Determination of material flaw size by intensity evaluation of polychromatic X-ray transmission

X-ray testing is a powerful tool for nondestructive quality control. Hidden structures can be made visible and the attenuation of the incident radiation in the probe can be used to determine film thickness or flaw extensions. Advanced intensity evaluation for polychromatic X-ray sources allows exact determination of thickness profiles in the beam direction and is compared to the usually applied assumption of monochromatic X-ray attenuation. Both cases, monochromatic as well as polychromatic attenuation, are discussed, the error introduced by making the assumption is shown and in consequence a gauge function for thickness measurement is introduced. Moreover, the influence of the different attenuation processes like photoabsorption, and coherent and incoherent scattering in the various energy ranges is investigated. As a result, a correction to incoherent scattering coefficients in special energy ranges is suggested.