86 Rn
Radon (pronounced /ˈreɪdɒn/ , -don ) is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of radium. It is one of the densest substances that remains a gas under normal conditions and is considered to be a health hazard due to its radioactivity. Its most stable isotope, 222 Rn, has a half-life of 3.8 days. Due to its high radioactivity, it has been less well-studied by chemists, but a few compounds are known.
Radon is formed as part of the normal radioactive decay chain of uranium. Uranium has been around since the earth was formed and its most common isotope has a very long half-life (4.5 billion years), which is the amount of time required for one-half of uranium to break down. Uranium, radium, and thus radon, will continue to occur for millions of years at about the same concentrations as they do now.
Radon is responsible for the majority of the mean public exposure to ionizing radiation. It is often the single largest contributor to an individual's background radiation dose, and is the most variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics, and basements. It can also be found in some spring waters and hot springs.
Epidemiological evidence shows a clear link between breathing high concentrations of radon and incidence of lung cancer. Thus, radon is considered a significant contaminant that affects indoor air quality worldwide. According to the United States Environmental Protection Agency, radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States.
History and etymology
Radon was the fifth radioactive element to be discovered, in 1900 by Friedrich Ernst Dorn, after uranium, thorium, radium and polonium. In 1900 Dorn reported some experiments in which he noticed that radium compounds emanate a radioactive gas which he named Radium Emanation ( Ra Em ). Before that, in 1899, Pierre and Marie Curie observed that the "gas" emitted by radium remained radioactive for a month. Later that year, Robert B. Owens and Ernest Rutherford noticed variations when trying to measure radiation from thorium oxide. Rutherford noticed that the compounds of thorium continuously emit a radioactive gas which retain the radioactive powers for several minutes and called this gas " emanation " (from Latin "emanare"—to elapse and "emanatio"—expiration), and later Thorium Emanation ( Th Em ). In 1901, he demonstrated that the emanations are radioactive, but credited the Curies for the discovery of the element. In 1903, similar emanations were observed from actinium by André-Louis Debierne and were called Actinium Emanation ( Ac Em ).
Several names were suggested for these three gases: exradio , exthorio , and exactinio in 1904; radon , thoron , and akton in 1918; radeon , thoreon , and actineon in 1919, and eventually radon , thoron , and actinon in 1920. The likeness of the spectra of these three gases with those of argon, krypton, and xenon, and their observed chemical inertia led Sir William Ramsay to suggest in 1904 that the "emanations" might contain a new element of the noble gas family.
In 1910, Sir William Ramsay and Robert Whytlaw-Gray isolated radon, determined its density, and determined that it was the heaviest known gas. They wrote that "L'expression de l'émanation du radium est fort incommode," (the expression of radium emanation is very awkward) and suggested the new name niton (Nt) (from the Latin "nitens" meaning "shining") in order to emphasize the property of gases that cause the phosphorescence of some substances, and in 1912 it was accepted by the International Commission for Atomic Weights. In 1923, the International Committee for Chemical Elements and International Union of Pure and Applied Chemistry (IUPAC) chose among the names radon (Rn), thoron (Tn), and actinon (An). Later, when isotopes were numbered instead of named, the element took the name of the most stable isotope, radon , while Tn became 220 Rn and An 219 Rn. As late as the 1960s, the element was also referred to simply as emanation . The first synthesized compound of radon, radon fluoride, was obtained in 1962.
The danger of high exposure to radon in mines, where exposures reaching 1,000,000 Bq/m 3 can be found, has long been known. In 1530, Paracelsus described a wasting disease of miners, the mala metallorum , and Georg Agricola recommended ventilation in mines to avoid this mountain sickness ( Bergsucht ). In 1879, this condition was identified as lung cancer by Herting and Hesse in their investigation of miners from Schneeberg, Germany. The first major studies with radon and health occurred in the context of uranium mining, first in the Joachimsthal region of Bohemia and then in the Southwestern United States during the early Cold War.
Characteristics
Physical form
Radon is a colorless and odorless gas, and therefore not detectable by human senses alone. At standard temperature and pressure, radon forms a monatomic gas with a density of 9.73 kg/m 3 , about 8 times the surface density of the Earth's atmosphere, 1.217 kg/m 3 , and is one of the heaviest gases at room temperature and the heaviest of the noble gases, excluding ununoctium. At standard temperature and pressure, radon is a colorless gas, but when it is cooled below its freezing point of 202 K (−71 °C; −96 °F), it has a brilliant phosphorescence which turns yellow as the temperature is lowered, and becomes orange-red as the air liquefies at temperatures below 93 K (−180.1 °C; −292.3 °F). Upon condensation, radon also glows because of the intense radiation it produces.
Being a noble gas, radon is not very chemically reactive. However, the 3.82 day half-life of radon-222 makes it useful in physical sciences as a natural tracer.
Isotopes
Main article: Isotopes of radonRadon has no stable isotopes. There are 36 radioactive isotopes that have been characterized which range from an atomic mass of 193 to 228. The most stable isotope is 222 Rn, which is a decay product of 226 Ra. It has a half-life of 3.823 days and decomposes by alpha particle emission into 218 Po. Among the decay daughters of this decay chain is also the highly unstable isotope 218 Rn. The naturally occurring 226 Ra is a product of the decay chain of 238 U. (See Decay chain of 238 U for all the decay products of 222 Rn.)
There are three other radon isotopes that have a half life of over an hour: 211 Rn, 210 Rn and 224 Rn. The 220 Rn isotope is a natural decay product of the most stable thorium isotope ( 232 Th), and is commonly referred to as thoron. It has a half-life of 55.6 seconds and also emits alpha radiation. Similarly, 219 Rn is derived from the most stable isotope of actinium ( 227 Ac)—named “actinon”—and is an alpha emitter with a half-life of 3.96 seconds. No radon isotopes are part of the other major decay series, that of neptunium ( 237 Np).
Chemistry
Radon is a member of the zero-valence elements that are called noble gases. It is inert to most common chemical reactions, such as combustion, because the outer valence shell contains eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. More than 248 kcal/mol is required to extract one electron from its shells (also known as the first ionization energy). However, due to periodic trends, radon has a lower electronegativity than the element one period before it, xenon, and is therefore more reactive. Radon is sparingly soluble in water, but more soluble than lighter noble gases. Radon is appreciably more soluble in organic liquids than in water. Early studies concluded that the stability of radon hydrate should be of the same order as that of the hydrates of chlorine ( Cl 2 ) or sulfur dioxide ( SO 2 ), and significantly higher than the stability of the hydrate of hydrogen sulfide ( H 2 S ).
Because of its price and radioactivity, experimental chemical research is seldom performed with radon, and as a result there are very few reported compounds of radon, all either fluorides or oxides. Radon can be oxidized by a few powerful oxidizing
Radon Control Program
3 Capitol Hill Room 206 Providence, RI 02908-5097 David Spink Radon Control Program Manager (401)222-7747 Fax (401) 222-2456
Radon Control Products homepage
Radon mitigation and measurement in western NC. A full-time full service professional radon company.
INFILTEC Air Leakage Control - Radon Gas Mitigation & Blower Doors ...
Assisting contractors and homeowners in solving radon gas mitigation, and building air leakage measurement and control problems since 1980. Call toll free (888) 349-7236 for help
Air Quality Control, Inc.
AQC was one of the first radon companies in the country and one of the first to guarantee the performance of its radon control systems. Since 1985, AQC has installed more than 10 ...
Radon Control Inc. | Customer Registration
Register Radon Control Inc./Crawlspace Supply Please complete the form below to apply to become a RCI/CSI customer. A representative will contact you to complete your registration.
Radon Control Inc. | Radon Control Inc. | A supplier of radon and ...
Radon Control and Crawlspace Supply carries a wide variety of quality products for radon reduction systems, including brand names including Radonaway radon fans, Fantech radon fans ...
Radon Control, Inc. - Home
Radon Control, Inc. specializes in radon reduction in all types of homes. We offer the highest quality and lowest price in Southern Illinois and the St. Louis area.
Radon Control Services
Radon Control Systems ... Safe Home = Safe Environment = Healthy People : Welcome to the Lafayette area's own radon mitigation service.
Radon Control Services, Inc.
Welcome to Radon Control Services. John Hastings founded Radon Control Services, Inc. in 2000 after installing several hundred systems with his former company Closer Look, Inc. a ...
Abbey Damp & Radon Control: damp and radon reduction in the West ...
A remedy to problems caused by damp and radon gas, offered by Abbey Damp & Control, based in Penzance, West Cornwall.