Semiempirical model of positron scattering and annihilation

Mitroy, Jim; Ivanov, Igor

doi:10.1103/physreva.65.042705

Cited by 75 publications

(141 citation statements)

References 69 publications

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“…This effect will be called the clustering effect and is well known in condensed-matter systems [33,34], positron-atom scattering systems [20,29,30,36], and positron-atom bound states [19,37].…”

Section: On the Nature Of Annihilation Enhancementmentioning

confidence: 99%

“…In this section a model potential description of the positron-ion collision is presented using the method of Mitroy and co-workers [29,32]. The effective Hamiltonian for the positron moving in the field of the ion is approximated by the model potential,…”

Section: Model Potential Descriptionmentioning

confidence: 99%

“…The annihilation of positrons in the model is written as [29] Z eff ͑J͒ = ͵d 3 rG J 1s ͑r͉͒⌽ J ͑r͉͒ 2 ,…”

Section: Model Potential Descriptionmentioning

confidence: 99%

“…Research on atomic systems [9,20,[29][30][31] has shown that there is a dynamical connection between the size of the lowenergy phase shifts and the annihilation parameter. An attractive interaction leads to the amplitude of the wave function being larger close to the origin, and therefore can be expected to increase the annihilation parameter.…”

Section: Heuristic Description Of Phase-shift Behaviormentioning

confidence: 99%

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Positron scattering and annihilation from hydrogenlike ions

2004

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The Kohn variational method is used with a configuration-interaction-type wave function to determine the J = 0 and J = 1 phase shifts and annihilation parameter Z eff for positron-hydrogenic ion scattering. The phase shifts are within 1 -2% of the best previous calculations. The values of Z eff are small and do not exceed unity for any of the momenta considered. At thermal energies Z eff is minute with a value of order 10 −50 occurring for He + at k = 0.05a 0 −1 . In addition to the variational calculations, analytic expressions for the phase shift and annihilation parameters within the Coulomb wave Born approximation are derived and used to help elucidate the dynamics of positron collisions with positive ions.

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Section: On the Nature Of Annihilation Enhancementmentioning

confidence: 99%

Section: Model Potential Descriptionmentioning

confidence: 99%

“…The annihilation of positrons in the model is written as [29] Z eff ͑J͒ = ͵d 3 rG J 1s ͑r͉͒⌽ J ͑r͉͒ 2 ,…”

Section: Model Potential Descriptionmentioning

confidence: 99%

Section: Heuristic Description Of Phase-shift Behaviormentioning

confidence: 99%

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Positron scattering and annihilation from hydrogenlike ions

2004

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“…The cross section for this process depends on the incident Ps energy, the initial state nl of Ps, and on the positron-atom binding energy ε b . Reaction (2) leads to rapid positron annihilation; the positron-atom bound state lifetime is [51,52] …”

Section: Introductionmentioning

confidence: 99%

Formation of positron-atom bound states in collisions between Rydberg Ps and neutral atoms

Swann¹,

Cassidy

Deller

et al. 2016

Phys. Rev. A

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Predicted twenty years ago, positron binding to neutral atoms has not yet been observed experimentally. A new scheme is proposed to detect positron-atom bound states by colliding Rydberg positronium (Ps) with neutral atoms. Estimates of the charge-transfer reaction cross section are obtained using the first Born approximation for a selection of neutral atom targets and a wide range of incident Ps energies and principal quantum numbers. We also estimate the corresponding Ps ionization cross section. The accuracy of the calculations is tested by comparison with earlier predictions for Ps charge transfer in collisions with hydrogen and antihydrogen. We describe an existing Rydberg Ps beam suitable for producing positron-atom bound states and estimate signal rates based on the calculated cross sections and realistic experimental parameters. We conclude that the proposed methodology is capable of producing such states and of testing theoretical predictions of their binding energies.

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Convergence of an s‐Wave calculation of the He ground state

Mitroy

Bromley

Ratnavelu

2006

Int J of Quantum Chemistry

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ABSTRACT:The configuration interaction (CI) method using a large Laguerre basis restricted to ᐉ ϭ 0 orbitals is applied to the calculation of the He ground state. The maximum number of orbitals included was 60. The numerical evidence suggests that the energy converges aswhere N is the number of Laguerre basis functions. The electron-electron ␦-function expectation converges as ⌬␦ N Ϸ A/N 5/ 2 ϩ B/N 6/ 2 ϩ . . . , and the variational limit for the ᐉ ϭ 0 basis is estimated as 0.1557637174(2) a 0 3 . It was seen that extrapolation of the energy to the variational limit is dependent on the basis dimension at which the exponent in the Laguerre basis was optimized. In effect, it may be best to choose a nonoptimal exponent if one wishes to extrapolate to the variational limit. An investigation of the natural orbital asymptotics revealed the energy converged as These studies have investigated the convergence of the energy with respect to the number of partial waves included in the wave function, and also with respect to the dimension of the radial basis.It has been known since 1962 [9] that the energy converges slowly with respect to J, the maximum angular momentum of any orbital included in the CI expansion. In particular, the leading term to the energy increment is known to behave as (1) at high J. Later work [1][2][3][4]6] showed that the energy increments can be written more generally as

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Semiempirical model of positron scattering and annihilation

Cited by 75 publications

References 69 publications

Positron scattering and annihilation from hydrogenlike ions

Positron scattering and annihilation from hydrogenlike ions

Formation of positron-atom bound states in collisions between Rydberg Ps and neutral atoms

Convergence of an s‐Wave calculation of the He ground state

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