# Absorption coefficient

From AMS Glossary

## absorption coefficient

Usually expressed as a volume absorption coefficient,

*k*_{v}, with units of reciprocal length (i.e., area per unit volume), but also as a mass absorption coefficient,*k*_{m}, with units of area per unit mass. The two are related by*k*_{v}= ρ*k*_{m}, where ρ is the density of the absorber.*See also*absorption optical thickness.