A Progress Report on Laser Resonance Chromatography

E. Romero Romero, M. Block, B. Jana, E. Kim, S. Nothhelfer, S. Raeder, H. Ramanantoanina, E. Rickert, J. Schneider, P. Sikora and M. Laatiaoui 

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. 

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New Developments in the Production and Research of Actinide Elements

M. Laatiaoui and S. Raeder 

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. 

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Resolution Characterizations of JetRIS in Mainz Using 164Dy

D. Münzberg, M. Block, A. Claessens, R. Ferrer, M. Laatiaoui, J. Lantis, S. Nothhelfer, S. Raeder and P. Van Duppen 

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. 

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


H. Ramanantoanina, A. Borschevsky, M. Block, and M. Laatiaoui   

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 that of the Lu+ homolog, with the multiplet manifold of the 7s2, 6d17s1 and 7s17p1 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. 

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Electronic Structure of Rf+ (Z=104) from ab initio calculations 

Harry Ramanantoanina, Anastasia Borschevsky, Michael Block, and Mustapha Laatiaoui                                                                                                                 October 19, 2021 

We report calculation of the energy spectrum and the spectroscopic properties of the superheavy element ion: Rf+. We use the four-component relativistic Dirac-Coulomb Hamiltonian and the multireference configuration interaction model to tackle the complex electronic structure problem that combines strong relativistic effects and electron correlation. We determine the energies of the ground and the low-lying excited states of Rf+, which originate from the 7s26d1,7s16d2,7s27p1, and 7s16d17p1 configurations. The results are discussed vis-à-vis the lighter homolog Hf+ ion. We also assess the uncertainties of the predicted energy levels. The main purpose of the presented calculations is to provide a reliable prediction of the energy levels and to identify suitable metastable excited states that are good candidates for the planned ion-mobility-assisted laser spectroscopy studies. 

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Recent progress in laser spectroscopy of the actinides

Michael Block, Mustapha Laatiaoui, Sebastian Raeder                                                                                                                                                                 October 10, 2020 

The interest to perform laser spectroscopy in the heaviest elements arises from the strong impact of relativistic effects, electron correlations and quantum electrodynamics on their atomic structure. Once this atomic structure is well understood, laser spectroscopy also provides access to nuclear properties such as spins, mean-square charge radii and electromagnetic moments in a nuclear-model independent way. This is of particular interest for the heaviest actinides around , a region of shell-stabilized deformed nuclei. The experimental progress of laser spectroscopy in this region benefitted from continuous methodological and technical developments such as the introduction of buffer-gas-stopping techniques that enabled the access to ever more exotic nuclei far-off stability. The key challenges faced in this endeavor are small yields, nuclides with rather short half-lives and the need to search for atomic transitions in a wide spectral range guided by theoretical predictions. This paper describes the basics of the most common experimental methods and discusses selected recent results on the atomic and nuclear properties of the actinides up to nobelium where pioneering experiments were performed at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. 

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Laser Resonance Chromatography of Superheavy Elements 

Mustapha Laatiaoui, Alexei A. Buchachenko, and Larry A. Viehland                                                                                                                                                    July 13, 2020

Optical spectroscopy constitutes the historical path to accumulate basic knowledge on the atom and its structure. Former work based on fluorescence and resonance ionization   spectroscopy enabled identifying optical spectral lines up to element 102, nobelium. The new challenges faced in this research field are the refractory nature of the heavier elements and the decreasing production yields. A new concept of ion-mobility-assisted laser spectroscopy is proposed to overcome the sensitivity limits of atomic structure investigations persisting in the region of the superheavy elements. The concept offers capabilities of both broadband-level searches and high-resolution hyperfine spectroscopy of synthetic elements beyond nobelium. 

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Exploiting Transport Properties for the Detection of Optical Pumping in Heavy Ions 


Mustapha Laatiaoui, Alexei A. Buchachenko, and Larry A. Viehland                                                                                                                                              July 13, 2020

We present a kinetic model for optical pumping in Lu+ and Lr+ ions as well as a theoretical approach to calculate the transport properties of Lu+ in its ground 1S0 and metastable
3D1 states in helium background gas. Calculations of the initial ion state populations, the field and temperature dependence of the mobilities and diffusion coefficients, and the ion arrival time distributions demonstrate that the ground- and metastable-state ions can be collected and discriminated efficiently under realistic macroscopic conditions.

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Mobility of the singly-charged lanthanide and actinide cations: trends and perspectives 

Alexei A. Buchachenko, Giorgio Visentin, Larry A. Viehland, and Mustapha Laatiaoui

31 May 2020

The current status of the 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, 5d 6s or 6s2. The previous theoretical work is extended here to ions of the actinide family with zero electron orbital momentum: Ac+ (7s2, 1S), Am+ (5f7 7s 9S°), Cm+ (5f7 7s2 8S°), No+ (5f14 7s 2S) and Lr+ (5f14 7s2 1S). 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 potential 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.

High-precision ab initio calculations of the spectrum of Lr+

E.V. Kahl, J.C. Berengut, M. Laatiaoui, E. Eliav, and A. Borschevsky

9 December 2019

The planned measurement of optical resonances in singly ionized lawrencium (Z = 103) requires accurate theoretical predictions to narrow the search window. We present high-precision, ab initio calculations of the electronic spectra of Lr+ and its lighter homologue lutetium (Z = 71). We have employed the state-of-theart relativistic Fock space coupled cluster approach as well as the configuration interaction with many-body perturbation theory (CI + MBPT) method to calculate atomic energy levels, g factors, and transition amplitudes and branching ratios. Our calculations are in close agreement with experimentally measured energy levels and transition strengths for the homologue Lu+, and are well converged for Lr+, where we expect a similar level of accuracy. These results present large-scale, systematic calculations of Lr+ and will serve to guide future experimental studies of this ion.