Prompt fission neutron anisotropy in low-multiplying subcritical plutonium metal assemblies

Journal Article · 26 September 2018 · Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment

DOI: https://doi.org/10.1016/j.nima.2018.09.085 · OSTI ID:1525316

Shin, Tony H. ^[1]; Di Fulvio, Angela ^[2]; Clarke, Shaun D. ^[2]; Chichester, David L. ^[3]; Pozzi, Sara A. ^[2]

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1. Univ. of Michigan, Ann Arbor, MI (United States); University of Michigan
2. Univ. of Michigan, Ann Arbor, MI (United States)
3. Idaho National Lab. (INL), Idaho Falls, ID (United States)

Fission neutron anisotropy, due to the kinematics of the fission process, has been studied for non-multiplying sources and highly multiplying subcritical plutonium metal assemblies (i.e. relatively long fission chains). The studies on highly multiplying assemblies show that the observed neutron-neutron angular distribution appear isotropic, while the studies on non-multiplying sources show that the neutron-neutron angular distribution appear anisotropic. No measured data exists, however, that investigates the dependence of neutron anisotropy on multiplication for low-multiplying assemblies. We have experimentally characterized the dependence of fission neutron anisotropy on multiplication for low-multiplying plutonium metal assemblies. Here, an array of 16 organic scintillators was used to measure plutonium metal assemblies (95% ²³⁹Pu, by mass) exhibiting a leakage multiplication of 1.0722(3) to 1.6006(4). Full neutron-neutron angular distributions were measured, and the fission neutron anisotropy was quantified with the ratio of neutron-neutron coincidences observed at 180° and 90°. The results show that the neutron-neutron angular distribution becomes more isotropic as the multiplication increases. Additionally, energy-angle correlations were also characterized showing that the angular distributions are more anisotropic when observing neutrons of higher energy.

• Research Organization: Univ. of Michigan, Ann Arbor, MI (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Office of Nonproliferation and Verification Research and Development (NA-22)
• Grant/Contract Number: NA0002534
• OSTI ID: 1525316
• Journal Information: Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, Journal Name: Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment Journal Issue: C Vol. 915; ISSN 0168-9002
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English