Small angle scattering

Small angle scattering or diffraction, ( KWS , engl. Small-angle scattering , SAS ) is a physical measurement technique for the investigation of structures whose dimensions are relatively large compared to the wavelength of the radiation used. Either X-rays ( small-angle x-ray scattering , SAXS ) or neutron radiation ( SANS ) are diffracted .

Basics

Scatter vector

With elastic scattering, the scattering vector has the amount

${\displaystyle q={\frac {4\pi }{\lambda }}\sin {\frac {\theta }{2}},}$

where is the wavelength of the radiation used and the scattering angle between the incident and the specifically considered diffracted beam. The incident wavelength is typically of a similar order of magnitude as in regular X-ray or neutron diffraction , i.e. a few angstroms , comparable between atomic distances. For small angles (from approximately to several orders of magnitude below), q also becomes very small and thus enables the investigation of relatively large structures. On this scale, the examined medium can be described in a continuum approximation by a scattering length - density function . ${\displaystyle \lambda }$ ${\displaystyle \theta }$ ${\displaystyle \theta }$ ${\displaystyle 10^{\circ }}$

variants

A variant of the small-angle scattering is the small-angle scattering with grazing incidence .

literature

• LA Feigin, DI Svergun: Structure Analysis by Small-Angle X-Ray and Neutron Scattering . Springer Science & Business Media, 2013, ISBN 978-1-4757-6624-0 .