If an Element is exposed to X-Rays of a certain energy (or wavelength) it is possible to transfer the x-ray energy to the orbital Electron making up the atoms of the element. The electrons move up an 'energy level' in the process. As these energised electrons fall back to their normal state, energy is released in the form of characteristic discrete x-ray Photons which are unique to the element in question. The process is used in analytical techniques where element identification is required.

The process is especially useful with materials which are made up of multiple elements (steel for example). XRF can be used to grade the steel by looking for % composition of certain elements such as chromium, molybdenum, and nickel. This can often be achieved with handheld XRF devices which are brought close to the specimen requiring analysis, and provides a near instantaneous results.