The development of synchrotron X-ray diffraction at Daresbury Laboratory and its legacy for materials imaging
R J Cernik
Abstract
This paper covers the instrument development, some selected science highlights and the legacy of the X-ray diffraction facilities on the synchrotron radiation source (SRS) at Daresbury Laboratory from 1985 until its closure in the autumn of 2008. The evolution of the data collection instrumentation; detector development and research in synchrotron powder diffraction is discussed. The legacy of the research that started at Daresbury and subsequently spread worldwide is also covered with a focus on X-ray colour diffraction imaging.
Introduction
The synchrotron radiation source (SRS) at Daresbury Laboratory, UK, was the world’s first synchrotron dedicated as a user facility offering a range of photon energies from infrared to hard X-rays. Between 1981 and 2008 the SRS provided insights into a very broad spectrum of scientific research including the collection of data used by Sir John Walker to help elucidate the operation of complex membrane proteins. He later won a part share of the 1997 Nobel Prize in chemistry for this work. Other prizes and accolades followed but when the SRS finally closed a commentary article in Nature entitled ‘two million hours of science’ said ‘the SRS has had a substantial role in what has truly become a revolution in characterization science. With over 5,000 papers published, research and instrumentation from the SRS continues to influence facilities across the world’ [1]
This paper tracks the developments in powder Diffraction that started at Daresbury Laboratory on station 9.1 later facilitating research using synchrotron powder diffraction worldwide. The first paper on the design of the powder beamline at Daresbury was published by Hatton et. al. in 1984 [2] followed shortly by an example of its use in high pressure research [3] . The early design of station 9.1 incorporated a two circle diffractometer with a single crystal goniometer attachment, energy dispersive diffraction, high pressure attachments, a diffracted beam analyser as well as step scanning scintillation counter. It seems incredible now, given the very large number of synchrotron powder diffraction publications, but there was not sufficient confidence at the time to dedicate a whole station to powder diffraction alone.
At the outset there was a strong demand from the user community to use this new hardware to dynamically study solid state reactions in-situ and at high temperatures as well as trying to solve crystal structures from the powder diffraction data alone. One of the author’s first jobs at Daresbury was to design/specify a furnace and position sensitive detector system for dynamic studies of chemical reactions1.
Our initially small group of users attempted experiments that became more successful as the storage ring itself became more reliable. Initially a series of well documented RF window failures (early 1980s) caused regular beam drop outs. As these problems were systematically resolved, by the pioneering efforts of the machine physicists of the time, the experiments became more reliable. By the beginning of 1986 there was a user group of approximately 35 researchers interested in X-ray diffraction who were scheduled, usually by telephone, by the powder project group chairman (Richard Catlow) and the new station master for 9.1 (the author). The subsequent development of e-mail and the internet2 made scheduling a moreprofessional exercise with allocation panels to cope with the heavy oversubscription that began very soon after the facility began to operate reliably. Early users will attest to the uncertain nature of finding the beam let alone being able to collect reliable data.
A problem of being first to develop a user facility from an operating synchrotron is that the main design faults are quickly recognised. A better design for subsequent machine lattices emerged from the work of Chasman and Green in the form of a double bend achromat, or DBA [4,5] . This simple lattice modification split the bending magnets into two sections with a focussing magnet in between to compensate for electron dispersion resulting in a much brighter source. It was not possible to upgrade the SRS with a DBA but in 1987 the SRS received its first big upgrade in the form of a new lattice that significantly increased the brightness of the source. This shutdown to install the new magnetic lattice lasted approximately 10 months and was the ideal opportunity to redesign the powder diffraction facilities.
1I spent a couple of hours in Neville Greaves’ office on my first day at work in Daresbury (Jan 2nd 1986) whilst he carefully explained to me the users’ ideas about dynamic experiments. He then delegated me with the task of specifying the design and procurement of a furnace/position sensitive detector system.
2Daresbury Laboratory was visited by several delegations from CERN during the 1980s in order to discover the type and content of data files that might be useful for exchanging scientific data helping to develop the HTML file structure.
Equipment development
It was clear by 1987 that a single multipurpose station was not satisfying the user communities’ demands. Experimental switchovers, competing sample geometries and detector changes lost nearly 35% of the available user time. The energy dispersive diffraction experiments were given their own station (9.7) [6] mainly for high pressure and time resolved studies of chemical reactions [7] . Station 9.1 was refurbished and optimised for high resolution powder diffraction in Debye Scherrer capillary mode [8] with a simple and effective channel cut monochromator to facilitate quick wavelength changes [9] . The breadth and line shape of the diffraction patterns from the refurbished station 9.1 was measured by series of standards [10] . By the late 1980s one powder station was insufficient for the growing demand to collect high resolution powder diffraction data. As a consequence, a new flat plate powder diffractometer was designed [11] with Hart Parrish parallel collimators as the main diffraction geometry [12,13] . This new diffractometer was initially installed on station 8.3 but was later moved to a purpose built station (2.3). The robustly engineered diffractometer had a number of design features to allow very accurate collection of diffraction data including the use of direct encoder closed loop feedbacks on the 2θ arm. This engineering was tested by measuring lattice parameters accurate to 5 parts in a million [14] and by testing indexing routines to very high accuracy [15] 3. The success of the 2.3 diffractometer design was borne out by improved versions appearing at the ESRF, Swiss Light Source; Swiss Norwegian beamline (at ESRF); NSLS2 and on I11 at the Diamond Light Source. The team responsible for these developments is shown in figure 1. Towards the middle of the 1990s three more experimental stations grew from the powder diffraction and X- ray physics user communities. Station 16.3 [16] was built to study charge density waves, magnetic and other properties of materials and station 9.8 [17] was built to cope with a new user demand from chemists wanting to solve single crystal structures from very small or highly imperfect crystals. The use of synchrotron radiation in this respect improved the signal-to- noise ratio for the weaker peaks and rapidly allowed access to far more measurable reflections. Station 9.8 was so successful it was later cloned on station 16.2.
3The lattice parameter measurement detected a 3 in 106 deviation from linear due to the diffractometer arm bending under gravity at very low and very high 2θ angles.
Figure 1 shows the X-ray diffraction team circa 1990, bottom row (from the left) Phil Pattison, Bob Cernik, Simon Clark, Mike Miller and Killian O’Reilly, top row (from left) Manolis Pantos, Dave Laundy, Richard Catlow, Graham Bushnell-Wye, Andy Fitch, Alf Neild, Eric Doohryee, one of our detector group summer students and Ian Sumner.
Subsequent single crystal experiments pushed the boundary between samples treated as powders and samples with powder grains which were essentially small single crystals. The energy dispersive high pressure community grew and developed a large volume press on station 16.4 [18] [19] and the final addition to diffraction/materials arsenal arrived with the construction of station 6.2 [20] [21] [22] to observe in-situ reactions in materials using a mixture of diffraction, X-ray absorption spectroscopy and small angle scattering.
Towards the end of the lifetime of the SRS station 9.5 became available and was converted to a bespoke high pressure station [23]. A very simple sideways beam deflection, diamond anvil cell and image plate system gave outstandingly low noise patterns for the interpretation of complex structures. For example it was shown how partial melting in the Earth’s mantle shapes geochemical structures in volcanic rocks [24]. The user groups on station 9.5 also showed how silicate mineral inclusions in diamonds form carbonatite melts in the mantle transition zone and deep upper mantle.
Detector development
From the early days of the establishment of synchrotron radiation at Daresbury it was realised that detectors would play a vital role in the success of the experiments and consequently this activity was strongly supported.
Initially detectors were built to cope with XRD and SAXS data on a fast timescale. Electronic area detectors and linear CMOS arrays tend to dominate data collection strategies today. However, at the time, gas filled, position sensitive proportional counters were a good way to obtain the required combination of low noise and speed. A unique combination of curved PSD for the wide angle (or powder diffraction) and quadrant detector was designed for fast, high spatial resolution data collection across length scales from microns to atoms [25].
Detector developments were not restricted to monochromatic techniques with the energy dispersive stations being upgraded with a three angle, 3 element Ge solid state detector [26]. This development had a number of benefits in overlapping reflections for 2θ calibration, extended length scales and better statistics.
In the early 1990s attention was drawn to the image plate detectors under development in Japan [27-35]. These detectors were two orders of magnitude more sensitive in the low photon flux region than film. This made them very attractive for 2D powder pattern recording as the Debye-Scherrer rings could be circularly integrated to give a large statistical improvement. In addition, by measuring the whole DS ring, preferred orientation and non- isotropic strain could be measured. These detectors were integrating devices but nevertheless revolutionised those experiments where only a limited volume of sample s available such as high pressure studies using diamond anvil cells [36].
Towards the end of the SRS lifetime a development from a UK funded research programme led to the design of a detector with a 20 X 20 array of energy sensitive pixels. This was used for the first time to collect energy dispersive data using a matching set of parallel collimators. The result was to simultaneously collect a series of diffraction patterns from specific gauge volumes inside the solid. For the first time an energy dispersive 3D map was built up on a number of test samples [37]. This detector was the forerunner of the HEXITEC system [38] which delivered an 80 X 80 array of energy sensitive CZT pixels with 500 eV resolution up to 150 keV4. This development allowed the subsequent development of X-ray colour imaging (or combined X-ray diffraction and tomography) described in the next section.
X-ray science, examples and legacy
High resolution powder diffraction
Powder diffraction spectra can be collected with parallel beam geometry at very high resolution to the extent that the instrumental resolution function can become almost negligible. Under these circumstances peaks that were not resolved using laboratory diffractometers became resolved, subtle features of microstructure and peak broadening became more understandable and Rietveld refinement took on a new, far higher, level of accuracy. The degree to which highly crystalline samples gave separated peaks led to a number of attempts to solve crystal structures directly from the powder diffraction data.
The first success came with cimetidine [39] which is a histamine antagonist used in the treatment of ulcers. Having several polymorphic forms and giving excellent diffraction data with a relatively small unit cell it was a good sample choice. The polymorph chosen had been previously solved by single crystal methods. However auto indexing was seen to give the correct cell with a very high figure of merit, peak decomposition and use of direct methods gave partial structures. The use of automatically recycled Fourier maps solved the structure and subsequent Rietveld refinement gave a very accurate structure. The final Fourier difference maps were even able to locate the hydrogen atoms although the methyl group was somewhat diffuse.
Other methods of structure solution [40] on the cimetidine data showed faster convergences for genetic algorithms and global optimisation for cimetidine and other organic structures such as ibuprofen. These authors subsequently published an efficient routine for solving structures from powders [41]. Other approaches using cycled Fourier and direct methods were optimised for powder data structure solution and are available freely for academic users, for example [42] and [43].
Despite hardware and software advances the solution of crystal structures from powder data alone is not guaranteed. It depends a great deal on the quality of the diffraction pattern although prior knowledge or use of supplementary data from electron microscopy (for example) can be successful. In the case of TNU-9 a high silica zeolite [44] was solved by a combination of synchrotron data from Daresbury and Brookhaven and high resolution transmission electron microscopy. Attfield et.al. [45] demonstrated the mechanism for the Verwy transition (where a material becomes insulating at low temperatures by freezing conduction electrons into a regular array) in iron oxyborate Fe2OBO3. Their results, based on the powder diffraction data refinements, supported the model where the system adopts a charge-ordered state below 317K, in which Fe2+ and Fe3+ ions are equally distributed over structurally distinct Fe sites. The use of synchrotron HRPD in crystal structure solution is now so widespread papers barely mention the technique focussing instead on the material and its applications. This research was greatly facilitated by the early experiments on station 9.1 at Daresbury.
Non-crystalline studies
The advent of synchrotron radiation gave a new and exciting direction to the study of non-crystalline materials by diffraction methods. The pioneering work of Zenike, Prins and Bernal (refs) showed how diffraction data could be used to build a model for liquids and amorphous or disordered systems. The method they described later became known as a radial distribution function (RDF) which is essentially the probability of finding two atoms separated by a distance r. The RDF contains structural information between pairs of atoms with the peak areas being determined by the number of atomic pairs at each distance. In effect this corresponds to the coordination numbers. The RDF is easy to interpret for an amorphous material containing only one type of atom, for example, amorphous carbon. Those samples containing more than one atomic species give rise to a more complex situation and it is not always possible to interpret the RDF with complete certainly as different pairs of atomic species can have almost the same interatomic distance and contribute to the same peak.
The detailed atomic structural study of non-crystalline samples with multiple atomic species was considered a real challenge but the advent of tuneable synchrotron radiation led to a considerable advance in the determination of atomic pair structures using both spectroscopic and diffraction methods. Using synchrotron radiation of varying incident energies it was possible to tune just below the absorption edge of a particular atomic species to change its scattering power. This method provides complementary information to X-ray absorption techniques like EXAFS. The resonant diffraction data provides information about the coordination of a specific atomic species, using scattering data obtained at two photon energies just below the absorption edge of the atomic species of interest. In contrast to EXAFS, scattering data are readily obtained at the low scattering vectors corresponding to the missing region from the EXAFS data. Thus, it provides considerably more information about next near neighbours and beyond, as well as systems with a broad spread in near neighbour distances. Generally, however, it cannot obtain information at large scattering vectors that are accessible to EXAFS. As a consequence, it often cannot resolve two different, almost equal interatomic distances. For a two component system αβ, if the α−α, α-β and β-β distances are close, the method cannot determine whether the neighbors of an α are α or β atoms – or some combination of αs and βs.
This latter shortcoming of anomalous X-ray scattering (AXS) has now been overcome. It has been known for a very long time that one can, in principle, distinguish between α-α, β-β and α-β neighbours with AXS by taking measurements at two photon energies just below the α edge and just below the β edge, as well as at one photon energy far from both edges[1].
From these data, one obtains α-β partial pair distribution functions (PPDFs) which give the number of β atoms surrounding an α atom at a distance r. The problem has been the extreme sensitivity of these PPDFs to experimental errors and, particularly, uncertainties in the inelastic scattering which must be subtracted from the measured intensities. What Ishii et al. have done to overcome this limitation is to use a diffracted beam analyser to eliminate the inelastic scattering experimentally [42]. This analyser consists of a Sagittally-focusing graphite monochromator which disperses the energies emanating from the sample onto a position-sensitive detector[53,46]. Thus at each scattering angle, an energy spectrum is measured with elastic, fluorescent and Compton peaks separately resolved. These data have resulted in a dramatic improvement in the quality of the derived PPDFs. The sample studied, amorphous MoGe3, is of interest because earlier work had suggested that MoGe3 is the metal-rich endpoint for phase separation in the sputtered Mo-Ge amorphous alloy system[75]. This is unexpected, as the first crystalline compound found in the equilibrium Mo-Ge system is MoGe2. Thus one important question for this study was whether a new compound is formed in the sputter-deposited alloys. The primary results of this study are shown in Figure 1, which shows the Ge-Ge, Ge-Mo, and Mo-Mo PPDFs. Analysis of the Mo-Ge PPDF implies an eight-fold coordination of Mo by Ge, – a conclusion unobtainable by EXAFS. Further, there is no evidence of phase-separation. Although not exploited in this paper, there is clearly additional information in the higher shells of the PPDFs due to the lower starting scattering vector.
These results highlight the great promise of AXS for the study of amorphous materials, especially binary alloys. It gives the electron density (and hence the atomic distribution).
High pressure research
In 1990 the image plate detectors described in the last section had risen to some prominence. An expeditionary party consisting of Richard Nelmes, Peter Hatton, Jeremy Cockcroft, Malcom McMahon and the author visited the Photon Factory (Tskuba, Japan) which was then the centre for image plate development especially connected with high pressure research. [46, 47]. The idea to take a diamond anvil cell with a small monochromatic beam and collect the whole, or most of, the available Debye Scherrer rings on an image plate area detector was quite new and very promising. The Daresbury detector group acquired a porotype image plate reader and station 9.1 was optimised for this type of high pressure research. Systematic studies of materials under high pressure yielded new insights into elemental and compound structure at elevated pressures. For example, the discovery of a new phase of Si [48], the high pressure structure of InSb [49] or the study of an incommensurate high pressure phase of group V metals [50].
Edmund Clerihew Bentley (1875-1956) was a detective fiction writer who was accredited with writing the following lines at the age of sixteen whist still at school: Sir Humphrey Davy, Abominated gravy. He lived in the odium. Of having discovered sodium. Sir Humphrey could not have imagined the complexity of the high pressure forms of sodium as elucidated by Gregoryanz et.al. [51]. They used single-crystal high-pressure diffraction techniques to observe seven different crystalline phases and noted that slight changes in pressure and/or temperature induce transitions between many structural modifications, several of which are highly complex.
The field of high pressure research grew so rapidly station 9.5 was adapted to collect data from samples in diamond anvil cells as described earlier. An example of this work came with an analysis of the mineral ikaiyite [52]. This was a low temperature (~ 0°C) modestly high pressure form of calcium carbonate formed by crystallisation out of carbonate rich sea water found in in deep sea lochs and fjords. The complex structure was solved by a mixture of HRPD at high pressure from Daresbury Laboratory and with deuterated sample neutron data. The mechanism of crystallisation could be responsible for capturing up to 4% of global carbon.
In-situ and dynamic studies of materials
The brightness and photon flux associated with synchrotron light made time resolved or dynamic experiments possible. At Daresbury Laboratory these were being planned in the early 1980s. Most conventional diffractometers at the time operated with a step scan approach which was clearly unsuitable for this type of research as a solid state transformation of the sample could take place before the data were fully collected. After many trials the first really successfully diffraction experiment (combined with spectroscopy) showed how the mineral aurichalcite decomposed with temperature into an industrially useful Cu on ZnO catalyst [53]. The 2D diffraction data showed the decomposition and the simultaneous EXAFS data showed the origins of the Zn clusters. This curved position sensitive detector was rather slow but stimulated the development of a family of linear solid state detectors for crystallography and diffraction [54]. The structure of aurichalcite was not known at the time the paper was published but a subsequent single crystal experiment on station 9.8 using a very small imperfect crystal solved the structure [55]. The reason why aurichalcite rather than its close mineral relative hydrozincite is preferable for catalysis decomposition lies with its crystal structure. Whereas hydrozincite has a regular ionic stacking arrangement aurichalcite has an alternate unit cell translation of 0.5. This leads to weaker hydrogen bonds and hence easier decomposition with temperature.
Many reactions happen at high temperature and pressures. It is relatively straightforward to build a cell to undertake these reactions. However it is often difficult, especially at high pressures, to design a system to allow a wide enough angle for the scattered light to emerge. For faster experiments where a limited exit aperture is available the energy dispersive diffraction technique is suitable. The inherent energy resolution is governed by the solid state detectors which is of the order of 2% dE/E. An example of a hydrothermal synthesis cell was reported by Evans et.al. [56]. Their experiment indicated how the course of a typical hydrothermal reaction could be followed, and showed the formation of a microporous tin chalcogenide phase. The starting compounds were mixed in the ratio Sn:S:NMe40H:H20 of 1:2;1:30 and sealed with a Teflon coated stirrer flea in the high pressure sample vessel (commonly known as a bomb5). The bomb was then placed in a metal block and spectra recorded every 300 s as the block was warmed to, and maintained at, 180 “C. The appearance of the new phase was clearly visible after 50 min, and its crystallization was observed. Their results showed that under these conditions the reaction proceeded smoothly towards the product phase. Another example of an in situ experiment involved the examination of the dispersive diffraction patterns showing the rapid hydration of tricalcium aluminate from the time water was added. The tricalcium aluminate starts to be consumed almost immediately followed by the growth of the inter-mediate phase; after about 200 s the intermediate phase disappears abruptly and simultaneously with the commencement of rapid stable hydrate growth. [57].
A natural logical step in the study of reaction chemistry using energy dispersive diffraction was to develop multiple detectors. A three element, liquid nitrogen cooled, Ge detector with an angular spread of approximately 7° 2θ demonstrated that better quality data could be collected over a wider energy range which reduced counting times and extended the range and complexity of the samples that could be studied. However this detector still had to be cooled and contained only 3 elements. A design for a multiple element Si detector showed promise but with high energy limitations above ~ 25 keV [58]. A detector capable of stopping a wide range of energies up to and beyond 150 keV required higher density semiconductor materials and bespoke ASICs.
5This term for a high T high P cell caused a major security alert when this apparatus was mailed to the Daresbury stores labelled ‘high pressure bomb’
This development came with the HEXITEC programme [59] and enabled the many of the colour X-ray imaging described in the next section.
Imaging using powder diffraction/scattering
The energy dispersive diffraction method can define a very small illuminated volume (gauge volume) in the sample if the incoming beam is small (cross section ~ 10-20 mm) and the diffracted beam collimator is also of the same dimension. This small volume was used to good effect when examining the scattering from the hydrothermal cell described earlier. The scattering from the surrounding vessel, windows and solution is not seen, only the gauge volume illuminated. It was realised by Hall et.al. that if a sample is scanned finely in x, y and z through this gauge volume a 3D image of the sample containing diffraction information can be built up [60]. This method is known as tomographic energy dispersive diffraction imaging or TEDDI. It has been used to characterise a range of materials. The inherent crystallographic data contained in each gauge volume has been shown to be reproducible and refineable when the data are corrected for absorption [61]. TEDDI has been used to study the penetration of iodine solution into chalk bedrock, to find the elemental distribution in cementitious materials and show the distribution of phases in samples of concrete [62, 63]. The crystallographic data has also been used to calculate the band structure of ferrite transformer cores to map the conductivity over the sample volume [64]. Cernik et. al. undertook a TEDDI study of the aerospace alloy Ti6246 in order to determine the crystallinity and phases across a weld. The type and orientation of the crystallites in the heat affected weld zone were shown to be surprisingly uniform and indicated possible weak points in the fabricated structure. The main drawback with TEDDI is the time required to collect data. A single detector and small beam requires a fine step and total data collection times between 12 and 24 hours.
A logical next step for the TEDDI method was to design a set of multiple or pixelated detectors, however this also required the construction of a set of multiple collimators. Both tasks presented a significant engineering challenge which was solved by a laser drilling assembly project [65] combined with the development of pixelated energy sensitive detectors from the ERD programme [66]. The potential for the detector-collimator combination was demonstrated by Cernik et.al. [37]. However successful the multiple collimator assembly might have been there were still several problems of manufacture, collimator alignment and speed of data collection and the shape of the gauge volume when the detector was at a low angle.
Lazzari et. al. showed how sample rotation similar to a tomographic rotation could resolve at least the gauge volume shape problem [67], similar tomographic diffraction measurements were carried out by Bluet et.al. [68]. The central idea of tomographic diffraction imaging is to collect a diffraction pattern (monochromatic or white beam), to rotate the sample a small amount and measure the scattering again. By taking 600 – 2000 measurements and performing an algebraic reconstruction the diffraction pattern at each gauge volume in the 3D solid sample can be reconstructed. In the case of the white beam measurements a 3D elemental map can be built up by calculating tomographic slices at specific energies. Similarly crystallographic phase maps can be obtained by calculating diffraction slices at specific reflections. The potential for 3D diffraction imaging or colour X–ray imaging is very large. A sample can be measured non-destructively and analysed for crystalline phases, strain profiles or elemental maps. Applications exist in the field of security imaging; medical biopsy; non–destructive testing (for example weld integrity or internal corrosion); aerospace engineering (strain maps); dental disease processes [69] or in energy materials where in situ chemistry can be mapped in 3D [70].
Figure 2 shows an example (courtesy C Egan University of Manchester) of a diffraction image showing changes in the crystal chemistry of a battery during discharge.
Figure 2 above shows the advantages of energy sensitive radiographs showing clear differences in the charge-discharge structure. In addition each point in the image contains diffraction data as shown. The methods have the ability to map 3D chemical changes during processing. Most recently the ability to show how nanomaterials and nanoparticles are forming has been reported [71]. Jacques et. al. took a small steel (optically opaque) reaction vessel containing palladium catalyst and, as a function of gas flow and temperature, took tomographic diffraction data to observe the oxidation processes during a realistic set of operating conditions. Before full crystallisation of the oxides a clustering of PdO nanoparticles was observed. The non-crystalline diffuse scattering was collected and reconstructed using a pair distribution function (PDF) approach. The data having been collected at high photon energies at the ESRF. The PDF 3D volume slices clearly showed how the nanoparticles cluster, and by implication, led to suggestions for improved reactor design. This was the first example of 3D PDF tomographic reconstruction and demonstrated the capability of colour X-ray imaging to any system, crystalline, nanocrystalline or amorphous. A recent mini review by Birkbak et.al. in nanoscale [71, 72] highlights applications for diffraction imaging in nanoscale chemistry.
Despite the very large potential for chemical and physical imaging the data collection process for a full tomographic reconstruction is still slow. Depending on the spatial resolution required, the number of sections to reduce artefacts and the diffraction scattering strength of the sample source it seems likely that much of this work will require access to high energy synchrotron beams. However it has been demonstrated recently [73-77] that laboratory based X-ray sources producing high end energy white beams from tungsten bremsstrahlung can, with the appropriate scattering geometry, deliver fluorescence and diffraction imaging rapidly. This has led to the development of bright and dark field tomography using either the scattered or transmitted information (or both).
The diffraction imaging field is just one example of the legacy of the X-ray diffraction work at Daresbury Laboratory. Although the SRS at Daresbury was not a special source (having relatively large emittance and low reliability compared with modern sources) the research undertaken there spanning 3 decades acted as a springboard for today’s more scientifically ambitious projects. The legacy of X-ray diffraction and other early experiments at the world’s first synchrotron user facility should not be underestimated.
Acknowledgements
The early 1980s X-ray/materials/detector team all played a large part in the scientific output of XRD at Daresbury, namely, but not exclusively, Neville Greaves, Richard Catlow, Phil Pattison, Andy Murray, Andy Fitch, Simon Clark, Graham Bushnell-Wye, Ian Langford, Eric Doorhyee, Barry Dobson, Gareth Derbyshire, Mike Hart, Rob Lewis, and at RAL, Paul Seller and more latterly Matts Wilson and Veale. I am also grateful to Dr C Egan for supplying figure 2. Thirty years after it started the equipment has been refined and optimised but the essential elements of those early Daresbury systems still remain.
I am grateful to EPSRC, CCLRC, STFC and the Leverhulme Trust for funding much of this work over a 30 year period.
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