Doppler-shifted emission from helium ions accelerated in solar flares

This paper concerns the Doppler-shifted Ly-alpha radiation emitted by He II (304 A) in ion beams accelerated in solar flares downward from the solar corona into the chromosphere, where they are slowed down and finally stopped. It is found that the radiation from He II ions with E(0) greater than or equal to 150 keV/amu initially at the top of the atmosphere would lie typically one order of magnitude above the background. The radiation from He ions moving initially with E(0) greater than or equal to 400 keV/amu should be observable as long as the beam is driven by the flare. Radiative electron capture provides an effective cooling mechanism.