Abstract
Abstract The properties of K isomers are reviewed. Energies and decay hindrance factors are considered in detail for selected isomers in the $$A \approx $$ A ≈ 160–190 region, focusing on pairing effects and the key K -mixing mechanisms that influence $$\gamma $$ γ -ray decay rates. The $$\beta $$ β -decay of K isomers is studied, indicating that, far from the valley of $$\beta $$ β stability, high- K $$\beta $$ β -decaying isomers will populate high- K states in the daughter nuclei. The challenges of revealing predicted, but as-yet undiscovered, long-lived isomers in the neutron-rich $$N \approx 116$$ N ≈ 116 prolate–oblate shape transition region are highlighted, and the occurrence of oblate high- K isomers is discussed. The 2015 multi-quasiparticle K -isomer table of Kondev, Dracoulis, and Kibédi is updated.