Simultaneous WDXRF Spectrometers

A simultaneous WDXRF system uses multiple channels, with each channel having its own crystal/detector combination optimized for a specihc element or background measurement. Instruments with as many as 40 hxed crystal/detector channels or as few as two are available. These systems are designed for specihc applications, such as the analysis of steel in a production facility where hundreds of samples must be analyzed for the same suite of elements every day. They have the advantage of being very fast compared with a sequential system, but are not hexible. 

Most simultaneous systems have the X-ray tube above the sample, with the sample facing up. As discussed earlier, this makes the analysis of liquids difficult or impossible. Several instrument manufacturers offer combination systems with a simultaneous set of channels as well as a sequential monochromator. These systems offer the speed needed for routine analysis and the hexibility needed for nonroutine analysis, but are expensive. 

When measuring trace and major elements simultaneously, the generator is normally set so that the trace elements can be measured with the highest possible intensity. Absorbers or attenuators are then needed for the major element channels to reduce their intensities so that they are in the operational range of the detectors. 

While the fixed channels are used exclusively for quantitative analysis, a scanner or movable channel may be installed in the vacuum chamber to provide qualitative analysis ability and some flexibility in what is otherwise a system with a fixed suite of elements. 

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Table 8.40 compares the main characteristics of WDXRF and EDXRF. Multidispersive XRF combines the benefits of the WDXRF technique for routine elemental analysis with the complete flexibility offered by EDXRF for nonroutine analysis. Clearly, modem XRF instrumentation is rather varied, ranging from simple benchtop EDXRF equipped with a low-power X-ray tube and high-resolution proportional counter for some key elements, to 4 kW simultaneous multichannel spectrometers with 28 fixed element channels for... 

There are three types of WDXRF instruments sequential spectrometers, which use a goniometer and sequentially measure the elements by scanning the wavelength simultaneous spectrometers, which use multiple channels, with each channel having its own crystal/detector combination optimized for a specific element or background measurement and hybrid spectrometers, which combine sequential goniometers or scanners with fixed channels as well as XRD channels and goniometers. Hybrid instruments will be discussed in Section 8.4 with XRD instruments. 

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