Helium Symmetric (e,2e) Data
- Excess Energy = 40eV -
page prepared by
Murray (25th July, 1996)
Figure 1. The (e,2e) Differential cross section for an incident electron of energy 64.6eV (40eV excess energy) above the helium ionisation threshold.
The results have been parameterised in terms of the irreducible basis set that is used to fit all of the data taken at Manchester. This allows the results to be presented using a common 'language'.
The results have been normalised to unity at the common normalisation point at 90 degrees. The Differential cross section shows clear forward and backward scattering lobes. The cross section in the forward direction is significantly larger than that in the backward direction, indicating that single binary collisions are increasingly dominating the overall structure at this energy. The non-central lobes seen in the perpendicular plane are approximately equal in magnitude to the central lobe in this geometry.
The parameterisation again allows a 3-D picture to be established of the differential cross section surface, where the surface is traced out by the magnitude of the differential cross section at a given detection angle (theta, phi) around the scattering geometry.
Figure 2 shows the result of this 3-D fitting to the data presented above.
Figure 2. A 3-D model of the differential cross section surface at an excess energy of 40eV.
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