Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where plutonium sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Size, to scale
Radius 155 pm — that is 0.155 nm, so about 3226 million of them side by side would span a millimetre.
Thermal range
Plutonium is liquid over a 2592 K window, from 913 K to 3505 K.
The story
The element that made the atomic age possible and powers spacecraft beyond the Sun's reach.
Glenn T. Seaborg, Edwin McMillan, Joseph W. Kennedy, and Arthur Wahl at the University of California, Berkeley, discovered plutonium in late 1940 and early 1941. This discovery would literally change the course of world history and end World War II.
Deuteron Bombardment: On December 14, 1940, the team bombarded uranium-238 with deuterons (heavy hydrogen nuclei) in Berkeley"s 60-inch cyclotron. They created neptunium-238, which then decayed into an unknown element with atomic number 94.
Chemical Isolation: Seaborg"s brilliant chemistry work in early 1941 successfully isolated and identified element 94. They discovered it was fissile like uranium-235 but could be chemically separated from uranium much more easily - a crucial advantage for weapons production.
Wartime Secrecy: The discovery was immediately classified as top secret. The Manhattan Project realized that plutonium offered a potentially easier path to nuclear weapons than enriching uranium-235, leading to the construction of massive production reactors at Hanford, Washington.
Trinity Test: The world"s first nuclear weapon test on July 16, 1945, in New Mexico used a plutonium implosion device. Three weeks later, a similar plutonium bomb was dropped on Nagasaki, Japan, ending World War II.
Planetary Theme: Following the pattern of neptunium (Neptune), the discoverers named element 94 "plutonium" after the dwarf planet Pluto. The name seemed especially fitting given Pluto"s association with the underworld, reflecting plutonium"s destructive potential.
Scientific Achievement: Glenn Seaborg won the Nobel Prize in Chemistry in 1951 for discovering plutonium and other transuranium elements. His work established the actinide series and revolutionized our understanding of heavy element chemistry.
Atomic Age Beginning: Plutonium"s discovery marked the true beginning of the Atomic Age. It enabled both nuclear weapons and nuclear power, fundamentally changing international relations, military strategy, and energy production for all future generations.
Applications
Nuclear Reactor Fuel: Plutonium-239 is one of the most important fissile materials for nuclear power generation. Mixed oxide (MOX) fuel containing plutonium provides a sustainable way to recycle nuclear waste while generating clean electricity for millions of homes worldwide.
Fast Breeder Reactors: Advanced reactor designs use plutonium as both fuel and breeding material, potentially providing centuries of clean nuclear energy while consuming existing nuclear waste. Countries like Russia, China, and India operate successful plutonium-fueled fast reactors.
Radioisotope Thermoelectric Generators (RTGs): Plutonium-238 powers some of humanity"s greatest space achievements, including the Voyager probes (now in interstellar space), the Curiosity and Perseverance Mars rovers, and the New Horizons mission to Pluto. These RTGs provide reliable power for decades in the harsh environment of space.
Deep Space Missions: Plutonium"s long half-life and high energy density make it irreplaceable for missions beyond Mars, where solar panels become ineffective. Future missions to the outer planets and interstellar space depend on plutonium power sources.
Cardiac Pacemakers: Plutonium-238 powered early cardiac pacemakers, providing reliable power for patients for over 20 years. While newer battery technologies have largely replaced them, some long-lived medical implants still use plutonium power sources.
Medical Research: Controlled amounts of plutonium isotopes are used in advanced medical research to understand radiation effects and develop new cancer treatments, though this requires the highest safety protocols.
Fundamental Research: Plutonium"s unique nuclear properties make it essential for studying nuclear fission, fusion reactions, and the behavior of heavy nuclei. This research advances our understanding of stellar nucleosynthesis and the origins of heavy elements in the universe.
Neutron Sources: Plutonium-beryllium neutron sources are used in research reactors, neutron activation analysis, and well-logging in the oil industry to locate underground resources.
Nuclear Fuel Recycling: In countries with advanced nuclear programs like France and Japan, plutonium extracted from spent nuclear fuel is recycled into new MOX (Mixed Oxide) fuel, reducing nuclear waste and extending uranium resources.
Research Laboratory Standards: Tiny quantities of plutonium isotopes serve as reference standards in nuclear laboratories for calibrating detection equipment and studying actinide chemistry.
NASA Missions: Plutonium-238 is the only practical power source for deep space missions. NASA"s limited supply powers critical missions like the Mars rovers and outer planet explorers, making it more valuable than gold for space exploration.
Nuclear Chemistry: Research facilities use plutonium to study transuranium element chemistry, nuclear decay processes, and the fundamental properties of heavy nuclei.
Neutron Activation Analysis: Plutonium-beryllium neutron sources help analyze the composition of materials in geology, archaeology, and materials science.
Critical Note: All plutonium applications are strictly regulated by international nuclear authorities. There are no consumer uses due to its extreme radioactivity and weapons potential.
Where it comes from
0 mg/kg of Earth's crust · more abundant than 0% of elements
Trace Natural Formation: While plutonium is essentially synthetic, incredibly tiny amounts (measured in parts per trillion) have been detected in uranium ore deposits like those in Gabon, Africa. These traces form through extremely rare natural nuclear reactions when uranium captures neutrons from cosmic rays or spontaneous fission.
Uranium Transmutation: Virtually all plutonium is produced artificially in nuclear reactors when uranium-238 absorbs neutrons and undergoes beta decay. This process occurs naturally in any uranium-fueled reactor, making plutonium a byproduct of nuclear power generation.
Controlled Production: Specialized production reactors can be optimized to maximize plutonium production by carefully controlling neutron flux and fuel exposure time. The quality and isotopic composition of plutonium depends heavily on these production parameters.
Worldwide Stockpiles: Approximately 500 metric tons of plutonium exist worldwide, mostly as byproducts of nuclear power generation. This represents one of the most carefully monitored and secured materials on Earth.
Weapons vs. Reactor Grade: Plutonium quality varies significantly - weapons-grade plutonium (>93% Pu-239) requires special production techniques, while reactor-grade plutonium contains multiple isotopes and is less suitable for weapons but excellent for power generation.
MOX Fuel Production: Countries like France reprocess spent nuclear fuel to extract plutonium for recycling into new fuel, creating a closed nuclear fuel cycle that reduces waste and extends uranium resources.
Handling
Plutonium is radioactive. It has no stable isotope — every nucleus decays. Handling requires appropriate shielding and licensing.
Lethal Radioactivity: Plutonium is one of the most toxic substances known to humanity. A microscopic particle of plutonium-239 inhaled into the lungs can cause lung cancer decades later. Even nanogram quantities pose serious health risks.
Alpha Radiation: Plutonium emits alpha particles that cannot penetrate skin but cause devastating damage if plutonium dust is inhaled or ingested. Alpha particles destroy cellular DNA and cause cancer, genetic mutations, and radiation sickness.
Long-Term Exposure: Plutonium-239 has a half-life of 24,100 years, meaning it remains dangerous for hundreds of thousands of years. Once in the body, it concentrates in bones and organs, causing lifelong radiation exposure.
Nuclear Security: All plutonium is subject to the highest international security protocols due to its weapons potential. Transport, storage, and handling require multiple authorization levels and armed security.
Containment Systems: Work with plutonium requires specialized glove boxes, negative pressure containment, continuous air monitoring, and emergency response teams. Even research quantities demand extraordinary safety measures.
Contamination Protocol: Any suspected plutonium exposure requires immediate medical attention from specialists trained in radiation medicine. Decontamination procedures are complex and time-critical.
Public Safety: Civilian exposure to plutonium is prevented through multiple regulatory barriers, international treaties, and physical security measures that make it one of the most tightly controlled materials on Earth.
Quick answers
Plutonium (symbol Pu) is element 94 on the periodic table, a actinide in period 7. The element that made the atomic age possible and powers spacecraft beyond the Sun's reach. At room temperature it is a solid, and it is radioactive.
[Rn] 5f⁶ 7s², giving 7 occupied shells holding 2, 8, 18, 32, 24, 8, 2 electrons respectively.Plutonium melts at 913 K (639.9 °C) and boils at 3505 K (3231.9 °C).
Plutonium has no stable isotope, so it has no standard atomic weight. The figure quoted, 244, is the mass number of its longest-lived known isotope.
Plutonium has a density of 19.85 g/cm³. Water is 1.0 g/cm³, so a block of plutonium is about 19.9× heavier.
Plutonium has a Pauling electronegativity of 1.28. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). Values in this middle band tend to form covalent rather than strongly ionic bonds.
Plutonium was discovered in 1940 by Seaborg, McMillan, Kennedy & Wahl. It is named after pluto, next out from Neptune.
Plutonium does not occur naturally on Earth in any meaningful quantity — it is made in a reactor or an accelerator.
Yes. Plutonium has no stable isotope — every one of its nuclei decays. Trace amounts occur naturally as decay products of heavier elements.