critical excitation energy, \(E_{\text{q}}\)

in in situ microanalysis
https://doi.org/10.1351/goldbook.C01394
Minimum energy to excite a specific analytical signal. The term is most frequently used in connection with the generation of X-ray spectra, designating the ionization (binding) energy of the orbital on which the transition ends.
Source:
PAC, 1983, 55, 2023. 'Nomenclature, symbols and units recommended for in situ microanalysis (Provisional)' on page 2027 (https://doi.org/10.1351/pac198355122023)