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
Young Members Group
The Young Members Group works to encourage and enable all young professional members to be actively involved in the efforts and endeavors of the Society at all levels (Professional Divisions, ANS Governance, Local Sections, etc.) as they transition from the role of a student to the role of a professional. It sponsors non-technical workshops and meetings that provide professional development and networking opportunities for young professionals, collaborates with other Divisions and Groups in developing technical and non-technical content for topical and national meetings, encourages its members to participate in the activities of the Groups and Divisions that are closely related to their professional interests as well as in their local sections, introduces young members to the rules and governance structure of the Society, and nominates young professionals for awards and leadership opportunities available to members.
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
First astatine-labeled compound shipped in the U.S.
The Department of Energy’s National Isotope Development Center (NIDC) on March 31 announced the successful long-distance shipment in the United States of a biologically active compound labeled with the medical radioisotope astatine-211 (At-211). Because previous shipments have included only the “bare” isotope, the NIDC has described the development as “unleashing medical innovation.”
Reimar Froehlich
Nuclear Science and Engineering | Volume 34 | Number 1 | October 1968 | Pages 57-66
Technical Paper | doi.org/10.13182/NSE68-A19366
Articles are hosted by Taylor and Francis Online.
The existence of a unique positive critical flux distribution and of a corresponding single positive eigenvalue (k-effective), which is greater than the absolute value of any other eigenvalue, is established for the discrete form of the steady-state multigroup diffusion equations. The assumptions here are considerably less restrictive than in formerly published papers. For example, arbitrary scattering matrices, general fission transfer matrices (not necessarily in multiplicative form), and internal nondiffusion regions are allowed. Furthermore, the transitivity assumption of the problem is replaced by weak conditions of connectedness, which are not only sufficient but also necessary for the existence statements. The theoretical and computational significance of the existence and positivity theorems are discussed. Several examples illustrate the generality of the results and the importance of the conditions of connectedness.