New collective structures in ¹⁷⁹Au and their implications for the triaxial deformation of the ¹⁷⁸Pt core

The extremely neutron-deficient isotope Au-179 has been studied by a combination of in-beam gamma-ray and isomeric-decay spectroscopy. For in-beam spectroscopy, the recoil-isomer tagging technique was employed, using the known 3/2(-), T-1/2 = 328 ns isomer. A new rotational band, associated with the unfavored signature band of the 1h(9/2) (R) 2 f(7/2) proton-intruder configuration, was revealed. A previously unknown, high-spin isomeric state with an excitation energy of 1743(17) keV and T-1/2 = 2.16(8) mu s was discovered. Five decay paths were identified, some of them feeding previously unknown non-yrast excited states, associated with the 1i(13/2) proton-intruder configuration. Calculations based on the particle-plus-triaxial-rotor model were performed to interpret the data. On the basis of these calculations, the new 1h(9/2) (R) 2 f(7/2) rotational band is interpreted as due to triaxial deformation of the underlying configuration with 132 ti 0.26 and gamma approximate to 27 degrees. Observed non-yrast states of the positive-parity 1i(13/2) intruder configuration are interpreted as due to triaxial deformation with beta(2) approximate to 0.26 and gamma approximate to 20 degrees.