Measurements of non-Rutherford cross sections for 4-15 MeV alpha particles on light elements from C to Si

These last years Ion Beam Analysis users show an interest in High Energy Alpha beams[1].
These beams can be used for on-site analysis by means of radioactive sources e.g. for space
application but they also offer a powerful combination of properties for the analysis of thick
layers (about 10 to 20 µm). This kind of layers is often met in cultural heritage applications
but can be also present on new materials. Contrary to this kind of materials where the
principal information needed is the in-depth profiles as the sample are of known
composition, for cultural heritage materials the combination of elemental analysis and their
in-depth distribution is essential as the nature of the material is a-priori not known. In this
perspective high energy alpha beams can produce really interesting results as their PIXE
cross-sections increase from 6 MeV while the lower penetration of the beam (comparing to
classical protons beams) allows to limit the analysis to the layer of interest. For the
elemental in depth distribution we take advantage of the good mass separation of the alpha
particles and the non-Rutherford phenomena allow the analysis even of light elements
which are of great interest in cultural heritage problematic as far as the cross section are
well tabulated.
Using two IBA facilities (AGLAE in Paris and the HE-HR beam line of the cyclotron in Liège
University[2]) we explored the backscattering cross section of numerous light elements
(from C to Si) from 4 to 15 MeV in order to check the lack in the literature, to verify the
deviation from Rutherford law and compare it to the existing theoretical models. We begin
to measure the needed cross sections using thick target in case of smooth cross section and
thin layers for exploring important variation of the cross section.