Absolute double differential ionization cross-section for electron impact: He

A complete set of absolute double differential cross-section (DDCS) for electron impact ionization of helium has been measured at an incident energyE 0=500 eV. The angular distributions of the ejected and scattered electrons between 40 and 435.5 eV have been measured over the angular range of (10÷145)o. This work supplements the mapping of DDCS for ejected electron energies close to (E 0-IP)/2 (IP is the He 1s ionization energy), a region where the experimental data are fragmentary. The possibility of representing the full Bethe surface with a simple functional form is investigated.