Proton-induced X-ray analysis was studied at the 5 MV Van de Graaff accelerator of Tohoku University with emphasis on backing materials and the angular dependence of the background due to bremsstrahlung. From the practical viewpoint, 4 μm Mylar films among Formvar, carbon and Mylar gave sufficiently low background spectra and good mechanical strength. The detection limit was much improved in the backward direction in comparison with that at 90° which has usually been adopted. A detection sensitivity on the subpicogram level was obtained for an extensive range of elements covering a wide range of atomic number using 4 μm Mylar film backing.
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