Low-lying structure and shape evolution in neutron-rich Se isotopes

Abstract

Neutron-rich $^{88,90,92,94}\mathrm{Se}$ isotopes were studied via in-beam $\ensuremath{\gamma}$-ray spectroscopy after nucleon removal reactions at intermediate energies at the Radioactive Isotope Beam Factory. Based on $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence analysis, low-lying excitation level schemes are proposed for these nuclei, including the ${2}_{1}^{+}, {4}_{1}^{+}$ states and ${2}_{2}^{+}$ states at remarkably low energies. The low-lying ${2}_{2}^{+}$ states, along with other features, indicate triaxiality in these nuclei. The experimental results are in good overall agreement with self-consistent beyond-mean-field calculations based on the Gogny D1S interaction, which suggests both triaxial degree of freedom and shape coexistence playing important roles in the description of intrinsic deformations in neutron-rich Se isotopes.