COLLECTIVE AND QUASI-PARTICLE STRUCTURES IN PB-192

The structure of 192Pb has been investigated using the Yb-173(Mg-24, 5 n) reaction at E(b) = 132 MeV. The level scheme has been extended up t o an excitation energy of 7 MeV and a spin of 23 HBAR. Two collective bands of levels linked by M1 transitions and four groups of states of non-collective character have been observed. Based on comparison with experimental data on odd-A Tl isotopes and with cranked shell-model ca lculations assuming an oblate shape, the collective Ml bands are inter preted as having an underlying proton 2-quasiparticle configuration co upled to a pair of rotation-aligned i13/2 neutrons. The four groups of non-collective level-sequences are understood as 4-quasiparticle exci tations associated with aligned neutron 2-quasiparticle states that in volve a mixture of neutron and proton degrees of freedom.