/ reɪdɑːn /
Rn · atomic number 86
Prevedi radon na: francuski · nemački
Gaseous emanation of radium.
A radioactive gaseous element formed by the disintegration of radium; the heaviest of the inert gasses; occurs naturally (especially in areas over granite) and is considered a hazard to health; SYN. Rn, atomic number 86.
Colorless, odorless, gaseous, radioactive, nonmetallic element, symbol Rn, atomic number 86, atomic weight 222. It is grouped with the inert gases and was formerly considered non-reactive, but is now known to form some compounds with fluorine. Of the 20 known isotopes, only three occur in nature; the longest half-life is 3.82 days.
Radon is the densest gas known and occurs in small amounts in spring water, streams, and the air, being formed from the natural radioactive decay of radium. Ernest Rutherford discovered the isotope Rn-220 in 1899, and Friedrich Dorn (1848–1916) in 1900; after several other chemists discovered additional isotopes, William Ramsay and R W Whytlaw-Gray isolated the element, which they named niton in 1908. The name radon was adopted in the 1920s.
The average radon radiation level found in a study of 40 British limestone caves was 2,900 Bequerels per cubic meter. This compares with the National Radiological Protection Board's set level of 200 Bequerels per cubic meter, at which removal of radon from homes is recommended. The highest levels were found in the Giant's Hole in Derbyshire, with values of around 155,000 Bequerels per cubic meter during the summer, which is the highest level ever recorded from a natural limestone cave. This compares with a maximum level of 54,000 Bequerels per cubic meter found in a limestone cave in the US. Levels up to 2.8 million Bequerels per cubic meter were recorded in abandoned mines in SW England—14,000 times the NRPB action level for homes.