Physics
Scientific paper
Aug 1975
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975icrc....5.1635r&link_type=abstract
In: International Cosmic Ray Conference, 14th, Munich, West Germany, August 15-29, 1975, Conference Papers. Volume 5. (A76-26851
Physics
Energy Spectra, Positron Annihilation, Solar Flares, Solar Flux, Time Dependence, X Ray Spectra, Gamma Rays, Nuclear Reactions, Particle Energy, Positronium
Scientific paper
The time dependence of the 0.51 MeV line in solar flares is determined by the following factors: variation with time of the rate of nuclear reactions which produce the positron emitters; mean lives of the positron emitters; slowing-down of the positrons which depends on the ambient density and magnetic field; and annihilation or positronium formation times of the positrons with free or bound electrons. The discussion is limited to the observed intensity-time profile of a 0.35-8 MeV gamma-ray emission and of a 0.51-MeV line calculated for three different ambient densities in the annihilation region. Major conclusions are that (1) MeV electrons and protons of at least 30 MeV/nuc have similar time dependences and hence a common origin in the flare region, which support a two-phase acceleration model in solar flares; and (2) the delayed character of the 0.51-MeV emission is clearly defined, where at a time when the rate of nuclear reactions is zero, there still is considerable 0.51-MeV emission.
Ramaty Reuven
Wang Hao-Tian
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