Accelerated and Ambient He Abundances from Gamma‐Ray Line Measurements of Flares

The γ-ray lines from 7 Be and 7 Li produced when flare-accelerated He nuclei interact with ambient He have been found to be surprisingly intense from measurements made by moderate-resolution γ-ray spectrometers on the Solar Maximum Mission ( SMM ) and Compton Gamma Ray Observatory ( CGRO ) satellites. These high intensities suggest either accelerated α/proton ratios ≳0.5 and/or an He/H abundance greater than 0.1 in the subcoronal regions where the particles interact. We have studied additional γ-ray lines in 20 flares produced by interactions of α particles on 56 Fe and other elements to resolve this ambiguity. These measurements indicate, on average, that the ambient He abundance is consistent with accepted photospheric values and that an enhanced concentration of He is present in flare-accelerated particles. Although there is evidence for the presence of accelerated 3 He, its concentration is only a fraction of accelerated 4 He. These studies also revealed a new weak line in the spectra at ~1.32 MeV that is attributed to an excited state of 55 Fe.