1eV - 50eV Excess Energy Helium (e,2e) Experimental Data Collected using Symmetric Geometry

page prepared by

A.J.Murray

22nd January, 1997.


Link to the (e,2e) Home Page

Access the Parameterisation of the (e,2e) differential cross section.

Look at the Computer controlled (e,2e) Spectrometer Hardware Page

Look at the Data where the Ion is left in an Excited State


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The following shows data collected over the incident energy range 1eV to 50eV above the ionisation threshold of Helium where the electron analysers are set to collect electrons of equal energy at equal angles with respect to the projection of the incident electron beam angle onto the detection plane:

intermediate plane geometry

The results at 1eV excess energy taken at Manchester in the perpendicular plane (Hawley-Jones et al J Phys B (1989)) and in coplanar geoemetry by the Paris group (Selles et al J Phys B (1979) are compared with a parameterisation in the Wannier picture derived by Fournier-Legarde et al J Phys B (1984).

The results at 3eV, 5eV and 10eV above threshold have recently been completed in Manchester.

Details of the results 20eV, 30eV, 40eV and 50eV above the ionisation threshold also collected at Manchester may be found in :

The experimental data is shown with the results of a parameterisation to this data using a set of universal irreducible tensorial angular functions as first proposed by

This parameterisation, and the associated results obtained from application of this model to the data, is more fully described in

Further details can also be found by accessing the WWW page: 3-D Angular (e,2e) Parameterisations


To see the results shown in the following graphs in a larger format, and to access the data, please open the link to each figure.

It should be noted that the data is normalisedwith respect to the detection angle at the point when the analysers are at a common angle of 180° in the detection plane. This point on the Differential Cross Section hypersurface is INDEPENDANT of the incident electron beam angle as discussed above.

Further, since there is an uncertainty as to the absolute differential cross sections as a function of energy, this point is normalised to unity. Resolution of this uncertainty in the future will then allow these results to be re-normalised to an absolute cross section.

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1eV Excess Energy ...............................................3eV Excess Energy

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5eV Excess Energy ...............................................10eV Excess Energy

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20eV Excess Energy ...............................................30eV Excess Energy

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40eV Excess Energy ...............................................50eV Excess Energy

To download the complete set of data from 1eV to 50eV in a text format without viewing the graphs, link to All Symmetric (e,2e) Data


Look at further results taken in the Perpendicular Plane

Look at results taken in coplanar geometry where the ion is left in an excited state

Look at the data which shows a very deep minimum in the DCS at 64.6eV Incident Energy

Look at the results ionising Argon also at 64.6eV Incident Energy


Access the Parameterisation of the (e,2e) differential cross section.

This includes a 3-D Quicktime movie of the angular evolution of the normalised differential cross section as a function of Excess Energy!


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