Heterogeneous Example: Shielding of Tin Disk by Pad of Paper.
A pad of white paper that is ¼” inch (6.4 mm) thick reduces the intensity of the lines of a pure tin disk by ~3-fold (Innov-X a-2000, Analytical mode, acquisition time 34 seconds). Note there are false positives due to the increased backscatter background from the paper in the 20-30 keV region, indicated by red arrows (LE = light elements, e.g., from C,O in the paper). Paper, wood and other light materials are weak absorbers of radiation and appear mostly invisible to x-rays. Thus, XRF is effective for detecting heavy elements embedded in a light matrix.