The PILATUS 1M detector, developed at the Paul Scherrer Institut, is a single-photon-counting hybrid pixel detector designed for macromolecular crystallography. With more than 1 million pixels covering an area of 243 x 210 mm, it is the largest such device constructed to date. The detector features a narrow point spread function, very fast readout and a complete absence of electronic noise. Unfortunately, this prototype detector has numerous defective pixels and sporadic errors in counting that complicate its operation. With appropriate experimental design, it was largely possible to work around these problems and successfully demonstrate the application of this technology to structure determination. Conventional coarse [phi]-sliced data were collected on thaumatin and a refined electron density map was produced that showed the features expected of a map at 1.6 A resolution. The results were compared with the performance of a reference charge-coupled device detector: the pixel detector is superior in speed, but showed higher R-factors because of the counting errors. Complete fine [phi]-sliced data sets recorded in the continuous-rotation mode showed the predicted advantages of this data collection strategy and demonstrated the expected reduction of R-factors at high resolution. A new readout chip has been tested and shown to be free from the defects of its predecessor; a PILATUS 6M detector incorporating this new technology is under construction.
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