Xrayattenuated

X-ray attenuation is the reduction in X-ray beam intensity as it passes through matter. The term Xrayattenuated is not standard in radiology and may be encountered as an informal descriptor for the same process. Attenuation underpins the contrast seen in radiographic images, as well as shielding design and dosimetry.

Mathematically, attenuation follows the Beer-Lambert law: I = I0 exp(-μx). I0 is the incident intensity, I is the transmitted intensity, x is the thickness of material, and μ is the linear attenuation coefficient for the material at the X-ray energy. The mass attenuation coefficient μ/ρ is often used with density ρ, since μ = (μ/ρ)ρ. Attenuation thus depends on both material composition and geometry, as well as the energy spectrum of the X-rays.

Attenuation results from absorption and scattering. At diagnostic energies, the main interactions are photoelectric absorption and Compton scattering. Photoelectric absorption increases sharply with atomic number Z and decreases with photon energy, while Compton scattering depends on electron density. Pair production is negligible at typical diagnostic energies but becomes relevant at higher energies.

Material properties determine attenuation: higher Z, greater density, and greater thickness lead to more attenuation. Energy dependence means the same material attenuates differently across the spectrum. In computed tomography, attenuation data are used to estimate tissue density and are often expressed in Hounsfield units. Standard reference databases, such as NIST XCOM, provide photon attenuation coefficients.

Applications include medical imaging, radiography, dosimetry, and shielding. Accurate attenuation data support image formation, dose calculations, contrast agent planning, and the selection of protective materials.