Characteristic X-ray

Characteristic X-rays were discovered by Charles Glover Barkla in 1909,[1] who later won the Nobel Prize in Physics for his discovery in 1917.

Characteristic X-rays are produced when an element is bombarded with high-energy particles, which can be photons, electrons or ions (such as protons).

After the electron has been ejected, the atom is left with a vacant energy level, also known as a core hole.

However, X-ray science has special terminology to describe the transition of electrons from upper to lower energy levels: traditional Siegbahn notation, or alternatively, simplified X-ray notation.

By posing that initially in the K shell there is a single vacancy (and, hence, a single electron is already there), as well as that the L shell is not entirely empty in the final state of the transition, this definition limits the minimal number of electrons in the atom to three, i.e., to lithium (or a lithium-like ion).

[4] In the case of two- or one-electron atoms, one talks instead about He-alpha and Lyman-alpha, respectively.

[5] This choice also places K-alpha firmly in the X-ray energy range.

K-beta emissions, similar to K-alpha emissions, result when an electron transitions to the innermost "K" shell (principal quantum number 1) from a 3p orbital of the third or "M" shell (with principal quantum number 3).

Accurate values of transition energies of Kα, Kβ, Lα, Lβ, and so on for different elements can be found in the atomic databases.