The linear attenuation coefficient is the infinitesimal probability of removal from the uncollided beam per unit path length. Its units are inverse length. In the homogeneous monoenergetic model, ; is the thickness leaving fraction uncollided. The mass attenuation coefficient is for material mass density . Removing a photon by scattering of light does not imply deposition of all its energy at that point; attenuation and energy absorption are different quantities.[ref]
2. The Mass Attenuation Coefficient. Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients by John H. Hubbell and Stephen M. Seltzer; NIST §2, mass thickness, Eq. (1), and total interaction cross section; distinction from the mass energy-absorption coefficient
A coefficient describing the locally absorbed fraction of an incident photon energy flow per path length, under a stated averaging convention. It is distinct from the total linear attenuation coefficient, which counts removal from an uncollided beam. Dividing by mass density gives an energy-absorption coefficient per mass.
The uncollided component decays exponentially when its removal probability per unit path length is constant. Scattered contributions require a separate transport treatment or a specified radiation buildup factor.
The linear attenuation coefficient divided by the material mass density.
An energy-weighted interaction coefficient for photons, accounting for the fraction transferred to charged particles after radiative losses. It differs from the removal-probability mass attenuation coefficient. With charged-particle equilibrium, its product with photon energy fluence gives the absorbed dose.
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