Mean lifetimes of states in ${}^{86}\mathrm{Nb}$ and ${}^{86}\mathrm{Zr}$ produced by the ${}^{58}\mathrm{Ni}{(}^{32}\mathrm{S}{,3pn)}^{86}\mathrm{Nb}$ and ${}^{58}\mathrm{Ni}{(}^{32}\mathrm{S}{,4p)}^{86}\mathrm{Zr}$ reactions at 130 MeV have been measured using the recoil-distance method. The $B\left(E2\mathrm{}\right)\mathrm{}$ strength of 11(2) W.u. for the $8^{+}\to 6^{+}$ transition in ${}^{86}\mathrm{Nb}$ implies weak collectivity at low excitation energies for the $\pi =+\mathrm{yrast}$ band. The weak dipole transition strength of the $8^{+}\to 7$ decay suggests that the configuration for the $7ħ$ state is different from that of the other yrast states. In general, the $B\left(E2\mathrm{}\right)\mathrm{}$ rates obtained for transitions in ${}^{86}\mathrm{Zr}$ agree with those previously published, thus supporting the suggestion of a weakly collective structure based on shell-model excitations at low energies. Hartree-Fock-Bogolyubov cranking calculations indicate a spherical shape for low-spin vacuum configuration states in ${}^{86}\mathrm{Zr}$.

• Received 11 December 1997

DOI:https://doi.org/10.1103/PhysRevC.57.2189