Goniometer horizontal

XR D-5 D/S. As the goniometer circle is horizontal, the table (Figure 9-5) can carry a fairly heavy load of instruments, samples, or accessories without risk of distorting the goniometer angle. Any value of 26 can be set reliably and quickly. Good performance is available at widely... 

The x-ray powder diffraction pattern of etodolac was obtained using a Rigaku MiniFlex powder diffraction system, equipped with a horizontal goniometer in the 0 /2-0 mode. The x-ray source was nickel-filtered K-a emission of copper (1.544056 A). A 10-mg sample was packed into an aluminum holder using a back-fill procedure, and was scanned over the range of 50 to 6 degrees 2-0, at a scan rate of 0.5 degrees 2-0/min. 

The correction of absorption depends on the geometry of the cell and the scattering volume. Different relationships have been proposed to correct the Rayleigh factor measured with conventional goniometers, in which the detector rotates around the sample m a horizontal plane (Brice et al. 1953, Forss et al. 1967, Pla et al. 1977). With LALLS (low angle laser light scattering) pho-... 

The orientation of both the goniometer axis and specimen surface (or specimen axis) with respect to the horizon, i.e. they may be located in a vertical or horizontal plane. 

Figure 3.7. Horizontal (left) and vertical (right) orientations of a flat sample. The location of the goniometer axis is shown using a dash-double dotted line with small filled circles at the ends. The dashed line indicates the location of the optical axis, which is the line connecting the focus of the x-ray tube, the receiving slit and the sample surface in the reflection geometry, or the sample center in the transmission geometry at 0 = 20 = 0°.

On the other hand, the simplicity of the goniometer arms motion in a horizontal plane, when the sample is located in a vertical plane (Figure 3.7, right), is offset by the need of more complicated sample preparation to ensure that it stays in place and does not fall of This is usually achieved by side packing the sample holder or by mixing a powder with a binder (e.g., x-ray amorphous and chemically inert petroleum jelly, oil, grease or varnish), which typically increase preferred orientation or background, respectively (see section 3.5 for more details on sample preparation). 

The orientation of the sample usually establishes the orientation of the goniometer axis, i.e. the axis around which both the detector and sample (or both the detector and x-ray source) rotate in a synchronized fashion during 0-20 or 0-0 data collection. A horizontal sample orientation implies that the goniometer axis is located in the horizontal plane, and a vertical sample orientation makes the goniometer axis vertical, as depicted in Figure 3.7. 

Figure 3.11. The schematic of the goniostat of a Scintag XDS2000 powder diffractometer with the horizontal axis and synchronized rotations of both the source and detector arms. This goniometer is equipped with a liquid nitrogen-cooled solid-state detector, which enables monochromatization of the diffracted beam by selecting a narrow energy window, thus registering only characteristic energy photons. R - is the radius of the goniometer.

A different goniostat with the horizontal orientation of the specimen and Bragg-Brentano geometry is shown in Figure 3.13. The x-ray tube housing is mounted on the movable arm, and both the x-ray source and the detector can be rotated in a synchronized fashion about the common horizontal goniometer axis (also see the schematic in Figure 3.10, middle). 

When you called the person in charge of the diffractometer D (see problem 4) she told you that the goniometer axis is horizontal and that the x-ray source arm is stationary. Do you need to worry about mixing your powder with a binder ... 

There is a large variety of specimen holders in use, each suited to some particular purpose. The simplest consists of a fixed post to which the specimen is attached with wax or plasticine. A more elaborate holder is required when it is necessary to set a crystal in some particular orientation relative to the x-ray beam. In this case, a three-circle goniometer is used (Fig. 5-7) it has three mutually perpendicular axes of rotation, two horizontal and one vertical, and is so constructed that the crystal, cemented to the tip of the short metal rod at the top, is not displaced in space by any of the three possible rotations. 

Fig. 8-22 Back-reflection Laue pattern of an aluminum crystal. The incident beam is parallel to [Oil], [Oil] points vertically upward, and [100] points horizontally to the left. Tungsten radiation, 30 kV, 19 mA, 40 min exposure, 5 cm specimen-to-film distance. (The light shadow at the bottom is that of the goniometer which holds the specimen.)...

Figure 2.8 Basic Bragg Brentano geometry. The dotted circle centred on the sample position represents the goniometer circle on which the image of the divergent source of X rays is focussed by diffraction from the flat plate sample. Strictly speaking, true focussing only occurs when the sample plate has a curved surface. However, given that the footprint of the beam on the sample plate is considerably smaller than the radius of the focussing circle, the fiat plate approximation works well in practice. The source is usually fixed and to collect the diffraction pattern the sample and detector are rotated by 6 and 26, respectively. An alternative is to fix the sample (usually in the horizontal position, e.g. useful for a liquid sample) and to move both the source and the detector by 6 and 6, respectively.

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