ABSOLUTE CROSS-SECTIONS FOR INNER-SHELL IONIZATION BY LEPTON IMPACT

We report absolute cross sections for K- and L-shell ionization of sil ver and gold targets, respectively, by lepton (electron, positron) imp act in the threshold region. The experiments were performed at the slo w positron source TEPOS facility at the linac of the Strahlenzentrum i n Giessen. A different behavior of positron and electron impact near t hreshold was observed. In comparison with theoretical calculations, ou r results suggest that the differences between electron and positron i mpact are mainly caused by the acceleration or deceleration of the inc ident projectile in the target nuclear field.