Abnormal signature inversion and multiple alignments in doubly odd126I

Abstract

High-spin states in ${}^{126}$I have been investigated by using in-beam $\ensuremath{\gamma}$-ray spectroscopy with the ${}^{124}$Sn(${}^{7}\text{Li},5n$)${}^{126}$I reaction at a beam energy of 48 MeV. The level scheme of ${}^{126}$I has been extended and modified considerably by adding about 80 new $\ensuremath{\gamma}$ rays and establishing five new bands. The configurations have been tentatively assigned for the yrast, yrare, and other excited bands with the help of triaxial projected shell-model (TPSM) and cranked shell-model calculations. The first band crossing in the yrast band is found due to alignments of a pair of ${({h}_{11/2})}^{2}$ neutrons. The first and the second band crossings in the yrare band are caused by the alignments of a pair of ${({d}_{5/2})}^{2}$ protons and a pair of ${({h}_{11/2})}^{2}$ neutrons, respectively. Due to the successive excitations of two, four, and six quasiparticles, the alignments in the yrare band present a gigantic rising feature. The yrast band exhibits a signature inversion at low spins and becomes normal after a reversion spin of ${I}_{\mathrm{rev}}=14$. The yrare band exhibits an abnormal signature inversion in which the signature inversion phase persists up to the highest spin. The signature inversions in ${}^{126}$I are well reproduced and successfully interpreted by the TPSM calculations. Some features of chirality are found for the four-quasiparticle (4qp) part of the yrast band and the 4qp excited band 2.