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SummaryThe influence of degree of dissociation on the diffraction contrast from a Frank dislocation for lll, 220, and 020 reflections has been investigated using the technique devised by Head and Humble for computing electron microscope images.The diffraction contrast from a dissociated Frank dislocation differs in several ways from that of an undissociated dislocation. For 111 reflections, strong contrast occurs when g. u oF O. For 220 reflections, images are single and continuous with strong contrast on one side only. The strong contrast does not invert from side to side for +g and -g. For 020 reflections the extent to which reversal of contrast occurs in ± g is a function of g, the beam direction, and the separation of the Shockley and stair-rod dislocations.The computations for an undissociated Frank dislocation are in general agreement with previous computations, but indicate that a Frank dislocation may show strong contrast for certain beam directions when g. b = ±l.

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