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ED-XRF counters with filters and targets that can reduce the background intensities by a factor of ten or more. Usually expressed in PPM per count-per-second cps or similar units, this is the other main factor for determining detection limits, repeatability, and reproducibility.
The relative excitation efficiency is improved by having more source x-rays closer to but above the absorption edge energy for the element of interest. WDXRF generally uses direct unaltered x-ray excitation, which contains a continuum of energies with most of them not optimal for exciting the element of interest.
EDXRF analyzers may use filter to reduce the continuum energies at the elemental. Filters may also be used to give a filter fluorescence line immediately above the absorption edge, to further improve excitation efficiency.
Here, the detector together with the associated electronics counts and sorts, according to energy, all of the photons that reach it. A pulse height spectrum that indicates the number of photons or impulses for a given energy is established. Using a filter, a portion of the exciting radiation can be screened out to avoid overloading the detector. Using a goniometer, only one wavelength from the spectrum is fed to the detector, i.
In order to conduct multiple element analyses, it is necessary to create a serial measuring program that drives to and analyzes all of the lines of interest; one after another. There are, however, so-called simultaneous spectrometers: In this case, there is a set channel for each element consisting of a fixed crystal with corresponding detector arranged around the sample.
When combined with a goniometer this forms a very fast, high performance XRF instrument that is especially useful for process control. In general, it is possible to say that the two techniques are complimentary; one supplements the other. WDXRF has a resolution and sensitivity advantage which is especially useful in the range of atomic numbers up to 30 and from 55 to What kind of sample preparation methods are possible?
However, the sequential nature of WDXRF instruments and the need to readjust the geometry between measurements make them operate slowly. When monochromators are used, the crystal and detector combination is in a fixed geometry. Each monochromator measures a single element but they all work simultaneously. This set-up offers speed and precision for a given set of elements. Some instruments feature small masks that restrict the analyzed area on the sample. Combined with appropriate sample movement, this allows the measurement of an individual spot of the sample.
When samples present a defect, the ability to analyze a small area in isolation can help determine the source of the defect.
XRF instruments with a spotting capability are used for this purpose in various industries like glass and metal production.
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