Abstract
For the further development of spin-echo techniques to label elastic scattering it is necessary to perform simulations of the Larmor precession of neutron spins in a magnetic field. The details of some of these techniques as implemented at the reactor in Delft are simulated. First, the workings of the magnetized foil flipper are simulated. A full virtual spin-echo small-angle neutron scattering instrument is built and tested without and with a realistic scattering sample. It is essential for these simulations to have a simulated sample that also describes the transmitted beam of unscattered neutrons, which usually is not implemented for the simulation of conventional small-angle neutron scattering (SANS) instruments. Finally, the workings of a spin-echo modulated small-angle neutron scattering (SEMSANS) instrument are simulated. The simulations are in good agreement with theory and experiments. This setup can be extended to include realistic magnetic field distributions to fully predict the features of future Larmor labelling elastic-scattering instruments. Configurations can now be simulated for more complicated combinations of SANS with SEMSANS.
Highlights
To obtain a high resolution with conventional scattering methods, normally the beam size, divergence or wavelength bandwidth have to be reduced, with a corresponding loss in flux
Spin-echo methods can circumvent this intensity problem (Mezei et al, 2002). These polarized neutron methods use the Larmor precession in magnetic fields to measure the change in energy or direction of scattered neutrons
A more recent variant of this technique is spin-echo modulated small-angle neutron scattering (SEMSANS) (Gahler, 2006; Bouwman et al, 2009; Sales et al, 2015), in which all polarization manipulations occur before the sample
Summary
To obtain a high resolution (e.g. smaller scattering vectors or smaller energy transfer) with conventional scattering methods, normally the beam size, divergence or wavelength bandwidth have to be reduced, with a corresponding loss in flux. For neutron scattering this can limit the highest resolution that can be practically achieved with an acceptable neutron count rate. A more recent variant of this technique is spin-echo modulated small-angle neutron scattering (SEMSANS) (Gahler, 2006; Bouwman et al, 2009; Sales et al, 2015), in which all polarization manipulations occur before the sample This makes it possible to combine SEMSANS and smallangle neutron scattering (SANS) (Bouwman et al, 2011). The data analysis for time-of-flight SE(M)SANS measurements is challenging because of finite size acceptances and scattering powers that are dependent on the wavelength (Li et al, 2019)
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