Energy-dispersive X-ray spectroscopy
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The energy dispersive X-ray spectroscopy (EDX or EDS) is a method used to determine the energy spectrum of X-ray radiation. It is mainly used in chemical analysis, in a X-ray fluorescence spectrometer (especially portable devices), or in an Electron Microprobe (e.g. inside an scanning electron microscope).
The detector is a semiconductor, usually silicon doped with lithium (Si(Li) detector). The semiconductor is polarised with a high voltage; when a X-ray photon hits the detector, it creates electron-hole pairs that drift due to the high voltage. The electric charge is collected, it is like charging a condensator; the increment of voltage of the condensator is proportional to the energy of the photon, it is thus possible to determine the energy spectrum. The condensator voltage is reset regularly to avoid saturation.
To reduce the electronic noise, the detector is cooled by Peltier effect or best by liquid nitrogen.
In recent years a new type of EDS detector has become commercially available based on a superconducting microcalorimeter. This microcalorimeter spectrometer has the simultaneous detection capabilities of the EDS combined with the high spectral resolution of the WDS. Unlike the semiconductor EDS the microcalorimeter measures the temperature change caused by the absorption of the x-ray photon in the detector, as such the detector must be maintained at ultra low temperatures (~100mK) by the use of liquid helium and/or an adiabatic demagnetisation refrigerator (ADR). In essence the microcalorimeter is a super sensitive thermometer. The microcalorimeter EDS has suffered from a number of drawbacks compared with conventional detectors which scientists are now addressing, these include; low count rates, poor collection efficiencies and small detector areas. These drawbacks have been overcome somewhat by the use of arrays of detectors and x-ray focusing optics.
See also
External Links
- The Science of Spectroscopy (http://www.scienceofspectroscopy.info) - supported by NASA, includes OpenSpectrum, a Wiki-based learning tool for spectroscopy that anyone can edit
- All About The Microcalorimeter (http://www.bonus.com/contour/Black_holes_sci/http@@/imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-micro.html)
- New Breakthrough in Cryogenic X-ray Microcalorimeters (http://www.nist.gov/public_affairs/releases/n96-47.htm)
- Microcalorimeter EDS With 3 eV Energy Resolution (http://www.xos.com/abstracts/daw2.htm)
- Princeton Gamma-Tech (http://www.pgt.com) - Manufacturers of Energy Dispersive Spectrometers for Microanalysis
- EDAX (http://www.edax.com) - Advanced Materials Analysis both EDS and WDS
- BRUKER-AXS (http://www.bruker-axs.de) - EDX & WDX Spectrometers and X-Ray Diffraction.
fr:Analyse dispersive en énergie de:Röntgenfluoreszenzanalyse