VACUUM CHAMBER FOR SYNCHROTRON POWDER DIFFRACTION. B. Palosz, S. Gierlotka, S. Stel'makh, S. Doyle⁺ & T. Wroblewski⁺. High Pressure Research Center "UNIPRESS",Warsw, POLAND; + Hasylab, DESY, Hamburg, GERMANY

Air scattering is a primary concern during experiments where weak and/or diffuse intensities are measured. We designed, manufactured and tested a chamber that allows for measurements of samples under vacuum at B2 powder diffractometer at Hasylab, Hamburg, Germany. The chamber is a flat half-cylinder with 300 mm radius. Kapton window 15 mm wide covers 2( range from -5 to 130 deg. The chamber is connected via a flexible bellow to the beam-leading tubes that reach the exit window of the monochromator tank where another kapton window is placed. Therefore the beam-definition slit, the beam monitor and the anti-scatter slit are under vacuum. The total length of the vacuum beam path is roughly 1600 mm. The sample is mounted on a goniometer head inside the chamber with all necessary degrees of freedom. Tests were performed with a scintillation detector and the wavelength of 1.158Å. The beam stop was a strip of lead attached to the chamber right behind the kapton window. It is positioned precisely by rotating the whole chamber mounted on the diffractometer circle. In standard setup the measurements start from 0.35 deg. 2(; lower angles can also be reached. For a short wavelength, 1.158Å, there was only little gain in the primary beam intensity. But the instrumental background at small and intermidiate angles was reduced by more than 2 orders of magnitude. Test measurements were performed on nanometric diamond and SiC samples. The setup allowed for simultaneous recording of small- and wide-angle data. The SAXS curve extended over 5 decades and the diffuse intensity in the intermediate angles was accurately determined. This chamber equiped with curved Image Plate will be a very effective tool for quantitative measurements of the intensity profiles of conventional polycrystals, nanocrystalline and non-crystalline materials.