Countering the effects of gravity on a small angle neutron scattering instrument

Abstract Small angle neutron scattering (SANS) is a powerful technique for determining chemical, biological and hard matter structures of materials over a wide range of length-scales. The larger the structure the smaller the scattering angles and the longer the collimation and detector distances need to be. In addition, in order to determine the structure of materials in the micron range long neutron wavelengths are required. The combination of the slow speed of long wavelength neutrons coupled with the large distances of the instrument results in a significant displacement of the beam with gravity. This can affect the neutron flux available, the resolution, the completeness of the signal on the detector and hence the largest length-scales that can be measured. Previous ideas of cancelling the effects of gravity have used prisms but this approach has problems working over the full height associated with typical sample sizes. This paper describes a different method using simple mirrors that can be exploited using existing components of SANS instruments and results in reducing the minimum momentum transfer by a factor of 5.