White-beam synchrotron X-ray topography was used to study the circular prismatic [00•1] dislocation loops which were commonly observed on the (00•1) plane in polycrystalline freshwater ice. A new method, which involved a detailed analysis of the effects of beam divergence upon the loop images, was developed in order to determine whether a loop was of vacancy or interstitial type. In an 00•2 image, one half of a loop (projected as an ellipse) appeared as a single image while the other half appeared as a double image. Experimentally, it was found that a 00•2 vector which was drawn from the center of a loop passed through the single image if the loop was of vacancy type, and through the double image if the loop was of interstitial type. This method of loop characterization was confirmed by making theoretical analyses of both the dislocation image widths and their strain fields.

F.Liu, I.Baker, M.Dudley: Philosophical Magazine A, 1995, 71[1], 1-14