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X-ray crystallography is the term used to describe the use of X-ray diffraction from a crystalline sample to obtain a picture of the internal structure of the crystal at the atomic level. Crystal structures are formed when the component atoms or molecules assemble into a closely packed array that has a repeating pattern in three dimensions. X-rays have a wavelength that is of the same order of magnitude as the spacings in the repeating crystal structure pattern, and are scattered by the electron cloud of the atoms. The combination of the atomic scattering and the repeating pattern produces diffraction, in which specific diffracted beams are emitted in a finite number of well-defined directions. If the directions and intensities of these diffracted beams are recorded, using an X-ray detector, it is possible to use a computer program that simulates the actions of an optical microscope to generate an image of the electron density distribution in the crystal structure, and thus allows us to identify the structure of molecules in the solid state. This technique was first introduced in the early part of the 20th century, and it has undergone many changes and improvements. Fundamental in the development of the technique has been improvement in the power of X-ray generation, in the technology of diffracted X-ray detection, and in the computer software used for processing the diffraction data and computing the image of the crystal structure. As these technologies developed, the power of the technique has improved enormously, but so has the cost. However, with high intensities, it is possible to shorten the time taken for one experiment, and with such highly productive sources it became logical to share them, and support many users who had produced crystals and needed to confirm or to know what the structure of the compound was. Accordingly, a shared facility for UK academic chemists was created in 1981, and this has been operating as a National Service since that time. The brief of the Service was to identify, acquire and operate the latest X-ray diffraction technology and make it available to users in other institutions. A major development was introduced in 2001, when access to the single crystal facility, Station 9.8, at the Daresbury Synchroton was integrated into the Service operation. This provides an incredibly high brightness X-ray beam, making it possible to study single crystals of only a few microns in size, equivalent to individual grains of a powder.For use of both the laboratory source at Southampton, and the synchrotron source, extension of the capability offered by the joint service has been possible, via the use of still developing software that can process data and resolve structures from very poor quality crystals / either with inherent growth defects or through damage due to their soft and squidgy nature. Success in handling these types of crystal, which are increasing in number, as chemists synthesise larger and more complex, fluffy molecules is crucial to the development of the chemistry of materials of current focus, and an understanding of their chemical and physical properties. The National Crystallography Service also brings together particular expertise in dealing with difficult samples that can not be investigated successfully elsewhere in the UK.
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