Po · Element 84 · Post-transition metal
Intensely radioactive: a gram of polonium-210 emits enough alpha particles to glow blue and self-heat to 500 degrees C.
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 polonium 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.
Same element, different neutrons
All polonium atoms have the same number of protons, 84, and differ only in their number of neutrons: those variants are its isotopes. None of them is stable. The longest-lived known isotope, Po-209, has 125 neutrons and a half-life of 124 yrs.
| ISOTOPE | Neutrons | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|---|
| Po-206 | 122 | — | 8.8 days | ε/β⁺ (94.55%), α (5.45%) |
| Po-207 | 123 | — | 5.80 hr | ε/β⁺ |
| Po-208 | 124 | — | 2.898 yrs | α |
| Po-209 longest-lived | 125 | — | 124 yrs | α |
| Po-210 | 126 | — | 138.376 days | α |
Here the classroom shortcut, rounded atomic mass (209) minus atomic number, gives the same answer: 125.
Decay modes
Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.
Size, to scale
Radius 150 pm — that is 0.15 nm, so about 3.33 million of them side by side would span a millimetre.
Thermal range
Polonium is liquid over a 708 K window, from 527 K to 1235 K.
The story
Intensely radioactive: a gram of polonium-210 emits enough alpha particles to glow blue and self-heat to 500 degrees C.
The discovery of polonium is one of the most emotionally charged stories in scientific history. In July 1898, Marie Skłodowska Curie and her husband Pierre Curie announced the discovery of a new radioactive element; a second, radium, followed in December 1898. They named the first "polonium" in honor of Marie's homeland, Poland, which had been erased from the map by foreign powers.
The name carried profound political meaning - Poland did not exist as an independent nation in 1898, having been partitioned between Russia, Prussia, and Austria. By naming her discovery "polonium," Marie made a bold statement about Polish identity and resistance that resonated throughout Europe.
"If the existence of this new metal is confirmed, we propose to call it polonium from the name of the country of origin of one of us," the Curies wrote in their paper, making this the first element named for a political cause.
The discovery began with Marie's PhD research into Henri Becquerel's mysterious "uranium rays" - what we now call radioactivity. Using an electrometer invented by Pierre and his brother Jacques Curie, Marie made a startling observation: pitchblende ore was more radioactive than pure uranium.
This seemed impossible. If uranium was the source of radioactivity, how could uranium ore be more radioactive than pure uranium? Marie hypothesized that pitchblende must contain unknown radioactive elements more powerful than uranium itself.
Working in a freezing, leaking shed, the Curies began the herculean task of processing tons of pitchblende residue from Austrian mines. They stirred huge vats of boiling ore with iron rods, often working 14-hour days in conditions that would horrify modern safety inspectors.
The Curies' method was brilliantly simple but brutally labor-intensive. They dissolved pitchblende in acid, then used fractional crystallization to separate compounds. They tested each fraction for radioactivity, following the "hot" fractions like bloodhounds following a scent.
By July 1898, they had isolated a bismuth-like fraction that was 400 times more radioactive than uranium. Demarçay could find no new spectral line; the claim rested on radioactivity alone. They had found polonium, though they had isolated only one ten-thousandth of a gram.
The discovery paper, by Pierre and Marie Curie, was published in Comptes Rendus in July 1898. Its conclusion was cautious: "We believe therefore that the substance which we have removed from pitchblende contains a metal not yet reported close to bismuth in its analytical properties."
The scientific community was skeptical. Dmitri Mendeleev himself questioned whether these were truly new elements or just radioactive forms of known substances. The Curies needed to isolate pure samples and determine atomic weights to prove their discoveries conclusively.
This led to years of backbreaking work. Marie processed literally tons of pitchblende residue, eventually obtaining a few tenths of a gram of radium chloride by 1902. Polonium proved even more elusive due to its radioactive decay - they were literally racing against time as their samples disappeared.
Willy Marckwald isolated about 3 milligrams of it in 1902 under the name radio-tellurium, and in 1905 it was shown to be polonium. The element's reality was established, though its rarity and radioactivity made detailed study nearly impossible.
The discovery of polonium came at a terrible personal cost. Both Marie and Pierre showed signs of radiation sickness - fatigue, painful hands, anemia. Pierre's health deteriorated rapidly, and he spoke of the "radiant matter" as both beautiful and dangerous.
Tragically, Pierre was killed in a street accident in 1906, just as their discoveries were gaining worldwide recognition. Marie continued their research alone, eventually becoming the first woman to win a Nobel Prize, and later the first person to win Nobel Prizes in two different sciences (Physics 1903, Chemistry 1911).
Marie's laboratory notebooks from this period remain radioactive to this day and are stored in lead-lined boxes at the Bibliothèque Nationale in Paris. They will remain dangerous for another 1,500 years - a permanent testament to the power of the elements she discovered.
The naming of polonium had profound political impact. When Poland regained independence in 1918, Marie Curie was hailed as a national hero. The element's name had kept the idea of Poland alive during its darkest period of foreign occupation.
Marie made several trips to the newly independent Poland, helping establish the Radium Institute in Warsaw and bringing radioactivity research to her homeland. She always maintained that science should serve humanity regardless of borders, but polonium's name ensured her patriotism would never be forgotten.
The discovery also established the Curie as a unit of radioactivity, immortalizing both Marie and Pierre in the language of science itself.
Tragically, polonium later gained infamy as an assassination weapon. The 2006 poisoning of Alexander Litvinenko in London brought worldwide attention to this obscure element, showing how Marie Curie's beautiful discovery could be perverted for evil purposes.
This modern tragedy serves as a reminder that scientific discoveries are morally neutral - their impact depends entirely on how humanity chooses to use them. Marie Curie discovered polonium to advance human knowledge; its later misuse would have horrified her.
The discovery of polonium launched the atomic age and transformed our understanding of matter itself. Marie's work established that radioactivity was an atomic property, not a molecular one, leading directly to modern atomic theory and nuclear physics.
Today, polonium continues to contribute to scientific knowledge through space missions, nuclear research, and medical applications, though always with the great caution that Marie and Pierre's suffering taught us was necessary.
Applications
Radioisotope Thermoelectric Generators (RTGs) on a few early spacecraft used polonium-210 as a heat source for converting thermal energy to electricity. Polonium-210 heat sources flew on the Soviet Kosmos 84 and 90 satellites (1965) and the Lunokhod Moon rovers, while NASA's flown RTGs used plutonium-238.
Spacecraft heating systems used polonium's alpha decay to provide reliable heat for maintaining instrument temperatures in the intense cold of space. Its 138-day half-life suited missions lasting months rather than years.
Neutron sources combining polonium-210 with beryllium produce neutrons for spacecraft instrumentation and planetary analysis. These compact sources enable remote sensing of subsurface composition on other planets.
Space missions switched to plutonium-238 because of its longer half-life and better safety characteristics, and no current mission uses polonium heat sources.
Alpha particle sources for physics research rely on polonium-210's pure alpha emission. Researchers use these sources to study alpha particle interactions, calibrate radiation detectors, and investigate nuclear processes.
Static elimination in sensitive scientific instruments uses tiny amounts of polonium-210 to neutralize static charges that could interfere with precision measurements. This application requires extremely small quantities and strict containment.
Neutron activation analysis employs polonium-beryllium neutron sources to identify trace elements in samples. This technique is valuable for archaeological dating, forensic analysis, and material characterization.
Radiochemical research uses polonium isotopes to study heavy element chemistry and nuclear physics. Polonium serves as a model for understanding the behavior of other heavy radioactive elements.
Antistatic devices in specialized manufacturing environments use polonium-210 sources to eliminate static electricity that could damage sensitive electronic components or cause fires in flammable atmospheres.
Thickness gauges employ polonium alpha sources to measure the thickness of thin materials like paper, plastic films, or metal foils. The alpha particles' absorption rate indicates material thickness with high precision.
Photographic industry historically used polonium-210 sources to neutralize static charges on film during processing, though this application has largely been replaced by safer alternatives.
Nuclear research also studies polonium because polonium-210 builds up in reactors cooled with lead-bismuth, where it is a radiation hazard.
Cancer research investigates polonium's biological effects to better understand radiation-induced cancer mechanisms. This research helps develop treatments for radiation exposure and improve radiation safety protocols.
Targeted alpha therapy research explores using polonium-based radiopharmaceuticals to deliver high-energy alpha particles directly to cancer cells, potentially providing more effective treatment with fewer side effects than conventional radiation therapy.
Biological tracer studies use minute amounts of polonium isotopes to track biological processes and understand how radioactive materials move through living systems.
Note: Medical applications remain largely experimental due to polonium's high toxicity and short half-life.
Nuclear weapons research has historically involved polonium as a neutron initiator, providing the initial neutron burst needed to trigger nuclear fission. Modern weapons use safer alternatives, but polonium remains important for research purposes.
Detection systems use polonium sources to test and calibrate radiation detection equipment used for nuclear security and treaty verification.
Forensic applications employ polonium's unique signature to trace sources of radioactive contamination and investigate nuclear incidents.
All military applications are highly classified and subject to strict international treaties and safeguards.
Brush electrodes in industrial equipment have long used polonium to eliminate static charges.
Antistatic brushes and ionizers with sealed polonium-210 sources (up to 500 microcuries) are still sold or leased under a US general license, for photography, laboratories and industry.
Sealed polonium-210 static eliminators remain its main commercial use; other uses are confined to research.
All polonium applications require strict safety measures and are limited to specialized facilities with appropriate containment, monitoring, and disposal capabilities. The element's high radiotoxicity means that even microscopic amounts can be lethal.
Polonium has virtually NO common uses accessible to the general public due to its intense radioactivity and toxicity. All applications are limited to specialized research, space, and military facilities.
A few early spacecraft used polonium-210 as a heat or power source. The Soviet Lunokhod 1 and 2 Moon rovers (1970, 1973) used polonium-210 heat sources to keep their instruments warm; the Apollo ALSEP stations ran on plutonium-238 SNAP-27 generators.
However, these applications are:
University and government laboratories use tiny amounts of polonium-210 for:
These uses require:
Sealed polonium sources have been used in:
Sealed polonium-210 static eliminators are still leased and sold today, although many applications have moved to other ionizer types. Any vintage equipment containing polonium sources requires professional hazmat disposal.
Cigarette smoke contains polonium-210 due to tobacco plants absorbing the element from soil and fertilizers. This wasn't intentional use, but represents the largest source of polonium exposure for the general public:
Everyone receives tiny amounts of polonium exposure from:
These natural sources provide extremely low exposure levels - millions of times less than dangerous amounts.
Polonium is NOT available to the public and should never be handled outside of authorized facilities. If you suspect polonium contamination:
The 2006 poisoning of Alexander Litvinenko demonstrated polonium's serious danger and why it remains one of the most restricted substances on Earth.
Where it comes from
2.00e-10 mg/kg of Earth's crust · more abundant than 27% of elements
Polonium does not occur naturally as a primordial element but is constantly being produced through the radioactive decay of uranium-238. In the uranium decay series, radon-222 decays to produce several polonium isotopes, primarily polonium-218, polonium-214, and polonium-210.
The decay sequence proceeds: Uranium-238 → … → Radon-222 → Polonium-218 → Lead-214 → Bismuth-214 → Polonium-214 → Lead-210 → Bismuth-210 → Polonium-210 → Lead-206 (stable)
This means polonium is continuously being created wherever uranium-238 exists, but it's also continuously decaying due to its short half-lives. The concentration reaches a secular equilibrium where production balances decay.
Polonium-210 is the longest-lived natural isotope and the best studied, with a half-life of 138.4 days; the artificial isotopes polonium-209 (124 years) and polonium-208 (2.9 years) live longer. Other natural polonium isotopes have much shorter half-lives, ranging from microseconds to minutes.
Polonium's crustal abundance is very low - about 2 × 10⁻¹⁰ mg per kg, a fraction of a part per quadrillion. This makes it one of the rarest naturally occurring elements, present only in trace amounts proportional to uranium content.
Uranium-bearing minerals contain the highest natural polonium concentrations, including:
Even in rich uranium ores, polonium concentrations are only about 0.1 milligram per tonne (about 0.1 part per billion), making extraction extremely challenging and expensive.
Seawater usually contains about 1 to 5 millibecquerels of polonium-210 per liter (a few billionths of a part per trillion by mass), produced by decay of dissolved lead-210 and by deposition from the atmosphere. Despite these very low concentrations, marine organisms can concentrate polonium in their tissues.
Marine food chain bioconcentration occurs because polonium behaves chemically similar to sulfur, incorporating into biological molecules. Some marine animals show polonium concentrations hundreds to thousands of times higher than seawater, particularly:
Freshwater systems typically contain even lower polonium levels than seawater, though concentrations can be elevated near uranium mining areas or in regions with high natural uranium content in groundwater.
Radon gas in buildings creates the primary source of human polonium exposure. Radon-222 from uranium decay in soil and building materials seeps into enclosed spaces, where it decays to produce polonium isotopes that attach to dust particles.
Indoor concentrations can be 10-100 times higher than outdoor air due to accumulation in poorly ventilated spaces. Polonium-218 and polonium-214 from radon decay contribute significantly to indoor radiation exposure.
Building materials containing natural uranium compounds (concrete, brick, stone) continuously produce small amounts of radon and subsequent polonium. Phosphate-based materials like certain ceramics can show slightly elevated levels.
Smoking indoors dramatically increases polonium concentrations, as tobacco smoke contains polonium-210 that deposits on surfaces and becomes resuspended in dust.
Cigarette tobacco represents one of the most concentrated natural sources of polonium-210 accessible to humans. Tobacco plants absorb polonium from soil and phosphate fertilizers, with concentrations typically ranging from 10-50 millibecquerels per gram of tobacco.
Phosphate fertilizers used in tobacco cultivation contain trace uranium that decays to produce polonium. The polonium becomes incorporated into plant tissues and concentrates in leaves used for cigarette production.
Cigarette smoke delivers polonium-210 directly to smokers' lungs, where alpha particles can cause significant tissue damage. A pack-a-day smoker receives an estimated annual radiation dose of 160 mSv to small areas of lung tissue - a localized dose; for the whole body, NCRP Report 160 puts a pack-a-day smoker's effective dose at about 0.36 mSv a year.
For smokers, this tobacco-related exposure, although natural in origin, is a major radiation source, exceeding exposures from nuclear weapons testing or power plant operations.
Uranium mining operations encounter polonium as a byproduct in ore processing. Mill tailings and processing residues contain equilibrium concentrations of polonium isotopes that require careful management as radioactive waste.
Phosphate mining for fertilizer production also encounters polonium, as phosphate rock often contains trace uranium. Processing plants must monitor for radioactive contamination and properly dispose of polonium-containing wastes.
Coal burning releases trace amounts of polonium into the atmosphere, as coal contains small amounts of uranium and its decay products. While concentrations are low, the large scale of coal combustion makes it a measurable source of environmental polonium.
Industrial production of polonium-210 occurs by neutron bombardment of bismuth-209 in nuclear reactors. This artificial production supplies the tiny quantities needed for research and specialized applications, as natural extraction would be impossibly expensive.
Atmospheric polonium-210 comes from radon-222 that escapes from soil and decays in the air; it returns to the surface in rain and dust.
Nuclear weapons testing in the mid-20th century released artificial polonium isotopes into the atmosphere. While this contamination has largely decayed away, it contributed to global polonium distribution for several decades.
Nuclear accidents like Chernobyl released some polonium isotopes, though most environmental contamination came from other radionuclides with longer half-lives.
Handling
Polonium is radioactive. It has no stable isotope — every nucleus decays. Handling requires appropriate shielding and licensing.
Polonium-210 is one of the most toxic substances known to science. Even microscopic amounts can cause death within weeks.
Alpha particle emission: Po-210 emits high-energy alpha particles (5.3 MeV) with high intensity. One gram of Po-210 produces about 1.66 × 10¹⁴ alpha particles per second, delivering massive radiation doses to nearby tissues.
Internal contamination: Alpha particles cannot penetrate skin but are extremely dangerous when inhaled, ingested, or absorbed through wounds. Once inside the body, they cause severe tissue damage at the cellular level.
Lethal dose: Swallowing about 1-3 GBq of Po-210, roughly 6-18 micrograms, is estimated to be fatal within a month. This is an amount barely visible to the naked eye - smaller than a grain of salt.
Radiation intensity: Gram for gram, Po-210 is about 4,500 times more radioactive than radium-226. A milligram emits as many alpha particles per second as about 4.5 grams of radium, making it one of the most radioactively dense materials possible.
Acute radiation syndrome: High-dose exposure causes rapid onset of nausea, vomiting, diarrhea, hair loss, and immune system collapse within days to weeks.
Multi-organ failure: Polonium targets multiple organ systems simultaneously:
Cancer risk: Even non-lethal exposures dramatically increase cancer risk, particularly lung cancer from inhalation. No safe level of exposure exists.
Genetic damage: Alpha particles cause severe DNA damage, leading to mutations and potential hereditary effects.
Alpha radiation detection: Polonium-210 emits almost only alpha particles, which cannot pass through clothing or the outer layer of skin. Survey meters with an alpha probe can find polonium on surfaces, but polonium inside the body cannot be detected with standard survey instruments and is hard to measure even with whole-body counters, so an intake is confirmed by testing urine or feces in specialized laboratories.
No immediate symptoms: Unlike chemical poisons, radiation poisoning symptoms appear hours to days after exposure, making immediate treatment challenging.
Specialized equipment needed: Detection requires alpha-sensitive instruments like ZnS scintillation detectors or specialized air sampling equipment.
Medical diagnosis: Polonium poisoning can be confirmed through urine and feces analysis, but requires specialized radiochemical laboratories.
Full containment required: All work must be performed in glove boxes with HEPA filtration and negative pressure containment systems.
Personal protection: Full-face supplied-air respirators, multiple layers of protective clothing, and constant radiation monitoring are mandatory.
No eating, drinking, smoking: Prohibited in any area where polonium might be present. Even microscopic contamination can be lethal.
Continuous monitoring: Real-time alpha radiation monitoring and regular bioassay testing for all workers.
Emergency procedures: Immediate decontamination protocols and rapid access to specialized medical treatment facilities.
Chelation: US radiation emergency guidance lists dimercaprol (BAL) as the preferred chelating agent for polonium, with succimer as an alternative.
Supportive care: Treatment focuses on managing symptoms and supporting organ function while radioactive decay reduces the source term.
Time-critical: Decontamination must occur within minutes to hours of exposure to be effective. Delayed treatment is largely ineffective.
Limits of treatment: DTPA, which is used for plutonium, americium and curium, is not a listed treatment for polonium, and supportive care remains essential.
Prognosis: Survival depends on exposure amount and time to treatment. High-dose exposures are almost invariably fatal within weeks to months.
Persistent contamination: Polonium-210's 138-day half-life means contaminated areas remain dangerous for several years (10 half-lives = 3.8 years for 99.9% decay).
Bioaccumulation: Polonium concentrates in biological tissues, particularly liver, kidneys, and spleen, leading to internal contamination through food chains.
Atmospheric dispersal: Polonium can form aerosols that spread contamination over wide areas. Indoor air filtration is critical in contaminated zones.
Decontamination: Requires specialized techniques and generates radioactive waste that must be managed under radiation protection rules, although its activity falls a thousandfold in under four years.
Highly regulated material: Regulated as byproduct material, not special nuclear material: production and use are licensed, and small sealed sources in antistatic devices are sold under a general license.
Oversight: National regulators license polonium-210 production and use; polonium is not nuclear material under the IAEA Statute, which covers uranium, thorium and plutonium.
Criminal penalties: Unauthorized possession, transfer, or use carries severe criminal penalties in most jurisdictions.
Security concerns: Potential use as a radiological weapon makes polonium a high-priority material for nuclear security agencies.
Never handle suspicious materials: If you suspect polonium contamination, immediately evacuate the area and contact emergency services.
Report unusual radiation readings: Any unexplained alpha radiation should be reported to nuclear regulatory authorities immediately.
Seek immediate medical attention: If exposure is suspected, go to the nearest major hospital emergency room immediately and inform them of possible radioactive contamination.
Quick answers
Polonium (symbol Po) is element 84 on the periodic table, a post-transition metal in period 6, group 16. Intensely radioactive: a gram of polonium-210 emits enough alpha particles to glow blue and self-heat to 500 degrees C. At room temperature it is a solid, and it is radioactive.
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴, giving 6 occupied shells with the distribution 2, 8, 18, 32, 18, 6. Its outer shell holds 6 electrons, which is what sets its bonding behaviour.Polonium melts at 527 K (253.9 °C) and boils at 1235 K (961.9 °C).
Polonium has no stable isotope, so it has no standard atomic weight. The figure quoted, 209, is the mass number of its longest-lived known isotope.
Polonium has no stable isotope. Its longest-lived known isotope, Po-209, has 125 neutrons (mass number 209 minus atomic number 84) and a half-life of 124 yrs. The classroom shortcut, rounded atomic mass (209) minus atomic number, gives the same 125.
Polonium has a density of 9.196 g/cm³. Water is 1.0 g/cm³, so a block of polonium is about 9.2× heavier.
Polonium has a Pauling electronegativity of 2. 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.
Polonium was discovered in 1898 by Marie & Pierre Curie. Origin of the name: Poland, Marie Curie's homeland.
Polonium makes up about 2.00e-10 mg/kg of the Earth's crust — genuinely rare, which is why it is expensive.
Yes. Polonium has no stable isotope — every one of its nuclei decays. Trace amounts occur naturally as decay products of heavier elements.