Evidence for octupole collectivity in $$^{172}{\mathrm {Pt}}$$

Abstract

Excited states in the extremely neutron-deficient nucleus 172 Pt were populated via 96 Ru( 78 Kr, 2 p) and 92 Mo( 83 Kr, 3n) reactions. The level scheme has been extended up to an excitation energy of ≈ 5 MeV and tentative spin-parity assignments up to I π = 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 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 172 Pt. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3 − state as a collective octupolevibrational state. a