A kind of X-ray fluorescence analysis involving the measurement of the wavelength spectrum of the emitted radiation e.g. by using a diffraction grating or crystal.
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2526 (https://doi.org/10.1351/pac199466122513)