Differential charge state fractions of He following ionization by fast H- projectiles

The differential charge state fractions of He ions produced an ionization by fast H-projectiles have been measured at projectile scattering angles between 0.25 and 1.59 mrad and an impact energy of 1.0 MeV. These charge state fractions have been measured for each of the possible final charge states of the H- projectile (H-, H and p+). Combined with earlier measurements of simple ionization (no change in projectile charge state) by protons and of capture and ionization by protons, some systematics can be noted. The fraction of doubly charged He ions exhibits a distinct peak between 0.9 and 1.1 mrad for simple ionization. A similar peak is seen at ≅0.55 mrad for ionization accompanied by either capture by protons or by single strippling of H-. The data for proton impact suggest that all the peaks are related to double ionization of the target. The double-ionization mechanisms will be discussed in terms of their possible contribution to the observed structures. (orig.)