The interpretation of real-space information from small-angle scattering experiments

The distance distribution function contains all the accessible information about the scattering medium. It is possible to determine the following particle parameters from this function: maximum dimension of the particle, radius of gyration, and zero-angle intensity (molecular weight). The shape of the distance distribution function enables one to distinguish and to recognize directly and rationally the following types of particles: compact globular particles; particles elongated in one dimension, with constant and with variable cross-section; spherical vesicles. The thickness of flat particles as well as the inner and outer diameter of spherical vesicles can be determined from the distance distribution function. Inhomogeneous particles with at least two regions of electron densities differing in their signs show typical features in the distance distribution. These characteristics can be found without further assumptions, independently of the shape of the particle. For concentric shells with different electron densities it is possible to obtain some general information about their structure. Residual concentration effects cannot be overlooked in real space. The formation of dimers can be analyzed with the aid of the distance distribution function.