JOURNAL OF X-RAYSCIENCE AND TECHNOLOGY 4, 290-300 (1994) Nondestructive Evaluation of Millimeter Scale Engineered Structures Using Synchrotron X-Ray Microtomography ANTHONY B. HMELO School of Engineering, Vanderbilt University, Box 6079 Station B, Nashville, Tennessee 37235 Received December 23, 1993; revised May 11, 1994 Synchrotron x-ray microtomography has matured into a practical tool for the metrology of small specimens, featuring a spatial resolution of a few micrometers. In this paper, the author examines the practice of monochromatic x-ray tomography, emphasizing the char- acteristics of synchrotron radiation sources that have enabled the evolution of this new imaging technology. These principles are illustrated using reconstructions of millimeter scale engineered structures fabricated from low atomic weight materials. These structures include spherical shells, considered as model inertial confinement fusion targets, and ex- amples of laser-welded aluminum alloys. © 1994Academic Press, Inc. INTRODUCTION Computerized x-ray tomography (CT) has been applied in the medical community to the study of human patients since the early 1970s. However, it is only within the past 10 years that this technique has been used for the nondestructive evaluation of small samples of nonbiological materials of industrial or scientific interest. With the increasing use of synchrotron radiation, concurrent with advances in detector tech- nology (1, 2) and computing power, monochromatic x-ray tomography of small samples can now reveal the internal structure at a resolution approaching 1 #m, and an ele- mental sensitivity of 1% under the best conditions. The first commercially available unit for the medical application of CT was the EMI scanner developed by Hounsfield at Central Research Laboratories of EMI Ltd., England. This scanner was first used at the MAYO clinic in 1973. Hounsfield (3) pioneered the application of CT to the human patient. However, the geometry of x- ray illumination and available flux make medical scanners undesirable tools for ma- terials research. X-ray tomography is finding a wide range of engineering applications assessing the integrity of materials, components, and structures. These applications are expected to proliferate as new high brightness tunable monochromatic x-ray sources, such as the Compton Backscatter X-ray Source at Vanderbilt University's Free Electron Laser Facility, become available. Computer assisted tomography has been used for a wide variety of inspection applications in industrial settings (4-6), as in the evaluation of assembled rocket nozzles (7) or space shuttle components. In this paper, we will use examples from our published and unpublished work, in which Vanderbilt University has been engaged, as examples of what is possible today and what we would like to see in the future. This series of experiments has progressed from the examination of 0895-3996/94 $6.00 290 Copyright © 1994by Academic Press, Inc. All rights of reproduction in any formreserved.