Crack Detective

Under the enormous strain of daily use, the materials used for jet engine turbines and high-pressure bolts can develop fine cracks that lead to disaster. Researchers can identify most of these defects via neutron radiography, a technique similar to x-ray photography; but some cracks are too fine to register. An alternative method, called phase-contrast imaging, can detect even more subtle features, but it requires special equipment running in stringent environmental conditions such as complete isolation from vibration. Recently, however, physicists at the National Institute of Standards and Technology, the University of Melbourne and the University of Missouri, Columbia, have produced high-resolution neutron radiographs using conventional apparatus. The technique works by combining the data from two standard neutron radiographs taken from different angles, then extracting the phase contrast using a computer algorithm. The technique may also be used to study biological tissues: for example, to better visualize tumor boundaries. -E. Jonietz

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