Excitation modes of elements in X-ray fluorescence

To induce X-ray fluorescence of elements in a sample, a source of photons or particles of sufficient energy is required. Generally these sources are produced by X-ray tubes of variable power or, for portable instruments, by radioisotopic sources. If the term of X-ray fluorescence is considered in the broadest sense of X-ray emission, other excitation processes employing particles (e , a) can be used. 

In an enclosed space maintained under vacuum a beam of electrons, accelerated through a PD of up to 100 kV, hits a target serving as the anode (called anticathode). 

Rhodium (4sRh) anticathode with a potential drop of 62 kV 

021 nm E = 59keV), gadolinium, etc. Nowadays, X-ray detectors are extremely sensitive and consequently the power demanded from the generators tends to be reduced. 

Besides the generators described above there are X-ray sources based on radioactive materials to provide the excitation of the sample. The advantage of using these materials is that an isotope can be selected to provide a mono-energetic beam of radiation that is optimized for the specific application. One method consists to select a radionuclide that is transformed by internal electron capture (lEC). This mode of decomposition corresponds to the transition of one level-K electron into the nucleus of the atom. For a nuclide X, the phenomenon is summarized as follows  

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