Level structures of {sup 96,97,98}Ru at high angular momentum

The high-spin level structures of {sup 96,97,98}Ru (Z=44) have been investigated using the {sup 65}Cu({sup 36}S,pxn){sup 96,97,98}Ru (x=4,3,2) 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{endash} 34{h_bar}, and excitation energies E{sub x}{approx}20{minus}24 MeV. Spherical shell model calculations have been performed and theoretical level energies compared with experimental values. Calculations using {sup 88}Sr as the core give a reasonable agreement for the observed energy levels up to J{le}16{h_bar} (the maximum angular momentum possible within this restricted model space). The higher angular momentum states are dominated by the {nu}(g{sub 9/2}){sup {minus}1} configuration, associated with breaking of the N=50 core. The experimental indications for this `core breaking` are (i) the observation of {gamma} rays with energies E{sub {gamma}}{approx} 2 MeV at intermediate spins and (ii) the fragmentation of {gamma}-ray intensity into a number of branches. A cascade of E2 transitions of nearly equal transition energies has been observed in {sup 98}Ru after the core breaking (J{ge}16{h_bar}), possibly manifesting vibrational behavior. {copyright} {ital 1998} {ital The American Physical Society}