High frequency and short wavelength
According to German standard DIN EN 12681 (2003-06, together with the VDG P541 82001 standard for thicker-walled parts) or according to the ASTM E689-10 standard, conventional X-ray (or other radiographic) testing is a non-destructive test for the two-dimensional inspection of components in order to locate internal defects. Due to their high frequency and short wavelength, x-rays can penetrate any material.
The x-rays always follow a straight-line trajectory; they cannot be diffracted or bent (as, for example, light rays). They can, however, be weakened by the atoms of the material as they travel through; parts of the ray are absorbed or diffused. How much of the initial radiation reaches the detector depends on the energy of the radiation, the part measurements (thickness), and the physical properties (density) of the material. Material defects, such as cracks, voids, inhomogeneities, etc., will have a different effect on the test radiation because of the differing density of the material at that point (in comparison to a “perfect” section of material). This difference is then measured by a detector (x-ray sensitive film), which records the intensity of the radiation exiting the test object (i.e., how much of the radiation “made it through”).