RADON, known formerly as radium emanation or as niton, is the gaseous element (Symbol Rn) of atomic number 86 and atomic weight 222 produced by the disintegration of radium. It was discovered by Dorn in 190o. Its relation to the elements ura nium and radium and to its successive products radium -A, -B, -C, -C', -D, and -E and polonium are discussed under RADIUM. Radon is the heaviest member of the group of inert gases helium, neon, argon, krypton and xenon, and, like these elements, it is totally unable to form chemical compounds with other elements, and therefore may be said to have no chemical properties whatever. Its physical properties are described under RADIOACTIVITY.
In a mineral or solid preparation of radium, radon remains with the solid material, little of it escaping into the air. The higher the temperature to which the solid is heated the more easily does it escape, and at a temperature of 800° C practically the whole of the radon is expelled. When a solution of radium in water or acid is kept in a closed flask, radon is evolved together with oxygen and hydrogen produced by the decomposition of the water. After purification (see RADIOACTIVITY) radon is sealed up in a tube and used for scientific, medical, or other work.
Radon expels an a-o particle of range 4.12 cm. and disintegrates at such a rate that it diminishes by one-half every 3.83 days. A quantity of radon, therefore, freed from its parent, falls to half its original amount in 3.83 days, to a quarter in 7.66 days, to an
eighth in 11.49 days, and so on. But it is a consequence of the disintegration theory of radioactivity that, in the solution of radium which has been freed from its radon, the latter grows as fast as it decays after separation from radium ; that is to say, in 3.83 days one-half, in 7.66 days three-quarters, and in 11.49 days seven-eighths of the equilibrium amount of radon has re formed in the radium solution. If therefore the radon be pumped off from the radium solution once a week, nearly three-quarters of the maximum amount may be removed, purified, sealed up and used for experimental work. The valuable radium solution need not then be directly handled in experimental work. It generates under conditions of safety the radon which, with its successive disintegration products, is as valuable for most experimental work as radium itself. Should an accident befall the tube of radon, time (in waiting for more to accumulate in the solution of radium) but not the value of the radium, is lost; the interest on one's money, so to speak, has been spent, but the capital itself is still safe in the bank. Radon in tubes, of course, is not permanent in the sense that radium is permanent, for it diminishes in the manner already explained ; but for most practical purposes that does not matter.