Practical Electron Microscopy and Database

The mean free path of X-rays in materials refers to the average distance that X-ray photons travel through a material before undergoing an interaction such as absorption or scattering. This parameter is crucial in X-ray-based techniques, such as X-ray diffraction (XRD) and X-ray fluorescence (XRF), as it determines the penetration depth and the amount of material that can be analyzed. The relatively large mean free paths of X-rays, particularly those of high-energy photons, allows signals to be collected from a large volume of the sample probed by the electron beam. The mean free path varies significantly depending on the energy of the X-rays and the composition of the material. For example, in a dense material like lead (Pb), the mean free path for X-rays with an energy of 10 keV is approximately 0.01 mm, whereas in a lighter material like silicon (Si), the same X-rays might have a mean free path of about 0.15 mm. At higher energies, such as 100 keV, X-rays can penetrate much deeper, with mean free paths in silicon extending to several centimeters. Understanding the mean free path is essential for selecting appropriate X-ray energies and materials for specific applications, ensuring accurate depth profiling and quantitative analysis in scientific and industrial settings.