Transuranium elements, discovery

E. M. McMillan and G. T. Seaborg (Berkeley) discoveries in the chemistry of the transuranium elements. 

Edwin M. McMillan (1951, chemistry discovery of the transuranium elements)... 

G. T. Seaborg and E. M. McMillan. The Nobel Prize for Chemistry for 1951 was awarded jointly to Glenn T. Seaborg and Edwin M. McMillan, both of the University of California, for their discoveries in the chemistry of the transuranium elements." Dr. Seaborg is chairman of the Division of Physical and Inorganic Chemistry at the University of California. Dr. McMillan worked at the Massachusetts Institute of Technology in connection with radar development, collaborated with J. Robert Oppenheimer in organizing the Los Alamos Scientific Laboratory, and did the initial work that led to the discovery of elements heavier than uranium. 

FERMIUM. ICAS 7440-72-4). Chemical element symbol Fm. at. no. 100. at. wt. 257 (mass number of the most stable isotope), radioactive metal of the Actinide series, also one of the Transuranium elements. During Ihe period 1953- 1954. a group of scientists at the Nobel Institute of Physics (Stockholm) bombarded U with l60 ions, producing and isolating a 30-min alpha emitter. Ibis was called -5"l(X). However, discovery of element 100 was noi claimed at that time. Subsequently, the isotope was identified and the 30-miu half-lile conlirmed. Both fermium and einsteinium were formed in a thermonuclear explosion that occurred in the South Pacific in 1952. The elements were identified by scientists from the University of California s Radiation Laboratory, the Argonne National Laboratory, and die Los Alamos Scientific Laboratory. It was observed that very heavy uranium isutopes lhal resulted from the action of the instantaneous neutron flux cm uranium (conlaincd in the explosive device) decayed lo form Es and Fm, The probable electronic configuration of... 

MCMILLAN, EDWIN M. (1907-1991). An American physicist who won the Nobel prize in chemistry in 1951 along with Glenn T. Seaborg lor their discoveries In the chemistry of the transuranium elements. His work included research in nuclear physics and particle accelerator development as well as microwave radar and sonar. He and his colleagues discovered neptunium and plutonium. He was the recipient of the Atoms for Peace prize in 1963. His Ph D. in Physics was awarded from Princeton University. 

The chemical elements are the building blocks of nature. All substances are combinations of these elements. There are (as of 2005) 113 known chemical elements with the heaviest naturally occurring element being uranium (Z = 92). The 22 heaviest chemical elements, the transuranium elements, are manmade. The story of their synthesis, their properties, their impact on chemistry and physics, and their importance to society is fascinating. This story is of particular importance to nuclear chemistry because most of our knowledge of these elements and their properties comes from the work of nuclear chemists, and such work continues to be a major area of nuclear chemical research. One of us (GTS) has been intimately involved in the discovery and characterization of these transuranium elements. 

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. 

Many chemists go to school for years and earn the top college degree before they make important discoveries in the lab, but James Andrew Harris took a different path. Harris graduated from college with a basic degree in chemistry, but then served in the Army and worked in a company lab before joining the team that discovered the transuranium elements rutherfordium and dubnium. 

These developments led directly to the discovery of four additional transuranium elements. It should be emphasized that these are products of the laboratory and that none of the transuranium elements exists in nature in any appreciable concentration. Different isotopes of these elements may be formed by several types of nuclear transformations those given here are simply illustrative. 

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]... 

In this sense, Lise Meitner had her title right, for the experiments and theories of nuclear physics and chemistry that were used to pursue the false transuranium elements did lead to the recognition of fission, and the scientists who worked most assiduously on the transuranium project were those who did, finally, succeed in making the discovery. 

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. 

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. 

E. Segre, A Mind Always in Motion The Autobiography of Emilio Segre (Berkeley, 1993), 152-153 Abelson, Discovery of Neptunium, in L. R. Morss and J. Fuger (eds.), Transuranium Elements, 53-55. 

Of special interest was the discovery of the transuranium elements, because this meant an extension of the Periodic Table of the elements. At present, 23 transuranium elements are known, beginning with elements 93 (Np = neptunium),... 

The most important method of production of the first transuranium elements is neutron irradiation of uranium. After the discovery of the neutron by Chadwick in 1932, this method was applied since 1934 by Fermi in Italy and by Hahn in Berlin. The method is based on the concept that absorption of neutrons by nuclides with atomic number Z leads to formation of neutron-rich nuclides that change by fi decay into nuclides with atomic numbers Z - -1. Unexpectedly, the experiments carried out by Hahn and Strassmann led to the discovery of nuclear fission in 1938. 

The discovery of Pu has been described in detail by Seaborg in his Plutonium Story (chapter 1 of the book The Transuranium Elements 1958). First, the separation of Pu from Th caused some difficulties, because both elements were in the oxidation state 4-4. After oxidation of Pu(IV) by persulfate to Pu(VI), separation became possible. Pu is produced in appreciable amounts in nuclear reactors (section 14.1), but it has not immediately been detected, due to its low specific activity caused by its long half-life. After the discovery of Pu, plutonium gained great practical importance, because of the high fission cross section of Pu by thermal neutrons. Very small amounts of Pu are present in uranium ores, due to (n, y) reaction of neutrons from cosmic radiation with The ratio Pu/ U is of the order of 10 In 1971, the longest-lived isotope of plutonium, Pu (ri/2 = 8.00 lO y) was found by Hoffman in the Ce-rich rare-earth mineral bastnaesite, in concentrations of the order of 10 gAg-... 

The discovery that a transmutation had happened started a flood of research. Soon after Harkins and Blackett had observed a nitrogen atom forming oxygen, other transmutation reactions were discovered by bombarding various elements with alpha particles. As a result, chemists have synthesized, or created, more elements than the 93 that occur naturally. These are synthetic elements. All of the transuranium elements, or those with more than 92 protons in their nuclei, are synthetic elements. To make them, one must use special equipment, called particle accelerators, described below. 

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