Chemistry Reference
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vector for any pixel, even if the pixel is not measuring Bragg scattering. The
“diffracted beam,” thereafter in this topic, does not necessarily imply that it is from
Bragg scattering.
2.3 DETECTOR SPACE AND DETECTOR GEOMETRY
2.3.1
Ideal Detector for Diffraction Pattern in 3D Space
An ideal detector is defined as a detector with the detecting surface covering the
complete diffraction space. Figure 2.6 shows an ideal detector in spherical shape
with the sample in the center of the sphere. The incident X-ray beam points to the
center of the sphere through the detector at 2u ¼180
. The direction of a diffracted
beam is defined by g (longitude) and 2u (latitude). Since the detector surface covers
the whole spherical surface, that is, 4p in solid angle, the ideal detector is
sometimes also referred to as 4p detector. In addition to the geometry definition,
an ideal detector should also have many desired physical properties, such as a large
dynamic range, small pixel size, and narrow point spread function, as well as many
other ideal properties. In practice, such an ideal detector does not exist. There are
many 2D detector technologies available, including photographic film, charge-
coupled device (CCD), image plate (IP), and multiwire proportional counter
(MWPC). Each technique has its advantages over the others. A typical 2D detector
has a limited detection surface and the detection surface can be a spherical,
cylindrical, or flat. The spherical or cylindrical detectors are normally designed
for a fixed sample-to-detector distance, while a flat detector has the flexibility to be
2
q
g
X-ray
FIGURE 2.6 Schematics of an ideal detector covering 4p solid angle.
