Structure of the neutron-rich N=86 isotope 140Xe, located northeast of a doubly-magic nucleus 132Sn, is investigated by β-γ spectroscopy. Two β-decay isomers in I140 are newly found in the study of two different β decays of I140 which were produced by two reactions (i) direct in-flight fission at a primary target and (ii) β decay of Te140 at an active stopper. Half-lives of the β decays of the ground state, the low-spin isomer, and the high-spin isomer are determined to be 0.38(2), 0.91(5), and 0.47(4) s, respectively. Decay schemes of the β decay of the high-spin isomer and of the mixed β decays of the ground state and the low-spin isomer in I140 to Xe140 are constructed using the information on γ-ray coincidence relation and γ-ray intensity. Nuclear structures of the low-lying states in Xe140 and I140 are discussed by comparing the experimental results to two theoretical calculations based on a large-scale shell model and the deformed Skyrme Hartree-Fock-Bogoliubov plus deformed quasiparticle-random-phase approximation. Possible candidates for (quasi-)γ-band members of 2+ and 4+ states and the octupole collective 1-state are proposed in Xe140. Increase of quadrupole, triaxial, and octupole collectivities is discussed with the increase of neutron and proton numbers.
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