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Projeto de investigação
ESTUDO DE VIOLAÇÃO DE PARIDADE EM SISTEMAS ATÓMICOS ALTAMENTE IONIZADOS POR MEIO DE DISPERSÃO DE RAYLEIGH E RAMAN
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Relativistic calculations of screening parameters and atomic radii of neutral atoms
Publication . Guerra, M.; Amaro, P.; Santos, J. P.; Indelicato, P.; LIBPhys-UNL; DF – Departamento de Física; Elsevier Science B.V., Amsterdam.
Calculations of the effective nuclear charge for elements with 1≤Z≤118 have been performed in a Dirac–Fock approach including all relativistic effects as well as contributions from quantum electrodynamics. Maximum charge density for every subshell of every element in the periodic table was also computed in the same framework as well as atomic radii based on the total charge density. Results were compared with the extensively cited works of Clementi et al., obtained in the 1960s with Roothan's self-consistent-field method.
Observation of strong two-electron-one-photon transitions in few-electron ions
Publication . Togawa, M.; Kühn, S.; Shah, Chintan; Amaro, Pedro; Steinbrügge, René; Stierhof, J.; Hell, N.; Rosner, Marieke; Fujii, K.; Bissinger, M.; Ballhausen, R.; Hoesch, M.; Seltmann, J.; Park, Sungnam; Grilo, Filipe; Porter, F. S.; Santos, José Paulo; Chung, M.; Stöhlker, T.; Wilms, J.; Pfeifer, Thomas; Brown, G. V.; Leutenegger, M. A.; Bernitt, Sven; Crespo López-Urrutia, José R.; DF – Departamento de Física; LIBPhys-UNL; American Physical Society
We resonantly excite the K series of O5+ and O6+ up to principal quantum number n=11 with monochromatic x rays, producing K-shell holes, and observe their relaxation by soft-x-ray emission. Some photoabsorption resonances of O5+ reveal strong two-electron-one-photon (TEOP) transitions. We find that for the [(1s2s)15p3/2]3/2;1/2 states, TEOP relaxation is by far stronger than the radiative decay and competes with the usually much faster Auger decay path. This enhanced TEOP decay arises from a strong correlation with the near-degenerate upper states [(1s2p3/2)14s]3/2;1/2 of a Li-like satellite blend of the He-like Kα transition. Even in three-electron systems, TEOP transitions can play a dominant role, and the present results should guide further research on the ubiquitous and abundant many-electron ions where electronic energy degeneracies are far more common and configuration mixing is stronger.
Reference-free measurements of the 1s2s2p 2 P1/2,3/2o →1s22s 2S1/2 and 1s2s2p 4P5/2→1s22s 2S1/2 transition energies and widths in lithiumlike sulfur and argon ions
Publication . Machado, Jorge; Bian, Guojie; Bian, Guojie; Paul, Nancy; Trassinelli, M.; Amaro, Pedro; Guerra, Mauro; Szabo, Csilla I.; Gumberidze, A.; Isac, J. M.; Santos, José Paulo; Desclaux, J. P.; Indelicato, Paul; LIBPhys-UNL; DF – Departamento de Física; American Physical Society
We have measured the widths and energies of the 1s2s2p2P1/2,3/2→1s22s2S1/2 transitions in lithiumlike sulfur and argon, as well as the energies of the forbidden 1s2s2p4P5/2→1s22s2S1/2 M2 transition in both elements. All measurements were performed with a double-flat-crystal spectrometer without the use of any reference line. The transition energy measurements have accuracies ranging from 2.3 to 6.4 ppm depending on the element and line intensity. The widths and the intensity ratios of the 1s2s2p2P1/2,3/2→1s22s2S1/2 lines have also been measured. These are reference-free measurements of transitions in core-excited lithiumlike ions and have an accuracy comparable to the best relative measurements. We have also performed multiconfiguration Dirac-Fock calculations of the widths, energies, and intensity ratios. An extensive comparison between existing experimental results and theory is performed, and Bayesian techniques are employed to extract the energy of the 1s2p24P1/2→1s22p2P1/2 transition in sulfur and identify contaminant transitions.
Measuring the α-particle charge radius with muonic helium-4 ions
Publication . Krauth, Julian J.; Schuhmann, Karsten; Ahmed, Marwan Abdou; Amaro, Fernando D.; Amaro, Pedro; Biraben, François; Chen, Tzu Ling; Covita, Daniel S.; Dax, Andreas J.; Diepold, Marc; Fernandes, Luis M. P.; Franke, Beatrice; Galtier, Sandrine; Gouvea, Andrea L.; Götzfried, Johannes; Graf, Thomas; Hänsch, Theodor W.; Hartmann, Jens; Hildebrandt, Malte; Indelicato, Paul; Julien, Lucile; Kirch, Klaus; Knecht, Andreas; Liu, Yi Wei; Machado, Jorge; Monteiro, Cristina M. B.; Mulhauser, Françoise; Naar, Boris; Nebel, Tobias; Nez, François; dos Santos, Joaquim M. F.; Santos, José Paulo; Szabo, Csilla I.; Taqqu, David; Veloso, João F. C. A.; Vogelsang, Jan; Voss, Andreas; Weichelt, Birgit; Pohl, Randolf; Antognini, Aldo; Kottmann, Franz; DF – Departamento de Física; LIBPhys-UNL; Nature Publishing Group
The energy levels of hydrogen-like atomic systems can be calculated with great precision. Starting from their quantum mechanical solution, they have been refined over the years to include the electron spin, the relativistic and quantum field effects, and tiny energy shifts related to the complex structure of the nucleus. These energy shifts caused by the nuclear structure are vastly magnified in hydrogen-like systems formed by a negative muon and a nucleus, so spectroscopy of these muonic ions can be used to investigate the nuclear structure with high precision. Here we present the measurement of two 2S–2P transitions in the muonic helium-4 ion that yields a precise determination of the root-mean-square charge radius of the α particle of 1.67824(83) femtometres. This determination from atomic spectroscopy is in excellent agreement with the value from electron scattering1, but a factor of 4.8 more precise, providing a benchmark for few-nucleon theories, lattice quantum chromodynamics and electron scattering. This agreement also constrains several beyond-standard-model theories proposed to explain the proton-radius puzzle2–5, in line with recent determinations of the proton charge radius6–9, and establishes spectroscopy of light muonic atoms and ions as a precise tool for studies of nuclear properties.
Laser excitation of the 1s-hyperfine transition in muonic hydrogen
Publication . Amaro, Pedro; Adamczak, A.; Ahmed, M. Abdou; Affolter, L.; Amaro, F. D.; Carvalho, Patricia; Chen, T. -L.; Fernandes, L. M. P.; Ferro, M.; Goeldi, D.; Graf, T.; Guerra, M.; Hänsch, Theodor; Henriques, C. A. O.; Huang, Y. -C.; Indelicato, P.; Kara, O.; Kirch, Klaus; Knecht, Andreas; Kottmann, Franz; Liu, Y. -W.; Machado, João; Marszalek, M.; Mano, R. D. P.; Monteiro, C. M. B.; Nez, F.; Nuber, J.; Ouf, A.; Paul, N.; Pohl, Randolf; Rapisarda, E.; Santos, J. M. F. dos; Santos, J. P.; Silva, P. A. O. C.; Sinkunaite, L.; Shy, J. -T.; Schuhmann, K.; Rajamohanan, S.; Soter, Anna; Sustelo, L.; Taqqu, David; Wang, L. -B.; Wauters, Frederik; Yzombard, P.; Zeyen, M.; Antognini, Aldo; DF – Departamento de Física; LIBPhys-UNL; SciPost
The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen (μp) with 1 ppm accuracy by means of pulsed laser spectroscopy to determine the two-photon-exchange contribution with 2×10-4 relative accuracy. In the proposed experiment, the μp atom undergoes a laser excitation from the singlet hyperfine state to the triplet hyperfine state, then is quenched back to the singlet state by an inelastic collision with a H2 molecule. The resulting increase of kinetic energy after the collisional deexcitation is used as a signature of a successful laser transition between hyperfine states. In this paper, we calculate the combined probability that a μp atom initially in the singlet hyperfine state undergoes a laser excitation to the triplet state followed by a collisional-induced deexcitation back to the singlet state. This combined probability has been computed using the optical Bloch equations including the inelastic and elastic collisions. Omitting the decoherence effects caused by the laser bandwidth and collisions would overestimate the transition probability by more than a factor of two in the experimental conditions. Moreover, we also account for Doppler effects and provide the matrix element, the saturation fluence, the elastic and inelastic collision rates for the singlet and triplet states, and the resonance linewidth. This calculation thus quantifies one of the key unknowns of the HFS experiment, leading to a precise definition of the requirements for the laser system and to an optimization of the hydrogen gas target where μp is formed and the laser spectroscopy will occur.
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SFRH/BPD/92329/2013