X-ray rotation

Dark-red crystals of another form of selenium have been grown from a CS2 solution. X-ray rotating crystal and Weisenberg methods showed the material to be orthorhombic (or nearly so) with the lattice constants a = 2632, b = 688, and c = 434 pm, resulting in a unit-cell volume of 7.86 x 10 22 cm3, which leads to a cell content of 28 atoms (observed density, 4.6 g/cm3) (25). Thus the material may consist of Se7 ring molecules. 

CVD of W-Re alloys has gained commercial importance for the production of X-ray rotating anodes, cones, tubes, and other shapes. Layer thickness for X-ray targets is 1 mm. As in CVD of pure tungsten, fluorides or chlorides of W and Re are also used as precursors. Densities over 99% of the theoretical can be obtained [6.1]. 

Figure 2. X-ray rotation photographs of (A) erionite and (B) offretite. Reflections with l odd are absent from (B), showing that c is halved for offretite.

The structures typically obtained as a consequence of shift non-uniqueness are analogous to nematic phase liquid crystals in the sense that there exists a unique chain direction, but the monomer repeat units in neighboring chains are not well correlated in longitudinal position. As a consequence, the x-ray rotation photographs about the chain axis direction (c) display either (1) sharp hkO reflections and progressively more diffuse hk reflection with increasing Z (2) diffuse reflection for all layers combined with a few sharp hkO reflections or (3) diffuse reflections on... 

Figure 13. Single-crystal X-ray rotation photographs taken about the (001) cleavage normal of two-layer kammererites with regular alternation of cations between I and II octahedral sites in successive layers. (From Lister and Bailey [1967].) (a) Regular stacking variety (b) semirandom stacking variety. Two-layer periodicity still evident in strong k = 3n reflections.

The divergent shape of the beam provides facilities for magnification in the distances of the source to detector and of the sources to the axis of rotation, which used in conjunction with a microfocus x-ray source opens the way to high resolution. 

Figure 3 A blade on the rotation table in front of the image intensifier Technical data of the X-Ray tubes are given in table 1.

This research examines the feasibility of a technique based upon the CT principle using a microfocus X-ray source with an image intensifier while the examined object is being rotated The attainable enlargement is up to 200. The data to be processed is collected from the whole surface of the image intensifier by a frame grabber and noise suppression is performed. 

In a commercial CT system an X-ray source and a set of detectors rotate around the examined object Two main difficulties that typical CT method meets are challenged in this study ... 

The setup as seen in Figure 1 mainly consists of a Varian Linatron 3000A linear accelerator (LINAC) as radiation source, a rotational stage for sample manipulation, and a two-dimensional high-energy x-ray detector array consisting of four amorphous silicon area detectors Heimann RIS 256. The source to detector distance is 3.7 m. 

The laminography method was developed initially for medical applications as a non-computer layer-by-layer visualization of the human body [1,2]. In this case an inclined initial X-ray beam projects an image of a specific layer of the object to the detector surface with defocusing of the other layers during a synchronous rotation of the object and the detector (Fig. 1). 

Laminographical approaches can be used for layer-by-layer visualization of the internal microstructure for the flat objects (multilayers, PCBs etc.), that caimot be reconstructed by computerized tomography because of the limited possibilities in rotation. Depth and lateral spatial resolutions are limited by the tube, camera and rotation accuracy. Microfocus X-ray tubes and digital registration techniques with static cameras allow improving resolution. Precision object manipulations and more effective distortion corrections can do further improvement. 

And a rotation of the emitter-receiver transducer around the "object" (or a rotation of the object) gives a annulus of center O and radii [Km, Km] [2]. The situation is identical to that of X-ray tomography (slice-by-slice spectral coverage), but with a band-pass spectral filter instead of a low-pass spectral filter. ... 

If the detection system is an electronic, area detector, the crystal may be mounted with a convenient crystal direction parallel to an axis about which it may be rotated under tlie control of a computer that also records the diffracted intensities. Because tlie orientation of the crystal is known at the time an x-ray photon or neutron is detected at a particular point on the detector, the indices of the crystal planes causing the diffraction are uniquely detemiined. If... 

As excited atoms, molecules, or ions come to equilibrium with their surroundings at normal temperatures and pressures, the extra energy is dissipated to the surroundings. This dissipation causes the particles to slow as translational energy is lost, to rotate and vibrate more slowly as rovibrational energy is lost, and to emit light or x-rays as electronic energy is lost. 

In scanning the wavelength range of the fluorescence the crystal must be smoothly rotated to vary the angle 6, and the detector must also be rotated, but at twice the angular speed since it is at an angle of 26 to the direction of the X-ray fluorescence beam. 

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