The high-spin level structures of ${}^{96,97,98}\mathrm{Ru}$ $\mathrm{}(Z=44\mathrm{})\mathrm{}$ have been investigated using the ${}^{65}\mathrm{Cu}{(}^{36}\mathrm{S},{pxn)}^{96,97,98}\mathrm{Ru}$ $\mathrm{}(x=4,3,2\mathrm{})\mathrm{}$ reactions. About 130 new transitions have been observed and unambiguously placed in the decay schemes of these nuclei. The level schemes have been extended up to spin $J\approx 22$– $34ħ$, and excitation energies $E_x\approx 20-24$ MeV. Spherical shell model calculations have been performed and theoretical level energies compared with experimental values. Calculations using ${}^{88}\mathrm{Sr}$ as the core give a reasonable agreement for the observed energy levels up to $J<~16ħ$ (the maximum angular momentum possible within this restricted model space). The higher angular momentum states are dominated by the $\nu {(g}_{9/2}{)}^{-1}$ configuration, associated with breaking of the $N=50\mathrm{}$ core. The experimental indications for this “core breaking” are (i) the observation of $\gamma$ rays with energies $E_{\gamma }\approx$ 2 MeV at intermediate spins and (ii) the fragmentation of $\gamma$-ray intensity into a number of branches. A cascade of $E2\mathrm{}$ transitions of nearly equal transition energies has been observed in ${}^{98}\mathrm{Ru}$ after the core breaking $(J>~16ħ)$, possibly manifesting vibrational behavior.

• Received 24 July 1997

DOI:https://doi.org/10.1103/PhysRevC.57.83