DISTORTED-WAVE BORN APPROXIMATION CALCULATIONS OF (E, 2E) REACTIONS

The distorted-wave Born approximation (DWBA) is discussed and samples of calculations are presented for ionization of the 2p inner shell of Ar, the 5p, 5s and 4d shells of Xe, and for ionization of He in asymmetric perpendicular plane geometry. Agreement with measurements of inner shell ionization of Ar is excellent. It is pointed out that triple differential cross sections for ionization of heavy atoms can exhibit much structure, which presents a challenge to both theory and experiment. Particular cases of 5s and 4d ionization of Xe are given as examples of situations worthy of experimental investigation. Comparison is made with very recent measurements of ionization of He in asymmetric perpendicular plane geometry. In agreement with experiment, DWBA shows at all incident energies a single main peak at phi = 180-degrees, where phi is the angle between the outgoing electrons. It is demonstrated that at high energies this peak arises from a double collision mechanism. This contrasts with energy-sharing ionization into the perpendicular plane where the double collision mechanism, dominant at high energies, gives a peak at phi = 90-degrees, and where with reducing energy this peak is replaced by one at phi = 180-degrees coming, from the single collision mechanism. Suggestions are made for further experiments.