Precession camera

Stoe Cie GmbH. P.O. Box 101302, Hilpert-strasse 10. 64295 Damistadt. Germany. Goniometer heads Debye-Scherrer cameras Guinier cameras Weissenberg cameras precession cameras Reciprocal Lattice Explorers powder diffrac-... 

Outline how you would interpret X-Ray diffraction data, if any, obtained for the following CPs and using the following X-Ray methods P(ANi)Cl P(Di-Ac)s Debye-Scherrer powder camera Weissenberg camera Precession camera Wide Angle X-Ray Diffraction Automated Diffractometer. 

Figure 1 Schematics of the electron diffractometer + precession interface device adapted to a TEM. Diffractometer can be adapted either below the camera plates, or in the 35mm port.

Electron diffractometry system with the combination of the precession technique can be very perspective experimental instrumentation for precise structural investigations. The technique can now be adapted in a commercial TEM (previously applied uniquely to electron diffraction cameras) taking advantage of the small beam size and can measure reflections in the ED pattern with same required precision for structure analysis. 

Buerger (1944) developed a very ingenious variant of the same basic idea in his precession camera. In this camera, the crystal does not rotate instead, its axis performs a precessing movement (Fig. 106). 

Fig. 106. Principle of Buerger s precession camera. The crystal does not rotate its axis processes. The lower diagram shows the situation 90° after the upper diagram.

Of the many types of X-ray cameras, only two are still in even occasional use in protein crystallography — the Buerger or precession camera and the rotation/oscillation camera. The precession camera is used primarily in... 

The precession camera (Fig. 4.23), although the more complicated in its motion, produces the simplest diffraction pattern. X rays enter through the black tube at left to strike the crystal, mounted in a goniometer head. Beyond the crystal are an annular-screen holder (smaller black square) and a film holder (larger black square). The remaining machinery moves crystal, screen, and film in a precessing motion about the X-ray beam. 

Figure 4.23 Precession camera with mounted goniometer head. To see a precession photograph, refer to Fig. 2.6. Photo courtesy of Charles Supper Company.

Precession cameras are complex but give the diffraction pattern in its simplest, most understandable form. Rotation/oscillation cameras are far simpler, merely providing means to rotate the crystal about an axis perpendicular to... 

Film diffraction data can be obtained by several techniques flat plate camera, cylindrical camera or precession camera. We chose the latter, because it records a relatively undistorted "slice" of diffraction transform (reciprocal space) (19,20). We felt that this characteristic of the precession technique outweighed the disadvantages of longer exposure times (this was lessened by use of a Helium atmosphere in the camera enclosure). For potassium bromide amylose, the fiber studied, this required exposure of a 79y x 79y x 300y fiber specimen for 45 hours (35kv,... 

In the program Corspot, the Lorentz factor used was of the form for precession camera data,... 

In the Buerger145 precession camera (1944) the motions of the crystal and the planar film holder were mechanically coupled to provide a distortion-free... 

The EPR/ENDOR measurements described here have been performed on single crystals which are accurately oriented with an x-ray precession camera, x-ray irradiated, and observed at ca. 10 K. The schematic diagram of the X-band EPR apparatus is shown in Figure 18-1 [12], This cavity is a modification of one previously described by Weil et al. [13], The EPR cavity is essentially a cast epoxy, wire wound TE011 cylindrical cavity with external 100 kHz modulation coils. The Cryo-Tip portion of the cavity can be raised 6 cm for x-irradiation and subsequently lowered into the microwave cavity for EPR measurements [14], In the microwave cavity the lowest temperature of the sample is approximately 6 K. However in the irradiation position the lowest temperature is about 10 K because the sample is not as effectively heat-shielded from the room temperature vacuum shroud. 

Since crystal and film are fixed, only a small part of reciprocal space can be observed at a time, but a reciprocal point of the diffracting volume scatters during the whole exposure time. By contrast, scanning techniques such as Weissenberg or precession cameras see a larger part of reciprocal space, but each reciprocal point stays only a short time on the Ewald sphere. 

The Laue method involves a stationary crystal and polychromatic ( white ) X rays. In the other camera methods, monochromatic radiation is used. In these cases the crystal may be oscillated over a small angular range (oscillation method) or rotated 360° about an axis (rotation method). The layer lines so formed may be selected individually. In the Weissenberg method, the oscillation of the crystal is coupled with a movement of the photographic film. The Buerger precession method, by a more complex motion of the instrument, produces an undistorted and magnified picture of the reciprocal lattice. 

Staudenmann, J.-L., Horning, R. D., and Knox, R. D. Buerger precession camera and overall characterization of thin films and flat-plate crystals. J. Appl. Cryst. 20, 210-221 (1987). 

Hajdu, J., McLaughlin, P. J., Helliwell, J. R., Sheldon, J., and Thompson,. 4 W. Universal crystal cooling device for precession cameras, rotation camera and diffractometer. J. Appl. Cryst. 18, 528-532 (1985). 

FIGURE 1.14 Seen here is the hk0 zone diffraction pattern from a crystal of M4 dogfish lactate dehydrogenase obtained using a precession camera. It is based on a tetragonal crystal system and, therefore, exhibits a fourfold axis of symmetry. The hole at center represents the point where the primary X-ray beam would strike the film (but is blocked by a circular beamstop). Note the very predictable positions of the diffraction intensities. All the intensities, or reflections, fall at regular intervals on an orthogonal net, or lattice. This lattice in diffraction space is called the reciprocal lattice. 

The precession camera is still the most useful instrument in the preliminary analysis of a crystal. It enables an undistorted photograph of a plane of the three-dimensional diffraction pattern to be recorded and is invaluable in the estimation of unit cell parameters, the detection of symmetry and for screening heavy atom derivatives (see, for example, Ch. 9 of Ref. 25 for a fuller description). 

During the freezing procedure the crystal water expands, therefore the crystal is somewhat damaged. Since X-ray pictures on the precession camera were also obtained after freezing, the crystal remained satis-... 

Deoxy mb single crystal (A) was calibrated on precession camera (see text). The R (q>) — values are plotted in Fig. 17. °) Deoxy mb single crystal (B) was calibrated by visual adjustment only therefore we give an error for q>. 

The earliest consideration of the polarisation correction with SR was for the precession camera and formulae were derived by Phillips et al (1977). 

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