Improved Signal-to-Background Ratio in Small-Angle X-ray Scattering Experiments with Synchrotron Radiation using an Evacuated Cell for Solutions

An evacuated, temperature-controlled cell has been built for use on the small-angle X-ray scattering instrument D24 at the synchrotron radiation facility LURE. The sample is placed in a quartz capillary sealed in a stainless-steel holder using a vacuum-tight glue. Several O rings provide a vacuum path upstream and downstream from the cell, so that the X-ray beam only meets the capillary walls and the solution under study between the slits and the beam stop, while the sample is maintained under atmospheric pressure. The cell temperature is controlled via a water circulation through a copper sheath in tight contact with the steel holder. The use of this cell results in a marked reduction of the background, as observed in two series of parallel experiments using a conventional cell and this evacuated cell. The decrease ranges from a factor of 2 at s 1 values larger than 0.008 Å⁻¹ to more than 15 at s = 0.00116 Å⁻¹, where s is the modulus of the scattering vector (s = 2sin θ/λ, 2θ is the scattering angle and λ is the wavelength of the X-rays).