Nuclei in the vicinity of doubly-magic ones often exhibit isomeric states arisen due to the low energies and/or high multipolarities of the gamma rays depopulating them. Around $^{208}$Pb these long-lived states often decay by electric octupole (E3) transitions. Their transition strength give information about their nature. In this region these can be collective, explained by the large number...
The coexistence of single-particle and collective degrees of freedom in atomic nuclei gives rise to various exotic phenomena. In nuclei with very asymmetric proton-to-neutron ratios, the strong nuclear interaction drives shell evolution which alters the orbital spacing, and in some cases even the ordering present in stable nuclei. Such changes in the structure can have profound consequences...
State-of-the-art optical clocks achieve precisions of 10−18 or better using ensembles of atoms in optical lattices or individual ions in radio-frequency traps. Promising candidates for use in atomic clocks are highly charged ions (HCIs) and nuclear transitions, which are largely insensitive to external perturbations and reach wavelengths beyond the optical range that are accessible to...
Shape coexistence occurs when the potential energy of the nucleus is characterized by local minima for different shapes. Excited states in the secondary minimum may become isomeric if the potential barrier separating the secondary minimum from the ground-state minimum is sufficiently pronounced. The first examples of such shape isomers were observed in the 1960s, as fission isomers in the...
The single particle (sp) structure of isomeric states of some well-deformed even-even
nuclei in the rare-earth and actinide regions is studied within a self-consistent Hartree-
Fock plus BCS approach (with blocking)[1]. The well studied Skyrme SIII parametrisation
is used for the particle-hole part of the nuclear interaction and a seniority force for its
residual part. The parameters of...
The ISOL technique of producing radioactive beams at TRIUMF [1] is well recognized for producing exotic species in both their ground- and isomeric states. The beta and beta-delayed-neutron decay of ground spin and isomeric states has been investigated with the GRIFFIN spectrometer [2], consisting of up to 16 Compton-suppressed hyper purity Germanium detectors for gamma-ray detection and...
The observation of proton radioactivity from nuclei beyond the proton drip line, provides a way to probe nuclear structure at the limits of stability. The existence of long-lived isomeric states can encourage the emission of a proton besides the ground state emission, and thus provide extra experimental information on exotic nuclei, that are difficult to produce and observe, due
to the very...
The common microscopic origin of nuclear metastability manifesting
in the wide energy range from the mega electronvolt excitations of
K-isomers in even-even nuclei to the exceptionally low-energy
excitation of several electronvolts in the $^{229m}$Th "clock"
isomer will be discussed. It will be shown in terms of relatively
simple nuclear-structure models that the very fine...
Today’s most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outper-formed by a nuclear clock, which employs a nuclear transition instead of an atomic shell transition. There is only one known nuclear state that could serve as a nuclear clock us-ing currently available technology, namely the isomeric...
Quasi-particle structure is vital to understanding the stability of the heaviest elements. The alpha decay and fission processes ultimately determine how long a nucleus will survive. Observations in the decay chains of 270Ds suggest that high-K multi-quasiparticle isomeric states can decay via alpha emission where the metastable state is longer lived than the ground state of the same nucleus....
Energy storage in chemicals, whether fuels or batteries, forms the basis for the U. S. Army’s many energy
and power applications. However, these materials are restricted in both energy density and longevity,
motivating interest in radioisotopes and nuclear isomers as a means of pushing beyond the “chemical
limit”. In particular, the potential for long‐lived isomers to enable production,...
The development of high-quality isomeric beams opens the possibility to probe the influence of nuclear isomers in stellar scenarios and provide experimentally constrained parameters to astrophysical reaction rates. Such is the case of the low-lying isomers along the rp-process nucleosynthesis path, or on Galactic $^{26}$Al.
In this talk, I'll discuss recent experimental efforts to develop...
Isomeric states may play an important role in the rp-process, but as of yet are not regularly included in sensitivity studies. In astrophysical environments, isomers may be populated through thermal excitation, as a beta-decay end product, or a combination of these. Significant isomeric populations can alter the effective beta decay rate of a given isotope, and proton capture on these isomers...
Neutron capture reactions play an important role in nuclear physics and other fields that seek to understand physical processes in which neutrons react with their environment. In particular, knowledge of capture cross sections is crucial for nuclear astrophysics applications. Many required capture cross sections are unknown and extremely difficult to determine experimentally, as their...
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...
Heavy nuclei are known to be produced by various nuclear processes such as r-, ν-, νp-, γ- and s-processes in massive stars as well as small-to-intermediate mass stars like AGBs. Several nuclear isomers in heavy nuclei play the critical roles in determining their final abundances. Especially, the first three r-, ν- and νp-processes among them are strongly affected by the ν-nucleus interactions...
The change of the shell structure in atomic nuclei, so-called nuclear shell evolution, occurs due to changes of major configurations through particle-hole excitations inside one nucleus, as well as due to variation of the number of constituent protons or neutrons. We have investigated how the shell evolution affects Gamow-Teller (GT) transitions, which dominate the $\beta$ decay in the...
Self-consistent configuration-constrained Total Routhian Surfaces (TRS) [1,2] have been developed to treat the collective rotations of quasiparticle states built on broken-pair excited configurations. Two types of interaction have been used for the configuration-constrained TRS calculations: the deformed Woods-Saxon potential and the two-body Skyrme force within the Hartree-Fock approximation...
The phenomenon of nuclear shape isomerism, which is an example of extreme shape coexistence in nuclei, arises from the existence of a secondary minimum in the nuclear potential energy surface (PES), at substantial deformation, separated from the primary energy minimum (the ground state) by a high potential energy barrier that hinders the transition between the minima. Shape isomers at spin...
The long-lived isomer in 229Th, first studied in the 1970s as an exotic feature in nuclear physics, is the only known candidate for the development of a nuclear clock. The transition energy between the ground and first excited states of 229Th is unusually small and amounts to only several eV, making it the only laser-accessible nuclear transition. An optical clock based on this transition...
Nuclear isomers can play a pivotal role in the nucleosynthesis of elements and can have various effects on the reaction path. Some of these "astromers" are however difficult to produce and their effects hard to study under laboratory conditions.
I will discuss two isomer-related projects that are planned at TRIUMF, utilizing the decay spectroscopy setup at the TITAN Electron Beam Ion Trap...
A unique feature of thorium-229 is its isomer with an exceptionally low excitation energy, proposed as a candidate for future optical clocks [1]. The small decay width is expected to outperform the accuracy of current state-of-the-art atomic clocks by an order of magnitude [2]. The current best values of the excitation energy are 8.28(17)eV and 8.10(17)eV [3,4]. These were determined using two...
Several aspects of the ELI-NP research program related to isomeric studies will be presented, namely, population of isomers and decay studies in γ-beam activation experiments, studies of doorway states for population or depopulation of isomers in γ-beam experiments and measurements of photofission product yields.
The possibilities for generation of γ beams with orbital angular momentum (OAM)...
An experiment on 4D-imaging of drip-line radioactivity near doubly-magic 56Ni was conducted at GANIL. Pictured with the ACTAR TPC, proton-emission branches from the 6457-keV, 10+ isomer in 54mNi were established [1]. These feature unusually high angular momentum, l=5 and l=7, respectively, which requires a dedicated theoretical treatment [2].
The completed proton-emission pattern of 54mNi...
Nuclear isomers often possess a unique configuration or shape that allows testing nuclear models and advancing the understanding of nuclear structure. In addition, in many cases isomers allow for an easier experimental identification and/or correlated and background-reduced data analysis. Our recent nuclear structure studies of neutron-rich Kr isotopes using prompt and delayed gamma...
The nuclear isomers are long-lived excited states, with half-lives ranging from nanoseconds to years. The reason behind their existence may vary from a region-to-region on the basis of hindrance mechanisms and nucleonic surroundings. Understanding the existence of isomers can shed light on both the basic modes of nucleonic motion, single-nucleon as well as collective, and their interplay....
Penning-trap mass spectrometry offers a way to determine excitation energies of isomeric states via high-precision mass measurements. The method is very useful for beta-decaying isomers with half-lives longer than around 100 ms. Excitation energies of such isomers are often challenging to unambiguously determine with other techniques. Penning-trap mass spectrometry can also reveal new isomeric...
Much attention has been drawn in recent years to the heaviest known self-conjugate nucleus, 100Sn, and its implications on nuclear structure models. Various decay experiments have been conducted to study the nucleus’ expected doubly-magic character of the closed proton and neutron shells. Direct measurements by means of mass-spectrometry or laser-spectroscopy are challenging due to its short...
In the study of isomer excitation and deexcitation, it is important to know the structure properties of isomers, and in addition, the intermediate states with detailed internal transitions (ITs) that connect isomers and the ground state [1,2]. Theoretical study of all these requires the modern many-body technique and knowledge on nuclear interactions. We apply two different shell models, the...
Astrophysics models usually take one of two approaches to nuclear reaction and decay rates: either they use the nuclear ground state properties, or they take a thermal equilibrium distribution of excited states. Nuclear isomers can invalidate both of these assumptions. If an isomer has a decay rate very different from the ground state rate, its inhibited transitions can cause it to fail to...
It is well known that 102Rh has a ground state with t1/2 = 207.3 days and an isomer at an excitation energy of 140.7 keV with t1/2 = 3.742-years. Following the irradiation of a rhodium chloride target with 35-MeV protons from Lawrence Berkeley National Laboratory's 88-Inch Cyclotron, we chemically separated the rhodium and palladium fractions and then counted them separately using high-purity...
We obtained some fascinating results on the $^{213}$Pb neutron-rich nucleus studied using the unique availability of a primary 1 GeV $A$ $^{238}$U beam and of the FRS-RISING setup at GSI. The products of the uranium fragmentation were separated in mass and atomic number and then implanted for isomer decay $\gamma$-ray spectroscopy. A level scheme from the decay of the $21/2^+$ isomer, based on...
Magic nuclei are the cornerstone of our understanding of the nuclear structure, and the double shell closure in $^{208}$Pb (Z=82, N=126) makes no exception. The persistence of these magic number far from $^{208}$Pb is a key issue for the understanding of heavy nuclei as well as for the r-process path. While the region beyond N=126 and below Z=82 is difficult to reach with multi-nucleon...
The lecture describes Otto Hahn's youth in Frankfurt and his growing interest in chemistry and how his teachers, professors Theodor Zincke (Marburg), Adolf von Bayer (Munich), William Ramsay (London), Ernest Rutherford (Montreal) and Emil Fischer (Berlin) paved the way for him to become one of the world's leading radiochemists. In addition to his important discoveries in the field of...
We discuss selected results of a large scale exotic symmetry research project addressing even-even nuclei with Z, N $>$ 10, including exotic and super-heavy nuclei -- calculations performed in multidimensional deformation spaces. In the presentation we focus on realistic nuclear mean-field theory results for two types of nuclear isomers: yrast-trap and K-isomers in axially symmetric nuclei,...
A high rate of producing nuclear isomers is critical for many applications, like nuclear clocks and nuclear γ-ray lasers etc. However, due to small production cross sections and quick decays, as well as limited intensities of driving beams, it is extremely difficult to achieve a high producing rate via traditional accelerators or reactors. Here, we present a pumping of nuclear isomeric states...
Despite being a well-studied nucleus close to stability, the $K$-shell X-ray and Auger fluorescence yield for scandium-44 are not very well defined. However, the low-lying nuclear structure of $^{44}_{21}$Sc and its population in $^{44}$Ti electron capture decay lends itself to extracting these quantities.
The first two excited states in $^{44}$Sc are isomeric and lie at 68 keV and 146 keV...
The nuclear structure of neutron-rich actinide $^{248}$Cf was investigated at the Tokai Tandem Accelerator Laboratory of the Japan Atomic Energy Agency. This isotopes lies two neutrons and two protons below the generally accepted $Z$=100 and $N$=152 deformed shell gaps, but recently the location of these gaps has been heavily debated and $Z$=98 has also been suggested. $^{248}$Cf was produced...
There are two fundamental kinds of excitation modes in the atomic nucleus: collective and single-particle excitations. So far, most of the theoretical effort has focused on the study of the former and the latter has been mostly treated by using the quasiparticle spectrum of neighboring nuclei [1] or the equal-filling approximation [2]. However, these approaches explicitly neglect time-odd...
In heavy and superheavy nuclei with Z > 100 several isomeric states are known to exist. Some of these isomers are rather long-lived and feature low excitation energies making their identification sometimes challenging. With the Penning-trap mass spectrometer SHIPTRAP at the GSI in Darmstadt, Germany, we can identify long-lived isomers and determine their excitation energy accurately. In recent...
When the liquid drop fission barrier vanishes in the fermium-rutherfordium region only the stabilization by quantum mechanics effects allows the existence of the observed heavier species. Those are in turn providing an ideal laboratory to study the strong nuclear interaction by in-beam methods as well as decay spectroscopy after separation [1].
Among the nuclear structure features to be...
A century after its discovery, isomerism has proven to be a very fertile tool for the study of nuclear structure, with an important impact on models development. As early as 1973, isomeric states were observed in the A~ 250 mass region in 250Fm and 254No by Ghiorso et al [1]. This region around Z = 100, N = 152 is characterized by prolate-deformed...
In terms of societal applications the nuclear isomer Tc-99m is most famous with about 30 million diagnostic procedures performed per year with Tc-99m radiopharmaceuticals. However, there are also less famous isomers with applications in nuclear medicine as well as infamous isomers that should be avoided as radionuclidic impurity. A review will be given on past, present and future of nuclear...
With their successful application of nuclear magnetic resonance NMR to investigate the structure of atoms in liquids and solids Felix Bloch and Edward Mills Purcell (Nobel prize 1952) opened new ways to study local aspects in solids via the hyperfine interaction of a nuclear moment with extra-nuclear fields. While for roughly half the elements no appropriate nuclei are available because of...
The exotic neutron-rich region around and beyond N=126 has long been pursued for investigation in many radioactive ion beam (RIB) facilities and it is still one of the major milestones of the latest generation of RIB laboratories. Because of the challenges in accessing the region due to the technical difficulties in producing, separating, and investigating neutron-rich N⩾ 126 nuclei, the...
Properties of deformed, neutron-rich nuclei in the A~110 and 160 mass regions are important for achieving better understanding of the nuclear structure where little is known owing to difficulties in the production of these nuclei at the present RIB facilities. They are essential ingredient in the interpretation of the r-process nucleosynthesis and are needed in fission-like applications since...
One of the most basic properties of nuclear states are their size. Yet, a microscopic understanding of the size behaviour of these nuclear isomers has proved challenging as it depends strongly on the region of the nuclear chart and type of nuclear isomer.
How the change in size (quantified by their change in charge radius) of nuclear isomers varies from their ground states gives important...
Half-life of short-lived bare isomer $^{94m}_{44}$Ru$^{44+}$ has been studied for the first time at the HIRFL-CSR facility in Lanzhou by employing the Isochronous Mass Spectrometry (IMS) method. It was populated in projectile fragmentation of a $^{112}$Sn beam on a $^{9}$Be target. Fragmentation products in the region of interest were passed through the radioactive ion beam line and injected...
The population and decay of isomeric states in the neutron-deficient nuclei around $A\sim100$ is important for astrophysical processes, as these states are often involved in vast reaction networks taking place at astrophysical sites. The general scarcity of cross section data for isomeric states in the p-process has provided the main motivation behind the present work. Experimental cross...
Around closed shells, intruder orbitals with large angular momentum difference and opposite parity compared to the ground state orbital lead to an accumulation of isomeric states. Below the $N=82$ shell, low-lying states in the even-$Z$, $N=81$ isotones are the $J^\pi = 1/2^{+}, 3/2^{+}$ and $11/2^{-}$ neutron-hole states, associated with the $s_{1/2}$, $d_{3/2}$, and $h_{11/2}$ orbitals,...
Isomeric nuclear states are nuclear states which decays with long lifetimes
(T1/2 > 10 ns) and generally reveals, a big change in angular momentum in its decay, a small matrix element or a small transition energy. By measuring lifetimes of isomeric states it’s possible to obtain information about this state wave function, being a robust test for nuclear models. There are several gamma-ray...
Neutron-deficient nuclei around mid-shell at $N \sim 104$ in the lead region provide many examples of shape coexistence and shape isomers. In order to study shape coexistence in this region, prompt and delayed $\gamma$-ray spectroscopy of the $^{187}$Pb, $^{183}$Hg and $^{188}$Bi isotopes produced in the reaction $^{50}$Cr+$^{142}$Nd$\to$$^{192}$Po$^{*}$ has been performed at the Argonne...
Isomers are major tools for the study of nuclear structure especially high-spin spectroscopy. Nuclear isomers occur throughout the nuclear chart, but high-K isomers are abundant in the rare-earth region. This type of isomer has an axially symmetric shape and possesses a quantum number “K”, corresponding to the projection of the total angular momentum onto the symmetry axis. Because of K...
In fact, nuclear isomers are studied in rapid neutron capture process so-called $r$ - process of the nucleosynthesis in neutron stars which occurs at the energy state about several MeV (dozens of GK) causing cooling of the star matter. Thus, isomers freeze out in thermal equilibrium due to cooling the neutron star matter by the $r$ - process, i.e. they can immediately be populated in the star...
Understanding the production and survival of $\mathrm{^{205}Pb}$ in stars is pivotal as $\mathrm{^{205}Pb}$ is the only short-lived radionuclide that is produced exclusively by the slow neutron capture process (s-process). The ratio of radioactive $\mathrm{^{205}Pb}$ to stable $\mathrm{^{204}Pb}$, when compared to the expected value from the continuous galactic nucleosynthesis, helps to...
The measurement and interpretation of isomeric ratios have provided information about the energy levels structure of nuclear systems and the angular momentum and reaction mechanism effects involved in the production of isomeric states in nuclei.
In the present work results of the investigation of the isomeric yield ratios $Y_m/Y_g$ of the reaction $^{198}Hg(\gamma,n)^{197m,g}Hg$ and...
Theoretical studies of superheavy nuclei are expected to bring in new opportunities and more exciting times in the arena of experimental activities eyeing on synthesis of new superheavy nuclei [1]. In this particular region of periodic chart, α-decay is the dominant decay mode in which transitions take place from ground-to-ground states [2] and also in or from isomeric state [3]. In the...
