An elementary body discovered in 1899 by Madame Curie in pitchblende, characterized by the phenomenon Radioactivity appears to be a manifestation of subatomic energy; the atom of radium being in a state of slow disintegration gives off a gaseous emanation, which has the spectrum of helium. Other radioactive substances are uranium, thorium, polonium, and actinium. It appears that radioactive elements are undergoing spontaneous transmutation into other elements.
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