Abstract
The use of active interrogation to induce delayed neutron emission is a well-established technique for the characterization of special nuclear materials. Delayed neutrons have isotope-characteristic spectral and temporal signatures, which provide the basis for isotope identification. However, in bulk materials that contain an appreciable fissile (e.g., 235U or 233U) fraction, such as highly enriched uranium (HEU), delayed neutrons have a high probability of inducing additional fissions. As a result, the overall delayed neutron signature consists of two distinct components: the "primary"delayed neutrons (emitted directly by fission fragments) and the "secondary prompt"fission neutrons produced in fission induced by primary delayed neutrons. These prompt products differ from "primary"delayed neutrons both in their energy spectra and in the presence of coincident radiation released by the parent fission event. The presence and relative quantity of prompt products from delayed fission depend on the cross section of the material in the energy range of delayed neutrons, which may differ significantly between isotopes, thus providing an exploitable means for isotope differentiation. In this work, we demonstrate two experimental approaches for discriminating between 235U and 238U isotopes based on the measurement of delayed neutron-induced fission products. First, HEU and depleted uranium objects are differentiated through the detection of high-energy prompt neutrons from delayed fission using both recoil-based organic liquid scintillators and thermalization spectra from a custom-built capture-gated composite detector. Secondly, coincident radiation measurements are used as the basis for discrimination by comparing the overall rates and time evolution of fission events when delayed neutrons are present.
| Original language | English |
|---|---|
| Article number | 014033 |
| Journal | Physical Review Applied |
| Volume | 14 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jul 2020 |
Funding
The authors would like to thank J. Mattingly of North Carolina State University and J. Hutchinson of Los Alamos National Laboratory for their assistance in organizing and executing the experimental campaign at the DAF. This work was supported by the U.S. Department of Homeland Security under Grants No. 2014-DN-077-ARI078-02 and No. 2015-DN-077-ARI096, and by the Consortium for Verification Technology and Consortium for Monitoring, Verification and Technology under U.S. Department of Energy National Nuclear Security Administration award numbers DE-NA0002534 and DE-NA0003920, respectively. The research of J. Nattress was performed under appointment to the Nuclear Nonproliferation International Safeguards Fellowship Program sponsored by the National Nuclear Security Administration’s Office of International Safeguards (NA-241).
| Funders | Funder number |
|---|---|
| National Nuclear Security Administration’s Office of International Safeguards | NA-241 |
| U.S. Department of Energy National Nuclear Security Administration | DE-NA0003920, DE-NA0002534 |
| U.S. Department of Homeland Security | 2014-DN-077-ARI078-02, 2015-DN-077-ARI096 |