(LET) Linear energy transfer is the ratio of energy transferred by an ionizing radiation traveling through a material per unit path length. LET depends on the kind of radiation, the density of the material, etc.
The higher the LET, the higher the biological damage through energy deposition along the particle track.

The attenuation of radiation is a decrease in intensity as a result of interactions by transmission through matter. X-ray beams attenuate due to photon absorption by the material or scattering. Both effects are energy dependent. The probability of absorption or scattering is a function of the photon energy. The photoelectric absorption is much more energy dependent than the Compton scatter effect.

See also Attenuation Correction, Linear Energy Transfer, Broad Beam and Ion Beam.