Angular dependence of energy loss in proton-helium collisions

Abstract

The energy loss of 50 to 250 keV protons scattered under single-collision conditions from He atoms is investigated in terms of its dependence on the angle of scattering. At the higher projectile energies we observe an enhanced energy loss at scattering angles around 0.5 mrad. Such a behavior cannot be understood on the basis of two-body scattering models. Based on our theoretical studies we show that the combined effects of the screened target potential and of electronic transitions have to be considered for the energy loss of proton scattering in light gases. As a representative example we display in Fig. 1 an energy-loss spectrum from 200 keV protons for a projectile scattering angle of 1 mrad. The dominant peak is due to elastic collisions and indicates an overall energy resolution of about 9 eV. The second peak at about 23 eV corresponds mainly to single-excitation processes. Double excitation should lead to energy losses between 58 and 79 eV and a structure seems to be present at those energies. Also displayed in Fig. 1

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Electronic Excitations of Slow Ions in a Free Electron Gas Metal: Evidence for Charge Exchange Effects

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