The absorption cross-section is closely related to molar absorptivity and mass absorption coefficient.
2.
The amount absorbed is dependent on the material's mass absorption coefficient and tends to decrease for incident photons of greater energy.
3.
For a given particle and its energy, the absorption cross-section of the target material can be calculated from mass absorption coefficient using:
4.
In this use, " opacity " is another term for the mass attenuation coefficient ( or, depending on context, mass absorption coefficient, the difference is described here ) \ kappa _ \ nu at a particular frequency \ nu of electromagnetic radiation.
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