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Division Spotlight
Isotopes & Radiation
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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Conference on Nuclear Training and Education: A Biennial International Forum (CONTE 2025)
February 3–6, 2025
Amelia Island, FL|Omni Amelia Island Resort
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!
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ANS standard updated for determining meteorological information at nuclear facilities
Following approval in October from the American National Standards Institute, ANSI/ANS-3.11-2024, Determining Meteorological Information at Nuclear Facilities, was published in late November. This standard provides criteria for gathering, assembling, processing, storing, and disseminating meteorological information at commercial nuclear power plants, U.S. Department of Energy/National Nuclear Security Administration nuclear facilities, and other national or international nuclear facilities.
Shay I. Heizler
Nuclear Science and Engineering | Volume 166 | Number 1 | September 2010 | Pages 17-35
Technical Paper | doi.org/10.13182/NSE09-77
Articles are hosted by Taylor and Francis Online.
The diffusion approximation for the Boltzmann (transport) equation suffers from several disadvantages. First, the diffusion approximation succeeds in describing the particle density only if it is isotropic, or close to isotropic. This feature causes the diffusion approximation to be quite accurate for highly isotropically scattering media but to yield poor agreement with the exact solution for the particle density in the case of nonisotropic behavior. To handle general media, the asymptotic diffusion approximation was first developed in the 1950s. The second disadvantage is that the parabolic nature of the diffusion equation predicts that particles will have an infinite velocity; particles at the tail of the distribution function will show up at infinite distance from a source in time t = 0+. The classical P1 approximation (which gives rise to the Telegrapher's equation) has a finite particle velocity but with the wrong value, namely, v/[square root of 3]. In this paper we develop a new approximation from the asymptotic solution of the time-dependent Boltzmann equation, which includes the correct eigenvalue of the asymptotic diffusion approximation and the (almost) correct time behavior (such as the particle velocity), for a general medium.