72}\mathrm{Co}$ to ${}^{70,72}\mathrm{Ni}$ were observed using the EXOGAM germanium detectors. The half life of ${}^{72}\mathrm{Co}$ was measured to be 62(3) ms and the level sequence of the lowest excited states in ${}^{72}\mathrm{Ni}$ was suggested, with the $2^{+}$ state at $1096\text{keV}$. An attempt to reproduce the level scheme in terms of shell-model calculations was undertaken. The reasons for the disappearance of the $8^{+}$ isomer in ${}^{72}\mathrm{Ni}$ are discussed.

• Received 3 April 2003

DOI:https://doi.org/10.1103/PhysRevC.68.044304