The Element Polonium (Po)
Polonium is a rare and highly radioactive metallic chemical element with atomic number 84 and symbol Po. It was discovered by Marie and Pierre Curie in 1898 and named after Marie Curie’s native country, Poland. It is notable for its intense radioactivity, primarily emitting alpha particles.
Natural Occurrence of Polonium
Polonium occurs naturally in extremely small quantities within the Earth’s crust. It is a decay product in the uranium-radium decay series, specifically formed from the decay of Radium-226. Consequently, it is found in uranium ores.
In India, uranium deposits exist in various regions, notably in Jaduguda, Jharkhand, and parts of Andhra Pradesh and Meghalaya. While these ores contain naturally occurring uranium and its decay products, including trace amounts of polonium, the concentration of polonium is exceptionally low, making direct extraction from these ores impractical for commercial purposes.
Industrial Production and Applications
Due to its rarity in nature, polonium for industrial and research applications is predominantly produced artificially. The most common method involves neutron irradiation of Bismuth-209 in a nuclear reactor. Bismuth-209 absorbs a neutron to become Bismuth-210, which then undergoes beta decay with a half-life of 5 days to form Polonium-210.
India possesses several operational nuclear reactors, such as those at Trombay (BARC), Tarapur, Rawatbhata, and Kaiga. These facilities have the capability to produce radioisotopes through neutron irradiation, although the specific large-scale production of polonium for commercial use is highly specialized and not a general industrial output. Any such production would be for specific strategic or research applications within the country’s atomic energy program.
Key Applications of Polonium
Despite its extreme radioactivity and toxicity, polonium has highly specialized applications:
- Antistatic Devices: Polonium-210 sources are utilized in brushes and devices designed to eliminate static electricity. The alpha particles emitted by polonium ionize the air molecules around the device, neutralizing static charges that can accumulate on surfaces like photographic film, textiles, or delicate electronic components. These are niche applications, not commonly found in general household items.
- Neutron Sources: When mixed with beryllium, polonium-210 creates a compact and reliable neutron source (Po-Be source). The alpha particles from polonium interact with beryllium nuclei, causing them to emit neutrons. These sources are used in various fields, including oil well logging, nuclear research, and as initiators in nuclear weapons.
- Radioisotope Thermoelectric Generators (RTGs): Polonium-210 has a high power density due to its intense alpha decay, generating significant heat. This heat can be converted into electrical energy using thermoelectric modules. While less common than Plutonium-238, polonium-based RTGs have been considered for powering spacecraft, satellites, and remote terrestrial applications where long-term, maintenance-free power is required.
- Calibration of Radiation Detectors: Due to its consistent and well-defined alpha particle emission energy, Polonium-210 is an excellent source for calibrating instruments that measure alpha radiation. This ensures the accuracy of radiation monitoring equipment used in scientific research, health physics, and environmental monitoring.
- Historical use in Spark Plugs: In the past, small amounts of polonium-210 were incorporated into some specialized aircraft spark plugs. The ionization of the air gap by alpha particles was believed to improve cold starting and ignition reliability by making the air more conductive. However, due to safety concerns, radioactivity, and the development of more effective spark plug technologies, this application is largely obsolete today.