**5. Discovery of radioactivity, radium and polonium**

In 1895, W.C. Röentgen discovered new rays, later named as the "Röentgen rays". One year later, in 1896, A.H. Becquerel (1852–1908) discovered the phenomenon of radioactivity by exposing a photographic plate to potassium uranyl sulphate. He determined that a form of invisible rays emitted by uranium salts had exposed the plate. His student, Maria Sklodowska-Curie (1867–1934), recognised that some samples of pitchblende, including pitchblende from the Jáchymov uranium deposit, have a higher radioactivity as pure uranium salts. Marie and Pierre Curie (1859–1906) discovered the new element radium, in the form of radium chloride, in 1898. They extracted the radium compound from residues originated by production of uranium colours in the Jáchymov factory. For first experiments of both researches in 1898, they obtained from the Jáchymov uranium colour factory 5 kg of these residues, later 100 kg of these residues. In these residues, Marie and Pierre Curie discovered along with radium a second new element, polonium [6, 7]. For isolation of both new elements, both researchers in 1899 obtained from the Jáchymov factory 1000 kg of residues. These residues were collaborated in bigger laboratories of the Société Centrale de Produits Chimiques in Paris [8]. In 1910, radium was isolated as a pure metal by M. Curie and A. L. Debirne thought a radium chloride electrolysis. Radium metal was first commercially produced in the beginning of the twentieth century by Biraco, a subsidiary company of Union Miniere du Haut Katanga in its Oolen plant in Belgium. In the Jáchymov uranium colour factory, radium chloride was produced from 1908. In the years 1909–1937, the Jáchymov factory produced 64.3 g of Ra. In years 1908–1933, radium chloride was produced for its use in medicine to produce radon gas, which in turn was used in cancer treatment. In 1934, the Jáchymov uranium factory started producing self-luminous paints for watches, aircraft switches, clocks and instrument dials. The total production of uranium ores from the Jáchymov ore deposit in years 1853–1945 was 469.5 t of U [9].

After the isolation of radium by Marie and Pierre Curie from pitchblende from Jáchymov, several other scientists started to isolate radium in small quantities. Later, some small companies purchased mine tailings from the Jáchymov uranium deposit and started isolating radium. In 1904, the Austrian government nationalised all mines in the Jáchymov and stopped exporting raw uranium ore. The formation of an Austrian monopoly and the strong urge of other countries to have access to radium led to a worldwide search for uranium ores. New uranium ore deposits were found in United States, Belgian Congo and Canada.
