High-spin states in127I

Abstract

In-beam $\ensuremath{\gamma}$ spectroscopy of the stable nucleus ${}^{127}$I has been studied experimentally using the ${}^{124}$Sn(${}^{7}$Li, 4$n\ensuremath{\gamma}$)${}^{127}$I reaction at a beam energy of 32 MeV. The high-spin level scheme of ${}^{127}$I is extended significantly. Negative-parity levels built on the $11/{2}^{\ensuremath{-}}$, $\ensuremath{\pi}{h}_{11/2}$ particle state are observed up to $(35/{2}^{\ensuremath{-}})$ and described as a decoupled band, extending our knowledge of decoupled structures to the most neutron-rich stable iodine isotope. Two $\ensuremath{\Delta}I=2$ yrast positive-parity sequences are proposed to be associated with the $\ensuremath{\pi}{g}_{7/2}$ configuration due to observations of several strong interband transitions, and two weakly populated $\ensuremath{\Delta}I=2$ positive-parity bands are newly identified and interpreted as arising mainly from the $\ensuremath{\pi}{d}_{5/2}$ configuration. Three-quasiparticle configurations are assigned to the ${I}^{\ensuremath{\pi}}=15/{2}^{+}$ and $23/{2}^{+}$ states according to the existing knowledge in neighboring nuclei; irregular noncollective and regular collective excitations built on these two ($15/{2}^{+}$ and $23/{2}^{+}$) states are observed to coexist at similar energies. The observed three-quasiparticle band structures are further interpreted with the aid of configuration-constrained potential energy surface calculations.