Experimental study of the ionisation of atomic hydrogen by fast H⁺and He²⁺ions

Abstract

Cross sections for the ionisation of ground state hydrogen atoms by 38-1500 keV H + and 125-2200 keV He 2+ ions have been determined using a crossed-beam technique. Collision products produced in the intersection of the primary ion beam with a highly dissociated thermal energy beam of hydrogen are identified by time-of-flight spectroscopy and counted using a coincidence technique. Cross sections sigma (H + ) for proton impact, which involve much smaller uncertainties and cover a wider energy range than previous measurements, now permit an accurate assessment of the validity of the various theoretical predictions. Cross sections sigma (He 2+ ) for He 2+ impact, the first such measurements, are also compared with theory and measured cross section ratios sigma (He 2+ )/ sigma (H + ) are considered in terms of the Z 2 scaling predicted by the Born approximation.