Doubly curved crystal optics can be used to enhance traditional wavelength dispersive XRF instruments. These diffraction-based optical crystals are capable of producing high-intensity monochromatic X-ray beams using low-power air-cooled X-ray tubes. According to Bragg's law of diffraction, these three-dimensionally shaped optical crystals selectively reflect extremely narrow wavelength bands of X-rays used for sample excitation.

Monochromatic wavelength dispersive X-ray fluorescence (MWD XRF) analyzers use two doubly curved crystal optics. A typical instrument includes a low-power X-ray tube, a point-to-point focusing crystal optic for excitation, a sample cell, a second focusing crystal optic for fluorescence collection, and an X-ray detector. The first focusing crystal optic captures a narrow bandwidth of X-rays from the source and focuses this high-intensity monochromatic beam onto the sample as a small spot. The monochromatic primary beam excites the sample and emits secondary characteristic fluorescence X-rays. The second DCC collection optic collects only the relevant characteristic X-ray wavelengths within a narrow bandwidth.

This configuration offers several advantages over conventional WDXRF systems. The signal-to-background ratio is improved through monochromatic excitation using the characteristic line of the X-ray source. Second, the focusing capability of the collection crystal optic allows the use of small-area X-ray counting detectors, which reduces detector noise and enhances reliability. Monochromatic excitation also simplifies quantification and matrix effect correction. This technology results in rugged, low-maintenance online analyzers with significantly lower detection limits and faster response times.


Monochromatic WDXRF using doubly curved crystal optics offers very high sensitivity for the specific sample elements of interest. This technology has been successfully applied to the determination of low sulfur content in petroleum products.