Excitation processes in helium

Abstract
An experimental study of the radiation emitted by helium under controlled electron impact is described. The observations are analyzed, together with those of previous workers, to yield values for the excitation functions of S, P and D states. The mechanism of excitation transfer between excited states is analysed in terms of radiative and collisional processes; cascade processes being found to be more important than has hitherto been assumed. The total inelastic (less ionization) cross-section at 108 eV is found to be 2·9 x 10-17 cm2.