Correlation of Upper-Atmospheric 7Be with Solar Energetic Particle Events
NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
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A surprisingly large concentration of radioactive 7Be was observed in the upper atmosphere at altitudes above 320 km on the LDEF satellite that was recovered in January 1990. We report on follow-up experiments on Russian spacecraft at altitudes of 167 to 370 km during the period of 1996 to 1999, specifically designed to measure 7Be concentrations in low earth orbit. Our data show a significant correlation between the 7Be concentration and the solar energetic proton fluence at Earth, but not with the overall solar activity. During periods of low solar proton fluence, the concentration is correlated with the galactic cosmic ray fluence. This indicates that spallation of atmospheric N by both solar energetic particles and cosmic rays is the primary source of 7Be in the ionosphere.
- Metallurgy and Metallography
- Nuclear Physics and Elementary Particle Physics