Interaction Volumes for Generation of Secondary Fluorescence (X-Rays)
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The volume, inside the specimen in which interactions occur while being struck with accelerating electrons, is called interaction volume. This volume depends on several factors such as atomic number of the materials of the specimen, accelerating voltage of the electron beam, and angle of the incident electron beam, because the materials with higher atomic number absorb or stop more electrons (having a smaller interaction volume), higher voltages penetrate farther into the sample and generate larger interaction volumes, and the greater the angle (further from normal) the smaller the volume. For comparison, Figure 4596 shows the interaction volumes for generations of secondary electrons, Auger electrons, backscattered electrons, characteristic X-rays, continuum X-rays, and secondary fluorescence (X-rays).

The interaction volumes for generations of secondary electrons, Auger electrons, backscattered electrons, characteristic X-rays, continuum X-rays, and secondary fluorescence (X-rays).
Figure 4596. The interaction volumes for generations of secondary electrons, Auger electrons, backscattered electrons, characteristic X-rays, continuum X-rays, and secondary fluorescence (X-rays).

In Electron Microscope (EM), X-ray fluorescence occurs as a result of photoelectric absorption of primary X-rays as the target atom relaxes from an excited state. These secondary X-rays may be produced both by characteristic or continuum x-rays. Since X-rays can penetrate much longer distances than incident electrons in materials, the range of fluoresced X-rays is greater (~10 times) than the interaction range of the primary electron at the same energy. The secondary X-ray interaction volume may be as much as 1000 times greater than the interaction volume of the primary X-rays.

 

 

 

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