Standardized Result Cutnell, John D. and Johnson, Kenneth W. Physics, 3rd edition . Nuclear Physics . Institute for Energy and Environmental Research. Plutonium belongs to the class of elements called transuranic elements whose atomic number is higher than 92, the atomic number of uranium.
Plutonium is the most economically important of the transuranic elements.
Plutonium-239 readily undergoes fission, and it is used for nuclear weapons and for energy. The atomic number of plutonium is 94. Isotopes of plutonium were first prepared and studied by the American chemist Glenn T. Seaborg and his associates at the University of California at Berkeley in 1941. Plutonium has 15 isotopes with mass numbers ranging from 232 to 246. All isotopes of plutonium are radioactive, but they have widely varying half-lives.