Development Of Low-Noise Direct-Conversion X-Ray Area Detectors For Protein Microcrystallography

Abstract

Protein microcrystallography is an active field of study in the synchrotron community, due to the fact that many proteins of scientific interest produce only small, weakly-diffracting crystals. New detectors must be developed to improve data quality and facilitate new experimental protocols, such as low-flux single-shot diffraction from microcrystals. The pioneering work in microcrystallography has been done primarily with phosphor-coupled CCDs and, more recently, with photon-counting pixel array detectors. However, both technologies have drawbacks that inhibit further development of the field. Phosphorcoupled CCDs have a large point spread function and relatively low signal-tonoise ratio (on the order of 0.5-1) for single x-ray photons. Photon-counting pixel array detectors have superior noise performance, but suffer from large pixel size and detector systematics which deserve consideration. To fill the need for a detector with small pixels and low x-ray equivalent noise, a deep-depletion CCD has been developed with 24 [MICRO SIGN]m x 24 [MICRO SIGN]m pixels and a point spread < 50 [MICRO SIGN]m FWHM. This device is based on the direct detection of xrays in silicon, which yields a large number of charge carriers per stopped x-ray, such that the signal from a single x-ray photon far outweighs the detector read noise. The design of this device will be described, along with characterization and initial protein crystallographic measurements.