Correction method for the asymmetry of the tangential beam in Couette (or Searle) geometry used in rheo-small-angle neutron scattering

A method of correcting the asymmetry in the scattering of the tangential beam configuration in a rheo-small-angle neutron scattering experiment is proposed. The asymmetry of the scattering in the tangential beam configuration can be attributed to the difference in pathlength for neutrons that are scattered toward compared with those which are scattered away from the axis of rotation of the shear cell. The pathlength problem is solved and a final expression for the two-dimensional scattering intensity is given. The results from these calculations are compared with experimental data, which offer a different option to correct this asymmetry, namely by just measuring the scattering of H₂O/D₂O mixtures with absolute scattering cross sections identical to those of the respective samples. However, the situation for anisotropic media is more complex and the correction procedure described here is less effective.