The effect of positronium formation on close-coupling calculations of positron-lithium collisions

Hewitt, R N; Noble, C. J.; Bransden, B H

doi:10.1088/0953-4075/25/11/022

Cited by 36 publications

(68 citation statements)

References 19 publications

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“…Chapuis et al (1994) deduced it from the difference between the total cross section and those of the charge exchange and ionization cross sections. However, the excitation crosssection for positron-He scattering evaluated with this method overestimates by a factor of ≈4 the experimental measurements (Coleman et al 1982;Mori & Suoeka 1994) and theoretical calculations (Parcell et al 1987;Hewitt et al 1992;Ficocelli Varrachio & Parcell 1992;Campbell et al 1998; see also Fig. 5.4 of CH2001).…”

Section: Heliummentioning

confidence: 76%

The lives and deaths of positrons in the interstellar medium

Guessoum

Jean

Gillard

2005

A&A

101

178

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Abstract. We reexamine in detail the various processes undergone by positrons in the interstellar medium (ISM) from their birth to their annihilation using the most recent results of positron interaction cross sections with atomic and molecular hydrogen, as well as helium. The positrons' lives are divided into two phases: the "in-flight" phase (between ≈1 MeV and tens of eV) and the thermal phase. The first phase is treated with a Monte Carlo simulation that allows us to determine the fraction of positrons that form positronium and annihilate as well as the characteristics of the annihilation emission as a function of the medium conditions. The second phase is treated with a binary reaction rate approach, with cross sections adopted from experimental measurement or theoretical calculations. An extensive search and update of the knowledge of positron processes was thus undertaken. New reaction rates and line widths have been obtained. We investigate the treatment of the complicated interactions between positrons and interstellar dust grains. Fully relevant data were not always available, but we were nonetheless able to reach satisfactory understanding of positron annihilation on grains, both qualitatively and quantitatively. All factors of the problem have been considered, including the grain size distribution and composition, the electric charge of the grains, the backscattering, positronium formation and ejection from the grain, the pick-off annihilation inside them and the partial destruction of dust in the hot regions of the ISM. New reaction rates and widths of the line resulting from the annihilation inside and outside of the grain have been obtained. The final results of our calculations (reaction rates and spectra) showed that dust is only important in the hot phase of the ISM, where it dominates all other processes. Combining the new calculations, we have constructed annihilation spectra for each phase of the ISM, considering various grain contents, as well as an overall combined spectrum for the ISM as a whole.

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Section: Heliummentioning

confidence: 76%

The lives and deaths of positrons in the interstellar medium

Guessoum

Jean

Gillard

2005

A&A

101

178

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“…However, convergence was poor due to the absence of Ps-formation channels [130]. Two-center expansion was employed by Guha and Ghosh [131], Basu and Ghosh [132], Abdel-Raouf [133], Hewitt et al [134], McAlinden et al [130] and Le et al [135]. As expected, these approaches gave better agreement with the experiment.…”

Section: Alkali Metalsmentioning

confidence: 82%

Recent progress in the description of positron scattering from atoms using the convergent close-coupling theory

Kadyrov

Bray

2016

J. Phys. B: At. Mol. Opt. Phys.

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Much progress in the theory of positron scattering on atoms has been made in the ten years since the review of Surko et al. [1]. We review this progress for few-electron targets with a particular emphasis on the two-centre convergent close-coupling and other theories which explicitly treat positronium (Ps) formation. While substantial progress has been made for Ps formation in positron scattering on few-electron targets, considerable theoretical development is still required for multielectron atomic and molecular targets.

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“…Refs. [1][2][3][4][5][6][7][8][9]). Alkali-metal atoms have been a subject of interest in several theoretical and experimental investigations in electron-and positron-atom collisions because of their various interesting properties : relatively simple structure, low ionization potentials, large polarizabilities and existence of resonance lines in the visible or quartz ultraviolet part of the electromagnetic spectrum (which make the alkali metals interesting as components of stellar atmosphere and other plasmas).…”

Section: Introductionmentioning

confidence: 99%

Total cross section prediction of the collisions of positrons and electrons with alkali atoms using Gradient Tree Boosting

2011

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A relatively new computational technique, namely gradient tree boosting (GTB), is presented for modeling the total cross sections of the scattering of positrons and electrons by alkali atoms in the low and intermediate energy regions. The calculations have been performed in the framework of gradient tree boosting (GTB). The GTB has been running based on the experimental data of the total collisional cross sections to produce the total cross sections for each alkali atom as a function of the incident energy of the projectile as well as the atomic number and the static dipole polarizability of the atom. Moreover our GTB model is used to predict the experimental data for total collisional cross sections that are not used in the training session. The calculated and predicted total collisional cross sections are compared with the experimental data. We find that the GTB technique shows a good match to the experimental data. To our knowledge, this is the first application of the GTB technique to the data of positron and electron collisions with alkali atoms at low and intermediate energies.

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The effect of positronium formation on close-coupling calculations of positron-lithium collisions

Cited by 36 publications

References 19 publications

The lives and deaths of positrons in the interstellar medium

The lives and deaths of positrons in the interstellar medium

Recent progress in the description of positron scattering from atoms using the convergent close-coupling theory

Total cross section prediction of the collisions of positrons and electrons with alkali atoms using Gradient Tree Boosting

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