The resolution functions of the time-of-flight pinhole SANS and multi-slit VSANS: a comparison between experiment and Mcstas simulation

In neutron scattering instrumentation, the resolution function critically bridges instrument design and data reliability. While traditional time-of-flight (TOF) pinhole SANS instruments approximate resolution functions using Gaussian distributions, multi-slit Very Small Angle Neutron Scattering (MS-VSANS) instruments require fundamentally different treatments in horizontal and vertical directions due to multi-slit collimation. Focusing on the MS-VSANS system at the China Spallation Neutron Source (CSNS), we derived its anisotropic resolution function from first principles and subsequently demonstrated its accuracy through comparisons between Mcstas simulations and experimental measurements. The derived model successfully predicted resolution smearing effects, showing quantitative agreement with both real-world data and virtual experiments in terms of absolute intensity and directional resolution. This work establishes a robust framework for interpreting slit-based VSANS data, while revealing that TOF-SANS’s Gaussian approximations fail to capture MS-VSANS’s directional decoupling. The experimentally validated resolution model provides critical insights for optimizing slit configurations and advancing applications requiring ultra-high angular resolution. Leveraging the experimentally validated resolution function, deploying this framework across MS-VSANS user facilities is essential for unlocking its full potential.