Evidence for octupole collectivity in 172Pt

Abstract

Excited states in the extremely neutron-deficient nucleus 172Pt were populated via 96Ru (78Kr , 2 p) and 92Mo (83Kr , 3 n) reactions. The level scheme has been extended up to an excitation energy of ≈5MeV and tentative spin-parity assignments up to Iπ= 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 negative-parity band. The lowest member 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 172Pt. 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.