| Identification | Back Directory | [Name]
radon | [CAS]
10043-92-2 | [Synonyms]
radon
alphatron
radon atom
INDOORRADON
radium emanation
niton /(222)radon/ | [EINECS(EC#)]
233-146-0 | [Molecular Formula]
Rn | [MDL Number]
MFCD01742917 | [MOL File]
10043-92-2.mol | [Molecular Weight]
222 |
| Chemical Properties | Back Directory | [Definition]
Gaseous radioactive element. Atomic number 86;
noble gas group of periodic table; aw 222;
valences = 2, 4, (6); 18 radioactive isotopes, all
short-lived. The radon-222 isotope has a half-life of
3.8 days, emits α-radiation.
| [Appearance]
colourless gas | [Melting point ]
-71°C | [Boiling point ]
bp -62° | [density ]
d0 (101.3 kPa) 9.73 kg/m3; d (normal bp) 4400 kg/m3 | [solubility ]
slightly soluble in H2O | [form ]
colorless gas | [color ]
colorless | [Stability:]
Radiochemically unstable. Chemically unreactive. | [Water Solubility ]
at 101.32kPa, 230mL/L H2O (20°C) [KIR78]; soluble organic solvents [MER06] | [History]
Radon was discovered in 1900 by Dorn,
who called it radium emanation. In 1908 Ramsay and Gray,
who named it niton, isolated the element and determined its
density, finding it to be the heaviest known gas. It is essentially
inert and occupies the last place in the zero group of gases
in the Periodic Table. Since 1923, it has been called radon.
Thirty-seven isotopes and isomers are known. Radon-222,
coming from radium, has a half-life of 3.823 days and is an
alpha emitter; Radon-220, emanating naturally from thorium
and called thoron, has a half-life of 55.6 s and is also an alpha
emitter. Radon-219 emanates from actinium and is called actinon.
It has a half-life of 3.9 s and is also an alpha emitter.
It is estimated that every square mile of soil to a depth of 6
inches contains about 1 g of radium, which releases radon in
tiny amounts to the atmosphere. Radon is present in some
spring waters, such as those at Hot Springs, Arkansas. On the
average, one part of radon is present to 1 × 1021 part of air. At
ordinary temperatures radon is a colorless gas; when cooled
below the freezing point, radon exhibits a brilliant phosphorescence
which becomes yellow as the temperature is lowered
and orange-red at the temperature of liquid air. It has been
reported that fluorine reacts with radon, forming radon fluoride.
Radon clathrates have also been reported. Radon is still
produced for therapeutic use by a few hospitals by pumping
it from a radium source and sealing it in minute tubes, called
seeds or needles, for application to patients. This practice
has now been largely discontinued as hospitals can order the
seeds directly from suppliers, who make up the seeds with the
desired activity for the day of use. Care must be taken in handling
radon, as with other radioactive materials. The main
hazard is from inhalation of the element and its solid daughters,
which are collected on dust in the air. Good ventilation
should be provided where radium, thorium, or actinium is
stored to prevent build-up of this element. Radon build-up
is a health consideration in uranium mines. Recently radon
build-up in homes has been a concern. Many deaths from
lung cancer are caused by radon exposure. In the U.S. it is
recommended that remedial action be taken if the air from
radon in homes exceeds 4 pCi/L. | [CAS DataBase Reference]
10043-92-2 | [IARC]
1 (Vol. 43, 78, 100D) 2012 | [EPA Substance Registry System]
Radon (10043-92-2) |
| Hazard Information | Back Directory | [Chemical Properties]
colourless gas | [Uses]
To initiate and influence chemical reactions, as a surface label in the study of surface reactions; in the determination of radium or thorium; in the study of the behavior of filters; in combination with Be or other light materials as a source of neutrons. | [Hazard]
As for radium. | [Description]
Radon, Rn, is a gaseous radioactive element from the noble gases in family eight on the periodic table. There are 18 radioactive isotopes of radon, all of which have short half-lives. For example, radon 222 has a half-life of 3.8 days. Radon is a colorless gas that is soluble in water. It can be condensed to a colorless transparent liquid and to an opaque, glowing solid. Radon is the heaviest gas known, with a density of 9.72 g/L at 32°F. | [Physical properties]
Radon gas fits the criteria to be classed as a noble element located in group 18(VIIIA) orgroup 0. It is the only noble “inert” gas that is naturally radioactive. It is the heaviest of thegases in group 18.
Radon gas is easily converted to a liquid and will become solid at the relatively hightemperature of –71°C. As a solid, it glows with a yellow light. Its melting point is –71°C, itsboiling point is –62°C, and its density is 0.00973g/cm3. | [Isotopes]
There are 37 isotopes of radon. All are radioactive. None are stable. They rangein mass numbers from Rn-196 to Rn-228. Their half-lives range from a few microsecondsto 3.8235 days for Rn-222, which is the most common. It is a gas that is the resultof alpha decay of radium, thorium, or uranium ores and underground rocks. | [Origin of Name]
Originally named “niton” after the Latin word for “shining,” it was
given the name “radon” in 1923 because it is the radioactive decay gas of the element
radium. | [Occurrence]
Radon’s source is a step in the transmutation of several elements: uranium → thorium →radium → radon → polonium → lead. (There are a number of intermediate decay productsand steps involved in this process.) Radon-222 forms and collects just a few inches below thesurface of the ground and is often found in trapped pockets of air. It escapes through poroussoils and crevices. | [Characteristics]
Radon is the heaviest of the noble gases and is the only one that is radioactive. It is thedecay product of radium, thorium, and uranium ores and rocks found underground. As itdecays, it emits alpha particles (helium nuclei) and is then transmuted to polonium andfinally lead. The Earth’s atmosphere is just 0.0000000000000000001% radon, but becauseradon is 7.5 times heavier than air, it can collect in basements and low places in buildingsand homes. | [Production Methods]
Radon can be isolated from radium by several methods. An aqueous solution of radium salt such as radium bromide is heated, liberating radon. Radioactive bombardment then decomposes water to oxygen and hydrogen. Radon is separated from the gaseous mixture by condensation in tiny tubes placed in liquid air. The tubes then are sealed by melting. A gold or platinum coating is applied to form the “radon seeds” used in radiation therapy.
Alternatively, a slightly acid solution of a soluble radium salt such as chloride or bromide is placed in a soft-glass vessel behind lead shielding. The solution is boiled. Radon is pumped out as needed and frozen into a cold trap at -95°C. Hydrogen and oxygen are the main impurities generated from radiolytic decomposition of water. They are recombined by sparking or applying a hot wire. Carbon dioxide, water vapor, acid vapor, and hydrocarbon impurities are removed by various chemical methods.
Radon can be obtained from radium salts in the solid phase too. At ordinary temperatures, certain mixtures containing radium salts such as radium mixed with barium, radium palmitates, or gels of radium mixed with iron(III) hydroxide or aluminum(III) hydroxide efficiently release radon. Although anyradium salt would emit radon, the latter can diffuse very slowly at room temperature through the walls of the container vessels. However, when a radium salt is heated above 600°C radon diffuses rapidly through the solid container vessels and escapes.
Radon also may be separated from gas streams by adsorption on activated charcoal or silica gel. At temperatures colder than dry ice, charcoal is an excellent adsorbent. Radon may be desorbed by heating the adsorbent in vacuum at 350°C. | [Carcinogenicity]
Radon and its isotopic forms radon-222 and radon-220 are known to be human carcinogens based on sufficient evidence of carcinogenicity from studies in humans. | [Source]
Uranium-238 is present in small
amounts in most rocks and soil. Uranium has a
half-life of 4.5 billion years.1 It decays to other
elements such as radium, which breaks down to
radon. Some of the radon moves to the soil
surface and enters the air, whereas some
remains below the soil surface and enters the
groundwater.
Radon-222 also undergoes radioactive
decay and has a radioactive half-life of 3.8 days.
Radon-220 and -219 have half-lives measured
in seconds and are not nearly as abundant as
Radon-222. Thus the discussion of radon
health effects here centers on Radon-222.
Radon-222 decays into radon daughters or
progeny, which are radioactive elements. Two
of these (polonium-218 and polonium-214)
emit alpha particles (high-energy, high-mass
particles, each consisting of two protons and two neutrons), which are highly effective in
damaging lung tissues. The decay rate of
radioactive elements has traditionally been
specified in curies (Ci). The curie is approximately
37 billion disintegrations (37 ￥ 109 disintegrations)
per second. In discussing radon,
the picocurie (pCi) is used, where 1 pCi is equal
to 1 × 10-12 Ci. |
| Safety Data | Back Directory | [RIDADR ]
3321 | [HazardClass ]
7 | [Safety Profile]
A carcinogen. A common air contaminant. Radon is a noble gas and thus is relatively unreactive. Radiation Hazard: Natural isotope *zORn (Thoron, Thorium Series), T1/2 = 55 seconds, decays to radoactive 2'6Po by alphas of 6.3 MeV. Natural isotope 222Rn (Uranium Series), T1/2 = 3.8 days, decays to radioactive permissible levels are gven for 222Rn in equilibrium with its daughters. The chief hazard from this isotope is inhalation of the gaseous element and its solid daughters, whch are collected on the normal dust of the air. Ths material is deposited in the lungs and has been considered to be a major causative agent in the hgh incidence of lung cancer found in uranium miners. Radon and its daughters bdd up to an equhbrium value in about a month from radum compounds, whde the bdd-up from uranium compounds is negligble. Good ventilation of areas where radium is handled or stored is recommended to prevent accumulation of hazardous concentration of Rn and its daughters. Accumulation of radon in homes has been implicated in increased incidence of lung cancers. This accumulation is found in wellinsulated buildtngs located over land that has concentrations of uranium | [Hazardous Substances Data]
10043-92-2(Hazardous Substances Data) | [Toxicity]
Radon is derived from the radioactive decay of radium. It is highly toxic and emits ionizing radiation. Lead shielding must be used in handling and storage. Radon has appeared naturally in the basements of homes, causing some concern for the residents. The primary uses are as a cancer treatment, a tracer in leak detection, in radiography, and in chemical research. |
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