Cross sections for ionization and fragmentation of by fast impact

Absolute cross sections have been measured for the first time for -impact ionization and fragmentation of at proton energies ranging from 0.2 to 2.0 MeV. The cross sections were in fairly good agreement with other electron-impact data in the high-velocity region, indicating that the charge transfer is negligible in the present energy range. Theoretical cross sections for plasmon excitations were also calculated and compared with the experimental ionization cross sections. Agreement between them was within a factor of two, indicating that the plasmon excitation contributes to the total ionization by about 50%. A careful analysis of the energy dependence of the cross sections for and ions indicates that these ions are produced from the same initial excited states created in collisions with ions.