FULLY DETERMINED (E,3E) EXPERIMENTS FOR THE DOUBLE-IONIZATION OF HELIUM

Angular distributions of the two ejected electrons following electron impact double ionization of helium have been measured using a multicoi ncidence multiangle (e,3e) spectrometer at an incident energy similar to 5.5 keV and equal outgoing energies E-b = E-c = 10 eV. The measured distributions are similar to photodouble ionization (hv, 2e) ones, bu t with evidence of additional nondipolar contributions which tend to t ill up the characteristic node at the mutual angle theta(bc) = 180 deg rees. They are also in satisfactory agreement with recent (e, 3e) calc ulations. [S0031-9007(98)07708-4].