Resolution of small-angle neutron scattering with a refractive focusing optic

A small-angle neutron scattering spectrometer that uses a refractive focusing optic can reach smaller values of the scattering vector, and with higher resolution, than that using pinhole collimation. The analytic expression for the resolution is independent of the sample size for one wavelength only, when the focusing lens images the source at the detector. At all other wavelengths the contribution from the sample size is non-zero. For a system that uses a range of wavelengths to increase the intensity without significantly degrading the instrumental performance, the contribution from the sample term is not zero, though it is small and less than that for the pinhole collimation system.