Applications of X-ray fluorescence

The relationship between the weight concentration of the element to be analysed and the intensity measured from one of its characteristic spectral lines is a complex one. For trace analysis several mathematical models have been developed to correlate fluorescence to the atomic concentration. A series of corrections must be introduced to account for inter-element interactions, preferential excitation, self-absorption and the fluorescence yield (the heavier atoms relax by internal conversion without photon emission). All of these factors require the reference samples to be practically the same structure and atomic composition than the sample under investigation, for all of the elements present. It is mostly because of these reasons that quantitative analysis by X-ray fluorescence is difficult to obtain. When operating upon a solid sample, a perfectly clean surface is important, preferably polished, since the analysis concerns the composition immediately close to the surface. 

This method is well adapted to quantitative analysis, where automatic identification of the spectral lines can be made by very sophisticated visual displays. Principal corrections (called ZAF) relate to atomic number (Z), nature of the isotope (A) and fluorescence (F). In semi-quantitative analysis, the software can give an approximate composition of the sample without the need for reference standards. 

6 a-rays detectors 6 a-rays sources X-rays detector 

X-ray microanalysis, for which samples must ideally be electrically conductors, allows element mapping in heterogeneous samples, if observed with a scanning electron microscope (cf Section 12.3.3). 

1 A solution is prepared with 8 g of potassium iodide and 92 g of water. 

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X-ray fluorescence spectrometry was the first non-destructive technique for analysing surfaces and produced some remarkable results. The Water Research Association, UK, has been investigating the application of X-ray fluorescence spectroscopy to solid samples. Some advantages of nondestructive methods are no risk of loss of elements during sample handling operations, the absence of contamination from reagents, etc. and the avoidance of capital outlay on expensive instruments and highly trained staff. 

Elemental qualitative analysis is a popular application of x-ray fluorescence spectroscopy. The values of the wavelengths reaching the detector are indicative of what elements are present in the sample. This is so because the inner-shell transitions giving rise to the wavelengths are specific to the element. Qualitative analysis... 

Bamford, S.A., D. Wegrzynek, E. Chinea-Cano, et al. 2004. Application of X-ray fluorescence techniques for the determination of hazardous and essential trace elements in environmental and biological materials. Nukleonika, 49 87-95. 

The theory of X-ray fluorescent emission was initially developed by Van Hamos (1945) for primary fluorescence and Gillam and Heal (1952) for secondary fluorescence. Their calculations were subsequently improved by Sherman (1956) and then Shiraiwa and Fujino (1966) who formulated the basic equations used in the quantitative application of X-ray fluorescence. 

Radiation from radioisotope sources can be used to excite characteristic X-rays in samples upon which the beam of radiation is directed. Detection and analysis of these X-rays yield information about the composition of the sample. This opens the field of analytical applications of X-ray fluorescence analysis. The most frequent applications are in the ore processing and the metal coating industries. 

Tt may be safe to say that the interest of environmental scientists in airborne metals closely parallels our ability to measure these components. Before the advent of atomic absorption spectroscopy, the metal content of environmental samples was analyzed predominantly by wet or classical chemical methods and by optical emission spectroscopy in the larger analytical laboratories. Since the introduction of atomic absorption techniques in the late 1950s and the increased application of x-ray fluorescence analysis, airborne metals have been more easily and more accurately characterized at trace levels than previously possible by the older techniques. These analytical methods along with other modem techniques such as spark source mass spectrometry and activation analysis... 

An X-ray generator itself constitutes an application of X-ray fluorescence and it is not surprising therefore that in the past spectrometers were conceived using the sample as the anticathode, on condition that it conducts electric current. The power required to induce fluorescence through a mechanism involving electrons is lower than that required by the impact of photons. 

Wien, K., Wissmann, D., Kolling, M. and Schulz, H.D. 2005a. Fast application of X-ray fluorescence spectrometry aboard ship how good is the new portable Spectro Xepos analyser. Geomarine Letters, in press. 

One of the very first quantitative applications of x-ray fluorescence spectrometry involved the analysis of copper-based alloys for trace metals. IWenty years later the rapid development in the use of speciality alloys for, among others, the aircraft industry, required the availability of fast, accurate multielement instrumental methods. In the early 1950s two methods seemed to hold promise— x-ray fluorescence and ultraviolet emission (UVE). At that time, x-ray fluorescence was a technique limited to a wavelength range of about 0.5 to 8.0 A, in other words, all elements down to atomic number 14(Si). Even though it was unable to measure the lower atomic numbers, especially the important element carbon, it was able to provide data for S and R This, along with (at that time) a perceived minimum problem of interelement interferences, made x-ray fluorescence an ideal choice for the nonferrous industry. However, the UVE technique was the method of choice for most ferrous industry-based problems. This situation was to persist into the 1960s until the classic work of Shiraiwa and Fujino [14] provided the means for accurate... 

Tutorial Learn more about applications of X ray fluorescence. 

Aubert B, Fragu P, Di Paola M, Rougier P, Tubiana M. 1981. Application of x-ray fluorescence to the study of iodine distribution and content in the thyroid. Eur.J.Nucl.Med. 

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