Note on “Superlarge” Structures and Their Phase Problem
Work carried out over the last few years1 suggests that it may be possible to extend x-ray diffraction techniques to the determination of structures of non-crystalline specimens of microti size, such as single small biological cells. Work to date has concentrated on showing that the diffraction from microscopic non-crystalline objects, while extremely faint, can be observed by employing high-intensity synchrotron x-ray sources, shifting to longer wavelengths, and increasing the coherence of the radiation. Assuming undulator radiation with high spatial coherence it is mainly the temporal coherence of the radiation which is at issue; assuming radiation of monochromaticity M the maximum resolution to which diffraction from a specimen of diameter a will normally extend is of the order of a/M. Using radiation with M=150 and individual cells of Minutocellus polymorphus with a=3µm we have observed pattern in 18A radiation to approximately 200A resolution, in good agreement with the above. Fig. 1 shows a portion of such a pattern. In certain special cases we have observed diffraction to 70A resolution.
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