535 K
17 pp.
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TitleThe Transuranium Elements: Early History (Nobel Lecture)
Author(s)McMillan, E. M.
Publication DateDecember 12, 1951
Report NumberUCRL-1619
Unique IdentifierACC0361
Other NumbersOSTI ID: 4392046
Research OrgUniversity of California Radiation Laboratory [Ernest Orlando Lawrence Berkeley National Laboratory (LBL, LBNL)], Berkeley, CA (US)
Contract NoW-7405-eng-48
Sponsoring OrgUS Atomic Energy Commission (AEC)
Subject74 Atomic and Molecular Physics; Transuranium Elements; Historical Aspects; Research Programs; Physics; Actinides; Neptunium; Separation Processes
Related Web PagesEdwin M. McMillan, Neptunium, Phase Stability, and the Synchrotron
AbstractIn this talk the author tells of the circumstances that led to the discovery of neptunium, the first element beyond uranium, and the partial identification of plutonium, the next one beyond that. The part of the story that lies before 1939 has already been recounted here in the Nobel lectures of Fermi and Hahn. Rather the author starts with the discovery of fission by Hahn and Strassmann. News of this momentous discovery reached Berkeley early in 1939. The staff of the Radiation Laboratory was put into a state of great excitement and several experiments of a nature designed to check and extend the announced results were started, using ionization chambers and pulse amplifiers, cloud chambers, chemical methods, and so forth. The author decided to do an experiment of a very simple kind. When a nucleus of uranium absorbs a neutron and fission takes place, the two resulting fragments fly apart with great violence, sufficient to propel them through air or other matter for some distance. This distance, called the "range", is quantity of some interest, and the author undertook to measure it by observing the depth of penetration of the fission fragments in a stack of thin aluminum foils. The fission fragments came from a thin layer of uranium oxide spread on a sheet of paper, and exposed to neutrons from a beryllium target bombarded by 8 Mev deuterons in the 37-inch cyclotron. The aluminum foils, each with a thickness of about half a milligram per square centimeter, were stacked like the pages of a book in immediate contact with the layer of uranium oxide. After exposure to the neutrons, the sheets of aluminum were separated and examined for radioactivity by means of an ionization chamber. The fission fragments of course are radioactive atoms, and their activity is found where they stop.
535 K
17 pp.
View Document 

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