RADONOGRAPHY

The applicability of a method called radonography (radon autoradiograp hy) is explored for the investigation of materials. The method is base d on a difference of adsorption and diffusion coefficients of radon fo r different solids. The specimen to be imaged is first exposed to a ra don atmosphere (of the order 10(7) Bq/m3) for a few days to collect ra don in the near surface layer. The specimen is then left in a radon-fr ee atmosphere for some hours to allow decay of the radon daughters pla ted out on the specimen surface during the exposure. Finally the speci men is placed in tight contact with a track etch detector for some day s to register alpha particles 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 adsorpt ion coefficients k(a) and k(b) was estimated by a simple model to be p roportional to 1-k(b)/k(a). Lateral spatial resolution, quoted in term s of image unsharpness, is of the order of the range of alpha particle s in the specimen (30 mum).