NDTnet 1998 Aug, Vol.3 No.8

Abstract

Conventional radiography and tomography are based on X-ray absorption inside the object. In this case the spatial resolution is limited by source and/or detector size. The density sensitivity is limited by the signal to noise level and the dynamic range. In the same time any transmitting X-ray image contains a phase information. Phase shift and space distribution can supply more detail information about the object structure. Typical techniques for phase restoration require a highly monochromatic plane-wave X-ray source (such as a synchrotron) with special optics like double-crystal monochromators and interferometers (1). As shown in (2) the phase information can be received also from an X-ray system with polychromatic source with high spatial coherence. This approach open new possibilities to implement phase-contrast techniques into desk-top X-ray systems with microfocus sealed sources. Because any irregularity of the object structure produces some phase shift, phase contrast microradiography and microtomography makes it possible to regnise small details even better than the tube spot size. In our tests we use a microfocus sealed tube with a spot size of 8µm operated at 70kV. The possibilities of phase-contrast microtomography are shown in Fig.

Fig.: Phase-contrast images of diamond (see text)

We use a small diamond with thin cracks (gletses) as the object. Because the crack thickness was less than the source spot size this gletses cannot be visualized by X-ray absorption. The left image shows the phase radiographic image with contrast enhancement in the crack. It differs from the absorption image in the sense that the phase-contrast cracks are visualized as extra density areas. The right side of the image shows the results of the microtomographic reconstruction from 400 phase-contrast microradiograms with different views. In the reconstructed cross section the internal steps of the cracks can be found.

References:
1. Ingal, V. N., Beliaevskaya, E. A. J. Phys. D;Appl. Phys. 1995,28..2314-2317.
2. Wilkins, S. W. et al. Nature 1996,384:335-338.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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