The natural radioactive elements

In 1898 there was discovered an element, radium, which con tinually and spontaneously emits light, heat, and other radiations. Investigation of these astonishing phenomena by the Curies and others revealed more than forty interrelated radioactive elements which, like radium, are unstable. They do not, however, occupy forty places in the periodic system, but are crowded into twelve places. The explanation for the existence of these numerous so-called radioactive isotopes and their genealogical descent from uranium and thorium were discovered independently by K. Fajans, F. Soddy, A. S. Russell, and A. Fleck. Since the original literature on the radioactive elements embraces such a vast field of research, the following account of their discovery is necessarily far from complete. 

The amazingly rapid development of the science of radioactivity is largely due to the brilliant work of M. Pierre Curie and his wife, Mme. Marie Sklodowska Curie. The former was born in Paris on May 15, 1859, and was educated by his cultured parents. Many happy hours were spent on excursions to the country, and thus this city child grew up in intimate contact with nature, collecting plants and animals and enjoying them in quiet contemplation. While serving as director of the laboratory under Paul Schiitzenberger at the School of Physics and Chem- 

Marie Sklodowska, a daughter of Dr. Sklodowski, a professor of physics and mathematics at the Warsaw gymnasium, was bom on November 7, 1867. Because of the early death of her gifted mother, the little girl grew up in her father s laboratory and under his instruction. She soon developed a passionate love of country and joined a secret society of students who organized evening classes for laborers and peasants. However, because of the limited opportunities for advanced study, she decided to leave her beloved motherland and go to Paris (99). 

Antoine-Henri Becquerel, 1852-1908. French physicist and engineer. Discoverer of the rays emitted by uranium. He carried out important researches on rotatory magnetic polarization, phosphorescence, infrared spectra, and radioactivity. His grandfather Antoine-Cesar-Becquerel (1788-1878), and his father, Alexandre-Edmond Becquerel (1820-1891), also made many important contributions to chemistry and physics. 

During the four years of her student life, she lived in a chilly little attic room, carrying the coal herself up the six flights of stairs, and cooking her simple meals over an alcohol lamp. This was Marie Sklodowska s introduction to the city which became her permanent home (4, 68). When she enrolled at the Sorbonne, Henri Poincare, the famous mathematical physicist, soon recognized her ability, and Professor Gabriel Lippmann also took great interest in her research. 

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Perhaps Perrin s continuing commitment is explained by the fact that his radiation hypothesis was an update of Marie and Pierre Curie s original explanation of radioactivity, that the apparently spontaneous emission of radiations and charged particles from molecules is activated by immanent radiations. The Curies supposed that radiations in the atmosphere or in the ether disturb the stability of the naturally radioactive elements. This hypothesis, like the radiation hypothesis of chemical activation, eventually succumbed to an explanation using electron configurations, adumbrated by the new quantum interpretation of matter and energy. 

The naturally radioactive elements usually decay by emitting alpha particles their final decay product is usually a stable isotope of Pb there are four such "families" (often with branching) ... 

Natural radioactivity is formed particularly by long-lived isotopes, i.e. by those with half-lives of 10 to 10 years. These isotopes are usually widely scattered in the soil. The activity level depends particularly on contents of uranium, thorium, radium and potassium the radiation energy of these elements represents as much as 98% of the total energy of radiation of all the natural radioactive elements in the soil. 

The displacement law provided for harmonious relationship between radioactive families and the periodic system of elements. After several successive alpha and beta decays the originators of the families converted into stable lead giving rise in the process to the natural radioactive elements found between uranium and bismuth in the periodic table. But then each box in the system had to accommodate several radioelements. They had identical nuclear charges but different masses, that is, they looked as varieties of a given element with identical chemical properties but different masses and radioactive characteristics. In December 1913 Soddy suggested the name isotopes for such varieties of elements (from the Greek for the common place ) because they occupy the same box in the periodic system. 

None cf the natural radioactive elements had such a short half-life, even the artificially synthesized element 85 had a half-life measured in hours. There were hopes to find other natural isotopes of francium with longer half-lives. But in fact francium-223 proved to be the only francium isotope found on Earth. 

As for the natural radioactive elements the champions here are the Curies who extracted polonium and radium from uranium ore. G. Seaborg took part in the discoveries of eight transuranium elements (from plutonium to mendele-vium). G. Flerov and his large group from Dubna played a decisive role in reliable syntheses of elements 102-107. 

We are fascinated by the achievements of Henri Becquerel and Marie Curie in their investigation of the naturally radioactive elements, uranium, radium, etc. These elements also have an everyday interest for us, with the debates about nuclear power and the problem of radon accumulation in homes. 

Figure4.2 A complete geochemical classification of elements. Notes Lan- is the element lanthanum and lanthanides of the naturally radioactive elements only Th and U are...

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