ERDA with an external helium ion micro-beam: Advantages and potential applications

• Published in: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 2001-07, Vol.181 (1), p.180-185
• Main Authors: Calligaro, T., Castaing, J., Dran, J.-C., Moignard, B., Pivin, J.-C., Prasad, G.V.R., Salomon, J., Walter, P.
• Format: Article
• Language: English
• Subjects: ERDA; External beam; Helium ion; Hydrogen analysis; Microprobe
• ISSN: 0168-583X; 1872-9584; 1872-9584; 0168-583X
• DOI: 10.1016/S0168-583X(01)00329-9

Preliminary ERDA experiments at atmospheric pressure have been performed with our external microprobe set-up currently used for the analysis of museum objects by PIXE, RBS and NRA. The objective was to check the feasibility of hydrogen (and deuterium) profiling with an external beam of 3-MeV helium ions. The standard scattering geometry (incident beam at 15° with respect to sample surface and emerging protons or deuterons at 15° in the forward direction) was kept, but the thin foil absorber was replaced by helium gas filling the space between the beam spot and the detector over a distance of about 84 mm. Several standards prepared by ion implantation, with well known H or D depth profiles, were first analysed, which indicated that the analytical capability was as good as under vacuum. A striking feature is the much lower surface peak than under vacuum, a fact that enhances the sensitivity for H analysis near the surface. The same type of measurement was then performed on different materials to show the usefulness of the technique. As a first example, we have checked that the incorporation of H or D into sapphire crystals during mechanical polishing is below the detection limit. Another example is the measurement of the H content in emeralds which can be used as an additional compositional criterion for determining the provenance of emeralds set in museum jewels. The advantages and limitations of our set-up are discussed and several possible applications in the field of cultural heritage are described.