Surzhykov, A., A. Volotka, F. Fratini, J. P. Santos, P. Indelicato, G. Plunien, Th Stöhlker, and S. Fritzsche. "
Angular correlations in the two-photon decay of heliumlike heavy ions."
Physical Review A 81 (2010): 042510.
AbstractThe two-photon decay of heavy, helium-like ions is investigated based on second-order perturbation theory and Dirac’s relativistic equation. Special attention has been paid to the angular emission of the two photons (i.e., how the angular correlation function depends on the shell structure of the ions in their initial and final states). Moreover, the effects from the (electric and magnetic) nondipole terms in the expansion of the electron-photon interaction are discussed. Detailed calculations have been carried out for the two-photon decay of the 1s2s1S0, 1s2s3S1, and 1s2p3P0 states of helium-like Xe52+, Au77+, and U90+ ions.
Surzhykov, A., J. P. Santos, P. Amaro, and P. Indelicato. "
Negative-continuum effects on the two-photon decay rates of hydrogenlike ions."
Physical Review A (Atomic, Molecular, and Optical Physics) 80 (2009): 052511.
AbstractTwo-photon decay of hydrogenlike ions is studied within the framework of second-order perturbation theory, based on the relativistic Dirac's equation. Special attention is paid to the effects arising from the summation over the negative-energy (intermediate virtual) states that occur in such a framework. In order to investigate the role of these states, detailed calculations have been carried out for the 2s1/2–>1s1/2 and 2p1/2–>1s1/2 transitions in neutral hydrogen H as well as for hydrogenlike xenon Xe53+ and uranium U91+ ions. We found that for a correct evaluation of the total and energy-differential decay rates, summation over the negative-energy part of Dirac's spectrum should be properly taken into account both for high-Z and low-Z atomic systems.
Santos, J. P., F. Parente, S. Boucard, and P. Indelicato. "
X-ray energies of circular transitions in sigmonic atoms."
Nuclear Instruments and Methods in Physics Research Section B 235 (2005): 206.
AbstractEnergies of the circular (n, ℓ = n − 1) 1 less-than-or-equals, slant n less-than-or-equals, slant 20 levels have been calculated for hydrogenlike sigmonic atoms with 1 less-than-or-equals, slant Z less-than-or-equals, slant 92, using the current world average sigma mass, as well as the electronic shift in Σ− + Ne e− + nucleus systems, where Ne stands for the number of electrons. The electronic influence on sigmonic orbitals has also been investigated through the computation of the hyperfine structure and the anomalous Σ− magnetic moment effects in sigmonic Be 2p states.
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.
AbstractAbstract. 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.
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