A small-angle camera for resonant scattering experiments at the storage ring DORIS

Resonant small-angle scattering is measured routinely in the wavelength range of 0.6 to 3.25 Å with the instrument X15 at the storage ring DORIS. The monochromatic beam with a vertical offset of 1.22 m is achieved by a double monochromator system with a constant exit slit. The small-angle instrument allows for sample-detector distances between 0.37 and 7.33 m. A multiwire proportional counter with a sensitive area of 200 × 200 mm detects the scattered intensity with a spatial resolution of 2 × 2 mm. Its sensitivity can be adapted to the requirements of the experiment by activating a drift chamber of 8 cm depth at the back end of the detector. The performance of the instrument as a function of the wavelength is described. The energy resolution is about 1 eV at the L₃ absorption edge of caesium, as shown by the resonant scattering of ferritin in 30% CsCl solution.