Radiography of concrete specimens using a neutron flux as the penetrating radiation has been used to identify and study microcracking. The key to the technique is the partial impregnation of the microcracks with a medium with a high neutron attenuation capacity, so as to result in a sharp contrast between the cracks and the surrounding solid mass. Gadolinium has been used as the neutron-attenuating contrast agent, which is applied in the form of an aqueous solution of gadolinium nitrate.
The resulting radiographs are compared with more conventional X-ray studies of the same specimens. Neutron radiography appears to be more effective than X-radiography for the identification of cracking.
We have used the TRIGA reactor and the Ion Beam Facility at Cornell to illustrate neutron induced autoradiography and PIXE analysis of known pigments in demonstration paintings made for our undergraduate course, ‘Art, Isotopes and Analysis’. A group of pigments were chosen containing elements with half-lives detectable by the neutron activation process. The pigments (suspended in a binding medium of linseed oil) were first painted on test swatches of acetate and their characteristic x-ray lines measured with a 5 Mev beam of protons directed through a thin Kapton film for external (in air) analysis (PIXE).Three layers of images, each painted with a different pigment, overlay one another. The painting is then taken to the TRIGA reactor for neutron activation. After activation, the painting is placed in contact with sheets of Polaroid type AR positive transparency film at different times after exposure. The gamma spectra during the sequence are also measured to provide identification of the ‘active’ isotopes during each film exposure.
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