Determination of the (He-3)/H ratio in the solar photosphere from flare gamma-ray line observations

The time dependence of the 2.223 MeV gamma-ray line emission from the capture of flare-produced neutrons in the solar photosphere provides a sensitive measure of the He-3 abundance there. Monte Carlo calculations have been made of this time dependence as a function of both He-3 abundance and observing angle for neutrons produced by thick-target interactions of flare-accelerated ions with a range of incident energy spectra and angular distributions. Assuming a mirroring distribution, suggested by other observations, it is found that the Solar Maximum Mission measurements of the time dependence of the 2.223 MeV line emission from the solar flare of June 3, 1982, imply a solar photospheric (He-3)/H ratio of (2.3 + or - 1.2) x 10 to the -5th at the 90 percent confidence level. 44 references