Octupole phonon excitations on the shell-model states in Xe, Cs, and Ba isotopes up to mass 142

Large-scale nuclear shell-model calculations are performed in Xe, Cs, and Ba isotopes up to mass 142 (Z ≥ 50 and N ≥ 82) beyond ¹³²Sn. All the single-particle levels in the one-major shells, six neutron (1f_7/2, 2p_3/2, 2p_1/2, 0h_9/2, 1f_5/2 and 0i_13/2) orbitals and five proton (0g_7/2, 1d_5/2, 1d_3/2, 0h_11/2, and 0s_1/2) orbitals are considered. For an effective two-body interaction, only one set of the multipole pairing, quadrupole-quadrupole interactions is employed and the strengths of the two-body interactions are set constant for all the nuclei considered. These interactions are phenomenologically determined to reproduce the experimental energy spectra in two-body systems. Some of the isomeric states are analyzed in terms of the shell-model configurations. Octupole correlated states are discussed by phenomenologically introducing a collective octupole phonon on top of each shell model state.