Distortion calibration of the PILATUS 1M detector

Abstract

The PILATUS 1M detector is a large area tiled X-ray detector for protein crystallography. One million 217 × 217 μ m 2 pixels cover an area of 24.3 × 20.0 cm 2 with 300 μ m thick silicon sensors. The readout electronics enable single photon counting and a readout time of 6.7 ms. Images from this detector are spatially distorted by the influence of three factors. First, the absorption properties of the silicon leads to parallax broadening by a fraction of a pixel, depending on the angle of incidence and the photon energy. A simulation was compared to experimental data. Second, the modular architecture causes a mechanical displacement of the modules from their assumed positions. The modules are positioned on average to a precision of ∼ 300 μ m . Third, to reduce the dead area the modules are tilted by 6 ∘ and are overlapped. This introduces large distortions of several pixels which depend on the sample to detector distance. An algorithm for distortion correction of CCD detector data was adapted to correct the data of the PILATUS 1M detector. The results of the metrology as well as the parallax shift were incorporated in these corrections. Images from a Ta-mask were used to test the corrections and quantify the remaining spatial distortion. The mask images were also used to refine the individual module positions. In order to verify the distortion corrections crystallographic standards were used. The result is that images of the detector can be spatially corrected to a precision of 74 μ m or about 0.34 pixel.