Observation of the 0(2)(+) and gamma bands in Ru-98, and shape coexistence in the Ru isotopes

Excited states in Ru-98 were investigated using gamma-ray spectroscopy following the beta-decay of Rh-98, and via the 100 Ru(p, t) reaction. Combining the results from the two experiments, two states were revised to have spin-parity of 4(+) and subsequently assigned to the 0(2)(+) and "gamma" bands, respectively. The observed structures in Ru-98 are suggested to be deformed and rotational, rather than spherical and vibrational, and fit well into the systematics of these excitations in the Ru isotopes. The 0(2)(+) excitation is suggested as a shape coexisting configuration. This observation eliminates some of the last remaining candidates for nearly harmonic vibrational nuclei in the Z approximate to 50 region. Beyond-mean-field calculations are presented that support shape coexistence throughout the Ru isotopes with N = 52-62, and suggest a smooth evolution of the shapes. (C) 2020 The Authors. Published by Elsevier B.V.