PIXE analysis of high Z complex matrices

The study of complex materials (nonhomogeneous matrices containing medium a nd/or heavy atoms as major elements) by PIXE requires the tailoring of the experimental set up to take into account the high S-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 achieva ble for low Z matrices (Z less than or equal to 20). Additionally, those hi gh Z matrices having a high absorption capability, are not always homogeneo us. The nonhomogeneity may be, on the one hand, a layered structure (which is uneasy to profile by RES if the material contains elements of neighbouri ng masses or if the layered structure extends on several microns) or, on th e other hand, inclusions which are to be localized, PIXE measurements at va rious incident energies (and with various projectiles (p, d, He-3, He-4)) a re then an alternative method to overcome those difficulties. The use of sp ecial filters to selectively decrease the intensity of the most intense X-r ay lines, the accurate calculation of the characteristic X-ray intensity ra tios (K alpha/K beta, L alpha/L beta) of individual elements, the computati on of the secondary X-ray fluorescence induced in thick targets are amongst the most important parameters to be investigated in order to solve these d ifficult analytical problems, Examples of Cr. Fe, Ni, Cu, Ag and Au based a lloys with various coatings as encountered in industrial and archaeological metallurgy are discussed, RES, PIGE and NRA are sometimes simultaneously n ecessary as complementary (or basic) approaches to identify corroded surfac e layers. (C) 1999 Published by Elsevier Science B.V. All rights reserved.