IMPACT PARAMETER DEPENDENCE OF THE ENERGY-LOSS OF FAST PROTONS IN SINGLE COLLISIONS WITH NOBLE-GAS ATOMS

The have measured energy loss spectra of protons with energies ranging from 50 to 250 keV interacting with noble gas atoms in small angle sc attering under single collision conditions. The high overall energy an d angular resolution of our setup allows for a reliable determination of the mean energy loss and straggling. We have measured these quantit ies in dependence on the angle of scattering and compare our data with theoretical work. In the collisions with helium atoms we find evidenc e for three-body effects in the stopping of the projectiles.