Structure of the neutron-rich $N=86$ isotope ${}^{140}\mathrm{Xe}$, located northeast of a doubly-magic nucleus ${}^{132}\mathrm{Sn}$, is investigated by $\beta \text{−}\gamma$ spectroscopy. Two $\beta$-decay isomers in ${}^{140}\mathrm{I}$ are newly found in the study of two different $\beta$ decays of ${}^{140}\mathrm{I}$ which were produced by two reactions (i) direct in-flight fission at a primary target and (ii) $\beta$ decay of ${}^{140}\mathrm{Te}$ at an active stopper. Half-lives of the $\beta$ 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 $\beta$ decay of the high-spin isomer and of the mixed $\beta$ decays of the ground state and the low-spin isomer in ${}^{140}\mathrm{I}$ to ${}^{140}\mathrm{Xe}$ are constructed using the information on $\gamma$-ray coincidence relation and $\gamma$-ray intensity. Nuclear structures of the low-lying states in ${}^{140}\mathrm{Xe}$ and ${}^{140}\mathrm{I}$ 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-)$\gamma$-band members of $2^{+}$ and $4^{+}$ states and the octupole collective $1^{-}$ state are proposed in ${}^{140}\mathrm{Xe}$. Increase of quadrupole, triaxial, and octupole collectivities is discussed with the increase of neutron and proton numbers.

• Received 15 January 2022
• Accepted 1 April 2022

DOI:https://doi.org/10.1103/PhysRevC.105.044325