Various collective states in the I124 nucleus

Abstract

The level structure of $^{124}\mathrm{I}$ ($Z=53, N=71$) has been studied via the $^{122}\mathrm{Sn}(^{7}\mathrm{Li},5n)^{124}\mathrm{I}$ reaction with a beam energy of 54 MeV. Through in-beam and out-of-beam $\ensuremath{\gamma}$-ray spectroscopy, the sophisticated low-lying levels including isomeric states and numerous collective states have been established for the first time. A positive-parity collective band built on the ${10}^{+}$ state at 1297 keV is interpreted as being associated with the combination of a proton and a neutron in the same intruder ${h}_{11/2}$ orbital, namely the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{h}_{11/2}$ configuration. This band shows a typical quadrupole vibrational character. In contrast, the negative parity bands based on the $\ensuremath{\pi}{g}_{7/2}\ensuremath{\nu}{h}_{11/2}$ configuration show a soft triaxial rotation. An isomeric ${8}^{\ensuremath{-}}$ state at 689 keV with a half-life of 14 ns can be explained as a K isomer due to a proton with an ${\mathrm{\ensuremath{\Omega}}}_{p}=9/2$ in the ${g}_{9/2}$ orbital coupled to a neutron with an ${\mathrm{\ensuremath{\Omega}}}_{n}=7/2$ in the ${h}_{11/2}$ orbital. The excited states based on this $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}{h}_{11/2}$ configuration show a coupled rotational structure. Another coupled rotational band built on the ${6}^{+}$ state at 714 keV is thought to be based on the $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}{d}_{3/2}$ configuration.