Uranium fission, discovery

The discovery of uranium fission by Enrico Fermi and L. Szilard at Columbia University opened the way for further advances. This work was done under the cloak of wartime secrecy and led directly to the atomic bomb, but its significance for the discovery of new elements was very great. 

In contrast, the chemists were left with little but fission debris - the earliest instance of radioactive fallout. The chemical data from the uranium investigation was essentially meaningless - the transuranium elements that had inspired such confidence turned out to be a messy cocktail of light elements from across the periodic table. [38] Moreover, chemists had not broken new ground with the fission discovery, since they were still saddled with the assumption that transuranium elements were transition elements. 

The existence of the element was recognized by Klaproth in 1789, but only in 1841 did Peligot actually isolate the metal itself. However, it was not until the discovery of uranium fission by Meitner, Hahn, and Strassmann in 1939 that it became commercially important. Its most important ores are uraninite (usually called pitchblend, and approximating to U02) and uranium vanadates. 

The Faculty of Science in Paris had appointed her as a lecturer in 1932, and in 1937 it conferred on her the title of professor. The year before, the French government had named her undersecretary of state for scientific research. In 1938 her research on the action of neutrons on the heavy elements was important in the discovery of uranium fission. The next year, the Legion of Honour inducted her as an officer. During World War II, Frederic led the underground resistance movement as the president of the Front National. 

Uranium was discovered by Klaproth in 1789. Until the discovery of uranium fission by Hahn and Strassman in 1939, uranium had little commercial importance its ores were sources of radium and small quantities were used for coloring glass and ceramics, but the bulk of the uranium was discarded. Uranium is important as a nuclear fuel its chemical importance lies in its being the prototype for the succeeding three elements. 

The news of Hahn, Meitner and Strassmann s discovery of nuclear fission was brought over by Niels Bohr at the very beginning of 1939. At that time I was laid up in the hospital with jaundice for about six weeks and Szilard was in town most of the time. He came down to the Infirmary every day and we discussed the uranium fission regularly. 

The history of science of the 20th century knows of many great discoveries and one of the greatest is the discovery of uranium fission under the effect of slow neutrons. The nuclei of uranium-235 isotopes are split into two fragments, each of which is an isotope of one of the elements at the centre of the periodic table. Isotopes of thirty odd elements from zinc to gadolinium can be produced in this way. The yield of the isotopes of element 61 has been calculated to be fairly high—approximately 3 per cent of the total amount of the fission products. 

In 1938, the experimental and theoretical cognition of nuclear fission by O. Hahn and F. Strassmann, and the theoretical explanation by L. Meitner and O. R. Frisch (1944 Nobel Prize to O. Hahn for. .. discovery of the fission of heavy elements...) made our last century the Uranium century. Radiopharmaceutical chemistry, interestingly, has made a significant and exclusively peaceful profit from this nuclear phenomenon, as the fission of uranium today provides an unrenouncable resource of radionuclides applied in nuclear medicine diagnosis and therapy. The uranium fission product l, for example, became a key radionucKde in the 1950s, when R. S. Yalow and S. A. Berson developed the approach of radioimmunoassay for quantitative in vitro analysis of physiological and biochemical processes (1977 Nobel prize to R. S. Yalow for. .. the development of radioimmunoassays...). 

Gr. technetos, artificial) Element 43 was predicted on the basis of the periodic table, and was erroneously reported as having been discovered in 1925, at which time it was named masurium. The element was actually discovered by Perrier and Segre in Italy in 1937. It was found in a sample of molybdenum, which was bombarded by deuterons in the Berkeley cyclotron, and which E. Eawrence sent to these investigators. Technetium was the first element to be produced artificially. Since its discovery, searches for the element in terrestrial material have been made. Finally in 1962, technetium-99 was isolated and identified in African pitchblende (a uranium rich ore) in extremely minute quantities as a spontaneous fission product of uranium-238 by B.T. Kenna and P.K. Kuroda. If it does exist, the concentration must be very small. Technetium has been found in the spectrum of S-, M-, and N-type stars, and its presence in stellar matter is leading to new theories of the production of heavy elements in the stars. 

The First Reactor. When word about the discovery of fission in Germany reached the United States, researchers thereafter found that (/) the principal uranium isotope involved was uranium-235 (2) slow neutrons were very effective in causing fission (J) several fast neutrons were released and (4) a large energy release occurred. The possibiUty of an atom bomb of enormous destmctive power was visualized. 

Nuclear fission is a process in which a heavy nucleus—usually one with a nucleon number of two hundred or more—separates into two nuclei. Usually the division liberates neutrons and electromagnetic radiation and releases a substantial amount of energy. The discoveiyi of nuclear fission is credited to Otto I lahn and Fritz Strassman. In the process of bombarding uranium with neutrons in the late 1930s, they detected several nuclear products of significantly smaller mass than uranium, one of which was identified as Ba. The theorectical underpinnings that exist to this day for nuclear fission were proposed by Lise Meitner and Otto Frisch. Shortly after Hahn and Strassman s discovery. 

Several alternative technologies that were heavily supported failed to become commercially viable. The most obvious case was the fast breeder reactor. Such reactors are designed to produce more fissionable material from nonfissionable uranium than is consumed. The effort was justified by fears of uranium exhaustion made moot by massive discoveries in Australia and Canada. Prior to these discoveries extensive programs to develop breeder reactors were government-supported. In addition, several different conventional reactor technologies were aided. The main ongoing nuclear effort is research to develop a means to effect controlled fusion of atoms. 

The development of chemistry itself has progressed significantly by analytical findings over several centuries. Fundamental knowledge of general chemistry is based on analytical studies, the laws of simple and multiple proportions as well as the law of mass action. Most of the chemical elements have been discovered by the application of analytical chemistry, at first by means of chemical methods, but in the last 150 years mainly by physical methods. Especially spectacular were the spectroscopic discoveries of rubidium and caesium by Bunsen and Kirchhoff, indium by Reich and Richter, helium by Janssen, Lockyer, and Frankland, and rhenium by Noddack and Tacke. Also, nuclear fission became evident as Hahn and Strassmann carefully analyzed the products of neutron-bombarded uranium. 

The discovery of this element is credited to J.A. Marinsky and L.E. Glendenin who, in 1945, identified its long-lived isotope Pm-147 (ti/2 2.64 years) in the fission products of uranium. They named the element after Prometheus, who according to Greek mythology stole fire from heaven. The element was first isolated from fission product wastes by G.W. Parker and P.M. Lantz in 1948. It first was recovered from natural sources by O. Erametsa in 1965. An amount less than 0.5 g was recovered from 20 tons of rare earths. 

The element was discovered in the pitchblende ores by the German chemist M.S. Klaproth in 1789. He named this new element uranium after the planet Uranus which had just been discovered eight years earlier in 1781. The metal was isolated first in 1841 by Pehgot by reducing the anhydrous chloride with potassium. Its radioactivity was discovered by Henry Becquerel in 1896. Then in the 1930 s and 40 s there were several revolutionary discoveries of nuclear properties of uranium. In 1934, Enrico Fermi and co-workers observed the beta radioactivity of uranium, following neutron bombardment and in 1939, Lise Meitner, Otto Hahn, and Fritz Strassmann discovered fission of uranium nucleus when bombarded with thermal neutrons to produce radioactive iso-... 

Modern nuclear power is based on harnessing the energy released in a fission reaction. The development of atomic energy started in the 1930s with the discovery that atoms could be split with neutrons. This discovery laid the foundation for building the first atomic bombs during World War 11. A basic reaction representing the fission of uranium can be represented as ... 

The first scientific attempts to prepare the elements beyond uranium were performed by Enrico Fermi, Emilio Segre, and co-workers in Rome in 1934, shortly after the existence of the neutron was discovered. This group of investigators irradiated uranium with slow neutrons and found several radioactive products, which were thought to be due to new elements. However, detailed chemical studies by Otto Hahn and Fritz Strassman in Berlin showed these species were isotopes of the known elements created by the fission of uranium into two approximately equal parts (see Chap. 11). This discovery of nuclear fission in December of 1938 was thus a by-product of man s quest for the transuranium elements. 

The discovery in 1938-1939 of nuclear fission of uranium, which led ultimately to the discovery of nuclear power, heralded a new, extraordinarily fruitful stage in Ya.B. s scientific activity. His interests were concentrated on the study of the mechanism of fission of heavy nuclei and, what proved particularly important, on the development of a theory of the chain fission reaction of uranium. During 1939-1943 Ya.B. wrote several papers which laid the foundation for this subject and were of fundamental value. We note that four of these papers, written in collaboration with Yu. B. Khariton, were done practically in two years before the war. The papers of this series form the foundation of modern physics of reactors and nuclear power they are widely known and do not require special commentary—a short review of the basic physical results is eloquent enough. 

The discovery of fission was a complete surprise and also a great shock, because it shattered fundamental ideas of nuclear behavior that had guided the investigation. The surprise was evident in the events of December 1938. On December 10, Enrico Fermi was awarded the Nobel Prize in physics. He and his group in Rome had been the first to irradiate uranium with neutrons and to propose that transuranium elements had been formed in the process. In his Nobel lecture, Fermi was so confident of the first two, elements 93 and 94, that he referred to them by name ausonium and hesperium. But at that very moment, the Berlin team of Otto Hahn, Lise Meitner, and Fritz Strafimann was on the verge of identifying barium among the uranium products. By the end of the year, they understood that uranium had split, explained the fission process, and concluded that the transuranium elements were false. When Fermi published his Nobel lecture, he added a footnote to that effect, but by then ausonium and hesperium were themselves footnotes (if that) in the history of science. [1]... 

With this, the goals of those who first sought artificial elements beyond uranium were realized. The understanding of nuclear behavior was deepened by the discovery of nuclear fission, and the periodic system was extended and clarified by the synthesis of transuranium elements. 

Hiroshima exploded with energy equivalent to about 20,000 tons of TNT.18 But where does all of this energy come from Unlike ordinary chemical reactions, nuclear fission does not involve breaking and forming chemical bonds. Instead, the energy comes from the loss of mass that accompanies the fission reaction. Most, if not all, of the students will be familiar with Einstein s famous equation, E = me2, but few are likely to understand what it means.19 In 1939, Lise Meitner and her nephew Robert Frisch reported their discovery of nuclear fission.20 They realized that the energy that accompanied the fission of uranium nuclei could be accounted for by using Einstein s equation. 

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