2.5.3.4. Naming Transitions

In theory, characteristic X-rays are named according to the shell being filled and the number of shells changed by the electron is indicated by a (1 shell), b (2 shells), or g (3 shells). However, spectrographic nomenclature was developed before atomic electronic structure was well-understood, producing many inconsistencies. In the example above, the 3d - 2p transition produces lines named La₁, La₂, and Lb₁; however, the Lb₁ line does not represent a transition of 2 shells. In 1991, the Union of Pure and Applied Chemistry recommended using an energy-level-based nomenclature, but this is not widely used. According to the UPAC scheme, the Ka₁ line would be called K-L₃. The transitions shown in Figure 2.5.3.4 are for the element barium (Ba), but spectral lines produced by a given transition have the same name in all atoms.

Figure 2.5.3.4. Electron energy level diagram for barium (Z = 56). The Greek letters show the nomenclature conventionally applied to the most probable electron transitions to the K, L and M shells, and the resulting characteristic X-ray emissions.

The table below lists the most important transitions and gives line names and intensities relative to the Ka, La or Ma line intensities.

 

X-RAY NAMES FOR SELECTED ELECTRON TRANSITIONS
Numbers in parentheses are relative intensities compared with alpha lines.

Copyright 1997-2003, James H. Wittke

Last update: 01/18/2006 01:47 PM.