Radon (element Rn) — properties, occurrence, health effects and uses
Radon (Rn, atomic number 86) is a colorless, odorless noble gas produced by uranium and radium decay. It is radioactive, can accumulate indoors, and is a known lung-cancer risk; mitigation is available.
Radon is a chemical element in the noble gas group, usually represented by the symbol Rn. It is the radioactive gas with atomic number 86 and is the heaviest of the naturally occurring noble gases under normal conditions. Radon is colorless, odorless and chemically inert, but its radioactivity gives it unique physical and health-related significance.
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Physical and nuclear characteristics
As a noble gas, radon rarely forms stable chemical compounds and behaves as a monatomic gas at ordinary temperatures. It has a relatively high density compared with air, so it tends to collect in low or enclosed spaces. Dozens of isotopes have been identified; there are about 27 known isotopes, produced through decay chains of heavier elements. The most common isotope in the environment is radon-222, which has a half-life of about three to four days (~3.8 days) and arises from the decay of radium-226 in the uranium-238 decay series.
Occurrence and formation
Radon is formed naturally by the radioactive decay of uranium and thorium present in rocks, soil and some building materials. Because it is a gas, radon can migrate through porous soil and enter buildings through cracks, sump pits, or other openings. Variability in local geology and house construction leads to wide differences in indoor radon concentrations from place to place.
Health risks and mitigation
Exposure to elevated radon levels is a public-health concern because inhaled radioactive decay products can damage lung tissue and increase the risk of lung cancer. It is commonly cited as the second leading cause of lung cancer after smoking. Risk can be reduced by testing indoor air and, when concentrations are high, installing remediation such as improved ventilation, sealing of foundation openings, or active soil depressurization systems. Measurement and action levels are expressed in units like becquerels per cubic meter or picocuries per liter, and many health agencies publish guidance on acceptable levels and remediation methods.
Uses, history and notable facts
- Discovery: Radon was first identified as a radioactive gas emerging from radium in work around the turn of the 20th century.
- Applications: Because of its radioactivity and short-lived isotopes, radon has been used historically in limited medical treatments and in geological studies such as groundwater tracing and studying soil gas dynamics.
- Public concern: Modern attention focuses on indoor air quality, measurement, and mitigation; awareness and testing programs are common in many countries.
Although chemically inert, radon’s radioactivity and mobility in the environment make it an important element in both earth sciences and public health. For further technical details, measurement guidance, and regional recommendations consult authoritative sources and testing services (periodic table and element data, isotope references, half-life and decay information).
History
Radon was discovered in 1900 by Friedrich Ernst Dorn.
In 1908, William Ramsay and Robert Whytlaw-Gray isolated a sufficient quantity of the gas to determine its density. Because it gave off light in the dark, they named it niton, after the Latin word nitens "luminous". In 1923, the terms radium emanation and niton were replaced by the term radon.
Properties
Like all noble gases, radon is almost chemically unreactive; with fluorine it reacts to form radon difluoride, whether compounds with oxygen have been observed is disputed. Under normal conditions, radon gas is colorless, odorless, tasteless; when cooled below its melting point, it becomes bright yellow to orange. As a filling in gas discharge tubes, radon produces red light. It is also by far the densest elemental gas, at 9.73 kg-m-3, except for the exotically rare astatine and hot diatomic iodine vapor.
Like its lighter group homologue xenon, radon is capable of forming true compounds. These can be expected to be more stable and diverse than those of xenon. The study of radon chemistry is greatly hindered by the high specific activity of radon, because the high-energy radiation leads to self-decomposition (autoradiolysis) of the compounds. Therefore, chemistry with ponderable amounts of these substances is not possible. Ab-initio and Dirac-Hartree-Fock calculations describe some properties of the not yet synthesized radon hexafluoride (RnF6).
As a radioactive gas with a very high density, radon can accumulate in physiologically significant quantities in buildings, especially in basements and the lower floors. In recent measurements, larger amounts of radon were also found on the upper floors of buildings where building materials such as unburnt clay were used.
The solubility of the isotope Rn-222 in water at 20 °C and 101.325 kPa is 259 ml/l.
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AlegsaOnline.com Radon (element Rn) — properties, occurrence, health effects and uses Leandro Alegsa
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