First observation of atomic levels for the element fermium (Z=100)

New Developments in the Production and Research of Actinide Elements

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.

Level Structure and Properties of Open f-Shell Elements

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 Th2+ ions with a 5f6d 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.

Mobility of the Singly-Charged Lanthanide and Actinide Cations: Trends and Perspectives

The current status of gaseous transport studies of the singly-charged lanthanide and actinide ions is reviewed in light of potential applications to superheavy ions. The measurements and calculations for the mobility of lanthanide ions in He and Ar agree well, and they are remarkably sensitive to the electronic configuration of the ion, namely, whether the outer electronic shells are 6s, 5d6s or 6s². The previous theoretical work is extended here to ions of the actinide family with zero electron orbital momentum: Ac⁺ (7s², ¹S), Am⁺ (5f⁷7s ⁹S°), Cm⁺ (5f⁷7s^{2 8}S°), No⁺ (5f¹⁴7s ²S), and Lr⁺ (5f¹⁴7s^{2 1}S). The calculations reveal large systematic differences in the mobilities of the 7s and 7s² groups of ions and other similarities with their lanthanide analogs. The correlation of ion-neutral interaction potentials and mobility variations with spatial parameters of the electron distributions in the bare ions is explored through the ionic radii concept. While the qualitative trends found for interaction potentials and mobilities render them appealing for superheavy ion research, lack of experimental data and limitations of the scalar relativistic ab initio approaches in use make further efforts necessary to bring the transport measurements into the inventory of techniques operating in "one atom at a time" mode.

Exploring the chemical nature of super-heavy main-group elements by means of efficient plane-wave density-functional theory

Presenting an accurate yet efficient plane-wave DFT approach for the computational exploration of the bulk properties of the super-heavy main-group elements including copernicium (Cn–Og, Z = 112–118).

Directed evolution of the periodic table: probing the electronic structure of late actinides

Recent investigations of the coordination chemistry and physical properties of berkelium (Z = 97) and californium (Z = 98) have revealed fundamental differences between post-curium elements and lighter members of the actinide series. This review highlights these developments and chronicles key findings and concepts from the last half-century that have helped usher in a new understanding of the evolution of electronic structure in the periodic table.

Towards high-resolution laser ionization spectroscopy of the heaviest elements in supersonic gas jet expansion

Resonant laser ionization and spectroscopy are widely used techniques at radioactive ion beam facilities to produce pure beams of exotic nuclei and measure the shape, size, spin and electromagnetic multipole moments of these nuclei. However, in such measurements it is difficult to combine a high efficiency with a high spectral resolution. Here we demonstrate the on-line application of atomic laser ionization spectroscopy in a supersonic gas jet, a technique suited for high-precision studies of the ground- and isomeric-state properties of nuclei located at the extremes of stability. The technique is characterized in a measurement on actinium isotopes around the N=126 neutron shell closure. A significant improvement in the spectral resolution by more than one order of magnitude is achieved in these experiments without loss in efficiency.

Fast chemical separations and laser mass spectrometry – tools for nuclear research

Fast chemical separation procedures applied in nuclear research require dedicated experimental techniques. Rapid discontinuous separation procedures are illustrated by an example to isolate technetium from fission products. The use of a gas jet and its combination with a thermochromatographic separation and with the continuous solvent extraction technique SISAK is described and examples are given for the investigation of short-lived fission products. The potential of resonance ionization mass spectrometry (RIMS) as a highly sensitive technique using different experimental systems is outlined for ultra trace analysis of long-lived plutonium and neptunium isotopes, including isotope ratio measurements of the plutonium isotopes. In addition, the precise determination of the first ionization potentials (IP) of ten actinide elements up to einsteinium and of technetium carried out by using the photoionization threshold method and requiring sample sizes of ∼ 1012atoms is presented.

First successful ionization of Lr (Z = 103) by a surface-ionization technique

We have developed a surface ionization ion-source as part of the JAEA-ISOL (Isotope Separator On-Line) setup, which is coupled to a He/CdI2 gas-jet transport system to determine the first ionization potential of the heaviest actinide lawrencium (Lr, Z = 103). The new ion-source is an improved version of the previous source that provided good ionization efficiencies for lanthanides. An additional filament was newly installed to give better control over its operation. We report, here, on the development of the new gas-jet coupled surface ion-source and on the first successful ionization and mass separation of 27-s (256)Lr produced in the (249)Cf + (11)B reaction.