Emanations and “induced” radioactivity: From mystery to (mis)use

Abstract

Radon, Rn; atomic number Z = 85; is a (gaseous) chemical element of which no stable but only radioactive isotopes exist. Three of them, namely actinon (219Rn), thoron (22~ and radon (222Rn) are the decay products of naturally occurring radioisotopes of radium: 223Ra, 224Ra and 226Ra, respectively. The natural Rn isotopes were discovered within the period 1899-1902 and at that time referred to as emanations because they came out (emanated) of sources/materials containing actinium, thorium and radium, respectively. The (somewhat mysterious) emanations appeared to disintegrate into radioactive decay products which by depositing at solid surfaces gave rise to "induced" radioactivity i.e. radioactive substances with various half-lives. Following the discovery of the emanations the volume of the research involving them and their disintegration products grew steeply. The identity of a number of these radioactive products was soon established. Radium-emanation was soon used as a source of RaD (21~ to be applied as an "indicator" (radiotracer) for lead in a study on the solubility of lead sulphide and lead chromate. Moreover, radium and its emanation were introduced into the medical practice. Inhaling radon and drinking radon-containing water became an accepted medicinal use (or misuse?) of that gas. Shortly after the turn of the century, the healing (?) action of natural springs (spas) was attributed to their radium emanation i.e. radon. Bathing in radioactive spring water and drinking it became very popular. Even today, bathing in radon-containing water is still a common medical treatment in J~chymov, Czech Republic.