Calculations Absorption Factor, Optimum Sample Thickness

4 Calculations Absorption Factor, Optimum Sample Thickness 

The absorption factor of an amorphous or polycrystalline material is computed by summation of incremental contributions from each atom. Thus it is easily computed. 

For all chemical elements, mass absorption coefficients ju/p are tabulated [13, 85] as a function of the X-ray wavelength. Chemical composition, mass density p, and thickness t of the sample are known. 

Example PET. Let us consider poly(ethylene terephthalate) (PET, [CioH%04, pp r=1.35 g/cm ) of Ipet =2 mm thickness and an X-radiation wavelength A= 

15418 nm (CuKa). We set up a table with one row for each chemical element and sum both the masses and the mass absorption coefficients multiplied by the masses. After normalization to the molecular mass of the PET monomer, 192.17 amu, we find ii/p)pet = 1291.97/192.17 cm /g a value 6.72 cm /g. Considering the density ppET we find for the linear absorption coefficient Ppet = 

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