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411 results on '"Walters, H R J"'

1. Positronium-Atom Collisions

Author

Walters, H R J, Yu, A C H, Sahoo, S, and Gilmore, Sharon

Subjects
Physics - Atomic Physics
Abstract

New results are presented for Ps(1s) scattering by H(1s), He(1$^1$S) and Li(2s). Calculations have been performed in a coupled state framework, usually employing pseudostates, and allowing for excitation of both the Ps and the atom. In the Ps(1s)-H(1s) calculations the H$^-$ formation channel has also been included using a highly accurate H$^-$ wave function. Resonances resulting from unstable states in which the positron orbits H$^-$ have been calculated and analysed. The new Ps(1s)-He(1$^1$S) calculations still fail to resolve existing discrepancies between theory and experiment at very low energies. The possible importance of the Ps$^-$ formation channel in all three collision systems is discussed., Comment: 19 pages, 8 figures. Nucl. Instrum. methods B Accepted

Published
2004
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2. Ionization of hydrogen and ionized helium by slow antiprotons

Author

Sahoo, S, Mukherjee, S C, and Walters, H R J

Subjects
Physics - Atomic Physics
Abstract

We study the ionization process involving antiproton and hydrogen in the energy range between 0.1 keV to 500 keV, using single center close coupling approximation. We construct the scattering wave function using B-spline bases. The results obtained for ionization of atomic hydrogen are compared with other existing theoretical calculations as well as with the available experimental data. The present results are found to be encouraging. We also employed this method to study the ionization of ionized helium in the energy range between 1 and 500 keV. On comparision, the present results are found to interpret well the cross section values calculated using other theories., Comment: 11 pages, 6 figures

Published
2004

23. (Ps, E+E-)

Author

Ludlow, John, Walters, H. R. J., Berakdar, J., editor, and Kirschner, J., editor

Published
2001
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26. Application of 6DIME: (γ,2e) on he

Author

Rasch, J., Whelan, Colm T., Lucey, S. P., Walters, H. R. J., Allan, R. J., editor, Guest, M. F., editor, Simpson, A. D., editor, Henty, D. S., editor, and Nicole, D. A., editor

Published
1999
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28. Positron Collisions with Atoms

Author

Walters, H. R. J., Kernoghan, Ann A., McAlinden, Mary T., Campbell, C. P., Burke, P. G., editor, Kleinpoppen, H., editor, Burke, Philip G., editor, and Joachain, Charles J., editor

Published
1997
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43. Collision of Li2+ with Li(2s) and Li(2p): differential and total ionization; discrete excitations; elastic scattering, and total cross section.

Author

Walters, H R J and Whelan, Colm T

Subjects
*ELASTIC scattering, *DIFFERENTIAL cross sections, *CONDUCTION electrons, *NUCLEAR charge, *MOMENTUM transfer, *ANGULAR momentum (Mechanics)
Abstract

The coupled pseudostate approximation (McGovern et al 2009 Phys. Rev. A 79 042707) has been applied to Li2+ + Li(2s, 2p0,±1) collisions at 16 MeV with emphasis on studying the fully differential ionization measurements of Ghanbari-Adivi et al in the azimuthal plane (2017 J. Phys. B: At. Mol. Opt. Phys. 50 215202). The states of the valence electron in the Li target are calculated using the model potential of Stein (1993 J. Phys. B: At. Mol. Opt. Phys. 26 2087). Altogether 164 states with angular momenta l = 0 to 9 are employed in the scattering calculation. It is assumed that the electron in the Li2+ is frozen in the 1s state and its screening of the Li2+ nucleus is fully taken into account. Previous calculations on this system (3DW-EIS and CDW-EIS) have treated the Li2+ as a bare ion with a nuclear charge of 2 au. Except for normalisation, agreement with the experimental data of Ghanbari-Adivi et al is generally quite good. But, where agreement is best it is found that the cross section is very much first Born. Except in one case, quite good accord is also obtained with the 3DW-EIS calculations of Ghanbari-Adivi et al, particularly on normalisation. Screening by the 1s electron has little effect on the fully differential calculations undertaken here. The double differential cross section d2σ/dEdqt and the single differential cross section dσ/dE are also calculated. Here 1s screening is found to be important at large (transverse) momentum transfers qt and large ejection energies E. In addition, the pseudostate approximation gives cross sections for discrete transitions, total ionization and total scattering. [ABSTRACT FROM AUTHOR]

Published
2020
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45. Positron scattering by atomic hydrogen using optical potentials and with positronium formation

Author

Walters, H. R. J

Subjects
Atomic And Molecular Physics
Abstract

The scattering is considered of positrons by H(ls) in a two-state model which incorporates optical potentials. The model explicitly describes elastic scattering, i.e., positron + H(ls) yields positron + H(ls) and Ps(ls) yields Ps(ls) + p. The inelastic processes positron + H(ls) yields positron + H* Ps(ls) + p yields Ps* + p where * stands for a state other than ls, are implicitly taken into account through the optical potentials, which also allow for polarization of H(ls) and Ps(ls).

Published
1990

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