Level structure of 123Cs observed from 123Ba decay and described using the IBFM and CQPC models

The decay of ¹²³Ba to ¹²³Cs has been studied with mass-separated sources. Singles spectra of γ-rays, X-rays and conversion electrons as well as γ - γ - t, γ - e ⁻ - t, and X - e ⁻ - t coincidences were recorded. A level scheme of ¹²³Cs has been constructed including 26 new excited states and 82 transitions. The existence of a I ^π = 11/2⁻, T _1/2 = 1.7 s isomer, bandhead of the h _11/2 band, is confirmed. Its excitation energy equals 156.3 keV. A new T _1/2 = 114 ns isomer has been established at 232 keV using the in-beam recoil catcher technique. It is assigned to the I ^π = 9/2⁺ bandhead of the gpg _9/2 band. Collective bands based on the 1/2⁺ ground state and first 3/2⁺ excited state are proposed. The level structure is described in the frame of the interacting boson-fermion and core-quasiparticle coupling models.