Absorption edge

Arête d'absorption (Fr). Absorptionskante (Ge). Spigolo di assorbimento(It). 吸収端 (Ja). край поглощения (Ru). Canto de absorción (Sp).

Definition

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, L_I, L_II, L_III, etc. corresponding to the creation of electron holes in the 122s22, 2s, 2p_1/2, 2p_3/2 etc. atomic subshells).

Associated with this transition is the absorption threshold (q.v.) characterized by the corresponding energy E₀.

Examples

For gallium: [math]\lambda_{K}[/math] = 1.1958 Ǻ; [math]\lambda_{L_{I}}[/math] = 9.5446 Ǻ; [math]\lambda_{L_{II}}[/math] = 10.8414 Ǻ; [math]\lambda_{L_{III}}[/math]= 11.1038 Ǻ.

For arsenic: [math]\lambda_{K}[/math] = 1.0448 Ǻ; [math]\lambda_{L_{I}}[/math] = 8.1195 Ǻ; [math]\lambda_{L_{II}}[/math] = 9.1187 Ǻ; [math]\lambda_{L_{III}}[/math]= 9.3617 Ǻ.

See also

• Absorption threshold
• Fermi level
• Section 4.2.3 of International Tables for Crystallography, Volume C