Radon is a natural radioactive noble-gas, that at the spontaneous radioactive disintegration in the ground of uranium 238 over Thorium, Protactinium, uranium 234, Thorium and radium 226 [2 page 72] originates and at the air escapes. It can practically throughout different concentrations , but also in mineral construction-materials occurs. The radon-concentration in buildings can originate through different sources, predominantly from the natural Radonausgasung of the ground. [2, page 71] [5, page 158] the concentration is in the house-inside always somewhat higher than outside, where she/it lies between 8 to 23 Bq/m3 air and the values of north to south increase. 
On average, the radioactivity is in the apartment opposite outside about 15 per cent higher. Especially then, if much pumice, chemistry-plaster, for the walls or decks, Cinders-materials and/or granite were used [3, page 12] some higher values became 1984 in examinations of barely 6000 apartments 40Bq/m3 in 50 per cent of the accomodations, in 10 per cent more highly 80 Bq/m3, measured more than 220 Bq/m3 and in 10 dwellings more than 500 Bq/m3 1 per cent.  at that time recommended limiting value the International radiation-protection-commission fee for the interior-air for old buildings with 200 and for new constructions with 100 Bq/m3 as allowable.
in 1991, an examination of the Bavarian department of the environment in the upper-Palatine nine-castle before the forest in the winter, if is aired less than in the summer, with average values of 415 Bq/m3 in 50 per cent of the examined apartments took place. The values were especially high in older buildings with the construction-materials, wood, clay and nature-stone with "natural" cellar-grounds. 
4200 people became in the study of the Karolinska college in Stockholm about radon and lung-cancer, from it 1350 at lung-cancer sickened, included. The radon-concentrations were measured in 9000 present and former apartments. It became covered a cancer-part payment 1,3-fold at the activity of radon with 50 Bq/m3 of 140 to 400 Bq/m3 about this in the result and determined 1,8-fold with over 500 Bq/m3 about this. 
The Federal office for radiation-protection (BfS) was involved at a throughout Europe implemented epidemiological study promoted by the European commission fee about lung-cancer and radon in lounges, that 2005 will publish. "Radon causes annually approximately with it 20.000 lung-cancer-fatalities (if cirka corresponds 9 per cent of all lung-cancer-cases) in the European union, from it for example 3.000 in Germany. It was observed that people, who live in spaces with radon-concentrations between 100 and 200 Bq/m3 space-air, a lung-cancer-risk higher by 20 percent, as people, has that in spaces with values below from 100 Bq/m3 lives. Consequently, a statistically significantly elevated lung-cancer-risk is available even below the radon-concentrations of 200 Bq/m3." 
The average interior-encumbrance is about 50 Bq/m3, cirka 3/4 comes out of the used construction-materials from it.  strongly elevated radon-concentration in lounges depends beside the geological conditions (construction-underground) as well as from further elements, density of the foundation and the foundation-plate respectively, basement, ventilation-habits, and so on.). She/it can be determined reliably only by measurement.
Already with simple measures like one wall-insulations or additional ventilation can be reduced the radon-concentration in lounges considerably. 
In Sweden, an increase of the dose 110 mrem was determined in strongly heat-dammed apartments until on 380 mrem. (Every radioactive radiation, whether of course or artificially, is live-hostile. [Prof. Fritz-Niggli] commendable therefore is an air-change of 2 until 3. [3 pages 17] particularly in badly aired spaces, as during the vacation or empty houses with locked doors and window menus, the radioactivity rises quickly and gains high values. 
In the table 1 is presented selected construction-materials. One recognizes a wide fluctuation-width, with what sand, limestone and nature-plaster comprise radioactive materials more inferior volumes. But also the location is crucial, became on the heath-grounds of the Lechfeldes, for example, south of Augsburg 3-12 μR /hour so or in the Fichtelgebirge, bath Berneck 15,8-18,9 μR /hour or measured on the clay-grounds northwest of Dachau 13,4-22,7 μR /hour
Table 1: Natural radioactive materials in construction-materials [Nanocurie / kg] [3, pages 9-10]
After the present-day condition of the realization, radon is after the smoke the second-most frequent cause of lung-cancer and by far the most important individual environment-influential factor on the human health. [1 and 4] especially dangerously is the combined effect of radon and smoking. [1 and 2] the tobacco-plants depletes beside the remaining cancer-poisons, radium, radon and her/its/their disintegration-products at.
The health effect of radon becomes like follows described. Originate one after the other another number of wider more short-lived, radioactive material, that reaches into the breath-air, at the radiaktiven disintegration (half-life 3,82 days). By the radon, the alpha-particle (helium-atomic nucleus) is emitted, which not very energy-richly, but the biggest action-cross section of all radioactive disintegration-products has.
Outside the human body, there is hardly an endangering. But in the lung, radon and its already above named carry disintegration-products short-lived, as Polonium, Bismut and lead, the radioactive isotopes to the general radiation-encumbrance with.  in the air takes up the heavy metals at the walls or furniture as well as at the fine-dust-particles (aerosol) (85-90 per cent) hovering in the air for itself. Form the free share the residual 10 per cent. Radon, that free and aerosol-bound heavy metals camp, itself when inhaling differently in the lung from.  a provision of the radiation-dose is through the consideration of the individual elements, that up to the duration of stay or meteorological data input hands, very complicates.
Spas and mineral water with radon (it then are salvation-waters from deep wells already 37000 Bq per liter) are used for the stimulation of the defense-strengths of the body, therefore is not damaging but serves the medical treatment. It depends much more on the dose and the long-time-impact. A workroom in the cellar therefore doesn't represent any problem.
The attempt to influence on an as low as possible radon-encumbrance at the new construction through the drawing selection of suitable lots is restricted through the real estate market. One can meet counter-measures and provision respectively through dense concrete-plate-foundations and no lounges or even accomodations in the basement or basement. This already is more difficult in the stock. But the simplest method is the sufficient and regular ventilation.
The heat-protection-regulation 95 admitted another air-change of 0,8 per hour, in the sense of the saving of energy in the EnEV varies the air-change-part payments between 0,45 and 0,6 /hour in compartment-balances brought forward even air-change-part payments were proposed by 0,2 to 0,3 /hour 
If one looks at the arbitrated values in the above named studies, so derives very easily leaves itself that also the permanent radon-concentration increases itself with every reduction of the air-change so and leads also to a higher lung-cancer-risk consequently. How the increase can be big, is shown in the above named examination of the Bavarian department of the environment. It should also be mentioned, however, that also the spore-encumbrance of mold just as with the always smaller expectant mandatory ventilation-part payment or other germination, dust-shares and chemical materials respectively material-mixture in the accomodations to takes that just as healths consequences can cause according to type and her/its/their interaction as material-mixture.
A sufficient and regular ventilation, about a lowering of this radon - and the other pollutant-concentration to reach and to keep to such a very low risk, is stopped by the determinations of the Energieeinsparverordnung, however.
A recommending contribution to the radiation and kernel-energy from Mr. Dr things. Böttiger.
Chemical & physical qualities:
Occurrences: in the air
Group-affiliation: VIII - noble-gas
Siedetemperatur: 211 K / -62ºC
Schmelztemperatur:202 K / -71ºC
Write poetry with 1013 mbar: 9,23 g/l
Kovalenter atom-radius: 222 pm
First ionization-energy: 10,75 eV
Electron-configuration: [Xe] 4f145d106s26p6
Number valence-electrons: 8
Number peels: 6
 Anja Schröder; Radon is second-most frequent cause of lung-cancer, information-service science from the 2.4.05 http://idw-online.de/pages/de/news99103
 Diel, Friedhelm; Interior encumbrances, recognizes, assesses, restores, contribution of the INC. ecological research-institute, construction-publishing house Wiesbaden 1993, S. 71ff
 institute for construction-biology, healthy living 1980 S. 3,9-10,12,17
 Daunderer, Max; Poison in the everyday life 1. Aufl., C.H. Beck series 1999, S. 158-160, 168
 Schwankner, Robert J.; arcus 1986 notebook 6
 federal-health-leaf 29, number. 3 March 1986
 smoke, Peter; The ventilation-replacement in a building www.ib-rauch.de / deliberation / luften.html