On the possibility of measuring the diffraction pattern of single micro objects. Volume 447

As two-dimensional x-ray microscopy develops, it is of interest to consider also possible three-dimensional imaging methods, in view of the thick-specimen capability of soft x-rays. The highest-quality 3-dimensional images of atomic assemblies today are produced by Fourier inversion of 1A x-ray or neutron diffraction patterns of crystalline specimens. The authors consider whether a similar form of imaging may be obtained with very small non-crystalline specimens using soft x-rays. Success would allow microscopic objects, such as biological cells, to be imaged in three dimensions and at resolutions of the order of 15A. As x-ray wavelengths increase from 1A, elastic scattering persists, Compton scattering decreases, and photoelectric absorption increases. The first and third of these give rise to coherent scattering and are effective in diffraction, while the second contributes an incoherent background and does not contribute to diffraction. They should expect that diffraction will exist in the soft x-ray region and with lower intrinsic background than in the shorter wavelength region. Small-angle diffraction patterns from multiple small objects (latex spheres) have indeed been observed in the soft x-ray region. Here, however, they are concerned with the possibility of measuring large-angle patterns, and from single small objects