Diffraction camera

Considering the fact that the X-ray diffraction pattern of a crystal depends on its lattice structure, pigment powders can be analyzed with a Debye-Scherrer diffraction camera to establish a correlation between X-ray diffraction and crystal modification. It is synthetically not possible to produce a defined crystal modification of a new pigment. Attempts to modify the preparative procedure or to apply different aftertreatment may result in a pigment of two or more crystalline forms, different not only in lattice structure, but also in color and performance. 

Figure 2. Diffraction camera for single-molecule electron diffraction. A Lanthanum hexaboride electron source is used. The laser and associated optics is rotated after each data readout for a new molecular beam orientation. Organic molecules are picked up within liquid helium droplets to form a molecular beam traversing the electron beam.

Figure 2. The scheme of the electron diffraction camera EMR-102 (produced by SELMI Ltd. (Sumy, Ukraine). 1 - Electron gun, 2-Two condenser lenses, 3 - Specimen holder, 4 -Chamber, 5 - Optical microscope, 6- Tubule, 7 - Photo-chamber.

Although measurements with diffractometer interfaced with EDC cameras have been performed at 80-100 kv, however, this old-type system has a lot of limitations linked to the extremely long time (several hours) to scan ED patterns and the beam size (from microns to mm) of the electron diffraction cameras. Again, the problem of correcting intensities from dynamical contribution has not been addressed satisfactory, as primary extinction (dynamical) corrections have been proposed for known stmctures using the Blackman formula . ... 

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. 

Assembly of the mounted crystal onto the X-ray diffraction camera... 

By simple geometry, in a flat-film diffraction camera the thickness of film traversed by the scattered X-rays increases with the Bragg... 

The x-ray studies were made with a high-temperature x-ray diffraction camera of Hume-Rothery design. This camera had a 9-cm. diameter and employed the Straumanis film setting. A fine Chromel-Alumel thermocouple within the furnace cavity and adjacent to the sample served to measure and control temperature. The sample temperature was calibrated against the thermocouple e.m.f. through a series of lattice-constant measurements on pure silver. 

Figure 3.13. The essential features of a simple electron diffraction camera.

The purest kind of radiation to use in a diffraction experiment is radiation which has itself been diffracted, since it is entirely monochromatic. If a single crystal is set to reflect the strong A"a component of the general radiation from an x-ray tube and this reflected beam is used as the incident beam in a diffraction camera, then the causes of background radiation listed under (1) and (2) above can be... 

The earlier work, before the invention of the electron microscope, was done with homemade apparatus called electron diffraction cameras. Many important studies were made of the structures of metal foils, electrodeposits, films deposited by evaporation, oxide films on metals, and surface layers due to polishing. 

Smith undertook an exhaustive study of the nature of these films. To do so, he had to build his own specialized vacuum system because he had to deposit his films on flat plates in order to examine them by electron diffraction. He also had to be able to transfer them into the electron diffraction camera without exposure to atmospheric contamination. For pressure measurements he, too, used a McLeod gauge because the ionization gauges one could build at that time were prone to outgassing, which would contaminate the films. He made films of a great many transition metals, in addition to nickel. 

Sodium bromide films were obtained by vacuum evaporation directly in the electron diffraction camera (EG—1) in a vacuum of approximately 5 10 mm amorphous celluloid films were used as the substrates. When they condensed, the NaBr crystallites tended to form grains. It was noted that the preferred orientation of the crystallites depended on the film thickness. When the film thickness was reduced, the preferred orientation disappeared. The thickness of... 

INTERLOCKS ON - Equipment with internal hazards, such as X-ray diffraction cameras, or areas in which the space is rendered unsafe to enter by the presence of a hazard, are often provided with a fail safe circuit, or interlock, which will turn off the equipment representing the problem if the circuit is broken. The sign provides a warning that the interlock is on to prevent access to the hazard. 

We have measured the X-ray scattering profile of maize PLB using the 3 metre, small-angle diffraction camera of Station 8.2 of the BBSRC Synchrotron facility at Daresbury (UK). A typical scattering pattern as measured and the corresponding pattern after... 

Electron diffraction is generally done with commercial electron microscopes using three techniques (i) transmission with a diffraction camera accessory, (ii) selected-area diffraction, and (hi) reflection diffraction. I n determining unit cell dimensions, the precision decreases in the order given above. Claims have been made of lattice parameter determinations accurate to 0.1 % by electron diffraction, but this is unrealistic, and a figure of about 1 % is more typical. 

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