TARGET AND MATRIX PROBLEMS IN THE DETERMINATION OF TRACE-ELEMENTS IN WOOD MATERIAL BY PIXE

Here, we present the analysis of wood to determine trace elements in t ree rings. We have irradiated wood pieces directly, for thick target P IXE, and also thin samples obtained by chemical treatment of the wood material. Proton beam energies of 2.2 and 6.6 MeV were used to irradia te the targets. A controlled amount of Yttrium was added to the soluti on during sample preparation as an internal standard. This simplifies the normalization of our PIXE results and permits a minimization of er rors in the determination of the solid angle and the proton total char ge. A calibration of the PIXE results was performed by using a referen ce material from the National Institute of Standards and Technology (N IST). This allowed fitting some parameters used in the quantitative an alysis program (TTPIXAN). Two problems related with thick target analy sis were solved: high background radiation and the impossibility to mo nitor the beam current. The background was diminished by the depositio n of a graphite layer on targets. A thin gold foil placed before the t arget, but shielded from the detector, permitted integration of the ch arge by a conductor wire. (C) 1998 Elsevier Science B.V.