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Members are devoted to applying nuclear science and engineering technologies involving isotopes, radiation applications, and associated equipment in scientific research, development, and industrial processes. Their interests lie primarily in education, industrial uses, biology, medicine, and health physics. Division committees include Analytical Applications of Isotopes and Radiation, Biology and Medicine, Radiation Applications, Radiation Sources and Detection, and Thermal Power Sources.
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General Kenneth Nichols and the Manhattan Project
Nichols
The Oak Ridger has published the latest in a series of articles about General Kenneth D. Nichols, the Manhattan Project, and the 1954 Atomic Energy Act. The series has been produced by Nichols’ grandniece Barbara Rogers Scollin and Oak Ridge (Tenn.) city historian David Ray Smith. Gen. Nichols (1907–2000) was the district engineer for the Manhattan Engineer District during the Manhattan Project.
As Smith and Scollin explain, Nichols “had supervision of the research and development connected with, and the design, construction, and operation of, all plants required to produce plutonium-239 and uranium-235, including the construction of the towns of Oak Ridge, Tennessee, and Richland, Washington. The responsibility of his position was massive as he oversaw a workforce of both military and civilian personnel of approximately 125,000; his Oak Ridge office became the center of the wartime atomic energy’s activities.”
K. Swaminathan, S. P. Tewari
Nuclear Science and Engineering | Volume 91 | Number 1 | September 1985 | Pages 95-108
Technical Paper | doi.org/10.13182/NSE85-A17131
Articles are hosted by Taylor and Francis Online.
A thermal neutron inelastic scattering kernel for polyethylene (PE) of any degree of crystallinity based on a recently proposed dynamic model is suggested. The dynamic model takes proper account of the anisotropic linear chain structure of PE that gives rise to an acoustic phonon frequency distribution function, which is quite different from the usual Debye type, and that has been successful in explaining the observed temperature variation of the specific heat of PE of different degrees of crystallinity. The expressions for zero-phonon and one-phonon neutron scattering cross sections are derived by making use of the frequency distribution function. The kernel incorporates the contribution of two-phonon acoustic modes and also that of optical modes. The kernel has been used to calculate the total scattering cross sections of thermal neutrons from crystalline and noncrystalline PE, including amorphous PE. The calculated values of total scattering cross sections are in reasonable agreement with the experimental results of 60 and 98% crystalline PE. The calculated values for amorphous PE are not very different from those for crystalline PE. Thus the total scattering cross sections are found to be independent of the degree of crystallinity in agreement with the experimental results. The details of the contribution of various scattering processes to the total scattering cross section for crystalline and amorphous PE are reported. The kernel has also been used to study the γij-neutron condensed system energy exchange observable for both crystalline and amorphous PE and has been compared with the equivalent isotropic Debye kernel. The γij values are found to be almost independent of the degree of PE crystallinity. Also, the γij values, as determined using the suggested scattering kernel, are quite different from those calculated using the Debye kernel, showing thereby the importance of the linear chain structure of three-dimensional PE crystal.