Spin-Echo Small-Angle Neutron Scattering Development

Abstract

Spin-Echo Small-Angle Neutron Scattering (SESANS) instrument is a novel SANS technique which enables one to characterize distances from a few nanometers up to the micron range. The most striking difference between normal SANS and SESANS is that in SESANS one gets information in real space, whereas in a SANS measurement one obtains data in reciprocal space which has to be Fourier transformed. Another important difference is that a fully divergent beam can be used which means high counting statistics. Larmor precession is the basic physical principle for SESANS: When a neutron enters a magnetic field the spin of the neutron precesses around the magnetic field. Larmor precession of neutrons is used to make a polarized beam precess through a symmetrical setup consisting of dipole electromagnets. Triangular precession regions are used to encode the scattering angle with the precession angle which is proportional to the momentum transfer. Magnetic field and line integral homogeneities are two requirements which the magnets have to meet in order to keep the initial polarization without scattering. The field homogeneity can be realized by optimizing the magnet parameters whereas external coils are needed for homogenizing the line integral. The possibilities of SESANS for measuring correlations directly are studied by model calculations. Furthermore, multiple scattering can be treated easily with SESANS in contrast to SANS.