Indiana University Center for the Exploration of Energy and Matter
Spin Echo Scattering Angle Measurement (SESAME) is an interferrometric technique that allows neutron scattering to measure spatial correlations in a non-traditional way. It may have several advantages over traditional methods including insensitivity to neutron-beam collimation, direct measurement of real-space correlation functions and automatic accounting for multiple scattering. All of the architectures that are being developed for this method require precise control of the magnetic field regions within which neutron spins precess so that that equivalent neutrons – i.e. those that undergo the same scattering process at different points in a scattering sample – experience the same Larmor phase shifts. I will discuss our group’s progress in designing these precession fields based on the use of various symmetries which cause aberrations to cancel, just as the spin echo method itself cancels aberrations (resolution effects) that result from finite beam collimation. I will also describe SESAME measurements of a simple diffraction grating in reflection geometry and the development of an exact dynamical theory which accounts quantitatively and without adjustable parameters for all of the features we have observed to date with such measurements, including differences between results obtained at pulsed and steady-state neutron sources.
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