PIXE analysis of high Z complex matrices

The study of complex materials (nonhomogeneous matrices containing medium and/or heavy atoms as major elements) by PIXE requires the tailoring of the experimental set up to take into account the high X-ray intensity produced by these main elements present at the surface, as well as the expected low intensity from other elements “buried” in the substrate. The determination of traces is therefore limited and the minimum detection limit is generally lower by at least two orders of magnitude in comparison with those achievable for low Z matrices (Z⩽20). Additionally, those high Z matrices having a high absorption capability, are not always homogeneous. The nonhomogeneity may be, on the one hand, a layered structure (which is uneasy to profile by RBS if the material contains elements of neighbouring masses or if the layered structure extends on several microns) or, on the other hand, inclusions which are to be localized. PIXE measurements at various incident energies (and with various projectiles (p, d, He3, He4)) are then an alternative method to overcome those difficulties. The use of special filters to selectively decrease the intensity of the most intense X-ray lines, the accurate calculation of the characteristic X-ray intensity ratios (Kα/Kβ, Lα/Lβ) of individual elements, the computation of the secondary X-ray fluorescence induced in thick targets are amongst the most important parameters to be investigated in order to solve these difficult analytical problems. Examples of Cr, Fe, Ni, Cu, Ag and Au based alloys with various coatings as encountered in industrial and archaeological metallurgy are discussed. RBS, PIGE and NRA are sometimes simultaneously necessary as complementary (or basic) approaches to identify corroded surface layers.