Data acquisition

The diffracted x-rays hit the CCD and form a two-dimensional intensity pattern on the detector plane. The horizontal axis of the detector (along the crystal axis of the curvature) corresponds to the energy axis of an x-ray spectrum, while the vertical axis serves mainly to collect more intensity. Events are collected into the CCD for a finite time. The time of a single acquisition is chosen depending on the count rate, so that multiple hits on one pixel are minimized. In order to select good x-ray events, the energy content of each pixel is analyzed by setting an appropriate energy window. Thanks to a good energy resolution of the CCD, this procedure allows to discriminate against higher order reflections and background events. The data are taken in a repetitive accumulation mode. Each two-dimensional image corresponding to a separate acquisition is filtered and then the different images are summed and finally projected to give a one-dimensional position spectrum.