Neutron-diffraction section topography: Observing crystal slices before cutting them

Abstract

The possibility of visualizing crystal defects within single crystals several centimeters thick by neutron‐diffraction section topography is demonstrated. The technique consists in photographically recording the Bragg‐diffracted beam produced by the crystal from a narrow incident neutron beam; in effect it amounts to investigating a slice of the specimen without cutting it. Subgrain boundaries and inclusions were visualized inside an as‐grown cylindrical crystal of Fe‐3% Si, 2 cm in diameter. The slice corresponding to the investigated region was subsequently cut out and studied by x‐ray diffraction topography, yielding positive identification of the subgrain structure observed on the neutron topographs before cutting. By using a Polaroid camera with a sensitive neutron scintillator, the gross features of the subgrain structure can be obtained in minutes. The orientation of the virtual slice is predetermined at will; by making several section topographs the complete subgrain structure of the crystal can be investigated nondestructively.