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Atoms
Volume 12
Issue 7
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Atoms, Volume 12, Issue 7 (July 2024) – 4 articles

Cover Story (view full-size image): The single-center convergent close-coupling (CCC) method was utilized to obtain a comprehensive set of cross sections for positron scattering on atomic boron for energies between 10−5 eV and 5000 eV. An accurate representation of the atomic structure was obtained, and excellent agreement was found with a previous experiment and the theory for excitation energies, oscillator strengths, and polarizabilities. To obtain positronium-formation and direct ionization cross sections, a model potential technique was used, together with the CCC method. From the current cross sections and previous CCC results for hydrogen and fluorine, the cross sections of positron scattering on BH, BF, BF2, and BF3 were obtained, with a modified independent atom approach. For all targets, good agreement with previous electron results was found at high energies. View this paper
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9 pages, 726 KiB  
Article
The Optical Model Absorption Term in the Frame of Fractional Derivatives
by Ibrahim Ghabar, Aliaa Burqan and Gharib Gharib
Atoms 2024, 12(7), 37; https://doi.org/10.3390/atoms12070037 - 10 Jul 2024
Viewed by 326
Abstract
The complex optical model has been widely used to describe the elastic scattering of the nucleon–nucleus. The imaginary term of the optical potential takes into account the non-elastic scattering processes. This term was taken to be a Woods–Saxon form factor or its derivative [...] Read more.
The complex optical model has been widely used to describe the elastic scattering of the nucleon–nucleus. The imaginary term of the optical potential takes into account the non-elastic scattering processes. This term was taken to be a Woods–Saxon form factor or its derivative to simulate the volume absorption or the absorption localized at the surface of the target, respectively. In this study, a fractional derivative of the Woods–Saxon potential with 0<α<1 was used, where α=0 and α=1 give the volume and the surface absorption form factor, respectively. Full article
(This article belongs to the Special Issue Over a Century of Nuclear Isomers: Challenges and Prospects)
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19 pages, 475 KiB  
Article
Calculations of Positron Scattering from Boron, BH, BF, BF2, and BF3
by Nicolas A. Mori, Haadi Umer, Liam H. Scarlett, Igor Bray and Dmitry V. Fursa
Atoms 2024, 12(7), 36; https://doi.org/10.3390/atoms12070036 - 10 Jul 2024
Viewed by 397
Abstract
The single-center convergent close-coupling (CCC) method is applied to calculate positron scattering from boron. A model potential approach is utilized to extract the positronium formation, direct ionization, and values between the positronium formation and ionization thresholds. We present results for total, electron loss, [...] Read more.
The single-center convergent close-coupling (CCC) method is applied to calculate positron scattering from boron. A model potential approach is utilized to extract the positronium formation, direct ionization, and values between the positronium formation and ionization thresholds. We present results for total, electron loss, elastic, momentum transfer, total bound state excitation, positronium formation, direct ionization, stopping power, and mean excitation energy from 10−5 eV to 5000 eV. For boron, there is only one other set of theoretical positron calculations for elastic and momentum transfer above 500 eV, which is in excellent agreement with the current CCC results. Using the current results for boron atoms and previous CCC calculations for hydrogen and fluorine atoms, positron scattering from BF, BF2, BF3, and BH molecules is calculated for energies between 0.1 eV and 5000 eV with a modified independent atom approach. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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16 pages, 459 KiB  
Article
Experimental and Theoretical Electron Collision Broadening Parameters for Several Ti II Spectral Lines of Industrial and Astrophysical Interest
by Lucía Isidoro-García, Isabel de Andrés-García, Juan Porro, Francisco Fernández and Cristóbal Colón
Atoms 2024, 12(7), 35; https://doi.org/10.3390/atoms12070035 - 9 Jul 2024
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Abstract
A Q-switched Nd:YAG laser was focused on the Pb–Ti alloy samples in several laser-induced breakdown experiments in order to measure the Stark parameters of several spectral lines (58) of singly ionized titanium, including the 3504.89 Å and 3510.83 Å lines (where we achieved [...] Read more.
A Q-switched Nd:YAG laser was focused on the Pb–Ti alloy samples in several laser-induced breakdown experiments in order to measure the Stark parameters of several spectral lines (58) of singly ionized titanium, including the 3504.89 Å and 3510.83 Å lines (where we achieved new experimental and theoretical values). The diagnostics of the laser-induced plasmas (electron density and electron temperature) were performed using Balmer’s H alpha line (6562.7 Å). The temperatures were obtained by the Boltzmann plot technique with spectral lines of Pb I (after correction for its evident self-absorption). Subsequently, the calculations by the Griem approach of the Stark broadening parameters for several spectral lines were performed using the Gaunt factors proposed by van Regemorter and those proposed by Douglas H. Sampson. In the latter case, the values obtained were very close to the experimental values. This enables us to assume that the calculations performed for the spectral lines of Ti II, without experimental information, are more accurate using the Gaunt factors proposed by Sampson. Full article
(This article belongs to the Special Issue Interaction of Electrons with Atoms and Molecules in Ionized Environments)
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15 pages, 3029 KiB  
Article
Efficient Time-Dependent Method for Strong-Field Ionization of Atoms with Smoothly Varying Radial Steps
by Nicolas Douguet, Mikhail Guchkov, Klaus Bartschat and Samantha Fonseca dos Santos
Atoms 2024, 12(7), 34; https://doi.org/10.3390/atoms12070034 - 3 Jul 2024
Viewed by 497
Abstract
We present an efficient numerical method to solve the time-dependent Schrödinger equation in the single-active electron picture for atoms interacting with intense optical laser fields. Our approach is based on a non-uniform radial grid with smoothly increasing steps for the electron distance from [...] Read more.
We present an efficient numerical method to solve the time-dependent Schrödinger equation in the single-active electron picture for atoms interacting with intense optical laser fields. Our approach is based on a non-uniform radial grid with smoothly increasing steps for the electron distance from the residual ion. We study the accuracy and efficiency of the method, as well as its applicability to investigate strong-field ionization phenomena, the process of high-order harmonic generation, and the dynamics of highly excited Rydberg states. Full article
(This article belongs to the Special Issue Applications of Ab-Initio Calculations in Atomic, Molecular, and Optical Physics)
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