Small-angle neutron scattering

Advantages of SANS over SAXS are its sensitivity to light elements, the possibility of isotope labelling, and the strong scattering by magnetic moments.

During a SANS experiment a beam of neutrons is directed at a sample, which can be an aqueous solution, a solid, a powder, or a crystal.

In zero order dynamical theory of diffraction the refractive index is directly related to the scattering length density and is a measure of the strength of the interaction of a neutron wave with a given nucleus.

The traditional solution is to increase the brightness of the source, as in Ultra Small Angle Neutron Scattering (USANS).

A crucial feature of SANS that makes it particularly useful for the biological sciences is the special behavior of hydrogen, especially compared to deuterium.

Figure 1 shows the scattering length density for water and various biological macromolecules as a function of the deuterium concentration.

An example in which SAXS, SANS and EM data has been used to build an atomic model of a large multi-subunit enzyme has recently been published.