<P> In 1910, Ramsay and Robert Whytlaw - Gray isolated radon, determined its density, and determined that it was the heaviest known gas . They wrote that "L'expression de l'émanation du radium est fort incommode", (the expression' radium emanation' is very awkward) and suggested the new name niton (Nt) (from the Latin "nitens" meaning "shining") to emphasize the radioluminescence property, 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 Rn and An was renamed Rn, which 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 . As late as the 1960s, the element was also referred to simply as emanation . The first synthesized compound of radon, radon fluoride, was obtained in 1962 . Even today, the word radon may refer to either the element or its isotope Rn, with thoron remaining in use as a short name for Rn to stem this ambiguity . </P> <P> The danger of high exposure to radon in mines, where exposures can reach 1,000,000 Bq / m, 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). In 1879, this condition was identified as lung cancer by Herting 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 . In the US, studies and mitigation only followed decades of health effects on uranium miners of the Southwestern United States employed during the early Cold War; standards were not implemented until 1971 . </P> <P> 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 United States, 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 . </P> <P> All discussions of radon concentrations in the environment refer to Rn . While the average rate of production of Rn (from the thorium decay series) is about the same as that of Rn, the amount of Rn in the environment is much less than that of Rn because of the short half - life of Rn (55 seconds, versus 3.8 days respectively). </P>

The time to lower the concentration of the gas to 37 of its original amount is its