The property of intrinsic luminosity is characteristic of radon in all states of aggregation, and is one evidence of the energy changes which accompany its disintegration. The intensity of the phosphorescence is greatest in the solid – possibly because of the lesser volume occupied – but both the gas and the liquid glow strongly. The colour of the light emitted by the solid varies from steel-blue at the melting-point to orange-red at lower temperatures. Heat is also given out during the disintegration of the emanation.
The continuous emission of energy is also shown by the slow decomposition of carbon dioxide, carbon monoxide, ammonia, hydrochloric acid, and water exposed to the action of radon. It has also been stated that when solutions of compounds of the elements of the carbon group (silicon, titanium, zirconium, thorium, and lead) are subjected to the action of radon, carbon dioxide is always produced. This suggests a possibility that there may be a breaking-down of the molecules of these elements with formation of carbon, the lowest member of the series. Radon will cause the oxidation of wet mercury, and turns ordinary white glass violet.
It was at one time supposed that a change of copper into lithium and of water into neon had been observed, but the validity of these observations is seriously open to question.
For one or two days after its isolation radon undergoes a slow contraction to about one-half its original volume; afterwards it slowly expands to about 3 to 3.5 times the original volume. This change corresponds to a change in the spectrum, that of radon disappearing completely after 3-4 days, and giving place to that of helium.
The cause of the contraction is obscure, but it has been observed in every sample hitherto prepared, and is, perhaps, due to impurities. The slow expansion which takes place afterwards may be satisfactorily explained on the hypothesis that the α-particles given out during the radioactive change of the radon have such a high velocity that they are forced into the walls of the containing vessel and are only evolved again quite slowly. It has been found that if radon is confined in a glass tube the walls of which have a thickness less than the range of its a-particles in glass, an accumulation of helium can be observed in the outer space. This supports the preceding explanation of the slow increase in volume, and further proves conclusively the identity of the helium atom with the α-particle. The period of half-change of radon is 3.75 days. The best solution and cost will be given by Radon Mitigation Mn Cost
It may be mentioned here that the evolution of helium from radium was first proved by Ramsay and Soddy, and confirmed by Himstedt and Meyer: the statement that the radioactive elements are elements undergoing decomposition was first made by Geoffrey Martin. Assuming that 5 α-particles are expelled during the complete disintegration of one atom of radium, the volume of helium produced per day from 1 gram of radium should be 0.439 cu. mm. at N.T.P.: experimental determinations of the amount have given figures in good agreement with this result. Since then its production during many other radioactive changes has been observed.