Radon

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In traces

1%

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90 %

In traces

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Radon [ ra ː dɔn, also: rado ː n] ( as radium from Latin radius, " ray", because of its radioactivity and Latin emanation " discharge " ) is a radioactive chemical element with the element symbol Rn and atomic number 86 in the periodic table it is in the 8 main group and is one of the noble gases.

All isotopes of radon are radioactive. The most stable isotope is 222Rn with a half-life of 3.8 days; it arises as a decay product of radium. Two other natural isotopes, 219Rn and 220Rn are sometimes referred to with their historical common name Actinon (An) and thoron (Tn ). In addition, radon has two other natural isotope, which almost never occur for various reasons in the Earth's atmosphere. Because the three relatively common isotopes of radon in homes ( as opposed to the natural environment ) can accumulate in poorly ventilated areas, they pose a health hazard and a significant radon exposure represents the main source of danger is not ultimately the radon itself, but its decay products, polonium isotopes which contribute most to exposure to alpha radiation. Radon has the total radiation levels on the surface of the earth by far the largest proportion ( average effective dose per person in Germany: about 1.1 mSv / year), followed by the direct terrestrial radiation of about 0.4 mSv / year, the direct cosmic radiation and occurring naturally in the food radioactive substances, each with about 0.3 mSv / year.

History

Radon was discovered in 1900 by Friedrich Ernst Dorn. Thorn called it radium emanation ( " from radium Going out "). 1908 insulated William Ramsay and Robert Gray Whytlaw a sufficient amount of gas to determine its density. Because it gave light in the dark, they called it Niton, after the Latin word nitens " bright ". In 1923, the names of radium emanation and Niton were replaced by the term radon.

Occurrence

On average, a radon atom is found in the Earth's atmosphere at 1021 molecules in the air. Radon is thus the rarest component of air. The sources of radon are in the rock and soil in existing traces of uranium and thorium, which decompose slowly. In the decay series radon is formed. This then diffuses from the uppermost soil layers in the atmosphere, the ground water in the basement, pipes, caves and mines. Radon from deeper soil layers does not reach the surface because it already breaks down on the way there.

Radon is therefore increasingly often in areas with high uranium and thorium content in the soil. These are mainly the low mountain range of granite rock, in Germany especially the Black Forest, the Bavarian Forest, the Fichtelgebirge and the Ore Mountains, in Austria the granite mountains in the forest district and Upper Austria. Here are primarily acidic and bright ( leukokrate ) rocks. Overall, radon comes in southern Germany, in much higher concentration than in northern Germany. In Switzerland, especially the Canton of Ticino is a pronounced radon Canton.

Some sources have a significant radon content, for example Bad Gastein, Bad Steben, Merano, Sibyllenbad, Menzenschwand, Bad Schlema, Bad Kreuznach, Bad Zell and Ischia in the Gulf of Naples. Bad Bramstedt has the Wettin source of the strongest, used for drinking cures radon source in the world.

Other places where radon is present in relatively high concentrations, in addition to uranium ore, fluorite or lead mines also laboratories and factories where uranium, radium and thorium are handled.

New studies point to a significantly increased 220Rn exposure in indoor air when walls of unbaked clay - are built or plastered - as in many half-timbered houses.

Properties

Like all noble gases, radon is chemically almost not reactive; only with fluorine it reacts to form radon fluoride. Under normal conditions, radon gas is colorless, odorless, tasteless; upon cooling below its melting point, it is bright yellow to orange. When filling in gas discharge tubes radon produces red light. Moreover, it is with 9.73 kg · m-3 is by far the densest elementary gas, apart from rare exotic hot diatomic astatine and iodine vapor.

Like its lighter group homologous xenon, radon is able to make real connections. It can be expected that these more stable and more varied than in xenon. The study of radon chemistry is very hampered by the high specific activity of radon, because the high-energy radiation self decomposition ( autoradiolysis ) leads the compounds. Chemistry with a weighable amounts of these substances is not possible. Ab initio and Dirac - Hartree-Fock calculations describe some properties of the not yet synthesized radon hexafluoride ( RNF6 ).

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

Use

In medical Radonbalneologie radon to stimulate the human immune system and thereby alleviate diseases. From a scientific perspective, the positive effect of radon has not been established. The radon passes through the inhalation of highly active radon-containing air or warm baths through the skin into the human organism. Under aspects of radiation protection, the additional radiation exposure caused by radon indeed small, but not negligible.

The Federal Environment Agency provides for the Radonbalneologie contraindications for the use in children and adolescents, and pregnant women.

In hydrology, the radon content of a water body can provide information on the groundwater supply. Rain water contains almost no radon, radon surface water is also almost free because merges into the atmosphere quickly radon from there. Groundwater, however, has radon levels that are orders of magnitude higher than those of surface waters. Therefore, a high content of radon in surface water is an indicator of the influence of groundwater.

In several countries, the earthquake prediction based on radon measurements. Slight tremors of the earth provide a faster propagation of the resulting radon gas in the soil than under normal conditions. In an underground chamber by the radon concentration increases measurably.

Radon measurements help in the search for uranium ore deposits. The size of the Radonexhalation, so the amount of radon gas escaping from the ground, depends on the radium content and the porosity of the substrate. During the Uranprospektion simple, passive radon measuring instruments working on the surface or close to be designed under on large areas. Above average measured values ​​indicative of higher uranium / radium concentrations and soil porosity and thus a possible deposit. There are geological processes that uranium and radium from the resulting separated. Therefore, the reference to uranium is not unique.

Isotopes

There are 34 and 4 Kernisomere isotopes of radon known, all are radioactive. The heaviest isotope of radon 229wurde 2008 at the CERN - ISOLDE isotope laboratory by bombarding uranium nuclei obtained with high-energy protons. Its half-life is 12 seconds.

In the three natural decay chains only the five isotopes 223Rn, 222Rn, 220Rn, 219Rn and 218Rn occur. One of the natural isotope is a beta emitter and four are alpha emitters. Will also result in the artificial neptunium series of alpha emitters 217Rn.

• Radon 223Rn produced in a side chain of the uranium - actinium series from the decay of radium 227Ra, which itself arises only with a probability of 0.000001 % of thorium 231Th. It is so rare that it almost does not occur in the Earth's atmosphere. Radon 223Rn decays with a half-life of 23.2 minutes through beta radiation in francium 223Fr. Radiologically, it is meaningless due to its rarity and the short half-life.

• Radon 222Rn decay product of radium is the isotope 226Ra in the uranium - radium series. It is the most stable isotope of radon and decays with the emission of alpha particles with a half -life of 3.823 days to polonium 218Po. If radiation protector of radon speak without further designation, they mean 222Rn. Widely applied (eg radon measurement), the term also includes the short-lived decay products.

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

• Radon 219Rn is a decay product of radium 223Ra in the uranium - actinium series, and also carries the designation Actinon. Its half-life of 3.96 seconds; it also decays with the emission of alpha particles to polonium 215Po. Radiologically, it is virtually meaningless.

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

• Radon 217Rn produced in a side chain of the neptunium series from the decay of radium 221Ra, the radium itself arises only with a probability of 0.1 % of francium 221Fr. The remaining 99.9 % of 221Fr decays to astatine 217At, which also decays with 0.01 % probability of radon 217Rn. The radon isotope, therefore, arises in two ways in a small amount in the neptunium series. Radon 217Rn decays with a half -life of only 54 milliseconds with the emission of alpha particles in polonium 213Po. It comes naturally because of the extremely short half-life practically non-existent and is therefore completely meaningless.

Extraction

If the above radioactive substances to radon decay, this can outgas. In a laboratory can be escaping from a sample radon field, separated by liquefying the residual air. The decay of one gram of radium 226Ra arise 0.64 cm3 radon 222Rn per month.

Safety

Classifications according to the Hazardous Substances Ordinance are not available because they only include the chemical hazard, which does not occur in noble gases. Important are the based on the radioactivity hazards.

According to studies by the World Health Organization, the incidence of lung cancer increases significantly with radiation levels of 100-200 Bq per cubic meter of air. The probability of cancer increases with the increase after each further 100 Bq/m3 in the air by 10%.