The name is kind of edgy - plutonium. It was produced in 1940 at the University California - Berkeley. It does not appear in nature, although it might have been present in the prehistoric past. After exposed to air for a short period of time, it has a dull appearance, and it is twice as dense as lead. The element is fissile - meaning that its nucleus can be split easily by neutrons and that it releases more neutrons, producing a self-sustaining reaction. At rest, Plutonium 239 emits alpha radiation, which is generally stopped by a sheet of paper or the human skin. But with a critical mass of 35 pounds, it releases dangerous gamma radiation, energy, and neutrons. (The critical mass can be reduced to 22 pounds with neutron deflectors and other clever engineering.)
In a conventional nuclear reactor, an atom of Uranium 235 will produce 2 or 3 neutrons and when Uranium 238 absorbs neutrons, Plutonium 239 is produced. Curiously, 1/3 of the energy produced by a conventional nuclear power plant is by Plutonium fissions, even though the original fuel for the reactor was uranium.
The United States has about 110 tons of weapons-grade plutonium in storage, produced from 1940 - 1994. In the early atomic days, scientists did not know how to dispose of waste and contaminated products. At the Hanford, Washington, nuclear production facility, they would dig deep trenches and bury the waste and contaminated vessels, trucks, etc. Antique plutonium tells that cleanup workers found 1/2 gram of plutonium in such a trench.
The plutonium was probably produced in 1944. It was in a glass jar, marked with red crayon. Also in the jar was lanthanum fluoride, which was used to separate Plutonium 239 from other nuclear waste until 1950. Weapons-grade plutonium is slow-baked in a reactor and because reactors have their own unique 'fingerprint', this antique plutonium was tracked to a reactor in Oak Ridge, TN.
Apparently there is more than a glass jar missing from the Russian stockpile. Missing Russian Plutonium Could Fuel 25 Nuclear Weapons, Former Air Force Chief Says explains Russia has lost over 360 pounds of weapons-grade plutonium. This could yield the equivalent of 25 World War II weapons. The author says that both Russia and American authorities are looking for it.