Polonium

Polonium is a rare, highly radioactive metalloid with the chemical symbol Po and atomic number 84. It belongs to Group 16 (the chalcogen group) of the periodic table, alongside oxygen, sulphur, selenium, tellurium, and livermorium. Polonium is best known for its extreme radioactivity and its role in scientific, industrial, and historical contexts. While it has few everyday applications due to safety concerns, it remains important in specialised industrial processes, space technology, and scientific research.

Discovery and Naming

Polonium was discovered in 1898 by Marie and Pierre Curie, who isolated it from pitchblende (uraninite) while researching radioactive substances. Marie Curie named the element polonium after her native country, Poland, as a symbol of national pride during a period of political partition.
This discovery was groundbreaking, as polonium was one of the first elements found to exhibit intense radioactivity, a phenomenon that helped lay the foundation of nuclear physics.

Physical and Chemical Properties

Polonium is a silvery-grey, brittle metal that tarnishes easily in air. It is volatile and chemically similar to tellurium and bismuth. However, its most distinctive property is its radioactivity.

• Atomic number: 84
• Atomic mass: 209 u (for its most stable isotope)
• Density: 9.32 g/cm³
• Melting point: 254°C
• Boiling point: 962°C
• Crystal structure: Simple cubic (unique among metals)
• Oxidation states: +2 and +4 (most common), with some compounds in +6
• Radioactivity: Emits strong alpha particles, which cannot penetrate skin but are deadly if inhaled or ingested.

Polonium has 33 known isotopes, all radioactive. The most widely used is polonium-210 (²¹⁰Po), with a half-life of 138.4 days.

Occurrence and Production

Polonium is extremely rare in nature, found in trace amounts in uranium ores—approximately 0.1 milligrams per tonne. Commercial quantities are produced synthetically in nuclear reactors by neutron irradiation of bismuth-209, which converts to polonium-210 through a nuclear reaction:

²⁰⁹Bi + n → ²¹⁰Bi → ²¹⁰Po + β⁻

Most global production occurs in Russia, as it possesses the necessary reactor infrastructure and experience in handling radioactive materials.

Everyday Applications

Polonium’s radioactivity and toxicity prevent its use in everyday consumer products. However, it plays subtle roles in specialised equipment and processes indirectly linked to daily life:

• Static eliminators: Polonium-210 was once used in anti-static brushes for removing dust from photographic films and precision instruments. The alpha particles neutralised static electricity effectively. Today, safer alternatives have replaced these devices.
• Smoke detectors: Early smoke detectors occasionally used small quantities of polonium isotopes, but modern devices now employ americium-241, which is less hazardous.

Direct public exposure to polonium has been phased out due to strict radiation safety regulations.

Industrial and Technological Applications

Despite limited everyday use, polonium has a few high-value industrial applications that exploit its intense alpha radiation and heat output:

• Static charge control: In certain manufacturing environments (especially paper, plastics, and textiles), polonium-210 sources are used to neutralise static electricity that can interfere with precision production or cause sparks. These applications are tightly regulated.
• Nuclear batteries (radioisotope thermoelectric generators, RTGs): Polonium-210 has been used as a heat source in specialised thermoelectric power systems. Its alpha decay releases considerable energy—about 140 watts per gram—making it useful in spacecraft and military satellites for short-duration missions.
• Neutron sources: When combined with beryllium, polonium acts as an efficient neutron emitter (Po-Be sources), historically used for initiating chain reactions in nuclear research and early weapon designs.
• Material research: Polonium’s radiation is used in alpha particle spectroscopy and radiation shielding studies to investigate the effects of ionising radiation on different materials.

Medical and Biological Aspects

Due to its extreme toxicity, polonium has no legitimate medical applications. However, it has been of scientific interest in radiobiology and toxicology because of its powerful alpha emissions.
Exposure to even microscopic amounts of polonium-210 can cause acute radiation syndrome (ARS), as seen in the 2006 poisoning of former Russian agent Alexander Litvinenko, which highlighted its lethal potential.
Biologically, polonium behaves similarly to selenium and tellurium, accumulating in organs such as the liver, spleen, and bone marrow. Because of its danger, handling polonium requires airtight containment, remote manipulation, and radiation shielding.

Economic Importance

Although polonium is produced in very small quantities—measured in tens of grams per year—it has high economic value in its niche uses. The following points summarise its economic role:

• Production concentration: Russia is the world’s principal producer, giving it near-monopoly control of supply.
• Market value: Due to complex handling requirements and rarity, polonium’s cost is extremely high, often exceeding tens of thousands of pounds per milligram.
• Export control: Polonium is a strategic material, subject to stringent international regulations under nuclear non-proliferation agreements.

Its economic relevance lies not in volume but in strategic significance, particularly in aerospace and defence contexts.

Environmental and Safety Considerations

Polonium poses significant radiological and environmental hazards if improperly managed:

• Radiation risk: Alpha particles cannot penetrate skin but are devastating when inhaled or ingested, damaging tissues at a microscopic level.
• Containment requirements: Industrial use of polonium is strictly controlled, typically under sealed sources to prevent contamination.
• Environmental persistence: Although its half-life is relatively short, improper disposal can contaminate local environments with long-lived decay products such as lead-206.
• Regulation: International agencies like the IAEA (International Atomic Energy Agency) and national bodies such as the UK Health Security Agency (UKHSA) enforce strict controls on polonium’s handling, storage, and transport.

Role in Science and Research

Polonium remains significant in scientific research, particularly in nuclear chemistry, radiation physics, and materials science.

• Study of alpha decay: Polonium’s isotopes are model systems for understanding nuclear decay processes and radiation energetics.
• Thermoelectric material research: Investigations into polonium-based heat sources have informed the development of alternative, longer-lasting radioisotopes for space exploration.
• Historical importance: The study of polonium was crucial to the early development of nuclear theory and contributed to the discovery of other radioactive elements.

Economic and Strategic Outlook

Although its industrial use has declined due to safety and regulatory constraints, polonium retains niche strategic importance:

• Aerospace applications may persist in contexts requiring short-term, high-density power sources.
• Scientific supply chains for polonium are likely to remain centralised under state-regulated facilities, mainly in Russia.
• Security concerns regarding polonium’s potential misuse ensure it remains tightly controlled within international nuclear policy frameworks.

As technology evolves, safer isotopes and non-radioactive alternatives are expected to further reduce reliance on polonium.