-
A prototype gas cell for the stopping, extraction and neutralization of radioactive nuclei from the SPIRAL2 Super Separator Spectrometer (S$^3$)
Authors:
W. Dong,
V. Manea,
R. Ferrer,
S. Franchoo,
S. Geldhof,
F. Ivandikov,
N. Lecesne,
D. Lunney,
V. Marchand,
E. Minaya Ramirez,
E. Morin,
S. Raeder
Abstract:
We present the design and simulation of a prototype gas cell for in-gas-jet laser-ionization and spectroscopy studies using the low energy branch of the SPIRAL2-S$^3$ radioactive-ion-beam facility. The prototype aims to demonstrate the possibility to reduce the extraction time of radioactive ions from the gas cell, while implementing a controlled neutralization mechanism, necessary for laser-spect…
▽ More
We present the design and simulation of a prototype gas cell for in-gas-jet laser-ionization and spectroscopy studies using the low energy branch of the SPIRAL2-S$^3$ radioactive-ion-beam facility. The prototype aims to demonstrate the possibility to reduce the extraction time of radioactive ions from the gas cell, while implementing a controlled neutralization mechanism, necessary for laser-spectroscopy studies. Different simulation methods of ion processes in gas are comparatively discussed. Design considerations and detailed simulations of the ion extraction time and efficiency are presented. A study of the dynamics of electrons obtained in the gas cell by ionization is also performed to assess the achievable electron densities.
△ Less
Submitted 17 January, 2026;
originally announced January 2026.
-
High-Resolution Laser Spectroscopy on the Hyperfine Structure of $^{255}$Fm (Z=100)
Authors:
M. Urquiza-González,
M. Stemmler,
T. E. Albrecht,
B. Bally,
M. Bender,
S. Berndt,
M. Block,
A. Brizard,
J. S. Andrews,
J. Bieron,
P. Chhetri,
H. Dorrer,
C. E. Düllmann,
J. G. Ezold,
S. Goriely,
M. J. Gutiérrez,
D. Hanstorp,
R. Hasse,
R. Heinke,
K. Hens,
S. Hilaire,
M. Kaja,
T. Kieck,
N. Kneip,
U. Köster
, et al. (14 additional authors not shown)
Abstract:
We report on high-resolution laser spectroscopy of $^{255}$Fm ($T_{1/2} = 20$h), one of the heaviest nuclides available from reactor breeding. The hyperfine structures in two different atomic ground-state transitions at 398.4~nm and 398.2~nm were probed by in-source laser spectroscopy at the RISIKO mass separator in Mainz, using the PI-LIST high-resolution ion source. Experimental results were com…
▽ More
We report on high-resolution laser spectroscopy of $^{255}$Fm ($T_{1/2} = 20$h), one of the heaviest nuclides available from reactor breeding. The hyperfine structures in two different atomic ground-state transitions at 398.4~nm and 398.2~nm were probed by in-source laser spectroscopy at the RISIKO mass separator in Mainz, using the PI-LIST high-resolution ion source. Experimental results were combined with hyperfine fields from various atomic ab-initio calculations, in particular using MultiConfigurational Dirac-Hartree-Fock theory, as implemented in GRASP18. In this manner, the nuclear magnetic dipole and electric quadrupole moments were derived to be $μ= -0.75(5)~ μ_\textrm{N}$ and $Q_\textrm{S} = +5.84(13)$~eb, respectively.
The magnetic moment indicates occupation of the $ν$~7/2[613] Nilsson orbital, while the large quadrupole moment confirms strong, stable prolate deformation consistent with systematics in the heavy actinides. Comparisons with available expectation values from nuclear theory show good agreement, providing a stringent benchmark for the used theoretical models.
These results revise earlier data and establish $^{255}$Fm as a reference isotope for future high-resolution studies.
△ Less
Submitted 25 November, 2025;
originally announced November 2025.
-
An experimental setup for the study of gas-cell processes for the S$^3$-Low Energy Branch
Authors:
E. Morin,
W. Dong,
V. Manea,
A. Claessens,
S. Damoy,
R. Ferrer,
S. Franchoo,
S. Geldhof,
T. Hourat,
Yu. Kudryavtsev,
N. Lecesne,
R. Leroy,
D. Lunney,
V. Marchand,
E. Minaya Ramirez,
S. Raeder,
S. Roset,
Ch. Vandamme,
P. Van den Bergh,
P. Van Duppen
Abstract:
We present an experimental setup dedicated to the study of in-gas ion processes and characterization of gas stopping cells for the Low Energy Branch of the Super Separator Spectrometer (S$^3$) at SPIRAL2-GANIL. The first application is the development of a new gas stopper with a neutralization mechanism designed for faster extraction of the radioactive ions. This development should enable in-gas-j…
▽ More
We present an experimental setup dedicated to the study of in-gas ion processes and characterization of gas stopping cells for the Low Energy Branch of the Super Separator Spectrometer (S$^3$) at SPIRAL2-GANIL. The first application is the development of a new gas stopper with a neutralization mechanism designed for faster extraction of the radioactive ions. This development should enable in-gas-jet laser spectroscopy and other low-energy experiments with shorter lived radioactive isotopes. We discuss in detail the motivation and objectives of these developments and we present the results of simulations performed in the design phase, as well as the first experimental results.
△ Less
Submitted 3 September, 2025;
originally announced September 2025.
-
Study of thorium in hypersonic gas jets: Ionization potentials of Th and Th$^+$
Authors:
A. Claessens,
F. Ivandikov,
M. Brasseur,
A. Dragoun,
Ch. E. Düllmann,
R. Ferrer,
Yu. Kudryavtsev,
P. Palmeri,
P. Quinet,
S. Raeder,
D. Renisch,
P. Van den Bergh,
P. Van Duppen
Abstract:
Laser ionization spectroscopy was performed on both neutral and singly ionized $^{232}$Th with the aim of identifying the nuclear-clock isomer in the singly charged ionic state of $^{229}$Th. A search for an efficient laser ionization scheme of $^{232}$Th$^+$ was conducted in an argon-filled gas cell. This revealed a congested spectrum due to collisional quenching effects and the presence of sever…
▽ More
Laser ionization spectroscopy was performed on both neutral and singly ionized $^{232}$Th with the aim of identifying the nuclear-clock isomer in the singly charged ionic state of $^{229}$Th. A search for an efficient laser ionization scheme of $^{232}$Th$^+$ was conducted in an argon-filled gas cell. This revealed a congested spectrum due to collisional quenching effects and the presence of several auto-ionizing states, one of which has a laser ionization efficiency of at least $1.2 \%$. Using a threshold approach, the second ionization potential was determined to be $12.300(9)\,$eV. The subsequent study on atomic $^{232}$Th validated the threshold approach. Conducting spectroscopy in a hypersonic gas jet, suppressed the gas-collision-induced quenching, revealing a Rydberg series that converges to the first ionization potential, determined to be $6.306879(14)\,$eV. The gas jet also cools down the thorium, allowing for high-resolution laser spectroscopy with a resolution of $240(30)\,$MHz. Using the Multiconfigurational Dirac-Hartree-Fock (MCDHF) method, the ionization potentials were computed, showing a relative difference of 0.06\% and 0.19\% between theory and our experimental values for the ionization potentials of Th and Th$^+$ respectively. Further calculations using a pseudo-relativistic Hartree-Fock method reveal strong mixing in the used intermediate state at $26113.27\,$cm$^{-1}$ of Th. A dedicated fast-extraction gas cell with $^{233}$U recoil sources was used to study $^{229}$Th$^+$ but no photo-ionization signal could be observed.
△ Less
Submitted 29 July, 2025;
originally announced July 2025.
-
$\textit{Ab initio}$ multiconfigurational calculations of experimentally significant energy levels and transition rates in Lr I $\left( Z=103 \right)$
Authors:
Joseph S. Andrews,
Andrey I. Bondarev,
Per Jönsson,
Jon Grumer,
Sebastian Raeder,
Stephan Fritzsche,
Jacek Bieroń
Abstract:
Large-scale multiconfigurational calculations are conducted on experimentally significant transitions in Lr I and its lanthanide homologue Lu I, exhibiting good agreement with recent theoretical and experimental results. A single reference calculation is performed, allowing for substitutions from the core within a sufficiently large active set to effectively capture the influence of the core on th…
▽ More
Large-scale multiconfigurational calculations are conducted on experimentally significant transitions in Lr I and its lanthanide homologue Lu I, exhibiting good agreement with recent theoretical and experimental results. A single reference calculation is performed, allowing for substitutions from the core within a sufficiently large active set to effectively capture the influence of the core on the valence shells, improving upon previous multiconfigurational calculations. An additional calculation utilising a multireference set is performed to account for static correlation effects which contribute to the wavefunction. Reported energies for the two selected transitions are 20716$\pm$550 $\text{cm}^{-1}$ and 28587$\pm$650 $\text{cm}^{-1}$ for $7\!s^2 8s~^{2} \! {S}_{1\!/\!2}$ $\rightarrow$ $7\!s^2 7\!p ~^{2} \! {P}^{o}_{1\!/\!2 }$ and $7\!s^2 7\!d ~^{2} \! {D}_{3\!/\!2 }$ $\rightarrow$ $7\!s^2 7\!p ~^{2} \! {P}^{o}_{1\!/\!2 }$, respectively.
△ Less
Submitted 21 May, 2025;
originally announced May 2025.
-
Electronic State Chromatography of Lutetium Cations
Authors:
Biswajit Jana,
EunKang Kim,
Aayush Arya,
Elisa Romero Romero,
Elisabeth Rickert,
Harry Ramanantoanina,
Sebastian Raeder,
Michael Block,
Mustapha Laatiaoui
Abstract:
Relativistic effects strongly influence the electronic structures of the heaviest elements, thereby shaping their chemical and physical properties. Studying ion mobility within a noble gas environment reveals how the ion-neutral interactions depend on the ion's electronic configurations, thus providing an avenue for exploring these effects. An ion mobility spectrometer with a cryogenic drift tube…
▽ More
Relativistic effects strongly influence the electronic structures of the heaviest elements, thereby shaping their chemical and physical properties. Studying ion mobility within a noble gas environment reveals how the ion-neutral interactions depend on the ion's electronic configurations, thus providing an avenue for exploring these effects. An ion mobility spectrometer with a cryogenic drift tube was developed to precisely measure the low-field reduced mobility of heavy lanthanide and actinide cations. The apparatus was characterized by optimizing the bunching operation of ions with a miniature RF coulomb buncher and evaluating the chromatography performance of the drift tube operated with helium buffer gas at a temperature of 298K. Systematic ion mobility measurements of lutetium cations (Lu$^{+}$) drifting in helium gas were carried out as a case study. The electronic state chromatography of Lu$^{+}$ has been demonstrated. The low-field reduced ion mobility for the ground and lowest meta-stable state of Lu$^{+}$ have been examined. In addition, the variation of both states' reduced mobility and the quenching of meta-stable population has been investigated under different reduced electric fields ($E/n_0$), the ratio of an electric field to neutral gas number density.
△ Less
Submitted 16 April, 2026; v1 submitted 15 July, 2024;
originally announced July 2024.
-
Laser Resonance Chromatography: First Commissioning Results and Future Prospects
Authors:
EunKang Kim,
Biswajit Jana,
Aayush Arya,
Michael Block,
Sebastian Raeder,
Harry Ramanantoanina,
Elisabeth Rickert,
Elisa Romero Romero,
Mustapha Laatiaoui
Abstract:
We report first results obtained during the commissioning of the Laser Resonance Chromatography (LRC) apparatus, which is conceived to enable atomic structure investigations in the region of the heaviest elements beyond nobelium. In our studies we first established optimum conditions for the operation of the different components of the setup, including the radio-frequency quadrupole ion buncher an…
▽ More
We report first results obtained during the commissioning of the Laser Resonance Chromatography (LRC) apparatus, which is conceived to enable atomic structure investigations in the region of the heaviest elements beyond nobelium. In our studies we first established optimum conditions for the operation of the different components of the setup, including the radio-frequency quadrupole ion buncher and the cryogenic drift tube, which was operated with helium buffer gas at relatively low electric fields. We used laser ablated hafnium, lutetium, and ytterbium cations to assess the chromatography performance of the drift tube at a gas temperature of $295$K. Arrival time distributions of singly charged lutetium revealed two distinct ion mobilities of this ion in the ground and metastable state in helium with a relative difference of about $19$%. By using $^{219}$Rn ions from a $^{223}$Ra recoil source the overall efficiency of the apparatus is found to be $(0.6\pm0.1)$%. The findings help to establish LRC on lutetium, which is the lighter chemical homolog of lawrencium.
△ Less
Submitted 29 June, 2024; v1 submitted 8 April, 2024;
originally announced April 2024.
-
High-resolution laser system for the S3-Low Energy Branch
Authors:
Jekabs Romans,
Anjali Ajayakumar,
Martial Authier,
Frederic Boumard,
Lucia Caceres,
Jean-Francois Cam,
Arno Claessens,
Samuel Damoy,
Pierre Delahaye,
Philippe Desrues,
Wenling Dong,
Antoine Drouart,
Patricia Duchesne,
Rafael Ferrer,
Xavier Flechard,
Serge Franchoo,
Patrice Gangnant,
Sarina Geldhof,
Ruben P. de Groote,
Nathalie Lecesne,
Renan Leroy,
Julien Lory,
Franck Lutton,
Vladimir Manea,
Yvan Merrer
, et al. (17 additional authors not shown)
Abstract:
In this paper we present the first high-resolution laser spectroscopy results obtained at the GISELE laser laboratory of the GANIL-SPIRAL2 facility, in preparation for the first experiments with the S$^3$-Low Energy Branch. Studies of neutron-deficient radioactive isotopes of erbium and tin represent the first physics cases to be studied at S$^3$. The measured isotope-shift and hyperfine structure…
▽ More
In this paper we present the first high-resolution laser spectroscopy results obtained at the GISELE laser laboratory of the GANIL-SPIRAL2 facility, in preparation for the first experiments with the S$^3$-Low Energy Branch. Studies of neutron-deficient radioactive isotopes of erbium and tin represent the first physics cases to be studied at S$^3$. The measured isotope-shift and hyperfine structure data are presented for stable isotopes of these elements. The erbium isotopes were studied using the $4f^{12}6s^2$ $^3H_6 \rightarrow 4f^{12}(^3 H)6s6p$ $J = 5$ atomic transition (415 nm) and the tin isotopes were studied by the $5s^25p^2 (^3P_0) \rightarrow 5s^25p6s (^3P_1)$ atomic transition (286.4 nm), and are used as a benchmark of the laser setup. Additionally, the tin isotopes were studied by the $5s^25p6s (^3P_1) \rightarrow 5s^25p6p (^3P_2)$ atomic transition (811.6 nm), for which new isotope-shift data was obtained and the corresponding field-shift $F_{812}$ and mass-shift $M_{812}$ factors are presented.
△ Less
Submitted 9 December, 2022;
originally announced December 2022.
-
Ab initio calculations of the spectrum of lawrencium
Authors:
E. V. Kahl,
S. Raeder,
E. Eliav,
A. Borschevsky,
J. C. Berengut
Abstract:
Planned optical spectroscopy experiments in lawrencium (Lr, Z = 103) require accurate theoretical predictions of the location of spectral lines in order to narrow the experimental search window. We present ab initio calculations of the atomic energy levels, transition amplitudes and g-factors for lawrencium, as well as its lighter homologue lutetium (Lu, Z = 71). We use the configuration interacti…
▽ More
Planned optical spectroscopy experiments in lawrencium (Lr, Z = 103) require accurate theoretical predictions of the location of spectral lines in order to narrow the experimental search window. We present ab initio calculations of the atomic energy levels, transition amplitudes and g-factors for lawrencium, as well as its lighter homologue lutetium (Lu, Z = 71). We use the configuration interaction with many-body perturbation-theory (CI+MBPT) method to calculate energy levels and transition properties, and benchmark the accuracy of our predicted energies using relativistic coupled-cluster codes. Our results are numerically converged and in close agreement with experimentally measured energy levels for Lu, and we expect a similar accuracy for Lr. These systematic calculations have identified multiple transitions of experimental utility and will serve to guide future experimental studies of Lr.
△ Less
Submitted 20 October, 2021; v1 submitted 20 March, 2021;
originally announced March 2021.
-
Recent progress in laser spectroscopy of the actinides
Authors:
Michael Block,
Mustapha Laatiaoui,
Sebastian Raeder
Abstract:
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 inde…
▽ More
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 $N = 152$, 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.
△ Less
Submitted 22 October, 2020;
originally announced October 2020.
-
Detection of missing low-lying atomic states in actinium
Authors:
Ke Zhang,
Dominik Studer,
Felix Weber,
Vadim M. Gadelshin,
Nina Kneip,
Sebastian Raeder,
Dmitry Budker,
Klaus Wendt,
Tom Kieck,
Sergey G. Porsev,
Charles Cheung,
Marianna S. Safronova,
Mikhail G. Kozlov
Abstract:
Two lowest-energy odd-parity atomic levels of actinium, 7s^27p 2P^o_1/2, 7s^27p 2P^o_3/2, were observed via two-step resonant laser-ionization spectroscopy and their respective energies were measured to be 7477.36(4) cm^-1 and 12 276.59(2) cm^-1. The lifetimes of these states were determined as 668(11) ns and 255(7) ns, respectively. In addition, these properties were calculated using a hybrid app…
▽ More
Two lowest-energy odd-parity atomic levels of actinium, 7s^27p 2P^o_1/2, 7s^27p 2P^o_3/2, were observed via two-step resonant laser-ionization spectroscopy and their respective energies were measured to be 7477.36(4) cm^-1 and 12 276.59(2) cm^-1. The lifetimes of these states were determined as 668(11) ns and 255(7) ns, respectively. In addition, these properties were calculated using a hybrid approach that combines configuration interaction and coupled-cluster methods in good agreement. The data are of relevance for understanding the complex atomic spectra of actinides and for developing efficient laser-cooling and ionization schemes for actinium, with possible applications for high-purity medicalisotope production and future fundamental physics experiments with this atom.
△ Less
Submitted 7 May, 2020;
originally announced May 2020.
-
High-Resolution Laser Spectroscopy of Long-Lived Plutonium Isotopes
Authors:
A. Voss,
V. Sonnenschein,
P. Campbell,
B. Cheal,
T. Kron,
I. D. Moore,
I. Pohjalainen,
S. Raeder,
N. Trautmann,
K. Wendt
Abstract:
Long-lived isotopes of plutonium were studied using two complementary techniques, high-resolution resonance ionisation spectroscopy (HR-RIS) and collinear laser spectroscopy (CLS). Isotope shifts have been measured on the $5f^67s^2\ ^7F_0 \rightarrow 5f^56d^27s\ (J=1)$ and $5f^67s^2\ ^7F_1 \rightarrow 5f^67s7p\ (J=2)$ atomic transitions using the HR-RIS method and the hyperfine factors have been e…
▽ More
Long-lived isotopes of plutonium were studied using two complementary techniques, high-resolution resonance ionisation spectroscopy (HR-RIS) and collinear laser spectroscopy (CLS). Isotope shifts have been measured on the $5f^67s^2\ ^7F_0 \rightarrow 5f^56d^27s\ (J=1)$ and $5f^67s^2\ ^7F_1 \rightarrow 5f^67s7p\ (J=2)$ atomic transitions using the HR-RIS method and the hyperfine factors have been extracted for the odd mass nuclei $^{239,241}$Pu. Collinear laser spectroscopy was performed on the $5f^67s\ ^8F_{1/2} \rightarrow J=1/2\; (27523.61\text{cm}^{-1})$ ionic transition with the hyperfine $A$ factors measured for $^{239}$Pu. Changes in mean-squared charge radii have been extracted and show a good agreement with previous non-optical methods, with an uncertainty improvement by approximately one order of magnitude. Plutonium represents the heaviest element studied to date using collinear laser spectroscopy.
△ Less
Submitted 6 March, 2017;
originally announced March 2017.
-
Offline trapping of $^{221}$Fr in a magneto-optical trap from implantation of an $^{225}$Ac ion beam
Authors:
M. Tandecki,
J. Zhang,
S. Aubin,
J. A. Behr,
R. Collister,
E. Gomez,
G. Gwinner,
H. Heggen,
J. Lassen,
L. A. Orozco,
M. R. Pearson,
S. Raeder,
A. Teigelhöfer
Abstract:
We demonstrate a new technique to prepare an offline source of francium for trapping in a magneto-optical trap. Implanting a radioactive beam of $^{225}$Ac, $t_{1/2} = 9.920(3)$ days, in a foil, allows use of the decay products, i.e.$^{221}$Fr, $t_{1/2} = 288.0(4)$ s. $^{221}$Fr is ejected from the foil by the $α$ decay of $^{225}$Ac. This technique is compatible with the online accumulation of a…
▽ More
We demonstrate a new technique to prepare an offline source of francium for trapping in a magneto-optical trap. Implanting a radioactive beam of $^{225}$Ac, $t_{1/2} = 9.920(3)$ days, in a foil, allows use of the decay products, i.e.$^{221}$Fr, $t_{1/2} = 288.0(4)$ s. $^{221}$Fr is ejected from the foil by the $α$ decay of $^{225}$Ac. This technique is compatible with the online accumulation of a laser-cooled atomic francium sample for a series of planned parity non-conservation measurements at TRIUMF. We obtain a 34% release efficiency for $^{221}$Fr from the recoil source based on particle detector measurements. We find that laser cooling operation with the source is $8^{+10}_{-5}$ times less efficient than from a mass-separated ion beam of $^{221}$Fr in the current geometry. While the flux of this source is two to three orders of magnitude lower than typical francium beams from ISOL facilities, the source provides a longer-term supply of francium for offline studies.
△ Less
Submitted 30 September, 2014;
originally announced October 2014.
-
Resonance ionization spectroscopy of thorium isotopes - towards a laser spectroscopic identification of the low-lying 7.6 eV isomer of Th-229
Authors:
Sebastian Raeder,
Volker Sonnenschein,
Tina Gottwald,
Ian Moore,
Michael Reponen,
Sebastian Rothe,
Norbert Trautmann,
Klaus Wendt
Abstract:
In-source resonance ionization spectroscopy was used to identify an efficient and selective three step excitation/ionization scheme of thorium, suitable for titanium:sapphire (Ti:sa) lasers. The measurements were carried out in preparation of laser spectroscopic investigations for an identification of the low-lying Th-229m isomer predicted at 7.6 +- 0.5 eV above the nuclear ground state. Using a s…
▽ More
In-source resonance ionization spectroscopy was used to identify an efficient and selective three step excitation/ionization scheme of thorium, suitable for titanium:sapphire (Ti:sa) lasers. The measurements were carried out in preparation of laser spectroscopic investigations for an identification of the low-lying Th-229m isomer predicted at 7.6 +- 0.5 eV above the nuclear ground state. Using a sample of Th-232, a multitude of optical transitions leading to over 20 previously unknown intermediate states of even parity as well as numerous high-lying odd parity auto-ionizing states were identified. Level energies were determined with an accuracy of 0.06 cm-1 for intermediate and 0.15 cm-1 for auto-ionizing states. Using different excitation pathways an assignment of total angular momenta for several energy levels was possible. One particularly efficient ionization scheme of thorium, exhibiting saturation in all three optical transitions, was studied in detail. For all three levels in this scheme, the isotope shifts of the isotopes Th-228, Th-229, and Th-230 relative to Th-232 were measured. An overall efficiency including ionization, transport and detection of 0.6 was determined, which was predominantly limited by the transmission of the mass spectrometer ion optics.
△ Less
Submitted 23 May, 2011;
originally announced May 2011.