Periodic Statistical Distortion of Unidirectionally Ordered Diffractors, with Application to Collagen

Publisher Website
Google Scholar
Abstract
The diffraction expected of distorted, one-dimensionally ordered cylinders (fibrils) is considered quantitatively. The distortion involved is statistically of cylindrical symmetry about any point in the fibril, and periodic along the fibril axis. An important case is that of the ``mixed perfect and imperfect fibril,'' in which, at some axial levels, distortion is absent, and at others it is appreciable. For such systems it is shown that the reciprocal-space disk corresponding to a given diffraction layer line may be regarded as composed of three sub-disks: one of perfection, whose central intensity is maximal and whose diameter is small and independent of layer-line index; another of longitudinal or axial imperfection, whose central intensity is also maximal; and a third, related to radial imperfection, whose intensity is noncentrally maximal. Both types of imperfection sub-disk expand linearly in diameter with increase in index. It is demonstrated briefly that certain dry collagen specimens exhibit small-angle diffraction in which the characteristics of the three types of sub-disk are apparent.