Classical Larmor precession explanation of SESANS
SESANS uses the usual principles of neutron spin echo to encode the scattering angle of the neutron irrespective of the collimation of the neutron beam, thus breaking the inverse relationship between measured intensity and resolution that plagues conventional SANS. The method is based on the Larmor precession of polarised neutrons in magnetic fields with inclined faces. This precession essentially encodes the neutron trajectory. Finally, the measured polarisation is a Fourier transform of the scattering cross-section and thus closely related to the scattering length density correlation function, which facilitates data interpretation. The sensitivity can be tuned by varying the applied magnetic field, the wavelength, the length of the set-up and the tilt angle of the interfaces. All these parameters can be combined into a single parameter, the spin-echo length, z, which is both an experimental scan parameter and the length cord between two scattering volumes in the sample. This is the parameter that is shown in SESANS measurements on the horizontal axis.
Spin-echo small angle neutron scattering in Delft, M.Th. Rekveldt, J. Plomp, W.G. Bouwman, W.H. Kraan, S.V. Grigoriev and M. Blaauw, Review of scientific Instruments 76 033901 (2005) http://dx.doi.org/10.1063/1.1858579