X‑COAT ‑ Characterisation of layered structures by a combination of X‑ray flourescence and Compton imaging

X-ray fluorescence is a method to measure the atomic composition of a substance or an object. The object is excited by a primary beam and the fluorescent photons emitted from the object are registered. The depth sensitivity depends mainly on the fluorescence energy of the atoms of interest. In addition, the primary beam will undergo Compton scattering. The Compton signal carries information on interior properties of the object and can, for example, be used to find voids in a layered object. The method is targeting paper mills and can be demonstrated for paper coated with CaCO3 where the depth sensitivity of the method ideally matches the typical coating thicknesses. For a coated paper the signal will be generated from the heavier atoms in the coating and essentially be proportional to the coating weight. In addition, Compton scattered photons from the light elements in the kernel will carry information of the thickness of the kernel. The combination of Xray fluorescence and Compton scattering is a general method that will be extended to other applications in future projects.