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Title: K-Alpha  
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Subject: Bohr model, X-ray, K-beta, Astronomical spectroscopy, Atomic physics
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Atomic levels involved in copper Kα and Kβ emission

In X-ray spectroscopy, K-alpha emission lines result when an electron transitions to the innermost "K" shell (principal quantum number 1) from a 2p orbital of the second or "L" shell (with principal quantum number 2). 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.

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. See Siegbahn notation for the newer IUPAC-recommended spectral notation system.

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 [1]. For such purposes, the energy of the line is adequately calculated to 2-digit accuracy by the use of Moseley's law: E = (10.2 eV)\left(Z-1\right)^2, where Z is the atomic number. For example, K-alpha for iron (Z = 26) is calculated in this fashion as 10.2 eV (25)2 = 6.38 keV energy. For astrophysical purposes, Doppler and other effects (such as gravitational broadening) show the iron line to no better accuracy than 6.4 keV. [2]

Values of Transition Energies

  • Values of different kinds of transition energies like K\alpha, K\beta, L\alpha, L\beta and so on for different elements can be found in the NIST X-Ray Transition Energies Database [1] and Spectr-W3 Atomic Database for Plasma Spectroscopy [2]
  • K-alpha emission values for hydrogen-sum and helium-like ions can be found on Table 1-5 of the LNBL X-Ray Data Booklet [3]


  1. ^ NIST X-Ray Transition Energies Database [3]
  2. ^ Spectr-W3 database [4]
  3. ^ Lawrence Berkeley National Laboratory X-Ray Data Booklet [5]
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