钚 (plutonium) is a radioactive chemical element with the symbol Pu and atomic number 94. It is a silvery-gray metal that is dense and heavy, primarily used as fuel in nuclear reactors and in the production of nuclear weapons. Plutonium is produced in nuclear reactors from uranium-238 through neutron capture. Plutonium has several isotopes, with plutonium-239 being the most significant for its use in nuclear applications. Due to its radioactivity, handling plutonium requires strict safety measures to prevent exposure. Its discovery in 1940 marked a significant advancement in nuclear chemistry and technology.