Siegbahn notation


The Siegbahn notation is used in X-ray spectroscopy to name the spectral lines that are characteristic to elements. It was introduced by Manne Siegbahn.
The characteristic lines in X-ray emission spectra correspond to atomic electronic transitions where an electron jumps down to a vacancy in one of the inner shells of an atom. Such a hole in an inner shell may have been produced by bombardment with electrons in an X-ray tube, by other particles as in PIXE, by other X-rays in X-ray fluorescence or by radioactive decay of the atom's nucleus.
Although still widely used in spectroscopy, this notation is unsystematic and often confusing. For these reasons, International Union of Pure and Applied Chemistry recommends another newer nomenclature. The table below shows a few of the common electronic levels with their names in Siegbahn and IUPAC notation.

History

The use of the letters K and L to denote X-rays originates in a 1911 paper by Charles Glover Barkla, titled The Spectra of the Fluorescent Röntgen Radiations. By 1913, Henry Moseley had clearly differentiated two types of x-ray lines for each element, naming them α and β. In 1914, as part of his thesis, Ivar Malmer, a student of Manne Siegbahn, discovered that the α and β lines were not single lines, but doublets. In 1916, Siegbahn published this result in the journal Nature, using what would come to be known as the Siegbahn notation.

K-alpha

K-alpha emission lines result when an electron transitions to the innermost "K" shell from a 2p orbital of the second or "L" shell. The line is actually a doublet, with slightly different energies depending on spin–orbit interaction energy between the electron spin and the orbital momentum of the 2p orbital. K-alpha is typically by far the strongest X-ray spectral line for an element bombarded with energy sufficient to cause maximally intense X-ray emission.
K-alpha emission is composed of two spectral lines, K-alpha1 and K-alpha2. The K-alpha1 emission is higher in energy and thus has a lower wavelength than the K-alpha2 emission. A larger number of electrons follow the K-alpha1 transition relative to the K-alpha2 transition which causes the K-alpha1 emission to be more intense than K-alpha2. For all elements, the ratio of the intensities of K-alpha1 and K-alpha2 is very close to 2:1. K-alpha1 and K-alpha2 are close enough in wavelength that an average of the two wavelengths, K-alpha, is used in x-ray diffractometry without separation by a monochromator, which would cause a significant loss in the intensity of the incident beam.
The analogous K-alpha spectra line in hydrogen is known as Lyman alpha; however because of hydrogen's small nuclear charge, this line is in the ultraviolet, not the X-ray range.
An example of K-alpha lines are those seen for iron as iron atoms radiating X-rays spiralling into a black hole at the center of a galaxy. For such purposes, the energy of the line is adequately calculated to 2-digit accuracy by the use of Moseley's law:, where Z is the atomic number and Ry=Rydberg energy=13,6 eV. For example, K-alpha for iron is calculated in this fashion. For astrophysical purposes, Doppler and other effects show the iron K-alpha line to better accuracy than 6.4 keV.

Values of transition energies

K-beta emissions, similar to K-alpha emissions, result when an electron transitions to the innermost "K" shell from a 3p orbital of the third or "M" shell.
Values can be found in the X-Ray Transition Energies Database.