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Radon

April 21, 2023

This article is about the chemical element. For other uses, see Radon (disambiguation).

Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through which thorium and uranium slowly decay into various short-lived radioactive elements and lead. Radon itself is the immediate decay product of radium. Its most stable isotope, 222Rn, has a half-life of only 3.8 days, making it one of the rarest elements. Since thorium and uranium are two of the most common radioactive elements on Earth, while also having three isotopes with half-lives on the order of several billion years, radon will be present on Earth long into the future despite its short half-life. The decay of radon produces many other short-lived nuclides, known as "radon daughters", ending at stable isotopes of lead.[3]

Radon, 86Rn
Radon
Pronunciation/ˈreɪdɒn/ ​(RAY-don)
Appearancecolorless gas
Mass number[222]
Radon in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Xe
↑
Rn
↓
Og
astatine ← radon → francium
Atomic number (Z)86
Groupgroup 18 (noble gases)
Periodperiod 6
Block  p-block
Electron configuration[Xe] 4f14 5d10 6s2 6p6
Electrons per shell2, 8, 18, 32, 18, 8
Physical properties
Phase at STPgas
Melting point202 K ​(−71 °C, ​−96 °F)
Boiling point211.5 K ​(−61.7 °C, ​−79.1 °F)
Density (at STP)9.73 g/L
when liquid (at b.p.)4.4 g/cm3
Critical point377 K, 6.28 MPa[1]
Heat of fusion3.247 kJ/mol
Heat of vaporization18.10 kJ/mol
Molar heat capacity5R/2 = 20.786 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 110 121 134 152 176 211
Atomic properties
Oxidation states0, +2, +6
ElectronegativityPauling scale: 2.2
Ionization energies
  • 1st: 1037 kJ/mol
Covalent radius150 pm
Van der Waals radius220 pm
Spectral lines of radon
Other properties
Natural occurrencefrom decay
Crystal structure ​face-centered cubic (fcc)
Thermal conductivity3.61×10−3  W/(m⋅K)
Magnetic orderingnon-magnetic
CAS Number10043-92-2
History
DiscoveryErnest Rutherford and Robert B. Owens (1899)
First isolationWilliam Ramsay and Robert Whytlaw-Gray (1910)
Isotopes of radon
Main isotopes[2] Decay
abun­dance half-life (t1/2) mode pro­duct
210Rn synth 2.4 h α 206Po
211Rn synth 14.6 h ε 211At
α 207Po
222Rn trace 3.8235 d α 218Po
224Rn synth 1.8 h β− 224Fr
 Category: Radon
| references

Unlike all other intermediate elements in the aforementioned decay chains, radon is, under standard conditions, gaseous and easily inhaled, and therefore a health hazard. It is often the single largest contributor to an individual's background radiation dose, but due to local differences in geology,[4] the level of exposure to radon gas differs from place to place. A common source is uranium-containing minerals in the ground, and therefore it accumulates in subterranean areas such as basements. Radon can also occur in some ground water like spring waters and hot springs.[5] Climate change may cause radon previously trapped underground to be released as permafrost thaws, particularly in areas like the Arctic, Alaska, Canada, Greenland and Russia. It is possible to test for radon in buildings, and to use techniques such as sub-slab depressurization for mitigation.[6][7]

Epidemiological studies have shown a clear link between breathing high concentrations of radon and incidence of lung cancer. Radon is a contaminant that affects indoor air quality worldwide. According to the United States Environmental Protection Agency (EPA), 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. About 2,900 of these deaths occur among people who have never smoked. While radon is the second most frequent cause of lung cancer, it is the number one cause among non-smokers, according to EPA policy-oriented estimates.[8] Significant uncertainties exist for the health effects of low-dose exposures.[9] Unlike the gaseous radon itself, radon daughters are solids and stick to surfaces, such as airborne dust particles, which can cause lung cancer if inhaled.[10]

Characteristics

 
Emission spectrum of radon, photographed by Ernest Rutherford in 1908. Numbers at the side of the spectrum are wavelengths. The middle spectrum is of Radium emanation (radon), while the outer two are of helium (added to calibrate the wavelengths).

Physical properties

Radon is a colorless, odorless, and tasteless[11] gas and therefore is not detectable by human senses alone. At standard temperature and pressure, it forms a monatomic gas with a density of 9.73 kg/m3, about 8 times the density of the Earth's atmosphere at sea level, 1.217 kg/m3.[12] It is one of the densest gases at room temperature and is the densest of the noble gases. Although colorless at standard temperature and pressure, when cooled below its freezing point of 202 K (−71 °C; −96 °F), it emits a brilliant radioluminescence that turns from yellow to orange-red as the temperature lowers.[13] Upon condensation, it glows because of the intense radiation it produces.[14] It is sparingly soluble in water, but more soluble than lighter noble gases. It is appreciably more soluble in organic liquids than in water. Its solubility equation is as follows,[15][16][17]

 

where   is the molar fraction of radon,   is the absolute temperature, and   and   are solvent constants.

Chemical properties

Radon is a member of the zero-valence elements that are called noble gases, and is chemically not very reactive. The 3.8-day half-life of radon-222 makes it useful in physical sciences as a natural tracer. Because radon is a gas at standard conditions, unlike its decay-chain parents, it can readily be extracted from them for research.[18]

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.[19] Its first ionization energy—the minimum energy required to extract one electron from it—is 1037 kJ/mol.[20] In accordance with periodic trends, radon has a lower electronegativity than the element one period before it, xenon, and is therefore more reactive. 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
2S).[21]

Because of its cost 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 powerful oxidizing agents such as fluorine, thus forming radon difluoride (RnF
2).[22][23] It decomposes back to its elements at a temperature of above 523 K (250 °C; 482 °F), and is reduced by water to radon gas and hydrogen fluoride: it may also be reduced back to its elements by hydrogen gas.[24] It has a low volatility and was thought to be RnF
2. Because of the short half-life of radon and the radioactivity of its compounds, it has not been possible to study the compound in any detail. Theoretical studies on this molecule predict that it should have a Rn–F bond distance of 2.08 ångström (Å), and that the compound is thermodynamically more stable and less volatile than its lighter counterpart xenon difluoride (XeF
2).[25] The octahedral molecule RnF
6 was predicted to have an even lower enthalpy of formation than the difluoride.[26] The [RnF]+ ion is believed to form by the following reaction:[27]

Rn (g) + 2 [O
2]+
[SbF
6]−
 (s) → [RnF]+
[Sb
2F
11]−
 (s) + 2 O
2 (g)

For this reason, antimony pentafluoride together with chlorine trifluoride and N
2F
2Sb
2F
11 have been considered for radon gas removal in uranium mines due to the formation of radon–fluorine compounds.[18] Radon compounds can be formed by the decay of radium in radium halides, a reaction that has been used to reduce the amount of radon that escapes from targets during irradiation.[24] Additionally, salts of the [RnF]+ cation with the anions SbF−
6, TaF−
6, and BiF−
6 are known.[24] Radon is also oxidised by dioxygen difluoride to RnF
2 at 173 K (−100 °C; −148 °F).[24]

Radon oxides are among the few other reported compounds of radon;[28] only the trioxide (RnO
3) has been confirmed.[29] The higher fluorides RnF
4 and RnF
6 have been claimed[29] and are calculated to be stable,[30] but their identification is unclear.[29] They may have been observed in experiments where unknown radon-containing products distilled together with xenon hexafluoride: these may have been RnF
4, RnF
6, or both.[24] Trace-scale heating of radon with xenon, fluorine, bromine pentafluoride, and either sodium fluoride or nickel fluoride was claimed to produce a higher fluoride as well which hydrolysed to form RnO
3. While it has been suggested that these claims were really due to radon precipitating out as the solid complex [RnF]+
2[NiF6]2−, the fact that radon coprecipitates from aqueous solution with CsXeO
3F has been taken as confirmation that RnO
3 was formed, which has been supported by further studies of the hydrolysed solution. That [RnO3F]− did not form in other experiments may have been due to the high concentration of fluoride used. Electromigration studies also suggest the presence of cationic [HRnO3]+ and anionic [HRnO4]− forms of radon in weakly acidic aqueous solution (pH > 5), the procedure having previously been validated by examination of the homologous xenon trioxide.[29]

The decay technique has also been used. Avrorin et al. reported in 1982 that 212Fr compounds cocrystallised with their caesium analogues appeared to retain chemically bound radon after electron capture; analogies with xenon suggested the formation of RnO3, but this could not be confirmed.[31]

It is likely that the difficulty in identifying higher fluorides of radon stems from radon being kinetically hindered from being oxidised beyond the divalent state because of the strong ionicity of radon difluoride (RnF
2) and the high positive charge on radon in RnF+; spatial separation of RnF
2 molecules may be necessary to clearly identify higher fluorides of radon, of which RnF
4 is expected to be more stable than RnF
6 due to spin–orbit splitting of the 6p shell of radon (RnIV would have a closed-shell 6s2
6p2
1/2 configuration). Therefore, while RnF
4 should have a similar stability to xenon tetrafluoride (XeF
4), RnF
6 would likely be much less stable than xenon hexafluoride (XeF
6): radon hexafluoride would also probably be a regular octahedral molecule, unlike the distorted octahedral structure of XeF
6, because of the inert pair effect.[32][33] Because radon is quite electropositive for a noble gas, it is possible that radon fluorides actually take on highly fluorine-bridged structures and are not volatile.[33] Extrapolation down the noble gas group would suggest also the possible existence of RnO, RnO2, and RnOF4, as well as the first chemically stable noble gas chlorides RnCl2 and RnCl4, but none of these have yet been found.[24]

Radon carbonyl (RnCO) has been predicted to be stable and to have a linear molecular geometry.[34] The molecules Rn
2 and RnXe were found to be significantly stabilized by spin-orbit coupling.[35] Radon caged inside a fullerene has been proposed as a drug for tumors.[36][37] Despite the existence of Xe(VIII), no Rn(VIII) compounds have been claimed to exist; RnF
8 should be highly unstable chemically (XeF8 is thermodynamically unstable). It is predicted that the most stable Rn(VIII) compound would be barium perradonate (Ba2RnO6), analogous to barium perxenate.[30] The instability of Rn(VIII) is due to the relativistic stabilization of the 6s shell, also known as the inert pair effect.[30]

Radon reacts with the liquid halogen fluorides ClF, ClF
3, ClF
5, BrF
3, BrF
5, and IF
7 to form RnF
2. In halogen fluoride solution, radon is nonvolatile and exists as the RnF+ and Rn2+ cations; addition of fluoride anions results in the formation of the complexes RnF−
3 and RnF2−
4, paralleling the chemistry of beryllium(II) and aluminium(III).[24] The standard electrode potential of the Rn2+/Rn couple has been estimated as +2.0 V,[38] although there is no evidence for the formation of stable radon ions or compounds in aqueous solution.[24]

Isotopes

Main article: Isotopes of radon

Radon has no stable isotopes. Thirty-nine radioactive isotopes have been characterized, with atomic masses ranging from 193 to 231.[39][40] The most stable isotope is 222Rn, which is a decay product of 226Ra, a decay product of 238U.[41] A trace amount of the (highly unstable) isotope 218Rn is also among the daughters of 222Rn.

Three other radon isotopes have a half-life of over an hour: 211Rn, 210Rn and 224Rn. The 220Rn isotope is a natural decay product of the most stable thorium isotope (232Th), and is commonly referred to as thoron. It has a half-life of 55.6 seconds and also emits alpha radiation. Similarly, 219Rn is derived from the most stable isotope of actinium (227Ac)—named "actinon"—and is an alpha emitter with a half-life of 3.96 seconds.[39] No radon isotopes occur significantly in the neptunium (237Np) decay series, though a trace amount of the (extremely unstable) isotope 217Rn is produced.

 
The radium or uranium series

Daughters

Main article: Decay chain § Uranium series

222Rn belongs to the radium and uranium-238 decay chain, and has a half-life of 3.8235 days. Its first four products (excluding marginal decay schemes) are very short-lived, meaning that the corresponding disintegrations are indicative of the initial radon distribution. Its decay goes through the following sequence:[39]

  • 222Rn, 3.82 days, alpha decaying to...
  • 218Po, 3.10 minutes, alpha decaying to...
  • 214Pb, 26.8 minutes, beta decaying to...
  • 214Bi, 19.9 minutes, beta decaying to...
  • 214Po, 0.1643 ms, alpha decaying to...
  • 210Pb, which has a much longer half-life of 22.3 years, beta decaying to...
  • 210Bi, 5.013 days, beta decaying to...
  • 210Po, 138.376 days, alpha decaying to...
  • 206Pb, stable.

The radon equilibrium factor[42] is the ratio between the activity of all short-period radon progenies (which are responsible for most of radon's biological effects), and the activity that would be at equilibrium with the radon parent.

If a closed volume is constantly supplied with radon, the concentration of short-lived isotopes will increase until an equilibrium is reached where the rate of decay of each decay product will equal that of the radon itself. The equilibrium factor is 1 when both activities are equal, meaning that the decay products have stayed close to the radon parent long enough for the equilibrium to be reached, within a couple of hours. Under these conditions, each additional pCi/L of radon will increase exposure by 0.01 working level (WL, a measure of radioactivity commonly used in mining). These conditions are not always met; in many homes, the equilibrium factor is typically 40%; that is, there will be 0.004 WL of daughters for each pCi/L of radon in the air.[43] 210Pb takes much longer (decades) to come in equilibrium with radon, but, if the environment permits accumulation of dust over extended periods of time, 210Pb and its decay products may contribute to overall radiation levels as well.

Because of their electrostatic charge, radon progenies adhere to surfaces or dust particles, whereas gaseous radon does not. Attachment removes them from the air, usually causing the equilibrium factor in the atmosphere to be less than 1. The equilibrium factor is also lowered by air circulation or air filtration devices, and is increased by airborne dust particles, including cigarette smoke. The equilibrium factor found in epidemiological studies is 0.4.[44]

History and etymology

 
Apparatus used by Ramsay and Whytlaw-Gray to isolate radon. M is a capillary tube, where approximately 0.1 mm3 were isolated. Radon mixed with hydrogen entered the evacuated system through siphon A; mercury is shown in black.

Radon was the fifth radioactive element to be discovered, in 1899 by Ernest Rutherford and Robert B. Owens at McGill University in Montreal,[45] after uranium, thorium, radium, and polonium.[46][47][48][49] In 1899, Pierre and Marie Curie observed that the gas emitted by radium remained radioactive for a month.[50] Later that year, Rutherford and Owens noticed variations when trying to measure radiation from thorium oxide.[45] Rutherford noticed that the compounds of thorium continuously emit a radioactive gas that remains radioactive for several minutes, and called this gas "emanation" (from Latin: emanare, to flow out, and emanatio, expiration),[51] and later "thorium emanation" ("Th Em"). In 1900, Friedrich Ernst Dorn reported some experiments in which he noticed that radium compounds emanate a radioactive gas he named "radium emanation" ("Ra Em").[52][53] In 1901, Rutherford and Harriet Brooks demonstrated that the emanations are radioactive, but credited the Curies for the discovery of the element.[54] In 1903, similar emanations were observed from actinium by André-Louis Debierne,[55][56] and were called "actinium emanation" ("Ac Em").

Several shortened names were soon suggested for the three emanations: exradio, exthorio, and exactinio in 1904;[57] radon (Ro), thoron (To), and akton or acton (Ao) in 1918;[58] radeon, thoreon, and actineon in 1919,[59] and eventually radon, thoron, and actinon in 1920.[60] (The name radon is not related to that of the Austrian mathematician Johann Radon.) 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.[57]

In the early 20th century in the US, gold contaminated with the radon daughter 210Pb entered the jewelry industry. This was from gold seeds that had held 222Rn that had been melted down after the radon had decayed.[61][62]

In 1909, Ramsay and Robert Whytlaw-Gray isolated radon and determined its melting temperature and approximate density. In 1910, they determined that it was the heaviest known gas.[63] They wrote that "L'expression l'émanation du radium est fort incommode" ("the expression 'radium emanation' is very awkward") and suggested the new name niton (Nt) (from Latin: nitens, shining) to emphasize the radioluminescence property,[64] 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 was renamed 220Rn and An was renamed 219Rn. This has caused some confusion in the literature regarding the element's discovery as while Dorn had discovered radon the isotope, he had not been the first to discover radon the element.[65]

As late as the 1960s, the element was also referred to simply as emanation.[66] The first synthesized compound of radon, radon fluoride, was obtained in 1962.[67] Even today, the word radon may refer to either the element or its isotope 222Rn, with thoron remaining in use as a short name for 220Rn to stem this ambiguity. The name actinon for 219Rn is rarely encountered today, probably due to the short half-life of that isotope.[65]

The danger of high exposure to radon in mines, where exposures can reach 1,000,000 Bq/m3, 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).[68][69] In 1879, this condition was identified as lung cancer by Harting 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 in the Joachimsthal region of Bohemia.[70] In the US, studies and mitigation only followed decades of health effects on uranium miners of the Southwestern US employed during the early Cold War; standards were not implemented until 1971.[71]

The presence of radon in indoor air was documented as early as 1950. Beginning in the 1970s, research was initiated to address sources of indoor radon, determinants of concentration, health effects, and mitigation approaches. In the US, the problem of indoor radon received widespread publicity and intensified investigation after a widely publicized incident in 1984. During routine monitoring at a Pennsylvania nuclear power plant, a worker was found to be contaminated with radioactivity. A high concentration of radon in his home was subsequently identified as responsible.[72]

Occurrence

See also: Radium and radon in the environment

Concentration units

 
210Pb is formed from the decay of 222Rn. Here is a typical deposition rate of 210Pb as observed in Japan as a function of time, due to variations in radon concentration.[73]

All discussions of radon concentrations in the environment refer to 222Rn. While the average rate of production of 220Rn (from the thorium decay series) is about the same as that of 222Rn, the amount of 220Rn in the environment is much less than that of 222Rn because of the short half-life of 220Rn (55 seconds, versus 3.8 days respectively).[3]

Radon concentration in the atmosphere is usually measured in becquerel per cubic meter (Bq/m3), the SI derived unit. Another unit of measurement common in the US is picocuries per liter (pCi/L); 1 pCi/L = 37 Bq/m3.[43] Typical domestic exposures average about 48 Bq/m3 indoors, though this varies widely, and 15 Bq/m3 outdoors.[74]

In the mining industry, the exposure is traditionally measured in working level (WL), and the cumulative exposure in working level month (WLM); 1 WL equals any combination of short-lived 222Rn daughters (218Po, 214Pb, 214Bi, and 214Po) in 1 liter of air that releases 1.3 × 105 MeV of potential alpha energy;[43] 1 WL is equivalent to 2.08 × 10−5 joules per cubic meter of air (J/m3).[3] The SI unit of cumulative exposure is expressed in joule-hours per cubic meter (J·h/m3). One WLM is equivalent to 3.6 × 10−3 J·h/m3. An exposure to 1 WL for 1 working-month (170 hours) equals 1 WLM cumulative exposure. A cumulative exposure of 1 WLM is roughly equivalent to living one year in an atmosphere with a radon concentration of 230 Bq/m3.[75]

222Rn decays to 210Pb and other radioisotopes. The levels of 210Pb can be measured. The rate of deposition of this radioisotope is weather-dependent.

Radon concentrations found in natural environments are much too low to be detected by chemical means. A 1,000 Bq/m3 (relatively high) concentration corresponds to 0.17 picogram per cubic meter (pg/m3). The average concentration of radon in the atmosphere is about 6×10−18 molar percent, or about 150 atoms in each milliliter of air.[76] The radon activity of the entire Earth's atmosphere originates from only a few tens of grams of radon, consistently replaced by decay of larger amounts of radium, thorium, and uranium.[77]

Natural

 
Radon concentration next to a uranium mine

Radon is produced by the radioactive decay of radium-226, which is found in uranium ores, phosphate rock, shales, igneous and metamorphic rocks such as granite, gneiss, and schist, and to a lesser degree, in common rocks such as limestone.[4][78] Every square mile of surface soil, to a depth of 6 inches (2.6 km2 to a depth of 15 cm), contains approximately 1 gram of radium, which releases radon in small amounts to the atmosphere.[3] On a global scale, it is estimated that 2.4 billion curies (90 EBq) of radon are released from soil annually.[79] This is equivalent to some 15.3 kilograms (34 lb).

Radon concentration can differ widely from place to place. In the open air, it ranges from 1 to 100 Bq/m3, even less (0.1 Bq/m3) above the ocean. In caves or ventilated mines, or poorly ventilated houses, its concentration climbs to 20–2,000 Bq/m3.[80]

Radon concentration can be much higher in mining contexts. Ventilation regulations instruct to maintain radon concentration in uranium mines under the "working level", with 95th percentile levels ranging up to nearly 3 WL (546 pCi 222Rn per liter of air; 20.2 kBq/m3, measured from 1976 to 1985).[3] The concentration in the air at the (unventilated) Gastein Healing Gallery averages 43 kBq/m3 (1.2 nCi/L) with maximal value of 160 kBq/m3 (4.3 nCi/L).[81]

Radon mostly appears with the decay chain of the radium and uranium series (222Rn), and marginally with the thorium series (220Rn). The element emanates naturally from the ground, and some building materials, all over the world, wherever traces of uranium or thorium are found, and particularly in regions with soils containing granite or shale, which have a higher concentration of uranium. Not all granitic regions are prone to high emissions of radon. Being a rare gas, it usually migrates freely through faults and fragmented soils, and may accumulate in caves or water. Owing to its very short half-life (four days for 222Rn), radon concentration decreases very quickly when the distance from the production area increases. Radon concentration varies greatly with season and atmospheric conditions. For instance, it has been shown to accumulate in the air if there is a meteorological inversion and little wind.[82]

High concentrations of radon can be found in some spring waters and hot springs.[83] The towns of Boulder, Montana; Misasa; Bad Kreuznach, Germany; and the country of Japan have radium-rich springs that emit radon. To be classified as a radon mineral water, radon concentration must be above 2 nCi/L (74 kBq/m3).[84] The activity of radon mineral water reaches 2,000 kBq/m3 in Merano and 4,000 kBq/m3 in Lurisia (Italy).[81]

Natural radon concentrations in the Earth's atmosphere are so low that radon-rich water in contact with the atmosphere will continually lose radon by volatilization. Hence, ground water has a higher concentration of 222Rn than surface water, because radon is continuously produced by radioactive decay of 226Ra present in rocks. Likewise, the saturated zone of a soil frequently has a higher radon content than the unsaturated zone because of diffusional losses to the atmosphere.[85][86]

In 1971, Apollo 15 passed 110 km (68 mi) above the Aristarchus plateau on the Moon, and detected a significant rise in alpha particles thought to be caused by the decay of 222Rn. The presence of 222Rn has been inferred later from data obtained from the Lunar Prospector alpha particle spectrometer.[87]

Radon is found in some petroleum. Because radon has a similar pressure and temperature curve to propane, and oil refineries separate petrochemicals based on their boiling points, the piping carrying freshly separated propane in oil refineries can become contaminated because of decaying radon and its products.[88]

Residues from the petroleum and natural gas industry often contain radium and its daughters. The sulfate scale from an oil well can be radium rich, while the water, oil, and gas from a well often contains radon. Radon decays to form solid radioisotopes that form coatings on the inside of pipework.[88]

Accumulation in buildings

 
Typical log-normal radon distribution in dwellings
 
Predicted fraction of U.S. homes having concentrations of radon exceeding the EPA's recommended action level of 4 pCi/L

High concentrations of radon in homes were discovered by chance in 1985 after the stringent radiation testing conducted at the new Limerick Generating Station nuclear power plant revealed that Stanley Watras, a construction engineer at the plant, was contaminated by radioactive substances even though the reactor had never been fueled.[89] Typical domestic exposures are of approximately 100 Bq/m3 (2.7 pCi/L) indoors. Some level of radon will be found in all buildings. Radon mostly enters a building directly from the soil through the lowest level in the building that is in contact with the ground. High levels of radon in the water supply can also increase indoor radon air levels. Typical entry points of radon into buildings are cracks in solid foundations and walls, construction joints, gaps in suspended floors and around service pipes, cavities inside walls, and the water supply.[11] Radon concentrations in the same place may differ by double/half over one hour. Also, the concentration in one room of a building may be significantly different from the concentration in an adjoining room.[3] The soil characteristics of the dwellings are the most important source of radon for the ground floor and higher concentration of indoor radon observed on lower floors. Most of the high radon concentrations have been reported from places near fault zones; hence the existence of a relation between the exhalation rate from faults and indoor radon concentrations is obvious.[citation needed]

The distribution of radon concentrations will generally differ from room to room, and the readings are averaged according to regulatory protocols. Indoor radon concentration is usually assumed to follow a log-normal distribution on a given territory.[90] Thus, the geometric mean is generally used for estimating the "average" radon concentration in an area.[91]

The mean concentration ranges from less than 10 Bq/m3 to over 100 Bq/m3 in some European countries.[92] Typical geometric standard deviations found in studies range between 2 and 3, meaning (given the 68–95–99.7 rule) that the radon concentration is expected to be more than a hundred times the mean concentration for 2% to 3% of the cases.

Some of the highest radon hazard in the US is found in Iowa and in the Appalachian Mountain areas in southeastern Pennsylvania.[93] Iowa has the highest average radon concentrations in the US due to significant glaciation that ground the granitic rocks from the Canadian Shield and deposited it as soils making up the rich Iowa farmland.[94] Many cities within the state, such as Iowa City, have passed requirements for radon-resistant construction in new homes. The second highest readings in Ireland were found in office buildings in the Irish town of Mallow, County Cork, prompting local fears regarding lung cancer.[95]

In a few places, uranium tailings have been used for landfills and were subsequently built upon, resulting in possible increased exposure to radon.[3]

Since radon is a colorless, odorless gas, the only way to know how much is present in the air or water is to perform tests. In the US, radon test kits are available to the public at retail stores, such as hardware stores, for home use, and testing is available through licensed professionals, who are often home inspectors. Efforts to reduce indoor radon levels are called radon mitigation. In the US, the EPA recommends all houses be tested for radon. In the UK under the Housing Health & Safety Rating System (HHSRS) property owners have an obligation to evaluate potential risks and hazards to health and safety in a residential property.[96]

Industrial production

Radon is obtained as a by-product of uraniferous ores processing after transferring into 1% solutions of hydrochloric or hydrobromic acids. The gas mixture extracted from the solutions contains H
2, O
2, He, Rn, CO
2, H
2O and hydrocarbons. The mixture is purified by passing it over copper at 993 K (720 °C; 1,328 °F) to remove the H
2 and the O
2, and then KOH and P
2O
5 are used to remove the acids and moisture by sorption. Radon is condensed by liquid nitrogen and purified from residue gases by sublimation.[97]

Radon commercialization is regulated, but it is available in small quantities for the calibration of 222Rn measurement systems, at a price, in 2008, of almost US$6,000 (equivalent to $7,551 in 2021) per milliliter of radium solution (which only contains about 15 picograms of actual radon at any given moment).[98] Radon is produced by a solution of radium-226 (half-life of 1,600 years). Radium-226 decays by alpha-particle emission, producing radon that collects over samples of radium-226 at a rate of about 1 mm3/day per gram of radium; equilibrium is quickly achieved and radon is produced in a steady flow, with an activity equal to that of the radium (50 Bq). Gaseous 222Rn (half-life of about four days) escapes from the capsule through diffusion.[99]

Concentration scale

Bq/m3 pCi/L Occurrence example
1 ~0.027 Radon concentration at the shores of large oceans is typically 1 Bq/m3.

Radon trace concentration above oceans or in Antarctica can be lower than 0.1 Bq/m3.

10 0.27 Mean continental concentration in the open air: 10 to 30 Bq/m3.

Based on a series of surveys, the global mean indoor radon concentration is estimated to be 39 Bq/m3.

100 2.7 Typical indoor domestic exposure. Most countries have adopted a radon concentration of 200–400 Bq/m3 for indoor air as an Action or Reference Level. If testing shows levels less than 4 picocuries radon per liter of air (150 Bq/m3), then no action is necessary. A cumulated exposure of 230 Bq/m3 of radon gas concentration during a period of 1 year corresponds to 1 WLM.
1,000 27 Very high radon concentrations (>1000 Bq/m3) have been found in houses built on soils with a high uranium content and/or high permeability of the ground. If levels are 20 picocuries radon per liter of air (800 Bq/m3) or higher, the home owner should consider some type of procedure to decrease indoor radon levels. Allowable concentrations in uranium mines are approximately 1,220 Bq/m3 (33 pCi/L)[100]
10,000 270 The concentration in the air at the (unventilated) Gastein Healing Gallery averages 43 kBq/m3 (about 1.2 nCi/L) with maximal value of 160 kBq/m3 (about 4.3 nCi/L).[81]
100,000 ~2700 About 100,000 Bq/m3 (2.7 nCi/L) was measured in Stanley Watras's basement.[101][102]
1,000,000 27000 Concentrations reaching 1,000,000 Bq/m3 can be found in unventilated uranium mines.
~5.54 × 1019 ~1.5 × 1018 Theoretical upper limit: Radon gas (222Rn) at 100% concentration (1 atmosphere, 0 °C); 1.538×105 curies/gram;[103] 5.54×1019 Bq/m3.

Applications

Medical

Main article: Radioactive quackery

An early-20th-century form of quackery was the treatment of maladies in a radiotorium.[104] It was a small, sealed room for patients to be exposed to radon for its "medicinal effects". The carcinogenic nature of radon due to its ionizing radiation became apparent later. Radon's molecule-damaging radioactivity has been used to kill cancerous cells,[105] but it does not increase the health of healthy cells.[citation needed] The ionizing radiation causes the formation of free radicals, which results in cell damage, causing increased rates of illness, including cancer.

Exposure to radon has been suggested to mitigate autoimmune diseases such as arthritis in a process known as radiation hormesis.[106][107] As a result, in the late 20th century and early 21st century, "health mines" established in Basin, Montana, attracted people seeking relief from health problems such as arthritis through limited exposure to radioactive mine water and radon. The practice is discouraged because of the well-documented ill effects of high doses of radiation on the body.[108]

Radioactive water baths have been applied since 1906 in Jáchymov, Czech Republic, but even before radon discovery they were used in Bad Gastein, Austria. Radium-rich springs are also used in traditional Japanese onsen in Misasa, Tottori Prefecture. Drinking therapy is applied in Bad Brambach, Germany, and during the early 20th century, water from springs with radon in them was bottled and sold (this water had little to no radon in it by the time it got to consumers due to radon's short half-life).[109] Inhalation therapy is carried out in Gasteiner-Heilstollen, Austria; Świeradów-Zdrój, Czerniawa-Zdrój, Kowary, Lądek Zdrój, Poland; Harghita Băi, Romania; and Boulder, Montana. In the US and Europe, there are several "radon spas", where people sit for minutes or hours in a high-radon atmosphere, such as at Bad Schmiedeberg, Germany.[107][110]

Radon has been produced commercially for use in radiation therapy, but for the most part has been replaced by radionuclides made in particle accelerators and nuclear reactors. Radon has been used in implantable seeds, made of gold or glass, primarily used to treat cancers, known as brachytherapy. The gold seeds were produced by filling a long tube with radon pumped from a radium source, the tube being then divided into short sections by crimping and cutting. The gold layer keeps the radon within, and filters out the alpha and beta radiations, while allowing the gamma rays to escape (which kill the diseased tissue). The activities might range from 0.05 to 5 millicuries per seed (2 to 200 MBq).[105] The gamma rays are produced by radon and the first short-lived elements of its decay chain (218Po, 214Pb, 214Bi, 214Po).

After 11 half-lives (42 days), radon radioactivity is at 1/2,048 of its original level. At this stage, the predominant residual activity of the seed originates from the radon decay product 210Pb, whose half-life (22.3 years) is 2,000 times that of radon and its descendants 210Bi and 210Po.

Scientific

Radon emanation from the soil varies with soil type and with surface uranium content, so outdoor radon concentrations can be used to track air masses to a limited degree. This fact has been put to use by some atmospheric scientists (Radon storm). Because of radon's rapid loss to air and comparatively rapid decay, radon is used in hydrologic research that studies the interaction between groundwater and streams. Any significant concentration of radon in a stream is a good indicator that there are local inputs of groundwater.

Radon soil-concentration has been used in an experimental way to map buried close-subsurface geological faults because concentrations are generally higher over the faults.[111] Similarly, it has found some limited use in prospecting for geothermal gradients.[112]

Some researchers have investigated changes in groundwater radon concentrations for earthquake prediction.[113][114][115] Increases in radon were noted before the 1966 Tashkent[116] and 1994 Mindoro[115] earthquakes. Radon has a half-life of approximately 3.8 days, which means that it can be found only shortly after it has been produced in the radioactive decay chain. For this reason, it has been hypothesized that increases in radon concentration is due to the generation of new cracks underground, which would allow increased groundwater circulation, flushing out radon. The generation of new cracks might not unreasonably be assumed to precede major earthquakes. In the 1970s and 1980s, scientific measurements of radon emissions near faults found that earthquakes often occurred with no radon signal, and radon was often detected with no earthquake to follow. It was then dismissed by many as an unreliable indicator.[117] As of 2009, it was under investigation as a possible precursor by NASA.[118]

Radon is a known pollutant emitted from geothermal power stations because it is present in the material pumped from deep underground. It disperses rapidly, and no radiological hazard has been demonstrated in various investigations. In addition, typical systems re-inject the material deep underground rather than releasing it at the surface, so its environmental impact is minimal.[119] However, similar things can be said about trivial releases from operating nuclear power plants.[citation needed]

In the 1940s and '50s, radon was used for industrial radiography.[120][121] Other X-ray sources, which became available after World War II, quickly replaced radon for this application, as they were lower in cost and had less hazard of alpha radiation.

Health risks

Main article: Health effects of radon

In mines

Radon-222 decay products have been classified by the International Agency for Research on Cancer as being carcinogenic to humans,[122] and as a gas that can be inhaled, lung cancer is a particular concern for people exposed to elevated levels of radon for sustained periods. During the 1940s and 1950s, when safety standards requiring expensive ventilation in mines were not widely implemented,[123] radon exposure was linked to lung cancer among non-smoking miners of uranium and other hard rock materials in what is now the Czech Republic, and later among miners from the Southwestern US[124][125][126] and South Australia.[127] Despite these hazards being known in the early 1950s,[128] this occupational hazard remained poorly managed in many mines until the 1970s. During this period, several entrepreneurs opened former uranium mines in the US to the general public and advertised alleged health benefits from breathing radon gas underground. Health benefits claimed included pain, sinus, asthma and arthritis relief,[129][130] but these were proven to be false and the government banned such advertisements in 1975.[131]

Since that time, ventilation and other measures have been used to reduce radon levels in most affected mines that continue to operate. In recent years, the average annual exposure of uranium miners has fallen to levels similar to the concentrations inhaled in some homes. This has reduced the risk of occupationally-induced cancer from radon, although health issues may persist for those who are currently employed in affected mines and for those who have been employed in them in the past.[132] As the relative risk for miners has decreased, so has the ability to detect excess risks among that population.[133]

Residues from processing of uranium ore can also be a source of radon. Radon resulting from the high radium content in uncovered dumps and tailing ponds can be easily released into the atmosphere and affect people living in the vicinity.[134]

In addition to lung cancer, researchers have theorized a possible increased risk of leukemia due to radon exposure. Empirical support from studies of the general population is inconsistent, and a study of uranium miners found a correlation between radon exposure and chronic lymphocytic leukemia.[135]

Miners (as well as milling and ore transportation workers) who worked in the uranium industry in the US between the 1940s and 1971 may be eligible for compensation under the Radiation Exposure Compensation Act (RECA). Surviving relatives may also apply in cases where the formerly employed person is deceased.

Not only uranium mines are affected by elevated levels of radon. Coal mines in particular are affected as well since coal may contain more uranium and thorium than commercially operational uranium mines.

Domestic-level exposure

Prolonged exposure to higher concentrations of radon has been linked to an increase in lung cancer.[136] Since 1999, there has been investigations worldwide on how radon concentrations are estimated. In the United States alone averages have been recorded to be at least 40 Bq/meters cubed. Steck et al. did a study on the variation between indoor and outdoor radon in Iowa and Minnesota. Higher radiation was found in a populated region rather than in unpopulated regions in Central America as a whole. In some northwestern Iowa and southwestern Minnesota counties, the outdoor radon concentrations exceed the national average indoor radon concentrations.[136] Despite the above average, both Minnesota and Iowa's numbers were exceptionally close, regardless of the distance. Accurate doses of radon is heavily needed to further understand the problems radon in total can have on a community. It is understood that radon poisoning does lead to bad health, and lung cancer, but with further research, controls could change results in radon emissions both inside and outside of housing units.[136]

Radon exposure (mostly radon daughters) has been linked to lung cancer in numerous case-control studies performed in the US, Europe and China. There are approximately 21,000 deaths per year in the US (0.0063% of a population of 333 million) due to radon-induced lung cancers.[8][137] In Slovenia, a country with a high concentration of radon, about 120 people (0.0057% of a population of 2.11 million) yearly die because of radon.[138][139] One of the most comprehensive radon studies performed in the US by epidemiologist R. William Field and colleagues found a 50% increased lung cancer risk even at the protracted exposures at the EPA's action level of 4 pCi/L. North American and European pooled analyses further support these findings.[140] However, the discussion about the opposite results is still continuing,[141][142][143] especially a 2008 retrospective case-control study of lung cancer risk which showed substantial cancer rate reduction for radon concentrations between 50 and 123 Bq/m3.[144]

Most models of residential radon exposure are based on studies of miners, and direct estimates of the risks posed to homeowners would be more desirable.[132] Because of the difficulties of measuring the risk of radon relative to smoking, models of their effect have often made use of them.

Radon has been considered the second leading cause of lung cancer and leading environmental cause of cancer mortality by the EPA, with the first one being smoking.[145] Others have reached similar conclusions for the United Kingdom[132] and France.[146] Radon exposure in homes and offices may arise from certain subsurface rock formations, and also from certain building materials (e.g., some granites). The greatest risk of radon exposure arises in buildings that are airtight, insufficiently ventilated, and have foundation leaks that allow air from the soil into basements and dwelling rooms.

Thoron (220Rn) was measured at comparatively high concentrations in buildings with earthen architecture, such as traditional half-timbered houses and modern houses with clay wall finishes. Because of its short half-life, thoron occurs only close to the earthen surfaces as its sources whereas its progeny can be found throughout the indoor air of such buildings. Therefore, radiation exposure occurs at any location within such houses. In different dwellings with earthen architecture in Germany, a study found annual internal radiation doses due to the inhalation of thoron and its progeny of up to several milli-Sieverts.[147]

Action and reference level

WHO presented in 2009 a recommended reference level (the national reference level), 100 Bq/m3, for radon in dwellings. The recommendation also says that where this is not possible, 300 Bq/m3 should be selected as the highest level. A national reference level should not be a limit, but should represent the maximum acceptable annual average radon concentration in a dwelling.[148]

The actionable concentration of radon in a home varies depending on the organization doing the recommendation, for example, the EPA encourages that action be taken at concentrations as low as 74 Bq/m3 (2 pCi/L),[74] and the European Union recommends action be taken when concentrations reach 400 Bq/m3 (11 pCi/L) for old houses and 200 Bq/m3 (5 pCi/L) for new ones.[149] On 8 July 2010, the UK's Health Protection Agency issued new advice setting a "Target Level" of 100 Bq/m3 whilst retaining an "Action Level" of 200 Bq/m3.[150] Similar levels (as in UK) are published by Norwegian Radiation and Nuclear Safety Authority (DSA)[151] with the maximum limit for schools, kindergartens, and new dwellings set at 200 Bq/m3, where 100 Bq/m3 is set as the action level.[152] In all new housings preventative measures should be taken against radon accumulation.

Inhalation and smoking

Results from epidemiological studies indicate that the risk of lung cancer increases with exposure to residential radon. A well known example of source of error is smoking, the main risk factor for lung cancer. In the US, cigarette smoking is estimated to cause 80% to 90% of all lung cancers.[153]

According to the EPA, the risk of lung cancer for smokers is significant due to synergistic effects of radon and smoking. For this population about 62 people in a total of 1,000 will die of lung cancer compared to 7 people in a total of 1,000 for people who have never smoked.[8] It cannot be excluded that the risk of non-smokers should be primarily explained by an effect of radon.

Radon, like other known or suspected external risk factors for lung cancer, is a threat for smokers and former smokers. This was demonstrated by the European pooling study.[154] A commentary[154] to the pooling study stated: "it is not appropriate to talk simply of a risk from radon in homes. The risk is from smoking, compounded by a synergistic effect of radon for smokers. Without smoking, the effect seems to be so small as to be insignificant."

According to the European pooling study, there is a difference in risk for the histological subtypes of lung cancer and radon exposure. Small-cell lung carcinoma, which has a high correlation with smoking, have a higher risk after radon exposure. For other histological subtypes such as adenocarcinoma, the type that primarily affects non-smokers, the risk from radon appears to be lower.[154][155]

A study of radiation from post-mastectomy radiotherapy shows that the simple models previously used to assess the combined and separate risks from radiation and smoking need to be developed.[156] This is also supported by new discussion about the calculation method, the linear no-threshold model, which routinely has been used.[157]

A study from 2001, which included 436 non-smokers and a control group of 1649 non-smokers, showed that exposure to radon increased the risk of lung cancer in non-smokers. The group that had been exposed to tobacco smoke in the home appeared to have a much higher risk, while those who were not exposed to passive smoking did not show any increased risk with increasing radon exposure.[158]

Ingestion

The effects of radon if ingested are unknown, although studies have found that its biological half-life ranges from 30 to 70 minutes, with 90% removal at 100 minutes. In 1999, the US National Research Council investigated the issue of radon in drinking water. The risk associated with ingestion was considered almost negligible.[159] Water from underground sources may contain significant amounts of radon depending on the surrounding rock and soil conditions, whereas surface sources generally do not.[160]

Ocean effects of radon

The major importance of understanding 222Rn flux from the ocean, is to know that the increase use of radon is also circulating and increasing in the atmosphere. Ocean surface concentrations have an exchange within the atmosphere, causing 222Rn to increase through the air-sea interface.[161] Although areas tested were very shallow, additional measurements in a wide variety of coastal regimes should help define the nature of 222Rn observed.[161] As well as being ingested through drinking water, radon is also released from water when temperature is increased, pressure is decreased and when water is aerated. Optimum conditions for radon release and exposure occurred during showering. Water with a radon concentration of 104 pCi/L can increase the indoor airborne radon concentration by 1 pCi/L under normal conditions.[78]

Testing and mitigation

Main article: Radon mitigation
 
A digital radon detector
 
A radon test kit

There are relatively simple tests for radon gas. In some countries these tests are methodically done in areas of known systematic hazards. Radon detection devices are commercially available. Digital radon detectors provide ongoing measurements giving both daily, weekly, short-term and long-term average readouts via a digital display. Short-term radon test devices used for initial screening purposes are inexpensive, in some cases free. There are important protocols for taking short-term radon tests and it is imperative that they be strictly followed. The kit includes a collector that the user hangs in the lowest habitable floor of the house for two to seven days. The user then sends the collector to a laboratory for analysis. Long term kits, taking collections for up to one year or more, are also available. An open-land test kit can test radon emissions from the land before construction begins.[8] Radon concentrations can vary daily, and accurate radon exposure estimates require long-term average radon measurements in the spaces where an individual spends a significant amount of time.[162]

Radon levels fluctuate naturally, due to factors like transient weather conditions, so an initial test might not be an accurate assessment of a home's average radon level. Radon levels are at a maximum during the coolest part of the day when pressure differentials are greatest.[78] Therefore, a high result (over 4 pCi/L) justifies repeating the test before undertaking more expensive abatement projects. Measurements between 4 and 10 pCi/L warrant a long-term radon test. Measurements over 10 pCi/L warrant only another short-term test so that abatement measures are not unduly delayed. Purchasers of real estate are advised to delay or decline a purchase if the seller has not successfully abated radon to 4 pCi/L or less.[8]

Because the half-life of radon is only 3.8 days, removing or isolating the source will greatly reduce the hazard within a few weeks. Another method of reducing radon levels is to modify the building's ventilation. Generally, the indoor radon concentrations increase as ventilation rates decrease.[3] In a well-ventilated place, the radon concentration tends to align with outdoor values (typically 10 Bq/m3, ranging from 1 to 100 Bq/m3).[8]

The four principal ways of reducing the amount of radon accumulating in a house are:[8][163]

  • Sub-slab depressurization (soil suction) by increasing under-floor ventilation;
  • Improving the ventilation of the house and avoiding the transport of radon from the basement into living rooms;
  • Installing a radon sump system in the basement;
  • Installing a positive pressurization or positive supply ventilation system.

According to the EPA,[8] the method to reduce radon "...primarily used is a vent pipe system and fan, which pulls radon from beneath the house and vents it to the outside", which is also called sub-slab depressurization, active soil depressurization, or soil suction. Generally indoor radon can be mitigated by sub-slab depressurization and exhausting such radon-laden air to the outdoors, away from windows and other building openings. "[The] EPA generally recommends methods which prevent the entry of radon. Soil suction, for example, prevents radon from entering your home by drawing the radon from below the home and venting it through a pipe, or pipes, to the air above the home where it is quickly diluted" and the "EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently".[164]

Positive-pressure ventilation systems can be combined with a heat exchanger to recover energy in the process of exchanging air with the outside, and simply exhausting basement air to the outside is not necessarily a viable solution as this can actually draw radon gas into a dwelling. Homes built on a crawl space may benefit from a radon collector installed under a "radon barrier" (a sheet of plastic that covers the crawl space).[8][165] For crawl spaces, the EPA states "An effective method to reduce radon levels in crawl space homes involves covering the earth floor with a high-density plastic sheet. A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors. This form of soil suction is called submembrane suction, and when properly applied is the most effective way to reduce radon levels in crawl space homes."[164]

See also


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External links

 
Wikimedia Commons has media related to Radon.
 
Look up radon in Wiktionary, the free dictionary.
 
Wikiversity has learning resources about Radon atom
  • Radon and radon publications at the United States Environmental Protection Agency
  • National Radon Program Services hosted by Kansas State University
  • UK maps of radon
  • Radon Information from Public Health England
  • Frequently Asked Questions About Radon at National Safety Council
  • Radon at The Periodic Table of Videos (University of Nottingham)
  • , James K. Otton, Linda C.S. Gundersen, and R. Randall Schumann
  • Home Buyer's and Seller's Guide to Radon An article by the International Association of Certified Home Inspectors (InterNACHI)
  • Toxicological Profile for Radon, Draft for Public Comment, Agency for Toxic Substances and Disease Registry, September 2008
  • Health Effects of Exposure to Radon: BEIR VI. Committee on Health Risks of Exposure to Radon (BEIR VI), National Research Council available on-line
  • UNSCEAR 2000 Report to the General Assembly, with scientific annexes: Annex B: Exposures from natural radiation sources.
  • Should you measure the radon concentration in your home?, Phillip N. Price, Andrew Gelman, in Statistics: A Guide to the Unknown, January 2004.
  • Radon in the Home- An Invisible Killer How serious can high levels of radon be in the home? Kevin Vitali

April 21, 2023
radon, this, article, about, chemical, element, other, uses, disambiguation, chemical, element, with, symbol, atomic, number, radioactive, colourless, odourless, tasteless, noble, occurs, naturally, minute, quantities, intermediate, step, normal, radioactive, . This article is about the chemical element For other uses see Radon disambiguation Radon is a chemical element with the symbol Rn and atomic number 86 It is a radioactive colourless odourless tasteless noble gas It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through which thorium and uranium slowly decay into various short lived radioactive elements and lead Radon itself is the immediate decay product of radium Its most stable isotope 222Rn has a half life of only 3 8 days making it one of the rarest elements Since thorium and uranium are two of the most common radioactive elements on Earth while also having three isotopes with half lives on the order of several billion years radon will be present on Earth long into the future despite its short half life The decay of radon produces many other short lived nuclides known as radon daughters ending at stable isotopes of lead 3 Radon 86RnRadonPronunciation ˈ r eɪ d ɒ n wbr RAY don Appearancecolorless gasMass number 222 Radon in the periodic tableHydrogen HeliumLithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine NeonSodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine ArgonPotassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine KryptonRubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine XenonCaesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury element Thallium Lead Bismuth Polonium Astatine RadonFrancium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Xe Rn Ogastatine radon franciumAtomic number Z 86Groupgroup 18 noble gases Periodperiod 6Block p blockElectron configuration Xe 4f14 5d10 6s2 6p6Electrons per shell2 8 18 32 18 8Physical propertiesPhase at STPgasMelting point202 K 71 C 96 F Boiling point211 5 K 61 7 C 79 1 F Density at STP 9 73 g Lwhen liquid at b p 4 4 g cm3Critical point377 K 6 28 MPa 1 Heat of fusion3 247 kJ molHeat of vaporization18 10 kJ molMolar heat capacity5R 2 20 786 J mol K Vapor pressureP Pa 1 10 100 1 k 10 k 100 kat T K 110 121 134 152 176 211Atomic propertiesOxidation states0 2 6ElectronegativityPauling scale 2 2Ionization energies1st 1037 kJ molCovalent radius150 pmVan der Waals radius220 pmSpectral lines of radonOther propertiesNatural occurrencefrom decayCrystal structure face centered cubic fcc Thermal conductivity3 61 10 3 W m K Magnetic orderingnon magneticCAS Number10043 92 2HistoryDiscoveryErnest Rutherford and Robert B Owens 1899 First isolationWilliam Ramsay and Robert Whytlaw Gray 1910 Isotopes of radonveMain isotopes 2 Decayabun dance half life t1 2 mode pro duct210Rn synth 2 4 h a 206Po211Rn synth 14 6 h e 211Ata 207Po222Rn trace 3 8235 d a 218Po224Rn synth 1 8 h b 224Fr Category Radonviewtalkedit referencesUnlike all other intermediate elements in the aforementioned decay chains radon is under standard conditions gaseous and easily inhaled and therefore a health hazard It is often the single largest contributor to an individual s background radiation dose but due to local differences in geology 4 the level of exposure to radon gas differs from place to place A common source is uranium containing minerals in the ground and therefore it accumulates in subterranean areas such as basements Radon can also occur in some ground water like spring waters and hot springs 5 Climate change may cause radon previously trapped underground to be released as permafrost thaws particularly in areas like the Arctic Alaska Canada Greenland and Russia It is possible to test for radon in buildings and to use techniques such as sub slab depressurization for mitigation 6 7 Epidemiological studies have shown a clear link between breathing high concentrations of radon and incidence of lung cancer Radon is a contaminant that affects indoor air quality worldwide According to the United States Environmental Protection Agency EPA 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 About 2 900 of these deaths occur among people who have never smoked While radon is the second most frequent cause of lung cancer it is the number one cause among non smokers according to EPA policy oriented estimates 8 Significant uncertainties exist for the health effects of low dose exposures 9 Unlike the gaseous radon itself radon daughters are solids and stick to surfaces such as airborne dust particles which can cause lung cancer if inhaled 10 Contents 1 Characteristics 1 1 Physical properties 1 2 Chemical properties 1 3 Isotopes 1 4 Daughters 2 History and etymology 3 Occurrence 3 1 Concentration units 3 2 Natural 3 3 Accumulation in buildings 3 4 Industrial production 3 5 Concentration scale 4 Applications 4 1 Medical 4 2 Scientific 5 Health risks 5 1 In mines 5 2 Domestic level exposure 5 2 1 Action and reference level 5 2 2 Inhalation and smoking 5 2 3 Ingestion 5 2 4 Ocean effects of radon 5 3 Testing and mitigation 6 See also 7 References 8 External linksCharacteristics Edit Emission spectrum of radon photographed by Ernest Rutherford in 1908 Numbers at the side of the spectrum are wavelengths The middle spectrum is of Radium emanation radon while the outer two are of helium added to calibrate the wavelengths Physical properties Edit Radon is a colorless odorless and tasteless 11 gas and therefore is not detectable by human senses alone At standard temperature and pressure it forms a monatomic gas with a density of 9 73 kg m3 about 8 times the density of the Earth s atmosphere at sea level 1 217 kg m3 12 It is one of the densest gases at room temperature and is the densest of the noble gases Although colorless at standard temperature and pressure when cooled below its freezing point of 202 K 71 C 96 F it emits a brilliant radioluminescence that turns from yellow to orange red as the temperature lowers 13 Upon condensation it glows because of the intense radiation it produces 14 It is sparingly soluble in water but more soluble than lighter noble gases It is appreciably more soluble in organic liquids than in water Its solubility equation is as follows 15 16 17 x exp B T A displaystyle chi exp B T A where x displaystyle chi is the molar fraction of radon T displaystyle T is the absolute temperature and A displaystyle A and B displaystyle B are solvent constants Chemical properties Edit Radon is a member of the zero valence elements that are called noble gases and is chemically not very reactive The 3 8 day half life of radon 222 makes it useful in physical sciences as a natural tracer Because radon is a gas at standard conditions unlike its decay chain parents it can readily be extracted from them for research 18 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 19 Its first ionization energy the minimum energy required to extract one electron from it is 1037 kJ mol 20 In accordance with periodic trends radon has a lower electronegativity than the element one period before it xenon and is therefore more reactive Early studies concluded that the stability of radon hydrate should be of the same order as that of the hydrates of chlorine Cl2 or sulfur dioxide SO2 and significantly higher than the stability of the hydrate of hydrogen sulfide H2 S 21 Because of its cost 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 powerful oxidizing agents such as fluorine thus forming radon difluoride RnF2 22 23 It decomposes back to its elements at a temperature of above 523 K 250 C 482 F and is reduced by water to radon gas and hydrogen fluoride it may also be reduced back to its elements by hydrogen gas 24 It has a low volatility and was thought to be RnF2 Because of the short half life of radon and the radioactivity of its compounds it has not been possible to study the compound in any detail Theoretical studies on this molecule predict that it should have a Rn F bond distance of 2 08 angstrom A and that the compound is thermodynamically more stable and less volatile than its lighter counterpart xenon difluoride XeF2 25 The octahedral molecule RnF6 was predicted to have an even lower enthalpy of formation than the difluoride 26 The RnF ion is believed to form by the following reaction 27 Rn g 2 O2 SbF6 s RnF Sb2 F11 s 2 O2 g For this reason antimony pentafluoride together with chlorine trifluoride and N2 F2 Sb2 F11 have been considered for radon gas removal in uranium mines due to the formation of radon fluorine compounds 18 Radon compounds can be formed by the decay of radium in radium halides a reaction that has been used to reduce the amount of radon that escapes from targets during irradiation 24 Additionally salts of the RnF cation with the anions SbF 6 TaF 6 and BiF 6 are known 24 Radon is also oxidised by dioxygen difluoride to RnF2 at 173 K 100 C 148 F 24 Radon oxides are among the few other reported compounds of radon 28 only the trioxide RnO3 has been confirmed 29 The higher fluorides RnF4 and RnF6 have been claimed 29 and are calculated to be stable 30 but their identification is unclear 29 They may have been observed in experiments where unknown radon containing products distilled together with xenon hexafluoride these may have been RnF4 RnF6 or both 24 Trace scale heating of radon with xenon fluorine bromine pentafluoride and either sodium fluoride or nickel fluoride was claimed to produce a higher fluoride as well which hydrolysed to form RnO3 While it has been suggested that these claims were really due to radon precipitating out as the solid complex RnF 2 NiF6 2 the fact that radon coprecipitates from aqueous solution with CsXeO3 F has been taken as confirmation that RnO3 was formed which has been supported by further studies of the hydrolysed solution That RnO3F did not form in other experiments may have been due to the high concentration of fluoride used Electromigration studies also suggest the presence of cationic HRnO3 and anionic HRnO4 forms of radon in weakly acidic aqueous solution pH gt 5 the procedure having previously been validated by examination of the homologous xenon trioxide 29 The decay technique has also been used Avrorin et al reported in 1982 that 212Fr compounds cocrystallised with their caesium analogues appeared to retain chemically bound radon after electron capture analogies with xenon suggested the formation of RnO3 but this could not be confirmed 31 It is likely that the difficulty in identifying higher fluorides of radon stems from radon being kinetically hindered from being oxidised beyond the divalent state because of the strong ionicity of radon difluoride RnF2 and the high positive charge on radon in RnF spatial separation of RnF2 molecules may be necessary to clearly identify higher fluorides of radon of which RnF4 is expected to be more stable than RnF6 due to spin orbit splitting of the 6p shell of radon RnIV would have a closed shell 6s2 6p21 2 configuration Therefore while RnF4 should have a similar stability to xenon tetrafluoride XeF4 RnF6 would likely be much less stable than xenon hexafluoride XeF6 radon hexafluoride would also probably be a regular octahedral molecule unlike the distorted octahedral structure of XeF6 because of the inert pair effect 32 33 Because radon is quite electropositive for a noble gas it is possible that radon fluorides actually take on highly fluorine bridged structures and are not volatile 33 Extrapolation down the noble gas group would suggest also the possible existence of RnO RnO2 and RnOF4 as well as the first chemically stable noble gas chlorides RnCl2 and RnCl4 but none of these have yet been found 24 Radon carbonyl RnCO has been predicted to be stable and to have a linear molecular geometry 34 The molecules Rn2 and RnXe were found to be significantly stabilized by spin orbit coupling 35 Radon caged inside a fullerene has been proposed as a drug for tumors 36 37 Despite the existence of Xe VIII no Rn VIII compounds have been claimed to exist RnF8 should be highly unstable chemically XeF8 is thermodynamically unstable It is predicted that the most stable Rn VIII compound would be barium perradonate Ba2RnO6 analogous to barium perxenate 30 The instability of Rn VIII is due to the relativistic stabilization of the 6s shell also known as the inert pair effect 30 Radon reacts with the liquid halogen fluorides ClF ClF3 ClF5 BrF3 BrF5 and IF7 to form RnF2 In halogen fluoride solution radon is nonvolatile and exists as the RnF and Rn2 cations addition of fluoride anions results in the formation of the complexes RnF 3 and RnF2 4 paralleling the chemistry of beryllium II and aluminium III 24 The standard electrode potential of the Rn2 Rn couple has been estimated as 2 0 V 38 although there is no evidence for the formation of stable radon ions or compounds in aqueous solution 24 Isotopes Edit Main article Isotopes of radon Radon has no stable isotopes Thirty nine radioactive isotopes have been characterized with atomic masses ranging from 193 to 231 39 40 The most stable isotope is 222Rn which is a decay product of 226Ra a decay product of 238U 41 A trace amount of the highly unstable isotope 218Rn is also among the daughters of 222Rn Three other radon isotopes have a half life of over an hour 211Rn 210Rn and 224Rn The 220Rn isotope is a natural decay product of the most stable thorium isotope 232Th and is commonly referred to as thoron It has a half life of 55 6 seconds and also emits alpha radiation Similarly 219Rn is derived from the most stable isotope of actinium 227Ac named actinon and is an alpha emitter with a half life of 3 96 seconds 39 No radon isotopes occur significantly in the neptunium 237Np decay series though a trace amount of the extremely unstable isotope 217Rn is produced The radium or uranium series Daughters Edit Main article Decay chain Uranium series 222Rn belongs to the radium and uranium 238 decay chain and has a half life of 3 8235 days Its first four products excluding marginal decay schemes are very short lived meaning that the corresponding disintegrations are indicative of the initial radon distribution Its decay goes through the following sequence 39 222Rn 3 82 days alpha decaying to 218Po 3 10 minutes alpha decaying to 214Pb 26 8 minutes beta decaying to 214Bi 19 9 minutes beta decaying to 214Po 0 1643 ms alpha decaying to 210Pb which has a much longer half life of 22 3 years beta decaying to 210Bi 5 013 days beta decaying to 210Po 138 376 days alpha decaying to 206Pb stable The radon equilibrium factor 42 is the ratio between the activity of all short period radon progenies which are responsible for most of radon s biological effects and the activity that would be at equilibrium with the radon parent If a closed volume is constantly supplied with radon the concentration of short lived isotopes will increase until an equilibrium is reached where the rate of decay of each decay product will equal that of the radon itself The equilibrium factor is 1 when both activities are equal meaning that the decay products have stayed close to the radon parent long enough for the equilibrium to be reached within a couple of hours Under these conditions each additional pCi L of radon will increase exposure by 0 01 working level WL a measure of radioactivity commonly used in mining These conditions are not always met in many homes the equilibrium factor is typically 40 that is there will be 0 004 WL of daughters for each pCi L of radon in the air 43 210Pb takes much longer decades to come in equilibrium with radon but if the environment permits accumulation of dust over extended periods of time 210Pb and its decay products may contribute to overall radiation levels as well Because of their electrostatic charge radon progenies adhere to surfaces or dust particles whereas gaseous radon does not Attachment removes them from the air usually causing the equilibrium factor in the atmosphere to be less than 1 The equilibrium factor is also lowered by air circulation or air filtration devices and is increased by airborne dust particles including cigarette smoke The equilibrium factor found in epidemiological studies is 0 4 44 History and etymology Edit Apparatus used by Ramsay and Whytlaw Gray to isolate radon M is a capillary tube where approximately 0 1 mm3 were isolated Radon mixed with hydrogen entered the evacuated system through siphon A mercury is shown in black Radon was the fifth radioactive element to be discovered in 1899 by Ernest Rutherford and Robert B Owens at McGill University in Montreal 45 after uranium thorium radium and polonium 46 47 48 49 In 1899 Pierre and Marie Curie observed that the gas emitted by radium remained radioactive for a month 50 Later that year Rutherford and Owens noticed variations when trying to measure radiation from thorium oxide 45 Rutherford noticed that the compounds of thorium continuously emit a radioactive gas that remains radioactive for several minutes and called this gas emanation from Latin emanare to flow out and emanatio expiration 51 and later thorium emanation Th Em In 1900 Friedrich Ernst Dorn reported some experiments in which he noticed that radium compounds emanate a radioactive gas he named radium emanation Ra Em 52 53 In 1901 Rutherford and Harriet Brooks demonstrated that the emanations are radioactive but credited the Curies for the discovery of the element 54 In 1903 similar emanations were observed from actinium by Andre Louis Debierne 55 56 and were called actinium emanation Ac Em Several shortened names were soon suggested for the three emanations exradio exthorio and exactinio in 1904 57 radon Ro thoron To and akton or acton Ao in 1918 58 radeon thoreon and actineon in 1919 59 and eventually radon thoron and actinon in 1920 60 The name radon is not related to that of the Austrian mathematician Johann Radon 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 57 In the early 20th century in the US gold contaminated with the radon daughter 210Pb entered the jewelry industry This was from gold seeds that had held 222Rn that had been melted down after the radon had decayed 61 62 In 1909 Ramsay and Robert Whytlaw Gray isolated radon and determined its melting temperature and approximate density In 1910 they determined that it was the heaviest known gas 63 They wrote that L expression l emanation du radium est fort incommode the expression radium emanation is very awkward and suggested the new name niton Nt from Latin nitens shining to emphasize the radioluminescence property 64 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 was renamed 220Rn and An was renamed 219Rn This has caused some confusion in the literature regarding the element s discovery as while Dorn had discovered radon the isotope he had not been the first to discover radon the element 65 As late as the 1960s the element was also referred to simply as emanation 66 The first synthesized compound of radon radon fluoride was obtained in 1962 67 Even today the word radon may refer to either the element or its isotope 222Rn with thoron remaining in use as a short name for 220Rn to stem this ambiguity The name actinon for 219Rn is rarely encountered today probably due to the short half life of that isotope 65 The danger of high exposure to radon in mines where exposures can reach 1 000 000 Bq m3 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 68 69 In 1879 this condition was identified as lung cancer by Harting 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 in the Joachimsthal region of Bohemia 70 In the US studies and mitigation only followed decades of health effects on uranium miners of the Southwestern US employed during the early Cold War standards were not implemented until 1971 71 The presence of radon in indoor air was documented as early as 1950 Beginning in the 1970s research was initiated to address sources of indoor radon determinants of concentration health effects and mitigation approaches In the US the problem of indoor radon received widespread publicity and intensified investigation after a widely publicized incident in 1984 During routine monitoring at a Pennsylvania nuclear power plant a worker was found to be contaminated with radioactivity A high concentration of radon in his home was subsequently identified as responsible 72 Occurrence EditSee also Radium and radon in the environment Concentration units Edit 210Pb is formed from the decay of 222Rn Here is a typical deposition rate of 210Pb as observed in Japan as a function of time due to variations in radon concentration 73 All discussions of radon concentrations in the environment refer to 222Rn While the average rate of production of 220Rn from the thorium decay series is about the same as that of 222Rn the amount of 220Rn in the environment is much less than that of 222Rn because of the short half life of 220Rn 55 seconds versus 3 8 days respectively 3 Radon concentration in the atmosphere is usually measured in becquerel per cubic meter Bq m3 the SI derived unit Another unit of measurement common in the US is picocuries per liter pCi L 1 pCi L 37 Bq m3 43 Typical domestic exposures average about 48 Bq m3 indoors though this varies widely and 15 Bq m3 outdoors 74 In the mining industry the exposure is traditionally measured in working level WL and the cumulative exposure in working level month WLM 1 WL equals any combination of short lived 222Rn daughters 218Po 214Pb 214Bi and 214Po in 1 liter of air that releases 1 3 105 MeV of potential alpha energy 43 1 WL is equivalent to 2 08 10 5 joules per cubic meter of air J m3 3 The SI unit of cumulative exposure is expressed in joule hours per cubic meter J h m3 One WLM is equivalent to 3 6 10 3 J h m3 An exposure to 1 WL for 1 working month 170 hours equals 1 WLM cumulative exposure A cumulative exposure of 1 WLM is roughly equivalent to living one year in an atmosphere with a radon concentration of 230 Bq m3 75 222Rn decays to 210Pb and other radioisotopes The levels of 210Pb can be measured The rate of deposition of this radioisotope is weather dependent Radon concentrations found in natural environments are much too low to be detected by chemical means A 1 000 Bq m3 relatively high concentration corresponds to 0 17 picogram per cubic meter pg m3 The average concentration of radon in the atmosphere is about 6 10 18 molar percent or about 150 atoms in each milliliter of air 76 The radon activity of the entire Earth s atmosphere originates from only a few tens of grams of radon consistently replaced by decay of larger amounts of radium thorium and uranium 77 Natural Edit Radon concentration next to a uranium mine Radon is produced by the radioactive decay of radium 226 which is found in uranium ores phosphate rock shales igneous and metamorphic rocks such as granite gneiss and schist and to a lesser degree in common rocks such as limestone 4 78 Every square mile of surface soil to a depth of 6 inches 2 6 km2 to a depth of 15 cm contains approximately 1 gram of radium which releases radon in small amounts to the atmosphere 3 On a global scale it is estimated that 2 4 billion curies 90 EBq of radon are released from soil annually 79 This is equivalent to some 15 3 kilograms 34 lb Radon concentration can differ widely from place to place In the open air it ranges from 1 to 100 Bq m3 even less 0 1 Bq m3 above the ocean In caves or ventilated mines or poorly ventilated houses its concentration climbs to 20 2 000 Bq m3 80 Radon concentration can be much higher in mining contexts Ventilation regulations instruct to maintain radon concentration in uranium mines under the working level with 95th percentile levels ranging up to nearly 3 WL 546 pCi 222Rn per liter of air 20 2 kBq m3 measured from 1976 to 1985 3 The concentration in the air at the unventilated Gastein Healing Gallery averages 43 kBq m3 1 2 nCi L with maximal value of 160 kBq m3 4 3 nCi L 81 Radon mostly appears with the decay chain of the radium and uranium series 222Rn and marginally with the thorium series 220Rn The element emanates naturally from the ground and some building materials all over the world wherever traces of uranium or thorium are found and particularly in regions with soils containing granite or shale which have a higher concentration of uranium Not all granitic regions are prone to high emissions of radon Being a rare gas it usually migrates freely through faults and fragmented soils and may accumulate in caves or water Owing to its very short half life four days for 222Rn radon concentration decreases very quickly when the distance from the production area increases Radon concentration varies greatly with season and atmospheric conditions For instance it has been shown to accumulate in the air if there is a meteorological inversion and little wind 82 High concentrations of radon can be found in some spring waters and hot springs 83 The towns of Boulder Montana Misasa Bad Kreuznach Germany and the country of Japan have radium rich springs that emit radon To be classified as a radon mineral water radon concentration must be above 2 nCi L 74 kBq m3 84 The activity of radon mineral water reaches 2 000 kBq m3 in Merano and 4 000 kBq m3 in Lurisia Italy 81 Natural radon concentrations in the Earth s atmosphere are so low that radon rich water in contact with the atmosphere will continually lose radon by volatilization Hence ground water has a higher concentration of 222Rn than surface water because radon is continuously produced by radioactive decay of 226Ra present in rocks Likewise the saturated zone of a soil frequently has a higher radon content than the unsaturated zone because of diffusional losses to the atmosphere 85 86 In 1971 Apollo 15 passed 110 km 68 mi above the Aristarchus plateau on the Moon and detected a significant rise in alpha particles thought to be caused by the decay of 222Rn The presence of 222Rn has been inferred later from data obtained from the Lunar Prospector alpha particle spectrometer 87 Radon is found in some petroleum Because radon has a similar pressure and temperature curve to propane and oil refineries separate petrochemicals based on their boiling points the piping carrying freshly separated propane in oil refineries can become contaminated because of decaying radon and its products 88 Residues from the petroleum and natural gas industry often contain radium and its daughters The sulfate scale from an oil well can be radium rich while the water oil and gas from a well often contains radon Radon decays to form solid radioisotopes that form coatings on the inside of pipework 88 Accumulation in buildings Edit The examples and perspective in this section may not represent a worldwide view of the subject You may improve this section discuss the issue on the talk page or create a new section as appropriate September 2021 Learn how and when to remove this template message Typical log normal radon distribution in dwellings Predicted fraction of U S homes having concentrations of radon exceeding the EPA s recommended action level of 4 pCi L High concentrations of radon in homes were discovered by chance in 1985 after the stringent radiation testing conducted at the new Limerick Generating Station nuclear power plant revealed that Stanley Watras a construction engineer at the plant was contaminated by radioactive substances even though the reactor had never been fueled 89 Typical domestic exposures are of approximately 100 Bq m3 2 7 pCi L indoors Some level of radon will be found in all buildings Radon mostly enters a building directly from the soil through the lowest level in the building that is in contact with the ground High levels of radon in the water supply can also increase indoor radon air levels Typical entry points of radon into buildings are cracks in solid foundations and walls construction joints gaps in suspended floors and around service pipes cavities inside walls and the water supply 11 Radon concentrations in the same place may differ by double half over one hour Also the concentration in one room of a building may be significantly different from the concentration in an adjoining room 3 The soil characteristics of the dwellings are the most important source of radon for the ground floor and higher concentration of indoor radon observed on lower floors Most of the high radon concentrations have been reported from places near fault zones hence the existence of a relation between the exhalation rate from faults and indoor radon concentrations is obvious citation needed The distribution of radon concentrations will generally differ from room to room and the readings are averaged according to regulatory protocols Indoor radon concentration is usually assumed to follow a log normal distribution on a given territory 90 Thus the geometric mean is generally used for estimating the average radon concentration in an area 91 The mean concentration ranges from less than 10 Bq m3 to over 100 Bq m3 in some European countries 92 Typical geometric standard deviations found in studies range between 2 and 3 meaning given the 68 95 99 7 rule that the radon concentration is expected to be more than a hundred times the mean concentration for 2 to 3 of the cases Some of the highest radon hazard in the US is found in Iowa and in the Appalachian Mountain areas in southeastern Pennsylvania 93 Iowa has the highest average radon concentrations in the US due to significant glaciation that ground the granitic rocks from the Canadian Shield and deposited it as soils making up the rich Iowa farmland 94 Many cities within the state such as Iowa City have passed requirements for radon resistant construction in new homes The second highest readings in Ireland were found in office buildings in the Irish town of Mallow County Cork prompting local fears regarding lung cancer 95 In a few places uranium tailings have been used for landfills and were subsequently built upon resulting in possible increased exposure to radon 3 Since radon is a colorless odorless gas the only way to know how much is present in the air or water is to perform tests In the US radon test kits are available to the public at retail stores such as hardware stores for home use and testing is available through licensed professionals who are often home inspectors Efforts to reduce indoor radon levels are called radon mitigation In the US the EPA recommends all houses be tested for radon In the UK under the Housing Health amp Safety Rating System HHSRS property owners have an obligation to evaluate potential risks and hazards to health and safety in a residential property 96 Industrial production Edit Radon is obtained as a by product of uraniferous ores processing after transferring into 1 solutions of hydrochloric or hydrobromic acids The gas mixture extracted from the solutions contains H2 O2 He Rn CO2 H2 O and hydrocarbons The mixture is purified by passing it over copper at 993 K 720 C 1 328 F to remove the H2 and the O2 and then KOH and P2 O5 are used to remove the acids and moisture by sorption Radon is condensed by liquid nitrogen and purified from residue gases by sublimation 97 Radon commercialization is regulated but it is available in small quantities for the calibration of 222Rn measurement systems at a price in 2008 of almost US 6 000 equivalent to 7 551 in 2021 per milliliter of radium solution which only contains about 15 picograms of actual radon at any given moment 98 Radon is produced by a solution of radium 226 half life of 1 600 years Radium 226 decays by alpha particle emission producing radon that collects over samples of radium 226 at a rate of about 1 mm3 day per gram of radium equilibrium is quickly achieved and radon is produced in a steady flow with an activity equal to that of the radium 50 Bq Gaseous 222Rn half life of about four days escapes from the capsule through diffusion 99 Concentration scale Edit Bq m3 pCi L Occurrence example1 0 027 Radon concentration at the shores of large oceans is typically 1 Bq m3 Radon trace concentration above oceans or in Antarctica can be lower than 0 1 Bq m3 10 0 27 Mean continental concentration in the open air 10 to 30 Bq m3 Based on a series of surveys the global mean indoor radon concentration is estimated to be 39 Bq m3 100 2 7 Typical indoor domestic exposure Most countries have adopted a radon concentration of 200 400 Bq m3 for indoor air as an Action or Reference Level If testing shows levels less than 4 picocuries radon per liter of air 150 Bq m3 then no action is necessary A cumulated exposure of 230 Bq m3 of radon gas concentration during a period of 1 year corresponds to 1 WLM 1 000 27 Very high radon concentrations gt 1000 Bq m3 have been found in houses built on soils with a high uranium content and or high permeability of the ground If levels are 20 picocuries radon per liter of air 800 Bq m3 or higher the home owner should consider some type of procedure to decrease indoor radon levels Allowable concentrations in uranium mines are approximately 1 220 Bq m3 33 pCi L 100 10 000 270 The concentration in the air at the unventilated Gastein Healing Gallery averages 43 kBq m3 about 1 2 nCi L with maximal value of 160 kBq m3 about 4 3 nCi L 81 100 000 2700 About 100 000 Bq m3 2 7 nCi L was measured in Stanley Watras s basement 101 102 1 000 000 27000 Concentrations reaching 1 000 000 Bq m3 can be found in unventilated uranium mines 5 54 1019 1 5 1018 Theoretical upper limit Radon gas 222Rn at 100 concentration 1 atmosphere 0 C 1 538 105 curies gram 103 5 54 1019 Bq m3 Applications EditMedical Edit Main article Radioactive quackery An early 20th century form of quackery was the treatment of maladies in a radiotorium 104 It was a small sealed room for patients to be exposed to radon for its medicinal effects The carcinogenic nature of radon due to its ionizing radiation became apparent later Radon s molecule damaging radioactivity has been used to kill cancerous cells 105 but it does not increase the health of healthy cells citation needed The ionizing radiation causes the formation of free radicals which results in cell damage causing increased rates of illness including cancer Exposure to radon has been suggested to mitigate autoimmune diseases such as arthritis in a process known as radiation hormesis 106 107 As a result in the late 20th century and early 21st century health mines established in Basin Montana attracted people seeking relief from health problems such as arthritis through limited exposure to radioactive mine water and radon The practice is discouraged because of the well documented ill effects of high doses of radiation on the body 108 Radioactive water baths have been applied since 1906 in Jachymov Czech Republic but even before radon discovery they were used in Bad Gastein Austria Radium rich springs are also used in traditional Japanese onsen in Misasa Tottori Prefecture Drinking therapy is applied in Bad Brambach Germany and during the early 20th century water from springs with radon in them was bottled and sold this water had little to no radon in it by the time it got to consumers due to radon s short half life 109 Inhalation therapy is carried out in Gasteiner Heilstollen Austria Swieradow Zdroj Czerniawa Zdroj Kowary Ladek Zdroj Poland Harghita Băi Romania and Boulder Montana In the US and Europe there are several radon spas where people sit for minutes or hours in a high radon atmosphere such as at Bad Schmiedeberg Germany 107 110 Radon has been produced commercially for use in radiation therapy but for the most part has been replaced by radionuclides made in particle accelerators and nuclear reactors Radon has been used in implantable seeds made of gold or glass primarily used to treat cancers known as brachytherapy The gold seeds were produced by filling a long tube with radon pumped from a radium source the tube being then divided into short sections by crimping and cutting The gold layer keeps the radon within and filters out the alpha and beta radiations while allowing the gamma rays to escape which kill the diseased tissue The activities might range from 0 05 to 5 millicuries per seed 2 to 200 MBq 105 The gamma rays are produced by radon and the first short lived elements of its decay chain 218Po 214Pb 214Bi 214Po After 11 half lives 42 days radon radioactivity is at 1 2 048 of its original level At this stage the predominant residual activity of the seed originates from the radon decay product 210Pb whose half life 22 3 years is 2 000 times that of radon and its descendants 210Bi and 210Po Scientific Edit Radon emanation from the soil varies with soil type and with surface uranium content so outdoor radon concentrations can be used to track air masses to a limited degree This fact has been put to use by some atmospheric scientists Radon storm Because of radon s rapid loss to air and comparatively rapid decay radon is used in hydrologic research that studies the interaction between groundwater and streams Any significant concentration of radon in a stream is a good indicator that there are local inputs of groundwater Radon soil concentration has been used in an experimental way to map buried close subsurface geological faults because concentrations are generally higher over the faults 111 Similarly it has found some limited use in prospecting for geothermal gradients 112 Some researchers have investigated changes in groundwater radon concentrations for earthquake prediction 113 114 115 Increases in radon were noted before the 1966 Tashkent 116 and 1994 Mindoro 115 earthquakes Radon has a half life of approximately 3 8 days which means that it can be found only shortly after it has been produced in the radioactive decay chain For this reason it has been hypothesized that increases in radon concentration is due to the generation of new cracks underground which would allow increased groundwater circulation flushing out radon The generation of new cracks might not unreasonably be assumed to precede major earthquakes In the 1970s and 1980s scientific measurements of radon emissions near faults found that earthquakes often occurred with no radon signal and radon was often detected with no earthquake to follow It was then dismissed by many as an unreliable indicator 117 As of 2009 it was under investigation as a possible precursor by NASA 118 Radon is a known pollutant emitted from geothermal power stations because it is present in the material pumped from deep underground It disperses rapidly and no radiological hazard has been demonstrated in various investigations In addition typical systems re inject the material deep underground rather than releasing it at the surface so its environmental impact is minimal 119 However similar things can be said about trivial releases from operating nuclear power plants citation needed In the 1940s and 50s radon was used for industrial radiography 120 121 Other X ray sources which became available after World War II quickly replaced radon for this application as they were lower in cost and had less hazard of alpha radiation Health risks EditMain article Health effects of radon In mines Edit Radon 222 decay products have been classified by the International Agency for Research on Cancer as being carcinogenic to humans 122 and as a gas that can be inhaled lung cancer is a particular concern for people exposed to elevated levels of radon for sustained periods During the 1940s and 1950s when safety standards requiring expensive ventilation in mines were not widely implemented 123 radon exposure was linked to lung cancer among non smoking miners of uranium and other hard rock materials in what is now the Czech Republic and later among miners from the Southwestern US 124 125 126 and South Australia 127 Despite these hazards being known in the early 1950s 128 this occupational hazard remained poorly managed in many mines until the 1970s During this period several entrepreneurs opened former uranium mines in the US to the general public and advertised alleged health benefits from breathing radon gas underground Health benefits claimed included pain sinus asthma and arthritis relief 129 130 but these were proven to be false and the government banned such advertisements in 1975 131 Since that time ventilation and other measures have been used to reduce radon levels in most affected mines that continue to operate In recent years the average annual exposure of uranium miners has fallen to levels similar to the concentrations inhaled in some homes This has reduced the risk of occupationally induced cancer from radon although health issues may persist for those who are currently employed in affected mines and for those who have been employed in them in the past 132 As the relative risk for miners has decreased so has the ability to detect excess risks among that population 133 Residues from processing of uranium ore can also be a source of radon Radon resulting from the high radium content in uncovered dumps and tailing ponds can be easily released into the atmosphere and affect people living in the vicinity 134 In addition to lung cancer researchers have theorized a possible increased risk of leukemia due to radon exposure Empirical support from studies of the general population is inconsistent and a study of uranium miners found a correlation between radon exposure and chronic lymphocytic leukemia 135 Miners as well as milling and ore transportation workers who worked in the uranium industry in the US between the 1940s and 1971 may be eligible for compensation under the Radiation Exposure Compensation Act RECA Surviving relatives may also apply in cases where the formerly employed person is deceased Not only uranium mines are affected by elevated levels of radon Coal mines in particular are affected as well since coal may contain more uranium and thorium than commercially operational uranium mines Domestic level exposure Edit Prolonged exposure to higher concentrations of radon has been linked to an increase in lung cancer 136 Since 1999 there has been investigations worldwide on how radon concentrations are estimated In the United States alone averages have been recorded to be at least 40 Bq meters cubed Steck et al did a study on the variation between indoor and outdoor radon in Iowa and Minnesota Higher radiation was found in a populated region rather than in unpopulated regions in Central America as a whole In some northwestern Iowa and southwestern Minnesota counties the outdoor radon concentrations exceed the national average indoor radon concentrations 136 Despite the above average both Minnesota and Iowa s numbers were exceptionally close regardless of the distance Accurate doses of radon is heavily needed to further understand the problems radon in total can have on a community It is understood that radon poisoning does lead to bad health and lung cancer but with further research controls could change results in radon emissions both inside and outside of housing units 136 Radon exposure mostly radon daughters has been linked to lung cancer in numerous case control studies performed in the US Europe and China There are approximately 21 000 deaths per year in the US 0 0063 of a population of 333 million due to radon induced lung cancers 8 137 In Slovenia a country with a high concentration of radon about 120 people 0 0057 of a population of 2 11 million yearly die because of radon 138 139 One of the most comprehensive radon studies performed in the US by epidemiologist R William Field and colleagues found a 50 increased lung cancer risk even at the protracted exposures at the EPA s action level of 4 pCi L North American and European pooled analyses further support these findings 140 However the discussion about the opposite results is still continuing 141 142 143 especially a 2008 retrospective case control study of lung cancer risk which showed substantial cancer rate reduction for radon concentrations between 50 and 123 Bq m3 144 Most models of residential radon exposure are based on studies of miners and direct estimates of the risks posed to homeowners would be more desirable 132 Because of the difficulties of measuring the risk of radon relative to smoking models of their effect have often made use of them Radon has been considered the second leading cause of lung cancer and leading environmental cause of cancer mortality by the EPA with the first one being smoking 145 Others have reached similar conclusions for the United Kingdom 132 and France 146 Radon exposure in homes and offices may arise from certain subsurface rock formations and also from certain building materials e g some granites The greatest risk of radon exposure arises in buildings that are airtight insufficiently ventilated and have foundation leaks that allow air from the soil into basements and dwelling rooms Thoron 220Rn was measured at comparatively high concentrations in buildings with earthen architecture such as traditional half timbered houses and modern houses with clay wall finishes Because of its short half life thoron occurs only close to the earthen surfaces as its sources whereas its progeny can be found throughout the indoor air of such buildings Therefore radiation exposure occurs at any location within such houses In different dwellings with earthen architecture in Germany a study found annual internal radiation doses due to the inhalation of thoron and its progeny of up to several milli Sieverts 147 Action and reference level Edit WHO presented in 2009 a recommended reference level the national reference level 100 Bq m3 for radon in dwellings The recommendation also says that where this is not possible 300 Bq m3 should be selected as the highest level A national reference level should not be a limit but should represent the maximum acceptable annual average radon concentration in a dwelling 148 The actionable concentration of radon in a home varies depending on the organization doing the recommendation for example the EPA encourages that action be taken at concentrations as low as 74 Bq m3 2 pCi L 74 and the European Union recommends action be taken when concentrations reach 400 Bq m3 11 pCi L for old houses and 200 Bq m3 5 pCi L for new ones 149 On 8 July 2010 the UK s Health Protection Agency issued new advice setting a Target Level of 100 Bq m3 whilst retaining an Action Level of 200 Bq m3 150 Similar levels as in UK are published by Norwegian Radiation and Nuclear Safety Authority DSA 151 with the maximum limit for schools kindergartens and new dwellings set at 200 Bq m3 where 100 Bq m3 is set as the action level 152 In all new housings preventative measures should be taken against radon accumulation Inhalation and smoking Edit Results from epidemiological studies indicate that the risk of lung cancer increases with exposure to residential radon A well known example of source of error is smoking the main risk factor for lung cancer In the US cigarette smoking is estimated to cause 80 to 90 of all lung cancers 153 According to the EPA the risk of lung cancer for smokers is significant due to synergistic effects of radon and smoking For this population about 62 people in a total of 1 000 will die of lung cancer compared to 7 people in a total of 1 000 for people who have never smoked 8 It cannot be excluded that the risk of non smokers should be primarily explained by an effect of radon Radon like other known or suspected external risk factors for lung cancer is a threat for smokers and former smokers This was demonstrated by the European pooling study 154 A commentary 154 to the pooling study stated it is not appropriate to talk simply of a risk from radon in homes The risk is from smoking compounded by a synergistic effect of radon for smokers Without smoking the effect seems to be so small as to be insignificant According to the European pooling study there is a difference in risk for the histological subtypes of lung cancer and radon exposure Small cell lung carcinoma which has a high correlation with smoking have a higher risk after radon exposure For other histological subtypes such as adenocarcinoma the type that primarily affects non smokers the risk from radon appears to be lower 154 155 A study of radiation from post mastectomy radiotherapy shows that the simple models previously used to assess the combined and separate risks from radiation and smoking need to be developed 156 This is also supported by new discussion about the calculation method the linear no threshold model which routinely has been used 157 A study from 2001 which included 436 non smokers and a control group of 1649 non smokers showed that exposure to radon increased the risk of lung cancer in non smokers The group that had been exposed to tobacco smoke in the home appeared to have a much higher risk while those who were not exposed to passive smoking did not show any increased risk with increasing radon exposure 158 Ingestion Edit The effects of radon if ingested are unknown although studies have found that its biological half life ranges from 30 to 70 minutes with 90 removal at 100 minutes In 1999 the US National Research Council investigated the issue of radon in drinking water The risk associated with ingestion was considered almost negligible 159 Water from underground sources may contain significant amounts of radon depending on the surrounding rock and soil conditions whereas surface sources generally do not 160 Ocean effects of radon Edit The major importance of understanding 222Rn flux from the ocean is to know that the increase use of radon is also circulating and increasing in the atmosphere Ocean surface concentrations have an exchange within the atmosphere causing 222Rn to increase through the air sea interface 161 Although areas tested were very shallow additional measurements in a wide variety of coastal regimes should help define the nature of 222Rn observed 161 As well as being ingested through drinking water radon is also released from water when temperature is increased pressure is decreased and when water is aerated Optimum conditions for radon release and exposure occurred during showering Water with a radon concentration of 104 pCi L can increase the indoor airborne radon concentration by 1 pCi L under normal conditions 78 Testing and mitigation Edit Main article Radon mitigation A digital radon detector A radon test kit There are relatively simple tests for radon gas In some countries these tests are methodically done in areas of known systematic hazards Radon detection devices are commercially available Digital radon detectors provide ongoing measurements giving both daily weekly short term and long term average readouts via a digital display Short term radon test devices used for initial screening purposes are inexpensive in some cases free There are important protocols for taking short term radon tests and it is imperative that they be strictly followed The kit includes a collector that the user hangs in the lowest habitable floor of the house for two to seven days The user then sends the collector to a laboratory for analysis Long term kits taking collections for up to one year or more are also available An open land test kit can test radon emissions from the land before construction begins 8 Radon concentrations can vary daily and accurate radon exposure estimates require long term average radon measurements in the spaces where an individual spends a significant amount of time 162 Radon levels fluctuate naturally due to factors like transient weather conditions so an initial test might not be an accurate assessment of a home s average radon level Radon levels are at a maximum during the coolest part of the day when pressure differentials are greatest 78 Therefore a high result over 4 pCi L justifies repeating the test before undertaking more expensive abatement projects Measurements between 4 and 10 pCi L warrant a long term radon test Measurements over 10 pCi L warrant only another short term test so that abatement measures are not unduly delayed Purchasers of real estate are advised to delay or decline a purchase if the seller has not successfully abated radon to 4 pCi L or less 8 Because the half life of radon is only 3 8 days removing or isolating the source will greatly reduce the hazard within a few weeks Another method of reducing radon levels is to modify the building s ventilation Generally the indoor radon concentrations increase as ventilation rates decrease 3 In a well ventilated place the radon concentration tends to align with outdoor values typically 10 Bq m3 ranging from 1 to 100 Bq m3 8 The four principal ways of reducing the amount of radon accumulating in a house are 8 163 Sub slab depressurization soil suction by increasing under floor ventilation Improving the ventilation of the house and avoiding the transport of radon from the basement into living rooms Installing a radon sump system in the basement Installing a positive pressurization or positive supply ventilation system According to the EPA 8 the method to reduce radon primarily used is a vent pipe system and fan which pulls radon from beneath the house and vents it to the outside which is also called sub slab depressurization active soil depressurization or soil suction Generally indoor radon can be mitigated by sub slab depressurization and exhausting such radon laden air to the outdoors away from windows and other building openings The EPA generally recommends methods which prevent the entry of radon Soil suction for example prevents radon from entering your home by drawing the radon from below the home and venting it through a pipe or pipes to the air above the home where it is quickly diluted and the EPA does not recommend the use of sealing alone to reduce radon because by itself sealing has not been shown to lower radon levels significantly or consistently 164 Positive pressure ventilation systems can be combined with a heat exchanger to recover energy in the process of exchanging air with the outside and simply exhausting basement air to the outside is not necessarily a viable solution as this can actually draw radon gas into a dwelling Homes built on a crawl space may benefit from a radon collector installed under a radon barrier a sheet of plastic that covers the crawl space 8 165 For crawl spaces the EPA states An effective method to reduce radon levels in crawl space homes involves covering the earth floor with a high density plastic sheet A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors This form of soil suction is called submembrane suction and when properly applied is the most effective way to reduce radon levels in crawl space homes 164 See also Edit Chemistry portalInternational Radon Project Lucas cell Pleochroic halo aka Radiohalo Radiation Exposure Compensation ActReferences Edit Haynes William M ed 2011 CRC Handbook of Chemistry and Physics 92nd ed Boca Raton FL CRC Press p 4 122 ISBN 1 4398 5511 0 Kondev F G Wang M Huang W J Naimi S Audi G 2021 The NUBASE2020 evaluation of nuclear properties PDF Chinese Physics C 45 3 030001 doi 10 1088 1674 1137 abddae a b c d e f g h Toxicological profile for radon Archived 2016 04 15 at the Wayback Machine Agency for Toxic Substances and Disease Registry U S Public Health Service In collaboration with U S Environmental Protection 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Jacobson J S Hershman D L Desai M Neugut A I 2008 Effect of breast cancer radiotherapy and cigarette smoking on risk of second primary lung cancer Journal of Clinical Oncology 26 3 392 398 doi 10 1200 JCO 2007 13 3033 PMID 18202415 Dauer L T Brooks A L Hoel D G Morgan W F Stram D Tran P 2010 Review and evaluation of updated research on the health effects associated with low dose ionising radiation Radiation Protection Dosimetry 140 2 103 136 doi 10 1093 rpd ncq141 PMID 20413418 Lagarde F Axelsson G Damber L Mellander H Nyberg F Pershagen G 2001 Residential radon and lung cancer among never smokers in Sweden Epidemiology 12 4 396 404 doi 10 1097 00001648 200107000 00009 JSTOR 3703373 PMID 11416777 S2CID 25719502 Risk Assessment of Radon in Drinking Water Nap edu 2003 06 01 Retrieved on 2011 08 20 Basic Information about Radon in Drinking Water Retrieved 2013 07 24 a b Wilkening Marvin H Clements William E 1975 Radon 222 from the ocean surface Journal of Geophysical Research 80 27 3828 3830 Bibcode 1975JGR 80 3828W doi 10 1029 JC080i027p03828 Baes Fred Answer to Question 10299 Submitted to Ask the Experts Health Physics Society Retrieved 2016 05 19 World Health Organization Radon and cancer fact sheet 291 a b Consumer s Guide to Radon Reduction How to fix your home EPA Retrieved 2010 04 03 Building radon out a step by step guide on how to build radonresistant homes DIANE Publishing p 46 ISBN 978 1 4289 0070 7 External links Edit Wikimedia Commons has media related to Radon Look up radon in Wiktionary the free dictionary Wikiversity has learning resources about Radon atom Radon and radon publications at the United States Environmental Protection Agency National Radon Program Services hosted by Kansas State University UK maps of radon Radon Information from Public Health England Frequently Asked Questions About Radon at National Safety Council Radon at The Periodic Table of Videos University of Nottingham Radon and Lung Health from the American Lung Association Radon s impact on your health Lung Association The Geology of Radon James K Otton Linda C S Gundersen and R Randall Schumann Home Buyer s and Seller s Guide to Radon An article by the International Association of Certified Home Inspectors InterNACHI Toxicological Profile for Radon Draft for Public Comment Agency for Toxic Substances and Disease Registry September 2008 Health Effects of Exposure to Radon BEIR VI Committee on Health Risks of Exposure to Radon BEIR VI National Research Council available on line UNSCEAR 2000 Report to the General Assembly with scientific annexes Annex B Exposures from natural radiation sources Should you measure the radon concentration in your home Phillip N Price Andrew Gelman in Statistics A Guide to the Unknown January 2004 Radon in the Home An Invisible Killer How serious can high levels of radon be in the home Kevin Vitali Retrieved from https en wikipedia org w index php title Radon amp oldid 1149252760, wikipedia, wiki, book, books, library,

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