The cross section within the small angle approximation for particles in a solution reads


<math>\frac{d \Sigma}{d \Omega} \equiv n \Delta \rho^2 V_p^2 \left| S(\mathbf{q})\right|^2 P(\mathbf{q})</math>



where the particle density is given by

<math>n = \frac{N}{V} </math>



The scattering length density contrast between the particles and the solvent reads

<math> \Delta \rho(\mathbf{r}) = \rho_b(\mathbf{r}) -  \rho_s  </math>



The particle form factor reads

<math> P(\mathbf{q}) =  \left|  \frac{1}{V}  \int dV e^{-i \mathbf{q} \cdot \mathbf{r}} \right|^2</math>