Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976apj...210..582c&link_type=abstract
Astrophysical Journal, vol. 210, Dec. 1, 1976, pt. 1, p. 582-592.
Astronomy and Astrophysics
Astrophysics
76
Gamma Rays, Positron Annihilation, Positronium, Solar Flares, Solar X-Rays, Spectral Line Width, Continuous Spectra, Coulomb Collisions, Distribution Functions, Energy Distribution, Free Electrons, Monte Carlo Method, Radiative Recombination, Solar Atmosphere, Temperature Effects
Scientific paper
The slowing down and annihilation of positrons and the formation of positronium in a solar flare plasma are investigated to determine how the width of the 0.511-MeV line and its strength relative to the three-photon continuum from positronium decay depend on the temperature and density of the medium in which the positron comes to rest. The calculations are limited to the cases of annihilation in a completely ionized plasma, in a partially ionized plasma with an electron/neutron density ratio of 1.0 or 0.1, and in an atomic gas with a very small ion density. Thermally averaged rate coefficients are obtained for the free annihilation of positrons and for positronium formation through radiative recombination in the fully ionized plasma. Positronium formation rates and the resultant energy distributions of the positronium atoms in the partially ionized medium are determined by numerically solving the Fokker-Planck equation in a medium where the ambient free electrons have a Maxwell-Boltzmann distribution of finite temperature but the density of the medium is sufficiently low that positronium atoms decay without further collisions following their formation. A Monte Carlo calculation is performed for the positron energy loss, positronium formation through charge exchange, and positronium breakup in the weakly ionized medium. The energy distributions of decaying positronium atoms and the relative number of triplet to singlet positronium decays are evaluated for ion concentrations and densities characteristic of the solar photosphere.
Crannell Carol J.
Joyce Geoffrey
Ramaty Reuven
Werntz Carl
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