ABSOLUTE TRIPLE-DIFFERENTIAL AND DOUBLE-DIFFERENTIAL CROSS-SECTIONS FOR IONIZATION OF HELIUM BY ELECTRON-IMPACT

The authors have measured absolute (e,2e) cross sections for electron impact ionisation of helium with a much higher accuracy than obtained before. In a coplanar symmetric geometry ( theta =45 degrees ) both outgoing electrons-with equal velocities-were detected in coincidence. The resulting experimental triple differential cross sections for incoming electrons of 200-2800 eV contain an experimental error smaller than 20%. At the same time the authors have determined the absolute double differential cross sections at 45 degrees to an accuracy of 10%. The data are compared with various theoretical results.