Slit, curved

Figure 3.13. The overall view of the goniostat of the Rigaku TTRAX rotating anode powder diffractometer with the horizontal goniometer axis, and synchronized rotations of both the x-ray source and detector arms. This goniometer is equipped with variable divergence, scatter and receiving slits, curved crystal monochromator, and scintillation detector. (Courtesy of Rigaku/MSC.)...

NaCl (d=0.56nm) or LiF (d=0.4nm) are frequently used as crystals. The X-rays bundles are collimated using systems of thin metal plates (thickness 50/zm) arranged parallel to each other at small separations (0.5mm). In this way the divergence can be limited to one degree or less. Alternatively, a curved crystal can be used this will cause radiation diverging from an entrance slit to be focused towards an exit slit. Curved crystals of alkali halides or mica can be used. 

The ratio 0/0 is thus a measure of the enhancement of the energy of adsorption in a micropore as compared with that on an open surface. In curve (i) of Fig. 4.9 this ratio is plotted as a function of d/r and, as is seen, the enhancement is still appreciable when d = l-Sr, but has almost disappeared when d = 2r , i.e. when the slit is only two molecular diameters wide. Even when d/r = 1, which corresponds to a single molecule tightly packed into the width of the slit, the enhancement is only 1-6-fold. The effect... 

Figure 18.14 The diffraction pattern of helices in fiber crystallites can be simulated by the diffraction pattern of a single slit with the shape of a sine curve (representing the projection of a helix). Two such simulations are given in (a) and (b), with the helix shown to the left of its diffraction pattern. The spacing between the layer lines is inversely related to the helix pitch, P and the angle of the cross arms in the diffraction pattern is related to the angle of climb of the helix, 6. The helix in (b) has a smaller pitch and angle of climb than the helix in (a). (Courtesy of W. Fuller.)...

Curved crystals can be used in three different ways, as we shall see. Each crystal is a cylinder that will be examinedjn right-section. Each receives x-rays from a slit parallel to the lens axis, the slit appearing as a point in the drawings. Such a slit is necessary with a cylindrical lens if the sample has breadth as well as length. 

Fig. 7-12. The curved-crystal spectrometer of Adler and Axelrod, showing a polished ore specimen in position. (1) Microscope stage (2) polished ore sample (3) crystal support block (4) Geiger counter and scatter slits. (Courtesy of Adler and Ayelrod and the U. S. Geological Survey.)...

The final optically clear solution is evaluated as to intensity of color at 555 m/x, and with slit width at 0.02 to 0.04 mm., on a Beckman spectrophotometer adjusted to 100% transmittance with an untreated sample freshly processed in parallel with the unknown sample. From a standard calibration curve (see Figure 3), the concentration of parathion may readily be ascertained, and an appropriate factor converts this value to micrograms of parathion present in the original field sample. 

Slit-focus cameras record scattering curves. The study of anisotropic material is cumbersome. It requires large samples which can be rotated step-wise in the beam which is typically between 1 to 3 cm long. 

If, in the detector plane, the effective slit is wider than the region of the pattern in which significant intensity is observed, the approximation of an infinite slit is valid. Let the slit be infinitively long in ft -direction but very narrow in 53-direction then in the tangent plane approximation the recorded scattering curve... 

The measured SAXS curve of the calibration sample must have been pre-processed in the usual way (cf. Sects. 7.3 - 7.6). Therefore it is important to have calibration samples with a well-defined thickness27. Because synchrotron beamlines can be adjusted to a fairly wide range of radiation power, it is important to have thin calibration samples for a high-power adjustment (e.g., common SAXS with wide slit openings) and thick calibration samples for low-power adjustments (e.g., USAXS with microbeam). For calibration samples from synthetic polymers, thicknesses ranging between 0.2 mm and 3 mm are reasonable. It appears worth to be noted that not only polymers, but as well glassy carbon [88] can be used as a solid secondary standard for the calibration to absolute intensity. 

A well-known device that performs a 2D projection of the scattering pattern is the Kratky camera. By integrating the intensity along the direction of the focus slit, it is collapsing the SAXS intensity on the plane that is normal to the slit direction. In general, 2D projections collapse the measured complete intensity not on a line, but on a plane. As in the case of the ID projections, the orientation of this plane can freely be chosen. The result of such a projection / 2 (Sj,Sk) is not a curve as was the case with the ID projection, but a 2D scattering pattern. Only in the case of 2D isotropy (i.e., / 2 (sjk) with sjk = Js2, + s ) the scattering pattern can be represented by a curve. 

A continuous source can be used for atomic absorption, but since only the center part of the band of wavelengths passed by the slit will be absorbed (due to the sharp line nature of atomic absorption), sensitivity will be sacrificed, and the calibration curve will not be linear. This curvature is because even at high concentrations, only a portion of the radiation passing through the slit will be absorbed, and the limiting absorbance will approach a finite value rather than infinity. With a sharp line source, the entire width of the source radiation is absorbed and so the absorption follows Beer s law. A continuous source works best with the alkali metals because their absorption lines are broader than for most other elements. Specificity is not as great with a continuous source because nearby absorbing lines or molecular absorption bands will absorb part of the source. 

The dispersive (+ n, - m ) mode has already been seen clearly with the duMond diagrams, Figure 2.10. Here, the curves are no longer identical and the crystals must be displaced from the parallel position in order to get simultaneous diffraction. As the crystals are displaced, so the band of intersection moves up and down the curve. When the curves become very different, the K 1 and K 2 intensities are traced out separately. Then the peaks are resolved in the rocking curve, and if no better beam conditioner is available it is important in such cases to remove the K 2 component with a slit placed after the beam conditioner. A slit placed in front of the detector, with the detector driven at twice the angular speed of the specimen, also works very well. This is in effect a low resolution triple-axis measurement. 

Fig. 1. The core particle, the DNA superhelix and H2B and H3 N-terminal tails, (a) Space-filling representation of the 2.8 A crystal structure of the 146 bp human a-satellite nucleosome core particle [22]. The dyad is in the plane of the paper and the superhelix axis slightly off that plane. Positive and negative numbers mark the superhelix locations (SHL) in the upper and lower gyres, respectively, and the dotted curve follows the path of the double helix axis, (b) Ribbon representation of the DNA superhelix slit along a line parallel to its axis, opened out and laid flat on the paper surface. SHL are also indicated, together with H2B and H3 tails passage points between the gyres. (From Fig. 5 in Ref [29].)...

IQiowledge of parameters such as reactivity ratios, is necessary for synthesis of polymer based resists, and an accurate method of analysis should be useful in various areas associated with resist development such as quality control. Raman spectroscopy provides a convenient, absolute, nondestructive method for compositional analysis of polymer systems which, if an internal standard is present, does not require standards of known composition or ancillary calibration curves. The accuracy, with appropriate selection of experimental conditions such as slit width and integration time, is limited only by the instrumentation. 

The type B hysteresis curve is associated with slit-shaped pores or the space between parallel plates. Type C hysteresis is produced by a mixture of tapered or wedge-shaped pores with open ends. Type D curves are also produced by tapered or wedge-shaped pores but with narrow necks at one or both open ends. Type E hysteresis results from McBain s bottleneck pores. In pores of this shape, emptying of the wide portion will be delayed during desorption until the narrow neck can evaporate. Therefore, the desorption curve exhibits a small slope at high relative pressures and a large slope where the wide part of the pore empties. 

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