100 Years of Nuclear Isomers

The exceptionally low energy of the isomeric first excited nuclear state of ${}^{229}$Th, which has recently been constrained to 8.28$\pm$0.17 eV (i.e. $\lambda$=149.7$\pm$3.1 nm) [1], allows for direct laser excitation with current technology. This offers the unique opportunity to develop a nuclear clock capable of competing or even outperforming existing atomic clocks. One of the next steps...

The isotope 229-thorium features a low-energy (8.28 ± 0.17 eV) nuclear-excited state, the so-called thorium isomer [1]. This unique property makes it the only nuclear transition accessible with current laser technology and therefore suitable for the operation as a nuclear clock. Such a clock has applications in fundamental physics [2] and the potential to surpass the precision achieved by...

The proxy-SU(3)symmetry is an extention of the Elliott SU(3), applicable in medium mass and heavy nuclei. It has been succesfully used in the prediction of: a) the dominance of the prolate over the oblate nuclear shape, b) the prolate-oblate shape transition and c) the islands of shape coexistence on the nuclear chart. The quadrupole electric transition probabilities among isomeric, positive...

The $^{229}$Th nucleus posses a metastable first excited state, i.e., an isomer, at around 8.19 eV. This state should be accessible via VUV light and presents a radiative lifetime of a few hours. These unique properties make $^{229}$Th a promising candidate for a nuclear clock with excellent accuracy $[1]$. However, due to the relatively large uncertainty on the isomeric state energy,...

Isotopes of Hg and Tl in the $\textit{A} \approx $ 200 region exhibit competition between collective and intrinsic modes of angular momentum generation. The neutron number $\textit{N} = 120$ appears to constitute a boundary, with lighter isotopes exhibiting collective behavior, and heavier ones displaying primarily single-particle excitations. Most of these isotopes lie close to the line of...

Nuclear Excitation by Electron Capture (NEEC) involves the capture of an electron into a vacant atomic orbital, with the simultaneous excitation of the nucleus, assumed due to virtual photon exchange, and is a possible mechanism that can depopulate isomers in hot-dense astrophysical plasmas. The first observation of NEEC was reported in Nature 2018 [1], via the depletion of the 6.85hour...

The extremely low-energy $^{229}$Th isomeric state has two possible decay channels towards the ground state: radiative decay and internal conversion (IC). Because of a $10^9$ difference in half-life, IC is the dominant channel. Blocking the IC decay channel is critical for high-precision measurements of the transition energy and for the realization of an efficient solid-state nuclear clock....

The long chain of Sn isotopes is a formidable testing ground for nuclear models studying the evolution of shell structure and interplay between pairing and quadrupole correlations. A transition from superfluid nuclei at midshell to spherical nuclei is also expected approaching the neutron shell closures at N = 50, where the seniority scheme can be adopted to describe the energy spectra....

The neutron-rich isotope rhenium-190 lies in the mass ≈170-190 region of the nuclide chart; a region known for the occurrence of a large number of metastable, isomeric nuclear states [1]. The formation of these states is caused by significant quadrupole deformations and are named K-isomers, due to the large angular momentum projection, K, on the nuclear deformation axis. These K-isomers...

Nuclear excitation by electron capture (NEEC) was initially proposed in 1976 by Goldanskii and Namiot [1] as the inverse internal conversion process.
The recent observation of NEEC in the $^{93}$Mo isomer depletion [2] caused a lively discussion [3, 4] and sparked new interest: the measured excitation probability $P_{exc}$ is unexpectedly larger than what is predicted by the state-of-the-art...

Nuclear isomers can store a large amount of energy over long periods of time, with a very high energy-to-mass ratio. Dynamical external control of such nuclear states has proven so far very challenging, despite ground-breaking incentives for a clean and efficient energy storage solution. Here, we describe a protocol to achieve the dynamical control of the isomeric nuclear decay via the process...

A considerable progress during the past decades was achieved in investigation of the interrelation of the atomic structure with the nuclear processes. Nuclear isomers can be effectively triggered by making use of a resonance with the electronic transitions, which can be further tuned either through changing the electron shell, or irradiating with resonance field of a laser [1,2]. Thus, it was...

The nuclear two-photon (2γ) decay is a rare decay mode in atomic nuclei whereby a nucleus in an excited state emits two gamma rays simultaneously. First order processes usually dominate the decay, however two-photon emission may become significant when first order processes are forbidden or strongly retarded, which can be achieved at the experimental storage ring ESR (GSI/FAIR). Within this...

The neutron-rich nuclei in the vicinity of $^{132}$Sn and $^{208}$Pb regions exhibit an abundance of nuclear isomers. The existence of the different isomers alludes to the dominance of proton or neutron excitations for low-lying states. Thus the observed structure and transition probabilities can be easily described in terms of the seniority scheme for the low-lying structure near Sn and Pb...

The elusive Thorium Isomer ($^{229m}$Th) with its unusually low-lying first excited state ($8.19 \pm 0.12$ eV or $\lambda= 150.4 \pm 2.2$ nm) represents the so far only candidate for the realization of an optical nuclear clock, potentially capable to outperform even state-of-the-art optical atomic clocks. Moreover, possible applications of a nuclear clock are not limited to time keeping, but...