transuranium elements
in chemistry, radioactive elements with atomic numbers greater than that of uranium (at. no. 92).
All the transuranium elements of the actinide series were discovered as synthetic radioactive isotopes at the Univ. of California at Berkeley or at Argonne National Laboratory; in order of increasing atomic number they are neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium. Of these only neptunium and plutonium occur in nature; they are produced in minute amounts in the radioactive decay of uranium. 1 Much of the study of the transuranium elements has taken place at the Lawrence Berkeley National Laboratory (at Berkeley, Calif.) and at the Joint Institute for Nuclear Research in Dubna, Russia; workers at both locations share credit for the independent discovery of rutherfordium, dubnium, and seaborgium (at. no. 104, 105, and 106, respectively), which are the first three transactinide elements. A German team at the Institute for Heavy Ion Research at Darmstadt discovered bohrium, hassium, meitnerium, darmstadtium, roentgenium, and ununbium (at. no. 107 through 112). The Dubna laboratory, with assistance from Berkeley, claims to have synthesized ununquadium (at. no. 114), and working jointly with the Lawrence Livermore National Laboratory (at Livermore, Calif.) claims to have produced ununtrium (at. no. 113) and ununpentium (at. no. 115). The Berkeley team claimed to have produced ununhexium (at. no. 116) and ununoctium (at. no. 118), but later retracted the claim for ununoctium after other laboratories failed to reproduce Berkeley’s results and a reanalysis of their data did not show the production of the element. Other research teams have since synthesized ununhexium directly. 2 Up to and including fermium (at. no. 100), the transuranium elements are produced by the capture of neutrons;
the transfermium elements are synthesized by the bombardment of transuranium targets with light particles or, more recently, by projecting medium-weight elements at targets of other medium-weight elements (see also synthetic elements). 3 Isotopes of the transuranium elements are radioactive because their large nuclei are unstable, and the transactinide, or superheavy, elements in particular have very short half-lives. However, on the basis of theories of nuclear structure, physicists have predicted that certain transactinide elements may have relatively stable isotopes. For example, an isotope of element 114 with mass number 298 (comprising 114 protons and 184 neutrons) should be very stable and resemble lead in its chemical properties. However, the three isotopes of element 114 that are claimed to have been synthesized have fewer than the requisite 184 neutrons.
Edwin Mattison McMillan was born on 18th September, 1907, at Redondo Beach, California. He is the son of Dr. Edwin Harbaugh McMillan, a physician, and his wife, Anne Marie McMillan, n?e Mattison, who both came from the State of Maryland and were both of English and Scottish descent. The boy spent his early years in Pasadena, California, and obtained his education in that state.
McMillan attended the California Institute of Technology, obtaining a B.Sc. degree in 1928, and taking his M.Sc. degree a year later, then transferring to Princeton University for Ph.D. in 1932. The same year he entered the University of California at Berkeley as a National Research Fellow. The thesis he submitted for Ph.D. was in the field of molecular beams, and the problem he undertook as a National Research Fellow was the measurement of the magnetic moment of the proton by a molecular beam method. After two years on this work and one as a research associate he became a Staff Member of the Radiation Laboratory under Professor E.O. Lawrence, studying nuclear reactions and their products, and helping in the design and construction of cyclotrons and other equipment, and a member of the Faculty in the Department of Physics at Berkely, being appointed Instructor in 1935, Assistant Professor in 1936, Associate Professor, 1941, and Professor in 1946.
During the Second World War, McMillan was on leave from November, 1940, to September, 1945, engaged on national defence research, serving (1940-1941) in the Radiation Laboratory, Massachusetts Institute of Technology; (1941-1942) U. S. Navy Radio and Sound Laboratory, San Diego; (1942-1945) Manhattan District, Los Alamos.
It was during 1945 that he had the idea of "phase stability" which led to the development of the synchroton and synchro-cyclotron; these machines have already extended the energies of artificially accelerated particles into the region of hundreds of MeV and have made possible many important researches.
McMillan returned to the University of California Radiation Laboratory as Associate Director from 1954-1958, when he was raised to Deputy Director and finally Director, in the same year.
In 1951 he received the 1950 Research Corporation Scientific Award, and in 1963 he shared the Atoms for Peace Award with Professor V. I. Veksler.
Professor McMillan is a Fellow of the American Physical Society and the American Academy of Arts and Sciences, a member of the National Academy of Sciences and the American Philosophical Society, and from 1954-1958 he served on the General Advisory Committee to the Atomic Energy Commission. In 1960 he was appointed to the Commission on High Energy Physics of the International Union of Pure and Applied Physics.
An honorary doctorate in science was awarded to him by the Rensselaer Polytechnic Institute in 1961, and by Gustavus Adolphus College in 1963.
While serving in the Faculty of Physics at Berkeley, McMillan married Elsie Walford Blumer, a daughter of Dr. George Blumer, Dean Emeritus of the Yale Medical School. There are three children of the marriage - Ann Bradford (1943), David Mattison (1945) and Stephen Walker (1949).
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