Evidence For Octupole Collectivity In Pt-172

Excited states in the extremely neutron-deficient nucleus Pt-172 were populated via Ru-96(Kr-78, 2p) and Mo-92(Kr-83, 3n) reactions. The level scheme has been extended up to an excitation energy of approximate to 5MeV and tentative spin-parity assignments up to I-pi = 18(+). Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negativeparity band. The lowestmember of this negative-parity structure was firmly assigned spin-parity 3(-). In addition, we observed an E3 transition from this 3(-) state to the ground state, providing direct evidence for octupole collectivity in Pt-172. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3(-) state as a collective octupole-vibrational state.