The sample is bombarded with X-rays. This excites the sample to generate X-ray fluorescence. The X-rays “shoot” individual electrons out of the atoms of the elements, primarily out of the inner atomic shells K and L. The resulting vacancies are filled up again by electrons from higher energy shells.
The excess energy of these electrons is then emitted in the form of X-ray fluorescence radiation. This radiation is characteristic for each element like a fingerprint and independent of the atom’s chemical bond. The intensity of the radiation is proportional to the concentration of the element in the sample.
In the case of wavelength dispersive X-ray fluorescence (WDXRF) each element is analyzed under optimal measurement conditions.
For this purpose individual combinations of measurement parameters are set corresponding to the concentration range and to prevent line overlaps:
The X-ray source and primary radiation filter guarantee that each element in the sample is optimally excited.
The masks cut out unwanted signals, e.g. from the sample cup.
The vacuum seal separates the sample chamber from the goniometer chamber. During loading the seal is closed and the goniometer chamber remains under vacuum. Therefore only the small volume of the sample chamber needs to be evacuated for solids or flushed with helium for liquids. During the measurement of liquids the vacuum seal stays closed to protect the components in case of spillage, safes helium and enhances the stability.
The collimators are used for improving resolution.
The analyzer crystals play a crucial role. They break down the multiple frequency fluorescence spectrum into the specific wavelengths for the elements. This signal separation is crucial for the outstanding resolution and sensitivity of WDXRF.
And finally, the detectors: For the detection of light elements a proportional counter and for the heavier elements a scintillation counter is used. Both detectors are perfectly suited to the respective energy range.
The S2 PUMA with HighSenseTM technology uses the 50-W end-window X-ray tube to directly excite X-ray fluorescence in a sample.
By setting the high voltage for the X-ray tube and choosing the filter material, the energy range is selected.
The Silicon Drift Detector with multi-channel analyzer detects the X-ray fluorescence radiation and accumulates counts to form an intensity versus energy spectrum of the sample.
Lighter elements with low-energy fluorescence are analyzed by either flushing the sample chamber with helium or by evacuating it with a vacuum pump.