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Safari, L., P. Amaro, J. P. Santos, and F. Fratini. "Angular and polarization analysis for two-photon decay of <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>2</mn><mi>s</mi></mrow></math>&." Physical Review A 90 (2014): 014502. AbstractWebsite

The amplitude of two-photon transitions between hyperfine states in hydrogenlike ions is derived based on the relativistic Dirac equation and second-order perturbation theory. We study angular and linear polarization properties of the photon pair emitted in the decay of $2s$ states, where spin-flip and non-spin-flip transitions are highlighted. We pay particular attention to hydrogenlike uranium, since it is an ideal candidate for investigating relativistic and high-multipole effects, such as spin-flip transitions. Two types of emission patterns are identified: (i) non-spin-flip transitions are found to be characterized by an angular distribution of the type $W($\theta${})$\sim${}1+{cos}^{2}$\theta${}$ while the polarizations of the emitted photons are parallel; and (ii) spin-flip transitions have somewhat smaller decay rates and are found to be characterized by an angular distribution of the type $W($\theta${})$\sim${}1$-${}1/3{cos}^{2}$\theta${}$ while the polarizations of the emitted photons are orthogonal, where $$\theta${}$ is the angle between photons directions. Deviations due to nondipole and relativistic contributions are evaluated for both types of transitions. This work is the first step toward exploring the effect of the nucleus over the angular and polarization properties of the photon pairs emitted by two-photon transitions.

Safari, L., P. Amaro, J. P. Santos, and F. Fratini. "Angular and polarization analysis for two-photon decay of <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>2</mn><mi>s</mi></mrow></math>&." Physical Review A 90 (2014): 014502. AbstractWebsite

The amplitude of two-photon transitions between hyperfine states in hydrogenlike ions is derived based on the relativistic Dirac equation and second-order perturbation theory. We study angular and linear polarization properties of the photon pair emitted in the decay of $2s$ states, where spin-flip and non-spin-flip transitions are highlighted. We pay particular attention to hydrogenlike uranium, since it is an ideal candidate for investigating relativistic and high-multipole effects, such as spin-flip transitions. Two types of emission patterns are identified: (i) non-spin-flip transitions are found to be characterized by an angular distribution of the type $W($\theta${})$\sim${}1+{cos}^{2}$\theta${}$ while the polarizations of the emitted photons are parallel; and (ii) spin-flip transitions have somewhat smaller decay rates and are found to be characterized by an angular distribution of the type $W($\theta${})$\sim${}1$-${}1/3{cos}^{2}$\theta${}$ while the polarizations of the emitted photons are orthogonal, where $$\theta${}$ is the angle between photons directions. Deviations due to nondipole and relativistic contributions are evaluated for both types of transitions. This work is the first step toward exploring the effect of the nucleus over the angular and polarization properties of the photon pairs emitted by two-photon transitions.

Safari, L., P. Amaro, S. Fritzsche, J. P. Santos, and F. Fratini. "Relativistic total cross section and angular distribution for Rayleigh scattering by atomic hydrogen." Phys. Rev. A 85 (2012): 043406. AbstractWebsite

We study the total cross section and angular distribution in Rayleigh scattering by hydrogen atom in the ground state, within the framework of Dirac relativistic equation and second-order perturbation theory. The relativistic states used for the calculations are obtained by making use of the finite basis-set method and expressed in terms of B splines and B polynomials. We pay particular attention to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction. It is shown that the angular distribution of scattered photons, while symmetric with respect to the scattering angle θ=90∘ within the electric dipole approximation, becomes asymmetric when higher multipoles are taken into account. The analytical expression of the angular distribution is parametrized in terms of Legendre polynomials. Detailed calculations are performed for photons in the energy range 0.5 to 10 keV. When possible, results are compared with previous calculations.

Safari, L., P. Amaro, S. Fritzsche, J. P. Santos, and F. Fratini. "Relativistic total cross section and angular distribution for Rayleigh scattering by atomic hydrogen." Physical Review A 85 (2012): 043406. AbstractWebsite

We study the total cross section and angular distribution in Rayleigh scattering by hydrogen atom in the ground state, within the framework of Dirac relativistic equation and second-order perturbation theory. The relativistic states used for the calculations are obtained by making use of the finite basis-set method and expressed in terms of B splines and B polynomials. We pay particular attention to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction. It is shown that the angular distribution of scattered photons, while symmetric with respect to the scattering angle θ=90∘ within the electric dipole approximation, becomes asymmetric when higher multipoles are taken into account. The analytical expression of the angular distribution is parametrized in terms of Legendre polynomials. Detailed calculations are performed for photons in the energy range 0.5 to 10 keV. When possible, results are compared with previous calculations.

Safari, L., P. Amaro, S. Fritzsche, J. P. Santos, S. Tashenov, and F. Fratini. "Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen." Phys. Rev. A 86 (2012): 043405. AbstractWebsite

A relativistic analysis of the polarization properties of light elastically scattered by atomic hydrogen is performed, based on the Dirac equation and second-order perturbation theory. The relativistic atomic states used for the calculations are obtained by making use of the finite basis set method and are expressed in terms of B splines and B polynomials. We introduce two experimental scenarios in which the light is circularly and linearly polarized, respectively. For each of these scenarios, the polarization-dependent angular distribution and the degrees of circular and linear polarization of the scattered light are investigated as a function of scattering angle and photon energy. Analytical expressions are derived for the polarization-dependent angular distribution which can be used for scattering by both hydrogenic as well as many-electron systems. Detailed computations are performed for Rayleigh scattering by atomic hydrogen within the incident photon energy range 0.5 to 5 keV. Particular attention is paid to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction.

Safari, L., P. Amaro, S. Fritzsche, J. P. Santos, S. Tashenov, and F. Fratini. "Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen." Physical Review A 86 (2012): 043405. AbstractWebsite

A relativistic analysis of the polarization properties of light elastically scattered by atomic hydrogen is performed, based on the Dirac equation and second-order perturbation theory. The relativistic atomic states used for the calculations are obtained by making use of the finite basis set method and are expressed in terms of B splines and B polynomials. We introduce two experimental scenarios in which the light is circularly and linearly polarized, respectively. For each of these scenarios, the polarization-dependent angular distribution and the degrees of circular and linear polarization of the scattered light are investigated as a function of scattering angle and photon energy. Analytical expressions are derived for the polarization-dependent angular distribution which can be used for scattering by both hydrogenic as well as many-electron systems. Detailed computations are performed for Rayleigh scattering by atomic hydrogen within the incident photon energy range 0.5 to 5 keV. Particular attention is paid to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction.

Safari, L., J. P. Santos, P. Amaro, K. Jankala, and F. Fratini. "Analytical evaluation of atomic form factors: Application to Rayleigh scattering." Journal of Mathematical Physics 56 (2015): 052105-9. AbstractWebsite
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Sampaio, J. M., T. I. Madeira, J. P. Marques, F. Parente, A. M. Costa, P. Indelicato, J. P. Santos, M. - C. Lépy, and Y. Ménesguen. "Approaches for theoretical and experimental determinations of K-shell decay rates and fluorescence yields in Ge." Physical Review A 89 (2014): 012512. AbstractWebsite
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Sampaio, J. M., T. I. Madeira, F. Parente, P. Indelicato, J. P. Santos, and J. P. Marques. "Relativistic calculations of M-shell photoionization and X-ray production cross-sections for Hg at 5.96 keV excitation energy." Radiation Physics and Chemistry 107 (2014): 36. AbstractWebsite

In this work we calculate photoionization and X-ray production cross-sections (XPCS) of M-shell vacancies in Hg at incident photon energy of 5.96 keV (low.

Sampaio, J. M., T. I. Madeira, F. Parente, P. Indelicato, J. P. Santos, and J. P. Marques. "Relativistic calculations of M-shell photoionization and X-ray production cross-sections for Hg at 5.96 keV excitation energy." Radiation Physics and Chemistry 107 (2015): 36. AbstractWebsite

In this work we calculate photoionization and X-ray production cross-sections (XPCS) of M-shell vacancies in Hg at incident photon energy of 5.96 keV (low.

Sampaio, J. M., M. Guerra, F. Parente, T. I. Madeira, P. Indelicato, J. P. Santos, and J. P. Marques. "Calculations of photo-induced X-ray production cross-sections in the energy range 1–150 keV and average fluorescence yields for Zn, Cd and Hg." Atomic Data and Nuclear Data Tables 111-112 (2016): 67-86. AbstractWebsite

Atomic Data and Nuclear Data Tables, 111-112 (2016) 67-86. doi:10.1016/j.adt.2016.02.001

Sampaio, J. M., M. Guerra, T. I. Madeira, F. Parente, P. Indelicato, J. P. Santos, and J. P. Marques. "Relativistic calculations of atomic parameters in Ununoctium." Journal of Physics: Conference Series 635 (2015): 092095-2. AbstractWebsite
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Sampaio, J. M., T. I. Madeira, J. P. Marques, F. Parente, A. M. Costa, P. Indelicato, J. P. Santos, M. - C. Lépy, and Y. Ménesguen. "Approaches for theoretical and experimental determinations of K-shell decay rates and fluorescence yields in Ge." Physical Review A 89 (2014): 012512. AbstractWebsite
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Sampaio, J. M., T. I. Madeira, M. Guerra, F. Parente, J. P. Santos, P. Indelicato, and J. P. Marques. "Dirac-Fock calculations of K−, L−, and M-shell fluorescence and Coster-Kronig yields for Ne, Ar, Kr, Xe, Rn, and Uuo." Physical Review A 91 (2015): 052507. AbstractWebsite
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Sampaio, J. M., T. I. Madeira, M. Guerra, F. Parente, P. Indelicato, J. P. Santos, and J. P. Marques. "Relativistic calculations of K-, L- and M-shell X-ray production cross-sections by electron impact for Ne, Ar, Kr, Xe, Rn and Uuo." Journal of Quantitative Spectroscopy and Radiative Transfer 182 (2016): 87-93. AbstractWebsite

Journal of Quantitative Spectroscopy and Radiative Transfer, 182 + (2016) 87-93. doi:10.1016/j.jqsrt.2016.05.012

Santos, J. P., J. P. Marques, M. C. Martins, P. Indelicato, E. P. Benis, T. J. M. Zouros, and F. Parente. "Energy levels, transition rates and lifetimes for Li-like ions with Z≤ 10 in the 1 s2 s( 3S)3ℓ states." Journal of Physics: Conference Series 635 (2015): 052060-2. AbstractWebsite
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Santos, J. P., C. Madruga, F. Parente, and P. Indelicato. "Relativistic transition probabilities for F-like ions with 10⩽Z⩽49." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 235 (2005): 171-173. AbstractWebsite

In the present work we have calculated several relativistic transition probabilities for the F-like ions with 10 less-than-or-equals, slant Z less-than-or-equals, slant 49, in the framework of the Multi-Configuration Dirac–Fock method, for applications on laserphysics and astrophysics. The lines considered correspond to transitions between levels of 2p43s, 2p43p and 2p43d configurations. The spectral fine structure is taken into consideration and the results for individual lines are given.

Santos, J. P., A. M. Costa, M. C. Martins, P. Indelicato, and F. Parente. "K X-Ray Energies and Transition Probabilities for He-, Li- and Be-like Praseodymium ions." Journal of Physics: Conference Series 388 (2012): 152018. AbstractWebsite

Theoretical transition energies and probabilities for He-, Li and Be-like Praseodymium ions are calcu- lated in the framework of the multi-configuration Dirac-Fock method (MCDF), including QED corrections. These calculated values are compared to recent experimental data obtained in the Livermore SuperEBIT electron beam ion trap facility [1].

Santos, J. P., J. Machado, Guojie Bian, Nancy Paul, M. Trassinelli, P. Amaro, M. Guerra, C. I. Szabo, A. Gumberidze, J. M. Isac, J. P. Santos, J. P. Desclaux, and P. Indelicato. "Reference-free measurements of the 1s2s2p2P1/2,3/2o\rightarrow1s22s2S1/2 and 1s2s2p4P5/2\rightarrow1s22s2S1/2 transition energies and widths in lithiumlike sulfur and argon ions." Physical Review A (2020). AbstractWebsite
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Santos, J. P., and F. Parente. "Ionisation of phosphorus, arsenic, antimony, and bismuth by electron impact." The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics 47 (2008): 339-350. AbstractWebsite
Abstract.  Total ionization cross sections of neutral phosphorus, arsenic, antimony, and bismuth atoms by electron impact are reported and compared to the only available experimental results by Freund et al. [Phys. Rev. A 41, 3575 (1990)]. These calculations take into account the possibilities that some target atoms used in the experiments were in metastable states close to the ground state, the excitation-autoionization of nsnp4 excited states may be substantial, and the ions produced in experiments may be in excited, low-lying metastable states. The cross sections for direct ionization calculations are based on the BEB model by Kim and Rudd [Phys. Rev. A 50, 3954 (1994)]. Plane-wave Born cross sections scaled by the method developed by Kim [Phys. Rev. A 64, 3954 032713 (2001)] are used to determine the contributions from excitation-autoionization. The combination of the BEB model and the scaled Born cross sections is in agreement with the experimental data by Freund et al. These theoretical data are useful to experimentalists and can be used to complete data tables needed for plasma or astrophysical studies.
Santos, Jose Paulo, Maria Conceição Martins, Ana Maria Costa, José Pires Marques, Paul Indelicato, and Fernando Parente. "Theoretical determination of K X-ray transition energy and probability values for highly charged ions of lanthanum and cerium." The European Physical Journal D 68 (2014): 244. AbstractWebsite
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Santos, J. P., M. Guerra, and F. Parente. "New expression for the K-shell ionization." Journal of Physics: Conference Series 388 (2012): 042047. AbstractWebsite

A new expression for the total K-shell ionization cross section by electron impact based on the rela- tivistic extension of the binary encounter Bethe (RBEB) model, valid from ionization threshold up to relativistic energies, is proposed. The new MRBEB expression is used to calculate the K-shell ionization cross sections by electron impact for the selenium atom. Comparison with all, to our knowledge, available experimental data shows good agreement.

Santos, J. P., A. M. Costa, M. C. Martins, F. Parente, and P. Indelicato. "Modeling praseodymium K X-ray lines in an electron beam ion trap." Eur. Phys. J. D 66 (2012): 202. AbstractWebsite

We study the most important processes for the creation of excited states in He-like through C- like praseodymium ions from the ions ground configurations, leading to the emission of K X-ray lines. Theoretical values for inner-shell excitation and ionization cross sections, transition probabilities and energies for the deexcitation processes, are calculated in the framework of the multi-configuration Dirac- Fock method, including QED corrections. Using these calculated values, a theoretical Kα X-ray spectrum is obtained, which is compared to recent experimental data obtained in the Livermore Super-EBIT electron beam ion trap facility.

Santos, J. P., P. Patté, F. Parente, and P. Indelicato. "Spontaneous relativistic two-photon decay rate mathematical expression in heliumlike systems." The European Physical Journal D 13 (2001): 27-31. AbstractWebsite

We derive a theoretical expression for the two-photon emission rate of two-electron systems, in a form suitable for easy implementation in numerical calculations. Racah algebra techniques were used to extended previous work on two-photon emission in hydrogen-like systems to more complex ones. The obtained expression is, as far as we are aware, the first general expression that gives the spontaneous two-photon decay rates of helium-like systems for any combination of multipoles.