This image of the atomic structure of uranyl acetate crystals was made using a scanning tunnelling electron microscope. Each bright spot represents a single uranium atom withi the crytal lattice, magnified 50 million times. Uranyl acetate is a soluble compound of the element uranium. It is one of the most important 'staining' agents used in the transmission electron microscopy of organic organisms, where it is impregnated into the specimen. The heavy uranium atoms are very effective at scattering electons.