Coupled-channel Optical Method Research Articles

Differential cross sections of positron–hydrogen collisions**Project supported by the Nanyang Normal University Science Foundation of China (Grant No. ZX2013017) and the National Natural Science Foundation of China (Grant Nos. 11174066, 61306007, and U1304114).

We make a detailed study on the angular differential cross sections of positron–hydrogen collisions by using the momentum-space coupled-channels optical (CCO) method for incident energies below the H ionization threshold. The target continuum and the positronium (Ps) formation channels are included in the coupled-channels calculations via a complex equivalent-local optical potential. The critical points, which show minima in the differential cross sections, as a function of the scattering angle and the incident energy are investigated. The resonances in the angular differential cross sections are reported for the first time in this energy range. The effects of the target continuum and the Ps formation channels on the different cross sections are discussed.

Electron impact excitation of 5p states of rubidium at 20 eV incident energy

The coupled-channel optical method (CCOM) is implemented in this work to study the scattering of electron on rubidium atom at 20 eV. In order to provide a realistic calculation, the continuum effect of the scattering system is accounted by incorporate an ab initio optical potential into the CCOM calculation. The differential cross sections (DCS), as well as the reduced Stokes parameters of 5p excitation are reported and compared to the available experimental and theoretical data.

Electron (positron) impact excitation (2p state) of lithium at intermediate energies

In this work, studies have been carried out to investigate theoretically the electron (positron)-impact-induced 2s → 2p lithium (Li) transition at 20 and 60 eV using the coupled-channel optical method (CCOM). The inelastic differential cross sections (DCS) together with the reduced Stokes parameters ( $$\bar P_1$$ , $$\bar P_2$$ , $$\bar P_3$$ ) and other parameters such as the alignment (γ, $$\bar P_l$$ ), orientation (L ⊥) and coherence parameters (P +) are reported in the present calculations. Comparison is made with other available theoretical and experimental measurements.

Unnatural parity resonance states in positron-excited hydrogen scattering

The coupled-channels optical method for positron scattering has been applied to investigate resonance states with unnatural parities in a positron-excited hydrogen system. The positronium formation channels and continuum channel are included via a complex equivalent local potential. Resonance states with angular momenta L = 1 to L = 2 and parities (−1)L+1 are calculated. Resonance energies and widths are reported and compared with other theoretical calculations. We found that the opening positronium formation channels play an important role in forming nondipole Feshbach resonances.

Total cross sections for low-energy positron-sodium scattering

A calculation of total cross sections for low-energy positron-sodium scattering has been performed using the coupled-channel optical method in which the ionization and positronium formation channels are included via a complex equivalent-local potential.

Resonance Structures in positron-hydrogen scattering

An application of the coupled channels optical method to energy-dependent phenomena, positron-hydrogen resonances below the n = 2 excitation threshold, is given. The equivalent local optical potential is used to account for the target polarization and positronium formation (Ps). The calculation included 9 explicitly physical coupled channels. The lowest S-wave resonance energy position and new resonances have been found. Angular dependence of the cross section in the resonance region has been investigated.

Feshbach resonances in positron scattering from sodium

We present an investigation of Feshbach resonances in positron-sodium scattering system. The momentum space coupled channels optical method including the positronium formation channels has been used. The first three partial-wave resonances below the Na(3p,4s,3d,4p) excitation and the Ps(n=2) formation thresholds are calculated. The Wigner cusp structures are also obtained just at these thresholds.

Threshold behaviors in positron scattering from atomic lithium near the first inelastic threshold

Differential cross sections have been investigated in the positron-lithium scattering system using momentum space coupled channels optical method. The angular range was from 10° to 160° and the energies were chosen to span the region containing the first excitation threshold of atomic lithium (1.848 eV). Threshold behaviors have been studied.

Resonances in the scattering of low-energy electron from Mg

We present the calculation of elastic scattering from magnesium by electrons in the energy range from 2 to 6 eV using the momentum space coupled-channel optical method. Several resonances have been located in the states with angular moment L=0 to 4. The results are compared with other theoretical results and measured data.

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.

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.

Positron-rubidium atom scattering at intermediate and high energies

In this work, the coupled-channel optical method (CCOM) is implemented in a study of positron-rubidium (Rb) scattering at intermediate and high energies. The CCOM provides a realistic calculation for positron-atom scattering where the ab-initio optical potential accounts for the omitted continuum effect in the scattering system. The integral, positronium (Ps) formation and total cross sections are compared to experimental and other theoretical data where available.

Feshbach resonances in positron scattering from sodium

S-, P- and D-wave Feshbach resonances in positron-sodium scattering have been investigated by using the momentum space coupled-channels optical method. The target continuum and positronium (Ps) formation channels are included via an optical potential. Feshbach resonances below the target excitation and Ps (n = 2) formation thresholds are predicted and the effects of channel-coupling scheme, target continuum and Ps formation channels on the resonance energy and resonance width are discussed. We have also found the Wigner cusp structures at the inelastic channel-opening thresholds in positron-sodium scattering cross sections.

Resonances in the scattering of low energy electrons from magnesium

An application of the coupled-channel optical method to energy-dependent phenomena, electron–magnesium resonances in the energy range from 2 to 6 eV, is presented. 14 physical channels are included in the calculations. The real part of equivalent local optical potential that presents the polarization of target is also included in the calculations. Good agreements with experimental observations are shown for the resonance positions. The corresponding widths of resonances have been obtained for the first time. A new resonance state has been predicted.

Total cross sections of positron—sodium scattering at low energies

A new calculation for the total cross section of positron—sodium scattering is performed in an energy range down to a few tenths of one electron volt using the coupled-channel optical method. The ionization continuum and the positronium formation channels are included via an equivalent-local complex potential. The role played by the break-up and rearrangement processes in the low energy positron-sodium scattering is also investigated. The total scattering cross section is reported and compared with the available theoretical and experimental data.

Coupled-channels optical calculation of positron—hydrogen resonances

An application of the coupled-channels optical method is given for the energy-dependent phenomena of positron-hydrogen resonances below the n = 2 excitation threshold. The equivalent local optical potential is used to account for the target polarization and positronium formation. The calculation includes 9 explicitly physical coupled channels. The lowest S-wave resonance energy position and new resonances are found. Angular dependence of the cross section in the resonance region are investigated.

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.

Optical Potential Study of Electron Scattering by Rubidium

The coupled-channel optical method (CCOM) has been implemented in a study of electronrubidium scattering. This method includes the continuum eect in the calculation via an ab-initio optical potential. Eight atomic states (5s, 5p, 4d, 6s, 6p, 5d, 7s, 7p) were used together with the continuum optical potential in the 5s-5s, 5s-5p, and 5p-5p coupling. The elastic, inelastic and total cross sections for electron-rubidium scattering at low and intermediate energies, ranging from 10 eV to 100 eV, are reported. The results are compared with available experimental and theoretical data.

Electron and positron scattering from atomic potassium

The present coupled-channels-optical method (CCO) provides a comprehensive theoretical calculation of electron-potassium atom and positron-potassium atom scattering at intermediate energies. The CCO calculations for various physical observables are compared with the convergent close-coupling method (CCC) and other theoretical results, as well as experimental data where available. The CCO provides good to fair agreement with results from the convergent close coupling calculations, which are considered to be the state of the art for alkali atoms in the electron channel.