From Online Dictionary of Crystallography
Discontinuité, arête d'absorption (Fr). Absorptionskante (Ge). Canto de absorción (Sp). край поглощения (Ru). Spigolo di assorbimento (It). 吸収端 (Ja)
An absorption edge is the energy at which there is a sharp rise (discontinuity) in the (linear) absorption coefficient of X-rays by an element, which occurs when the energy of the photon corresponds to the energy of a shell of the atom (K, LI, LII, LIII, etc. corresponding to the creation of electron holes in the 122s22, 2s, 2p1/2, 2p3/2 etc. atomic subshells).
Associated with this transition is the absorption threshold (q.v.) characterized by the corresponding energy E0.
For gallium: λK = 1.1958 Ǻ; = 9.5446 Ǻ; = 10.8414 Ǻ; = 11.1038 Ǻ;
For arsenic: λK = 1.0448 Ǻ; = 8.1195 Ǻ; = 9.1187 Ǻ; = 9.3617 Ǻ;