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

Abstract

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.

Authors:
 [1];  [1];  [1];  [2];  [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
  2. Idaho National Lab. (INL), Idaho Falls, ID (United States)
Publication Date:
Research Org.:
Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA), Office of Nonproliferation and Verification Research and Development (NA-22)
OSTI Identifier:
1525316
Grant/Contract Number:  
NA0002534
Resource 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: 915; Journal Issue: C; Journal ID: ISSN 0168-9002
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY

Citation Formats

Shin, Tony H., Di Fulvio, Angela, Clarke, Shaun D., Chichester, David L., and Pozzi, Sara A. Prompt fission neutron anisotropy in low-multiplying subcritical plutonium metal assemblies. United States: N. p., 2018. Web. doi:10.1016/j.nima.2018.09.085.
Shin, Tony H., Di Fulvio, Angela, Clarke, Shaun D., Chichester, David L., & Pozzi, Sara A. Prompt fission neutron anisotropy in low-multiplying subcritical plutonium metal assemblies. United States. https://doi.org/10.1016/j.nima.2018.09.085
Shin, Tony H., Di Fulvio, Angela, Clarke, Shaun D., Chichester, David L., and Pozzi, Sara A. Thu . "Prompt fission neutron anisotropy in low-multiplying subcritical plutonium metal assemblies". United States. https://doi.org/10.1016/j.nima.2018.09.085. https://www.osti.gov/servlets/purl/1525316.
@article{osti_1525316,
title = {Prompt fission neutron anisotropy in low-multiplying subcritical plutonium metal assemblies},
author = {Shin, Tony H. and Di Fulvio, Angela and Clarke, Shaun D. and Chichester, David L. and Pozzi, Sara A.},
abstractNote = {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.},
doi = {10.1016/j.nima.2018.09.085},
journal = {Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment},
number = C,
volume = 915,
place = {United States},
year = {2018},
month = {9}
}

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Figures / Tables:

Table 1 Table 1: The isotopic composition of a single PANN plate. Isotope mass is corrected for decay, and the 133 mass uncertainty was calculated using the known uncertainty in the half-life of each isotope.

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Works referencing / citing this record:

Simulation of the Nondestructive Assay of 237 Np Using Active Neutron Multiplicity Counting
journal, September 2019