A Large Area CMOS Detector for Shutterless Collection of X-ray Diffraction Data
Driven by enormous market potential in medical imaging, recent developments in CMOS devices have improved their radiation hardness, response linearity, readout noise, thermal noise, and dynamic range, such that they are now 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 29.5 x 28.2 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 phosphor screen.
A special feature of these systems is that they can be read out continuously at up to 30 frames/sec with excellent dynamic range, without interrupting data collection.We have installed this system on beamline 4.2.2 of the Advanced Light Source synchrotron. Excellent data sets are now routinely recorded with this system. Typical data sets are 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 over a 180 range. Such 1,800-frame datasets are easily processed with standard data analysis programs (e.g. D*TREK, XDS). Experimental anomalous dispersion phases are determined in the Phoenix program suite. 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 CMOS systems (active areas up to 56 x 59 cm2 with 33 x 106 pixels) can now also be made.