Double differential cross sections for electron and positron impact ionization of helium

Double differential cross sections (DDCS) for electron and positron impact ionization of helium atom have been calculated for asymmetric geometry at some selected sets of incident (Ei=200 and 300 eV) and ejected (E2=10 and 20 eV) energies. In the present prescription, the projectile-electron correlation term in the final channel has been taken into account in the framework of the eikonal approximation and the final state wavefunction satisfies the asymptotic boundary condition for asymmetric geometry. Cross sections are presented versus the ejected angle and are compared with the experiments for electron impact. Reasonable agreement is noted with the measurements of Mueller-Fiedler et al. for lower E2 and Shyn et al. for higher E2. ((orig.))