Definitions and Formulae
The measured intensity of transmitted through a layer of material with thickness is related to the incident intensity according to the inverse exponential power law that is usually referred to as Beer–Lambert law:
where denotes the path length. The attenuation coefficient (or linear attenuation coefficient) is .
The Half Value Layer (HVL) signifies the thickness of a material required to reduce the intensity of the emergent radiation to half its incident magnitude. It is from these equations that engineers decide how much protection is needed for "safety" from potentially harmful radiation. The attenuation factor of a material is obtained by the ratio of the emergent and incident radiation intensities .
The linear attenuation coefficient and mass attenuation coefficient are related such that the mass attenuation coefficient is simply, where is the density in g/cm3. When this coefficient is used in the Beer-Lambert law, then "mass thickness" (defined as the mass per unit area) replaces the product of length times density.
The linear attenuation coefficient is also inversely related to mean free path. Moreover, it is very closely related to the absorption cross section.
Read more about this topic: Attenuation Coefficient
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