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.