Neutron refraction by cylindrical metal wires

Undesired Small-Angle Neutron Scattering (SANS) from interior features of an object can be minimised by reducing the sample thickness. However, refraction effects produced by the exterior shape of the object depend upon the scattering cross-section and not on the thickness of the object. In the field of polarised neutrons a wire coil is often used to manipulate the polarisation vector of the neutron. In this paper, we show that the cylindrical shape of the wire together with the refractive index introduces an angular distribution in the neutron beam. This can be observed in instrumentation sensitive to SANS. We show results measured on three different SANS instruments: Ultra Small-Angle Neutrons Scattering (USANS), Spin-Echo Small-Angle Neutron Scattering (SESANS) and a Time-of-Flight (TOF) SESANS. These results are all in good agreement with the theory of refraction.