After reading this article you will learn about:- 1. Principle of X-Ray Fluorescence 2. Apparatus and Working of X-Ray Fluorescence 3. Applications.
Principle of X-Ray Fluorescence:
This depends on atomic number and wavelength of incident radiation. When an element is placed in a beam of X-rays then these rays are absorbed. The absorbing atoms become excited and then emit X-rays with wavelengths characteristic of emitting atoms. This technique has been given the name X-ray fluorescence.
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Apparatus and Working of X-Ray Fluorescence:
This diagram of the apparatus used for X-ray fluorescence is shown above.
The fluorescence intensity is first measured which helps in the qualitative determination of the element. For this purpose K the wavelength of fluorescence is calculated by Bragg’s equation
nλ = 2d sin θ
where d = spacing between crystal layers of analytical crystal and θ = angle
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The comparison of λ with known λ of elements given in chart help in identifying the clement.
Applications of X-Ray Fluorescence:
The X-ray fluorescence has been proved very helpful in the analysis of metals and non-metals with atomic number greater than 12.
(1) Qualitative Analysis:
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The Qualitative analysis can be carried out by measuring the angle of diffraction of fluorescent X-rays. With the help of this angle, the wavelength of fluorescence can be easily calculated. As each element fluoresces at a characteristic wavelength hence fluorescing element can easily be identified in the air polluted samples.
(2) Quantitative Analysis:
By measuring the intensity of fluorescence at wavelength characteristic of element, Quantitative analysis from polluted samples of food, fertilizers, agricultural products, rocks, solids etc. can easily be carried out. The fluorescence spectra are very simple.
Sometimes back ground emission from one element may overlap line emission from another element. Hence to measure the intensity of peak Y, a correction must be made for the background of X.
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This can be done by the following way:
Suppose intensity of X = 60 units
Suppose intensity of Y = 50 units
The true intensity of peak X = 10 units
(3) This technique is also used for the determination of trace elements in plants and foods; the detection of insecticides on fruit and leaves; the determination of phosphorous in fertilizers; the detection of fodder elements, such as selenium, known to be harmful in large quantities.