Thorium is a naturally occurring radioactive chemical element with the symbol Th and atomic number 90. Radium is a chemical element with symbol Ra and atomic number 88. In nature, radium is found in uranium ores in trace amounts as small as a seventh of a gram per ton of uraninite. Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with symbol U and atomic number 92. Uranium occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite. Plutonium is a transuranic radioactive chemical element with the symbol Pu and atomic number 94. Plutonium was first made by Glenn T. Seaborg, Joseph W. Kennedy, Edward M. McMillan and Arthur C. Wahl at the University of California, Berkley in 1940. It is, therefore, an artificial element (although it is found in extremely small quantities in nature.) It was created for use in the atomic bomb. Plutonium is usually manufactured artificially in special reactors designed and built especially for this task. Trace amounts of plutonium have also been found naturally inside some uranium ores. It's virtually nonexistent, however, in the soil.
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