Competition between pairing-assisted tunneling and single-particle alignment in the decay of high-Kisomeric states

In an axially symmetric, strongly rotating quadrupole deformed nucleus, the projection K of the angular momentum along the symmetry axis is a partially conserved quantity. A K isomer (K=25) at low excitation energy has been observed in ${}_{}{}^{182}{}_{}{}^{}\mathrm{Os}$ which decays into the ground-state band (K=0). The associated electromagnetic lifetime at spin I≊25 can be interpreted in terms of tunneling of a system displaying strong pairing fluctuations across a barrier which separates configurations in which the nucleus rotates about the symmetry axis and about an axis perpendicular to it. A hindrance factor ≊${10}^{\mathrm{-}6}$–${10}^{\mathrm{-}9}$ for the process is calculated, in overall agreement with the data.