Plutonium-240 exhibits a high rate of spontaneous fission, raising the neutron flux of any sample containing it. Trace quantities arise in natural uranium-238 deposits when uranium-238 captures neutrons emitted by decay of other uranium-238 atoms.Д«oth plutonium-239 and plutonium-241 are fissile, meaning that they can sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. Plutonium is the element with the highest atomic number to occur in nature. Wartime secrecy prevented the University of California team from publishing its discovery until 1948. Since uranium had been named after the planet Uranus and neptunium after the planet Neptune, element 94 was named after Pluto, which at the time was considered to be a planet as well.

First, neptunium-238 ( half-life 2.1 days) was synthesized, which subsequently beta-decayed to form the new element with atomic number 94 and atomic weight 238 (half-life 88 years). Plutonium was first synthetically produced and isolated in late 1940 and early 1941, by a deuteron bombardment of uranium-238 in the 1.5-metre (60В in) cyclotron at the University of California, Berkeley. It is radioactive and can accumulate in bones, which makes the handling of plutonium dangerous. When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder that is pyrophoric. It reacts with carbon, halogens, nitrogen, silicon, and hydrogen. The element normally exhibits six allotropes and four oxidation states. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94.

Define stockpile syndrome