Small-angle neutron scattering geometry with ring-shaped collimation for compact neutron sources

The neutron flux of compact neutron sources is low, making it difficult to measure scattered neutrons with a typical small-angle neutron scattering (SANS) geometry. A SANS geometry with ring-shaped collimation (r-SANS) was thus developed to enable experiments to be conducted using low-flux neutron source facilities. In this geometry, circumferentially collimated beams hit a sample. The scattered neutron flux is high on the ring center axis because scattered neutrons with each nominal scattering angle are superimposed on each point of the ring center axis. A He-3 point detector - which has higher neutron counting efficiency compared with that of a typical scintillation detector and can also properly distinguish neutron from gamma events - is set on the ring center axis. These features make high signal-to-noise ratio experiments possible. Monte Carlo (MC) simulation studies were conducted to evaluate the characteristics of the r-SANS geometry. The results show that oblique incident neutrons, which cause cross-talk, asymmetrically smear the scattering intensity, and increase the incident neutrons. To study the feasibility of the r-SANS geometry, it was tested at the Kyoto University Accelerator-driven Neutron Source (KUANS), which is one of the most compact and has one of the lowest neutron fluxes among available neutron beam facilities. Two types of porous silica gels, HC-N and C-500HG, were examined. As reference, the same samples were analyzed using a small-angle X-ray scattering (SAXS) spectrometer under a typical pinhole geometry. To consider the smearing effect of the r-SANS geometry, MC simulations with SAXS experimental results were conducted. The simulated results agree with the r-SANS experimental results. In addition, to show the consistency of the scattering model parameters determined via r-SANS with those via SAXS, a parameter survey was performed, revealing reasonable agreement between the results.