Neutron Scattering Experiments with a Binary Critical Mixture for the Determination of the Critical Exponent ζ

Small angle neutron scattering experiments are carried out with an isobutyric acid (COOD)/deuterium oxide mixture of critical composition. The scattering patterns are measured at small temperature differences ( T ‐ T c ) ≦ 1.0 K above the critical temperature T c . In his temperature range and for scattering vectors larger than 0.03 Å −1 the critical scattering was found to be independent of temperaure. From these data the experimental correlation scaling function g exp ( x ) is constructed for values of the scaling variable x in the range 4 < x < 540. The Fisher‐Langer approximation of the correlation scaling function and its asymptotic form for large values of x are fitted to g exp ( x ). In this way a value of the critical exponent η of η = 0.039 ± 0.009 is obtained. It is based on the analysis of the experimental correlation scaling function composed of five scattering patterns obtained at five different temperature differences (Δ T ≤ 1.0 K). The analysis of 4 individual scattering patterns (Δ T ≤ 0.08 K) gives η = 0.037 ± 0.006.