Microprobe x-ray fluorescence with the use of point-focusing diffractors

A toroidal point-focusing mica crystal diffractor was used to focus monochromatic x rays from a microfocus x-ray source operated at 0.1 mA and 30 kV. The Cu Kα x-ray focal spot of 50 μm×85 μm had 1.6×104 photons/s/μm2. Microprobe x-ray fluorescence (MXRF) spectra were recorded with a Si(Li) energy dispersive detector for bulk specimens of GaAs, Si, and Muscovite. Low background due to monochromatic excitation resulted in predicted detection limits as low as 2 ppm for a measurement time of 500 s. Laboratory MXRF systems based on point-focusing diffractors were shown to provide lower detection limits, larger working distance, and higher theoretical intensity than systems using capillary optics.