Toward a new lower limit for the minimum scattering vector on the very small angle neutron scattering spectrometer at Laboratoire Leon Brillouin

The main characteristics of the very small angle neutron scattering spectrometer (VSANS) under construction at the Laboratoire Leon Brillouin are a multibeam pinhole collimator converging onto an image plate detector. By combining tiny collimation (diaphragms of around I or 2 mm in diameter) with the small pixel size of the detector (0.15 x 0.15 mm), very high resolution measurements can be achieved. The resolution function of the instrument contains a contribution from gravity, which is reduced by the intermediate masks of the collimator. Owing to the relatively short length of the VSANS instrument (around 14 m), this effect remains weak, in good agreement with the predictions. With a prototype multibeam collimator, an incident wavelength of 0.9 nm and the detector located at 6 m from the sample, it is possible to access q values as low as 4 x 10(-3) nm(-1) with very high q resolution. Promising preliminary experiments with high q resolution are reported, which open up new fields to the SANS technique.