Prompt Photofission Neutron Detection in Depleted Uranium

• Published in: Physical review applied 2023-05, Vol.19 (5), Article 054073
• Main Authors: Jinia, A.J., Maurer, T.E., Meert, C.A., Pakari, O.V., Clarke, S.D., Kim, H.S., Wentzloff, D.D., Pozzi, S.A.
• Format: Article
• Language: English
• Subjects: Actinides; Fission; Metrology; Neutrons; NUCLEAR PHYSICS AND RADIATION PHYSICS; Photonuclear reactions; Scintillators; Solid-state detectors; X-ray techniques
• ISSN: 2331-7019; 2331-7019
• DOI: 10.1103/PhysRevApplied.19.054073

The detection of prompt photofission neutrons during active interrogation is a strong indication of the presence of special nuclear materials. However, the high-energy photons used for interrogation create a very challenging radiation environment for the detection of prompt fission signatures. These challenges include detector saturation and pulse pile-up. Additionally, there is an elevated neutron background that further challenges the detection of prompt fission neutrons. This background is produced because of (γ, Xn) photonuclear reactions in the surrounding high-Z materials. Here, we demonstrate the detection of prompt photofission neutrons in these challenging environments. Depleted uranium (DU) and lead targets are interrogated with bremsstrahlung photons produced by a 9-MV electron linear accelerator. Fast neutrons are detected with trans-stilbene organic detectors, and scintillation pulses are analyzed using a previously developed and demonstrated artificial neural network system. We observe a 5 times higher photoneutron count rate when the lead target is replaced with the DU target. Additionally, we observe a difference in the photoneutron light-output distributions of lead and DU. Here, this difference in the measured distributions is due to the difference in the photoneutron-energy spectra; DU photoneutrons are emitted with (γ, n) and watt-energy spectra, whereas lead photoneutrons are emitted with only the (γ, n) spectrum.