The universal critical-scattering function (CSF) has been measured on a ${\mathrm{CO}}_2$ sample at critical density by small-angle neutron scattering. The experiment was designed and conducted in such a way as to reach an accuracy of 0.3% in the determination of the CSF in the large-Q range. Several approximate equations proposed in the literature are used to model the results, and their validity is discussed, but the main purpose of this work was to produce accurate data in the region of the crossover between the Ornstein-Zernike and critical regimes.

• Received 18 March 1998

DOI:https://doi.org/10.1103/PhysRevB.58.12038