During the 1990's, macromolecular crystallography became progressively more dependent on synchrotron X-ray sources for diffraction data collection. Detectors of this diffraction data at synchrotron beamlines have evolved over the decade, from film to image phosphor plates, and then to CCD systems. These changes have been driven by the data quality and quantity improvements each newer detector technology provided. The improvements have been significant. It is likely that newer detector technologies will be adopted at synchrotron beamlines for crystallographic diffraction data collection in the future, but these technologies will have to compete with existing CCD detector systems which are already excellent and are getting incrementally better in terms of size, speed, efficiency, and resolving power. Detector development for this application at synchrotrons must concentrate on making systems which are bigger and faster than CCDs and which can capture weak data more efficiently. And there is a need for excellent detectors which are less expensive than CCD systems.
A 2D photon counting digital pixel array detector is being designed for static and time resolved protein crystallography. This room temperature detector will significantly enhance monochromatic and polychromatic protein crystallographic throughput data rates by more than two or three orders of magnitude when compared to present data collection systems. The detector has an unbounded photon counting dynamic range and exhibits superior spatial resolution when compared to present crystallographic phosphor imaging plates or phosphor coupled CCD detectors. The detector is a high resistivity N-type Si with a pixel pitch of (150 X 150) microns, and a thickness of 300 microns that is bump bonded to an application specific integrated circuit. The event driven readout of the detector is based on the column architecture and allows an independent pixel bit rate above 1 million photons/sec. The device provides energy discrimination and sparse data readout that yields minimal dead time. This type of architecture allows an almost continuous (frame-less) data acquisition, a feature not found in any current detector being used for protein crystallographic applications. For the targeted detector size of (1000 X 1000) pixels, average hit rates greater than 1011 photons/sec for the complete detector appears achievable. This paper will present an overview of the hybridized detector performance which includes the analog amplifier response and the photon counting capabilities of the (16 X 16) array operating with both digital and analog circuitry. Also the operation of the serial interface will be described.
We have designed two different X-ray pixel array readout Integrated Circuits for silicon pixel detectors operating between 4 keV and 25 keV. The first allows full readout of the deposited charge for each X-ray photon and is intended for imaging X-ray spectroscopy. The second is a photon counting device capable of very high rates (1 MHz per pixel) but without energy resolution. This paper compares the architectures of these two detectors and presents experimental data from complete bump-bonded devices. These detectors have many applications from X-ray diffraction to material inspection and satellite based X-ray imaging.
The 4 X 4 multiple CCD X-ray detector installed in the beamline 45XU of the SPring-8 facility in Japan was examined by acquiring X-ray diffraction images of lysozyme crystals. The detector system was calibrated at the beamline by observing X-ray images of a flood-field and a mask pattern generated by the synchrotron radiation X-ray beam. It was found in the present work that the quality of the X-ray images observed is limited by an unexpected spike noise, the origin of which was suspected to be the (gamma) -rays emitted from the radioisotopes remaining in the X-ray scintillating screen. Image analysis carried out with a median filter predicted, however, that the image quality could be as high as designed, once the noise as well as the grain colonization is removed from the screen.
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 system's detective quantum efficiency and minimize optical distortions. Full system specifications and a novel crystallographic data processing are presented.
This paper presents work done using a detector array integrated on a single silicon chip and shows its physical characteristics and performance. The emphasis here is on array uniformity and the accurate measure of incident intensities. All arrays suffer non-uniformity to some extent due to manufacturing tolerances. The influence of this on measured data is considered and two approaches to correction are presented: (1) It is shown that spectra built up by measurement of single events can yield accurate peak intensities and positions. (2) Where spectra are measured in the normal way by summing many events before readout (higher dynamic range) a correction for non-uniformity is desirable. A new correction algorithm is illustrated.
After 3 years experience of operating very large area (210 mm X 210 mm) CCD-based detectors at the Advanced Photon Source, operational experience is reported. Four such detectors have been built, two for Structural Biology Center (APS-1 and SBC-2), one for Basic Energy Sciences Synchrotron Radiation Center (Gold-2) at Argonne National Laboratory's Advanced Photon Source and one for Osaka University by Oxford Instruments, for use at Spring 8 (PX-210). The detector is specifically designed as a high resolution and fast readout camera for macromolecular crystallography. Design trade-offs for speed and size are reviewed in light of operational experience and future requirements are considered. Operational data and examples of crystallography data are presented, together with plans for future development.
This paper presents two novel applications of X-ray diffraction studies and their preliminary results using an MSGC. One involves the rapid analysis of single crystal structures using information on both the position and timing of incident X-rays. With this application, crystal structures of organic molecules could be obtained in a measurement time of 1 approximately 10 minutes. The other involves time-resolved X-ray diffraction measurements on the order of milliseconds. The time variation of the SAXS (small angle X-ray scattering) pattern of the protein solution was measured up to a frame time of 10 milli-seconds.
An intermediate electron multiplier for a MicroStrip Gas Chamber has been developed using a capillary plate. Our purpose was to develop a capillary plate as an intermediate electron multiplier able to be steadily operated under a medium gain of about one hundred and under a high counting rate. The capillary plate used here consists of a bundle of fine glass capillaries each with a diameter of 100 micrometers and a thickness of 1 mm, and has a 9.5 X 9 cm2 detection area and a 57% opening aperture ratio. In order to avoid the charge-up effect on the surfaces of the capillaries, some conductivity was added on the capillaries surfaces, and consequently about a 40 M(Omega) resistivity appeared between both sides of the plate. The conductivity dramatically improved the plates performance: the capillary plate was operated stable with counting rates up to 105 cps/mm2 and no decrease in the gas gain was observed. The capillary plate sufficiently satisfies the requirements for a pre-amplification device for an MSGC. In this paper, a 2D MSGC combined with the above conductive capillary plate was examined, and found to achieve stable operation with a sufficient gain under a high counting rate with no discharge problems.
The RAPID detector system previously reported on in SPIE volume 2521, has successfully completed the final stage of its commissioning. During this period several of the Synchrotron Radiation Source User groups were invited to perform trial experiments with the new detector system. Over a period of one month in late 1998 several types of experiments were performed on the flagship small angle scattering station 16.1, ranging from polymer diffraction rheometry to time resolved muscle diffraction. The results and detector assessments from some of these experiments are presented. A discussion is made of refinements to the system which would further enhance its performance.
Modern X-ray diffraction applications demand for imaging detectors with large pixel number, high intensity precision, high rate capability and dead time free operation. Detailed studies with a simulation program, which has been developed to investigate the performance of different detector types, show that a large area gaseous single photon counter is very well suited to meet the aforementioned requirements. The prototype detector, which has been built according to the specification profile from the simulations, belongs to a new generation of gaseous detectors using novel technologies for both gas amplification (using a MicroCAT) and position encoding (using 2D resistive charge division). This local interpolation method combines the advantages of a pure pixel read-out (high local and global rate capability) with those of a projecting read-out (small number of channels). The current prototype system has an active area of 28 X 28 mm2 with effectively 140 X 140 pixels. Various test measurements at synchrotron light sources with biological samples have been performed demonstrating the good spatial resolution (around 300 micrometers FWHM), the high intensity precision (only Poisson limited) and the high rate capability (exceeding 1 MHz spot rate). Moreover, time resolved measurements in the microsecond domain have been performed, and fine angular slicing has been applied to protein crystallography experiments. The detector has a high reliability and robustness, particularly when compared to conventional gaseous detectors, and the extension of the technology used to larger active areas is feasible.
A position-sensitive ionization chamber has been developed with backgammon-type-segmented electrodes. This novel detector possesses a linear range of 8 mm for determining the incident position of the X-ray beam incoming. The position resolution was found to be better than 10 micrometers , probably close the sub-micrometer region. Owing to its high spatial resolution, the position-sensitive ionization chamber was able to commit that the gradual decrease observed in the X-ray beam intensity at the BL44B2 of the SPring-8 facility was mainly due to the spatial variation of the X-ray beam position in time. The present work also confirmed the applicability of the novel detector to the feedback correction system for the beam stabilization.
Free-standing polycrystalline diamond films grown by microwave plasma CVD technique were tested for detection X- ray radiation from a synchrotron source. Two different configurations of collection electrodes on diamond were used. The first (sandwich) geometry uses a thin amorphous conducting layers formed by nitrogen ion irradiation on both sides of the diamond plate. The second (planar) one, which showed better characteristics, comprises of an interdigitated planar array of metallic contacts on a face exposed to photon flux. However, in both cases a polarization effect that leads to a decrease of the detector response with exposition time, was observed. Better device performance is expected for diamond films of improved quality.