Double-crystal diffractomete

Grazing Incidence X-Ray Diffraction Grazing Incidence X-Ray Diffraction Double Crystal Diffractometer... 

In Fig. 8-38(a), fixed crystal M, which should be as nearly perfect as possible, is set to reflect Ktx radiation in the direction of crystal C, which is to be examined. Crystal C is then rotated ( rocked ) through the Bragg angle 6g, while the beam reflected by it is measured in a fixed counter with a wide slit. The resulting curve of intensity vs. 0 is called a rocking curve and the instrument itself a double-crystal diffractometer. 

The double-crystal diffractometer method is not topographic. However, Weissmann and his associates [8.30] have obtained semitopographic information by photographing the beam diffracted by crystal C for various angular positions of this crystal. 

The classical camera for anomalous dispersion studies is the double crystal diffractometer, using perfect Si or Ge-crystals [43, 44] (Fig. 17 a). The energy resolution of... 

The peak reflectivity of a Si-crystal is at 6 A only 0.15, which reduces the reflectivity to 2 10 2 in a double crystal diffractometer. Consequently, a recently developed diffractometer for softer wavelength employs a single crystal optics [46] (Fig. 17 b). As experimental experience with softer X-rays in SAXS is still very limited, the following discussion will be restricted to the double crystal diffractometer camera with Amax a 3 A. 

The SANS method is a widely used tool in research. There are three different SANS techniques the pinhole SANS, the double-crystal diffractometer (DCD), and the focusing SANS. 

Fewster obtains this from the increase of satellite widths as a function of satelhte order. The trae integral breadths or FWHM values are first found with a double or multiple crystal diffractometer this is simple measurement, and with a powder... 

A double crystal monochromator providing a 6kH of 10-4 is followed by a flat platinum coated mirror for harmonic rejection. A Huber five-circle diffractometer is mounted to allow the 30x30 cm2 two-dimen-... 

The Biology Department beam line includes a station for protein crystallography (with Supper oscillation camera and FAST TV diffractometer) and a station for small angle diffraction (with a three-circle goniostat and MWPC electronic area detector). The latter station may be available for optimised anomalous dispersion crystallographic studies. The optical design for each consists of a bent pre-mirror, double crystal monochromator and bent post-mirror the mirrors have rhodium coatings (Wise and Schoenborn 1982). 

Participating research teams Naval Research Laboratory At the NSLS a large number of participating research teams (PRTs) have established beam lines on the NSLS and a number of instruments use diffractometers as well as oscillation cameras. One of these, for instance, is the Naval Research Laboratory (NRL) and National Bureau of Standards PRT as part of this effort, NRL is constructing a materials analysis X-ray beam line. The beam optics design consists of a platinum coated copper pre-mirror dynamically bent to approximate a parabolic cylinder, followed by a fixed-exit double crystal monochromator and a platinum coated fused silica cylinder bent to approximate an ellipsoid. The hutch contains a six-circle diffractometer (Kirkland, Nagel and Cowan 1983). 

Using three spherical crystals - the standard ylide crystal provided by Siemens Analytical Instrumentation, ruby and ammonium hydrogen tartrate (Enraf-Nonius standard crystal) - such an experiment has been carried out using two SMART CCD diffractometers. Before integration [8], all of the cell axes were multiplied by 2. Duplicate measurements were then averaged, and all odd reflections with values of F2 > 15 esd s were compared with the reflection with double the indices to obtain the best value of k for the expression F kl = kF h2k2). The average values of k obtained for the two diffractometers were 0.0014(2) and 0.00106(5). 

A, and fl = 90.48°. The 2-pyridyl ring and p-tolyl group make dihedral angles of 29.7° and 55.3° respectively with the double bond plane. The inter-aryl dihedral angle is 106.5°. The data was obtained on crystals grown from a solution of the compound in anisole. A Picker FACS-1 diffractometer with CuK radiation was used for the measurements, or... 

The instmment shown in Figure 2.4 is a double-axis instrument. The first axis is the adjustment of the beam conditioner, the second is the scan of the specimen through the Bragg angle. It is irrelevant to this definition that a practical diffractometer may contain a dozen or more controlled axes , for example, to tune and to align the beam conditioner, to locate the specimen in the beam, to align and to scan the specimen and to control shts. It is the differential movement of the two main axes that make the measnrement and determine the precision and accuracy of the instrument. This is the basic high resolntion diffractometer, which is now widely nsed for measniements of crystal perfection, epilayer composition and thickness. 

This design is shown in Fig. (8). It has come up with the forthcoming use of resonant scattering in the soft X-ray region At wavelengths longer than 2 A the maximum reflectivity more and more falls below 100% reflectivity. With Ge(lll) at a wavelength of 6 A the reflectivity reaches no more than 15 % A double monochromator would transmit at most 0.15 0,15 = 2.5% of the incident radiation. The use of only one crystal monochromator minimizes this loss. The price to be paid is the vertical rotation of the diffractometer around the monochromator axis. 

Several low-temperature devices have been described for protein crystallography. In the device of Marsh and Petsko [216] a jet of cold dry Nj gas is directed at the crystal. This simple and inexpensive device is good for temperatures around — 4°C. For diffractometers there are a number of devices manufactured commercially [217], which are suitable for very low temperatures. For the oscillation camera, the device of Bartunik and Schubert [233] is recommended. The flow cell is surrounded by a double-walled cylindrical chamber composed of mylar (8 pm thick). A diffuse stream of N2 gas passes through the inner chamber and cools the sample. Icing is prevented... 

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