2.5 Characteristic radiation

Historically the x-ray emission groups of lines were denoted based on the shells the electron would occupy after a transition. If the electron moves to a K shell vacancy, the emission is called K. If the transition leads to occupying a vacancy in the L shells then is call L, and so on. Such denotation was established by Siegbahn and the characteristic emission energies within one group (K, L or M) were denoted based on the probability to occur (α for the more intense lines, β for the next, γ and so on).

The notation according to the IUPAC is based on the end and origin shells for each transition, as represented in the Figure below. Therefore K_α1 emission corresponds to K-L3, K_β1 to K-M3, L_α1 to L3-M5, L_α2 to L3-M4 and so on.