Review of metastable states in heavy nuclei

Abstract

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.

Three-quasiparticle isomer in Ta173 and the excitation energy dependence of K -forbidden transition rates

“…4) is consistent with the earlier analysis [6], thus lending support to the significance of this correlation. A similar correlation had been demonstrated previously for four-and five-quasiparticle isomers [24], later extended to higher quasiparticle numbers [4,5,25]. It can be interpreted [24] as a statistical K-mixing effect which depends on the nuclear level density.…”

“…High-K isomers, with half-lives ranging from nanoseconds to years, can provide sensitive access to weakly populated excited-state structures in deformed nuclei [1][2][3][4][5]. The K quantum number represents the angular momentum projection on the nuclear symmetry axis, and transitions that violate the K-selection rule, i.e., those with multipole order λ < K, probe the symmetry-breaking mechanisms.…”

“…Despite the large body of data on these "K-forbidden" transitions [3], the understanding of the corresponding transition rates remains poor. Nevertheless, the systematic variation of hindrance factors has the potential to provide critical predictive power [2,5,6], which may be helpful in the study of exotic nuclei.…”

High-K isomers: some of the questions

“…Extension of the f ν systematics from two-quasiparticle to multi-quasiparticle isomers is discussed elsewhere [4,5,7,14]. For multi-quasiparticle states, it is evident that the level density is an important variable.…”

“…During my PhD, we made an experimental study of high-spin states in 172 Hf [1,2], and we thus embarked on a life-long journey exploring long-lived, excited states in deformed nuclei, the so-called K isomers. Amongst our many joint publications are a 1999 Nature review of isomers [3]; a 2001 review focussed on high-K isomers [4]; and finally an in-depth isomer review, soon to be published [5], that Dracoulis worked on until shortly before he died. He also published other related reviews, notably his recent Nobel symposium paper [6], and a new and comprehensive K-isomer tabulation [7].…”