Interaction between slow positrons and atoms

Positron scattering and annihilation on noble gas atoms is studied ab initio using many-body theory methods for positron energies below the positronium formation threshold. We show that in this energy range the many-body theory yields accurate numerical results and provides a nearcomplete understanding of the positron-noble-gas-atom system. It accounts for positron-atom and electron-positron correlations, including the polarization of the atom by the positron and the nonperturbative process of virtual positronium formation. These correlations have a large effect on the scattering dynamics and result in a strong enhancement of the annihilation rates compared to the independent-particle mean-field description. Computed elastic scattering cross sections are found to be in good agreement with recent experimental results and Kohn variational and convergent close-coupling calculations. The calculated values of the annihilation rate parameter Z eff (effective number of electrons participating in annihilation) rise steeply along the sequence of noble gas atoms due to the increasing strength of the correlation effects, and agree well with experimental data.

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“…Hence, it is possible to derive a diagrammatic expansion for Z eff [17,25,26]. Figure 4 shows the set of main annihilation diagrams.…”

Section: B Scattering Phase Shiftsmentioning

confidence: 99%

Positron scattering and annihilation on noble-gas atoms

2014

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“…The first one operates for both atoms and molecules, and involves positron annihilation in flight, as it is passing the target. It is enhanced if the positron possesses a virtual of weakly bound level close to zero energy [23,32]. However, this enhancement is limited to Z eff 10 3 for room-temperature or higher positron energies (see Sec.…”

Section: Annihilation Mechanismsmentioning

confidence: 99%

Positron annihilation in large polyatomic molecules. The role of vibrational Feshbach resonances and binding

Gribakin

Lee

2008

Eur. Phys. J. D

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Abstract. We analyse the process of rapid positron annihilation in large polyatomic molecules due to positron capture into vibrational Feshbach resonances. Resonant annihilation occurs in molecules which can bind positrons, and we analyse positron binding to alkanes using zero-range potentials. Related questions of spectra of annihilation gamma quanta and molecular fragmentation following annihilation, are discussed briefly.

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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%

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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Interaction between slow positrons and atoms

Cited by 65 publications

References 12 publications

Positron scattering and annihilation on noble-gas atoms

Positron scattering and annihilation on noble-gas atoms

Positron annihilation in large polyatomic molecules. The role of vibrational Feshbach resonances and binding

Positron scattering and annihilation from hydrogenlike ions

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