Attenuation Versus Absorption
The terms "mass attenuation coefficient", "mass absorption coefficient", and "mass extinction coefficient" are almost always used interchangeably. However, in certain situations they are distinguished, as follows.
When a narrow (collimated) beam of light passes through a substance, the beam will lose intensity due to two processes: The light can be absorbed by the substance, or the light can be scattered (i.e., the photons can change direction) by the substance. Just looking at the narrow beam itself, the two processes cannot be distinguished. However, if you set up a detector to measure light leaving in different directions, or conversely try using a non-narrow beam, you can measure how much of the lost intensity was scattered, and how much was absorbed.
In this context, the "mass absorption coefficient" measures how quickly the beam would lose intensity due to the absorption alone, while "mass attenuation coefficient" measures the total loss of narrow-beam intensity, including scattering as well. The "mass extinction coefficient" can be either.
Read more about this topic: Mass Attenuation Coefficient
Famous quotes containing the word absorption:
“These philosophers dwell on the inevitability and unchangeableness of laws, on the power of temperament and constitution, the three goon, or qualities, and the circumstances, or birth and affinity. The end is an immense consolation; eternal absorption in Brahma.”
—Henry David Thoreau (1817–1862)