Angular dispersive cameras

The optics of angular dispersive small angle scattering cameras differ according to the field of application. Thus the double monochromator camera is mainly used for anomalous dispersion experiments (Fig. 21) By varying the Bragg angle of two 

Schematic design of a double monochromator small-angle scattering camera. The first monochromator is at 24 m from the source. I denotes two ionization chambers. No focussing elements are used 

Ionization chambers on both sides of the sample are used to determine the absorption (Fig. 22). The scattered photons are recorded by a 200 x 200 mm proportional counter, area detector which is separated from the beamline by a mylar window. 

This camera does not use focussing elements. The cross section of the beam is defined by slits at the entrance of the instrument and close to the sample. As the first monochromator is — for architectural reasons — located 24 m from the source point, a considerable fraction of the beam is lost in order to reduce the beam size to the spatial resolution of the detector ( 2 x 2 mm). The recent introduction of segmented monochromators suggests to use the second crystal as a focussing element which would increase the intensity at the sample considerably. 

Double focussing, mirror-monochromator cameras are optimized for maximum flux at the sample. This type of camera is hence mainly used for real time diffraction studies on biological samples and polymers (see Sect. 4). Such a camera is shown in Fig. 23. The first optical element could only be placed at 20 m 

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