Time Dependences of the 0. 51 and 2. 2 MeV Lines in Solar Flares
Abstract
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.
- Publication:
-
International Cosmic Ray Conference
- Pub Date:
- August 1975
- Bibcode:
- 1975ICRC....5.1635R
- Keywords:
-
- Energy Spectra;
- Positron Annihilation;
- Solar Flares;
- Solar Flux;
- Time Dependence;
- X Ray Spectra;
- Gamma Rays;
- Nuclear Reactions;
- Particle Energy;
- Positronium;
- Solar Physics