What is Plutonium?
Plutonium is a dense, radioactive metal in the actinide series. It exhibits multiple solid allotropes with sharply different densities and mechanical properties. It’s chemically reactive, forms various oxidation states in solution, and is mostly man-made in reactors through neutron capture of uranium-238.
Key Properties
Physical
| Density (α-phase) | 19.8 g·cm−3 |
| Melting Point | 640 °C |
| Boiling Point | 3228 °C |
| Allotropes | α, β, γ, δ, δ′, ε |
Chemical
| Oxidation States | +3 to +6 |
| Common Compounds | PuO₂, PuF₆, PuCl₃ |
| Corrosion | Forms protective oxides; sensitive to humidity |
Nuclear
| Fissile Isotope | Pu-239 |
| Half-life (Pu-239) | 24 110 years |
| Half-life (Pu-238) | 87.7 years |
Principal Isotopes
Pu-238
Used in RTGs for space missions; strong α-emitter providing consistent heat.
Pu-239
Fissile isotope used in energy research and historically in nuclear weapons.
Pu-240
Higher spontaneous fission rate; limits use in weapons-grade material.
Pu-241 / Pu-242
Pu-241 β-decays to Am-241 (γ-emitter); Pu-242 has very long half-life.
History & Discovery
- 1940: Glenn T. Seaborg’s team synthesizes plutonium at UC Berkeley.
- 1943–45: Large-scale production at Hanford during the Manhattan Project.
- 1950s–present: Reactor research, safeguards, and evolving safety standards.
- 1960s–today: Pu-238 RTGs power deep-space missions (Voyager, Cassini, Mars Rovers).
Applications
Space Power
Pu-238 RTGs supply decades of reliable power and heat to spacecraft operating beyond solar range.
Energy Research
Pu-239 blended with uranium forms MOX fuel, improving resource utilization and reducing waste volume.
Safeguards & Disposition
International programs focus on secure handling, non-proliferation, and conversion of surplus material.
Safety & Environment
Radiological Effects
- Alpha radiation is blocked by skin but hazardous if inhaled or ingested.
- Fine particles may remain in lungs for decades, increasing cancer risk.
Handling & Waste
- Operations occur in sealed gloveboxes with HEPA filtration and criticality-safe geometry.
- Waste requires long-term geologic isolation and continuous monitoring.
References & Further Reading
Cite This Page
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FAQ
Is plutonium naturally occurring?
Trace amounts form in uranium ores, but almost all usable plutonium is reactor-produced.
Why use Pu-238 for RTGs?
Its α-decay produces steady heat and minimal penetrating radiation, ideal for long-duration missions.
Can a reactor explode like a bomb?
No—the configuration and control systems prevent the rapid assembly needed for a nuclear detonation.