Energy-Loss of Positrons in Foils

The Giessen slow positron source TEPOS delivers intense beams in the energy range between some eV and 6 keV; with postacceleration up to 80 keV. Results for remoderation are described shortly. Further the energy-losses of positrons with incident energy of 6-20 keV through thin aluminium foils were measured. Cross sections for K- and L-shell ionization of thin silver and gold targets by positron and electron impact have been determined at projectile energies of 30-70 keV. The experimental results are presented in detail; they are confirmed by calculations in plane-wave-Born approximation which include an electron exchange term and account for the deceleration or acceleration of the incident projectile in the nuclear field of the target atom.