In 1901 Elster and Geitel found that a radioactive emanation is present in the atmosphere.
Helium is relatively abundant in many minerals, all of which are radioactive, and contain uranium or thorium as important constituents.
Another radioactive substance - ionium - was isolated from carnotite, a uranium mineral, by B.
There is more radium than any other radioactive element, but its excessive rarity may be gauged by the facts that Mme.
The study of radium and radioactivity led before long to the further remarkable knowledge that these so-called radioactive materials project into surrounding space particles or corpuscles, some of which are identical with those projected from the cathode in a high vacuum tube, together with others of a different nature.
Hard on this came the recognition of the fact that freely charged positive and negative ions are always present in the atmosphere, and that a radioactive emanation can be collected.
After the discovery of the radioactive properties of uranium by Henri Becquerel in 1896, it was noticed that some minerals of uranium, such as pitchblende, were more active than the element itself, and this circumstance suggested that such minerals contained small quantities of some unknown substance or substances possessing radioactive properties in a very high degree.
After removing the uranium, it was found that the bismuth separated with a very active substance - polonium; this element was afterwards isolated by Marckwald, and proved to be identical with his radiotellurium; that the barium could be separated with another active substance - radium; whilst a third fraction, composed mainly of the rare earths (thorium, &c.), yielded to Debierne another radioactive element - actinium, which proved to be identical with the emanium of Giesel.
And Mme Curie subjected a large amount of pitchblende to a laborious process of fractionation, with the result that in 1898 they announced the existence in it of two highly radioactive substances, polonium and radium.
Bemont in 1898; it was so named on account of the intensity of the radioactive emanations which it yielded.
Mache thinks that the ionization observed in the atmosphere may be wholly accounted for by the radioactive emanation.