Date of Award
Doctor of Philosophy (PhD)
Environmental Engineering and Earth Science
Timothy A DeVol
Nicole E Martinez
Glenn A Fugate
Accurate neutron measurements in international safeguards are dependent on the knowledge of significant sources of neutrons emitted in an item, which can include neutrons from induced or spontaneous fission and (alpha, n) reactions. In particular, the neutron energy spectrum is needed to accurately characterize the detector response to neutrons of a range of energies. Neutron energy spectra for neutron emitters in international safeguards are typically not well-established, particularly for (alpha, n) reactions. A novel neutron spectrometer using the inverse Bonner sphere concept was developed in this work to experimentally establish neutron energy spectra for international safeguards purposes. Well-characterized neutron sources, namely 252Cf, were heavily relied upon in this work. However, discrepancies in the fissioning characteristics between 252Cf sources were discovered that needed to be addressed prior to developing the novel neutron spectrometer. Gamma-ray signatures from spontaneous fission products and odd-numbered Cf isotopes present in the 252Cf spectrum were used to confirm or query source age and isotopic ratios for five 252Cf sources. MCNP simulations were then employed for proof-of-concept of the inverse Bonner sphere spectrometer (iBSS) and sensitivity analyses to the response functions and a priori information in the input guess spectrum. Application of the iBSS was then presented as a tool for experimentally verifying neutron energy spectra in SOURCES-4C.
Watson, Mara, "Developing a Novel Neutron Spectrometer Using the Inverse Bonner Sphere Concept for International Safeguards" (2021). All Dissertations. 2767.