Microscopic description of triaxiality in Ru isotopes with covariant energy density functional theory

Abstract

Background: Triaxiality in nuclear low-lying states has attracted great interest for many years. Recently, reduced transition probabilities for levels near the ground state in $^{110}\mathrm{Ru}$ have been measured and provided strong evidence of a triaxial shape of this nucleus.Purpose: The aim of this work is to provide a microscopic study of low-lying states for Ru isotopes with $A\ensuremath{\approx}100$ and to examine in detail the role of triaxiality and the evolution of quadrupole shapes with the isospin and spin degrees of freedom.Method: Low-lying excitation spectra and transition probabilities of even-even Ru isotopes are described at the beyond-mean-field level by solving a five-dimensional collective Hamiltonian with parameters determined by constrained self-consistent mean-field calculations based on the relativistic energy density functional PC-PK1.Results: The calculated energy surfaces, low-energy spectra, and intraband and interband transition rates, as well as some characteristic collective observables, such as $E({4}_{\mathrm{g}.\mathrm{s}.}^{+})/E({2}_{\mathrm{g}.\mathrm{s}.}^{+}),E({2}_{\ensuremath{\gamma}}^{+})/E({4}_{\mathrm{g}.\mathrm{s}.}^{+})$, and $B(E2;{2}_{\mathrm{g}.\mathrm{s}.}^{+}\ensuremath{\rightarrow}{0}_{\mathrm{g}.\mathrm{s}.}^{+})$ and $\ensuremath{\gamma}$-band staggerings, are in good agreement with the available experimental data.Conclusions: The main features of the experimental low-lying excitation spectra and electric transition rates are well reproduced and, thus, strongly support the onset of triaxiality in the low-lying excited states of Ru isotopes around $^{110}\mathrm{Ru}$.