A large area CMOS detector for shutterless collection of x-ray diffraction data

Recent developments in CMOS devices have improved their radiation hardness, response linearity, readout noise and thermal noise, making them suitable for x-ray crystallography detectors. Large (14.8 x 9.4 cm) CMOS sensors with a pixel size of 100 x100 microns are now available that can be butted together on three sides. We have fabricated a 6-tile system in a 2x3 array with a 28.2 x 29.5 cm continuous imaging area. To make an x-ray detector the CMOS sensor is covered with a 3 mm flat fibre-optic plate (for radiation protection) and a Gd2O2S:Tb scintillator screen. A special feature of these systems is that they can be read out continuously at 10 frames/sec with excellent dynamic range without interrupting data collection. We have installed this system at beamline 4.4.2 of the Advanced Light Source synchrotron. Anomalous diffraction data were recorded without an x-ray shutter, rotating the crystal sample continuously with an exposure time of 0.1 sec/frame and a rotation speed of 1°/sec for 180 degrees. The 1,800 frame datasets were processed in D*TREK and XDS data analysis programs and experimental phases were determined in PHENIX. The crystallographic results are typically significantly better than equivalent data recorded on a conventional CCD system, due to the 10X finer angular resolution of the recorded data. Very large systems can now be made that would have an active area of 56 x 59 cm2 with 33 x 106 pixels.