Charge States and Energy-Dependent Composition of Solar-Flare Particles

Abstract
During a weak solar flare, energy spectra of He, O, and Fe from 0.2 to ∼ 30 MeV per nucleon were measured with glass and plastic detectors exposed on the Apollo 16 spacecraft. The spectra were very steep and the abundance ratios Fe/O and O/He decreased rapidly with energy, approaching solar atmospheric ratios at energies above ∼ 5 MeV per nucleon. The shapes of the rigidity spectra suggest that the ions were completely stripped while being accelerated.