Plutonium is one of the most famous and feared elements ever created. Born in a lab in 1940, it changed the course of World War II just five years later through the Manhattan Project. This silvery metal is so energy-dense that a ball the size of an orange could power an entire city. One kilogram of Pu-239 packs the punch of 20,000 tons of TNT.
But plutonium is more than a weapon. It powers the Voyager probes flying through interstellar space and the Curiosity rover on Mars. Without it, humanity could never explore the far solar system, where sunlight is too faint for solar panels.
In its pure form, plutonium is a silvery-gray metal that tarnishes in air, turning yellowish. It feels warm to the touch from its own radioactive heat. It holds the record with 6 allotropic forms — more than any other element. When heated, it actually shrinks instead of expanding. Extremely unusual for a metal.
Today the world has over 2,000 tons of plutonium — from spent nuclear fuel and dismantled warheads. Scientists are looking for ways to safely use these stockpiles: as fuel for next-generation reactors or energy sources for deep-space missions.
Plutonium is extraordinarily dangerous. Pu-239 is a powerful alpha emitter with a half-life of 24,110 years. Inhaling even a few micrograms of dust can cause lung cancer. Alpha particles cannot penetrate skin, but inside the body they shred cell DNA. Work with plutonium is only possible in sealed gloveboxes with remote handling. It must be stored in special containers under constant monitoring to ensure the mass never approaches the critical threshold.
Voyager 1 and Voyager 2 have been flying through interstellar space for over 47 years — still running on RTGs fueled by plutonium-238. They are the farthest human-made objects from Earth.
Plutonium was a secret element. During WWII it was called simply '49' — from the last digits of atomic number 94 and isotope 239. Its existence was hidden from the world for years.
A chunk of plutonium feels warm to the touch — it heats itself through radioactive decay. One kilogram of Pu-238 puts out 560 watts of heat, like a powerful light bulb.
Plutonium has 6 different crystal forms (allotropes) — an absolute record among all elements. And when heated, it shrinks instead of expanding.
The element was named after Pluto, then the ninth planet. Uranium → Neptunium → Plutonium mirrors the order of the planets: Uranus, Neptune, Pluto.
The critical mass of plutonium-239 is just 10 kg — a sphere only 10 cm across. Bring that much together and you get a nuclear explosion equal to 20,000 tons of TNT.
| Isotope | Mass (u) | Abundance | Half-life | Decay |
|---|---|---|---|---|
238Pu☢ | 238.049560 | synthetic | 87.7 years | α |
239Pu☢ | 239.052163 | synthetic | 24110 years | α |
240Pu☢ | 240.053813 | synthetic | 6561 years | α |
241Pu☢ | 241.056851 | synthetic | 14.35 years | β− |
244Pu☢ | 244.064204 | synthetic | 8.00×10⁷ years | α |
Cyclotron bombardment of uranium