Lifetime study of particle-hole excitations in the semimagic nucleus Ru-94- art. no. 014309

The recoil-distance Doppler-shift technique was employed to determine lifet imes of high-spin states in the semimagic nucleus Ru-94. The nuclei were po pulated using the reaction Ni-58(Ca-40,4p) at a beam energy of 145 MeV, and the gamma radiation from their decay was detected in six EUROBALL cluster detectors. A total of 23 reduced transition probabilities and limits for fi fteen further transitions were extracted and compared to large-scale shell model calculations, considering different configuration spaces and residual interactions. The information deduced on transition strengths turned out t o be essential for the correct assignment of the calculated to the experime ntal excited states. The results indicate that the 13(2)(-) (6919 keV), 14( 1)(-) (7970 keV), and the 15(1)(-) (8133 keV) levels have pure proton pi(f( 5/2))(-1) pi(g(9/2))(5) configurations, whereas all other excited states ab ove 6.3 MeV are built from a neutron g(9/2)-->d(5/2) excitation across the N = 50 shell closure, coupled to up to six valence protons. Strong M1 trans itions were found in a stretched dipole cascade within the sequence of neut ron core-excited states at positive parity, while the strengths of the tran sitions between core-excited and pure proton states were proven to be small , similar as in Rh-95.