Atoms

16 pages, 5924 KiB

Open AccessArticle

Setup for the Ionic Lifetime Measurement of the ^229mTh³⁺ Nuclear Clock Isomer

by Kevin Scharl, Shiqian Ding, Georg Holthoff, Mahmood Irtiza Hussain, Sandro Kraemer, Lilli Löbell, Daniel Moritz, Tamila Rozibakieva, Benedict Seiferle, Florian Zacherl and Peter G. Thirolf

Atoms 2023, 11(7), 108; https://doi.org/10.3390/atoms11070108 - 24 Jul 2023

Cited by 1 | Viewed by 1339

Abstract

For the realization of an optical nuclear clock, the first isomeric excited state of thorium-229 (^229mTh) is currently the only candidate due to its exceptionally low-lying excitation energy (

8.338 \pm 0.024

eV). Such a nuclear clock holds promise not only [...] Read more.

For the realization of an optical nuclear clock, the first isomeric excited state of thorium-229 (^229mTh) is currently the only candidate due to its exceptionally low-lying excitation energy (

8.338 \pm 0.024

eV). Such a nuclear clock holds promise not only to be a very precise metrological device but also to extend the knowledge of fundamental physics studies, such as dark matter research or variations in fundamental constants. Considerable progress was achieved in recent years in characterizing ^229mTh from its first direct identification in 2016 to the only recent observation of the long-sought-after radiative decay channel. So far, nuclear resonance as the crucial parameter of a nuclear frequency standard has not yet been determined with laser-spectroscopic precision. To determine another yet unknown basic property of the thorium isomer and to further specify the linewidth of its ground-state transition, a measurement of the ionic lifetime of the isomer is in preparation. Theory and experimental investigations predict the lifetime to be 10³–10⁴ s. To precisely target this property using hyperfine structure spectroscopy, an experimental setup is currently being commissioned at LMU Munich. It is based on a cryogenic Paul trap providing long-enough storage times for ^229mTh ions, that will be sympathetically cooled with ⁸⁸Sr⁺. This article presents a concept for an ionic lifetime measurement and discusses the laser-optical part of a setup specifically developed for this purpose. Full article

(This article belongs to the Special Issue Over a Century of Nuclear Isomers: Challenges and Prospects)

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20 pages, 425 KiB

Open AccessArticle

Exponentially Correlated Hylleraas–Configuration Interaction Studies of Atomic Systems. III. Upper and Lower Bounds to He-Sequence Oscillator Strengths for the Resonance ¹S→¹P Transition

by James S. Sims, Bholanath Padhy and María Belén Ruiz Ruiz

Atoms 2023, 11(7), 107; https://doi.org/10.3390/atoms11070107 - 22 Jul 2023

Cited by 1 | Viewed by 1166

Abstract

The exponentially correlated Hylleraas–configuration interaction method (E-Hy-CI) is a generalization of the Hylleraas–configuration interaction method (Hy-CI) in which the single

r_{i j}

of an Hy-CI wave function is generalized to a form of the generic type [...] Read more.

The exponentially correlated Hylleraas–configuration interaction method (E-Hy-CI) is a generalization of the Hylleraas–configuration interaction method (Hy-CI) in which the single

r_{i j}

of an Hy-CI wave function is generalized to a form of the generic type

r_{i j}^{ν_{i j}} e^{- ω_{i j} r_{i j}}

. This work continues the exploration, begun in the first two papers in this series (on the helium atom and on ground and excited

S

states of Li II), of whether wave functions containing both linear and exponential

r_{i j}

factors converge more rapidly than either one alone. In the present study, we examined not only 1

s^{2}

^{1} S

states but 1s2p

^{1} P

states for the He I, Li II, Be III, C V and O VII members of the He isoelectronic sequence as well. All

^{1} P

energies except He I are better than previous results. The wave functions obtained were used to calculate oscillator strengths, including upper and lower bounds, for the He-sequence lowest (resonance)

^{1} S \to

^{1} P

transition. Interpolation techniques were used to make a graphical study of the oscillator strength behavior along the isoelectronic sequence. Comparisons were made with previous experimental and theoretical results. The results of this study are oscillator strengths for the 1

s^{2}

^{1} S \to

1s2

p^{1} P

He isoelectronic sequence with rigorous non-relativistic quantum mechanical upper and lower bounds of (0.001–0.003)% and probable precision ≤ 0.0000003, and were obtained by extending the previously developed E-Hy-CI formalism to include the calculation of transition moments (oscillator strengths). Full article

(This article belongs to the Special Issue Recent Advances in Atomic and Molecular Spectroscopy)

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14 pages, 629 KiB

Open AccessArticle

Towards Understanding Incomplete Fusion Reactions at Low Beam Energies: Modified Sum Rule Model

by Bhushan Bhujang and Pragya Das

Atoms 2023, 11(7), 106; https://doi.org/10.3390/atoms11070106 - 21 Jul 2023

Viewed by 858

Abstract

We investigated the enhanced production of nuclei formed via incomplete fusion (ICF) reactions near and above the Coulomb barrier energies (5–8 MeV/A). The cross-sections of the evaporation residues formed in the reactions—

^{11}

B+

^{124}

Sn,

^{10}

B+

^{124}

Sn and

^{11}

B+ [...] Read more.

We investigated the enhanced production of nuclei formed via incomplete fusion (ICF) reactions near and above the Coulomb barrier energies (5–8 MeV/A). The cross-sections of the evaporation residues formed in the reactions—

^{11}

B+

^{124}

Sn,

^{10}

B+

^{124}

Sn and

^{11}

B+

^{122}

Sn—were measured using off-line gamma-ray spectrometry. The sum rule model (SRM) by Wilczyński et al. predicted the cross-section values too low compared to our experimental results. In earlier studies, the same model has been very successful in explaining ICF reactions at high beam energies (>10 MeV/A). We, therefore, modified the SRM, specifically incorporating the energy dependence in the definition of critical angular momentum

ℓ_{c r}

. The resulting modified SRM gave an improved theoretical estimate for the reactions we studied. Full article

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

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25 pages, 404 KiB

Open AccessReview

On Invariant Vectors in the Presence of Electric and Magnetic Fields

by Jean-Christophe Pain

Atoms 2023, 11(7), 105; https://doi.org/10.3390/atoms11070105 - 20 Jul 2023

Viewed by 853

Abstract

In this non-exhaustive review, we discuss the importance of invariant vectors in atomic physics, such as the Laplace–Runge–Lenz vector, the Redmond vector in the presence of an electric field, the Landau–Avron–Sivardièrevector when the system is subject to a magnetic field, and the supergeneralized [...] Read more.

In this non-exhaustive review, we discuss the importance of invariant vectors in atomic physics, such as the Laplace–Runge–Lenz vector, the Redmond vector in the presence of an electric field, the Landau–Avron–Sivardièrevector when the system is subject to a magnetic field, and the supergeneralized Runge–Lenz vector for the two-center problem. The application to the Stark and Zeeman effects are outlined. The existence of constants of motion in the charge-dyon system is also briefly mentioned. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas, Including Cases with External Electric and Magnetic Fields and Laser Plasma Interaction)

17 pages, 3206 KiB

Open AccessArticle

Role of Simple Spatial Gradient in Reinforcing the Accuracy of Temperature Determination of HED Plasma via Spectral Line-Area Ratios

by Greg A. Riggs, Mark E. Koepke, Ted S. Lane, Thomas E. Steinberger, Pawel M. Kozlowski and Igor E. Golovkin

Atoms 2023, 11(7), 104; https://doi.org/10.3390/atoms11070104 - 12 Jul 2023

Viewed by 1006

Abstract

We report on the simulation of temperature gradients in tamped NaFMgO target-foil plasma, heated and backlit by z-pinch dynamic hohlraum radiation. Our approach compares the spectroscopic output of a collisional-radiative model (prismspect) with soft X-ray absorption spectra collected on Sandia National [...] Read more.

We report on the simulation of temperature gradients in tamped NaFMgO target-foil plasma, heated and backlit by z-pinch dynamic hohlraum radiation. Our approach compares the spectroscopic output of a collisional-radiative model (prismspect) with soft X-ray absorption spectra collected on Sandia National Laboratories’ (SNL) Z Pulsed Power Facility. The pattern of minimum

χ^{2}

is seen to agree with an efficient, three-parameter model. Results show that a negligible gradient in electron temperature

T_{e}

is consistent with experimental data, justifying the assumptions of previous work. The predicted sensitivity of line spectra to the gradient-aligned profile of

T_{e}

is documented for each spectral feature, so that the line-area ratio between a pair of spectral features may be assessed as a proxy for the existence and quantification of such gradients. Full article

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8 pages, 2626 KiB

Open AccessArticle

Role of Gas Pressure in Quasi-Phase Matching in High Harmonics Driven by Two-Color Laser Field

by Sergey Stremoukhov

Atoms 2023, 11(7), 103; https://doi.org/10.3390/atoms11070103 - 07 Jul 2023

Viewed by 899

Abstract

The results of a study on the effect of pressure in a medium consisting of a set of gas jets separated by vacuum gaps, interacting with two-color laser fields formed by the fundamental and the second harmonics of a laser, are presented herein. [...] Read more.

The results of a study on the effect of pressure in a medium consisting of a set of gas jets separated by vacuum gaps, interacting with two-color laser fields formed by the fundamental and the second harmonics of a laser, are presented herein. It has been demonstrated that a decrease in pressure leads to a shift in the region of harmonics where quasi-phase matching (QPM) occurs towards shorter wavelength radiation, accompanied by an increase in the efficiency of amplification of these harmonics. A feature of this process is the identical power-law character of the shift in the region and the increase in the efficiency of harmonic QPM amplification. Additionally, the study presents the results of the effect of inaccurately setting the width of the gas jets on the shape of the spectrum of harmonic QPM amplification. Full article

(This article belongs to the Special Issue Recent Progress in Strong-Field Atomic and Molecular Physics)

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12 pages, 1031 KiB

Open AccessArticle

Variational Approaches to Two-Dimensionally Symmetry-Broken Dipolar Bose–Einstein Condensates

by Yong-Chang Zhang and Fabian Maucher

Atoms 2023, 11(7), 102; https://doi.org/10.3390/atoms11070102 - 06 Jul 2023

Cited by 2 | Viewed by 1127

Abstract

It has been shown that quantum fluctuations in dipolar Bose–Einstein condensates (BECs) lead to a stabilisation against collapse, thereby providing access to a range of states with different symmetries. In this paper, we discuss variational approaches to approximately determine the phase diagrams for [...] Read more.

It has been shown that quantum fluctuations in dipolar Bose–Einstein condensates (BECs) lead to a stabilisation against collapse, thereby providing access to a range of states with different symmetries. In this paper, we discuss variational approaches to approximately determine the phase diagrams for dipolar BECs that are trapped along the dipolar orientation and otherwise infinite in the perpendicular direction (thermodynamic limit). The two-dimensional symmetry breaking occurs in the plane perpendicular to the polarisation axis. We show in detail how to derive approximate expressions that are valid in a region where modulations to an otherwise unmodulated perfect superfluid emerge gradually with a small modulation amplitude and compare the results to rigorous numerics. Full article

(This article belongs to the Special Issue Recent Trends on Quantum Fluctuations in Ultra-Cold Quantum Gases)

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14 pages, 408 KiB

Open AccessArticle

Mean-Field Description of Cooperative Scattering by Atomic Clouds

by Nicola Piovella

Atoms 2023, 11(7), 101; https://doi.org/10.3390/atoms11070101 - 29 Jun 2023

Viewed by 857

Abstract

We present analytic expressions for the scattering of light by an extended atomic cloud. We obtain the solution for the mean-field excitation of different atomic spherical distributions driven by a uniform laser, including the initial build up, the steady state and the decay [...] Read more.

We present analytic expressions for the scattering of light by an extended atomic cloud. We obtain the solution for the mean-field excitation of different atomic spherical distributions driven by a uniform laser, including the initial build up, the steady state and the decay after the laser is switched off. We show that the mean-field model does not describe subradiant scattering due to the negative interference of the photons scattered by N discrete atoms. Full article

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

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Atoms, Volume 11, Issue 7 (July 2023) – 8 articles

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