Kevin James Moon

High spatial resolution scintillator screens coupled to CCD detectors for X-ray imaging applications

Abstract New generations of X-ray imaging detectors are being developed for X-ray diffraction studies using both conventional sources and synchrotron beam lines. In many cases, these detectors utilise a scintillator screen to convert the X-ray photon energy into scintillation light. However, the spatial resolution is limited due to the diffusion of light that occurs within the scintillator layer. Results are presented for a scintillation screen that improves the spatial resolution through the use of a specially prepared fibre optic surface where the clad glass has been selectively etched away to leave the protruding columns of core glass. When evaporated onto this surface, the scintillator grows as extensions of these pillars forming discrete columns which individually act as light guides for the scintillation light. A calculation of the system DQE is presented and used to predict the performance to 8 keV X-rays. A Monte Carlo simulation of the X-ray interaction in CsI is also used to evaluate the system DQE above the K shell absorption edges (33 and 37 keV) and therefore determine the useful energy range of the scintillator.

SR instrumentation for optimized anomalous scattering and high resolution structure studies of proteins and nucleic acids (invited)

Crystal structure solution by anomalous dispersion methods has been greatly facilitated using the rapidly tunable station 9.5 at the Daresbury SRS. Both SIROAS and MAD techniques, with IP data, have been used in the phasing of a brominated nucleotide and a seleno deaminase, respectively. The electron density maps in each case are interpretable. Throughput of projects could be improved upon with a better duty cycle detector. Another category of data collection is that at very high resolution. Detailed structure refinement pushes the limits of resolution and data quality. Station 9.5 has been used to collect high resolution (1.4 A) native data for the protein concanavalin A. This utilized very short wavelengths (0.7 A), the image plate, and crystal freezing. A total of 155 407 measurements from two crystals benefited from the on‐line nature of the IP detector device, but a slow and quick pass are required to capture the full dynamic range of the data. There are data seen to 1.2 A and beyond for a pure Mn su...

Charge‐coupled imagers for time‐resolved macromolecular crystallography

There exists considerable promise for the use of charge‐coupled device (CCD) imagers in the fast recording of parts of macromolecular crystal Laue diffraction patterns. As part of this development CCD tests have been made with direct detection of Laue patterns from a small molecule test crystal and a protein crystal. Merging R factors (on intensity), for strong reflections, of 3% have been obtained. A time‐slicing scheme for a CCD camera is discussed based on the stacking of slices held in storage in the CCD in the submillisecond time resolution range.

Large area high-resolution CCD-based X-ray detector for macromolecular crystallography

An X-ray detector system for macromolecular crystallography based on a large area charge-coupled device (CCD) sensor has been developed as part of a large research and development programme for advanced X-ray sensor technology, funded by industry and the Particle Physics and Astronomy Research Council (PPARC) in the UK. The prototype detector consists of two large area three-sides buttable charge-coupled devices (CCD 46-62 EEV), where the single CCD area is 55.3 mm 41.5 mm. Overall detector imaging area is easily extendable to 85 mm 110 mm. The detector consists of an optically coupled X-ray sensitive phosphor, skewed fibre-optic studs and CCDs. The crystallographic measurement requirements at synchrotron sources are met through a high spatial resolution (2048 1536 pixel array), high dynamic range (B10 5 ), a fast readout (B1 s), low noise (o10e) and much reduced parallax error. Additionally, the prototype detector system has been optimised by increasingits efficiency at low X-ray energies for use at conventional lab sources. The system design of the prototype detector is discussed and the proposed method for crystallographic data processing is briefly outlined. r 2002 Elsevier Science B.V. All rights reserved.

High-speed acquisition system for Laue diffraction patterns

Abstract A high-speed acquisition system employing a single direct-detection CCD, for use in time-resolved Laue diffraction studies, is described. As the system is intended as a diagnostic tool to augment conventional whole pattern recording methods, it is designed to be as flexible as possible in terms of its operating modes.

Development of large-area CCD-based x-ray detector for macromolecular crystallography

The design and development of an area CCD-based X-ray detector system, using the first CCD imagers specially designed for macromolecular crystallography, is presented. The system is intended to produce the highest quality data for physically small crystals at synchrotron sources through the use of large CCDs--that is approaching wafer scale. This work is part of a large research and development program for advanced X-ray sensor technology, funded by industry and the Particle Physics and Astronomy Research Council in the UK. The detector has been optimized by increasing its efficiency at low X-ray energies for conventional laboratory sources, and offers fast readout and high dynamic range needed for efficient measurements at synchrotron sources. The detector consists of CCDs optically coupled to a X-ray sensitive phosphor via skewed fiber-optic studs. The individual three- sides buttable CCD consists of 2048 X 1536 27 micrometers square pixels (55.3 X 41.5 mm). The pixel size has been optimized to match diffraction spot profiling needs and the high dynamic range required for such applications. The multiple amplifier outputs possess switched responsivity to maximize the trade-off between signal handling capabilities and linearity. The readout noise is 5 electrons rms at a 1 MHz pixel rate at the high responsivity setting. A prototype detector system comprising two close-butted cooled CCDs is being developed. This system employs a high-efficiency scintillator with very low point spread function, skewed optical-fiber studs (instead of the more usual demagnifying tapers) to maximize the systems detective quantum efficiency and minimize optical distortions. Full system specifications and a novel crystallographic data processing are presented.

Time-Resolved Biological and Perturbation Chemical Crystallography: Laue and Monochromatic Developments

Time-resolved macromolecular x-ray crystallography is a new capability for structural analysis driven by continuing improvements in synchrotron x-ray sources, optics, and detectors (image plates and CCDs). Protein crystal Laue data (stationary crystal and polychromatic x-rays) were recorded at SRS Daresbury station 9.5 and ESRF Grenoble beamline 3, and processed with the Daresbury Laue software package. The Laue method allows exposure times set by the synchrotron electron bunch width, e.g. 50 picoseconds. The instruments and methods developments widen opportunities for perturbation chemical crystallography studies too. A temperature dependent phase transition of a liquid crystal nickel-octahexylphthalocyanine is studied with a rapid readout CCD detector. Structure solution by molecular replacement methods with Laue data is reported for orthorhombic lysozyme. By use of tetragonal lysozyme as a test case it is shown that with fine angular intervals, wide total angular coverage of Laue exposures and the deconvolution of multiples, good connectivity of electron density maps can be realized. The monochromatic rotating crystal method offers possibilites of extremely fast rotations which allow a complete data set to be recorded onto a single image--large-angle oscillation technique (LOT). the processed LOT data looks promising. LOT electron density maps are presented.