Helium Symmetric (e,2e) Data

- Excess Energy = 20eV -

page prepared by

Andrew Murray (25th July, 1996)

20eV excess (e,2e) graph

Figure 1. The (e,2e) Differential cross section for an incident electron of energy 44.6eV (20eV 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 backward direction is still larger than that in the forward direction, although the lobes are starting to become more equal in size. Extra lobes are clearly seen in the perpendicular plane.

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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