Competing structures in the beyond neutron N=104 midshell nucleus 184Pb

Proton-neutron configurations in atomic nuclei can manifest in a variety of different structures, and exotic nuclei provide fruitful ground for exploring their relation to fundamental symmetries. Here, we report on in-beam γ-ray spectroscopy of the very neutron-deficient 184Pb nucleus using the JUROGAM II spectrometer at the RITU separator in a recoil-decay tagging experiment. For the first time, transitions from the non-yrast states have been observed in a Pb nucleus beyond the neutron N=104 midshell. In comparison to neighboring Pb isotopes and theoretical models, de-excitation patterns from these states are similar to those associated with predominantly oblate shapes in heavier Pb isotopes. Together with the known predominantly prolate yrast band and the spherical ground state, this suggests that triple-shape coexistence prevails in the 184Pb nucleus.