Energy dependence of binary encounter electron emission in collisions of screened heavy Bi26+ ions with He gas targets

Double differential emission cross sections d(2)sigma/dE(e)d Omega(e) (DDCS ) of electron emission in collisions of highly charged and partially stripp ed ions with gas targets deviate dramatically from the predictions of simpl e theories like the First Born and Binary Encounter (BE) Approximation [C. Kelbch et al., Z. Phys. D 22, 713 (1992) and P. Richard er al., J. Phys. B 23, L213 (1990)] ([1],[2]). In our experiment the electron emission cross s ections were investigated in collisions of partially stripped Bismuth ions with Helium gas targets at projectile energies in the range 1.4 less than o r equal to E-p less than or equal to 6.0 MeV/u. DDCS of electron emission h ave been measured as a function of the electron emission energy E-e and the observation angle delta(e). The data show systematic enhancement of the BE electron emission for all projectile energies. For the lowest projectile e nergy the predicted diffraction structures in the Binary Encounter peak wer e observed at angles between 35 degrees and 45 degrees.