Analysis of water scattering used for calibration of small-angle neutron scattering (SANS) measurements

In a SANS study of critical scattering on CO,, we were faced with the problem of achieving highest resolution: a deviation from the Q(-2) power law of a few percent had to be characterized and critical fluctuations in the size range between 10 and 1000 Angstrom were measured. Experiments were done in the broad Q-range available at the instrument D11 at ILL, using several wavelengths (4.5 less than or equal to lambda (Angstrom) less than or equal to 10) and sample-to-detector positions (1.7 less than or equal to L (m) less than or equal to 35.7). In this paper we discuss the problem of calibration using a water sample at different experimental configurations, i.e, sample-to-detector distances and wavelengths. We consider geometric effects and the efficiency of the two-dimensional BF(3)-multidetector, as well as inelasticity- and multiscattering effects as a function of incident wavelength and water thickness. (C) 2000 Elsevier Science B.V. All rights reserved.