Positron Impact Ionisation of H and He Atoms: The Continuum Model

Ratnavelu, Kuru

doi:10.1071/ph910265

Cited by 13 publications

(11 citation statements)

References 10 publications

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“…On the theoretical side, the results of calculations by Janev & Solov'ev (1998) fit the previous measurements below 40 eV, whereas those of Ratnavelu (1991) are in good accord with the data above 30 eV but slightly overestimate the cross-section in the 150−300 eV range.…”

Section: Hydrogensupporting

confidence: 77%

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: Hydrogensupporting

confidence: 77%

The lives and deaths of positrons in the interstellar medium

Guessoum

Jean

Gillard

2005

A&A

101

178

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“…In figure 2, we show the ionization cross sections calculated with the CCO(3, 3) and CCO(6, 3) together with the CC(28, 3) and CC(30, 3) models. We also depict the ionization cross section of Ratnavelu (1991). The present CCO(3, 3) and CCO(6, 3) confirm the qualitative and quantitative features of the continuum optical potential of Ratnavelu.…”

Section: L384supporting

confidence: 71%

“…It is highly probable that the inclusion of the f-pseudostates in the work of Kernoghan et al may explain these differences. We also depict the ionization cross sections of Ratnavelu (1991) which show good agreement with the UCL data for E > 30 eV. Ratnavelu (1991) had used the continuum optical potential method of McCarthy and Stelbovics (1983a) to calculate these ionization cross sections.…”

mentioning

confidence: 60%

“…We also depict the ionization cross sections of Ratnavelu (1991) which show good agreement with the UCL data for E > 30 eV. Ratnavelu (1991) had used the continuum optical potential method of McCarthy and Stelbovics (1983a) to calculate these ionization cross sections. The scarcity of theoretical studies, and the differences that exist between the theoretical predictions of the ionization cross sections, motivated the present work to study positron scattering by atomic hydrogen at intermediate energies.…”

mentioning

confidence: 60%

“…In the present work the Q-space considered only includes the continuum channels. The details of calculating the complex polarization potential for the continuum can be found in McCarthy and Stelbovics (1983b) and Ratnavelu (1991) and will not be described here.…”

mentioning

confidence: 99%

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