Abstract
Cross sections for ionization with excitation and for doubleexcitation in helium are evaluated in a full second Borncalculation. These full second Born calculations are comparedto calculations in the independent electron approximation, wherespatial correlation between the electrons is removed. Comparison is also made to calculations in the independent timeapproximation, where time correlation between the electrons isremoved. The two-electron transitions considered here arecaused by interactions with incident protons and electrons withvelocities ranging between 2 and 10 au. Good agreementis found between our full calculations and experiment, exceptfor the lowest velocities, where higher Born terms are expectedto be significant. Spatial electron correlation, arising frominternal electron-electron interactions, and time correlation,arising from time ordering of the external interactions, canboth give rise to observable effects. Our method may be usedfor photon impact.
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