Comparison of argon and helium (e, 2e) differential cross sections at 64.6eV using symmetric detection energies and angles

Symmetric (e, 2e) differential cross section measurements for argon at an i ncident energy of 64.6 eV are presented from the coplanar to the perpendicu lar plane geometry. The outgoing electrons were detected at symmetric scatt ering angles and with the same energy. These measurements are compared with analogous results at the same incident energy using helium as the target. The argon (e, 2e) cross section shows a rich and complex structure as the s cattering geometry changes, while the very deep interference minimum found in helium is missing.