X-Rays and Spectra
An X-ray is created when a high energy electron emitted from the beam interacts with a tightly bound inner shell electron of an atom in the specimen. When the electron beam energy exceeds the energy of the electron in its orbit (called binding energy), an electron can be ejected from the inner shell. The atom is then left in an excited state, until an electron from an outer shell drops down and fills the vacancy. When this transition occurs, the atom relaxes back down to its lowest energy state, or ground state, upon releasing energy. The released energy can be produced in two different ways, one of them being X-rays. In this characteristic X-ray process, a photon is released that equals the precise difference in binding energy between the two shells.
X-rays are detected with special instrumentation, and processed electronically into a histogram of X-ray events, referred to as a spectrum, which depicts counts versus energy. A spectrum consists of characteristic emissions (peaks) for detected elements overlaying a background. This background is formed when beam electrons pass through the atom without striking an orbiting electron. The beam electron slows down as it passes through the atom. That energy loss is expressed as background or continuum radiation in the spectra.
In the periodic table, all elements with an atomic number above that of sulfur possess visible multiple electron shells. When excited, electron transitions can occur from more than one of these shells. These transitions are strictly defined and lead to a special naming convention in X-ray work.
Emission from an L shell falling into a K orbit vacancy is called a Kα X-ray. When an M shell electron fills a K shell vacancy, the emitted X-ray is called Kβ. Kβ X-rays will always be higher in energy than Kα X-rays because the K-M energy difference is greater than the K-L energy.