ANGULAR-DEPENDENCE OF ENERGY-LOSS IN PROTON-HELIUM COLLISIONS

The energy loss of 50 to 250 keV protons scattered under single-collis ion conditions from He atoms is investigated in terms of its dependenc e on the angle of scattering. At the higher projectile energies we obs erve an enhanced energy loss at scattering angles around 0.5 mrad. Suc h a behavior cannot be understood on the basis of two-body scattering models. Based on our theoretical studies we show that the combined eff ects of the screened target potential and of electronic transitions ha ve to be considered for the energy loss of proton scattering in light gases.