Li-7 and Be-7 de-excitation lines - Probes for accelerated particle transport models in solar flares

The photon energy spectrum of a spectral feature composed of the 429 and 478 keV gamma-ray lines from Be-7 and Li-7 (produced by interactions of flare-accelerated alpha particles with ambient He in the solar atmosphere) depends on the angular distribution of the interacting accelerated particles. This spectrum is calculated for limb and disk-centered flares using a loop model for the transport of the ions. The resulting spectra are compared with data from the April 27, 1981 limb flare obtained with the gamma-ray spectrometer on SMM, providing convincing evidence for the existence of the (Li-7)-(Be-7) feature in this flare. By comparing the fluence of this feature with that of the 511 keV line, it is shown that the accelerated alpha particle abundance or the ambient He abundance, or both, must be enhanced.