ra·di·o·graph n.
 1. An instrument for measuring and recording solar radiation.
 2.  An image or picture produced upon a sensitive surface, as of a photographic or fluorescent plate, by some form of penetrating radiation other than light, as X-rays, beta rays, etc.; esp., a picture of the internal structure of opaque objects traversed by the rays; a skiagraph.  When the picture is produced upon photographic film by X-rays, the picture is usually called an X-ray photo or X-ray.  When an image is produced on photographic film by a radioactive substance in close proximity to the film, in a manner so as to record the spatial distribution of the radioactive substance, the resulting image is called an autoradiograph or {autoradiogram}.