Helium Symmetric (e,2e) Data

- Excess Energy = 5eV -

page prepared by

Andrew Murray (20th January, 1999)

5eV excess (e,2e) graph

Figure 1. The (e,2e) Differential cross section for an incident electron of energy 29.6eV (5eV 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 no longer has the Wannier model structure, and forward and backward scattering lobes are starting to evolve. The cross section in the backward direction is seen to be larger than that in the forward direction, indicating the importance of second order scattering effects from the core.

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.

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