   #copyright

Radon

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


               86                astatine ← radon → francium
               Xe
               ↑
               Rn
               ↓
               Uuo

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                        Name, Symbol, Number radon, Rn, 86
                                               Chemical series noble gases
                                             Group, Period, Block 18, 6, p
                                                      Appearance colorless
                                                   Atomic mass (222) g/mol
                         Electron configuration [Xe] 4f^14 5d^10 6s^2 6p^6
                                   Electrons per shell 2, 8, 18, 32, 18, 8
                                                       Physical properties
                                                                 Phase gas
                                              Density (0 °C, 101.325 kPa)
                                                                  9.73 g/L
                                                      Melting point 202  K
                                                   (-71.15 ° C, -96 ° F)
                                                     Boiling point 211.3 K
                                                 (-61.85 ° C, -79.1 ° F)
                                            Critical point 377 K, 6.28 MPa
                                         Heat of fusion 3.247 kJ·mol^−1
                                   Heat of vaporization 18.10 kJ·mol^−1
                         Heat capacity (25 °C) 20.786 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                          P/Pa   1  10  100 1 k 10 k 100 k
                                         at T/K 110 121 134 152 176   211

                                                         Atomic properties
                                     Crystal structure cubic face centered
                                                        Oxidation states 0
                                 Electronegativity no data (Pauling scale)
                                      Ionization energies 1st: 1037 kJ/mol
                                              Atomic radius (calc.) 120 pm
                                                    Covalent radius 145 pm
                                                             Miscellaneous
                                            Magnetic ordering non-magnetic
                      Thermal conductivity (300 K) 3.61 mW·m^−1·K^−1
                                            CAS registry number 10043-92-2
                                                         Selected isotopes

                  CAPTION: Main article: Isotopes of radon

                             iso    NA  half-life   DM    DE ( MeV)   DP
                            ^211Rn syn  14.6 h    Epsilon 2.892     ^211At
                                                  Alpha   5.965     ^207Po
                            ^222Rn 100% 3.824 d   Alpha   5.590     ^218Po

                                                                References

   Radon ( IPA: /ˈreɪdɒn/) is a chemical element in the periodic table
   that has the symbol Rn and atomic number 86. A radioactive noble gas
   that is formed by the disintegration of radium, radon is one of the
   heaviest gases and is considered to be a health hazard. The most stable
   isotope is ^222Rn which has a half-life of 3.8 days and is used in
   radiotherapy. Radon gas can accumulate in buildings, and drinking
   water, and cause lung cancer , causing potentially 20,000 deaths in the
   European Union each year, with an estimated 20,000 additional deaths
   per year in the US. Radon is a significant contaminant that impacts
   indoor air quality worldwide.

Notable characteristics

   Essentially chemically inert, but radioactive, radon is the heaviest
   noble gas and one of the heaviest gases at room temperature. (The
   heaviest known gas is Uranium hexafluoride, UF[6].) At standard
   temperature and pressure radon is a colorless gas, but when it is
   cooled below its freezing point (202K ; -71°C ; -96°F) it has a
   brilliant phosphorescence which turns yellow as the temperature is
   lowered, and becomes orange- red at the temperatures air liquefies
   (below 93K ; -180°C).

   Natural radon concentrations in Earth's atmosphere are so low that
   radon-rich water in contact with the atmosphere will continually lose
   radon by volatilization. Hence, ground water has a higher concentration
   of ^222Rn than surface water. Likewise, the saturated zone of a soil
   frequently has a higher radon content than the unsaturated zone due to
   diffusional losses to the atmosphere.

Applications

   In the United States and Europe there are a few "radon spas," where
   people sit for minutes or hours in a high-radon atmosphere in the
   belief that airborne radiation will invigorate or energize them. The
   same applies to the hot water spas of Misasa, Tottori, Japan, where
   water is naturally rich in radium and exhales radon. There is no
   scientific evidence for this belief, except possibly radiation
   hormesis, nor any known biological mechanism by which such an effect
   could occur.

   Because of radon's rapid loss to air and comparatively rapid decay,
   radon is used in hydrologic research that studies the interaction
   between ground water, streams and rivers. Any significant concentration
   of radon in a stream or river is a good indicator that there are local
   inputs of ground water.

   Radon accumulates in underground mines and caves. Good ventilation
   should therefore be maintained in mines, and in some countries, guides
   in tourist caves are classified as "radiation workers", whose time of
   exposure is monitored. Tourism of caves is not generally considered a
   significant hazard for the relatively brief visits by members of the
   general public.

   Some researchers have looked at elevated soil-gas radon concentrations,
   or rapid changes in soil radon concentrations, as a predictor for
   earthquakes. Results have been generally unconvincing but may
   ultimately prove to have some limited use in specific locations.

   Radon soil-concentration has been used in an experimental way to map
   close-subsurface geological faults, because concentrations are
   generally higher over the faults. Similarly it has found some limited
   use in geothermal prospecting.

   Radon is a known pollutant emitted from geothermal power stations,
   though it disperses rapidly, and no radiological hazard has been
   demonstrated in various investigations. The trend in geothermal plants
   is to reinject all emissions by pumping deep underground, and this
   seems likely to ultimately decrease such radon hazards further.

   Radon emanation from the soil varies with soil type and with surface
   uranium content, so outdoor radon concentrations can be used to track
   air masses to a limited degree. This fact has been put to use by some
   atmospheric scientists.

   Although some physicians once believed that radon can be used
   therapeutically, there is no evidence for this belief and radon is not
   currently in medical use, at least in the developed world.

   Radon has also been used to remove tumors. A capsule is placed in the
   patient near the tumor where the radiation will kill the cancerous
   cells. The surrounding cells are safe because of the short half-life of
   radon.

History

   Radon (named after radium) was discovered in 1900 by Friedrich Ernst
   Dorn, who called it radium emanation. In 1908 William Ramsay and Robert
   Whytlaw-Gray, who named it niton (Latin nitens meaning "shining";
   symbol Nt), isolated it, determined its density and that it was the
   heaviest known gas. It has been called “radon” since 1923.

   The first major studies of the health concern occurred in the context
   of uranium mining, first in the Joachimsthal region of Bohemia and then
   in the American Southwest during the early Cold War. Because radon is a
   daughter-product of uranium, uranium mines have high concentrations of
   radon and its highly radioactive daughter products. Many Native
   Americans, Mormons, and other miners in the Four Corners region would
   later contract lung cancer and other pathologies as a result of high
   levels of exposure to radon gas while mining uranium for the Atomic
   Energy Commission in the mid-1950s. Safety standards instituted
   required expensive ventilation and as such were not widely implemented
   or policed.

   The danger of radon exposure in dwellings was discovered in 1984 with
   the case of Stanley Watras, an employee at the Limerick nuclear power
   plant in Pennsylvania. Watras set off the radiation alarms (see Geiger
   counter) on his way into work for two weeks straight while authorities
   searched for the source of the contamination. They were shocked to find
   that the source was astonishingly high levels of radon in his house's
   basement and it was not related to the nuclear plant. The risks
   associated with living in his house were estimated to be equivalent to
   smoking 135 packs of cigarettes every day. Following this event, which
   was highly publicized, national radon safety standards were set and
   radon detection and ventilation became a standard homeowner concern.

   Radon is cited as the number one cause of lung cancer after cigarette
   smoking and radon induced lung cancer is thought to be the 6th leading
   cause of cancer death overall.

Occurrence

   On average, there is one atom of radon in 1 x 10^21 molecules of air.
   Radon can be found in some spring waters and hot springs. The towns of
   Misasa, Japan, and Bad Kreuznach, Germany boast radium-rich springs
   which emit radon.

   Radon exhausts naturally from the ground, particularly in certain
   regions, especially (but not only) regions with granitic soils. Not all
   granitic regions are prone to high emissions of radon. Depending on how
   houses are built and ventilated, radon may accumulate in basements and
   dwellings.

   The European Union recommends that action should be taken starting from
   concentrations of 400 Bq/m^3 for old houses and 200 Bq/m^3 for new
   ones. Health Canada has a guideline from 1988 that recommends action
   when the annual average concentration in a normal living area exceeds
   800 Bq/m^3, although they are proposing a new guideline that lowers the
   action level to 200 Bq/m^3. Source . The National Council on Radiation
   Protection and Measurement ( NCRP) in the US recommends action for any
   house with a concentration higher than 8  pCi/L. The United States
   Environmental Protection Agency ( EPA) strongly recommends action for
   any house with a concentration higher than 148 Bq/m^3 (given as 4
   pCi/L), and encourages action starting at 74 Bq/m^3 (given as 2 pCi/L).
   EPA radon risk level tables including comparisons to other risks
   encountered in life are available in their citizen's guide. Nearly one
   in 15 homes in the U.S. has a high level of indoor radon according to
   their statistics. The U.S. Surgeon General and EPA recommend all homes
   be tested for radon. Since 1985, millions of homes have been tested for
   radon in the U.S.

   Radon emitted from the ground has been shown to accumulate in the air
   if there is a meteorological inversion and little wind. Concentrations
   may exceed legal guidelines for short periods. It is not clear that any
   health effects would be epidemiologically detectable.

Compounds

   Some experiments indicate that fluorine can react with radon and form
   radon fluoride. Radon clathrates have also been reported.

Isotopes

   There are twenty known isotopes of radon. The most stable isotope is
   ^222Rn, which is a decay product ( daughter product) of ^226Ra, has a
   half-life of 3.823 days and emits alpha particles. ^220Rn is a natural
   decay product of thorium and is called “thoron.” It has a half-life of
   55.6 seconds and also emits alpha radiation. ^219Rn is derived from
   actinium, is called “actinon,” is an alpha emitter and has a half-life
   of 3.96 seconds.

   The full decay series of ^238U which produces natural radon is as
   follows (with half-lives):
   ^238U (4.5 x 10^9 yr), ^234Th (24.1 days), ^234Pa (1.18 min), ^234U
   (250,000 yr), ^230Th (75,000 yr), ^226Ra (1,600 yr), ^222Rn (3.82
   days), ^218Po (3.1 min), ^214Pb (26.8 min), ^214Bi (19.7 min), ^214Po
   (164 µs), ^210Pb (22.3 yr), ^210Bi (5.01 days), ^210Po (138 days),
   ^206Pb (stable).

Toxicity and precautions

   Radon is a radiological poison and a carcinogen. Some of the daughter
   products from radioactive decay of radon (such as polonium) are also
   toxic. Since radon is a gas, its decay products form a very fine
   particle that is both toxic and radioactive. This can potentially stick
   in the lungs and do far more damage than the radon itself.

   Based on studies carried out by the National Academy of Sciences in the
   United States, radon is the second most common cause of lung cancer
   after cigarette smoking, accounting for 15,000 to 22,000 cancer deaths
   per year in the US alone according to the National Cancer Institute
   (USA). On January 13, 2005, the Surgeon General of the United States
   reported that over 20,000 Americans die each year of radon-related lung
   cancer. Moreover, radon decay products (e.g. polonium-210) is also be
   present in tobacco smoke. Radon is a daughter product of the decay of
   uranium - 238. The USEPA recommends homes be fixed if an occupant's
   long-term exposure will average 4 picocuries per liter (pCi/L) or
   higher.

   No level of radon exposure is safe. Studies performed by R. William
   Field et al. at the University of Iowa have demonstrated a 50%
   increased lung cancer risk with prolonged radon exposure at the EPA's
   action level of 4 pCi/L. Recent pooled epidemiologic radon studies by
   Dan Krewski et al. (2005; 2006) and Sarah Darby et al. (2005) have also
   shown an increased lung cancer risk from radon below the U.S. EPA's
   action level of 4 pCi/L.

   ASTM E-2121 is a standard for reducing radon in homes as far as
   practicable below 4 picocuries per liter (pCi/L) in indoor air. In the
   U.S., about one in every 15 homes has a radon level above this
   standard.

   Radon test kits are commercially available. In the U.S., single test
   kits can cost about $10. The kit includes a collector that the user
   hangs in the basement for a few days (2 to 7). The user then sends the
   collector to a laboratory for analysis. The National Environmental
   Health Association provides a list of radon measurement professionals.
   Long term kits, taking collections for up to one year, are also
   available. An open land test kit can test radon emissions from the land
   before construction begins. The USEPA and the National Environmental
   Health Association, have identified 15 types of radon testing.

   Radon levels fluctuate naturally. An initial test might not be an
   accurate assessment of your home's average radon level. Transient
   weather can affect short term measurements. Therefore, a high result
   (over 4 pc/l) justifies repeating the test before undertaking more
   expensive abatement projects. Measurements between 4 and 10 pc/l
   warrant a long term radon test. Measurements over 10 pc/l warrant only
   another short term test so that abatement measures are not unduly
   delayed. Purchasers of real estate are advised to delay or decline a
   purchase if the seller has not successfully abated radon to 4 pc/l or
   less.

   The National Environmental Health Association (NEHA) administers a
   voluntary National Radon Proficiency Program (NRPP) for radon
   professionals consisting of individuals and companies wanting to take
   training courses and examinations to demonstrate their competency. A
   list of mitigation service providers is available. Indoor radon can be
   mitigated by sealing basement foundations, water drainage, or by
   sub-slab de-pressurization. In severe cases, mitigation can use air
   pipes and fans to exhaust sub-slab air to the outside. Indoor
   ventilation systems are more effective, but exterior ventilation can be
   cost-effective in some cases. Modern construction that conserves energy
   by making homes air tight exacerbates the risks of radon exposure, if
   radon is present in the home. Older homes with more porous construction
   are more likely to vent radon naturally. Ventilation systems can be
   combined with a heat exchanger to recover energy in the process of
   exchanging air with the outside. Homes built on a crawl space can
   benefit from a radon collector installed under a radon barrier (a sheet
   of plastic that covers the crawl space).

Radon therapy

   Radon therapy is an unscientific disease treatment that has been
   historically used in some spa resorts around the world. Beneficial
   health effects of radon have never been clinically proved, and
   considering radon's toxicity and the associated risks for health (radon
   causes lung cancer) it is not advised to undertake radon therapy.

   Radioactive water baths have been applied since 1906 in Joachimsthal,
   Czech Republic, but even before radon discovery they were used in Bad
   Gastein, Austria. Hot radium-rich spring releasing radon is also used
   in traditional Japanese onsen in Misasa, Tottori prefecture. Drinking
   therapy is applied in Bad Brambach, Germany. Inhalation therapy is
   carried out in Gasteiner-Heilstollen, Austria, in Kowary, Poland and in
   Boulder, Montana, United States.
   Retrieved from " http://en.wikipedia.org/wiki/Radon"
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   with only minor checks and changes (see www.wikipedia.org for details
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