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Mass attenuation coefficients of selected elements for X-ray photons with energies up to 250 keV. The mass attenuation coefficient, or mass narrow beam attenuation coefficient of a material is the attenuation coefficient normalized by the density of the material; that is, the attenuation per unit mass (rather than per unit of distance).
X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric and/or electronic structure of matter. [1] The experiment is usually performed at synchrotron radiation facilities, which provide intense and tunable X-ray beams. Samples can be in the gas phase, solutions, or solids. [2]
The attenuation coefficient describes the extent to which the radiant flux of a beam is reduced as it passes through a specific material. It is used in the context of: X-rays or gamma rays, where it is denoted μ and measured in cm −1;
The x-ray absorption coefficient is usually normalized to unit step height. This is done by regressing a line to the region before and after the absorption edge, subtracting the pre-edge line from the entire data set and dividing by the absorption step height, which is determined by the difference between the pre-edge and post-edge lines at the ...
Absorption attenuates the secondary X-rays leaving the sample. For example, the mass absorption coefficient of silicon at the wavelength of the aluminium Kα line is 50 m 2 /kg, whereas that of iron is 377 m 2 /kg. This means that fluorescent X-rays generated by a given concentration of aluminium in a matrix of iron are absorbed about seven ...
In those situations, the most general form of the Beer–Lambert law states that the total attenuation can be obtained by integrating the attenuation coefficient over small slices dz of the beamline: = = (), = = (). These formulations then reduce to the simpler versions when there is only one active species and the attenuation coefficients are ...
However, attenuation coefficients vary with the energy of the X-rays, and, crucially, the ratio of the attenuation coefficients also varies. DXA uses two energies of X-ray. The difference in total absorption between the two can be used, by suitable weighting, to subtract out the absorption by soft tissue, leaving just the absorption by bone ...
The absorption coefficient is fundamentally the product of a quantity of absorbers per unit volume, [cm −3], times an efficiency of absorption (area/absorber, [cm 2]). Several sources [2] [12] [3] replace nσ λ with k λ r, where k λ is the absorption coefficient per unit density and r is the density of the gas.