How can X-ray fluorescence identify the elements in a material?

X-ray fluorescence identifies elements in a material by utilizing the unique atomic structure of each element. The process functions as follows:12

• Excitation: A material is bombarded with a primary beam of high-energy X-rays. This radiation removes an electron from an inner shell of an atom, creating a vacancy and leaving the atom in an unstable, ionized state.341
• Emission: To regain stability, an electron from a higher-energy outer shell drops down to fill the inner-shell vacancy. As the electron transitions to this lower energy state, it releases energy in the form of a secondary, or fluorescent, X-ray photon.143
• Identification: Because the energy levels of an atom's inner shells are determined by its nuclear charge, the emitted X-rays have energies characteristic of that specific element. By measuring the energy and intensity of these diagnostic X-rays, scientists can identify which elements are present and calculate their concentration within the sample.1234

This method is highly effective because these core-level energy "fingerprints" remain largely unperturbed by the atom's chemical environment.2