MISANS, a method for quasi-elastic small angle neutron scattering experiments

The use of a pulsed neutron source is convenient for spin-echo techniques not only because of the gain in neutron economy (Nuc. Inst. and Meth. 164 (1979) 153), but also because the number of parameters varied during a scan is reduced. The recently proposed modulated-intensity small angle neutron scattering (MISANS) instrument uses the MIEZE technique, a variant of the neutron resonance spin-echo (NRSE). The adaptation of this method to a small angle neutron scattering (SANS) spectrometer provides the possibility to study slow dynamics with energy changes in the neV-range. The advantage of MIEZE compared to other spin-echo techniques is that all polarizing neutron optics can be installed upstream of the sample, so that the signal is indifferent to depolarization at the sample position and an area detector can be operated very easily. This paper discusses the changes to the SASI spectrometer at the IPNS in Argonne required to insert the MIEZE components on the existing beamline.