Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session KW5: Electron and Positron Collisions with Atoms |
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Chair: Klaus Bartschat, Drake University Room: Village Square |
Wednesday, October 2, 2013 1:30PM - 2:00PM |
KW5.00001: Positron collisions from simple atoms and positronium-hydrogen collisions Invited Speaker: S.J. Ward I plan to present calculations of three-body, effective three-body and four-body collisions at low energies that involve a positron. We applied the hyperspherical hidden crossing method with a correction term to Ps formation in low energy e$^+$-H [1,2], e$^+$-Li [2,3,4] and e$^+$-Na collisions [2]. We considered the alkali atoms Li and Na as effective one-electron atoms, so that e$^+$-Li collisions and e$^+$-Na collisions can be considered as effective three-body collisions. The calculations provide an explanation of the extremely small S-wave Ps formation cross section for e$^+$-H, e$^+$-Li and e$^+$-Na collisions in terms of destructive interference. The S-wave cross section for Ps formation in e$^+$-Li and in e$^+$-Na collisions increases with decreasing momentum of the incoming Ps, which is consistent with the Wigner threshold law [5]. We have also studied at low-energies a fundamental four-body Coulomb process, that of elastic Ps-H scattering [6]. Using the Kohn variational method (and variants of this method) we have computed accurate $^{1,3}$S- and $^{1,3}$P-wave phase shifts. We also have some preliminary $^{1,3}$D-wave phase shifts.\\[4pt] [1] S.~J.~Ward, J.~H.~Macek and S.~Yu.~Ovchinnikov, Phys.~Rev.~A {\bf 59}, 4418 (1999).\\[0pt] [2] S.~J.~Ward and J.~Shertzer, New.~J.~Phys. {\bf 14}, 025003 (2012).\\[0pt] [3] S.~J.~Ward and J.~Shertzer, Phys.~Rev. A {\bf 68}, 032720 (2003).\\[0pt] [4] S.~J.~Ward, J.~Shertzer, S.~Yu.~Ovchinnikov, and J.~H.~Macek, Phys.~Rev.~A {\bf 75}, 012713 (2007).\\[0pt] [5] P. Wigner, Phys.~Rev. {\bf 73}, 1002 (1948).\\[0pt] [6] Denton Woods, S.~J.~Ward and P.~Van Reeth, Bull.~Am.~Phys.~Soc. {\bf 58}, no.~6, p.~175 (2013). [Preview Abstract] |
Wednesday, October 2, 2013 2:00PM - 2:15PM |
KW5.00002: Rearrangement processes in low-energy positron scattering on hydrogen and the alkali metals Igor Bray, A.V. Lugovskoy, A.S. Kadyrov We apply the two-center convergent close-coupling (CCC) method to the calculation of low-energy positron scattering on atomic hydrogen and the alkali metals. Our primary interest is in the near-threshold exothermic rearrangement processes. Examples include positronium (Ps) formation for the alkali metals at near-zero positron energy, and (anti)hydrogen formation in near-threshold Ps-(anti)proton scattering. The cross sections for such processes are infinite at threshold, and we investigate their behavior in the vicinity of threshold. [Preview Abstract] |
Wednesday, October 2, 2013 2:15PM - 2:30PM |
KW5.00003: A simple approach to calculating positronium formation Allan Stauffer, Robert McEachran We have developed a simple method to calculate positronium formation in positron-atom scattering based on an idea first proposed by Reid and Wadehra [1]. We have applied it to positron scattering from neon, argon, krypton and xenon. Our method involves lowering the threshold for direct ionization, I, by 6.8 eV, the binding energy of positronium, and calculating the ionization cross section using our complex optical potential approach [2]. By subtracting the cross section for ionization calculated with the unmodified threshold for ionization we obtain the result for positronium formation. Since the positronium formation cross section goes to zero more rapidly than for direct ionization, we have taken this into account by linearly raising the threshold for ionization until it coincides with I for incident positron energies above 120 eV. We have found that our cross sections calculated this way are in better overall agreement with experimental measurements than more elaborate theoretical calculations.\\[4pt] [1] D.D. Reid and J.M. Wadehra 1996 J. Phys. B 29 L127\\[0pt] [2] R.P. McEachran and A.D. Stauffer 2013 J. Phys. B 46 03 [Preview Abstract] |
Wednesday, October 2, 2013 2:30PM - 3:00PM |
KW5.00004: Electron Impact Single and Double Ionization of Helium calculated with Generalized Sturmian Functions Invited Speaker: Dario Mitnik The single and double ionization of He induced by the collision of high incident energy electrons still remains a challenging problem for theoreticians. Several ab initio calculations (see [1]) of excitation-ionization disagree which each other and with the experimental data [2]. A similar situation is found for the double ionization of He [3]. In this talk, we will provide cross sections for both processes calculated by using the Generalized Sturmian Functions method [4,5]. Comparisons with experimental data [6] and with other calculations will be presented.\\[4pt] [1] J.M. Ngoko Djiokap et al, Phys. Rev. A 81, 042712 (2010).\\[0pt] [2] C. Dupre et al, J. Phys. B 25, 259 (1992).\\[0pt] [3] L.U. Ancarani, et al, J. Phys.: Conf. Ser. 212, 012025 (2010).\\[0pt] [4] D M Mitnik et al, Comp. Phys. Comm. 182 1145 (2011).\\[0pt] [5] G. Gasaneo et al, Accepted in Adv. Quantum Chem. (2013).\\[0pt] [6] A Lahmam-Bennani et al, J. Phys. B 42 165201 (1999); A. Kheifets et al, J. Phys. B 32, 5047 (1999). [Preview Abstract] |
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