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a radioactive transuranic element that is similar to uranium; found in minute quantities in uranium ores but is usually synthesized in nuclear reactors; 13 isotopes are known with the most important being plutonium 239

a solid silvery gray radioactive transuranic element whose atoms can be split when bombarded with neutrons; found in minute quantities in uranium ores but is usually synthesized in nuclear reactors.

Plutonium. A naturally radioactive element of the actinide metals series. It has the atomic symbol Pu, atomic number 94, and atomic weight 242. Plutonium is used as a nuclear fuel, to produce radioisotopes for research, in radionuclide batteries for pacemakers, and as the agent of fission in nuclear weapons.