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

 Univ. of Michigan, Ann Arbor, MI (United States)
 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 (NA22)
 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 01689002
 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 lowmultiplying 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 lowmultiplying subcritical plutonium metal assemblies. United States. doi: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 lowmultiplying subcritical plutonium metal assemblies". United States. doi:10.1016/j.nima.2018.09.085. https://www.osti.gov/servlets/purl/1525316.
@article{osti_1525316,
title = {Prompt fission neutron anisotropy in lowmultiplying 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 nonmultiplying sources and highly multiplying subcritical plutonium metal assemblies (i.e. relatively long fission chains). The studies on highly multiplying assemblies show that the observed neutronneutron angular distribution appear isotropic, while the studies on nonmultiplying sources show that the neutronneutron angular distribution appear anisotropic. No measured data exists, however, that investigates the dependence of neutron anisotropy on multiplication for lowmultiplying assemblies. We have experimentally characterized the dependence of fission neutron anisotropy on multiplication for lowmultiplying 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 neutronneutron angular distributions were measured, and the fission neutron anisotropy was quantified with the ratio of neutronneutron coincidences observed at 180° and 90°. The results show that the neutronneutron angular distribution becomes more isotropic as the multiplication increases. Additionally, energyangle 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}
}
Web of Science
Figures / Tables:
Works referencing / citing this record:
Simulation of the Nondestructive Assay of ^{237} Np Using Active Neutron Multiplicity Counting
journal, September 2019
 Hua, Michael Y.; Goddard, Braden; Lloyd, Cody
 Nuclear Science and Engineering, Vol. 194, Issue 2
Figures / Tables found in this record: