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.
In 1901 Elster and Geitel found that a radioactive emanation is present in the atmosphere.
The study of radium and radioactivity (see 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.
Bemont in 1898; it was so named on account of the intensity of the radioactive emanations which it yielded.
There is more radium than any other radioactive element, but its excessive rarity may be gauged by the facts that Mme.
Wynn's gentleness, Gabriel's ultimatum, the radioactive lake.
Mache (62) thinks that the ionization observed in the atmosphere may be wholly accounted for by the radioactive emanation.
In this case too it is associated with radioactive matter, which is almost ubiquitous.
It is remarkable as always containing helium and radioactive elements (see Radioactivity).