Radonography

Abstract

The applicability of a method called radonography (radon autoradiography) is explored for the investigation of materials. The method is based on a difference of adsorption and diffusion coefficients of radon for different solids. The specimen to be imaged is first exposed to a radon atmosphere (of the order 10 7 Bq/m 3) for a few days to collect radon in the near surface layer. The specimen is then left in a radon-free atmosphere for some hours to allow decay of the radon daughters plated out on the specimen surface during the exposure. Finally the specimen is placed in tight contact with a track etch detector for some days to register alpha panicles emitted by radon (and its progeny) from the surface layer of a thickness equal to the range of alpha particles in the specimen. The inhomogeneity of the specimen is revealed as the spatial variation of the track density. The image contrast associated with the interfacial region of two materials characterized by adsorption coefficients k a and k b , was estimated by a simple model to be proportional to 1− k b / k a . Lateral spatial resolution, quoted in terms of image unsharpness, is of the order of the range of alpha particles in the specimen (30 μm).