Attenuation length
In physics, the attenuation length or absorption length is the distance  into a material when the probability has dropped to  that a particle has not been absorbed. Alternatively, if there is a beam of particles incident on the material, the attenuation length is the distance where the intensity of the beam has dropped to , or about 63% of the particles have been stopped. Mathematically, the probability of finding a particle at depth  into the material is calculated by the Beer–Lambert law:

. In general  is material- and energy-dependent. See also
 Beer's Law
 Mean free path
 Attenuation coefficient
 Attenuation (electromagnetic radiation)
 Radiation length

References
 
 https://web.archive.org/web/20050215215652/http://www.ct.infn.it/~rivel/Glossario/node2.html

External links
 http://henke.lbl.gov/optical_constants/atten2.html

Particle physics
Experimental particle physics