Radioactive elements discovery

The isolation and identification of 4 radioactive elements in minute amounts took place at the turn of the century, and in each case the insight provided by the periodic classification into the predicted chemical properties of these elements proved invaluable. Marie Curie identified polonium in 1898 and, later in the same year working with Pierre Curie, isolated radium. Actinium followed in 1899 (A. Debierne) and the heaviest noble gas, radon, in 1900 (F. E. Dorn). Details will be found in later chapters which also recount the discoveries made in the present century of protactinium (O. Hahn and Lise Meitner, 1917), hafnium (D. Coster and G. von Hevesey, 1923), rhenium (W. Noddack, Ida Tacke and O. Berg, 1925), technetium (C. Perrier and E. Segre, 1937), francium (Marguerite Percy, 1939) and promethium (J. A. Marinsky, L. E. Glendenin and C. D. Coryell, 1945). 

F. W. Aston (Cambridge) discovery, by means of the mass spectrograph, of isotopes in a large number of non-radioactive elements and for enunciation of the whole-number rule. 

E. Fermi (Rome) demonstration of the existence of new radioactive elements produced by neutron irradiation and for the related discovery of nuclear reactions brought about by slow neutrons. 

Although the Curies noted that one equivalent gram of radium released one hundred calorics of heat per hour, they were uninterested in the practical implications of this, as they were both devoted to pure scientific discovery. During their work with pitchblende in 1898, the Curies discovered two new radioactive elements, which they named polonium (in honor of Marie s homeland) and radium. By 1902 they had isolated a pure radium salt and made the first atomic weight determination. 

The first person to identify the hydrogen ion as a component of all atoms was Ernest Rutherford. Rutherford had his hand in virtually every aspect of atomic research. By 1919, he had discovered alpha and beta rays, found a new element (radon), won a Nobel Prize for his work with radioactive elements, and demonstrated that atoms had nuclei. For good measure, in 1914, he was knighted. However, still more discoveries and honors awaited him. 

The radioactive element is a silvery, shiny, soft metal that is chemically similar to calcium and barium. It is found in tiny amounts in uranium ores. Its radioactivity is a million times stronger that that of uranium. Famous history of discovery (in a shed). Initially used in cancer therapy. Fatal side effects. Small amounts are used in luminous dyes. Radium was of utmost importance for research into the atom. Today its reputation is rather shaky as its decay gives rise to the unpleasant radon (see earlier). In nuclear reactors, tiny amounts of actinium are formed from radium. 

FIGURE 88 Dating methods. Shortly after the discovery of radioactivity, at the beginning of the twentieth century, it was found that the decay of radioactive elements could be used to keep track of time. Many of the dating techniques developed since then are, therefore, based on radioactive decay phenomena, but others, such as the hydration of obsidian, amino acid racemization, and dendrochronology, are based on other physical, chemical, or biological phenomena. 

Lind (1961) defines radiation chemistry as the science of the chemical effects brought about by the absorption of ionizing radiation in matter. It can be said that in 1895, along with X-rays, Roentgen also discovered the chemical action of ionizing radiation. He drew attention to the similarity of the chemical effects induced by visible light and X-rays on the silver salt of the photographic plate. This was quickly followed by the discovery of radioactivity of uranium by Becquerel in 1896. In 1898, the Curies discovered two more radioactive elements—polonium and radium. 

The Development of Modern Chemistry. Harper and Row, New York, 1964, xii + 851 pp. including illustrations, Appendixes, (Discovery of the Elements, Discovery of Natural Radioactive Isotopes, Radioactive Decay Series, Nobel Prize Winners in Chemistry, Physics, and Medicine), and Bibliographic Notes. 

Marie (NLP 1903, NLC 1911 ) and Pierre (NLP 1903 ) Curie took up further study of Becquerel s discovery. In their studies, they made use of instrumental apparatus, designed by Pierre Curie and his brother, to measure the uranium emanations based on the fact that these emanations turn air into a conductor of electricity. In 1898, they tested an ore named pitchblende from which the element uranium was extracted and found that the electric current produced by the pitchblende in their measuring instrument was much stronger than that produced by pure uranium. They then undertook the herculean task of isolating demonstrable amounts of two new radioactive elements, polonium and radium, from the pitchblende. In their publications, they first introduced the term radio-activity to describe the phenomenon originally discovered by Becquerel. After P. Curie s early death, M. Curie did recognize that radioactive decay (radioactivity) is an atomic property. Further understanding of radioactivity awaited the contributions of E. Rutherford. 

It was first identified and named brevium, meaning brief, by Kasimir Fajans and O. H. Gohring in 1913 because of its extremely short half-life. In 1918 Otto Hahn (1879—1968) and Lise Meitner (1878-1968) independently discovered a new radioactive element that decayed from uranium into (actinium). Other researchers named it uranium X2. It was not until 1918 that researchers were able to identify independently more of the elements properties and declare it as the new element 91 that was then named protactinium. This is another case in which several researchers may have discovered the same element. Some references continue to give credit for protactinium s discovery to Frederich Soddy (1877—1956) and John A. Cranston (dates unknown), as well as to Hahn and Meitner. 

In 1898 Mme. Curie in Paris and Professor G. C. Schmidt at the University of Munster, working independently, found that thorium, like uranium, is radioactive (43). This discovery opened up a vast new field of research as a result of which thorium is now known to be the parent substance of an entire series of radioactive elements. The story of their discovery will be reserved, however, for a later chapter. 

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 creation, by neutron bombardment of uranium, of the so-called transuraniums is based on the discovery of artificial radioactivity by M. and Mme. Joliot-Curie. Irene Curie was bom in Paris in September, 1897, the elder daughter of M. and Mme. Pierre Curie of honored memory. Both in Poland and in France she had many relatives who were devoting their lives to science, and from her earliest childhood she lived in a scientific atmosphere, among distinguished chemists and physicists. When Irene was less than a year old, her mother discovered the radioactive element polonium, which was destined to play an important part in the later researches of both mother and daughter. A few months later M. and Mme. Curie discovered another element of even greater importance, which they named radium. 

Since not many natural radioactive elements are in existence analysis by radiochemical methods was rather limited until it became possible to "induce radioactivity artificially in some of the non-radioactive elements, as was first done in 1934 by I. Curie F.Joliot(Ref 1). This discovery greatly broadened the application of radiochemical analysis. The first application of artificial radio activation for the identification of constituents in a mixt was reported by Meinke (Ref 16) to have been done in 1936 by Hevesy 8t Levi (Ref 2). 

For example, a picture form of green with envy could include the discovery of a rare, radioactive element that glows enough to turn the faces of onlookers green with envy. ... 

At the end of long and hard days, they isolated a new element. From pitchblende , an uranium ore, they obtained a new element which radiates rays similar to uranium. They named this new element polonium to honor the memory of Poland, Marie Curie s homeland. This discovery led to the discovery of radium which made the Curies famous. With the discoveries of these new radioactive elements, the number of such elements reached four. They were uranium, thorium, polonium and radium. 

There is nothing like the development of the periodic table through time to give one a sense of the pace of chemical discovery. Lavoisier listed close to thirty elements, and this number more than doubled when Mendeleev invented the periodic table. Since then, we have added the lanthanides and actinides, as well as a stream of artificial radioactive elements. 

In spite of all the new approaches which illuminated the outer regions of the atom, the center or nucleus of the atom continued to remain a bundle of uncertainties. Something of the composition of the nuclei of a few elements was already known. This information came from a study of the spontaneous disintegration of radium and other radioactive elements, such as thorium, polonium, uranium, and radon. These elements break down of their own accord into simpler elements. Soon after the Curies discovery of radium, Rutherford and Frederick Soddy, his student and collaborator, had found that the spontaneous breaking down of radium resulted in the emission of three types of rays and particles. Radium ejected alpha particles (ionized helium atoms), beta particles (electrons), and gamma rays (similar to X-rays). In radioactive elements, at least, it was believed that the nucleus contained electrons, protons, and electrified helium particles. 

Mendeleeff had found himself forced to leave a number of places in his system unoccupied. He believed correctly that elements as yet unknown would find their places in these gaps. His accurate prediction of the properties of these missing elements, which he named eka-boron, eka-aluminium and eka-silicon, was brilliantly confirmed a short time later by the discovery of scandium (21), gallium (31) and germanium (32). The Inert (or Rare) Gases discovered later by Rayleigh and Ramsay could also be readily included in the system. Again, the latest, non-radioactive elements discovered, hafnium (72) [Von Hevesy and Coster, (1923)] and rhenium (75) [Nod-... 

There are three names coimected with the discovery of radioactivity Henry Bec-querel, who discovered this phenomenon in 1896 [2] Maria Sklodowska-Curie, who named this process radioactivity and her husband Pierre Curie [3]. They stated that uranium salts emit ionizing rays and, furthermore, Maria Sklodowska-Curie discovered that thorium gives off the same rays. She proved that radiation was not the outcome of some interaction of molecules, but must come from an atom itself this discovery was absolutely revolutionary. Maria and Pierre discovered the first two radioactive elements, polonium and radium. There are about 20 radioactive elements and about 50 radionuclides in the natural environment. 

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