C. POWELL, P. FOWLER & D. PERKINS / SCIENCE PHOTO LIBRARY C. POWELL, P. FOWLER & D. PERKINS / SCIENCE PHOTO LIBRARY
The radioactive emission of alpha particles from radium is dramatically illustrated in this photo. A speck of radium salt was placed on a special emulsion on a photographic plate; when developed, the emulsion reveals the dark tracks of alpha particles emitted by the radium. Radium is the most powerful radioactive substance known; it emits radiation a million times more intensely than uranium. It was discovered by Marie Curie in 1898.
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