Sensitive inspection of void defects using synchrotron refraction imaging with quantitative modelling of contrast enhancement

Synchrotron radiation imaging with refraction enhancement was successfully applied to image air voids in opaque plastic materials, which otherwise could hardly be depicted(1). It was suggested that this imaging technique had a superior performance in nondestructive testing of small voids in plastics(1). It has been recognised in previous works that the edge enhancement effect due to X-ray refraction improves the visibility of detailed structures in synchrotron radiation imaging(2-6). For minute objects, however, highlighted boundaries are only weakly delineated in synchrotron radiation refraction images; instead, the object contrast becomes intense, thus enhancing the visualisation(1, 7, 8). In particular, the contrast of small air inclusions is dominantly enhanced within plastic materials in synchrotron radiation refraction images. The purpose of the present study was to quantify the contrast increase of air voids for the first time in synchrotron radiation refraction imaging. This effect will be assessed quantitatively by fitting edge profiles to an analytical cubic curve and simulating the overlap of edge profiles when the edges are close to each other in small structures.