Double and single ionization of helium by high velocity fully stripped ions

The ratio, R, of the double ionization cross section to that of single ionization for helium by fully stripped carbon, oxygen, silicon and sulphur ions in the energy range of 2.8 to 6.3 MeV amu -1 have been measured. The data obtained using carbon and oxygen projectiles show that in this energy range R is in better agreement with the fit given by Knudsen et al. (1984) than measurements using N 7+ projectiles in the energy range 10-30 MeV amu -1 and Kr 36+ projectiles with energies 0.5 and 1 GeV amu -1 .