Small-angle X-ray scattering

Small-angle X-ray scattering (SAXS) measures X-rays scattered through small angles to reveal nanoscale structures and size distributions in materials and solutions.

Scattering vector: A vector describing the change in wavevector between an incident wave and a scattered wave. SAXS data are commonly plotted against its magnitude, which maps angles to structural length scales.
Small-angle X-ray scattering of proteins: The use of SAXS to characterize the size, shape, and assembly of proteins in solution. This application shows how SAXS studies biomolecules without requiring crystals.
X-ray: Electromagnetic radiation with wavelengths shorter than ultraviolet light and energetic enough to probe atomic-scale matter. Its wavelength sets the angles and length scales accessible in SAXS.
Wide-angle X-ray scattering: An X-ray scattering method that measures larger angles to probe atomic and molecular-scale order. Its larger angles resolve shorter distances than SAXS typically targets.
Peter Debye: A Dutch-American physicist and chemist whose work established foundational theories of molecular scattering and structure. Debye's scattering theory helped frame how diffuse X-ray patterns encode particle structure.
Guinier approximation: A low-angle approximation relating scattering intensity to the radius of gyration of a particle. It extracts an overall particle size from the near-origin portion of a SAXS curve.
X-ray reflectivity: An X-ray method that measures reflected intensity to determine structure perpendicular to a surface or thin film. It probes layered surfaces, whereas SAXS commonly measures bulk or solution structures.
Elastic scattering: Scattering in which the incoming and outgoing waves have the same energy. SAXS analysis generally interprets direction changes without an energy shift.
Small-angle neutron scattering: A small-angle scattering method using neutrons to reveal nanoscale structures and component contrasts. Neutron scattering offers isotope-sensitive contrast that complements X-ray electron-density contrast.
X-ray diffraction: The scattering of X-rays by matter, used to infer structural order from the resulting intensity pattern. SAXS is a low-angle branch of X-ray scattering and diffraction methods.

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