Differential cross sections for single ionisation of He and D2 by fast protons

Differential cross sections for single ionisation of He and D2 by protons have been measured at impact energies of 3 and 6 MeV, and proton scattering angles between 0.1 and 1.0 mrad. A clear shoulder has been observed at an angle of 0.55 mrad. This feature in the differential cross sections is attributed to binary encounters between the protons and the quasi-free target electrons. The measured data are in good agreement in shape and magnitude with both a first Born approximation calculation of the ionisation and with a simple calculation of Rutherford scattering from free electrons. (author)