Zhou Ya-Jun

Resonances in Positron Hydrogen Scattering above the H (n = 2) Threshold

We investigate high partial wave resonances in positron-hydrogen scattering using the momentum-space coupled-channels optical method above the H (n = 2) threshold. Resonances with angular momenta of L = 0–6 are reported. Ionization continuum and positronium formation channels are included via a complex equivalent local potential. Comparisons with the existing theoretical results are presented.

Coupled-channel optical calculation for positron-lithium scattering

Positron scattering with atomic lithium is investigated by using a coupled-channel optical method. The ionization continuum and positronium formation channels are taken into account via a complex equivalent-local optical potential. The positronium formation cross sections and the ionization cross sections, as well as the total scattering cross sections, are reported at energies above 3 eV and compared with available experimental and theoretical data.

Resonance phenomena and threshold features in positron—helium scattering

Investigations of resonances and threshold behaviors in positron—helium scattering have been made using the momentum-space coupled-channels optical method. The positronium formation channels are considered via an equivalent-local complex potential. The s-wave resonances and the Wigner cusp feature at the positronium (n = 1) formation threshold are compared with the previous reports. The p- and the d-wave resonances and a Wigner cusp feature at the positronium (n = 2) formation threshold are reported for the first time.

Second-order Born calculation of coplanar symmetric (e, 2e) process on Mg

The second-order distorted wave Born approximation (DWBA) method is employed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e, 2e) collisions for magnesium at excess energies of 6 eV–20 eV. Comparing with the standard first-order DWBA calculations, the inclusion of the second-order Born term in the scattering amplitude improves the degree of agreement with experiments, especially for backward scattering region of TDCS. This indicates that the present second-order Born term is capable to give a reasonable correction to DWBA model in studying coplanar symmetric (e, 2e) problems of two-valence-electron target in low energy range.

Ionization cross sections for electron scattering from metastable rare-gas atoms (Ne* and Ar*)

The optical-model approach has been used to investigate the electron-impact ionization of metastable rare-gas atoms. A complex equivalent-local polarization potential is obtained to describe the ionization continuum channels. We have calculated the cross sections for collisional ionization of the metastable atoms Ne* and Ar* by electrons in the energy range from threshold to 200 eV. The present results are in agreement with the available experimental measurements and other theoretical calculations.

Study of (e, 2e) process on potassium at 6 eV–60 eV above threshold in a second-order Born approximation

The standard distorted wave Born approximation (DWBA) method has been extended to second-order Born amplitude in order to describe the multiple interactions between the projectile and the atomic target. Second-order DWBA calculations have been preformed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e, 2e) collisions for the alkali target potassium at excess energies of 6 eV–60 eV. Compared with the previous first-order DWBA calculations, the present theoretical model improves the degree of agreement with experiments, especially for the backward scattering angle region of TDCS. This indicates that the present second-order Born term is capable of giving a reasonable correction to the DWBA model in studying coplanar symmetric (e, 2e) problems in low and intermediate energy ranges.

Positron Impact Transitions of Atomic Sodium

We present a new investigation of elastic and inelastic positron-sodium scattering by using the coupled-channel optical method (CCO) at an incident energy region of 2–100 eV. The ionization continuum and positronium formation channels have been included via a complex equivalent-local optical potential. The present calculations are compared with available theoretical data and our investigation indicates that the inclusion of ionization and Ps-formation channels in the present calculations has a significant effect on the cross sections of elastic and inelastic positron-sodium scattering at lower energies.

Positronium Formation in Positron-Lithium Scattering

The positronium formation process in positron scattering with atomic lithium is investigated using the coupled-channel optical method. The cross sections of positronium formation into the n = 1 and n = 2 levels from 2 to 60 eV are reported. The present results show reasonable agreement with the available experimental measurements and theoretical calculations.

Triple-differential cross section for single ionization of H2 by electron impact

The triple-differential cross section (TDCS) for the (e, 2e) ionization of a hydrogen molecule is calculated using the molecule distorted-wave Born approximation (MDWBA). Distorted waves are obtained by solving momentum-space coupled-channel Lippmann—Schwinger equations, including the ground state and the lowest-lying electronic state of b3Σu. TDCSs at the incident energy 100 eV in coplanar asymmetric geometry are reported. The present calculations are compared with the available experimental measurements and the theoretical results.

Second-Order Born Effect in Single Ionization of Argon by Electron Impact

We extend the standard distorted wave Born approximation (DWBA) to include the second-order Born amplitude in order to describe the multiple interactions between a projectile and an atomic target. Both the first- and second- order DWBA models are used to calculate triply differential cross sections (TDCS) of coplanar (e, 2e) on atomic argon with the scattered electron energy fixed at 500 eV, the scattering angle at 6° and the ejected electron energies at 37, 74 and 205 eV. Overall agreements with experimental measurements have been obtained in shape, and the second-order DWBA model improves the calculations as expected, especially for recoil peak of TDCS.