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Figure 2
Size–divergence diagram for X-ray scattering. The horizontal axis represents the size of the specimens to be studied and the required divergence of the beam is shown on the left-hand vertical axis. The right-hand axis gives the corresponding unit-cell dimension. This would be on the limit of being resolved with an X-ray beam of this divergence using 1 Å radiation. Three sources are shown as curved lines having emittances of 7, 2 and 0.02 mm mrad. These are based on FWHM (2.35σ) values for the beam size and divergence. The flux from these sources in a 0.01% bandpass (as given by a crystal monochromator) is shown. This diagram is, therefore, a slice at a bandpass of 0.01% through the three-dimensional size–divergence–bandpass diagram. Filled circles represent the requirements for some representative samples or experiments. Fine φ slicing refers to the case where one is collecting data in fine rotation increments and the incident beam divergence matches the crystal perfection.

Journal logoBIOLOGICAL
ISSN: 1399-0047
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