attenuaatiokerrointa

Attenuaatiokerroin, in English attenuation coefficient, is a parameter used in radiative transport to quantify how strongly a material absorbs or scatters a beam of photons. For monochromatic photons, the transmitted intensity I after traveling a distance x in the material is described by Beer-Lambert law: I(x) = I0 e^{-μ x}, where μ is the linear attenuation coefficient of the material, and I0 is the incident intensity.

In addition to the linear attenuation coefficient, the mass attenuation coefficient μ/ρ is commonly used. It is defined as μ/ρ = μ / ρ and has units of cm^2/g. The two are related by μ = (μ/ρ) ρ, where ρ is the material density. The mass attenuation coefficient is particularly useful when comparing different materials because it depends mainly on composition and photon energy, while μ also depends on density.

μ depends strongly on photon energy and material composition. At different energies, different interaction processes dominate: photoelectric absorption at low energies, Compton scattering in intermediate energies, and electron-positron pair production at high energies. In many energy ranges, higher atomic number Z and higher density increase the attenuation coefficient, leading to stronger attenuation of the beam.

Applications of the attenuation coefficient include shielding design in nuclear, medical, and industrial contexts; radiography and computed tomography in medical imaging; and dose calculations for radiation protection. The attenuation coefficient can be measured experimentally from transmission data or obtained from tabulated data and databases such as XCOM or NIST.

For neutrons, a related concept is described by macroscopic cross sections and attenuation lengths, which depend on neutron energy and the material’s composition.