Atoms

9 pages, 1256 KiB

Open AccessArticle

Double and Triple Photoionization of CCl₄

by Antônio Carlos Fontes dos Santos, Joselito Barbosa Maciel, Alexandre Braga Rocha and Gerardo Gerson Bezerra de Souza

Atoms 2024, 12(12), 74; https://doi.org/10.3390/atoms12120074 - 21 Dec 2024

Viewed by 619

Abstract

(1) Background: Fragmentation after double and triple photoionization of the CCl₄ molecule in the valence, Cl 2p, and C 1s regions have been reported; (2) Methods: We have used photoion-photoion (PIPICO) coincidence technique combined with synchrotron radiation. In addition, [...] Read more.

(1) Background: Fragmentation after double and triple photoionization of the CCl₄ molecule in the valence, Cl 2p, and C 1s regions have been reported; (2) Methods: We have used photoion-photoion (PIPICO) coincidence technique combined with synchrotron radiation. In addition, ab initio quantum mechanical calculations were done at multiconfigurational self-consistent and multireference configuration interaction to describe ground and inner-shell states; (3) Results: We have observed coincidences involving singly and doubly charged fragments coming from the doubly and triply ionized molecule. We have also found a well agreement between the quantum mechanical calculations and the total ion yield spectrum. It is shown that the Cl⁺ ion is the predominant product resulting from the fragmentation of the doubly and triply charged CCl₄ molecule. The CCl⁺ + Cl⁺ pair is the dominant coincidence in the spectra from valence up to the C 1s edge; (4) Conclusions: The kinetic energy of the fragments is compatible with the Coulomb explosion model. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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12 pages, 354 KiB

Open AccessOpinion

Limits to the Precision of Atomic Lifetime Measurements

by Elmar Träbert

Atoms 2024, 12(12), 73; https://doi.org/10.3390/atoms12120073 - 20 Dec 2024

Viewed by 760

Abstract

The mean lives of certain levels in atoms or not so highly charged ions have been measured with a precision on the order of 0.1%. This is better than most other atomic lifetime measurements, but is still much less precise than many measurements [...] Read more.

The mean lives of certain levels in atoms or not so highly charged ions have been measured with a precision on the order of 0.1%. This is better than most other atomic lifetime measurements, but is still much less precise than many measurements of other entities. Why is it that atomic level lifetime and transition rate measurements are not much more precise? Full article

(This article belongs to the Special Issue Atom and Plasma Spectroscopy)

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7 pages, 310 KiB

Open AccessArticle

Calculation of the Breit–Rosenthal Effect in Bi I

by Tarje Arntzen Røger and Jonas R. Persson

Atoms 2024, 12(12), 72; https://doi.org/10.3390/atoms12120072 - 20 Dec 2024

Viewed by 651

Abstract

Corrections to the measured nuclear magnetic moments obtained from hyperfine structure measurements include the Breit–Rosenthal effect. In this paper, we present results from calculations on Bi using the GRASP2018 code. The results indicate that the Breit–Rosenthal effect is on the order of 0.1 [...] Read more.

Corrections to the measured nuclear magnetic moments obtained from hyperfine structure measurements include the Breit–Rosenthal effect. In this paper, we present results from calculations on Bi using the GRASP2018 code. The results indicate that the Breit–Rosenthal effect is on the order of 0.1

% {fm}^{- 2}

, the same order of magnitude as neighbouring elements, while some atomic states may have one order of magnitude smaller values. The ground state

6 p^{3} {}^{4}S_{3 / 2}^{o}

is more sensitive to the Breit–Rosenthal effect, and hence the hyperfine anomaly, with a value of −0.25

% {fm}^{- 2}

. Full article

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23 pages, 9832 KiB

Open AccessArticle

Ion Manipulation from Liquid Xe to Vacuum: Ba-Tagging for a nEXO Upgrade and Future 0νββ Experiments

by Dwaipayan Ray, Robert Collister, Hussain Rasiwala, Lucas Backes, Ali V. Balbuena, Thomas Brunner, Iroise Casandjian, Chris Chambers, Megan Cvitan, Tim Daniels, Jens Dilling, Ryan Elmansali, William Fairbank, Daniel Fudenberg, Razvan Gornea, Giorgio Gratta, Alec Iverson, Anna A. Kwiatkowski, Kyle G. Leach, Annika Lennarz, Zepeng Li, Melissa Medina-Peregrina, Kevin Murray, Kevin O’Sullivan, Regan Ross, Raad Shaikh, Xiao Shang, Joseph Soderstrom, Victor Varentsov and Liang Yang Show full author list Hide full author list

Atoms 2024, 12(12), 71; https://doi.org/10.3390/atoms12120071 - 19 Dec 2024

Viewed by 826

Abstract

Neutrinoless double beta decay (

0 ν β β

) provides a way to probe physics beyond the Standard Model of particle physics. The upcoming nEXO experiment will search for

0 ν β β

decay in ¹³⁶Xe with a projected half-life sensitivity [...] Read more.

Neutrinoless double beta decay (

0 ν β β

) provides a way to probe physics beyond the Standard Model of particle physics. The upcoming nEXO experiment will search for

0 ν β β

decay in ¹³⁶Xe with a projected half-life sensitivity exceeding

10^{28}

years at the 90% confidence level using a liquid xenon (LXe) Time Projection Chamber (TPC) filled with 5 tonnes of Xe enriched to ∼90% in the

β β

-decaying isotope ¹³⁶Xe. In parallel, a potential future upgrade to nEXO is being investigated with the aim to further suppress radioactive backgrounds and to confirm

β β

-decay events. This technique, known as Ba-tagging, comprises extracting and identifying the

β β

-decay daughter ¹³⁶Ba ion. One tagging approach being pursued involves extracting a small volume of LXe in the vicinity of a potential

β β

-decay using a capillary tube and facilitating a liquid-to-gas phase transition by heating the capillary exit. The Ba ion is then separated from the accompanying Xe gas using a radio-frequency (RF) carpet and RF funnel, conclusively identifying the ion as ¹³⁶Ba via laser-fluorescence spectroscopy and mass spectrometry. Simultaneously, an accelerator-driven Ba ion source is being developed to validate and optimize this technique. The motivation for the project, the development of the different aspects, along with the current status and results, are discussed here. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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19 pages, 495 KiB

Open AccessArticle

State-Selective Double Photoionization of Atomic Carbon and Neon

by Frank L. Yip

Atoms 2024, 12(12), 70; https://doi.org/10.3390/atoms12120070 - 16 Dec 2024

Viewed by 899

Abstract

Double photoionization (DPI) allows for a sensitive and direct probe of electron correlation, which governs the structure of all matter. For atoms, much of the work in theory and experiment that informs our fullest understanding of this process has been conducted on helium, [...] Read more.

Double photoionization (DPI) allows for a sensitive and direct probe of electron correlation, which governs the structure of all matter. For atoms, much of the work in theory and experiment that informs our fullest understanding of this process has been conducted on helium, and efforts continue to explore many-electron targets with the same level of detail to understand the angular distributions of the ejected electrons in full dimensionality. Expanding on previous results, we consider here the double photoionization of two

2 p

valence electrons of atomic carbon and neon and explore the possible continuum states that are connected by dipole selection rules to the coupling of the outgoing electrons in ³P, ¹D, and ¹S initial states of the target atoms. Carbon and neon share these possible symmetries for the coupling of their valence electrons. Results are presented for the energy-sharing single differential cross section (SDCS) and triple differential cross section (TDCS), further elucidating the impact of the initial state symmetry in determining the angular distributions that are impacted by the correlation that drives the DPI process. Full article

(This article belongs to the Special Issue Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A Tribute to Barry Irwin Schneider)

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16 pages, 418 KiB

Open AccessArticle

Two-Electron Atomic Systems—A Simple Method for Calculating the Ground State near the Nucleus: Some Applications

by Evgeny Z. Liverts and Rajmund Krivec

Atoms 2024, 12(12), 69; https://doi.org/10.3390/atoms12120069 - 14 Dec 2024

Viewed by 623

Abstract

A simple method of non-relativistic variational calculations of the electronic structure of a two-electron atom/ion, primarily near the nucleus, is proposed. The method as a whole consists of a standard solution of a generalized matrix eigenvalue equation, all matrix elements of which are [...] Read more.

A simple method of non-relativistic variational calculations of the electronic structure of a two-electron atom/ion, primarily near the nucleus, is proposed. The method as a whole consists of a standard solution of a generalized matrix eigenvalue equation, all matrix elements of which are reduced to a numerical calculation of one-dimensional integrals. The distinctive features of the method are as follows: The use of the hyperspherical coordinate system. The inclusion of logarithms of the hyperspherical radius R in the basis functions, similar to the Fock expansion. Using a special basis function including the leading angular Fock coefficients to provide the correct behavior of the wave function near the nucleus. The main numerical parameters characterizing the properties of the helium atom and a number of helium-like ions near the nucleus are calculated and presented in tables. Among others, the specific coefficients,

a_{21}

, of the Fock expansion, which can only be calculated using a wave function with the correct behavior near the nucleus, are presented in table and graphs. Full article

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18 pages, 2145 KiB

Open AccessArticle

Modified Ji-Huan He’s Frequency Formulation for Large-Amplitude Electron Plasma Oscillations

by Stylianos Vasileios Kontomaris, Anna Malamou, Ioannis Psychogios and Gamal M. Ismail

Atoms 2024, 12(12), 68; https://doi.org/10.3390/atoms12120068 - 12 Dec 2024

Viewed by 792

Abstract

This paper examines oscillations governed by the generic nonlinear differential equation

{u^{″} = ω}_{p 0}^{2} (1 - u \mp \frac{2 β^{2}}{u^{γ}}),

where

ω_{p 0}, β

and

γ

are positive constants. The aforementioned differential [...] Read more.

This paper examines oscillations governed by the generic nonlinear differential equation

{u^{″} = ω}_{p 0}^{2} (1 - u \mp \frac{2 β^{2}}{u^{γ}}),

where

ω_{p 0}, β

and

γ

are positive constants. The aforementioned differential equation is of particular importance, as it describes electron plasma oscillations influenced by temperature effects and large oscillation amplitudes. Since no analytical solution exists for the oscillation period in terms of

ω_{p 0}, β, γ

and the oscillation amplitude, accurate approximations are derived. A modified He’s approach is used to account for the non-symmetrical oscillation around the equilibrium position. The motion is divided into two parts:

u_{m i n} \leq u < u_{e q}

and

u_{e q} < u \leq u_{m a x}

, where

u_{m i n}

and

u_{m a x}

are the minimum and maximum values of

u

, and

u_{e q}

is its equilibrium value. The time intervals for each part are calculated and summed to find the oscillation period. The proposed method shows remarkable accuracy compared to numerical results. The most significant result of this paper is that He’s approach can be readily extended to strongly non-symmetrical nonlinear oscillations. It is also demonstrated that the same approach can be extended to any case where each segment of the function

f (u)

in the differential equation

u^{″} + f (u) = 0

(for

u_{m i n} \leq u < u_{e q}

and for

u_{e q} < u \leq u_{m a x}

) can be approximated by a fifth-degree polynomial containing only odd powers. Full article

(This article belongs to the Special Issue Electronic, Photonic and Ionic Interactions with Atoms and Molecules)

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17 pages, 1138 KiB

Open AccessArticle

Charge Transfer Excitation of NeAr⁺ Ions in Collisions with Electrons

by Alexander Narits, Konstantin Kislov and Vladimir Lebedev

Atoms 2024, 12(12), 67; https://doi.org/10.3390/atoms12120067 - 12 Dec 2024

Viewed by 607

Abstract

We study the resonant processes of the excitation of weakly bound

{NeAr}^{+}

ions in collisions with the free electrons of Ne/Ar mixture plasma under conditions typical of the active media of gas lasers and plasma-based UV radiation sources. The transitions leading to [...] Read more.

We study the resonant processes of the excitation of weakly bound

{NeAr}^{+}

ions in collisions with the free electrons of Ne/Ar mixture plasma under conditions typical of the active media of gas lasers and plasma-based UV radiation sources. The transitions leading to the population of charge transfer electronic terms are considered. Using an original theoretical approach developed recently, we study the dependences of the cross-sections of several competing resonant processes on the incident electron energy and the gas temperature of the plasma. The role of the continuous states of internuclear motion is discussed. We highlight the specific features of the processes considered that stem from the low binding energy of

{NeAr}^{+}

ions and demonstrate that, in the weakly bound systems, the efficiencies of different charge transfer excitation channels differ greatly from those obtained for ions with moderate dissociation energies. Full article

(This article belongs to the Special Issue Electronic, Photonic and Ionic Interactions with Atoms and Molecules)

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17 pages, 6807 KiB

Open AccessArticle

Many-Body Effects in a Composite Bosonic Josephson Junction

by Sudip Kumar Haldar and Anal Bhowmik

Atoms 2024, 12(12), 66; https://doi.org/10.3390/atoms12120066 - 11 Dec 2024

Cited by 1 | Viewed by 793

Abstract

In standard bosonic Josephson junctions (BJJs), particles tunnel between two single-well potentials linked by a finite barrier. The dynamics of standard BJJs have been extensively studied, both at the many-body and mean-field levels of theory. In the present work, we introduce the concept [...] Read more.

In standard bosonic Josephson junctions (BJJs), particles tunnel between two single-well potentials linked by a finite barrier. The dynamics of standard BJJs have been extensively studied, both at the many-body and mean-field levels of theory. In the present work, we introduce the concept of a composite BJJ. In a composite BJJ, particles tunnel between two double-well potentials linked by a finite potential barrier between them. We focused on the many-body facets of quantum dynamics and investigate how the complex structure of the junction influences the tunneling. Employing the multiconfigurational time-dependent Hartree method for bosons, highly accurate many-boson wavefunctions were obtained, from which properties were computed. We analyzed the dynamics using the survival probability, the degree of fragmentation of the junction, and the fluctuations of the observables, and discuss how the many-boson tunneling behaved, and how it may be controlled, using the composite nature of the junction. A central result of this work relates to the degree of fragmentation of composite BJJs with different numbers of bosons. We provide strong evidence that a universal degree of fragmentation into multiple time-dependent modes takes place. Further applications are briefly discussed. Full article

(This article belongs to the Section Cold Atoms, Quantum Gases and Bose-Einstein Condensation)

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11 pages, 983 KiB

Open AccessReview

A Critical Look at Density Functional Theory in Chemistry: Untangling Its Strengths and Weaknesses

by Konstantinos P. Zois and Demeter Tzeli

Atoms 2024, 12(12), 65; https://doi.org/10.3390/atoms12120065 - 11 Dec 2024

Cited by 1 | Viewed by 1589

Abstract

Density functional theory (DFT) is a commonly used methodology favored by experts and non-experts alike. It is a useful tool for the investigation of atomic, molecular and surface systems, offering an efficient and often reliable approach to calculate ground state properties such as [...] Read more.

Density functional theory (DFT) is a commonly used methodology favored by experts and non-experts alike. It is a useful tool for the investigation of atomic, molecular and surface systems, offering an efficient and often reliable approach to calculate ground state properties such as electron density, total energy and molecular structure. However, fundamental issues are not rare. Of course, no one can really question the bold impact of DFT on modern chemical science. It is not only the way research is conducted that has been influenced by DFT, but also textbooks, datasets and our chemical intuition as well. In this review, issues pertaining to DFT are discussed, and it is pointed out that without a clear understanding of why we use calculations, an effective combination of experiment and theory will never be accomplished. Using low-level theoretical frameworks surely does not shed light on profound problems. To excel in our scientific field and make good use of our tools, we must very carefully decide which methodologies we are to employ. Full article

(This article belongs to the Section Quantum Chemistry, Computational Chemistry and Molecular Physics)

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16 pages, 1489 KiB

Open AccessArticle

Theoretical Study of the Dissociative Recombination and Vibrational (De-)Excitation of HCNH⁺ and Its Isomers by Electron Impact

by Mehdi Adrien Ayouz and Arnaud Buch

Atoms 2024, 12(12), 64; https://doi.org/10.3390/atoms12120064 - 3 Dec 2024

Cited by 1 | Viewed by 939

Abstract

Protonated hydrogen cyanide, HCNH⁺, is one of the most important molecules of interest in the astrophysical and astrochemical fields. This molecule not only plays the role of a reaction intermediary in various types of interstellar reactions but was also identified in [...] Read more.

Protonated hydrogen cyanide, HCNH⁺, is one of the most important molecules of interest in the astrophysical and astrochemical fields. This molecule not only plays the role of a reaction intermediary in various types of interstellar reactions but was also identified in Titan’s upper atmosphere. The cross sections for the dissociative recombination (DR) and vibrational (de-)excitation (VE and VDE) of HCNH⁺ and its

{CNH}_{2}^{+}

isomer are computed using a theoretical approach based on a combination of the normal mode approximation for the vibrational states of the target ions and the UK R-matrix code to evaluate electron-ion scattering matrices for fixed geometries of ions. The theoretical convoluted DR cross section for HCNH⁺ agrees well with the experimental data and a previous study. It was also found that the DR of the

{CNH}_{2}^{+}

isomer is important, which suggests that this ion might be present in DR experiments of HCNH⁺. Moreover, the ab initio calculations performed on the H₂CN⁺ isomer predict that this ion is a transition state. This result was confirmed by the study of the reaction path of the HCNH⁺ isomerization that was carried out by evaluating the intrinsic reaction coordinate (IRC). Finally, thermally averaged rate coefficients derived from the cross sections are provided for temperatures in the 10–10,000 K range. A comprehensive set of calculations is performed to assess the uncertainty of the obtained data. These results should help in modeling non-LTE spectra of HCNH⁺, taking into account the role of its most stable isomer, in various astrophysical environments. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms and Molecules in Ionized Environments)

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12 pages, 2269 KiB

Open AccessArticle

Cross-Sections for Projectile Ionization, Electron Capture, and System Breakdown of C⁵⁺ and Li²⁺ Ions with Atomic Hydrogen

by Saed J. Al Atawneh

Atoms 2024, 12(12), 63; https://doi.org/10.3390/atoms12120063 - 2 Dec 2024

Viewed by 702

Abstract

For many disciplines of science, all conceivable collisional cross-sections and reactions must be precisely known. Although recent decades have seen a trial of large-scale research to obtain such data, many essential atomic and molecular cross-section data are still missing, and the reliability of [...] Read more.

For many disciplines of science, all conceivable collisional cross-sections and reactions must be precisely known. Although recent decades have seen a trial of large-scale research to obtain such data, many essential atomic and molecular cross-section data are still missing, and the reliability of the existing cross-sections has to be validated. In this paper, we present projectile ionization, electron capture, and system breakdown cross-sections in carbon (C⁵⁺) ions and lithium (Li²⁺) ion collisions with atomic hydrogen based on the Monte Carlo models of classical and quasi-classical trajectories. According to our expectation, the QCTMC results show higher results in comparison to standard CTMC data, emphasizing the role of the Heisenberg correction constraint, especially in the low-energy regime. On the other hand, at high energy, the Heisenberg correction term has less influence as the projectile momentum increases. We present the total cross-sections of projectile ionization, electron capture, and system breakdown in C⁵⁺ ions and Li²⁺ ion collisions with atomic hydrogen in the impact energy range from 10 keV to 160 keV, which is of interest in astrophysical plasmas, atmospheric sciences, plasma laboratories, and fusion research. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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18 pages, 763 KiB

Open AccessArticle

Critical Impact of Isospin Asymmetry in Elucidating Magicity Across Isotonic Chains of Different Mass Regions Using Relativistic Energy Density Functional

by Praveen K. Yadav, N. Biswal, R. N. Panda, S. Mishra, Raj Kumar and M. Bhuyan

Atoms 2024, 12(12), 62; https://doi.org/10.3390/atoms12120062 - 28 Nov 2024

Viewed by 548

Abstract

This study provides a comprehensive examination of the surface properties—particularly the symmetry energy and its contributing components—of isotonic chains across various mass ranges, including light, medium, heavy, and superheavy nuclei. We establish a correlation between nuclear symmetry energy and isospin asymmetry in different [...] Read more.

This study provides a comprehensive examination of the surface properties—particularly the symmetry energy and its contributing components—of isotonic chains across various mass ranges, including light, medium, heavy, and superheavy nuclei. We establish a correlation between nuclear symmetry energy and isospin asymmetry in different mass regions along isotonic chains with magic and semi-magic neutron numbers of N = 20, 40, 82, 126, and 172. Our approach integrates the coherent density fluctuation model within the relativistic mean-field (RMF) framework, utilizing both the non-linear NL3 and density-dependent DD-ME2 parameter sets. The methodology employs the Brueckner energy density functional in conjunction with our recently developed relativistic energy density functional (relativistic-EDF). The relativistic parameterization of the EDF at local density facilitates a consistent exploration of isospin-dependent surface properties across the nuclear landscape. In the present work, we successfully reproduce established shell closures and demonstrate that the relativistic approach yields significantly improved predictions for recognized magic numbers, particularly Z = 28 and 50. Additionally, we present compelling evidence for the presence of novel shell and sub-shell closures, specifically at Z = 34, 58, 92, and 118. These findings contribute to a nuanced understanding of nuclear surface properties while serving as a benchmark for future investigations and validations of nuclear models. Full article

(This article belongs to the Section Nuclear Theory and Experiments)

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12 pages, 456 KiB

Open AccessArticle

Mutual Neutralization in Collisions of Li⁺ with O⁻

by Åsa Larson and Ann E. Orel

Atoms 2024, 12(12), 61; https://doi.org/10.3390/atoms12120061 - 28 Nov 2024

Viewed by 628

Abstract

The total and differential cross-sections and final state distribution for mutual neutralization in collisions of Li⁺ with O⁻ were calculated using an ab initio quantum mechanical approach based on potential energy curves and non-adiabatic coupling elements computed with the multi-reference configuration [...] Read more.

The total and differential cross-sections and final state distribution for mutual neutralization in collisions of Li⁺ with O⁻ were calculated using an ab initio quantum mechanical approach based on potential energy curves and non-adiabatic coupling elements computed with the multi-reference configuration interaction method. The final state distributions favored channels with excited oxygen states, indicating a strong effect of electron correlation, and the electron transfer could not be described by a simple one-electron exchange process. Full article

(This article belongs to the Special Issue Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A Tribute to Barry Irwin Schneider)

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15 pages, 1189 KiB

Open AccessArticle

Application of Atomic Spectroscopy of Trapped Radioactive Ions in Nuclear Physics

by Ruben P. de Groote

Atoms 2024, 12(12), 60; https://doi.org/10.3390/atoms12120060 - 21 Nov 2024

Viewed by 1005

Abstract

A review is given of precision measurements of hyperfine constants and nuclear g-factors measured with ions confined in ion traps. The nuclear physics observables which can be extracted from these types of measurements are discussed. The feasibility of future nuclear structure studies [...] Read more.

A review is given of precision measurements of hyperfine constants and nuclear g-factors measured with ions confined in ion traps. The nuclear physics observables which can be extracted from these types of measurements are discussed. The feasibility of future nuclear structure studies using precision atomic spectroscopy of trapped radioactive atoms, produced with accelerator-driven approaches, is discussed. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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