Attenuation coefficient
[3] Most commonly, the quantity measures the exponential decay of intensity, that is, the value of downward e-folding distance of the original intensity as the energy of the intensity passes through a unit (e.g. one meter) thickness of material, so that an attenuation coefficient of 1 m−1 means that after passing through 1 metre, the radiation will be reduced by a factor of e, and for material with a coefficient of 2 m−1, it will be reduced twice by e, or e2.The attenuation coefficient describes the extent to which the radiant flux of a beam is reduced as it passes through a specific material.Generally, for electromagnetic radiation, the higher the energy of the incident photons and the less dense the material in question, the lower the corresponding attenuation coefficient will be.The spectral directional attenuation coefficient in frequency and spectral directional attenuation coefficient in wavelength of a volume, denoted μΩ,ν and μΩ,λ respectively, are defined as[6] where When a narrow (collimated) beam passes through a volume, the beam will lose intensity due to two processes: absorption and scattering.In this context, the "absorption coefficient" measures how quickly the beam would lose radiant flux due to the absorption alone, while "attenuation coefficient" measures the total loss of narrow-beam intensity, including scattering as well.Note that in logarithmic units such as dB, the attenuation is a linear function of distance, rather than exponential.This has the advantage that the result of multiple attenuation layers can be found by simply adding up the dB loss for each individual passage.However, if intensity is desired, the logarithms must be converted back into linear units by using an exponential:Engineers use these equations predict how much shielding thickness is required to attenuate radiation to acceptable or regulatory limits.