Discovery of Radium Element

Radium

When the Curies and G. Bemont analysed pitchblende they noticed a higher radioactivity of one more fraction, apart from the bismuth fraction. After they had succeeded in extracting polonium they started to analyse the second fraction thinking that they could find yet another unknown radioactive element.

The new element was named radium from the Latin radius meaning ray. The birthday of radium was December 26, 1898. When the members of the Paris Academy of Sciences heard a report entitled “On a new highly radioactive substance contained in pitchblende”. The authors reported that they had managed to extract from the uranium ore tailings a substance containing a new element whose properties are very similar to those of barium. The amount of radium contained in barium chloride proved to be sufficient for recording its spectrum. This was done by the well–known French spectral analyst E. Demarcay who found a new line in the spectrum of the extracted substance. Thus, two methods–radiometry and spectroscopy–almost simultaneously substantiated the existence of a new radioactive element.

The position of radium among the natural radioactive elements (of course, excluding thorium uranium) almost immediately proved to be the most favourable one owing to many reasons. The half–life of radium was soon found to be fairly long, namely, 1 600 years. The content of radium in the uranium ores was much higher than that of polonium (4 300 times higher); this contributed to natural accumulation of radium. Furthermore, the intensity of alpha radiation of radium was sufficiently high to allow an easy monitoring of its behaviour in various chemical procedures. Finally, a distinguishing feature of radium was that it evolved a radioactive gas known as emanation (see p. 183). Radium was a convenient subject for studies owing to a favourable combination of its properties and therefore it became the first radioactive element (again, with the exception of uranium and thorium) to find its permanent place in the periodic system without long delay. Firstly, chemical and spectral studies of radium demonstrated that in all respects it belongs to the subgroup of alkaline earth metals; secondly, its relative atomic mass could be determined accurately enough. To do be obtained. The Curies worked ceaselessly for 45 months in their ill–equipped laboratory processing uranium ore tailings from Bohemian mines. They performed fractional crystallization about 10 000 times and finally obtained a priceless prize–0.1 g of radium chloride. The history of science knows no more noble examples of enthusiastic work. This amount was sufficient for measurements and on March 28, 1902, Marie Curie reported that the relative atomic mass of radium was 225.9 (which does not differ much from the current figure of 226.02). This value just suited the suggested position of radium in the periodic system.

The discovery of radium was the best substantiated one among the many alleged discoveries of radioactive elements, which soon followed. Every year more new discoveries were reported. Radium was also the first radioactive element obtained in the metallic form.

Marie Curie and her collaborator A. Debierne electrolyzed a solution containing 0.106 g of radium chloride. Metallic radium deposited on the mercury cathode forming amalgam. The amalgam was put into an iron vessel and heated under a hydrogen flow to remove mercury. Then grains of silvery whitish metal glistened at the bottom of the vessel.

The discovery of radium was one of the major triumphs of science. The studies of radium contributed to fundamental changes in our knowledge of the properties and structure of matter and gave rise to the concept of atomic energy. Finally, radium was also the first radioactive element to be practically used (for instance, in medicine).

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