Energy Transfer to Electrons in Fast Proton Collisions

When a fast charged particle traverses a medium it leaves energy primarily by interactions with atomic electrons. Calculations regarding track structure, therefore, require knowledge of the energy and angular distribution of secondary electrons as a source term. Distributions for electrons ejected from several target gases by protons with energies from 300 to 2000 keV have been measured. This paper describes the cross section for energy transfer in primary proton interactions as deduced from the measured electron ejection cross sections. Distributions of kinetic energy transferred to electrons ejected from representative low atomic number targets are presented and effects on these distributions resulting from changes in incident proton energy and atomic number of the target are described. Comparisons are made of measured and calculated cross sections to show the degree of applicability of current theory.