X-ray tomographic microscopy for non-destructive inspection and advanced materials characterization. Final report, May 22, 1992--May 21, 1994

摘要

This was a CRADA to transfer the x-ray tomographic microscope technology to the Quality Technology Center of General Electric Air Craft Engines Division in Ohio. The x-ray tomographic microscope (XTM) is a high resolution, three-dimensional imaging system that can be used to image materials microstructures noninvasively. The apparatus consists of an x-ray source, x-ray collimators, sample positioning stages, a fluorescent screen to convert x-rays to visible light, an optical lens, and a thermoelectrically cooled charge coupled device detector. The details of the microscope's design have been described elsewhere. In practice, the sample to be imaged is positioned on a rotating stage. The sample is initially translated out of the x-ray path, and an image is obtained of the incident x-ray beam (the reference image). Next, the sample is placed between the x-ray path and the scintillator, and another image, the projection image, is acquired. The ratios of the logarithms of the reference image and the projection image provide values of the integrated x-ray attenuation through the sample. By rotating the sample in discrete angular increments through 180 degrees, enough data can be obtained to reconstruct the two-dimensional projection images into a three-dimensional image of the mineral density distribution in the sample. This reconstruction procedure, known as reconstruction from projections, is usually performed with the technique of Fourier-filtered back-projection. Using the present microscope, a 1 cubic centimeter volume can be imaged with five micrometer volume elements in about one hour or less.