Coincidence study of the electron impact ionisation of neon: momentum density determination and test of various scattering models

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Abstract
Triple differential cross sections for the ionisation of the 2p and 2s orbitals or neon by 8 keV electron impact are measured in a coplanar e-2e experiment under very asymmetric conditions. The angular distributions are made absolute by comparing with the corresponding double differential cross sections for the scattered electrons separately measured on an absolute scale via Bethe sum rule normalisation. A large scattering angle, the plane-wave impulse approximation is found to be satisfactorily reduce the 2p data to a Hartree-Fock momentum distribution, both in shape and magnitude while it fails for the 2s data where magnitude is concerned, although both 2p and 2s ionisation are measured under identical conditions. Excellent agreement with experiment is obtained when using a first Born-Coulomb approximation. At small scattering angles, none of the theoretical models considered succeeds in completely describing the experiment, especially for the recoil intensity. The overall best agreement is obtained using the Born-Coulomb calculations. However, the adjustable effective ion charge appears to be different for the binary and recoil intensities, and it also a function of scattering angle.