High-Kisomerism in rotational nuclei

Abstract

High-K isomers are excited metastable excitations that are found amongst the rotational states of deformed atomic nuclei. They exemplify the coexistence of single-particle and collective degrees of freedom. We review their properties and their theoretical description based on extensions of the Nilsson–Strutinsky approach. Emphasis is given to the limits of K-isomer existence, exotic shapes, fission, K-isomer collective rotations, and the possibilities for isomer manipulation.

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.…”

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.…”

K selection in the decay of the (ν52[532]⊗32[411]

“…Less abundant are K-isomers measured in the A ≈ 130, 150 and actinide regions [2,3]. Interestingly, the neutron-rich A ∼ 100 region, where the K quantum number is expected to play a major role as a result of the prevalence of axiallydeformed ground-states, has a scarcity of observed K isomers formed from multi-quasiparticle states, fewer than even the transuranic elements [3,4]. Perhaps more intruiging is the formation of K-isomeric states in 98 Sr [5] and 100 Sr [6], without the anologous states in the respective zirconium isotones being observed as isomeric.…”

“…The (ν 5 2 [532] ⊗ 3 2 [411]) 4 − state in 102 Zr, populated in the β-decay of 102 Y, has been measured to be isomeric with a mean lifetime of 9.5(7) ns. It decays via four transitions, two of which are ∆K = 2 (to the 3 + and 4 + members of the 2 + γ band) and one is ∆K = 4 (to the 4 + member of the ground state 0 + band).…”