Simultaneous wavelength-dispersive spectrometers

The instrumentation for EM uses the same type of X-ray spectrometers discussed in detail in Chapter 8, with an electron beam as the source and a UHV system that includes the sample compartment. An ED X-ray spectrometer allows the simultaneous collection and display of the X-ray spectrum of all elements from boron to uranium. The ED spectrometer is used for rapid qualitative survey scans of sample surfaces. The wavelength dispersive spectrometer has much better resolution and is used for quantitative analysis of elements. The WD spectrometer is usually equipped with several diffracting crystals to optimize resolution and to cover the entire spectral range. The electron beam, sample stage, spectrometer, data collection, and processing are all under computer control. 

Among wavelength-dispersive spectrometers, a distinction can be made between single-channel instruments and multi-channel spectrometers. In the former type of instrument, a single dispersive crystal/detector combination is used to sequentially measure the X-ray intensity emitted by a sample at a series of wavelengths when this sample is irradiated with the beam from a high power (2—4 kW) X-ray tube. In a multi-channel spectrometer, many crystal/detector sets are used to measure many X-ray Unes/elements simultaneously. 

Since modern FTIR spectrometers can operate in a rapid scan mode with approximately 50 ms time resolution, TRIR experiments in the millisecond time regime are readily available. Recent advances in ultra-rapid scanning FTIR spectroscopy have improved the obtainable time resolution to 5 ms. Alternatively, experiments can be performed at time resolutions on the order of 1-10 ms with the planar array IR technique, which utilizes a spectrograph for wavelength dispersion and an IR focal plane detector for simultaneous detection of multiple wavelengths. ... 

X-ray spectroscopy is nowadays applied mostly in the form of X-ray fluorescence, where scanning monochannel machines, sequence spectrometers and simultaneous spectrometers are used in wavelength dispersive X-ray fluorescence. The introduction of bent analyser-crystals extended the method to smaller samples, thus marking another step toward microprobe analysis. 

In this analysis, three wavelength-dispersive X-ray spectrometers were used to simultaneously measure the characteristic X-ray intensities for copper, barium, and yttrium, at each point in the scan, producing two-dimensional X-ray intensity arrays. Complete quantitative analysis corrections, using the NBS theoretical matrix correction procedure FRAME (2), were performed at each picture element (pixel) in the image scan. 

There are two types of MIR spectrometers, dispersive and Fourier-transform (FT) spectrometers. Today FT spectrometers are used predominantly. The most significant advantage of FT spectrometers is that radiation from all wavelengths is measured simultaneously, whereas in dispersive spectrometers all wavelengths are measured consecutively. Therefore, a FT spectrometer is much faster and... 

Understanding how nanoenergetic materials are both made and consumed requires the ability to monitor these processes widi real time in-situ diagnostic techniques. Laser Induced Breakdown Spectroscopy (LIBS) is an optical technique that can detect all the elements simultaneously from very small sanq>les of material. Only four elements are needed to implement this technique an excitation source, delivery and collecting optics, a detector with wavelength dispersion capability, and a conqtuter for control and anal is. Because of these relatively sinq>le requirements, a conq>lete LIBS system can be made contact, rugged, and fairly ine q>ensively. Spectrometers are now becoming commercially... 

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