Nach der Anmeldung stehen Ihnen an einigen Stellen der Seite erweiterte Informationen zur Verfügung.

Publikationen von
Zhongwen Wu

Alle Publikationen des HI Jena

2022

Z. Yang, Z. He, G. Xiong, K. Yao, Y. Yang, B. Wei, Y. Zou, Z. Wu, Z. Tian, Y. Ma, C. Wu, X. Gao, and Z. Hu
Apparent change of the 3C/3D line intensity ratio in neonlike ions
Optics Express 30, 25326 (2022)

Abstract: The resonance 3C ([(2p(5))(1/2)3d(3/2)](J=1)->[2p(6)](J=0)) to intercombination 3D ([(2p(5))(3/2) 3d(5/2)](J=1)->[2p(6)](J=0)) line intensity ratio of neonlike ions has been studied. The measured line intensity ratio for neonlike Xe44+ ions shows an apparent change, which is reproduced by the calculations using the relativistic configuration interaction plus many-body perturbation theory. It is clearly elucidated that the change in the 3C/3D line intensity ratio is caused by strong configuration mixing between the upper levels of the 3D and 3F ([(2p(5))(1/2)3s](J=1)->[2p(6)](J=0)) lines. The present measurement allows us to discuss the 3C/3D line intensity ratio for the highest-Z ions hitherto, which suggests that the experiment-theory discrepancy in the 3C/3D line intensity ratio of neonlike ions diminishes with increasing atomic number Z and further trends to vanish at higher-Z ions. Furthermore, the present study provides benefits to better understand configuration mixing effect in the radiative opacity of hot plasmas. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

2021

Z. W. Wu, Z. Q. Tian, J. Jiang, C. Z. Dong, and S. Fritzsche
Hyperfine-induced effects on the K {α_1} angular distribution following electron-impact excitation of heliumlike spin- 1/2 Tl⁷⁹⁺ ions
Physical Review A 104, 062814 (2021)
Kein Abstract vorhandenLinkBibTeX

2020

Z. W. Wu, Z. Q. Tian, J. Jiang, C. Z. Dong, and S. Fritzsche
Hyperfine-induced effects on angular emission of the magnetic-quadrupole line 1s2p(3/2) P-3(2) -> 1s(2) S-1(0) following electron-impact excitation of Tl79+ ions
Physical Review A 102, 042813 (2020)
Kein Abstract vorhandenLinkBibTeX

2017

Z. Wu, A. Volotka, C. Dong, and S. Fritzsche
Dielectronic recombination of highly charged ions with spin-polarized electrons
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 408, 130 (2017)

Abstract: Angular distribution and linear polarization of photon emission following dielectronic recombination of initially lithium-like ions with spin-polarized electrons are studied. In particular, a general expression is derived for the alignment parameter of the doubly excited states produced via the resonant capture of spin-polarized electrons. By means of the alignment parameter, moreover, the angular distribution and linear polarization of the subsequently emitted photons are further obtained. Detailed computations are performed for the 1s2 2s J0=1/2+εe-→1s2s2 2p1/2 J=1→1s2 2s2 Jf=0+γ resonant electron capture and subsequent radiative decay of iodine ions. It is found that the spin polarization of the incident electrons changes only the q=±1 components of the alignment parameter A2q. As a consequence, the electron spin polarization contributes weakly to the γ photon angular distribution and linear polarization that are dominantly determined by the A20 parameter.

Z. W. Wu, A. V. Volotka, A. Surzhykov, and S. Fritzsche
Angle-resolved x-ray spectroscopic scheme to determine overlapping hyperfine splittings in highly charged heliumlike ions
Physical Review A 96, 012503 (2017)

Abstract: An angle-resolved x-ray spectroscopic scheme is presented for determining the hyperfine splitting of highly charged ions. For heliumlike ions, in particular, we propose to measure either the angular distribution or polarization of the 1s2p ^3P_{1,F} -> 1s^2 ^1S_{0,F_f} emission following the stimulated decay of the initial 1s 2s ^1S_{0,F_i} level. It is found that both the angular and polarization characteristics of the emitted x-ray photons strongly depend on the (relative) splitting of the partially overlapping hyperfine 1s 2p ^3P_{1,F} resonances and may thus help resolve their hyperfine structure. The proposed scheme is feasible with present-day photon detectors and allows a measurement of the hyperfine splitting of heliumlike ions with a relative accuracy of about 10^{-4}.

M. Herdrich, G. Weber, A. Gumberidze, Z. Wu, and Th. Stöhlker
Fast calculator for X-ray emission due to Radiative Recombination and Radiative Electron Capture in relativistic heavy-ion atom collisions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 408, 294 (2017)

Abstract: Abstract In experiments with highly charged, fast heavy ions the Radiative Recombination (RR) and Radiative Electron Capture (REC) processes have significant cross sections in an energy range of up to a few GeV / u . They are some of the most important charge changing processes in collisions of heavy ions with atoms and electrons, leading to the emission of a photon along with the formation of the ground and excited atomic states. Hence, for the understanding and planning of experiments, in particular for X-ray spectroscopy studies, at accelerator ring facilities, such as FAIR, it is crucial to have a good knowledge of these cross sections and the associated radiation characteristics. In the frame of this work a fast calculator, named RECAL, for the RR and REC process is presented and its capabilities are demonstrated with the analysis of a recently conducted experiment at the Experimental Storage Ring (ESR) at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany. A method is presented to determine unknown X-ray emission cross sections via normalization of the recorded spectra to REC cross sections calculated by RECAL.

Z. Wu
Angular Correlation and Polarization of X-rays Emitted from Highly Charged Ions
Dissertation
Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät (2017)

Abstract: In collisions of highly charged ions with electrons or light, ions are usually excited to one of their excited states and, then, may stabilize radiatively under the emission of fluorescence photons. Detailed studies on the emitted photons can help understand the structure and collision dynamics of the ions. When compared with total decay rates, angle-resolved properties such as angular correlation and polarization of emitted photons were found more sensitive to various interactions and effects and, actually, have helped provide new insights into electron-electron and electron-photon interactions in the presence of strong Coulomb fields. For this reason, such kind of studies has attracted considerable interest in both theory and experiment.

Until now, however, almost all studies of x-ray angular correlation and polarization were performed for photons emitted from well-isolated energy levels. Little attention was paid so far to photon emissions from two or more overlapping resonances of ions. In this thesis, we develop a novel theoretical formalism to study radiative decay from the overlapping resonances. Special attention is paid to the question of how the splitting of these resonances affect the angular and polarization properties of emitted photons. Calculations are performed based on the density matrix theory and multi-configuration Dirac-Fock method. The obtained results from several case studies show that the photon angular distribution and polarization are strongly affected by the splitting and sequence of the overlapping resonances. Therefore, we suggest that accurate angle-resolved measurements of photon emissions may serve as a tool to identify level splitting and sequence of overlapping resonances in excited highly charged ions, even if they cannot be spectroscopically resolved. When applied to the isotopes with non-zero nuclear spin, moreover, such a tool can also be used to determine hyperfine splitting and associated nuclear parameters.

2016

Z. W. Wu, A. V. Volotka, A. Surzhykov, C. Z. Dong, and S. Fritzsche
Level sequence and splitting identification of closely spaced energy levels by angle-resolved analysis of fluorescence light
Physical Review A 93, 063413 (2016)

Abstract: The angular distribution and linear polarization of the fluorescence light following the resonant photoexcitation is investigated within the framework of density matrix and second-order perturbation theory. Emphasis has been placed on “signatures” for determining the level sequence and splitting of intermediate (partially) overlapping resonances, if analyzed as a function of photon energy of incident light. Detailed computations within the multiconfiguration Dirac–Fock method have been performed, especially for the 1s^2 2s^2 2p^6 3s,Ji=1/2+γ1 → (1s^2 2s 2p^6 3s)_1 3p3/2,J=1/2,3/2 → 1s^2 2s^2 2p^6 3s,Jf=1/2+γ2 photoexcitation and subsequent fluorescence emission of atomic sodium. A remarkably strong dependence of the angular distribution and linear polarization of the γ2 fluorescence emission is found upon the level sequence and splitting of the intermediate (1s^2 2s 2p^6 3s)_1 3p3/2,J=1/2,3/2 overlapping resonances owing to their finite lifetime (linewidth). We therefore suggest that accurate measurements of the angular distribution and linear polarization might help identify the sequence and small splittings of closely spaced energy levels, even if they cannot be spectroscopically resolved.

T. Kämpfer, I. Uschmann, Z. W. Wu, A. Surzhykov, S. Fritzsche, E. Förster, and G. G. Paulus
Linear polarization of the characteristic x-ray lines following inner-shell photoionization of tungsten
Physical Review A 93, 033409 (2016)

Abstract: The linear polarization of the characteristic lines Lα1 (3d5/2→2p3/2) and Lα2 (3d3/2→2p3/2), following inner-shell photoionization of neutral tungsten, is analyzed both experimentally and theoretically. In the experiment, a tungsten target is photoionized by the primary emission of an x-ray tube with incident photon energies in the range of 10.2–30 keV. The σ and π components of the emitted fluorescence are measured by using a spectropolarimeter, based on x-ray diffraction at Bragg angles close to 45∘. The degree of linear polarization of the Lα1 and Lα2 lines is determined to be +(1.6±0.5)% and −(7±2)%, respectively. In addition, this degree of polarization is calculated within the framework of the density-matrix theory as a function of the incident photon energy. These calculations are in good agreement with the experimental results and show only a weak dependence of the degree of polarization on the energy of the incident photoionizing photon.

2015

Z. W. Wu, S. Fritzsche, and A. Surzhykov
Nuclear magnetic dipole moment effect on the angular distribution of the K-alpha lines
Physica Scripta 166, 014029 (2015)

Abstract: We present a theoretical analysis of the fine-structure transitions for helium-like heavy ions with non-zero nuclear spin. The angular distribution of these transitions is studied for its sensitivity with regard to the nuclear magnetic dipole moment. Detailed calculations, performed for the helium-like Sn48+, Xe52+ and Tl79+ ions with nuclear spin I=1/2, indicate that the emission pattern of the fine-structure resolved photons is significantly affected by the nuclear magnetic dipole moment and that this effect can be addressed experimentally at present storage ring facilities.

Z. W. Wu, A. Surzhykov, N. M. Kabachnik, C. Z. Dong, and S. Fritzsche
Linear polarization of x-rays emitted in the decay of highly-charged ions via overlapping resonances
Journal of Physics: Conference Series 635, 012020 (2015)

Abstract: The linear polarization of x-rays, emitted from highly-charged ions, has been studied within the framework of the density matrix theory and the multiconfiguration Dirac-Fock method. Emphasis was placed especially on two-photon cascades that proceed via intermediate overlapping resonances. For such two-step cascades, we here explore how the level-splitting of the resonances affects the linear polarization of the x-rays, and whether modifications in the degree of polarization may help determine small level-splittings in multiply- and highly-charged ions, if carefully analyzed along isoelectronic sequences. Detailed calculations are carried out for the 1s 2p2 J_i = 3/2 → 1s 2s 2p J = 1/2, 3/2 + γ1 → 1s2 2s J_f = 1/2 + γ1 + γ2 radiative cascade of lithium-like W^71+ ions. For this cascade, a quite remarkable increase of the (degree of) linear polarization is found for the second-step γ2 photons, if the level-splitting becomes smaller than Δω ≲ 0.2 a.u. ≈ 5.4 eV. Accurate polarization measurements of x-rays may therefore be also utilized in the future to ascertain small level-splittings in multiply- and highly-charged ions.

Z. W. Wu, A. Surzhykov, and S. Fritzsche
Reply to “Comment on `Hyperfine-induced modifications to the angular distribution of the Kα₁ x-ray emission' ”
Physical Review A 91, 056502 (2015)

Abstract: In a recent work, the Kα₁ (1s 2p₃/₂ ¹,³P₁,₂ → 1s² ¹S₀) x-ray emission following the radiative electron capture into initially hydrogen-like ions has been explored for ions with nonzero nuclear spin (I ≠ 0). A rather strong influence upon the angular distribution of the (hyperfine- and fine-structure averaged) Kα₁ radiation was found, especially for isotopes with nuclear spin I=1/2, while this effect are less important for isotopes with nuclear spin I>1/2. Two comments were made by Inal and Benmouna about this work with regard to (i) the incoherent summation of the individual hyperfine components of the 1s2p3/2 1P1→1s21S0 transition and (ii) the treatment of the hyperfine-induced E1-M2 multipole mixing in the 1s 2p3/2 ³P₂ → 1s², ¹S₀ fine-structure component. While we agree with the first comment and here provide updated anisotropy parameters, the hyperfine-induced modification of the Kα₁ emission remains valid and may help in the future to determine the nuclear parameters of radioactive isotopes. We also explain that the hyperfine-induced E1-M2 mixing has already been fully taken into account in our previous work.

2014

Z. W. Wu, N. M. Kabachnik, A. Surzhykov, C. Z. Dong, and S. Fritzsche
Determination of small level splittings in highly charged ions via angle-resolved measurements of characteristic x rays
Physical Review A 90, 052515 (2014)

Abstract: The angular distribution and the photon-photon angular correlation have been investigated for the x-ray emission from two-step radiative cascades that proceed via overlapping intermediate resonances. In particular, density matrix theory is applied in order to explore how the splitting of these intermediate levels affects the subsequent x-ray emission and whether measurements of photon angular distributions may help reveal level crossings in highly charged ions, if analyzed along isoelectronic sequences. Detailed computations within the multiconfiguration Dirac-Fock method were performed especially for the two-step 1s2p2J_i=1/2,3/2→1s2s2pJ=1/2,3/2+γ1→1s22sJ_f=1/2+γ1+γ2 cascade of lithiumlike ions, for which a level crossing of the two 1s2s2pJ=1/2,3/2 intermediate resonances occurs in the range 74≤Z≤79. For this cascade, a remarkably strong depolarization effect, associated with the finite lifetime of these intermediate levels, is found for the angular distribution and the photon-photon correlation function for all level splittings Δω≲0.2a.u.≈5.4 eV. We therefore suggest that accurate angle-resolved measurements of the x-ray emission may serve also as a tool for determining small level splittings in excited highly charged ions.