A study of density fluctuations near the critical point of fluid Se by small angle X-ray scattering

Abstract Small angle X-ray scattering (SAXS) measurements for dense Se vapour have been carried out to investigate the characteristics of the density fluctuations near the critical density region. For this reason the correlation lengths of the density fluctuations and the number-density fluctuations have been measured precisely at different temperatures and pressures near the critical point. In this experiment a new spectrometer with a high brilliance source is used and SAXS spectra are detected using an imaging plate. Less noisy spectra with better fitting conditions to calculate correlation lengths of density fluctuations are found. Larger values of the correlation length of density fluctuations (and also the number-density fluctuations) are obtained near the critical density region, which agrees with the results of our previous experiments [J. Non-Cryst. Solids 250–252 (1999) 531]. The correlation length of the density fluctuations increases as we approach to the critical point of fluid Se along the path of critical density region.