X-ray microanalysis with the electron probe

The elements present can be identified from the wavelengths, and the amounts of each element can be determined from the intensities. The method is limited, as are all fluorescence methodSj by the low intensity of the fluorescent radiation nonetheless, detection of a few parts per million of an element is easily achieved. (For quantitative analysis, comparison with standard substances of known composition is necessary.) The method has the advantage of being very rapid and nondestructive. 

In this technique, a finely focused electron beam impinges on the sample (Fig. 24.25). The width of the beam is of the order of 1 um. The electron beam is energetic enough to excite the x-ray spectrum of the various elements in the sample. We analyze the spectrum of emitted x-rays and identify the elements, which can also be determined quantitatively. The technique is enormously useful, but it has the disadvantage that the sample must be inside the vacuum chamber of the electron gun. We mount the sample on an adjustable stage so that the position of the spot on the sample can be accurately fixed—and reproduced if necessary. By moving the sample and repeating the analysis, we can study any variation in composition with location. 

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