The mean ionic charge of solar energetic particles provides critical information for the determination of the source and the acceleration region of the ions. Gradual events show at energies < 0.5 MeV/amu a mean ionic charge of Qm
≈ 10 for iron ions, suggesting a solar wind origin and acceleration by coronal or interplanetary shock waves. Impulsive events show a large increase of Qm
(Fe) at 0.1–0.5 MeV/amu from 11 to 20. This can only be explained by acceleration and ionisation in a plasma of sufficiently high density in the low corona, at altitudes of < 0.3 RS
: solar radius).