New collective structures in Au 179 and their implications for the triaxial deformation of the Pt 178 core
The extremely neutron-deficient isotope 179 Au has been studied by a combination of in-beam γ-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 ⊕2f 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) µs 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 ⊕2f 7/2 rotational band is interpreted as due to triaxial deformation of the underlying configuration with β 2 ≈ 0.26 and γ ≈ 27°. In conclusion, observed non-yrast states of the positive-parity 1i 13/2 intruder configuration are interpreted as due to triaxial deformation with β 2 ≈ 0.26 and γ ≈ 20°.