Showing papers by "Igor Bray published in 2009"
TL;DR: In this paper, a surface-integral approach utilizing analytically known asymptotic forms of the two-body and three-body scattering wavefunctions is presented.
58 citations
TL;DR: The photon energy dependence of the K-shell double photoionization (DPI) of Mg, Al, and Si is reported and universal scaling of the DPI cross sections with the effective nuclear charge for neutral atoms is revealed.
Abstract: We report on the photon energy dependence of the K-shell double photoionization (DPI) of Mg, Al, and Si. The DPI cross sections were derived from high-resolution measurements of x-ray spectra following the radiative decay of the K-shell double vacancy states. Our data evince the relative importance of the finalstate electron-electron interaction to the DPI. By comparing the double-to-single K-shell photoionization cross-section ratios for neutral atoms with convergent close-coupling calculations for He-like ions, the effect of outer shell electrons on the K-shell DPI process is assessed. Universal scaling of the DPI cross sections with the effective nuclear charge for neutral atoms is revealed.
51 citations
TL;DR: In this paper, the authors report on the extension of the recently formulated relativistic convergent close-coupling (RCCC) method to include the Breit and M\o{}ller interactions.
Abstract: We report on the extension of the recently formulated relativistic convergent close-coupling (RCCC) method to include the Breit and M\o{}ller interactions. The inclusion of these relativistic effects ensures that the RCCC method is now capable of calculating electron scattering excitation and ionization cross sections for highly charged ions. We have calculated the polarization of the Lyman-${\ensuremath{\alpha}}_{1}$ x-ray line emitted by hydrogenlike ${\text{Ti}}^{21+}$, ${\text{Ar}}^{17+}$, and ${\text{Fe}}^{25+}$ ions excited by electron impact. We find that account of Breit relativistic corrections is important to resolve the discrepancy between experiment and theoretical calculations. For the much heavier hydrogenlike ${\text{U}}^{91+}$ ion where the M\o{}ller interaction becomes important we present the estimate of the polarization of the Lyman-${\ensuremath{\alpha}}_{1}$ x-ray line and performed a calculation of the total ionization cross section.
45 citations
TL;DR: In this article, the grand total and positronium-formation cross sections for positrons scattered by helium within the impact energy range from 10 to 60 eV were measured using a high-resolution trap-based pulsed positron beam.
Abstract: Measurements of the grand total and positronium-formation cross sections for positrons scattered by helium within the impact energy range from 10 to 60 eV are presented. All measurements presented here use a high-resolution $(\ensuremath{\sim}70\text{ }\text{meV})$ trap-based pulsed positron beam. Scattering is studied using a high-magnetic field, and absolute measurements of the scattering cross sections are obtained without the need for normalization to other cross sections. We also present single center, convergent close coupling calculations of the total cross section. A detailed study of the cross section to investigate the possibility of scattering resonances and channel coupling has been made. Comparisons with previous cross-section measurements and theoretical calculations are also included.
33 citations
TL;DR: In this article, a combined experimental and theoretical investigation of the fully differential cross section for electron-impact ionization of neon and xenon was performed under coplanar asymmetric kinematics, at intermediate incident electron energies, and for a range of scattered electron detection angles.
Abstract: We present a combined experimental and theoretical investigation of the fully differential cross section for electron-impact ionization of neon and xenon. The experiments were performed under coplanar asymmetric kinematics, at intermediate incident electron energies, and for a range of scattered electron detection angles. The experimental results are compared with three calculations: a convergent close-coupling calculation, a distorted-wave Born approximation (DWBA) calculation with inclusion of the Gamow factor, and a hybrid $\mathrm{DWBA}+R$-matrix calculation. The comparison between the experimental and theoretical results highlights the importance of the description of postcollision interaction, and the results exhibit interesting orbital-dependent differences.
23 citations
TL;DR: In this article, the authors examined the time-dependent close-coupling (TDCC) approach to electron-impact single ionization of helium and study the convergence properties of their method.
Abstract: We examine the time-dependent close-coupling (TDCC) approach to electron-impact single ionization of helium and study the convergence properties of our method. As an example, we compare our calculations to recent measurements of the triple differential cross sections from He after 102 eV electron impact, made for asymmetric electron energies and a variety of electron geometries. We find that our calculations compare well to the measurements and to convergent close-coupling calculations.
23 citations
TL;DR: In this paper, the energy range from threshold to 1000 eV using state-of-the-art experimental and theoretical approaches has been studied for direct ionization of ground-state Li+(1s21S0) and metastable Li(1s2s 3S1) ions by electron impact.
Abstract: Direct ionization of ground-state Li+(1s21S0) and metastable Li+(1s2s 3S1) ions by electron impact has been studied in the energy range from threshold to 1000 eV using state-of-the-art experimental and theoretical approaches. Absolute cross sections obtained by crossing a beam of Li+(1s2) ions with a beam of electrons and results of convergent close coupling (CCC) calculations agree within experimental error bars of approximately 10%. Mixed beams of Li+(1s2) and Li+(1s2s 3S) ions were also prepared and apparent cross sections were measured. Good agreement with CCC theory is obtained assuming suitable fractions of metastable ions in the parent beam.
22 citations
TL;DR: In this article, a detailed formulation of the relativistic convergent close-coupling (RCCC) method based on the solution of the Dirac equation describing electron scattering from quasi-one-electron atoms is presented.
Abstract: We present a detailed formulation of the relativistic convergent close-coupling (RCCC) method which is based on the solution of the Dirac equation describing electron scattering from quasi-one-electron atoms. A square-integrable Dirac $L$ spinor basis has been used to obtain a set of target states representing both the bound and continuum spectra of the target. A set of momentum-space coupled Lippmann-Schwinger equations for the $T$ matrix is then formulated and solved. We use spin asymmetries, particularly those that are identically zero in a nonrelativistic formulation, to check the accuracy of the RCCC method and find good agreement with experiment on a broad energy range.
20 citations
TL;DR: In this paper, the convergent close-coupling (CCC) formalism was applied to single-photon two-electron ionization of the lithium atom in its ground state.
Abstract: We apply the convergent close-coupling (CCC) formalism to single-photon two-electron ionization of the lithium atom in its ground state. We treat this reaction as single-electron photon absorption followed by inelastic scattering of the photoelectron on a heliumlike ${\text{Li}}^{+}$ ion. The latter scattering process can be described accurately within the CCC formalism. We obtain integrated cross sections of single photoionization leading to the ground and various excited states of the ${\text{Li}}^{+}$ ion as well as double photoionization extending continuously from the threshold to the asymptotic limit of infinite photon energy. Comparison with available experimental and theoretical data validates the CCC model.
17 citations
TL;DR: In this article, the contribution of off-shell effects is fully taken into account and shown to be significant, at high energies as much as a half of the total electron transfer cross section comes from the offshell effects.
Abstract: Proton and antiproton collisions with atomic hydrogen are investigated using the atomic-orbital close-coupling method. After a suitable transformation, the method leads to coupled three-dimensional momentum-space integral equations for the half-off-shell scattering amplitudes. These equations are further reduced to two-dimensional ones using the symmetry properties of the transition amplitudes. The resulting equations are solved directly without partial-wave expansion. The total and differential cross sections for electron transfer in proton collisions with the ground state of atomic hydrogen are calculated. The contribution of off-shell effects is fully taken into account and shown to be significant. We find that the off-shell effects can both increase or decrease the cross sections substantially depending on energy. At high energies as much as a half of the total electron transfer cross section comes from the off-shell effects. This contradicts classical and iterative estimates which predict the off-shell effects to be small. The significance of the off-shell effects in elastic scattering of protons falls with increasing energy to the estimated levels. The calculated cross section results agree well with experiment over a wide energy range. The total and differential cross sections for elastic scattering of antiprotons are also calculated and compared with the corresponding results for protons. Above 200 keV there is practically no difference between the cross sections for scattering of protons or antiprotons. The off-shell effects for elastic scattering of antiprotons are generally smaller than those for scattering of protons.
15 citations
TL;DR: In this article, experimental and theoretical studies of the electron-impact excitation of the zinc atoms are reported, highlighting the significance of both channel coupling to the continuum and the inner $3d$-shell electrons.
Abstract: Experimental and theoretical studies of the electron-impact excitation of the $(4s4p)\text{ }{^{1,3}P}_{1}$, $(4s5s)\text{ }{^{3}S}_{1}$, and $(4s4d)\text{ }^{1,3}D$ states of zinc atoms are reported. Relative emission cross sections were measured from the excitation thresholds to 50 eV incident energy. Theoretical angle-integrated and emission cross sections were obtained using the convergent close-coupling and $B$-spline $R$-matrix methods. The measured data were normalized to theory and are discussed in terms of electron spin and correlation effects. The studies highlight the significance of both channel coupling to the continuum and the inner $3d$-shell electrons.
TL;DR: In this article, the authors presented new normalized experimental differential cross sections for electron impact excitation of the n = 2 states in helium, where the incident electrons have energies in the range 23.5 −35 eV, while the scattered electrons are detected over the angular range 10 −130°.
Abstract: In this paper, we present new normalized experimental differential cross sections for electron impact excitation of the n = 2 states in helium. The incident electrons have energies in the range 23.5–35 eV, while the scattered electrons are detected over the angular range 10–130°. Corresponding theoretical results from our convergent close-coupling approach are also presented and in general are in very good accord with our measured data. Where possible, a comparison of the present experimental and theoretical results with those from previous measurements is also made. The case for the n = 2 levels in helium constituting a benchmark cross section data set is examined.
TL;DR: In this article, convergent close-coupling calculations of double photoionization DPI of the Kshell of alkaline-earth metal atoms Be, Mg, and Ca from the threshold to the nonrelativistic limit of infinite photon energy were performed.
Abstract: We perform convergent close-coupling calculations of double photoionization DPI of the K-shell of alkaline-earth metal atoms Be, Mg, and Ca from the threshold to the nonrelativistic limit of infinite photon energy. Theoretical double-to-single photoionization cross-section ratios for Mg and Ca are compared with experimental values derived from high-resolution x-ray spectra following the radiative decay of the K-shell double vacancy. We investigate the role of many-electron correlations in the ground and doubly-ionized final states played in the DPI process. Universal scaling of DPI cross section with an effective nuclear charge is examined in neutral atoms in comparison with corresponding heliumlike ions.
TL;DR: In this article, the electron-impact total ionization cross sections for B3+ have been determined both experimentally and theoretically using the convergent close-coupling (CCC) method.
Abstract: The electron-impact total ionization cross sections for B3+ have been determined both experimentally and theoretically. The experiment was carried out using a parent beam with B3+ ions in a mix of ground 11S and metastable 23S states. The convergent close-coupling (CCC) method has been used to calculate the corresponding cross sections and, by matching with experiment, the ratio of the initial target states in the beam has been determined. Good agreement with experiment across a broad energy range is obtained, particularly when indirect ionization processes are included in the calculations.
01 Nov 2009
TL;DR: In this article, the convergent close-coupling method, which includes positronium formation, was used to calculate positron-helium scattering. But it was shown that in the Ore-gap region only two-center expansions can give convergent results.
Abstract: The convergent close-coupling method, which includes positronium formation, is used to calculate positron-helium scattering. Low-energy elastic cross sections and Ore-gap total cross sections are calculated using equal number of pseudo-states from the atomic and positronium centers. We show that in the Ore-gap region only two-center expansions can give convergent results.
01 Nov 2009
TL;DR: In this article, the energy range from threshold to 1000 eV using state-of-the-art experimental and theoretical approaches has been studied for direct ionization of ground-state Li(1s2 1S0) and metastable Li( 1s2s 3S1) ions by electron impact.
Abstract: Direct ionization of ground-state Li+(1s2 1S0) and metastable Li+(1s2s 3S1) ions by electron impact has been studied in the energy range from threshold to 1000 eV using state-of-the-art experimental and theoretical approaches. Absolute experimental cross sections are in good agreement with the results of convergent close coupling (CCC) calculations.
TL;DR: In this paper, the photon energy dependence of double 1s photoionization of light atoms and compare the cross sections for hollow atom and He-like ion production were investigated using the Fribourg high-resolution x-ray spectrometer installed at the ID21 and ID26 beam lines at the ESRF.
Abstract: We report on the investigation of the photon energy dependence of double 1s photoionization of light atoms and compare the cross sections for hollow atom and He-like ion production. Measurements of the Kα hypersatellite x-ray spectra of Mg, Al, and Si were carried out using the Fribourg high-resolution x-ray spectrometer installed at the ID21 and ID26 beam lines at the ESRF. The double-to-single photoionization cross section ratios were derived as a function of the incident photon beam energy and compared to convergent close-coupling (CCC) calculations for He-like ions. The dynamical electron-electron scattering contribution to the DPI cross-sections was found to be more important for neutral atoms than for the He isoelectronic series.
01 Nov 2009
TL;DR: In this paper, the relativistic convergent close-coupling method was used to perform calculations of electron scattering from cesium and gallium atoms, and differential, integrated and ionization cross sections and spin asymmetries were calculated from 1 to 500 eV.
Abstract: We have used relativistic Convergent Close-Coupling method to perform calculations of electron scattering from cesium and gallium atoms. Differential, integrated and ionization cross sections and spin asymmetries have been calculated from 1 to 500 eV and compared with available experimental data and results of other calculations.
01 Nov 2009
TL;DR: In this paper, a surface-integral formulation of scattering theory is presented, which is valid for both short-range and Coulombic longe-range interactions, and general definitions for the potential scattering amplitude are given.
Abstract: Basic features of a new surface-integral formulation of scattering theory are outlined. This formulation is valid for both short-range and Coulombic longe-range interactions. New general definitions for the potential scattering amplitude are given. For the Coulombic potentials the generalized amplitude gives the physical on-shell amplitude without recourse to a renormalization procedure. New post and prior forms for the amplitudes of breakup, direct and rearrangement scattering in a Coulomb three-body system are presented.
01 Sep 2009
TL;DR: In this paper, the convergent close-coupling method was applied to electron impact ionization of atoms and ions, and the results showed excellent agreement with experiment, but some long-standing discrepancies still remain.
Abstract: We report on the recent applications of the convergent close-coupling method to electron impact ionisation of atoms and ions. Total and fully differential cross sections are considered. Some excellent agreement with experiment is identified, but some long-standing discrepancies still remain.
01 Sep 2009
TL;DR: In this article, the authors used relativistic convergent close-coupling method to obtain cross sections for elastic scattering and excitations of the 4P3/2 ground state of gallium atoms for incident electron energies ranging from 0.1 to 500 eV.
Abstract: Theoretical study of electron scattering from the 4P1/2 ground state of gallium atoms is reported. We have used relativistic convergent close-coupling method to obtain cross sections for elastic scattering and excitations of the 4P3/2, 5S1/2, 5P1/2,3/2 and 4D3/2,5,2 states for incident electron energies ranging from 0.1 to 500 eV. Comparison of our results with recent theoretical estimates that have been used in plasma modeling shows significant discrepancies for all considered transitions.
01 Nov 2009
TL;DR: In this article, the non-relativistic convergent close-coupling method was extended into the relativistic domain and applied to electron impact collision processes for highly charged hydrogen-like ions.
Abstract: Recently the non-relativistic convergent close-coupling method has been extended into the relativistic domain [1]. When applied to electron impact collision processes for highly charged hydrogen-like ions, the RCCC method that utilizes relativistic kinematics and the Coulomb interaction in the absence of QED Breit and Moller corrections is suitable for target ions with atomic number Z up to Z ≈ 30. For Z larger than 30, such QED corrections become significant and must be included in the calculations. We have modified the RCCC computer code accordingly and report the results for Z = 100 selected excitation cross sections and for U91+ ionization cross sections which were found to be in good agreement with previous calculations of Fontes et al.[2].
01 Nov 2009
TL;DR: In this paper, the electron-impact ionization of potassium at a broad range of energies for the case where it is the valence electron that is ejected was calculated using the convergent close-coupling method.
Abstract: We calculate electron-impact ionization of potassium at a broad range of energies for the case where it is the valence electron that is ejected. The convergent close-coupling method is used to calculate the total and fully differential cross sections. The unusual shape of the total ionization spin asymmetries measured by Baum et al. [1] is explained. However, agreement with the fully differential cross section measurements of Murray [2] is somewhat mixed.
01 Nov 2009
TL;DR: In this article, the differences of atomic and molecular ionization were explored at equivalent electron kinematics to explore the differences in atomic and molecule ionization. Fully differential cross sections (FDCS) were obtained covering the whole solid angle in order to critically test theoretical calculations.
Abstract: Electron impact single ionization of helium and the hydrogen molecule is studied at equivalent electron kinematics to explore the differences of atomic and molecular ionization. Fully differential cross sections (FDCS) were obtained covering the whole solid angle in order to critically test theoretical calculations.
01 Nov 2009
TL;DR: In this paper, the photon energy dependence of the double K-shell ionization cross sections for light atoms and He-like ions is reported. And the relative contribution of the initial-state correlations and final-state electron-electron interactions to the Kshell DPI is addressed.
Abstract: The photon energy dependence of the double K-shell ionization cross sections for light atoms and He-like ions is reported. The K-shell double photoionization DPI cross-sections for hollow atom production are compared to those of the corresponding He-like counterparts. The relative contribution of the initial-state correlations and final-state electron-electron interactions to the K-shell DPI is addressed. A semiempirical universal scaling of the double photoionization cross sections with the effective nuclear charge for neutral atoms in the range 2 ≤ Z ≤ 47 is established.
01 Nov 2009
TL;DR: In this article, the authors defined the cross sections for the creation, destruction, and transfer of atomic multipole moments by both elastic and inelastic scattering of electrons by atomic targets.
Abstract: We have defined, by completely quantum mechanical methods, the cross sections for the creation, destruction, and transfer of atomic multipole moments by both elastic and inelastic scattering of electrons by atomic targets. Most of the cross sections so obtained agree in form with those obtained by semiclassical methods by Fujimoto and coworkers. We also used the Converged Close-Coupling (CCC) method to calculate numerically some of the above cross sections for selected transitions in H and Ba.
01 Sep 2009
TL;DR: Generalization of scattering theory to charged particles is presented in this paper, which is based on a surface-integral approach, and new general definitions for the breakup amplitude in a three-body system valid for both short-range and long-range Coulombic interactions are given.
Abstract: Generalisation of scattering theory to charged particles is presented. It is based on a surface-integral approach. New general definitions for the breakup amplitude in a three-body system valid for both short-range and long-range Coulombic interactions are given.