Thursday, June 3, 2021

Discovery of radium and polonium

In 1891 Maria Sklodowska (1867-1934) moved to Paris from her native Poland to undertake scientific studies. In 1895 she married Pierre Curie (1859-1906), a physicist renowned for his work on magnetism and his theory on symmetry in physical phenomena.

Marie started work in Pierre’s laboratory in Rue Lhomond, Paris, using pitchblende uranium ore from the Joachimstal mine in Poland, at that time ruled by Austria. She tried to identify which substances and minerals besides pitchblende could also emit ionizing radiation.

Marie Curie developed an apparatus, the electroscope, for measuring radioactivity more accurately, as the photographic plate method was too crude.

Pierre Curie joined her in her research. To their surprise, the radioactivity of some of the ores were three to four times greater than could be accounted for on the basis of just their uranium and thorium content.

Marie treated the ore and, following Fresenius chemistry methodology, she separated several salt fractions and measured the radioactivity in each fraction. The Curies decided they had found a new element since, although the sample was far from pure, it was far more radioactive than either U or Th. They called it polonium (after Poland, Marie’s native country).

The symbol Po is written for the first time in the laboratory note book on 13 July 1893 by the hand of Pierre Curie. The article published in the Comptesrendus de l’ Académie des Sciences announces the discovery of a new element, more radioactive than uranium, but not seen as yet.

In the physical and chemical separation procedure applied to treat the uranium ore, they observed also high radiation emission in another chemical fraction containing barium. They hypothesized that eventually other substance with a chemical behavior close to barium could be present. Unlike uranium and polonium, radium does not occur freely in nature, the Curies and their assistant Andre were able to extract about 1 milligram of radium from nearly 10 tons of pitchblende in 1902.

The Curies wrote: “There is a strong reason to believe that the substance obtained contains a new element. We propose to name it as Radium. This new radioactive substance obtained probably still contains a large amount of barium mixed therein, but radium radioactivity seems enormous”. The Curies and their assistant Andre were able to extract about 1 milligram of radium from nearly 10 tons of pitchblende, according to the Royal Society of Chemistry.

Pure radium was isolated in 1902 by electrolysis by Marie Curie and Andre Debierne, a French chemist, according to New World Encyclopedia.
Discovery of radium and polonium

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