radon

This article deals with the chemical element radon. For more meanings, see Radon (disambiguation) .

properties
[ Xe ] 4 f 14 5 d 10 6 s 2 6 p 6 86 para Periodic table
General
Name , symbol , atomic number	Radon, para. 86
Element category	Noble gases
Group , period , block	18 , 6 , p
Appearance	colorless
CAS number	10043-92-2
EC number	233-146-0
ECHA InfoCard	100.030.120
Mass fraction of the earth's envelope	6.1 · 10 −11  ppm
Atomic
Atomic mass	222 u
Covalent radius	150 pm
Van der Waals radius	220 pm
Electron configuration	[ Xe ] 4 f 14 5 d 10 6 s 2 6 p 6
1. Ionization energy	10.74850 eV ≈ 1 037.07 kJ / mol
2. Ionization energy	21st.4 (1.9) eV ≈ 2 060 kJ / mol
3. Ionization energy	29.4 (1.0 eV) ≈ 2 840 kJ / mol
4. Ionization energy	36.9 (1.7) eV ≈ 3 560 kJ / mol
5. Ionization energy	52.9 (1.9) eV ≈ 5 100 kJ / mol
Physically
Physical state	gaseous
Crystal structure	Cubic area-centered
density	9.73 kg m −3
magnetism	diamagnetic
Melting point	202 K (−71 ° C)
boiling point	211.3 K (−61.8 ° C)
Molar volume	(solid) 50.50 · 10 −6 m 3 · mol −1
Heat of evaporation	16.4 kJ / mol
Heat of fusion	2.89 kJ mol −1
Thermal conductivity	0.00364 W m −1 K −1
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP 210 para {syn.} 2.4 h α 6.159 206 Po ε 2,374 210 at 211 para {syn.} 14.6 h ε 2,892 211 at α 5.965 207 Po 212 para {syn.} 23.9 min α 6.385 208 Po ... ... ... ... ... ... 217 para {syn.} 0.54 ms α 7,889 213 Po 218 para in traces 35 ms α 7.263 214 Po 219 para 1 % 3.96 s α 6,946 215 Po 220 para 9% 55.6 s α 6.405 216 Po 221 para {syn.} 25.0 min β - 221 Fr α 217 Po 222 para 90  % 3.824 d α 5,590 218 Po 223 para {syn.} 24.3 min β - 2.007 223 Fr 224 para {syn.} 107 min β - 224 Fr
For other isotopes see list of isotopes
Hazard and safety information
Radioactive
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Radon [⁠ ʁaːdɔn ⁠] , also: [⁠ ʁadoːn ⁠] (such as radium because of its radioactivity of Latin radius "beam") is a radioactive chemical element with the element symbol Rn and atomic number  86. In the periodic table , it is in of the 8th  main group or the 18th  IUPAC group and is therefore one of the noble gases (hence the ending -on as an analogy).

All isotopes of radon are radioactive. The most stable - and at the same time naturally occurring - isotope is ²²² Rn with a half-life of 3.8 days; it arises as a decay product from the radium isotope ²²⁶ Ra. Two other natural isotopes, ²¹⁹ Rn and ²²⁰ Rn, are sometimes referred to by their historical trivial names actinon (An) and thoron (Tn), respectively. The fourth natural isotope ²¹⁸ Rn does not play a quantitative role in comparison to the three aforementioned.

Since radon can accumulate in houses (in contrast to the natural environment) in poorly ventilated rooms, it represents a health hazard and considerable radon pollution. Ultimately, the main source of danger is not radon itself, but its decay products, with polonium isotopes contribute most to exposure to alpha radiation. Radon has by far the largest share of the total amount of radiation on the earth's surface (average effective dose per person in Germany: about 1.1  mSv / year), followed by direct terrestrial radiation with about 0.4 mSv / year, the direct cosmic radiation Radiation and the radioactive substances naturally occurring in food, each with around 0.3 mSv / year.

history

With his publication from 1899, Ernest Rutherford is considered the discoverer of radon. Friedrich Ernst Dorn , who is also often credited with the discovery, quotes Rutherford's results in his work from 1900.

In 1909, William Ramsay and Robert Whytlaw-Gray isolated a sufficient amount of the gas to determine its melting point and density . The radioactive gas was initially called radium emanation (" emanating from radium"). Because it gave off light in the dark, it was also called niton in literature , after the Latin word nitens "shining".

In 1923 the terms radium emanation and niton were replaced by the term radon .

Occurrence

On average there is one radon atom in the earth's atmosphere for every 10 ²¹ molecules in the air . The sources of radon are traces of uranium and thorium in the rock and in the soil , which slowly decay. Radon is formed in their decay series . This then diffuses from the uppermost soil layers into the atmosphere, into the groundwater , into cellars, pipelines, caves and mines. Radon from deeper layers of the earth does not reach the surface, as it decays on the way there.

For this reason, radon occurs more frequently in areas with high levels of uranium and thorium in the soil. These are mainly the low mountain ranges made of granite rock , in Germany especially the Black Forest , the Bavarian Forest , the Fichtel Mountains and the Ore Mountains , in Austria the granite mountains in the Waldviertel and Mühlviertel . Acid and light-colored ( leucocrate ) rocks are mainly found here . Overall, radon occurs in significantly higher concentrations in southern Germany than in northern Germany. In Switzerland, the canton of Ticino in particular is a pronounced radon region; in Belgium it is the eastern and south-eastern part. (see Limburg coal district )

Some springs have a significant proportion of radon, for example Bad Gastein , Bad Kreuznach , Bad Schlema , Bad Steben , Bad Zell , Ischia in the Gulf of Naples, Menzenschwand , Meran , Sibyllenbad and Umhausen in the Ötztal . With the Wettin spring, Bad Brambach has the most powerful radon spring in the world used for drinking cures.

Other places where radon occurs in relatively high concentrations are, in addition to uranium ore, fluorspar or lead mines and heaps and sedimentation basins of uranium mining, laboratories and factories in which uranium, radium or thorium are handled.

properties

Like all noble gases , radon is almost non-reactive chemically; it reacts with fluorine to form radon difluoride , whether compounds with oxygen have been observed is a matter of dispute . Under normal conditions , radon gas is colorless, odorless, tasteless; on cooling below its melting point, it turns bright yellow to orange. When filled in gas discharge tubes , radon generates red light. In addition, at 9.73 kg · m ^{−3, it} is by far the densest elementary gas, if one disregards the exotic and rare astatine and hot diatomic iodine vapor.

Like its lighter group-homologous xenon , radon is able to form real compounds. It can be expected that these are more stable and diverse than with xenon. The study of radon chemistry is hindered by the high specific activity of radon, because the high-energy radiation leads to self-decomposition (autoradiolysis) of the compounds. A chemistry with weighable amounts of these substances is therefore not possible. Ab initio and Dirac-Hartree-Fock calculations describe some properties of the not yet synthesized radon hexafluoride (RnF ₆ ).

As a radioactive gas with a very high density, radon can accumulate in buildings, especially in basements and the lower floors, in physiologically significant amounts. In more recent measurements, if building materials such as unfired clay were used in buildings, larger amounts of radon were also found on the upper floors.

The solubility of the isotope Rn-222 in water is 259 ml / l at 20 ° C and 101.325 kPa.

meaning

The healing radon , advertisement of the Saxon state baths in Bad Elster . With the Wettin spring, Bad Brambach has a water spring with a particularly high radon content worldwide.

In medical radon balneology , radon is said to stimulate the human immune system and thereby alleviate diseases. From a scientific point of view, no positive effects of radon can be proven. Radon enters the human organism through the inhalation of highly active radon-containing air or in baths through the skin. In terms of radiation protection, the additional radiation exposure from radon is low, but not negligible. The Federal Environment Agency sees contraindications for radon balneology for use in children, adolescents and pregnant women.

In hydrology , the radon content of a body of water can provide information about its groundwater supply. Rainwater contains almost no radon, and surface water is also almost radon-free, since radon is quickly released into the atmosphere from there. Groundwater, on the other hand, has radon concentrations that are orders of magnitude higher than those of surface water. Therefore, a high level of radon in surface water is an indicator of the influence of groundwater.

In several countries the earthquake forecast is also based on radon measurements . Slight vibrations in the ground ensure that the radon gas produced in the ground spreads faster than under normal conditions. As a result, the radon concentration rises measurably in underground cavities.

Radon measurements help in the search for uranium ore deposits . The size of the radon exhalation , i.e. the amount of radon gas escaping from the soil, depends on the radium content and the porosity of the subsoil. During uranium prospection, simple, passively working radon measuring devices are laid out on the earth's surface or just below it in large areas. Above-average measured values ​​indicate higher uranium / radium concentrations and soil porosity and thus a possible deposit. There are geological processes that separate uranium and the radium produced from it. Therefore the reference to uranium is ambiguous.

Isotopes

There are 34 known isotopes and 4 nuclear isomers of radon, all of which are radioactive. The heaviest radon isotope to date ²²⁹ was obtained in 2008 in the CERN isotope laboratory ISOLDE by bombarding uranium nuclei with high-energy protons. Its half-life is 12 seconds.

In the three natural chains of decay only the four isotopes ²²² Rn, ²²⁰ Rn, ²¹⁹ Rn and ²¹⁸ Rn occur, which are all alpha emitters. In addition, the alpha emitter ²¹⁷ Rn is created in the now artificial neptunium series .

• Radon ²²² Rn is the decay product of the radium isotope ²²⁶ Ra in the uranium-radium series . It is the most stable isotope of radon and, with the emission of alpha particles, breaks down to polonium ²¹⁸ Po with a half-life of 3.823 days . When radiation protectionists speak of radon without any further designation, they mean ²²² para. Generally used (e.g. radon measurement), the term also includes short-lived decay products.

• Radon ²²⁰ Rn is a decay product of radium ²²⁴ Ra in the thorium series . Radiation guards often refer to it as a thoron. Its half-life is 55.6 seconds; it also disintegrates with the emission of alpha particles to form Polonium ²¹⁶ Po. It can be emitted from unfired clay in buildings. In terms of radiation exposure, it can be very important, since with the same activity concentration as ²²² Rn from the ²²⁰ Rn secondary products (especially polonium), a 14-fold higher radiation exposure must be observed.

• Radon ²¹⁹ Rn is a decay product of Radium ²²³ Ra in the uranium-actinium series and is also called actinone. Its half-life is 3.96 seconds; it also disintegrates with the emission of alpha particles to polonium ²¹⁵ Po. Radiologically it is practically meaningless.

• Radon ²¹⁸ Rn is formed in a side chain of the uranium-radium series during the decay of astatine ²¹⁸ At with a probability of 0.1%, the astatine itself is only produced with a probability of 0.02% from polonium ²¹⁸ Po. Radon ²¹⁸ Rn decays with a half-life of only 35 milliseconds with the emission of alpha particles in Polonium ²¹⁴ Po. Due to its extremely short half-life, it has practically no time to get into the earth's atmosphere. It is therefore meaningless radiologically.

• Radon ²¹⁷ Rn is formed in a side chain of the neptunium series when the radium ²²¹ Ra decays , the radium itself is only formed with a probability of 0.1% from Francium ²²¹ Fr. The remaining 99.9% of the ²²¹ Fr decays to Astat ²¹⁷ At , which also decays to Radon ²¹⁷ Rn with a probability of 0.01% . The radon isotope therefore arises in two ways in small quantities in the Neptunium series. Radon ²¹⁷ Rn decays with a half-life of only 54 milliseconds with the emission of alpha particles in Polonium ²¹³ Po. Of course, because of its extremely short half-life, it practically does not occur and is therefore completely meaningless.

Extraction

If the radioactive substances mentioned above break down to form radon, it can outgas. Radon escaping from a sample can be captured in a laboratory and separated from the remaining air by liquefying it. When one gram of radium ²²⁶ Ra decays , 0.64 cm³ of radon ²²² Rn is produced per month.

safety instructions

Classifications according to the CLP regulation are not available because they only include chemical hazards that do not occur with noble gases. The dangers based on radioactivity are important .

According to studies by the World Health Organization , the incidence of lung cancer from radon in indoor air increases linearly, the long-term limit recommended by the WHO is 100  Bq per cubic meter of indoor air. The probability of lung cancer increases approximately with an increase of 100 Bq / m³ in the room air by 10%.

In 2018, radon measurements were carried out in 3,400 residential properties in the federal state of Salzburg in Austria and it was determined that a limit of 300 Bq per cubic meter of air was exceeded in 10% of the apartments.

See also

• Radon decay products
• Radon protection

literature

• AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , pp. 417-429.
• Henning von Philipsborn: Radon and radon measurement. Part I. In: Die Geoswissenschaften , 8, 1990, 8, pp. 220–228, doi: 10.2312 / geoswissenschaften.1990.8.220 . Part II. In: Die Geoswissenschaften, 8, 1990, 10, pp. 324–338, doi: 10.2312 / geoswissenschaften.1990.8.324 .

Web links

Commons : Radon  - collection of images, videos and audio files

Wiktionary: Radon  - explanations of meanings, word origins, synonyms, translations

• Radon (UmweltWissen - Bavarian State Office for the Environment ; PDF file; 377 kB)
• Radon at the Federal Office for Radiation Protection
• Interactive radon presentation , State Office for Geology and Mining Rhineland-Palatinate
• Press release of the Federal Environment Ministry from June 19, 2007 on the effects of radiation on humans and the like. a. from radon-related lung cancer (around 1,800 deaths from radon in Germany every year)
• Basics, metrology and measured variables on the subject of radon. Physikalisch-Technische Bundesanstalt (PTB)
• Radon at the Federal Office of Public Health

Individual evidence

1. ^ Harry H. Binder: Lexicon of the chemical elements , S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. ↑ The values ​​for the properties (info box) are taken from www.webelements.com (Radon) , unless otherwise stated .
3. ↑ Manjeera Mantina, Adam C. Chamberlin, Rosendo Valero, Christopher J. Cramer, Donald G. Truhlar: Consistent van der Waals Radii for the Whole Main Group. In: J. Phys. Chem. A. 2009, 113, pp. 5806-5812, doi: 10.1021 / jp8111556 .
4. ↑ ^{a b c d e} Entry on radon in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 13, 2020.
5. ↑ ^{a b c d e} Entry on radon at WebElements, https://www.webelements.com , accessed on June 13, 2020.
6. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Properties of the Elements and Inorganic Compounds, pp. 4-69.
7. ↑ The hazards emanating from radioactivity do not belong to the properties to be classified according to the GHS labeling. With regard to other hazards, this element has either not yet been classified or a reliable and citable source has not yet been found.
8. ^ Ernest Rutherford, Robert Bowie Owens: Thorium and Uranium Radiation . In: Trans. R. Soc. Can. tape 2 , 1899, pp. 9-12 .
9. ↑ Ernst Dorn: About the emanation emitted by radioactive substances. In: Treatises of the Natural Research Society in Halle . Volume 23, 1901, pp. 1–15 urn : nbn: de: hebis: 30-1090447 .
10. ↑ James L. Marshall, Virginia R. Marshall: Ernest Rutherford, The "True Discoverer" of Radon . In: Bull. Hist. Chem. Band 28 , 2003, p. 76-83 .
11. ^ Robert Whytlaw Gray, sir. William Ramsay: Some Physical Properties of Radium Emanation . In: J. Chem. Soc. Trans. Band 95 , 1909, pp. 1073-1085 .
12. ↑ ^{a b c} Klaus Hoffmann: Can you make gold? Crooks, jugglers and scholars. From the history of the chemical elements . Urania-Verlag, Leipzig / Jena / Berlin 1979, no ISBN, p. 67.
13. ^ FW Aston, GP Baxter, B. Brauner, A. Debiernem A. Leduc, TW Richards, F. Soddy, G. Urbain: Report of the international committee on chemical elements . In: J. Am. Chem. Soc. tape 45 , 1923, pp. 867-874 .
14. ↑ Annual report 2004 of the Radiation Protection Department of the Swiss Federal Office of Public Health , p. 15.
15. ↑ Federal Agency for Nuclear Control : Homepage ( Memento of the original from September 24, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . 
16. ↑ Peter Hacker, Wolfram Mostler: Radon in the outer Ötztal - geological aspects . (PDF; 555 kB) Lecture on October 14, 1999.
17. ↑ Ulrich Koch, Jens Heinicke: The Bad Brambacher mineral springs. Hydrogeology, genesis and seismohydrological features. ( Memento of the original from February 25, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) accessed on November 24, 2014. 
18. ↑ M. Schläger, Kh. Murtazaev, B. Rakhmatuloev, P. Zoriy, B. Heuel-Fabianek: Radon Exhalation of the Uranium Tailings Dump Digmai, Tajikistan . In: Radiation & Applications , Volume 1, No. 3, 2016, pp. 222–228, doi: 10.21175 / RadJ.2016.03.041 .
19. ^ Sykes group: Recent Advances in Noble-Gas Chemistry . In: Advances in Inorganic Chemistry , Volume 46. Academic Press, 1998, ISBN 978-0-12-023646-6 , pp. 91-93 (accessed November 2, 2012).
20. ↑ Michael Filatov, Dieter Cremer: Bonding in Radon Hexafluoride: An Unusual Relativistic Problem? In: Phys. Chem. Chem. Phys. , 2003, 5 'pp. 1103-1105, doi: 10.1039 / b212460m .
21. ^ ^{A b} Holger Dambeck: Researchers warn of radiation in mud houses . Spiegel Online , April 18, 2012; Retrieved April 19, 2012.
22. ↑ IUPAC Solubility Data Series , 1979, Vol. 2, p. 228
23. ↑ The healing radon. Retrieved December 22, 2017 . 
24. ^ A. Erzberger, E. Schwarz, T. Jung: Radon balneology. In: Federal Office for Radiation Protection (Ed.): Environmental Medical Information Service. No. 3, 2000, p 9, ISSN  1862-4189 , umweltbundesamt.de (PDF).
25. ↑ Deutschlandfunk, Research News: The Oracle in Abruzzo , January 20, 2009.
26. ↑ D. Neidherr, G. Audi, D. Beck, K. Blaum, Ch. Böhm, M. Breitenfeldt, RB Cakirli, RF Casten, S. George, F. Herfurth, A. Herlert, A. Kellerbauer, M. Kowalska , D. Lunney, E. Minaya-Ramirez, S. Naimi, E. Noah, L. Penescu, M. Rosenbusch, S. Schwarz, L. Schweikhard, T. Stora: Discovery of ²²⁹ Rn and the Structure of the Heaviest Rn and Ra Isotopes from Penning-Trap Mass Measurements , in: Phys. Rev. Lett. , 2009 , 102 , 112501, doi: 10.1103 / PhysRevLett.102.112501 .
27. ↑ Accurate measurement of radioactive thoron. (July 2011): "For the risk assessment, the exact measurement (of thoron) is very important, because with the same activity concentration, the radiation exposure of the thoron-derived products is 14 times higher than that of the secondary products of radon."
28. ↑ radon in webelements.com
29. ↑ PDF from the Federal Environment Ministry ( memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. . 
30. ↑ Radon levels increased in every tenth apartment orf.at, June 23, 2018, accessed on June 23, 2018.