STP716: Neutron Diffraction Tomography: A Unique 3D Inspection Technique for Crystals Using an Intensifier TV System

    Davidson, JB
    Development engineer and senior engineering technologist, Instrumentation and Controls Division, Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Case, AL
    Development engineer and senior engineering technologist, Instrumentation and Controls Division, Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Pages: 13    Published: Jan 1980


    Abstract

    This paper describes the application of phosphor-intensifier-television (TV) techniques to neutron topography and tomography of crystals. The older, analogous X-ray topography using wavelengths ≈ 1.5Å is widely used for surface inspection. However, the crystal must actually be cut in order to see diffraction anomalies beneath the surface. Because 1.5-Å thermal neutrons are highly penetrating, much larger and thicker specimens can be used. Also, since neutrons have magnetic moments, they are diffracted by magnetic structures within crystals. In neutron volume topography, the entire crystal or a large part of it is irradiated, and the images obtained are superimposed reflections from the total volume. In neutron diffraction tomography (or section topography), a collimated beam irradiates a slice (0.5 to 10 mm) of the crystal. The diffracted image is a tomogram from this part only. A series of tomograms covering the crystal can be taken as the specimen is translated in steps across the narrow beam. Grains, voids, twinning, and other defects from regions down to 1 mm in size can be observed and isolated. Although at present poorer in resolution than the original neutron and film methods, the TV techniques are much faster and, in some cases, permit real-time viewing. Two camera systems are described: a counting camera having a 150-mm 6Li-ZnS screen for low-intensity reflections which are integrated in a digital memory, and a 300-mm system using analog image storage. Topographs and tomograms of several crystals ranging in size from 4 to 80 mm are shown.

    Keywords:

    neutron diffraction tomography, neutron topography crystal inspection, neutron television camera, image intensifier, nondestructive testing, directional solidification, radiography


    Paper ID: STP27511S

    Committee/Subcommittee: E07.05

    DOI: 10.1520/STP27511S


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