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单词 atomic mass number
释义 DictionarySeemass number

Atomic Energy Commission


Atomic Energy Commission

(AEC), former U.S. government commission created by the Atomic Energy Act of 1946 and charged with the development and control of the U.S. atomic energy program following World War II. At the time, debate centered around the question of whether the commission should be predominantly military or civilian. The act provided for a five-member commission appointed by the President with the advice and consent of the Senate, as well as a military liaison committee which the AEC was directed to advise and consult with on all atomic energy matters that related to military applications. A civilian advisory committee to the AEC was also created and from 1946 to 1952 this committee was chaired by J. Robert OppenheimerOppenheimer, J. Robert
, 1904–67, American physicist, b. New York City, grad. Harvard (B.A., 1925), Ph.D. Univ. of Göttingen, 1927. He taught at the Univ. of California and the California Institute of Technology from 1929 (as professor from 1936) until his appointment
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, who had directed the development of the atomic bombatomic bomb
or A-bomb,
weapon deriving its explosive force from the release of nuclear energy through the fission (splitting) of heavy atomic nuclei. The first atomic bomb was produced at the Los Alamos, N.Mex., laboratory and successfully tested on July 16, 1945.
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 but who opposed the manufacture of the hydrogen bombhydrogen bomb
or H-bomb,
weapon deriving a large portion of its energy from the nuclear fusion of hydrogen isotopes. In an atomic bomb, uranium or plutonium is split into lighter elements that together weigh less than the original atoms, the remainder of the mass
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. The AEC became the center of a nation-wide controversy in 1954 as a result of Oppenheimer's suspension (1953) as a consultant to the commission on the alleged grounds that he was a security risk.

The activities of the AEC included the production of fissionable materials, the manufacture and testing of nuclear weapons, the development of nuclear reactors for military and civilian use, and research in biological, medical, physical, and engineering sciences. Although the bulk of the AEC's work was in the field of atomic weaponry, it was also involved in projects relating to the peaceful uses of atomic energy (e.g., the development of atomic power plants for the production of electricity). The AEC was dissolved in 1974 and its responsibilities transferred to the Energy Research and Development Administration (these functions are now under the Department of Energy) and the Nuclear Regulatory Commission.

Bibliography

See R. G. Hewlett and O. E. Anderson, Jr., A History of the United States Atomic Energy Commission (2 vol., 1962–69); C. Allardice and E. Trapnell, The Atomic Energy Commission (1974).

atomic mass number


a·tom·ic mass num·ber

(ă-tom'ik mas nŭm'bĕr) The mass of the atom of a particular isotope relative to hydrogen 1 (or to one twelfth the mass of carbon 12), generally very close to the whole number represented by the sum of the protons and neutrons in the atomic nucleus of the isotope; it is not to be confused with the atomic weight of an element, which may include a number of isotopes in natural proportion.

atomic mass number

A number equal to the sum of all the neutrons and the protons in an atom's nucleus. See: mass numberSee also: number

a·tom·ic mass num·ber

(ă-tom'ik mas nŭm'bĕr) The mass of the atom of a particular isotope relative to hydrogen 1 (or to one twelfth the mass of carbon 12), generally very close to the whole number represented by the sum of the protons and neutrons in the atomic nucleus of the isotope; it is not to be confused with the atomic weight of an element, which may include a number of isotopes in natural proportion.
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