X-Ray Fluorescence in Biological Sciences. Группа авторов

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Название X-Ray Fluorescence in Biological Sciences
Автор произведения Группа авторов
Жанр Химия
Серия
Издательство Химия
Год выпуска 0
isbn 9781119645580



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target="_blank" rel="nofollow" href="#ulink_c3b8c86e-6783-5064-ac34-61a309d6efc9">(4.2)equation

      where, E is the energy of incident X‐ray beam (in keV) undergoing total reflection, ρ is the density in g/cm3 of the second medium, and Z and A are the atomic number and atomic mass of the second medium, respectively. The above formula holds true only for the X‐ray energies above the absorption edges of the medium [8–10].

      It is clear from the above elaboration that for a glancing angle lower than the critical angle, there will be no refraction and the X‐ray beam falling on the sample is totally reflected from the second medium back to first medium. This means that the penetration of X‐rays in the medium, when the glancing angle is below the critical angle, is negligible and this is very advantageous for TXRF analysis. Thus, three physical quantities: critical angle, reflectivity, and penetration depth, are important parameters for TXRF analysis. The critical angle is already discussed in detail above.

Support material Critical angle for Mo Kα (17.44 keV) (Degrees) Reflectivity for Mo Kα (17.44 keV) at critical angle Critical angle for WLα (8.39 keV) (Degrees) Reflectivity for W Lα (8.39 keV) at critical angle
Plexiglas 0.08 0.932 0.16 0.879
Glassy Carbon 0.08 0.939 0.17 0.884
Boron Carbide 0.10 0.93 0.21 0.876
Quartz 0.10 0.855 0.21 0.734
Platinum 0.28 0.394 0.58 0.453
Gold 0.26 0.387 0.55 0.448
Schematic illustration of the advantages of TXRF analysis involving efficient sample excitation, X-ray detection and reduction in spectra background compared to that of EDXRF background.

      4.4.3 TXRF Instrumentation for Trace Element Determination