Atomic Number: 86
Atomic Mass: 222.0 amu (atomic mass units)
Melting Point: minus 71.0 C (202.15 K, minus 95.8 F)
Boiling Point: minus 61.8 C (211.35 K, minus 79.24 F)
Number of Protons: 86
Number of Electrons: 86
Number of Neutrons: 136
Classification: Noble Gas
Crystal Structure: Cubic
Density @ 293 K: 0.00973 grams per cubic centimeter
Friedrich Ernst Dorn in Germany discovered the radioactive noble gas radon in 1900. He originally named the element niton from the Latin "nitens" which means shining. Known as radon since 1923, its name relates to the element radium from which it is derived.
Radon is produced from the alpha decay of radium. There is only one compound that has been confirmed as being made by this element and that is radon fluoride. When chilled to its frozen state, below minus 71 C, radon develops a brilliant phosphorescence this becomes yellow at lower temperatures eventually appearing as an orange color at the temperature of liquid air.
All the isotopes of radon are unstable. The most stable isotope is radon-222, which has a half-life of 3.8 days and decays by alpha decay to form another radioactive element polonium-218. Thirty-eight isotopes of radon have been identified. Of these radon-214 has the shortest half-life at 0.24 microseconds.
Radon gas is considered a health hazard. Alpha emitters are normally considered less harmful than other radioactive elements as the alpha particles can be easily stopped. However, radon, being a gas, can be inhaled and so reach living tissue. In addition, as radon decays it forms solid radioactive elements with longer half-lives. These solid radioactive elements can accumulate in dust and be inhaled. Radon gas can build up in homes, which are built on areas in which underlying rocks are rich in the ores of the elements uranium, thorium and radium. These rocks are normally igneous rocks such as granite. In areas of high risk of radon build-up monitors can be installed in homes to measure radon levels. Ensuring adequate ventilation of the house also alleviates the risk.
The main use of radon is in the radiotherapy of certain types of cancer. Its short half-life means that it has to be supplied from a radium source as required. One gram of radium-226 produces 0.0001 milliliters of radon per day.
Seismologists are examining fluctuating levels of radon gas in earthquake zones to see if it could be useful in earthquake prediction.