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Atomic Structure of the Heaviest Elements

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A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: closed (30 April 2022) | Viewed by 39998

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Special Issue Editors

Dr. Mustapha Laatiaoui

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Guest Editor

Department Chemie, Johannes Gutenberg University, 55128 Mainz, Germany
Interests: superheavy elements; laser spectroscopy; ion mobility spectrometry

Dr. Sebastian Raeder

E-Mail Website
Guest Editor

GSI Helmholtz Center for Heavy Ion Research, 64291 Darmstadt, Germany
Interests: superheavy elements; laser spectroscopy; trace analysis

Special Issue Information

Dear Colleagues,

Actinides exhibit a remarkable transition in terms of applied and fundamental research as they comprise the heaviest naturally occurring as well as fully manmade chemical elements. They have attracted the attention of atomic spectroscopists since their discovery as it was believed that many of their elemental properties could be deduced from knowledge of the electron configuration. The tiny quantity production of these elements did not prevent scientists from performing elaborate and extensive spectroscopy, such as with huge spectrographs. Thus, essential data about the atomic structure up to element 99 – einsteinium – were obtained even if some spectral lines could not be (or not correctly) assigned back then.

Today, we are much further along in atomic spectroscopy, although the actinides are far from being fully explored. In addition to better model descriptions of the atom, recent developments and advances in the field of optical spectroscopy have not only led to a better understanding of the atomic structure of the already measured elements but also to tackling the superheavy elements previously considered experimentally inaccessible.

This Special Issue of Atoms covers recent theoretical and experimental work about the atomic structure of actinides as well as related topics, such as transport properties in gases, nuclear properties, and medical applications. With the advancing technology for production and handling of actinides and transactinides, we hope that this issue will serve as a useful resource for future work in the field of optical spectroscopy and accelerator-based laser ion sources. We welcome original research articles as well as review articles on specific topics.

Dr. Mustapha Laatiaoui
Dr. Sebastian Raeder
Guest Editors

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Keywords

optical spectroscopy
actinides
transactinides
superheavy elements
transport properties
atomic structure
electronic configuration
ion–atom interaction
relativistic effects
electron correlations

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Published Papers (13 papers)

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Research

11 pages, 2572 KiB

Open AccessArticle

A Progress Report on Laser Resonance Chromatography

by Elisa Romero Romero, Michael Block, Biswajit Jana, Eunkang Kim, Steven Nothhelfer, Sebastian Raeder, Harry Ramanantoanina, Elisabeth Rickert, Jonas Schneider, Philipp Sikora and Mustapha Laatiaoui

Atoms 2022, 10(3), 87; https://doi.org/10.3390/atoms10030087 - 6 Sep 2022

Cited by 6 | Viewed by 2222

Abstract

Research on superheavy elements enables probing the limits of nuclear existence and provides a fertile ground to advance our understanding of the atom’s structure. However, experimental access to these atomic species is very challenging and often requires the development of new technologies and experimental techniques optimized for the study of a single atomic species. The Laser Resonance Chromatography (LRC) technique was recently conceived to enable atomic structure investigations in the region of the superheavy elements. Here, we give an update on the experimental progress and simulation results. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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9 pages, 1191 KiB

Open AccessArticle

New Developments in the Production and Research of Actinide Elements

by Mustapha Laatiaoui and Sebastian Raeder

Atoms 2022, 10(2), 61; https://doi.org/10.3390/atoms10020061 - 8 Jun 2022

Cited by 4 | Viewed by 2700

Abstract

This article briefly reviews topics related to actinide research discussed at the virtual workshop Atomic Structure of Actinides & Related Topics organized by the University of Mainz, the Helmholtz Institute Mainz, and the GSI Helmholtz Centre for Heavy Ion Research, Darmstadt, Germany, and held on the 26–28 May 2021. It includes references to recent theoretical and experimental work on atomic structure and related topics, such as element production, access to nuclear properties, trace analysis, and medical applications. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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8 pages, 2046 KiB

Open AccessEditor’s ChoiceArticle

The NEXT Project: Towards Production and Investigation of Neutron-Rich Heavy Nuclides

by Julia Even, Xiangcheng Chen, Arif Soylu, Paul Fischer, Alexander Karpov, Vyacheslav Saiko, Jan Saren, Moritz Schlaich, Thomas Schlathölter, Lutz Schweikhard, Juha Uusitalo and Frank Wienholtz

Atoms 2022, 10(2), 59; https://doi.org/10.3390/atoms10020059 - 1 Jun 2022

Cited by 10 | Viewed by 3019

Abstract

The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher cross-sections. The main drawback of this technique is the wide angular distribution of the transfer products, which makes it challenging to catch and prepare them for precision measurements. To overcome this obstacle, we are building the NEXT experiment: a solenoid magnet is used to separate the different transfer products and to focus those of interest into a gas-catcher, where they are slowed down. From the gas-catcher, the ions are transferred and bunched by a stacked-ring ion guide into a multi-reflection time-of-flight mass spectrometer (MR-ToF MS). The MR-ToF MS provides isobaric separation and allows for precision mass measurements. In this article, we will give an overview of the NEXT experiment and its perspectives for future actinide research. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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11 pages, 2469 KiB

Open AccessArticle

Resolution Characterizations of JetRIS in Mainz Using ¹⁶⁴Dy

by Danny Münzberg, Michael Block, Arno Claessens, Rafael Ferrer, Mustapha Laatiaoui, Jeremy Lantis, Steven Nothhelfer, Sebastian Raeder and Piet Van Duppen

Atoms 2022, 10(2), 57; https://doi.org/10.3390/atoms10020057 - 28 May 2022

Cited by 6 | Viewed by 2428

Abstract

Laser spectroscopic studies of elements in the heavy actinide and transactinide region help understand the nuclear ground state properties of these heavy systems. Pioneering experiments at GSI, Darmstadt identified the first atomic transitions in the element nobelium. For the purpose of determining nuclear properties in nobelium isotopes with higher precision, a new apparatus for high-resolution laser spectroscopy in a gas-jet called JetRIS is under development. To determine the spectral resolution and the homogeneity of the gas-jet, the laser-induced fluorescence of ¹⁶⁴Dy atoms seeded in the jet was studied. Different hypersonic nozzles were investigated for their performance in spectral resolution and efficiency. Under optimal conditions, a spectral linewidth of about 200–250 MHz full width at half maximum and a Mach number of about 7 was achieved, which was evaluated in context of the density profile of the atoms in the gas-jet. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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12 pages, 2086 KiB

Open AccessArticle

Probing the Atomic Structure of Californium by Resonance Ionization Spectroscopy

by Felix Weber, Christoph Emanuel Düllmann, Vadim Gadelshin, Nina Kneip, Stephan Oberstedt, Sebastian Raeder, Jörg Runke, Christoph Mokry, Petra Thörle-Pospiech, Dominik Studer, Norbert Trautmann and Klaus Wendt

Atoms 2022, 10(2), 51; https://doi.org/10.3390/atoms10020051 - 24 May 2022

Cited by 5 | Viewed by 2604

Abstract

The atomic structure of californium is probed by two-step resonance ionization spectroscopy. Using samples with a total amount of about

2 \times 10^{10}

Cf atoms (ca. 8.3 pg), ground-state transitions as well as transitions to high-lying Rydberg states and auto-ionizing states above [...] Read more.

The atomic structure of californium is probed by two-step resonance ionization spectroscopy. Using samples with a total amount of about

2 \times 10^{10}

Cf atoms (ca. 8.3 pg), ground-state transitions as well as transitions to high-lying Rydberg states and auto-ionizing states above the ionization potential are investigated and the lifetimes of various atomic levels are measured. These investigations lead to the identification of efficient ionization schemes, important for trace analysis and nuclear structure investigations. Most of the measurements are conducted on

^{250}

Cf. In addition, the isotope shift of the isotopic chain

^{249 - 252}

Cf is measured for one transition. The identification and analysis of Rydberg series enables the determination of the first ionization potential of californium to

E_{IP} = 50, 666.76 (5)

{cm}^{- 1}

. This is about a factor of 20 more precise than the current literature value. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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9 pages, 294 KiB

Open AccessEditor’s ChoiceArticle

Electronic Structure of Lr⁺ (Z = 103) from Ab Initio Calculations

by Harry Ramanantoanina, Anastasia Borschevsky, Michael Block and Mustapha Laatiaoui

Atoms 2022, 10(2), 48; https://doi.org/10.3390/atoms10020048 - 9 May 2022

Cited by 8 | Viewed by 2393

Abstract

The four-component relativistic Dirac–Coulomb Hamiltonian and the multireference configuration interaction (MRCI) model were used to provide the reliable energy levels and spectroscopic properties of the Lr

^{+}

ion and the Lu

^{+}

homolog. The energy spectrum of Lr

^{+}

is very similar to [...] Read more.

^{+}

ion and the Lu

^{+}

homolog. The energy spectrum of Lr

^{+}

is very similar to that of the Lu

^{+}

homolog, with the multiplet manifold of the 7s

^{2}

, 6d

^{1}

^{1}

and 7s

^{1}

^{1}

configurations as the ground and low-lying excited states. The results are discussed in light of earlier findings utilizing different theoretical models. Overall, the MRCI model can reliably predict the energy levels and properties and bring new insight into experiments with superheavy ions. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

30 pages, 1379 KiB

Open AccessArticle

Update of Atomic Data for the First Three Spectra of Actinium

by Alexander Kramida

Atoms 2022, 10(2), 42; https://doi.org/10.3390/atoms10020042 - 22 Apr 2022

Cited by 4 | Viewed by 2722

Abstract

The present article describes a complete reanalysis of all published data on observed spectral lines and energy levels of the first three spectra of actinium (Ac I–III). In Ac I, three previously determined energy levels have been rejected, 12 new energy levels have been found; for six previously known levels, either the J values or the energies have been revised, and the ionization energy has been redetermined with an improved accuracy. In the line list of Ac I, three previous classifications have been discarded, 16 new ones have been found, and three have been revised. In Ac II, 16 new energy levels have been established, and 36 new identifications have been found for previously observed but unclassified lines. In both Ac I and Ac II, new sets of transition probabilities have been calculated. For all three spectra, complete datasets of critically evaluated energy levels, observed lines, and transition probabilities have been constructed to serve as recommended data on these spectra. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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12 pages, 2051 KiB

Open AccessArticle

Advancing Radiation-Detected Resonance Ionization towards Heavier Elements and More Exotic Nuclides

by Jessica Warbinek, Brankica Anđelić, Michael Block, Premaditya Chhetri, Arno Claessens, Rafael Ferrer, Francesca Giacoppo, Oliver Kaleja, Tom Kieck, EunKang Kim, Mustapha Laatiaoui, Jeremy Lantis, Andrew Mistry, Danny Münzberg, Steven Nothhelfer, Sebastian Raeder, Emmanuel Rey-Herme, Elisabeth Rickert, Jekabs Romans, Elisa Romero-Romero, Marine Vandebrouck, Piet Van Duppen and Thomas Walther Show full author list Hide full author list

Atoms 2022, 10(2), 41; https://doi.org/10.3390/atoms10020041 - 21 Apr 2022

Cited by 6 | Viewed by 3006

Abstract

RAdiation-Detected Resonance Ionization Spectroscopy (RADRIS) is a versatile method for highly sensitive laser spectroscopy studies of the heaviest actinides. Most of these nuclides need to be produced at accelerator facilities in fusion-evaporation reactions and are studied immediately after their production and separation from the primary beam due to their short half-lives and low production rates of only a few atoms per second or less. Only recently, the first laser spectroscopic investigation of nobelium (

Z = 102

) was performed by applying the RADRIS technique in a buffer-gas-filled stopping cell at the GSI in Darmstadt, Germany. To expand this technique to other nobelium isotopes and for the search for atomic levels in the heaviest actinide element, lawrencium (

Z = 103

), the sensitivity of the RADRIS setup needed to be further improved. Therefore, a new movable double-detector setup was developed, which enhances the overall efficiency by approximately 65% compared to the previously used single-detector setup. Further development work was performed to enable the study of longer-lived (t

_{1 / 2} > 1

h) and shorter-lived nuclides (t

_{1 / 2} < 1

s) with the RADRIS method. With a new rotatable multi-detector design, the long-lived isotope

^{254}

Fm (t

_{1 / 2} = 3.2 h

) becomes within reach for laser spectroscopy. Upcoming experiments will also tackle the short-lived isotope

^{251}

No (t

_{1 / 2} = 0.8 s

) by applying a newly implemented short RADRIS measurement cycle. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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10 pages, 618 KiB

Open AccessArticle

Observation of Collisional De-Excitation Phenomena in Plutonium

by Andrea Raggio, Ilkka Pohjalainen and Iain D. Moore

Atoms 2022, 10(2), 40; https://doi.org/10.3390/atoms10020040 - 20 Apr 2022

Cited by 2 | Viewed by 2881

Abstract

A program of research towards the high-resolution optical spectroscopy of actinide elements for the study of fundamental nuclear structure is currently ongoing at the IGISOL facility of the University of Jyväskylä. One aspect of this work is the development of a gas-cell-based actinide laser ion source using filament-based dispensers of long-lived actinide isotopes. We have observed prominent phenomena in the resonant laser ionization process specific to the gaseous environment of the gas cell. The development and investigation of a laser ionization scheme for plutonium atoms is reported, focusing on the effects arising from the collision-induced phenomena of plutonium atoms in helium gas. The gas-cell environment was observed to greatly reduce the sensitivity of an efficient plutonium ionization scheme developed in vacuum. This indicates competition between resonant laser excitation and collisional de-excitation by the gas atoms, which is likely being enhanced by the very high atomic level density within actinide elements. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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6 pages, 2138 KiB

Open AccessArticle

Extending Our Knowledge about the ²²⁹Th Nuclear Isomer

by Benedict Seiferle, Daniel Moritz, Kevin Scharl, Shiqian Ding, Florian Zacherl, Lilli Löbell and Peter G. Thirolf

Atoms 2022, 10(1), 24; https://doi.org/10.3390/atoms10010024 - 14 Feb 2022

Cited by 6 | Viewed by 3778

Abstract

The first nuclear excited state in

^{229}

Th possesses the lowest excitation energy of all currently known nuclear levels. The energy difference between the ground- and first-excited (isomeric) state (denoted with

^{229 m}

Th) amounts only to ≈8.2 eV (≈151.2 nm), which results [...] Read more.

The first nuclear excited state in

^{229}

Th possesses the lowest excitation energy of all currently known nuclear levels. The energy difference between the ground- and first-excited (isomeric) state (denoted with

^{229 m}

Th) amounts only to ≈8.2 eV (≈151.2 nm), which results in several interesting consequences: Since the excitation energy is in the same energy range as the binding energy of valence electrons, the lifetime of

^{229 m}

Th is strongly influenced by the electronic structure of the Th atom or ion. Furthermore, it is possible to potentially excite the isomeric state in

^{229}

Th with laser radiation, which led to the proposal of a nuclear clock that could be used to search for new physics beyond the standard model. In this article, we will focus on recent technical developments in our group that will help to better understand the decay mechanisms of

^{229 m}

Th, focusing primarily on measuring the radiative lifetime of the isomeric state. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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15 pages, 1223 KiB

Open AccessArticle

First Offline Results from the S³ Low-Energy Branch

by Jekabs Romans, Anjali Ajayakumar, Martial Authier, Frederic Boumard, Lucia Caceres, Jean-François Cam, Arno Claessens, Samuel Damoy, Pierre Delahaye, Philippe Desrues, Antoine Drouart, Patricia Duchesne, Rafael Ferrer, Xavier Fléchard, Serge Franchoo, Patrice Gangnant, Ruben P. de Groote, Sandro Kraemer, Nathalie Lecesne, Renan Leroy, Julien Lory, Franck Lutton, Vladimir Manea, Yvan Merrer, Iain Moore, Alejandro Ortiz-Cortes, Benoit Osmond, Julien Piot, Olivier Pochon, Blaise-Maël Retailleau, Hervé Savajols, Simon Sels, Emil Traykov, Juha Uusitalo, Christophe Vandamme, Marine Vandebrouck, Paul Van den Bergh, Piet Van Duppen, Matthias Verlinde, Elise Verstraelen and Klaus Wendt Show full author list Hide full author list

Atoms 2022, 10(1), 21; https://doi.org/10.3390/atoms10010021 - 9 Feb 2022

Cited by 7 | Viewed by 4049

Abstract

We present the first results obtained from the S

^{3}

Low-Energy Branch, the gas cell setup at SPIRAL2-GANIL, which will be installed behind the S

^{3}

spectrometer for atomic and nuclear spectroscopy studies of exotic nuclei. The installation is currently being commissioned offline, [...] Read more.

We present the first results obtained from the S

^{3}

Low-Energy Branch, the gas cell setup at SPIRAL2-GANIL, which will be installed behind the S

^{3}

spectrometer for atomic and nuclear spectroscopy studies of exotic nuclei. The installation is currently being commissioned offline, with the aim to establish optimum conditions for the operation of the radio frequency quadrupole ion guides, mass separation and ion bunching, providing high-efficiency and low-energy spatial spread for the isotopes of interest. Transmission and mass-resolving power measurements are presented for the different components of the S

^{3}

-LEB setup. In addition, a single-longitudinal-mode, injection-locked, pumped pulsed-titanium–sapphire laser system has been recently implemented and is used for the first proof-of-principle measurements in an offline laser laboratory. Laser spectroscopy measurements of erbium, which is the commissioning case of the S

^{3}

spectrometer, are presented using the

4 f^{12} 6 s^{2}

^{3} H_{6} \to 4 f^{12} (^{3} H) 6 s 6 p

optical transition. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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10 pages, 2285 KiB

Open AccessEditor’s ChoiceArticle

Structure Calculations in Nd III and U III Relevant for Kilonovae Modelling

by Ricardo F. Silva, Jorge M. Sampaio, Pedro Amaro, Andreas Flörs, Gabriel Martínez-Pinedo and José P. Marques

Atoms 2022, 10(1), 18; https://doi.org/10.3390/atoms10010018 - 7 Feb 2022

Cited by 10 | Viewed by 2690

Abstract

The detection of gravitational waves and electromagnetic signals from the neutron star merger GW170817 has provided evidence that these astrophysical events are sites where the r-process nucleosynthesis operates. The electromagnetic signal, commonly known as kilonova, is powered by the radioactive decay of freshly synthesized nuclei. However, its luminosity, colour and spectra depend on the atomic opacities of the produced elements. In particular, opacities of lanthanides and actinides elements, due to their large density of bound–bound transitions, are fundamental. The current work focuses on atomic structure calculations for lanthanide and actinide ions, which are important in kilonovae modelling of ejecta spectra. Calculations for Nd III and U III, two representative rare-earth ions, were achieved. Our aim is to provide valuable insights for future opacity calculations for all heavy elements. We noticed that the opacity of U III is about an order of magnitude greater than the opacity of Nd III due to a higher density of levels in the case of the actinide. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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16 pages, 1005 KiB

Open AccessEditor’s ChoiceArticle

Level Structure and Properties of Open f-Shell Elements

by Stephan Fritzsche

Atoms 2022, 10(1), 7; https://doi.org/10.3390/atoms10010007 - 12 Jan 2022

Cited by 12 | Viewed by 3520

Abstract

Open f-shell elements still constitute a great challenge for atomic theory owing to their (very) rich fine-structure and strong correlations among the valence-shell electrons. For these medium and heavy elements, many atomic properties are sensitive to the correlated motion of electrons and, hence, require large-scale computations in order to deal consistently with all relativistic, correlation and rearrangement contributions to the electron density. Often, different concepts and notations need to be combined for just classifying the low-lying level structure of these elements. With Jac, the Jena Atomic Calculator, we here provide a toolbox that helps to explore and deal with such elements with open d- and f-shell structures. Based on Dirac’s equation, Jac is suitable for almost all atoms and ions across the periodic table. As an example, we demonstrate how reasonably accurate computations can be performed for the low-lying level structure, transition probabilities and lifetimes for Th

^{2 +}

ions with a

5 f 6 d

ground configuration. Other, and more complex, shell structures are supported as well, though often for a trade-off between the size and accuracy of the computations. Owing to its simple use, however, Jac supports both quick estimates and detailed case studies on open d- or f-shell elements. Full article

(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)

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