Plutonium
actinideProperties
| Property | Value |
|---|---|
| Atomic Mass | 244 amu |
| Category | actinide |
| Period | 7 |
| Electron Configuration | [Rn] 5f6 7s2 |
| Electronegativity | 1.28 (Pauling) |
| Oxidation States | 6, 5, 4, 3 |
| Melting Point | 912.5 K (639.4 °C) |
| Boiling Point | 3505 K (3231.8 °C) |
| Density | 19.86 g/cm³ |
| Discovered By | Glenn T. Seaborg, Arthur Wahl, Joseph W. Kennedy, Edwin McMillan (1940) |
About Plutonium
Plutonium is the metallurgist's nightmare and the nuclear engineer's workhorse. Seaborg, McMillan and colleagues at Berkeley made the first microgram of ²³⁸Pu in 1940 by deuteron-bombarding U-238, and within a few years ²³⁹Pu — fissile, breedable in U-238 blanket assemblies — became the fissile material in the Trinity test and the Fat Man core. The metal itself has six allotropic phases between room temperature and its melting point at 640 °C, with density swings of more than 25% between phases; that's why weapons-grade Pu is alloyed with a percent or so of gallium to stabilize the workable δ-phase. Aqueous Pu chemistry is just as awkward — the +3, +4, +5 and +6 oxidation states can coexist in the same beaker because their reduction potentials sit within a few hundred millivolts of each other, which is why PUREX reprocessing relies on careful redox control with Fe(II) and hydroxylamine. The non-fissile ²³⁸Pu (88-yr half-life, 0.56 W/g from alpha decay) is the thermal source in every RTG NASA flies past Jupiter, including the Voyagers, Cassini, New Horizons, Curiosity and Perseverance.
Fun Fact
The Voyager 1 spacecraft, now over 24 billion kilometers from Earth in interstellar space, is still transmitting data back to us powered by the steady warmth of decaying plutonium-238, over 45 years after launch.
Common Uses
- ²³⁹Pu fissile fuel in nuclear weapon pits and fast-spectrum reactors
- MOX fuel (PuO₂/UO₂) in light-water and fast reactors as a U-238 breeding product
- ²³⁸Pu radioisotope thermoelectric generators on Voyager, Cassini, New Horizons, and Mars rovers
- Pu-Be neutron sources for well logging and laboratory neutron activation
- PUREX-process actinide separation chemistry for spent-fuel reprocessing