Low lying isomers in the region of superheavy nuclei

TL;DR

This paper surveys low-lying, long-lived isomeric states in superheavy nuclei (Z>100), focusing on states with $T_{1/2}$ typically exceeding $1~\mu s$ and classifying them into spin, seniority, $K$, and shape isomers. It traces the historical development of isomer concepts, outlines experimental approaches (fusion-evaporation, in-flight separation, $\alpha$/$\gamma$/$CE$ spectroscopy), and compiles extensive systematics across even-Z, odd-mass, and odd-odd regions, highlighting both well-established cases and many unresolved questions. The work emphasizes the role of Nilsson-level predictions, deformation landscapes, and hindrance effects in shaping observed isomerism, and it underscores the need for higher-statistics data and refined theory to constrain shell evolution in the heaviest nuclei. Overall, it provides a comprehensive status snapshot and a roadmap for future experimental and theoretical efforts to map the complex isomeric structure of transfermium elements.

Abstract

In the present study we want to give an overview on low lying isomeric states in the heaviest nuclei. After a short report on the early history on the discovery of nuclear isomerism and attempts to understand their physical nature, decay probabilities and structure of all low lying isomeric states in heaviest nuclei with half-lives typically longer than one microsecond are presentet. Special emphasisis is laid on cases where the above mentioned properties are still unclear or under discussion. We do not claim to have solved the problems in that cases, we rather want to give som hints for further discussions.

Figures (48)

• Figure 1: Simplified decay schemes for $^{212}$Bi and $^{234}$Pa; the decay branches shown for $^{212}$Bi do not add up to 100$\%$ as some weaker $\beta^{-}$ and $\alpha$ decays are not shown in this simplified decay scheme.
• Figure 2: Lifetimes for 2$^{l}$ multipole radiation according to C.F. von Weizsäcker Weizs1936 (black squares) and H.A. Bethe Bethe1937 (red dots) for a nucleus of Z = 90 and $\Delta$E = 500 keV.
• Figure 3: Partial level scheme of $^{210}$Pb; data taken from Fire96. Transition energies are given in keV.
• Figure 4: Angular momentum coupling schemes; a) single unpaired nucleon with nucleon orbital angular momentum and spin vectors in 'parallel'; b) single unpaired nucleon with nucleon orbital angular momentum and spin vectors 'anti-parallel'; c) coupling scheme for two unpaired nucleons (for nonrotating nuclei).
• Figure 5: a) Sketch of a shape isomer, b) decay scheme of the shape isomer in $^{238}$U.