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Title: Using anisotropies in prompt fission neutron coincidences to assess the neutron multiplication of highly multiplying subcritical plutonium assemblies

There is a significant and well-known anisotropy between the prompt neutrons emitted from a single fission event; these neutrons are most likely to be observed at angles near 0° or 180° relative to each other. However, the propagation of this anisotropy through different generations of a fission chain re-action has not been previously studied. We have measured this anisotropy in neutron–neutron coincidences from a subcritical highly-multiplying assembly of plutonium metal. The assembly was a 4.5 kg α-phase plutonium metal sphere composed of 94% 239Pu and 6% 240Pu by mass. Data were collected using two EJ-309 liquid scintillators and two EJ-299 plastic scintillators. The angular distribution of neutron–neutron coincidences was measured at 90° and 180° and found to be largely isotropic. Simulations were performed using MCNPX-PoliMi of similar plutonium metal spheres of varying sizes and a correlation between the neutron multiplication of the assembly and the anisotropy of neutron–neutron coincidences was observed. In principle, this correlation could be used to assess the neutron multi-plication of an unknown assembly.
Authors:
 [1] ;  [1]
  1. North Carolina State Univ., Raleigh, NC (United States). Dept. of Nuclear Engineering
Publication Date:
Grant/Contract Number:
NA0002534; NA0002576
Type:
Accepted Manuscript
Journal Name:
Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment
Additional Journal Information:
Journal Volume: 825; Journal Issue: C; Journal ID: ISSN 0168-9002
Publisher:
Elsevier
Research Org:
Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation (NA-20)
Contributing Orgs:
Department of Nuclear Engineering, North Carolina State University, Raleigh, NC 27695, USA
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; Passive interrogation; Plutonium; Nonproliferation; Special nuclear material; Neutron angular anisotropy; Neutron detectors
OSTI Identifier:
1367549
Alternate Identifier(s):
OSTI ID: 1359655; OSTI ID: 1487109

Mueller, J. M., and Mattingly, J.. Using anisotropies in prompt fission neutron coincidences to assess the neutron multiplication of highly multiplying subcritical plutonium assemblies. United States: N. p., Web. doi:10.1016/j.nima.2016.04.027.
Mueller, J. M., & Mattingly, J.. Using anisotropies in prompt fission neutron coincidences to assess the neutron multiplication of highly multiplying subcritical plutonium assemblies. United States. doi:10.1016/j.nima.2016.04.027.
Mueller, J. M., and Mattingly, J.. 2016. "Using anisotropies in prompt fission neutron coincidences to assess the neutron multiplication of highly multiplying subcritical plutonium assemblies". United States. doi:10.1016/j.nima.2016.04.027. https://www.osti.gov/servlets/purl/1367549.
@article{osti_1367549,
title = {Using anisotropies in prompt fission neutron coincidences to assess the neutron multiplication of highly multiplying subcritical plutonium assemblies},
author = {Mueller, J. M. and Mattingly, J.},
abstractNote = {There is a significant and well-known anisotropy between the prompt neutrons emitted from a single fission event; these neutrons are most likely to be observed at angles near 0° or 180° relative to each other. However, the propagation of this anisotropy through different generations of a fission chain re-action has not been previously studied. We have measured this anisotropy in neutron–neutron coincidences from a subcritical highly-multiplying assembly of plutonium metal. The assembly was a 4.5 kg α-phase plutonium metal sphere composed of 94% 239Pu and 6% 240Pu by mass. Data were collected using two EJ-309 liquid scintillators and two EJ-299 plastic scintillators. The angular distribution of neutron–neutron coincidences was measured at 90° and 180° and found to be largely isotropic. Simulations were performed using MCNPX-PoliMi of similar plutonium metal spheres of varying sizes and a correlation between the neutron multiplication of the assembly and the anisotropy of neutron–neutron coincidences was observed. In principle, this correlation could be used to assess the neutron multi-plication of an unknown assembly.},
doi = {10.1016/j.nima.2016.04.027},
journal = {Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment},
number = C,
volume = 825,
place = {United States},
year = {2016},
month = {4}
}