Multiparticle-octupole coupling and magnetic moments of h _{9 2}ⁿ isomers in N = 126 isotones

The influence of particle-vibration coupling on the g-factors of the |(h _{9 2})ⁿ〉 isomers in the N = 126 isotones is assessed using the multiparticle-octupole-coupling model. According to the model, admixtures of the configuration |(h _{9 2})^n-1f _{7 2}〉 in the yrast 8⁺ and 21 2^- states, nominally associated with the configuration |(h _{9 2})ⁿ〉, increase with n. On its own, the octupole mixing mechanism therefore predicts g-factors for these states that increase with the number of valence protons. This trend is the opposite of that predicted by core-polarization blocking. Combining multiparticle-octupole coupling and first-order core-polarization blocking significantly reduces the discrepancy between the experimental and theoretical g-factors of these states. We conclude that the observed breakdown in additivity for the g-factors of the |(h _{9 2}ⁿ)〉 isomers in the N = 126 isotones arises primarily from first-order core-polarization blocking and the combination of configuration mixing due to multiparticle-octupole coupling and shell-model residual interactions.