Abstract.The structure of nuclear isomeric states is reviewed in the context of their role in contemporary nuclear physics research. Emphasis is given to high-spin isomers in heavy nuclei, with A 150. The possibility to exploit isomers to study some of the most exotic nuclei is a recurring theme. In spherical nuclei, the role of octupole collectivity is discussed in detail, while in deformed nuclei the limitations of the K quantum number are addressed. Isomer targets and isomer beams are considered, along with applications related to energy storage, astrophysics, medicine, and experimental advances.

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The structure and decay properties of high-K isomers in 176 Hf have been studied using beam sweeping techniques and the Gammasphere multi-detector array. A new ∆K = 8 decay branch, from a K π = 22 − , six-quasiparticle, isomeric (t 1/2 = 43µs) state at 4864 keV to the 20 − state of a K π = 14 − band, has been identified. The reduced hindrance factor per degree of K forbiddenness for this decay is measured to be unusually low (f ν = 3.2), which suggests K mixing in the states 2

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Excited states in 180 Ta have been identified using the 176 Yb( 11 B,␣3n) 180 Ta and 176 Yb( 7 Li,3n) 180 Ta reactions and associated time-correlated ␥-ray spectroscopy, including particle-␥ coincidences for channel selection. As well as identifying the rotational band based on the 9 Ϫ two-quasiparticle state at 75 keV, at least eight other low-lying two-quasiparticle states and associated rotational bands have been established. Lifetimes in the few nanosecond region were isolated using ␥-␥-time techniques. Most of the observed two-quasiparticle states and some of the band members can be identified with states known from particle transfer studies. The properties of the observed ⍀ n Ϯ⍀ p partners of 1 ϩ and 8 ϩ bands from the 9/2 ϩ ͓624͔ 7/2 ϩ ͓404͔ configuration and the 0 Ϫ and 9 Ϫ pair from the 9/2 ϩ ͓624͔ 9/2 Ϫ ͓514͔ configuration are discussed. High-K structures identified include the band based on the four-quasiparticle 45 s, 15 Ϫ isomer, a 32 ns, four-quasiparticle 18 (ϩ) isomer, and a six-quasiparticle 19 (Ϫ) intrinsic state and its band. Configuration assignments are aided by analysis of the in-band decay properties, which confirm, for example, a predominantly 3 configuration for the 15 Ϫ isomer. The results are compared with multiquasiparticle calculations. A number of yrast high-K sixand eight-quasiparticle states which could be accessible in future studies are predicted.