Next Issue
Volume 8, June
Previous Issue
Volume 8, December

Table of Contents

Atoms, Volume 8, Issue 1 (March 2020) – 9 articles

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Cover Story (view full-size image) Among numerous diagnostic tools for multimillion-degree fusion plasmas, neutral beam spectroscopy [...] Read more.
Order results
Result details
Select all
Export citation of selected articles as:
Open AccessArticle
Positron Impact Excitation of the nS States of Atomic Hydrogen
Atoms 2020, 8(1), 9; https://doi.org/10.3390/atoms8010009 - 03 Mar 2020
Viewed by 196
Abstract
The excitation cross sections of the nS states, n = 2 to 6, of atomic hydrogen at various incident positron energies (10.23 to 300 eV) were calculated using the variational polarized-orbital method. Nine partial waves were used to obtain converged cross sections. The [...] Read more.
The excitation cross sections of the nS states, n = 2 to 6, of atomic hydrogen at various incident positron energies (10.23 to 300 eV) were calculated using the variational polarized-orbital method. Nine partial waves were used to obtain converged cross sections. The present results should be useful for comparison with results obtained from other theories and approximations. The positron-impact cross section was found to be higher than the electron-impact cross sections. Experimental and other theoretical results are discussed. The threshold law of excitation is discussed and the cross sections in this region were seen to obey the threshold law proportional to ( ln k f ) 2 . Cross sections were calculated in the Born approximation also and compared to those obtained using the variational polarized orbital method. Full article
(This article belongs to the Special Issue Interactions of Positrons with Matter and Radiation)
Show Figures

Figure 1

Open AccessArticle
Atomic Data for Calculation of the Intensities of Stark Components of Excited Hydrogen Atoms in Fusion Plasmas
Atoms 2020, 8(1), 8; https://doi.org/10.3390/atoms8010008 - 18 Feb 2020
Viewed by 292
Abstract
Motional Stark effect (MSE) spectroscopy represents a unique diagnostic tool capable of determining the magnitude of the magnetic field and its direction in the core of fusion plasmas. The primary excitation channel for fast hydrogen atoms in injected neutral beams, with energy in [...] Read more.
Motional Stark effect (MSE) spectroscopy represents a unique diagnostic tool capable of determining the magnitude of the magnetic field and its direction in the core of fusion plasmas. The primary excitation channel for fast hydrogen atoms in injected neutral beams, with energy in the range of 25–1000 keV, is due to collisions with protons and impurity ions (e.g., He 2 + and heavier impurities). As a result of such excitation, at the particle density of 10 13 –10 14 cm 3 , the line intensities of the Stark multiplets do not follow statistical expectations (i.e., the populations of fine-structure levels within the same principal quantum number n are not proportional to their statistical weights). Hence, any realistic modeling of MSE spectra has to include the relevant collisional atomic data. In this paper we provide a general expression for the excitation cross sections in parabolic states within n = 3 for an arbitrary orientation between the direction of the motion-induced electric field and the proton-atom collisional axis. The calculations make use of the density matrix obtained with the atomic orbital close coupling method and the method can be applied to other collisional systems (e.g., He 2 + , Be 4 + , C 6 + , etc.). The resulting cross sections are given as simple fits that can be directly applied to spectral modeling. For illustration we note that the asymmetry detected in the first classical cathode ray experiments between the red- and blue-shifted spectral components can be quantitatively studied using the proposed approach. Full article
(This article belongs to the Special Issue Plasma Spectroscopy in the Presence of Magnetic Fields)
Show Figures

Figure 1

Open AccessArticle
Empirical Line Lists in the ExoMol Database
Atoms 2020, 8(1), 7; https://doi.org/10.3390/atoms8010007 - 17 Feb 2020
Viewed by 262
Abstract
The ExoMol database aims to provide comprehensive molecular line lists for exoplanetary and other hot atmospheres. The data are expanded by inclusion of empirically derived line lists taken from the literature for a series of diatomic molecules, namely CH, NH, OH, AlCl, AlF, [...] Read more.
The ExoMol database aims to provide comprehensive molecular line lists for exoplanetary and other hot atmospheres. The data are expanded by inclusion of empirically derived line lists taken from the literature for a series of diatomic molecules, namely CH, NH, OH, AlCl, AlF, OH + , CaF, MgF, KF, NaF, LiCl, LiF, MgH, TiH, CrH, FeH, C 2 , CP, CN, CaH, and triplet N 2 . Generally, these line lists are constructed from measured spectra using a combination of effective rotational Hamiltonian models for the line positions and ab initio (transition) dipole moments to provide intensities. This work results in the inclusion of 22 new molecules (36 new isotopologues) in the ExoMol database. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
Show Figures

Figure 1

Open AccessArticle
Monte Carlo Simulation of γγ Correlation Functions
Atoms 2020, 8(1), 6; https://doi.org/10.3390/atoms8010006 - 10 Feb 2020
Viewed by 294
Abstract
γγ correlation functions are mathematical expressions that describe the angular distribution of cascade γ-rays emitted from an atomic nucleus. Cascade transitions may occur in either a two-step deexcitation or through an excitation-deexcitation process of a particular energy level inside the [...] Read more.
γ γ correlation functions are mathematical expressions that describe the angular distribution of cascade γ -rays emitted from an atomic nucleus. Cascade transitions may occur in either a two-step deexcitation or through an excitation-deexcitation process of a particular energy level inside the nucleus. In both cases, the nucleus returns to its ground energy state. Spin and parity of the excited state can be determined experimentally using the asymmetry of the angular distribution of the emitted radiation. γ γ correlation functions are only valid for point-like targets and detectors. In the real experiments, however, neither the target nor the detector is point-like. Thus, misassignment of the spin-parity of energy levels may easily take place if only the analytical equations are considered. Here, we develop a new Monte Carlo simulation method of the γ γ correlation functions to account for the extended target and detector involved in spin-parity measurements using nuclear resonance fluorescence of nuclei. The proposed simulation tool can handle arbitrary geometries and spin sequences. Additionally, we provide numerical calculations of a parametric study on the influence of the detection geometry on the angular distribution of the emitted γ -rays. Finally, we benchmark our simulation by comparing the simulation-estimated asymmetry ratios with those measured experimentally. The present simulation can be employed as a kernel of an implementation that simulates the nuclear resonance fluorescence process. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
Show Figures

Figure 1

Open AccessArticle
Hyperfine Anomaly in Eu Isotopes and the Universiability of the Moskowitz–Lombardi Formula
Atoms 2020, 8(1), 5; https://doi.org/10.3390/atoms8010005 - 03 Feb 2020
Viewed by 213
Abstract
A method for determining the hyperfine anomaly, without using the nuclear magnetic moments, is used on a series of unstable isotopes of Eu. The large number of experimental data in Eu makes it possible to extract the hyperfine anomaly for a number of [...] Read more.
A method for determining the hyperfine anomaly, without using the nuclear magnetic moments, is used on a series of unstable isotopes of Eu. The large number of experimental data in Eu makes it possible to extract the hyperfine anomaly for a number of unstable isotopes. Calculations of the Bohr–Weisskopf effect and hence the hyperfine anomaly are performed using the particle-rotor formalism. The result from the calculations and experiments is compared with other theoretical calculations and the empirical Moskowitz–Lombardi formula. The results show that the Moskowitz–Lombardi formula is not universal. Full article
Open AccessArticle
Atomic Data Needs in Astrophysics: The Galactic Center “Scandium Mystery”
Atoms 2020, 8(1), 4; https://doi.org/10.3390/atoms8010004 - 22 Jan 2020
Viewed by 254
Abstract
Investigating the Galactic center offers unique insights into the buildup and history of our Galaxy and is a stepping stone to understand galaxies in a larger context. It is reasonable to expect that the stars found in the Galactic center might have a [...] Read more.
Investigating the Galactic center offers unique insights into the buildup and history of our Galaxy and is a stepping stone to understand galaxies in a larger context. It is reasonable to expect that the stars found in the Galactic center might have a different composition compared to stars found in the local neighborhood around the Sun. It is therefore quite exciting when recently there were reports of unusual neutral scandium, yttrium, and vanadium abundances found in the Galactic center stars, compared to local neighborhood stars. To explain the scandium abundances in the Galactic center, we turn to recent laboratory measurements and theoretical calculations done on the atomic oscillator strengths of neutral scandium lines in the near infrared. We combine these with measurements of the hyper fine splitting of neutral scandium. We show how these results can be used to explain the reported unusual scandium abundances and conclude that in this respect, the environment of the Galactic center is not that different from the environment in the local neighborhood around the sun. Full article
Show Figures

Figure 1

Open AccessEditorial
Acknowledgement to Reviewers of Atoms in 2019
Atoms 2020, 8(1), 3; https://doi.org/10.3390/atoms8010003 - 20 Jan 2020
Viewed by 242
Abstract
The editorial team greatly appreciates the reviewers who have dedicated their considerable time and expertise to the journal’s rigorous editorial process over the past 12 months, regardless of whether the papers are finally published or not [...] Full article
Open AccessArticle
Electron Broadening Operator Including Penetrating Collisions for Hydrogen
Atoms 2020, 8(1), 2; https://doi.org/10.3390/atoms8010002 - 14 Jan 2020
Viewed by 304
Abstract
The expression of the electron broadening operator including the effect of penetrating collisions, i.e., for which the incoming electron enters the extent of bound-electron wave-functions, is rather complicated, even for hydrogen. It involves integrals of special functions, the evaluation of which deserves scrutiny. [...] Read more.
The expression of the electron broadening operator including the effect of penetrating collisions, i.e., for which the incoming electron enters the extent of bound-electron wave-functions, is rather complicated, even for hydrogen. It involves integrals of special functions, the evaluation of which deserves scrutiny. We present a simple approximate form of the electron collision operator for hydrogen including penetration effects, both in direct and interference terms. The new expression is accurate and easy to compute. In the Penetration Standard Theory, the collision operator is convergent whatever the value of the maximum impact parameter. However, when penetration theory is not valid anymore, it should be questioned. We discuss the problem of strong collisions when penetration effects are taken into account. Full article
(This article belongs to the Special Issue Atomic and Ionic Collisions with Formation of Quasimolecules)
Show Figures

Figure 1

Open AccessArticle
Calculations of Resonance Parameters for the Doubly Excited 1P° States in Ps Using Exponentially Correlated Wave Functions
Atoms 2020, 8(1), 1; https://doi.org/10.3390/atoms8010001 - 31 Dec 2019
Viewed by 294
Abstract
Recent observations on resonance states of the positronium negative ion (Ps) in the laboratory created huge interest in terms of the calculation of the resonance parameters of the simple three-lepton system. We calculate the resonance parameters for the doubly excited 1 [...] Read more.
Recent observations on resonance states of the positronium negative ion (Ps) in the laboratory created huge interest in terms of the calculation of the resonance parameters of the simple three-lepton system. We calculate the resonance parameters for the doubly excited 1P° states in Ps using correlated exponential wave functions based on the complex-coordinate rotation method. The resonance energies and widths for the 1P° Feshbach resonance states in Ps below the N = 2, 3, 4, 5 Ps thresholds are reported. The 1P° shape resonance above the N = 2, 4 Ps thresholds are also reported. Our predications are in agreement with the available results. Few Feshbach resonance parameters below the N = 4 and 5 Ps thresholds have been reported in the literature. Our predictions will provide useful information for future resonance experiments in Ps. Full article
(This article belongs to the Special Issue Interactions of Positrons with Matter and Radiation)
Show Figures

Figure 1

Previous Issue
Next Issue
Back to TopTop