Abstract
Recent advances in X-ray detector technology have resulted in the introduction of segmented detectors composed of many small detector modules tiled together to cover a large detection area. Due to mechanical tolerances and the desire to be able to change the module layout to suit the needs of different experiments, the pixels on each module might not align perfectly on a regular grid. Several detectors are designed to permit detector sub-regions (or modules) to be moved relative to each other for different experiments. Accurate determination of the location of detector elements relative to the beam-sample interaction point is critical for many types of experiment, including X-ray crystallography, coherent diffractive imaging (CDI), small angle X-ray scattering (SAXS) and spectroscopy. For detectors with moveable modules, the relative positions of pixels are no longer fixed, necessitating the development of a simple procedure to calibrate detector geometry after reconfiguration. We describe a simple and robust method for determining the geometry of segmented X-ray detectors using measurements obtained by serial crystallography. By comparing the location of observed Bragg peaks to the spot locations predicted from the crystal indexing procedure, the position, rotation and distance of each module relative to the interaction region can be refined. We show that the refined detector geometry greatly improves the results of experiments.
Highlights
The advent of X-ray Free Electron Lasers has necessitated the development of integrating Xray detectors capable of full frame readout at the pulse repetition rate of the X-ray source
We found that we needed several thousand indexed patterns to refine the position of each panel of the CSPAD individually (32 rigid groups), but when the geometry of each quadrant was well characterized using some previously measured data and the geometry could be refined only at the level of quadrants (4 rigid groups), the number of indexed patterns was drastically reduced to a couple of hundred. 4.5 Suggested refinement procedure An optimal sample to refine the detector geometry would fill the entire detector with Bragg peaks
We have described a simple scheme by which the detector module geometry can be optimized using serial crystallography data, resulting in sub-pixel accuracy in the determination of the positions and orientations of detector modules
Summary
The advent of X-ray Free Electron Lasers has necessitated the development of integrating Xray detectors capable of full frame readout at the pulse repetition rate of the X-ray source. Movable modules introduce the necessity of determining the relative locations of each module with respect to the beam-sample interaction point each time the detector configuration is changed. It makes the process of generating an image from the measured data more complicated. The detector geometry is progressively refined by comparing the location of measured Bragg peaks to the location of peaks predicted once the crystal reciprocal lattice vectors have been determined using autoindexing [11,12] This method can be applied using either a dedicated calibration sample or, in the case of an SFX experiment, from the serial crystallography data itself. This technique can be applied post facto for improvement of previously collected serial crystallography data
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
