Multi-quasiparticle isomers involving proton-particle and neutron-hole configurations in $^{131}$I and $^{133}$I

The iodine isotopes with Z = 53 have attracted considerable interest because they exhibit a transition from more collective nature in the middle of the neutron shell to spherical shell-model structure as the number of neutrons increases toward the N = 82 closed shell. We have populated excited states in $^{131}$I$_{78}$ and $^{133}$I$_{80}$ using multi-nucleon transfer from $^{136}$Xe, with the aim of understanding the effect of neutron holes on nuclear structure. By means of time-correlated $\gamma $-ray coincidence spectroscopy and the measurement of $\gamma $-ray angular correlations, a J$^{\pi }$= 19/2$^{-}$ isomer at 1918 keV, with a half-life of 24(1) $\mu$s, has been identified in $^{131}$I, as well as nanosecond isomers with 23/2$^{+}$ in both isotopes. A T$_{1/2}$ = 25(3) ns isomer at 4308 keV in $^{131}$I is suggested to have J$^{\pi }$ = (31/2$^{-}$, 33/2$^{-})$ and is primarily attributed to the coupling of an odd proton in the d$_{5/2}$ or g$_{7/2}$ orbit with the ($\pi ^{2})_{0+}$ ($\nu $h$_{11/2}^{-3}$ d$_{3/2}^{-1})_{15-}$ configuration in $^{130}$Te responsible for the 15$^{-}$ isomer in that nucleus. In this presentation, the observed level properties will be compared with predictions of a shell-model calculation based on a j-j coupling scheme.