Porod

Porod is a surname and a term used in physics and materials science. The most widely known use is Porod's law, which appears in the context of small-angle scattering (SAS) of X-rays or neutrons from materials composed of two or more phases separated by sharp interfaces. The law describes the asymptotic, high-q behavior of the scattering intensity: as the scattering vector q becomes large, the intensity I(q) decays roughly as q to the power of minus four. A common formulation is I(q) ∝ (Δρ)^2 S / q^4, where Δρ is the difference in scattering-length density between the phases and S is the interfacial area per unit volume. This relation reflects how smooth, well-defined boundaries contribute to the scattering signal and is used to estimate surface area and to assess the sharpness of interfaces in nanoparticles, polymers, porous materials, and other dispersed systems.

Extensions and deviations of Porod's law arise when interfaces are rough, diffuse, or fractal. In such cases the decay exponent can differ from four, and the prefactor carries information about the roughness and geometry of the interface. Porod's law remains a standard diagnostic tool in small-angle X-ray and neutron scattering, often applied together with model fits to extract morphological parameters from experimental data.

As a surname, Porod is borne by several individuals across science and other fields. The term Porod's law thus serves both as a specific physical principle and as part of a family name encountered in academic and professional contexts.