Effect of Coriolis mixing on lifetime of isomeric states in heavy nuclei

Abstract

The effect of Coriolis $K$ mixing on the $\ensuremath{\gamma}$ decay of one-quasiparticle isomeric states is examined in transfermium nuclei with neutron number $N=153$. We consider a core-plus-quasiparticle coupling in which the $K$ mixing sharply increases if the isomeric quasiparticle state closely approaches the rotational state with the same angular momentum $I$, but built on another quasiparticle state which is either directly coupled to the isomeric ($\mathrm{\ensuremath{\Delta}}K=1$) or connected with it through the intermediate mixing quasiparticle orbitals ($\mathrm{\ensuremath{\Delta}}K>1$). This mechanism is likely to explain the 38-ns ${K}^{\ensuremath{\pi}}=7/{2}^{+}$ isomer in $^{251}\mathrm{Cf}$ which is quasidegenerated with an ${I}^{\ensuremath{\pi}}=7/{2}^{+}$ rotation state built on ${K}^{\ensuremath{\pi}}=1/{2}^{+}$. Our model explains the enhancement of its decay by three orders of magnitude compared to the ${K}^{\ensuremath{\pi}}=7/{2}^{+}$ isomer in $^{249}\mathrm{Cm}$. We suggest that the same mechanism could be of general importance for the isomer decay properties in a wide range of heavy odd-mass nuclei.