Beta-gamma spectroscopy of the neutron-rich 150Ba

Abstract

Excited states in the neutron-rich nucleus 150Ba have been observed via β–γ spectroscopy at the Radioactive Isotope Beam Factory, RIKEN Nishina Center. The 150Ba ions were produced by the in-flight fission of a 238U beam with an energy of 345 MeV/nucleon. The E(2+) energy of 150Ba was identified at 100 keV, which is the lowest known in the neutron-rich Ba isotopes. A γ-ray peak was also observed at 597 keV. A mean-field calculation with a fully 3D real space was performed and a static octupole deformation was obtained for the Ba isotopes. Kπ = 0− and 1− excited states with significant octupole collectivity were newly predicted at around or lower than 1 MeV on the ground state of 150Ba by a random-phase approximation calculation. The 597 keV γ ray can be interpreted as a negative-parity state, showing that 150Ba may possess octupole collectivity.