Search

Members of the Nondestructive Evaluation Section at the Lawrence Livermore National Laboratory (LLNL) are implementing the advanced three-dimensional imaging technique of x- and gamma-ray computed tomography (CAT or CT) for industrial and scientific obscured object evaluation. This technique provides internal and external views of materials, components, and assemblies nonintrusively. Our work includes building of CT scanners as well as data preprocessing, image reconstruction, display and analysis algorithms. These capabilities have been applied to a variety of industrial and scientific NDE applications. We have used CT to study various objects with obscured features at our laboratory ranging in size from 1 mm3 to 1 m3. In these studies, CT has revealed flaws (e.g. cracks, voids, and inclusions), internal and external dimensional information, differences in elemental composition or material density, and other important material characteristics. CT has also been used to localize, identify, and quantify radioisotopes within canisters. As illustrative examples, we describe how CT was instrumental in the analysis of concrete specimens, diesel engine thermocouple plugs, jet engine turbine blades, ballistic target materials, and radioactive waste canisters.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This document establishes the software design, nomenclature, and conventions for industrial Computed Tomography (CT) used in the Nondestructive Evaluation Section at Lawrence Livermore National Laboratory. It is mainly a users guide to the technical use of the CT computer codes, but also presents a proposed standard for describing CT experiments and reconstructions. Each part of this document specifies different aspects of the CT software organization. A set of tables at the end describes the CT parameters of interest in our project. 4 refs., 6 figs., 1 tab.

X-ray computed axial tomography (CAT or CT) is an advanced imaging technique which provides three-dimensional nondestructive inspection and characterization of materials, components and assemblies. The Lawrence Livermore National Laboratory (LLNL) and the Mason Hanger-Silas Mason Co., Pantex Plant are cooperating to examine the use of CT Technology to inspect high-explosive (HE) pressings. The goals of this joint project are to study the HE pressing process using computed tomography scanners, to provide a foundation for the further development of industrial CT scanners, and to work with the private sector on the design and implementation of an automated CT inspection scanner to be used in the manufacturing process of high explosives at the Pantex Plant. The early detection of defective HE pressings will reduce the cost and improve the safety of the high-explosives production cycle. At present, all pressings are bulk density tested. In addition, samples are randomly selected from each pressing lot for destructive core sampling to obtain an estimate of internal density gradients. CT is a viable technology for a high-explosives inspection system. CT measures density variations, detects foreign inclusions and voids with a probability of detection as good as or better than present inspection techniques. In addition, CT canmore » be fully automated to allow for a 100% sample inspection. LLNL has the advantage of several different in-house built CT scanners to bring to bear on the inspection of high explosives. A preliminary study was performed to evaluate the LLNL CT scanners and prove the characterization principles associated with CT on small PBX9502 high-explosive samples. This paper summarizes the results obtained, and introduces the capabilities of LLNL's Nondestructive Evaluation Section CT scanners. 36 refs., 50 figs.« less

In x-ray and ion-beam computerized tomography, there are a number of reconstruction effects, manifested as artifacts, that can be attributed to the geometry of the experimental setup and of the object being scanned. In this work, we will examine four geometric effects that are common to first-and third-generation (parallel beam, 180 degree) computerized tomography (CT) scanners and suggest solutions for each problem. The geometric effects focused on in this paper are: X-pattern'' artifacts (believed to be caused by several errors), edge-generated ringing artifacts (due to improper choice of the reconstruction filter and cutoff frequency), circular-ring artifacts (caused by employing uncalibrated detectors), and tuning-fork artifacts (generated by an incorrectly specified center-of-rotation). Examples of four effects are presented. The X-pattern and edge-generated ringing artifacts are presented with actual experimental data introducing the artifact. given the source of the artifact, we present simulated data designed to replicate the artifact. Finally, we suggest ways to reduce or completely remove these artifacts. The circular-ring and tuning-fork artifacts are introduced with actual experimental data as well, while digital signal processing solutions are employed to remove the artifacts from the data. 15 refs., 12 figs.