High-spin level scheme of doubly odd128I

Abstract

High-spin states in the odd-odd ${}^{128}$I have been studied experimentally using the ${}^{124}$Sn(${}^{7}$Li, 3n$\ensuremath{\gamma}$)${}^{128}$I reaction at beam energies of 28 and 32 MeV. A level scheme built on the known ${T}_{1/2}=175$ ns, (${6}^{\ensuremath{-}})$ isomer has been established. The low-lying states in the level scheme have been proposed to be associated with the $\ensuremath{\pi}{d}_{5/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ and $\ensuremath{\pi}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ two-quasiparticle excitations. The strongly populated negative-parity states, forming a bandlike structure, have been assigned to be based on the $\ensuremath{\pi}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ configuration. The $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ multiplet ${9}^{+}$, ${10}^{+}$, and ${11}^{+}$ members have been identified according to the systematics of the corresponding level structures observed in the lighter odd-odd iodine isotopes. The two-quasiparticle configuration assignments are supported by the nucleon pair approximation and empirical shell-model calculations.