Heterogeneous Example: Shielding of XRF by Plastic Container
This 1-mm thick acrylic holder decreased the intensity of the XRF signal from a pure cadmium sample by ~25%. In this case, the background from the holder led to false positives in routine analytical (metal/alloy)mode. The radiation backscattered from the thick plastic is interpreted by the quantitation software as a positive for other elements with emission lines in the region of 20-30 keV (Ag and In, indicated with red arrows). An experienced analyst would generally be able to identify likely false positives by looking at the spectrum.
Shown to the right is a comparison with the much thinner 1-mil Mylar sheet, which has essentially no effect on the XRF analysis. Plastic and other carbon-based materials are mostly transparent to the XRF signal.