X-ray diffraction and scattering on disordered systems using synchrotron radiation

This review describes the utilisation of synchrotron X-radiation (SR) in protein crystallography. For the general reader a brief discussion is given of the basics of protein structure analysis including an outline of the problems of sample radiation damage, the inherent weakness of individual reflections and the large amounts of data that need to be collected as well as the 'phase problem' of crystallography. The properties of synchrotron radiation emitted by relativistic electrons in simple circular orbits in bending magnets and by more sophisticated electron motions induced in wiggler or undulator magnets are discussed. The impact of newer high brightness synchrotron radiation sources in protein crystallography is assessed. The instrumentation required to monochromatise and focus the radiation onto typically small protein crystal samples and to detect the diffraction pattern is described. Both step scanning and energy dispersive techniques to optimise anomalous dispersion are covered. A gazetteer is given of the instruments providing data collection facilities for protein crystallography which are available on SR sources around the world. The modifications that are needed to standard data processing techniques are dealt with, taking account, for instance, of the position, angle and wavelength correlatable properties of photons incident to a sample from an SR source; properties which affect reflection prediction in both camera or diffractometer work.

http://iopscience.iop.org/article/10.1088/0034-4885/47/11/001/pdf

Synchrotron X-radiation protein crystallography: instrumentation, methods and applications

X-ray photoionization of elements and the detection of their characteristic fluorescent radiation has long been a basic research tool in atomic physics (see Chapter 4) It is also a widely applied analytical technique for the determination of elemental composition in support of both research and technology The analytical application is the subject of this chapter Synchrotron radiation must offer some important advances over present analytical techniques or little justification can be found for the use of a facility remote to most users The analytical capabilities of the limited synchrotron facilities available will not supply all the routine analytical services required However, increasing demands on analytical services caused by advanced technologies and growing concern for environmental monitoring is exceeding the performance capabilities of standard analytical methods Justifications for applying synchrotron radiation to measurements of chemical composition include lowering of the detection limits, reducing heat or damage to the sample, improving the spatial resolution and contrast of microprobe analysis, reducing the time for analysis, improving the means of chemical identification by measuring absorption edge shifts or exafs, providing more accurate quantitative analysis, and extending analytical measurements to samples, configurations, and environments that are impractical, if not impossible, to analyze with present techniques

X-Ray Fluorescence Microprobe for Chemical Analysis

X-ray monochromator geometry for focusing synchrotron radiation above 10 keV

Monochromators for X - Ray Synchrotron Radiation

An X-ray focusing monochromator for small-angle diffraction studies was designed for use with the synchrotron radiation from the storage ring, SPEAR, at the Stanford Linear Accelerator Center. It incorporates a 7 cm long silicon crystal, cut at 8°30′ to the (111) planes and bent to a logarithmic spiral curvature for horizontal focusing and monochromatization. A 120 cm long elliptically curved float-glass mirror is used for vertical focusing, and provides means of eliminating higher-order harmonics of smaller wavelength. With SPEAR operating at 3.7 GeV, 20 mA, the two elements produce a 0.5 × 0.5 mm focused beam with an intensity of 6 × 108 photons s−1. The diffraction pattern of frog sciatic nerve myelin obtained with this system was compared with that obtained with a 300 W conventional microfocus X-ray source and a toroidal camera. The new system shows a 190-fold gain in the integrated intensity on photographic film. Synchrotron radiation provides a broad X-ray spectrum. The monochromator is tunable to any wavelength between 0.5 and 3 A, with a total wavelength spread in the focused beam of about 0.01 at 1.74 A. The broad spectrum allows wavelength selection for anomalous-scattering experiments.

A focusing monochromator for small-angle diffraction studies with synchrotron radiation

A total‐reflecting mirror of 120‐cm length was designed and built to focus synchrotron radiation emanating from the electron–positron storage ring at the Stanford Linear Accelerator Center (SPEAR). The reflecting surface is of unpolished float glass. The bending and tilt mechanism allows very fine control of the curvature and selectability of the critical angle for wavelengths ranging from 0.5 to 3.0 A. Elliptical curvature is used to minimize aberrations. The mirror is placed asymmetrically onto the ellipse so as to achieve a tenfold demagnification of the source. The bending mechanism reduces nonelastic deformation (flow) and minimizes strains and stresses in the glass despite its length. Special design features assure stability of the focused image. The mirror reduces the intensity of shorter wavelength harmonics by a factor of approximately 100.

/pdf/remotely-controlled-mirror-of-variable-geometry-for-small-2hkge85uqz.pdf

S. Samson

Papers

A focusing monochromator for small-angle diffraction studies with synchrotron radiation

Remotely controlled mirror of variable geometry for small‐angle x‐ray diffraction with synchrotron radiation