Analyses and simulations of spin-echo small-angle neutron scattering instrument

Abstract

Spin echo small-angle neutron scattering (SESANS) is a novel technique that measures correlation functions in real space. Recent theoretical study on SESANS has enabled the interpretation of this correlation function. It has also revealed the range of applications and limitations of the SESANS technique. On a two-dimensional SESANS instrument, the experimental correlation function is the pair-distance distribution function of the scattering particle. On a one-dimensional instrument, the correlation function is an integral function of the pair-distance distribution function. SESANS is suitable for studying particles from a nanometer to a few tens of micrometers in size, a range that is similar to that covered by the traditional Bonse-Hart ultra-small-angle neutron scattering instrument. The greatest advantage of SESANS lies in the fact that it can use divergent neutron beams, thus drastically increasing the counting rate. The resolution of a SESANS instrument is limited by the integrated Larmor precession field and by the neutron wavelength. Because any SESANS instrument will have a limited momentum transfer coverage, truncation errors can result in the measured correlation functions. The effect of the inhomogeneity of the Larmor field can be handled as smearing. On a one-dimensional SESANS instrument, the off-plane scatterings also result into smearing effects.