Theoretical and Experimental Studies on the Electron Impact Ionization of Helium at Intermediate Energies

In this work, triple differential cross section (TDCS) results on the electron impact ionization of He are presented. The experiments were performed in a coplanar asymmetric geometry with an incident electron energy of E-0 = 250 eV and scattered electron angles (theta(s)) of 7, 15, and 30 degrees, then compared with the theoretical calculations derived using the first and second Born approximations. The first Born term was calculated analytically, and the second Born term was determined in the closure approximation using semi-analytical calculations. The theoretical results were corrected by the so-called Gamow factor in order to include post-collision effects (PCI). A better agreement was found between the theoretical and experimental data for 7 and 30 degrees. As a result, we conclude that the inclusion of higher order effects is necessary to describe the ionization process.