Nuclear Isomers at the Extremes of Their Properties

The longer-lived excited nuclear states, referred as nuclear isomers, existdue to the hindered decays owing to their peculiar nucleonic structuralsurroundings. Some of these conditions, being exceptionally rare and limited toachieve, elevate certain isomers to the status of extreme and unusual isomersamong their kin. For example, the E5 coupling of single-particle orbitals israre and so are E5 decaying isomers. This review delves into some of suchremarkable isomers scattered across the nuclear landscape while highlightingthe possibilities to find more of them. Unique properties of some of them,harbor the potential for transformative applications in medicine and energy. Anexciting example is that of the lowest energy isomer known so far in^229Th, which may help realize the dream of an ultra-precise nuclear clockin the coming decade. These isomers also offer an insight into the extremes ofnuclear structure associated with them, which leads to their unusual status inenergy, half-life, spin etc. The review attempts to highlight isomers withhigh-multipolarities, high-spins, high-energies, longest half-lives, extremelylow energy, etc. A lack of theoretical understanding of the decay rates,half-lives and moments of these isomers is also pointed out.