[′eks ‚rā flu̇′res·ənt i¦mish·ən spek′träm·əd·ər] (spectroscopy) An x-ray crystal spectrometer used to measure wavelengths of x-ray fluorescence; in order to concentrate beams of low intensity, it has bent reflecting or transmitting crystals arranged so that the theoretical curvature required can be varied with the diffraction angle of a spectrum line.