José Paulo Santos

The spontaneous two-photon emission in hydrogenlike ions is investigated within the framework of second- order perturbation theory and Dirac’s equation. Special attention is paid to the angular correlation of the emitted photons as well as to the degree of linear polarization of one of the two photons, if the second is just observed under arbitrary angles. Expressions for the angular correlation and the degree of linear polarization are expanded in powers of cosine functions of the two-photon opening angle, whose coefficients depend on the atomic number and the energy sharing of the emitted photons. The effects of including higher (electric and magnetic) multipoles upon the emitted photon pairs beyond the electric-dipole approximation are also discussed. Calculations of the coefficients are performed for the transitions 2s1/2 → 1s1/2, 3d3/2 → 1s1/2, and 3d5/2 → 1s1/2, along the entire hydrogen isoelectronic sequence (1 Z 100).

We combined different experimental techniques with a theoretical approach to determine a consistent set of diagram lines energies and binding energies. We propose an original approach consisting in determining the mass attenuation coefficients in an energy range covering the L-, M- and N- absorption edges, including a detailed evaluation of the associated uncertainties, to derive precisely the binding energies. We investigated the Lα, Lβ and M spectra of Gd with an independantly calibrated high-resolution anti-parallel double-crystal x-ray spectrometer. All the lines were identified and found in excellent agreement with the binding energies previously derived. Morever, we identified for the first time M5−O2, M4−O2,3 and M4−N2,3 diagram lines.

The most important processes for the creation of chlorine ion excited states from the ground configurations of Cl 10+ to Cl 15+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, were studied. Theoretical values for inner-shell excitation and ionization cross-sections, including double KL and triple KLL ionization, transition probabilities and energies for the de-excitation processes, were calculated in the framework of the multi-configuration Dirac–Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kα x-ray spectrum was obtained, which was then compared with recent experimental data.

The most important processes for the creation of chlorine ion excited states from the ground configurations of Cl 10+ to Cl 15+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, were studied. Theoretical values for inner-shell excitation and ionization cross-sections, including double KL and triple KLL ionization, transition probabilities and energies for the de-excitation processes, were calculated in the framework of the multi-configuration Dirac–Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kα x-ray spectrum was obtained, which was then compared with recent experimental data.

The most important processes for the creation of S12+ to S14+ ions excited states from the ground configurations of S9+ to S14+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double-KL and triple-KLL ionizations, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multiconfiguration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kalpha x-ray spectrum is obtained, which is compared to recent experimental data.

The most important processes for the creation of S12+ to S14+ ions excited states from the ground configurations of S9+ to S14+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double-KL and triple-KLL ionizations, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multiconfiguration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kalpha x-ray spectrum is obtained, which is compared to recent experimental data.

In this paper we review the different relativistic and QED contributions to energies, ionic radii, transition probabilities and Landé g-factors in super-heavy elements, with the help of the MultiConfiguration Dirac-Fock method (MCDF). The effects of taking into account the Breit interaction to all orders by including it in the self-consistent field process are demonstrated. State of the art radiative corrections are included in the calculation and discussed. We also study the non-relativistic limit of MCDF calculation and find that the non-relativistic offset can be unexpectedly large.

In this paper we review the different relativistic and QED contributions to energies, ionic radii, transition probabilities and Landé g-factors in super-heavy elements, with the help of the MultiConfiguration Dirac-Fock method (MCDF). The effects of taking into account the Breit interaction to all orders by including it in the self-consistent field process are demonstrated. State of the art radiative corrections are included in the calculation and discussed. We also study the non-relativistic limit of MCDF calculation and find that the non-relativistic offset can be unexpectedly large.Topical Issue on the Atomic Properties of the Heaviest Elements

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Nuclear Inst. and Methods in Physics Research, B, 408 (2017) 100-102. doi:10.1016/j.nimb.2017.04.015

The use of a vacuum double crystal spectrometer, coupled to an electron-cyclotron resonance ion source (ECRIS), allows to measure low-energy x-ray transitions energies in highly-charged ions with accuracies of the order of a few parts per million. We have used this installation to measure the 1s2p 1 P1 - 1s2 1 S0 diagram line and the 1s2s 3 S1 - 1s2 1 S0 forbidden M1 transition energies in helium-like argon, the 1s2s2p 2 P j 1s2 2s 2 S1/2 transitions in lithium-like argon and the 1s2s2 2p 1 P1 - 1s2 2s2 1 S0 transition in beryllium-like argon. These transition measurements have accuracies between 2 and 4 ppm depending on the line intensity. Thanks to the excellent agreement between the simulations and the measurements, we were also able to measure the transition width of all the allowed transitions. The results are compared to recent QED and relativistic many-body calculations.

The use of a vacuum double crystal spectrometer, coupled to an electron-cyclotron resonance ion source (ECRIS), allows to measure low-energy x-ray transitions energies in highly-charged ions with accuracies of the order of a few parts per million. We have used this installation to measure the 1s2p 1 P1 - 1s2 1 S0 diagram line and the 1s2s 3 S1 - 1s2 1 S0 forbidden M1 transition energies in helium-like argon, the 1s2s2p 2 P j 1s2 2s 2 S1/2 transitions in lithium-like argon and the 1s2s2 2p 1 P1 - 1s2 2s2 1 S0 transition in beryllium-like argon. These transition measurements have accuracies between 2 and 4 ppm depending on the line intensity. Thanks to the excellent agreement between the simulations and the measurements, we were also able to measure the transition width of all the allowed transitions. The results are compared to recent QED and relativistic many-body calculations.

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Radiationless transition rates to L1 vacancy states have been calculated ab initio in the Dirac-Fock approximation. The calculations include quantum-electrodynamic corrections. Results in the jj coupling scheme for all possible L1 transitions are tabulated for elements Yb and Hg.

The determination of atomic masses from highly ionized atoms using Penning Traps requires precise values for electronic binding energies. In the present work, binding energies of several ions (from several elements) are calculated in the framework of two relativistic many-body methods: Relativistic Many-Body Perturbation Theory (RMBPT) and Multi-Configuration Dirac– Fock (MCDF). The ions studied in this work are: Cl (He and Li-like), Se (F and Ne-like), Cs (He, Be, Ne, Al, Cl, Ar, K, Kr, Xe-like and neutral Cs), Hg, Pb and U (Br and Kr-like). Some of them are presented in this paper. Cesium has been treated in more details, allowing for a systematic comparison between MCDF and RMBPT methods. The Cs ions binding energies allow for the determination of atomic Cs mass, which can be used in a QED-independent fine structure constant determination.

The transition probabilities of Kα hypersatellite lines and energy shifts with respect to the corresponding diagram lines are computed using the Dirac–Fock model for several values of atomic number Z throughout the periodic table. The influence of the Breit interaction on the Kα₁^h/Kα₂^h line intensity ratio, Kα₁^h and Kα₂^h line energy shifts and Kα₁^h to Kα₂^h line energy splitting is evaluated. Double-K shell hole threshold values for selected elements with 23 ⩽Z⩽ 30, calculated within the same approach, are compared with available experimental results.

The transition probabilities of K&alpha; hypersatellite lines and energy shifts with respect to the corresponding diagram lines are computed using the Dirac&ndash;Fock model for several values of atomic number <I>Z</I> throughout the periodic table. The influence of the Breit interaction on the K&alpha;<SUB>1</SUB><SUP>h</SUP>/K&alpha;<SUB>2</SUB><SUP>h</SUP> line intensity ratio, K&alpha;<SUB>1</SUB><SUP>h</SUP> and K&alpha;<SUB>2</SUB><SUP>h</SUP> line energy shifts and K&alpha;<SUB>1</SUB><SUP>h</SUP> to K&alpha;<SUB>2</SUB><SUP>h</SUP> line energy splitting is evaluated. Double-K shell hole threshold values for selected elements with 23 &les;<I>Z</I>&les; 30, calculated within the same approach, are compared with available experimental results.

Physica Scripta, 90(2015) 054009. doi:10.1088/0031-8949/90/5/054009

Energies and transition probabilities of Kβ hypersatellite lines are computed using the Dirac–Fock model for several values of Z throughout the periodic table. The influence of the Breit interaction on the energy shifts from the corresponding diagram lines and on the Kβh1/Kβh3 intensity ratio is evaluated. The widths of the double-K hole levels are calculated for Al and Sc. The results are compared to experiment and to other theoretical calculations.Al_Sc_Mg_Ti

Energies and transition probabilities of Kβ hypersatellite lines are computed using the Dirac–Fock model for several values of Z throughout the periodic table. The influence of the Breit interaction on the energy shifts from the corresponding diagram lines and on the Kβh1/Kβh3 intensity ratio is evaluated. The widths of the double-K hole levels are calculated for Al and Sc. The results are compared to experiment and to other theoretical calculations.

Energies of two-electron one-photon transitions from initial double K-hole states were computed using the Dirac–Fock model. The transition energies of competing processes, the Ka hypersatellites, were also computed. The results are compared with experiment and to other theoretical calculations.

We present recent results in the field of total binding energy calculations, Land&shchcy; factors, quantum electrodynamics corrections and lifetime that are of interest for ion traps and ion sources. We describe in detail MCDF and RMBPT calculation of ionic binding energies, which are needed for the determination of atomic masses from highly charged ion measurements. We also show new results concerning Land&shchcy; factor in 3-electron ions. Finally we describe how relativistic calculations can help understand the physics of heavy ion production ion sources.

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