ANS is committed to advancing, fostering, and promoting the development and application of nuclear sciences and technologies to benefit society.
Explore the many uses for nuclear science and its impact on energy, the environment, healthcare, food, and more.
Division Spotlight
Reactor Physics
The division's objectives are to promote the advancement of knowledge and understanding of the fundamental physical phenomena characterizing nuclear reactors and other nuclear systems. The division encourages research and disseminates information through meetings and publications. Areas of technical interest include nuclear data, particle interactions and transport, reactor and nuclear systems analysis, methods, design, validation and operating experience and standards. The Wigner Award heads the awards program.
Meeting Spotlight
ANS Student Conference 2025
April 3–5, 2025
Albuquerque, NM|The University of New Mexico
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
Latest Magazine Issues
Apr 2025
Jan 2025
Latest Journal Issues
Nuclear Science and Engineering
May 2025
Nuclear Technology
April 2025
Fusion Science and Technology
Latest News
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.”
S. R. Bierman, E. D. Clayton
Nuclear Science and Engineering | Volume 55 | Number 1 | September 1974 | Pages 58-66
Technical Paper | doi.org/10.13182/NSE74-A23966
Articles are hosted by Taylor and Francis Online.
There has been considerable interest in the use of fixed neutron absorbers (poisons) for criticality control since their use would permit safely handling larger quantities of nuclear materials with reduced probability of criticality. The effectiveness of such absorbers as neutron poisons depends on self-shielding effects which in turn are determined by the magnitude of the absorption cross sections and their variation with energy, the thickness of material, and the neutron-energy spectrum. For the fixed poisons to be considered as either a primary or secondary means of criticality control, their use must be based on a firm knowledge of these effects. To obtain experimental data in this area, the reactivity worth of two such materials, copper and copper containing 1 wt% cadmium, was recently measured in two different energy spectrums and at different thicknesses up to ≈2½ cm. The results of these measurements are presented in this paper and provide a set of clean, well-defined, poisoned critical assemblies that can be used to check calculational techniques and cross-section data., In the relatively thermalizwd neutron-energy spectrum, very little additional absorption was observed in the copper plate at thicknesses greater than ≈2½ cm or in the copper-cadmium plate at thicknesses greater than 1 cm. At thicknesses greater than these, self-shielding precluded any additional absorption, and the change in reactivity was due almost entirely to the additional void being introduced into the system by the poison plates., In the relatively fast neutron energy spectrum, neutron absorption was observed to continually increase with plate thickness for both sets of plates. However, in this spectrum the void effects, caused by the presence of the poison plates, had a greater reactivity worth, over the thickness range covered, than the neutron absorption., In either spectrum, the 1 wt% cadmium in the copper contributed significantly to the neutron absorption. Of course, the cadmium was found to be worth much more in the thermalized spectrum.