Yrast three - quasiparticle K isomers in neutron - rich 181 Hf

Long-lived isomeric states in nuclei are unique laboratories for studying the detailed properties of nuclear wave functions. From an experimental standpoint, transitions deexciting long-lived isomers provide clean information on wave-function admixtures, since a better signal-to-noise ratio is achieved if short-lived excitations are allowed to decay away. From a theoretical perspective, a long-lived isomeric state is a manifestation of underlying symmetries of the nuclear wave function. K isomers ~where K is the projection of the total angular momentum of a deformed nucleus onto its axis of symmetry! form a special subset that showcases the competition and rich dynamics between collective and single-particle excitations in a deformed system. In this work, K isomers are used to locate and follow the evolution of individual Nilsson states and their couplings in a previously unexplored neutron-rich region of the nuclear chart and provide a groundwork for future exploration of rotational excitations built on these new isomers. High-K configurations at low excitation energy abound in the A'180 region of the nuclear chart, where deformed nuclei with axial symmetry have valence nucleons in Nilsson orbitals with large angular momentum projections on the symmetry axis. The Hf (Z572) isotopes offer an especially robust platform for a systematic study of high-K physics, with rigid axial deformations persisting over a wide range of spin and isospin. While yrast high-K isomers have long been predicted @1,2# to dominate the excitation spectrum of neutron-rich (A.180) Hf nuclei, recent calculations @3# suggest oblate rotation as a collective mode at high spins. Limi-