A Search for Solar Flare Positrons

Abstract

The detection of solar γ-ray line emission and observations of the isotopes ^2H, ^3H and ^3He in solar cosmic rays provide direct evidence for the occurrence of high energy nuclear reactions in solar flare events. Appreciable numbers of other reaction products, including positrons with energies near ~ 1 MeV, should also be produced in such events. We have searched for positrons in the 0.16-1.6 MeV energy interval during 5 "^3He rich" solar particle events observed by the Caltech Electron/Isotope Spectrometers on IMP 7 and 8. Based on calculations of positron and ^3He production at the sun, and using a simplified model of interplanetary propagation, we might expect comparable fluences of positrons and ^3He to be observed. Summing over these 5 events, however, we find the 0.16 to 1.6 MeV positron fluence to be < 10% of the > 1 MeV/nuc ^3He fluence. This suggests that other processes, such as preferential trapping by the solar magnetic field, may be important.

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