Tuesday, February 10, 2009

What is XRF?

X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays.

XRF is an analytical method for determining the chemical composition of all kinds of materials. The materials can be solid, liquid, power, filtered or then form. XRF can also somtimes be used to determine the thickness and composition of layers and coatings.
The method is fast, accurate and non-destructive and usually requires only a minimum of sample preparation. Applications are very broad and include the metal, cement, oil, plastic and food industries along with mining, mineralogy and geology and environmental analysis of water and waste materials. XRF is also a very useful analysis technique for research and pharmacy.
XRF - Spectrometer system can be divided into two main group:
1. Energy Dispersive System (EDXRF) and
2. Wavelength Dispersive System (WDXRF)

The elements that can be analysed and their detection level mainly depend on the spectrometer system used. The elemental range for EDXRF goes from Sodium to Uranium (Na to U). For WDXRF it is even wider, from Beryllium to Uranium (Be to U). The concentration range goes from sub -ppm level to 100%. Generally speaking the elements with high atomic numbers have better detection limits than lighter elements.
Precision and reproducibility of XRF analysis very high. very accurate results are possible when good standard specimans are available, but also in applications where no specific standard can be found.

The measurement time depends on the number of elements to be determined the required accuracy, and varies between seconds and 30 minutes. The analysis time after a measurements is only very few seconds.

Energy dispersive spectrometry
In energy dispersive spectrometers (EDX or EDS), the detector allows the determination of the energy of the photon when it is detected. Detectors historically have been based on silicon semiconductors, in the form of lithium-drifted silicon crystals, or high-purity silicon wafers.

Wavelength dispersive spectrometry
In wavelength dispersive spectrometers (WDX or WDS), the photons are separated by diffraction on a single crystal before being detected. Although wavelength dispersive spectrometers are occasionally used to scan a wide range of wavelengths, producing a spectrum plot as in EDS, they are usually set up to make measurements only at the wavelength of the emission lines of the elements of interest.

The characteristic radiation produced directly by the X-rays coming from the source is called "PRIMARY FLUORESCENCE" while that produced in the sample by primary fluorescence of other atoms is called "SECONDARY FLUORESCENCE"

3 comments:

  1. nice topic regarding sulphur analysis.

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  2. describes the generation of source and analyser very simply.

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  3. In the absence of readily available standards, the SpectroStandard® XRF Reference Materials Preparation Kit offers an alternate choice in accommodating infrequent or "out of the ordinary" sample unknowns. The unique assemblage of assorted compounds contains 50 elements to prepare "in-lab" reference materials for single or multiple elemental analyses.

    XRF Sample Preparation

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