FORMATION OF HE- IONS IN CHARGE-CHANGING COLLISIONS DURING PASSAGE OF FAST HELIUM BEAMS THROUGH HYDROGEN

The role of fast metastable helium atoms in the formation of He- ions by charge-changing collisions during the passage of 100 kev helium beams through hydrogen has been investigated quantitatively. It is shown that He - ions are formed by collisions involving one-electron capture by fast metastable helium atoms while all other possible production mechanisms are found to be relatively insignificant. A lower bound of 5·4 ± 0·4 × 10-18 cm2 is obtained for the cross section for He- formation from He(2 3S) atoms.