Structure and decay of a four-quasiparticle15−isomer inTa180

A four quasiparticle high-K isomer with a meanlife of 45(2) μs has been identified at 1451 keV in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$, populated in the ${}_{}{}^{176}{}_{}{}^{}\mathrm{Yb}$ ${(}^{11}$B,α3n${)}^{180}$Ta reaction. The isomer decays into a rotational band which is associated with the two-quasiparticle $9^{\mathrm{-}}$ isomer at 75.3 keV. Analysis of the branching ratios within that band and the magnetic moment for the $9^{\mathrm{-}}$ isomer, supports the configuration assignment to the $9^{\mathrm{-}}$ isomer. The K hindrance for the E2 decay of the ${15}^{\mathrm{-}}$ isomer to the $9^{\mathrm{-}}$ band is substantially lower than that for an apparently similar ${15}^{\mathrm{-}}$ isomer in ${}_{}{}^{178}{}_{}{}^{}\mathrm{Ta}$, a difference which can be attributed partly to a change from the π9/$2^{\mathrm{-}}$[514]${\nu }^3$9/$2^{+}$ [624]7/$2^{\mathrm{-}}$[514]5/$2^{\mathrm{-}}$[512] configuration in ${}_{}{}^{178}{}_{}{}^{}\mathrm{Ta}$ to the ${\mathrm{\pi }}^3$9/$2^{\mathrm{-}}$[514]7/$2^{+}$[404]5/$2^{+}$[402]ν9/$2^{+}$[624] configuration in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$. The reduced hindrance factors for E2 decays from related four-quasiparticle isomers in the isotopes ${}_{}{}^{176,178,180}{}_{}{}^{}\mathrm{Ta}$ match the hindrances of the corresponding E2 decays from component $6^{+}$ core states in the hafnium isotopes, ${}_{}{}^{174,176,178}{}_{}{}^{}\mathrm{Hf}$. © 1996 The American Physical Society.