  A vacuum-compatible photon-counting hybrid pixel detector has been installed
in the ultra-high vacuum (UHV) reflectometer of the four-crystal monochromator
(FCM) beamline of the Physikalisch-Technische Bundesanstalt (PTB) at the
electron storage ring BESSY II in Berlin, Germany. The setup is based on the
PILATUS3 100K module. The detector can be used in the entire photon energy
range accessible at the beamline from 1.75 to 10 keV. Complementing the already
installed vacuum-compatible PILATUS 1M detector used for small-angle scattering
(SAXS) and grazing incidence SAXS (GISAXS), it is possible to access larger
scattering angles. The water-cooled module is located on the goniometer arm and
can be positioned from -90{\deg} to 90{\deg} with respect to the incoming beam
at a distance of about 200 mm from the sample. To perform absolute scattering
experiments the linearity, homogeneity and the angular dependence of the
quantum efficiency, including their relative uncertainties, have been
investigated. In addition, first results of the performance in wide-angle X-ray
scattering (WAXS), X-ray diffraction (XRD) and X-ray reflectometry (XRR) are
presented.
