In the XRF Spectrometry technique elements in a sample can be identified. This occurs when high-energy X-ray photons are emitted from a source (X-ray tube) and strike the sample. The photons from the X-ray tube have enough energy to knock electrons out of the innermost orbital of atoms in the sample. When a high energy photon hits an atom, it may knock electrons out of inner orbitals. When this occurs, the atoms become ions, which are unstable. Electrons seek stability and the lowest possible energy state. Therefore, a more energetic electron from an outer orbital will move into the newly vacant space in the inner orbital. Electrons in outer shells have more energy then electrons in more inner orbitals. They need to release this excess energy as they drop down to fill the vacancy in the inner shell. This released energy is given off as a photon which can be detected by an x-ray detector. The energy of the emitted energy is equal to the difference in energies between the 2 orbitals and is characteristic of the element fluorescing.