A frame‐store pn‐junction CCD detector was applied to the energy‐dispersive X‐ray Laue diffraction study of a γ‐LiAlO2 crystal with white synchrotron radiation. Exploiting the simultaneous spatial and energy resolution of the detector the crystallographic unit cell of γ‐LiAlO2 could be determined without any a priori information about the sample. The potential for application in X‐ray structure analysis is tested by comparing experimental structure factors taken under a single exposure with those calculated from the known crystal structure. After correcting the measured spot intensities by angular and energy‐dependent parameters, the agreement between experimental and theoretical kinematical structure factors is better than 10%.
A new approach to achieve sub-pixel spatial resolution in a pnCCD detector
with 75 × 75 μm2 pixel size is proposed for X-ray applications in
single photon counting mode. The approach considers the energy dependence of
the charge cloud created by a single photon and its split probabilities
between neighboring pixels of the detector based on a rectangular model for
the charge cloud density. For cases where the charge of this cloud becomes
distributed over three or four pixels the center position of photon impact
can be reconstructed with a precision better than 2 μm. The predicted
charge cloud sizes are tested at selected X-ray fluorescence lines emitting
energies between 6.4 keV and 17.4 keV and forming charge clouds with size
(rms) varying between 8 μm and 10 μm respectively. The 2 μm
enhanced spatial resolution of the pnCCD is verified by means of an x-ray
transmission experiment throughout an optical grating.
A crystal of hen egg‐white lysozyme was analyzed by means of energy‐dispersive X‐ray Laue diffraction with white synchrotron radiation at 2.7 Å resolution using a pnCCD detector. From Laue spots measured in a single exposure of the arbitrarily oriented crystal, the lattice constants of the tetragonal unit cell could be extracted with an accuracy of about 2.5%. Scanning across the sample surface, Laue images with split reflections were recorded at various positions. The corresponding diffraction patterns were generated by two crystalline domains with a tilt of about 1° relative to each other. The obtained results demonstrate the potential of the pnCCD for fast X‐ray screening of crystals of macromolecules or proteins prior to conventional X‐ray structure analysis. The described experiment can be automatized to quantitatively characterize imperfect single crystals or polycrystals.
This paper describes a novel method for fast online analysis of X-ray Laue spots taken by means of an energy-dispersive X-ray 2D detector. Current pnCCD detectors typically operate at some 100 Hz (up to a maximum of 400 Hz) and have a resolution of 384 × 384 pixels, future devices head for even higher pixel counts and frame rates.The proposed online data analysis is based on a computer utilizing multiple Graphics Processing Units (GPUs), which allow for fast and parallel data processing. Our multi-GPU based algorithm is compliant with the rules of stream-based data processing, for which GPUs are optimized. The paper's main contribution is therefore an alternative algorithm for the determination of spot positions and energies over the full sequence of pnCCD data frames. Furthermore, an improved background suppression algorithm is presented.The resulting system is able to process data at the maximum acquisition rate of 400 Hz. We present a detailed analysis of the spot positions and energies deduced from a prior (single-core) CPU-based and the novel GPU-based data processing, showing that the parallel computed results using the GPU implementation are at least of the same quality as prior CPU-based results. Furthermore, the GPU-based algorithm is able to speed up the data processing by a factor of 7 (in comparison to single-core CPU-based algorithm) which effectively makes the detector system more suitable for online data processing.
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