A quantitative analysis of fast metastable helium atoms in collisions involving electron loss

The attenuation of a fast beam of helium atoms by electron-loss collisions during passage through hydrogen has been carefully investigated. The measurements allow the metastable atom population of the beam to be determined and, for the first time, permit separate measurements of the electron-loss cross sections for both ground-state and metastable helium atoms. At 120 kev these are 7.3 ± 0.8 and 48 ± 8 cm 2 × 10 -17 respectively.