APPLICATIONS OF DELAYED NEUTRON ACTIVATION ANALYSIS TO SUPPORT THE CURRENT AND FUTURE ANALYTICAL MEASUREMENT ACTIVITIES OF NIST
Kelly P. Grogan, Donna J. O’Kelly, Richard M. Lindstrom, and George P. Lamaze
Delayed Neutron Activation Analysis (DNAA) is a method for measuring fissile elements (e.g. 235U, 233U, and 239Pu) in a variety of materials. Advantages of DNAA include the potential for rapid measurements (5 minutes or less), non-destructive and matrix-independent analyses, as well as selective and sensitive (sub-nanogram detection limits for 235U) measurements of fissile elements. The DNAA system housed at the NIST Center for Neutron Research (NCNR) is one of the world’s premier facilities for DNAA measurements due to the highly thermalized and stable neutron flux from the RT2 facility at the NBSR reactor.
The present work addresses three applications of DNAA (two current and one future application) to the analytical measurement activities at NIST. Delayed neutron activation analysis measurements have recently been applied to the quantification of the uranium content in NIST standard reference materials including geological materials such as SRMs 2586 (Trace Elements in Soil with Lead from Paint) and 1633c (Trace Elements in Coal Fly Ash) and agricultural materials such as SRMs 1547 (Peach Leaves) and 1570a (Trace Elements in Spinach Leaves). These measurements are utilized for SRM certification or for the enhancement of current certificates with the addition of new values. The NIST DNAA system is also currently being applied to the determination of uranium correction factors that are necessary for the quantification of increasingly important rare earth elements in NIST SRMs by instrumental neutron activation analysis (INAA). Rare earth elements are frequently produced as fission products of uranium thus complicating their measurement by INAA. Prior determination of uranium content by DNAA facilitates the determination and application of a correction factor that addresses the additional rare earth element content that may be generated during INAA analysis. Finally, DNAA at NIST has the potential to be developed into a powerful tool for nuclear forensics. The threat of illicit and clandestine nuclear activities has become a significant concern for Homeland Security in the current global climate. Delayed neutron activation analysis is a promising technique for the accurate, sensitive, and rapid measurements of fissile materials necessary to characterize nuclear materials and address this threat. Work is ongoing to incorporate simultaneous and time-tagged gamma-spectroscopy detection with the current DNAA system that would allow for the identification of specific fissile isotopes and would ultimately facilitate determination of the fissile material source.