Various Nuclear Structures in Xe140 Studied by Β Decay of Ground and Isomeric States in I…

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